Customized Bentonite Pellets: Manufacturing, Performance

December 2013

Working Reports contain information on work in progress

or pending completion.

Pieti Marjavaara

Erika Holt

Vi l le Sjöblom

VTT

Working Report 2012-62

Customized Bentonite Pellets:Manufacturing, Performance and

Gap Filling Properties

ABSTRACT

The goal of this work was to provide knowledge about how to manufacture customized bentonite pellets and how customized bentonite pellets perform in practice during the nuclear repository construction process. The project was mainly focused on laboratory experimental tests to optimize the pellet filling by customizing the raw materials and pellet manufacturing. Bentonite pellets were made using both extrusion and roller compaction methods. The pellets were intended for use in gaps between compacted bentonite and the rock walls in both buffer deposition holes and tunnel backfilling. Performance of different types of custom-made pellets were evaluated with regard to their ease of manufacturing, density, crush strength, abrasion resistance, water holding capacity, free swelling and also their thermal conductivity. These evaluations were done in both Finland (by VTT) and Canada (by AECL). Over 50 different varieties of pellets were roller-compaction manufactured at AECL in Canada and 20 types of extrusion pellets at VTT in Finland. The parameters that were varied during manufacturing included: bentonite raw material type, water content, pellet sizes, bentonite compaction machine parameters, use of recycled pellets, and addition of two different types of filler (illite or granitic sand) at varying addition percentages. By examining the pellets produced with these methods and materials the performance and behaviour of the bentonite pellets were evaluated in laboratory with selected tests. The work done using extrusion pellets showed that it was possible to manufacture pellets with higher water contents, up to 21 % from MX-80. This water content value was higher than what was typically possible using roller-compaction method in this study. Higher water content values allow closer compatibility with the designed bentonite buffer water content. The extrusion tests also showed that the required production simulation runs could be made successfully with reference type of MX-80 bentonite raw material at 17 % water content for 6 mm and 8 mm sizes of bentonite pellet diameters. This means that it is possible to produce in house customized extruded pellets for future tests domestically.

Keywords: KBS-3V, spent nuclear fuel repository, buffer, bentonite block, artificial wetting, gap filling, bentonite pellets, customized pellets.

MUKAUTETUT BENTONIITTIPELLETIT: VALMISTUS JA TEKNISET OMINAISUUDET

TIIVISTELMÄ

Työn tavoitteena oli tutkia bentoniittipellettien valmistusta mittatilaustyönä ja niiden käytännön toimivuutta ydinjätteen loppusijoitusprosessin yhteydessä. Työ keskittyi pää-asiassa laboratoriokokeisiin, joissa tutkittiin raaka-aineena käytettävän bentoniitin omi-naisuuksien säädön ja valmistusmenetelmien vaikutusta pelletteihin. Pellettejä valmis-tettiin sekä pursottamis- että puristusmenetelmillä. Näiden pellettien ajateltu käyttö-tarkoitus on toimia täytteenä bentoniittilohkojen ja kallion välisissä raoissa loppu-sijoitusreiässä sekä tunnelitäytön ja kallion välissä tunneliosuudella. Yli 50 erilaista pellettityyppiä valmistettiin puristusmenetelmällä AECL:n laborato-riossa ja 20 eri pellettityyppiä tehtiin VTT:n laboratoriossa pursottamalla. Valmistus-kokeissa käytettiin ja muunneltiin erilaisia parametreja, joita olivat mm. bentoniitti-tyyppi, kosteuspitoisuus, pellettien koko, valmistuslaitteiden säätöarvot, uudelleen kierrätettyjen pellettien käyttö ja toisen täytteenä toimivan raaka-aineen lisääminen (illiitti- tai graniittihiekka). Näitä eri tavoin ja ominaisuuksin valmistettuja pellettejä arvioitiin valituilla laboratoriomenetelmillä niiden toimivuuden ja käyttäytymisen suhteen. Näitä olivat mm. valmistuksen helppous, tiheys, murskautuminen, kulutuk-senkestävyys, veden pidätyskyky, paisuminen ja lämmönjohtuminen. Kokeita tehtiin molemmissa valmistukseen osallistuneissa laboratoriossa, Suomessa VTT:n ja Kana-dassa AECL:n toimesta. Pursottamismenetelmällä pystyttiin valmistamaan tässä tutkimuksessa pellettejä, joiden kosteuspitoisuus oli korkeampi kuin puristamalla valmistettujen pellettien. MX-80 bentoniitillä tehtiin onnistuneesti 21 % kosteusprosenttiin asti pursotettuja pellettejä. Korkeilla pellettien kosteusprosenttiarvoilla on mahdollista saada vastaavuus puskuri-lohkojen suunnitellun kosteusarvon kanssa. Pursottamiskokeet osoittivat myös, että 17 % kosteusprosentin omaavia pursotettuja pellettejä pystyttiin valmistamaan simuloidun tuotannon määrän verran 6 mm ja 8 mm halkaisijoissa. Tämä tarkoittaa sitä, että mahdollisissa tulevissa tutkimuksissa voidaan käyttää kotimaassa valmistettuja mittatilaustyönä optimoituja pursotettuja bentoniittipellettejä. Avainsanat: KBS-3V, loppusijoituspaikka, puskuri, bentoniittilohko, bentoniittipelletti, rakotäyttö, raon kastelu.

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TABLE OF CONTENTS

ABSTRACT TIIVISTELMÄ

1 OBJECTIVE ............................................................................................................. 3

2 BACKGROUND ....................................................................................................... 5

3 METHODOLOGY .................................................................................................... 7 3.1 International co-operation with AECL in pellet studies ................................... 7 3.2 Gap filling tests ............................................................................................... 7 3.3 Artificial wetting............................................................................................... 8 3.4 Extrusion manufacturing ............................................................................... 11 3.4.1 Abrasion resistance test .................................................................... 15 3.4.2 Water filtration tests .......................................................................... 15 3.4.3 Thermal conductivity ......................................................................... 16 3.4.4 Pellet crushing tests .......................................................................... 18 3.4.5 Pellet length measurements of extruded pellets ............................... 20

4 MATERIALS .......................................................................................................... 21 4.1 Bentonite pellets ........................................................................................... 21

5 RESULTS ............................................................................................................ 23 5.1 Results from the co-operation work with AECL ............................................ 23 5.1.1 Main results ......................................................................................... 23 5.1.2 Conclusions ......................................................................................... 28 5.2 Results from the Gap filling tests .................................................................. 29 5.3 Results from the Artificial Wetting tests ........................................................ 29 5.3.1 Summary ............................................................................................. 29 5.4 VTT extrusion pellet manufacturing .............................................................. 33 5.4.1 Goals and test program ....................................................................... 33 5.4.2 Results ................................................................................................ 34 5.4.3 Conclusions ......................................................................................... 44 5.4.4 Other VTT laboratory test results ........................................................ 45

6 DISCUSSION ........................................................................................................ 59 6.1 Discussion and conclusions ......................................................................... 59 6.2 Future work recommendations ..................................................................... 60

REFERENCES ............................................................................................................ 61

APPENDIX 1: Individual WETTING test details ............................................................ 63

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1 OBJECTIVE

The goal of this work was to provide knowledge about how to manufacture customized pellets and how customized bentonite pellets perform in practice during the nuclear repository construction process. The work was based upon the experience of earlier pellet related projects (Marjavaara et al. 2011 and Holt et al. 2011) and co-operation with other research partners who also share the interest in the bentonite pellet behaviour. The results provided knowledge about performance of customized pellets compared to existing literature and experience gained with commercially available pellets. The results from this work also provided means for making recommendations in the detailed design for use of pellets in the deposition holes and backfill. They also aid in safety case analysis for long-term performance of pellets having tailored properties. The project was focused on laboratory experimental tests at VTT using several customized bentonite pellets as material and on a study of extrusion pellet manufacturing in VTT laboratory facilities.

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2 BACKGROUND

In the current Posiva’s vertical deposition hole buffer design the 50 mm (±25 mm) gap between the bentonite buffer and the surrounding bedrock is to be filled with bentonite pellets. The pellets are to be poured into the gap, without vibration or consolidation to achieve a bulk density of 1075 kg/m3 (Juvankoski et al. 2012). The benefit of using gap filler is that it improves the properties of the components within the whole system, with respect to thermal, mechanical and chemical transfer. In the tunnel backfilling, the gap between the backfill blocks and tunnel rock surface are also filled with pellets. The gap width between the blocks and the theoretical tunnel wall/roof shall be 100 mm. The dry density of the backfill pellet fill shall be within the range of 900-1100 kg/m3 (Keto et al. 2012). The pellets should have water storage capacity while emplacing the backfill blocks to maintain ideal working conditions. In the future, it is envisioned that there could be full scale, on-site manufacturing of pellets from raw bentonite. Yet current knowledge about bentonite pellet performance published in literature and in research experience has been obtained mostly when using a few limited sources of commercially available pellets. Recent Posiva research projects on gap filling (Marjavaara et al. 2011) and wetting behaviour (Holt et al. 2011) have been limited to using commercial bentonite fillers, such as Cebogel and Ibeco Seal (Figure 1). Cebogel pellets have a nominal diameter of 6.5 mm and average length about 12 mm, but lengths can be as high as 25 mm which could be a problem for filling a small gap. The Ibeco Seal granules have a much finer grain size and do not allow for easy water flow or filtration.

a) Cebogel pellets b) Ibeco Seal S-FGS granular

Figure 1. Commercially available pellets that have been used in recent studies.

A project was done during 2011 at AECL in Manitoba, Canada (in cooperation with NWMO, Posiva and SKB) to investigate properties of customized bentonite pellets (Kim et al. 2012). During that project manufacturing small laboratory scale batches of pellets by roller-pressing were done. Their goal was to look at varying compositions and production methods to obtain custom pellets with optimized properties. Measurements after production were limited to bulk density together with thermal, hydraulic and mechanical characterizations of the individual pellets. The main parameters altered during AECL manufacturing included:

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- bentonite type (MX-80, Milos clay, etc.) - pellet size (10 mm, 20 mm, square, pill, ovoid) - additives (fine quartz, illitic clay, etc.) - production variables (load, recompacting, water content, etc.)

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3 METHODOLOGY

3.1 International co-operation with AECL in pellet studies

Canadian Nuclear Waste Management Organization (NWMO) and Posiva both have an interest in developing clay pellets for use in the sealing systems of their repositories. To customize the properties of the bentonite pellets for optimization needs of both of the interested parties was the base of co-operation idea. The Atomic Energy of Canada Limited (AECL) was chosen by NWMO to perform the research. AECL research with pellets was done through all of year 2011. The experimental pellet work in cooperation with Posiva consisted of the production of approximately 70 batches of customized pellets and initial characterization was done by AECL (Kim et al. 2012). The manufactured pellets were for both backfill and for the buffer-rock gap. Primarily buffer-gap pellets were chosen to be studied further in Finland. VTT assisted AECL in reviewing results from the production process. Suggestions were provided for how to further optimize the pellet properties. From the AECL results, six of the best performing and most promising pellet types were selected for further testing. Four pellet types were from buffer production, while two were from backfill pellets. Batches of approximately 100 kg of each of the six pellets types were produced by AECL and sent to VTT during the summer of 2011. The pellet bulk densities were above 1000 kg/m3 for all the pellets.

3.2 Gap filling tests

The behaviour of the customized bentonite pellets when filled to a gap was studied. This was investigated using the gap filling test arrangement developed at VTT and earlier studied with commercially available pellets (Marjavaara et al. 2011). The custom roller compacted pellets from AECL and VTT’s extrusion manufactured pellets were put into a gap of 35 mm, with a surface face of 200 cm width by 114 cm height. The pellets were poured into the gap, using only the free falling technique without additional compaction or vibration. Other methods for placement, such as spraying, would have required larger batch sizes of raw material and work better with taller test setups. During the filling the mass of each pellet bucket was measured in order to get the total mass of poured pellets. After filling, first the pellet surface was leveled with a wooden mallet and then the pellet height was measured using digital images taken at various locations. The schematic of the test arrangement is given in Figure 2.

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Figure 2. Gap filling test arrangement loaded with pellets.

The gap filling test provided information on the bulk density achieved from the pellets after filling in the simulated deposition hole environment. Assessment considered aspects of compaction ability, achievable low to high range of density, and handling considerations such as dust. Other details of the testing procedure followed the existing VTT methodology (Marjavaara et al. 2011). The poured pellet density was also measured both by AECL and VTT. The assessment in Finland was measured using a gap filling experimental arrangement as stated earlier. For the AECL pellet assessment about 70 kg of pellets were placed by free falling alone, without the aid of vibration or compaction. Only 4 of the 6 pellet types were tested, due to a lack of materials. For each pellet type the filling test was repeated three times.

3.3 Artificial wetting

The behaviour of the customized bentonite pellets when subjected to wetting was studied. This was investigated by using the artificial wetting test arrangement developed at VTT and earlier studied with commercially available pellets (Holt et al. 2011). The custom pellets were put into a 50 mm gap created by centre block and cylinder steel wall. Then the system was closed and wetted by introducing water through valves. Initial plans were to have the centre cores made of the isostatically-compacted bentonite blocks or stack of bentonite disks. This was later changed and a dummy steel insert cylinder was manufactured and used to simulate the bentonite buffer, rather than using the actual highly compacted bentonite blocks. The swelling of bentonite block will create more pressure than the pellet filling so it could mask the differences in pellets. Also when the centre block is made from bentonite there will be a bentonite-bentonite

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reaction surface where the drier centre will draw water from moister pellet filling. To study this was not in the actual scope of the project. The schematic of the wetting chamber test arrangement is given in Figure 3. The average test durations were around two weeks. The tests with the reference type of pellets and AECL custom pellets were commissioned first. The artificial wetting tests were finished with using VTT’s extruded pellets.

Figure 3. Artificial wetting test cylinder dimensions and locations of pressure sensors.

During wetting of the pellets, the generated radial and axial swelling pressures were measured. Other measurements like system temperature and lid movement were also monitored. Post-testing material assessment included measures of density distribution and water content. Prior to the wetting test, some preliminary tests were done on pellets to assess their water infiltration ability. It was beneficial to do some simplified water filtration tests to assess the ability of water to percolate through the pellets before the actual artificial wetting test. These were done in small laboratory glass tubes and gave an indication of the volume of water which could be added during the artificial wetting scenario. Other details of the testing procedure followed the existing VTT methodology (Holt et al. 2011). All the pellet artificial wetting tests were done with cylinder shaped dummy steel core which substituded the actual bentonite buffer block. The steel core was centered in the test cylinder so that the gap between core and cylinder wall was 50 mm wide evenly. The actual amount of the bentonite pellets and water added for each test varied due to different density and compacting properties of the test pellets. The pellets were installed by pouring them freely until the pellet layer was about 2 mm below the steel cylinder top surface. This prevented the pellets to get packed or change preload force created by cylinder’s lid installation. Figure 4 shows three example pictures from the wetting test preparation stages.

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Figure 4. a) The dummy steel middle core, b) Test #10, Buffer Test pellets, c) Test #18,VTT extruded MX-80.

After the tests were comissioned the bentonite pellet mass and dummy steel core were extracted from the test cylinder by using compressed air. The moist bentonite pellet material was fastened to the steel core quite tight. The bentonite material was sampled as two vertical columns at the same places as the pressure sensors were located. From each vertical column five samples were taken. The sampling was done sensor installation column 1 (sensors 1, 5 and 9) and installation column 3 (3, 7 and 11). The sensor placement details are shown in Figure 5. Figure 6 presents three example images from commercial Cebogel pellet test during the sampling procedures. The samples were analyzed for their water content and bulk density values by paraffin wax method.

Figure 5. Pressure sensor layout and numbering.

Figure 6. Test #11Cebogel pellets sampling after wetting test.

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3.4 Extrusion manufacturing

The customized pellets developed with AECL co-operation were manufactured by roll-pressing technique. The commercially available pellets that have been tested earlier within Posiva’s programs have been mostly produced by extrusion. For comparison purposes, it was beneficial to understand how customized pellets may be similar or different than commercial products, based on the manufacturing method. Therefore, the same mixture compositions were used to produce pellets both by roller compaction at AECL laboratory and by extrusion at VTT laboratory. The extrusion tests were divided in three separate sessions. In the first phase, early 2012, a small extrusion pelleting machine was used and the main goal was to get operating staff familiar to work with bentonite material and to see if the pelleting by extrusion can be done with the available raw material compositions. In the second phase during spring 2012, several different batches of bentonite pellets were done of a few kilos each. The last session in autumn 2012 was done with a medium-scale machine and had a main goal of producing over 100 kg batches of pellets having 17 % water content of MX-80 bentonite raw material. This water content is the same as the current buffer reference design for buffer gap filling bentonite pellets (Juvankoski et al. 2012). The first extrusion pellets were tested and studied at VTT. Based on the initial results, more optimization studies were done with the extrusion equipment. The later scope of testing was to evaluate the pellet manufacturing process, with adjustments to parameters such as bentonite water content, bentonite feed rate to the extrusion machine, impact of cutting tools for controlling pellet length. The gap filling performance assessment of extruded pellets was done along with some other measurements such as crush strength and previously mentioned artificial wetting. The VTT extrusion tests were done at VTT’s Jyväskylä facilities, where presses are typically used for manufacturing biofuel pellets. The Amandus-Kahl 14-175 flat-die press setup was used in the first two extrusion test phases (Figure 8).

Figure 7. Extrusion machine details: (a) Pellet extrusion die (b) die and coller wheels.

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Figure 8. VTT’s small pellet extrusion machine.

As mentioned earlier the actual making of the extruded pellets was divided in to three separate test sessions. For the first test there were two different targets. The first was to see how bentonite pelleting process works in overall and to have extrusion lab personnel some first-hand experience how to work with bentonite raw material. The second target was to test pellet length cutting settings to achieve desired pellet lengths. Also the water content of some bentonite raw material was varied. These preliminary tests were made with small scale Amandus-Kahl 14-175 flat-die press. After the preliminary tests a second set of tests was commissioned using the same press with equipment parameters gained from the first session such as raw material feed rate and pellet length cutting settings. This time several different types of bentonite raw materials and mixtures were used. The exact same bentonite materials and mixtures were received from Canada (AECL) which were used by them during pellet production by roller pressing. The amounts of produced patches of extruded pellets were between 2-20 kg each. Third test session had a primary goal of producing 6 mm and/or 8 mm diameter MX-80 pellets from 17 % water content raw material at least 100 kg batch or more in one continuous run. The secondary goal was set to be the same pellet sizes but from 21 %-23 % water content MX-80 raw material. To achieve these batch sizes a larger extrusion equipment had to be used. The machine available to do this was older model from the same manufacturer called Kahl Kahletta C28-360 2K. Also to get 100 kg of pellet batch the machine needed to be running continuously without overheating for some time

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(close to 60 minutes) which was also set as one of the secondary goals for production run simulation. The three extrusion tests were done in the following order: 1. Preliminary tests with small scale press done in 02/2012

Material: MX-80 (VTT)

Water content: 12-16 %

5 pellet batches

8 mm hole diameter die used

Material: MX-80 (VTT)

Water content: 13-16 %

7 pellet batches, each about 10 kg

7 mm and 8 mm hole diameter dies used

2. More detailed tests with small scale press done in 03/2012

Materials MX-80 (VTT)

75 % MX-80 + 25 % Illite (VTT)

100 % Milos B (VTT)

100 % Milos A (VTT)

75 % MX-80 + 25 % Sand (VTT)

Cebogel, extruded (commercial product tested with others)

Water content 16-21 %

1 Pellet batches per each material (5kg)

8 mm hole diameter die used

3. Production simulating run with medium scale press done in 09/2012

Material: MX-80

Water content 16 % and 21 %

5 pellet batches, each over 100 kg

6 mm and 8 mm hole diameter dies used

The Figure 9 shows the schematics and dimensions of the pellet pressing machine. The pelleting machine was driven with 3 kW motor and in normal use the current consumption was approximately 6 A during pressing.

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Figure 9. Amandus-Kahl 14-175 flat-die press (picture source Kahl).

Figure 10 shows the pan roller wheel, pelleting die and pellet cutting tool which were the main components having an important role during bentonite pelleting.

a) b)

Figure 10. Pan roller wheel above die a) and cutting tool b).

The third test session pellet pressing was done with Kahl Kahletta C28-360 2K medium scale press. There were two new 8 and 6 mm dies which needed a break in period. This was done by pelleting a mixture from spruce shell and filler until machining oils and marks were polished away from the die hole’s inside surfaces. After this break in period the dies were ready to be used. The initial distance of the cutting blade was set to 15 mm. Five bentonite pellet batches were done with different water contents.

Die diameter 175 mmPan grinder roller width 29 mmDrive motor power 3 kWWeight 260 kg

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3.4.1 Abrasion resistance test

The abrasion resistance of the bentonite pellets was assessed by using the Micro-Deval test. This test was done according to the EN standard method (EN 1097-1:2011), using the alternative Method A of having dry conditions where no water is added to the drum. Prior to the pellet testing, some preliminary trials were done to establish if the standard limits would be followed or if a modified version would be used. The test parameters were set to get partial degradation of the pellets, so that the wear resistance could be compared between pellet types. In the pellet abrasion resistance tests, 500 grams of pellets were oven-dried for 24 hours at 110°C. They were then cooled and placed in the drum along with 5000 grams of steel balls. The drum was then sealed and subjected to 12 000 revolutions with a speed of 100 revolutions per minute. After the test the lost material was screened on a size 1.6 mm sieve and the mass loss percentage is reported. Figure 11 shows the test equipment.

Figure 11. Micro-Deval test equipment.

3.4.2 Water filtration tests

Water filtration test were done with two different test set ups. The first smaller tests were done with laboratory glass scale equipment. The water absorption and swelling of bentonite pellets were tested prior to the artificial wetting tests. The tests were performed in glass decanters of volume 3000 ml and/or 5000 ml, depending on the amount of pellets used (2000ml or 4000ml). For watering clean tap water was used. The tests were performed in open vessels in which case upward swelling was also possible. Pellets were poured in and tap water was added until all pellets were covered. Water was added during the tests at all times when the surface was dry and capable of absorbing more water. Tests were ended when the surface was no longer capable of absorbing water. Measurements during tests were done on the amount of water that could be added and how much swelling of the bentonite pellets was happening. After tests, water contents were measured for samples from next to the glass and middle of the mass at top, center and bottom of the glass decanter.

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A test was also done with a long pellet filled tube (2020 mm long, 88 mm inner diameter), to evaluate the water inflow and means of artificially wetting through the pellets. This work was done to support the in-situ buffer test commissioned in ONKALO shortly after. The second test setup was larger but still in laboratory scale. The reference roller-compacted MX-80 Buffer Test bentonite pellets were tested in this system. The laboratory testing was done by using a vertical plastic tube, to study the flow rate, watering nozzle operation and pellet behaviour at the start of the wetting. The pellets were installed by pouring them up to 1600 mm level in smaller batches, without any compaction method. A watering nozzle was installed at the 800 mm level on the side of the tube. The pellets were watered with tap water by a pump. The exact pumping pressure was not monitored in the initial laboratory test.

3.4.3 Thermal conductivity

The thermal conductivity of the bentonite pellets were measured for one pellet type with two test methods: thermal probe method and heat flow meter method. The chosen pellet type for both of the tests was the reference roller compacted Buffer Test pellet.

3.4.3.1 Thermal probe method

The thermal probe method employs a heat source inserted into the bentonite pellets whereby heat energy is applied continuously at a given rate. The thermal conductivity of the bentonite pellets can be determined by analyzing the temperature response adjacent to the heat source via a thermal sensor. This method reflects the rate at which heat is conducted away from the probe. The more detailed description of this method can be found from the standard ASTM D5334 – 08. During the tests the bentonite pellets were hand compacted into the plastic cylinder which diameter was 150 mm and the height was 200 mm (Figure 12). The length of the thermal probe was 160 mm. The thermal conductivity tests were performed three times with the same bentonite pellet sample. Thermal conductivity of the bentonite pellets is depending on the water content and density of the pellets, size and shape of the individual pellet and the geometry of the gap in the bentonite buffer. The accuracy of the thermal conductivity measurement method is depending on the boundary conditions like the sample size in the test equipment.

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Figure 12. Thermal conductivity measurement of the bentonite pellets with thermal probe method.

3.4.3.2 Heat flow meter method

The heat flow meter is an assembly that measures the density of heat flow rate through the specimen by a temperature difference generated by this density of heat flow rate crossing the specimen and the heat flow meter itself. The more detailed description of this method can be found from standard EN 12667:2001. During the tests the bentonite pellets were hand compacted into insulated frame which dimensions were in 450 mm * 450 mm * 80 mm (Figure 13). The frame was then inserted to the machine which did the measurements over one weekend.

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Figure 13. Thermal conductivity measurement of the bentonite pellets with heat flow meter method.

3.4.4 Pellet crushing tests

Compression tests were carried out to determine the crush strength of an individual pellet. Since the measured strength depends on the compression rate, a constant rate was used in all tests. Canadian AECL had used a compression rate of 1 mm/min in their pellet tests, so it was decided that the same rate should also be used in the VTT tests to get comparable results. The strength measured will also depend on the size and shape of the pellets. This is not a problem with roller pressed pillow-shaped pellets since they all are approximately similar in size. Extruded pellets, however, are of varying lengths which means that the individual results cannot be directly compared. This can be solved by measuring the length of each pellet and then normalising the results by dividing the force by the length of the pellet to get results in force per unit length. Even then, only the results of similarly shaped pellets should be compared with one another. The crush tests were done with a computer controlled hydraulic press (Figure 14). The compressive force was measured with a 10 kN force transducer, that was set to 0–1000 N sensitivity. The displacement of the piston was also recorded. The maximum force was taken as the crush strength, and also the displacement at the maximum was noted. Finally, the water content of the pellets was determined by drying them in a ventilated oven at 105 °C for 24 hours or until no mass change. In addition to these crush strength tests, some preliminary test were already carried out when the pellets were extruded. A hand screw, shown in Figure 16, was also used to measure the compressive strength for one batch of MX-80 pellets from first extrusion tests. The results were then compared to those obtained with the computerized hydraulic press. The hand screw is convenient because it can be used at the pellet manufacturing plant to get instant results without requiring sophisticated laboratory equipment.

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Figure 14. Hydraulic press and force transducer setup.

Figure 15. Close-up pictures of a Cebogel pellet being crushed. Pellet length is approximately 19 mm.

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Figure 16. The hand screw operated crush device and close-up of installed pellet. Pellet diameter is approximately 8 mm.

3.4.5 Pellet length measurements of extruded pellets

The pellet length variation was measured by a digital slide gauge with an integrated foot pedal triggering which enabled fast data input. For length measurements a batch of 100 pellets were randomly chosen from a large quantity of pellets from each studied material. The pellet extrusion machine makes one end of the pellet concave and the other convex (Figure 17). When a pellet is measured with a slide gauge, the resulted length does not take the concave part of the pellet into account. Therefore, the effective length of extruded pellets is less (0.2-1.0 mm) than values reported in this report.

Figure 17. Extrusion machine makes one end of pellets concave.

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4 MATERIALS

4.1 Bentonite pellets

The pellets used during this study are presented in Table 1. Two commercially made pellets were used as references during laboratory trials. One reference type was made by roller compaction and the other by extrusion. The roller compacted reference pellets were designated as Buffer Test pellets and they were made by Hosokawa Bepex in Germany. The raw material for these pellets was MX-80 bentonite. The pellet naming comes from that they were used in underground in-situ Buffer test trials done in ONKALO at 40 % scale. Cebogel QSE pellets which were made by Cebo Holland in Holland were used as the reference pellets of extruded type. The pellets were made from Milos A bentonite raw material. These pellets are quite common and have been used in many other studies. In Table 1 three physical dimensions are given for roller compacted pellets and for extruded the pellet diameter and average length if it was available.

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Table 1. Summary table of the pellets used in laboratory trials.

Milos A is also known as IBECO RWC and AC200. Milos B is also known as IBECO RWC BF.

L x W x H (mm) or L (mm)

Ø (mm)

Buffer Test Roller compacted MX-80 Hosokawa Bepex Germany 12 x 12 x 6 - 16

Cebogel QSE Extruded MILOS A Cebo Holland Holland 11 6.3 20

100% Wyoming, small (AECL) Roller compacted MX-80 AECL Canada 23 x 15 x 9 - 9

100% Wyoming, large (AECL) Roller compacted MX-80 AECL Canada 10 x 10 x 6 - 10

100% Milos A (AECL) Roller compacted MILOS A AECL Greece 10 x 10 x 6 - 11

100% Milos B (AECL) Roller compacted MILOS B AECL Greece 10 x 10 x 6 - 10

75% Wyom. + 25% Illite (AECL) Roller compacted 75% MX-80 25% Illite AECL Canada 10 x 10 x 6 - 9

75% Wyom. + 25% Sand (AECL) Roller compacted 75% MX-80 25% Sand AECL Canada 10 x 10 x 6 - 6

MX-80 (VTT1.1) Extruded, test 1 MX-80 VTT Finland 12 8 13













75% Wyom. + 25% Illite (VTT2.2) Extruded, test 2 75% MX-80 + 25% Illite VTT Finland 12 8 16

Milos A (VTT2.3) Extruded, test 2 100% Milos A VTT Finland 11 8 16

Milos B (VTT2.4) Extruded, test 2 100% Milos B VTT Finland 11 8 16

75% Wyom. + 25% Sand (VTT2.5) Extruded, test 2 75% MX-80 + 25% Sand VTT Finland 11 8 17

MX-80 (VTT2.6) Extruded, test 2 (overheated #1) MX-80 VTT Finland - 8 21

MX-80 (VTT2.7) Extruded, test 2, (overheated #2) MX-80 VTT Finland - 8 21






Sample Name Manufacturing method Bentonite type ManufacturerPellet size

Manufacturing location

Water content (%)

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5 RESULTS

5.1 Results from the co-operation work with AECL

5.1.1 Main results

5.1.1.1 Pellet visual characterization

Upon delivery of the AECL roller-compacted pellets to Finland, the 100% Wyoming bentonite large pellets showed longitudinal cracks. The cracks were concentrated around the interface between the roller-compacted halves and occurred in about 90% of the received pellets. It was suspected that the original batch of pellets shipped to Finland may have been exposed to poor handling or storage (such as freezing), thus causing the cracking. Another batch of these same large pellets was received from AECL for comparison purposes. Microscopic studies were done to compare the two batches. A Wild M8 stereo microscope with a QWin image analyzer was used. Figure 19 and Figure 20 show examples of the microscopy images.

Figure 18. 100 % Wyoming large roller compacted pellets from AECL. Left: AECL’s storage samples, Right: Initial samples received at VTT..

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Figure 19. a) AECL storage large roller compacted pellets, height of photo 11 mm. b) Initial samples received at VTT, height of photo 11 mm.

Figure 20. c) AECL storage large roller-compacted pellets, height of photo 4 mm. d) Initial samples received at VTT, height of photo 4 mm.

It was determined that all of the pellets were similar, with the AECL pellets also exhibiting cracking. The cracking did not appear to hinder performance with respect to strength or swelling. It is expected that in the future the cracking could be avoided by increasing the water content of the bentonite and further optimizing the roller compacting process.

5.1.1.2 Pour density comparison

The poured density was measured by both research partners. The assessment in Finland was measured using a gap filling experimental arrangement. For the AECL pellet assessment about 70 kg of pellets were placed by free falling alone, without the aid of vibration or compaction. Only 4 of the 6 pellet types were tested, due to a lack of materials. For each pellets type the filling test was repeated three times. The error calculated for the gap filling volume method (accounting for manual measurements of height and weight) was 3.4 %, corresponding to a potential variation in dry density of 32 kg/m3. The results of the gap filling bulk and dry density measurements are given in Table 2. The correlation to AECL results is presented in Figure 21, based on dry density. This was done because there was a slight loss of moisture between the time the pellets were measured in Canada and Finland (about 1 %), as seen from Table 2.

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Table 2. Density and moisture content results of AECL roller-compacted pellets when assessed in Finland.

Figure 21. Correlation of poured dry density.

5.1.1.3 Abrasion test

The abrasion resistance of the bentonite pellets was assessed using the Micro-Deval test. Figure 22 shows the samples before and after the testing.

Sample nameWater

content (%)

Gap fill, Bulk

density (kg/m3)

Gap fill, Dry

density (kg/m3)

100% Wyoming, small (AECL) 8,9 1112 1021100% Wyoming, large (AECL) 8,9 1092 100375% Wyom. + 25% Illite (AECL) 5,2 - -

75% Wyom. + 25% Sand (AECL) 8,3 1118 1032100% Milos A (AECL) 10,5 1047 948100% Milos B (AECL) 9,6 - -Cebogel QSE 21,9 1050 861Buffer Test 16,8 1067 914

26

Figure 22. Large bentonite pellets for measuring wear resistance, a) before test, b) after test.

The abrasion resistance of pellets is tested to given an indication of how the different pellets would react to handling. The risk of cracking, flaking or disintegration due to wear and movement could be assessed. Table 3 presents the test results of the abrasion test. The mass loss is presented as the average of two tests. For comparison, Buffer Test pellets and Cebogel extruded pellets were also tested. The table also provides references to standard Finnish aggregates tested in dry conditions (Vuorinen 1999).

Table 3. Results of MicroDeval test.

It was expected that there may be some correlation between the wear resistance and strength of the pellets. Material having a higher strength may have better resistance to deterioration which would be indicated by a low value of mass loss. Table 4 shows the results of the both the abrasion resistance and crush strength tests, along with the water contents of the various pellets. Figure 23 demonstrates the relationship between these

Sample Name Mass Loss (%)

Reference: Buffer Test (roller compacted pellets, MX-80) 9,78Reference: Cebogel QSE, extruded pellets 45,95100% Wyoming, small (AECL) 65,31100% Wyoming, large (AECL) 16,3475% Wyom. + 25% Sand (AECL) 33,0475% Wyom. + 25% Illite (AECL) 57,12100% Milos A (AECL) 38,51100% Milos B (AECL) 24,08

Reference Good aggregate A [2] an amphibolite composed of amphibole and feldspar 2,3Reference Good aggregate B [2] a granite composed mainly of quartz and feldspar 2,3Reference Weak aggregate C [2] a limestone 8,6

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two parameters for the tested pellets. For equivalent bentonite type and water content (Wyoming bentonite with water content 5-9 %), the trend held true that pellets with higher crush strength values had lower mass loss i.e. better abrasion resistance. The references Cebogel and Buffer Test pellets had much higher water contents (17-22 %) and thus cannot be directly compared to the other pellets. Comparing the three bentonite types, it appears that they all have relatively the same crush strength, though the mass loss was significantly higher for the 100 % Wyoming bentonite compared to Milos A and Milos B.

Table 4. Results for wear resistance comparison.

Figure 23. Relationship between abrasion resistance (mass loss) and crush strength.

Sample nameMass loss

(%)Crush strength

(N)Water

content (%)Buffer Test 9,8 136 16,8100% Wyoming, large (AECL) 16,3 235 8,9100% Milos B (AECL) 24,1 100 9,675% Wyom. + 25% Sand (AECL) 33 169 5,2100% Milos A (AECL) 38,5 85 10,5Cebogel QSE 46 170 21,975% Wyom. + 25% Illite (AECL) 57,1 129 8,3100% Wyoming, small 65,3 89 8,9

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Figure 24. Mass loss and crush strength data.

5.1.2 Conclusions

The co-operation with Canadian NWMO has shown that many pellet-fill materials have low thermal conductivity (generally <0.5 W/(m·K)), which limits the rate of heat transfer from the spent fuel canister to the surrounding rock (Kim et al. 2012). Therefore the performance of different types of custom-made pellets were evaluated with regard to their ease of manufacturing, density, crush strength, abrasion resistance, water holding capacity, free swelling and also their thermal conductivity. All of the roller-compacted pellets had individual pellet wet densities in the order of 2000 kg/m3. When loosely poured, the dry density of the fill typically was in the order of 1100 to 1200 kg/m3. This could be improved to ~1400 kg/m3 using vibratory compaction. Pellets made with silica sand and illite additives had dry densities slightly higher than this. However, pellets containing additives have lower Effective Montmorillonite Dry Densities (EMDDs) than 100 % bentonite which adversely affects their hydraulic conductivities and swelling pressures. The addition of Wyoming bentonite fines (i.e., 80 mesh granules), vibrated into the pore space between the pellets increased dry density to >1500 kg/m3. However, maximum thermal conductivity values measured on pellets densified by vibratory compaction were close to 0.6 W/(m·K) and appears to be the maximum achievable for as-placed pellets without the addition of fines to the void space between the pellets, artificial wetting, or different, much higher thermal conductivity additives. The roller-compacted pellets having the best performance in placement trials were the smallest size (~9 mm diameter and 6 mm thick). The gravimetric water content of these pellets was limited to 7-15 % for manufacturing reasons. There was a good correlation between crush strength and abrasion resistance of the pellets. The water holding capacity of this size of pellet, which is desired during tunnel backfilling, was improved when using lower quality bentonite Milos B (Ibeco RWC-BF) compared to MX-80 or Milos AC200 in the case of poured pellets. It should be noted that in the case of tunnel

(Wyoming)y = ‐0,3456x + 98,302

R² = 0,9306

(Milos A, B & MX‐80)y = ‐0,5329x + 81,14

R² = 0,9453

0

10

20

30

40

50

60

70

80

0 50 100 150 200 250

Mass Loss (%)

Crush Strength (N)

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backfilling, spraying the pellets in place with slight moisture addition may alter the results.

5.2 Results from the Gap filling tests

As mentioned earlier in the Section 5.1.1.2 four batches of roller compacted pellets were measured to determine their gap filling properties. The gap filling tests were also performed for two types of the VTT manufactured MX-80 extruded pellets. These batches were produced during the third extrusion test session. The pellets were made from 17% water content MX-80 raw bentonite material with 6 mm and 8 mm nominal diameters. In the Figure 25 these results are shown as dry density values with reference pellet values (Cebogel with two installation methods and Buffer Test pellets).

Figure 25. Dry density pellet filling values from VTT tests of the roller compacted pellets.

5.3 Results from the Artificial Wetting tests

5.3.1 Summary

The artificial wetting tests were performed for ten different pellet types. The regular test duration was between 14-18 days except for one test which lasted 7 days. Table 5 shows more detailed summary information about each test. The test numbering starts from 10 because it was continuation labelling for other testing done at the same time with the same equipment.

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Table 5. Artificial wetting test summary of pellets.

The amount of water used in each bentonite pellet test varied. This was because the pellets from different shapes and sizes create variety in void capacity between the individual pellets. The mass of used water and the mass of tested bentonite is presented in Figure 26 below.

Figure 26. Mass of water and pellets in wetting tests.

Test # DatesDuration (days)

Type of BentoniteWater

added (kg)Mass of

pellets (kg)

Pellets moisture

content (%)

Bulk density (kg/m3)

Bulk fill, gapfill test (kg/m3)

Moisture content (%)

after test

Bulk density after test (kg/m3)

10 26.10-2.11 7 Buffer Test 11,5 16,4 16,2 1123 1067 59,9 994,7

11 9.11 - 25.11 16 Cebogel 7,4 15,0 20,1 1030 1107 69,64 906,0

12 28.11 - 14.12 16100% Wyoming,

small (AECL)7,2 17,0 9,2 1165 1112 50,54 1079,3

13 16.12 - 3.1 18 Buffer Test 6,3 14,0 16,4 959 1067 69,49 951,7

14 4.1 - 19.1 15100% Wyoming,

large (AECL)6,7 17,0 10,6 1166 1092 56,16 1082,7

15 20.1 - 3.2 14100% Milos A

(AECL)7,2 15,8 11,6 1083 1047 67,56 944,9

16 6.2 - 22.2 16100% Milos B

(AECL)7,2 16,2 13,1 1106 - 65,55 967,3

17 28.2 - 15.3 1675% Wyom. + 25%

Illite (AECL)7,0 17,4 10,0 1195 1118 52,24 1084,9

18 21.3 - 5.4 15 MX-80 (VTT) 6,9 15,7 23,6 1075 - 76,12 869,6

19 11.4 - 27.4 1675% Wyom. + 25%

Sand (AECL)7,2 17,9 7,4 1229 46,38 1137,0

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Figure 27 shows the average results from water content and bulk density determinations for all the tests.

Figure 27. Average values of water content and density measurement in wetting tests.

Figure 28 shows the plots of water/bentonite ratio and measured lid force over the final water contents.

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Figure 28. Average values of water content (%) and dry density (kg/m3) measurement in artificial wetting tests.

The artificial wetting test cylinder was originally designed for the wetting of the bentonite buffer with small gap and no pellet filling. In that case the surface of the swelling bentonite is smooth and even. When the same equipment is used with bentonite gap filler it has some limitations. The sensing surface diameter of each pressure transducer is about 10 mm. How the individual pellets arranged during the filling was a random process and it could not be controlled. In front of the pressure sensor the pellet filling could have a void or it may have been in direct contact with pellets. Some of the sensors were measuring higher radial pressure values when the swelling started which could have been from swelling of a single pellet. In other cases the pressure sensor could have been in the front of boundary or void space and the point like radial pressure value was lower than average. A picture from post-test sample is presented in Figure 29 which shows the actual marks on bentonite pellet filling left by pressure transducers. All the results are presented as an average of each layer.

Figure 29. The pressure transducer location schematic and example pictures from the markings made by the sensors at test #15 on Milos A bentonite.

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The were some variation in measured radial pressures at different heigth levels (Figure 30). Also the different bentonite materials produced varying pressure levels. The measured radial pressure levels correlated with the measured water content values as shown in Figure 30. Sample locations with low water content values, which means higher density, produced higher radial pressures.

Figure 30. Radial pressures from different height levels and the radial pressure over and water content correlation graph.

In the Appendix 1 more details from each individual pellet test is presented.

5.4 VTT extrusion pellet manufacturing

5.4.1 Goals and test program

The making of the extruded pellets was divided in to three test sessions. For the first test there were two different targets. The first was to see how bentonite pelleting process works in overall and to have extrusion lab personnel some first-hand experience how to work with bentonite material. Second target was to test pellet length cutting settings to achieve desired pellet lengths. Also the water content of some bentonite raw material was varied. These preliminary tests were made with small scale Amandus-Kahl 14-175 flat-die press. After preliminary tests a second set of tests was commissioned using the same press with equipment parameters gained from the first session such as raw material feed rate and pellet length cutting settings. This time several different types of bentonite raw materials and mixtures were used. The exact same bentonite materials and mixtures were received from Canada (AECL) which were used by them in roller pressing pellet production. The amounts of produced pellets were between 2-20 kg for each batch. Third test session had a primary goal of producing 6 mm and/or 8 mm diameter MX-80 pellets from 17 % water content raw material at least 100 kg batch in one continuous run. The secondary goal was set to be the same pellet sizes but from 21 % water content MX-80 raw material. To achieve these goals a larger extrusion equipment had to be used. Also to get this size of pellet batch the machine needed to be running continuously without overheating for some time (close to 60 minutes) which was also set as one of the secondary goals for production run simulation.

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5.4.2 Results

5.4.2.1 1st preliminary test session with small scale press

At the start of the first test session at VTT laboratory the basic principles of pelleting and pellet pressing machinery were studied first hand. The material used in first test session was MX-80 bentonite (Table 6 ) mixed to five different water contents water contents with Hobart H400 mixers. Minimum pelleting batch with Amandus-Kahl 14-175 flat-die press was known to be around 2-5 kg so to be on the safe side 10 kg batches of each five water contents were premixed.

Table 6. MX-80 material batches which were used in the first test session.

During the first tests it was learned that the speed of both the feeding and pan grinding roller have a great effect on the pressing machine capacity and functionality. If there is too much bentonite material fed to the pan, the grind roller ploughs and pushes it around and upwards. If there is not enough material between the die and the pan grinder roller there will become an empty space. This leads to the capacity decreasing. The empty space should be full of bentonite material to provide an optimal situation where the pan grinding roller can compress the material into the holes of the pelleting die. If the material feed is too high, or with certain material properties the current can raise up to 9-10 A. This will result in overheating and then the safety heat detector will turn off the machine. Also when the material is considered too dry the drive motor has to work more because of increased friction to produce pellets. To avoid overheating in this case the feeding speed and pan grinder roll speed need to be set lower than usual compared to the normal operation for biofuel pelleting. The pan grinder roller is controlled by frequency converter to provide a step less speed variation. The pellet production capacity can be set higher by changing the speed of the feed setting and by increasing grinding roller speed. It was also learned that the raw bentonite powder passed straight through the pelleting dies and the compression process did not start. To fix this, a high water content bentonite paste needed to be fixed to glue the die holes shut. After this step the bentonite powder stayed inside the die and the pan roller wheels could start compressing and thus the actual pelleting process could start. The second target was to attempt to modify the length of the pellets. This was done by changing the place of cutting machine’s blade. Table 7 shows seven different pellets batches that were tested. All of these were MX-80 bentonite but with different water

Sample name Bentonite type Water content (%)

MX-80 (VTT1.1) MX-80 12,2MX-80 (VTT1.2) MX-80 13,4MX-80 (VTT1.3) MX-80 14,3MX-80 (VTT1.4) MX-80 15,8MX-80 (VTT1.5) MX-80 16,6

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contents. It can be noted that sample number 12 had the pelleting current over 10 A thus resulting in the pellet machine overheating (sample name VTT1.12). This happened because a low water content bentonite was used with the smaller die hole diameter. When the die hole size is reduced the actual number of holes in the die increases since more smaller holes can be located in the same space. This results also in the increase of die hole wall surface area which in turn means more friction forces. It was noted that the small pelleting machine was under powered to be used with dies having lots of small (<8 mm) holes closely spaced.

Table 7. Pelleting machine setting and MX-80 bentonite material details during testing.

The results of overheating can also be seen in the Figure 31 where the water contents are plotted before and after extrusion with the maximum temperature during the test. In batch one and two the maximum temperature was quite high comparing to others and this may be the reason why it looks like the water content has dropped down after the extrusion process. In batch seven there was a severe overheating problem and the water content decreased. The recorded maximum temperature was not quite as high in this batch as batches one and two but this could be a measuring issue. The temperature metering thermocouple was set into the box where the pellets dropped after they were extruded. When the overheating was happening right after starting the pelleting process there was not enough pellets to upraise the temperature in the box. In addition, the maximum temperature does not indicate the cumulative heat amount that drains from the material during whole the process.

Sample name Bentonite type Water content (%) Current (A) Die (mm)Cutting tool distamce

from die (mm)

MX-80 (VTT1.6) MX-80 13 4-6 8 9MX-80 (VTT1.7) MX-80 14 4-6 8 9MX-80 (VTT1.8) MX-80 14 4-6 8 13MX-80 (VTT1.9) MX-80 14,5 4-6 8 32MX-80 (VTT1.10) MX-80 14,5 4-6 8 21MX-80 (VTT1.11) MX-80 15 4-6 8 18MX-80 (VTT1.12) MX-80 13 >10 7 11,4

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Figure 31. Water contents before and after test with maximum temperature.

Table 8 shows how the cutting blade distances from the die affected the length of the final pellets. Increasing individual pellet length by enlarging the gap between the die and the cutting blade works up to a certain point. After this the pellet breaks to smaller pieces by itself. This is depended on the properties of the pellet raw material such as microstructure of material, water content and temperature. Also the dimensions of the pelleting die holes have an effect

Table 8. Cutting tool distance effect to pellet length.

The conclusions from the first test session are as follows. After the gluing of the holes of the die with moist bentonite paste, the pellet pressing went well with all water contents for 8 mm pellets and having batch sizes of a few kilograms. The speed setting of the pan grinding rolls to 80 rpm seemed to suit for bentonite pelleting with the tested raw materials and water contents. Overall it was found that the bentonite powder could be pressed with the small scale Amandus-Kahl 14-175 flat-die press and the length of

Sample name Cutting tool distance

from die (mm)Pellet length

(mm)Standard deviation

MX-80 (VTT1.6) 9 11,8 3,5MX-80 (VTT1.7) 9 12,0 3,4

MX-80 (VTT1.8) 13 12,1 3,7MX-80 (VTT1.9) 32 15,8 5,7MX-80 (VTT1.10) 21 17,0 5,6MX-80 (VTT1.11) 18 15,2 4,4MX-80 (VTT1.12) 11,4 15,5 7,4

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the pellet could be modified up to a certain level by adjusting the placement of the cutting blade.

5.4.2.2 2nd test session with small scale press

The second test session had two main targets. The first was to produce extruded pellets from the exact same bentonite raw material which was previously used in the roller press pelleting. The second target, based on the successful first test session, was to be able to manufacture enough pellets to use them in the gap filling wall test. Table 9 shows the types of pellets made in this session. The last one, Cebogel commercial pellets, is mentioned in the list since it was used as a reference but it came already in the pre-manufactured pellet shape to VTT.

Table 9. Pellet types which were made at the second test session.

During the pelleting process the first goal was successfully filled. All the material batches received from AECL were used and pelleted by extrusion. The second goal was not however reached and not enough MX-80 pellets could be produced to be used for tests which require more than a few kilograms of material. The gap filling wall test needs about 70-90 kg batch of pellets and this could not be achieved this time. The pelleting of MX-80 at a 16-20 % water content had worked in session one when only several kilograms were made. Now when the need was a decade larger the pelleting resulted in problems with machine overheating. Also the small extrusion machine was noted to be under powered for longer use with demanding material such as bentonite. However two fairly large batches of MX-80 extruded pellets were made but the quality of the pellets seemed questionable. These pellets were studied further and their crush strengths were evaluated along other pellets. These results are later shown in section 5.4.4.1 and in the graphs of results these pellets have been marked as “failed”.

5.4.2.3 3rd test session with medium scale press

The third test session was set to have a primary goal of producing 6 mm and/or 8 mm diameter MX-80 pellets from 17 % water content raw material and at least a 100 kg batch or more in one continuous run. This was needed so that the gap filling wall test could be commissioned and the second test session had failed to produce good quality pellets in this large quantity. The secondary goal was to obtain the same pellet sizes but from 21 % water content MX-80 raw material. To be able to manufacture this size of pellet batches the pellet extrusion machine needed to be running continuously without

Sample name Bentonite typeWater content

(%)MX-80 (VTT2.2) 75% MX-80 + 25% Illite 16,2MX-80 (VTT2.3) 100% Milos A 16,3MX-80 (VTT2.4) 100% Milos B 16,2MX-80 (VTT2.5) 75% MX-80 + 25% Sand 16,6MX-80 (VTT2.6) MX-80 (overheated #1) 21MX-80 (VTT2.7) MX-80 (overheated #2) 21

Cebogel QSE Ceboqel 20

38

overheating for some time (close to 60 minutes) which was also set as one of the secondary goals for the production run simulation. The third test session pellet pressing was done with Kahl Kahletta C28-360 2K medium scale press. Two batches of MX-80 bentonite material were used with different water contents of 17 % and 21 %. Five bentonite pellet batches were done with different water contents (Table 10). Batch number two was send directly to Posiva for future storage and use and the other four were tested in at VTT.

Table 10. MX-80 material which were used in test two.

During the pelleting process the temperature of the produced pellets were measured with thermocouples attached to logger. The temperature graph showed an increase when pelleting material was changed from 17 % to 21 % water content. For the 8 mm diameter pellets the increase was about 17-18 °C and for the 6 mm pellets about 12-13 °C. The maximum temperatures were observed with 17 % water content raw material and were around 75 °C for both of the pellet sizes. At this temperature level there was no overheating problems observed and the pellets showed good visual quality. Figure 32 shows the achieved production capacity of the different water content raw material and pellet diameter. The average production capacity for the medium size pelleting machine was found to be about 130 kg/h. There were not any issues when the medium size pellet production machine was used though it needed some fine tuning to find the right parameters because the dimensions were different. For example, the distance from the cutter blade to die needed to be checked but also usable information from earlier tests, like high water content bentonite paste to glue the die holes could be used immediately.

Sample name Bentonite type Die (mm)water content

(%)Purpose

MX-80 (VTT3.1) MX-80 8 21 for gap fillingMX-80 (VTT3.2) MX-80 8 21 for later useMX-80 (VTT3.3) MX-80 8 17 for gap fillingMX-80 (VTT3.4) MX-80 6 21 for gap fillingMX-80 (VTT3.5) MX-80 6 17 for gap filling

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Figure 32. Pellet production capacity.

5.4.2.4 Pellet length of extruded pellets

The pellet length variations were studied from the pellets made in 2nd and 3rd extrusion sessions. The measured results are presented in the following subsections.

5.4.2.5 VTT Pellets - Length variation from the 2nd extrusion test

All of the manufactured bentonite pellets were extruded with the same cut blade setting. This means that the overall deviation of the equipment, handling and material properties of the used bentonite raw material type created the possible length distribution differences. Commercial Cebogel pellets were also measured for a reference. The average pellet length for all material batches stayed within 0.5 mm from each other (11.0-11.5 mm), while the maximum measured lengths being between 17-20 mm. The summary of the results is presented in Table 11. The individual graphs are presented from Figure 33 - Figure 38.

Table 11. Pellet length variation summary from the 2nd extrusion test.

Average StDev Min MaxMX-80 (VTT2.6) 11,0 3,1 4,3 17,6

75% MX-80 + 25% Illite (VTT2.2) 11,5 3,0 3,9 19,6

100% Milos B (VTT2.3) 11,5 3,1 4,1 20,4100% Milos A (VTT2.4) 11,5 2,5 6,6 18,875% MX-80 + 25% Sand (VTT2.5) 11,0 2,6 5,3 18,5Cebogel QSE 10,7 3,8 4,6 20,5

Length (mm)Bentonite type

40

Figure 33. VTT extruded MX-80 pellet length variation.

Figure 34. VTT extruded MX-80+ illite mixture pellet length variation.

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Figure 35. VTT extruded Milos A pellet length variation.

Figure 36. VTT extruded Milos B pellet length variation.

0

5

10

15

20

25

30

2 4 6 8 10 12 14 16 18 20 22 More

Frequency

Length (mm)

100% Milos B (VTT2.4)

42

Figure 37. VTT extruded MX-80 + sand pellet length variation.

Figure 38.Commercial Cebogel QSE pellet length variation.

5.4.2.6 VTT Pellets - Length variation from the 3rd extrusion test

All the manufactured bentonite pellets were again extruded with the same cut blade setting. The average pellet lengths for 17% water content MX-80 6 mm and 8 mm pellets were almost identical (12.2 and 12.4 mm). The average pellet lengths for 21% water content MX-80 6 mm and 8 mm pellets were also almost identical (14.5 and 14.7 mm) when compared to each other but about 2 mm longer than the lower water content pellets. The summary of the results is presented in 12. The individual graphs are presented from Figure 39 - Figure 42.

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Table 12. Pellet length variation summary.

Figure 39. VTT extruded 6mm 17% MX-80 pellet length variation.

Figure 40. VTT extruded 6mm 21 % MX-80 pellet length variation.

Average StDev Min MaxMX-80, 6mm, 17% (VTT3.4) 12,2 3,5 4,3 18,6MX-80, 6mm, 21% (VTT3.5) 14,7 2,3 7,2 18,6MX-80, 8mm, 17% (VTT3.3) 12,4 2,6 5,6 16,6MX-80, 8mm, 21% (VTT3.1) 14,5 2,1 6,7 18,2

Bentonite typeLength (mm)

44



5.4.3 Conclusions

It was found that bentonite with a water content of 16-24 % can be pelleted with extrusion press machinery. As expected, the raw material water content when the extrusion is used needs to be higher than with roll-pressing machines. With roll-pressed pellets the water content can be 10 % or even lower. However the Finnish buffer reference design has a target pellet water content of 17 % ±1 % to be used in the gap between buffer and deposition hole rock wall. It was shown that this kind of pellets can be produced by extrusion technique in good quality. It should be noted that the commercial available pellets, like Cebogel QSE, can have even higher water content.

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For instance, some commercial batches have been measured to have as high as 26 % water content. The pellet length distribution is also a factor when the gap filling properties are considered. The relatively narrow gap of 50 mm gives limits to the individual pellet length. As a rule of thumb one can consider that each individual pellet should not exceed more than 1/3 of the gap size to prevent bridging. This means in the gap filling scenario that the maximum pellet length should be kept less than about 17 mm. Commercial available pellets are not generally manufactured with this in mind nor are they sorted or sieved to meet this criteria. This feature could be however added as a requirement when bentonite pellet procurements are made to commercial factories. In this study the extrusion process was tuned so that the pellet median size was close to the target 14-15 mm in length, which made the pellets behave more constant during gap filling and saved the sieving process. The goal of making the 8mm diameter extruded pellets from 17 % water content raw material in good quality was achieved. Also 6mm diameter extruded pellets were successfully made from the same raw material with as good quality. With higher 21 % water content, the same diameter pellets were also made having the same satisfactory results. This knowledge can later be put to use for example if large scale experiments need extruded pellets.

5.4.4 Other VTT laboratory test results

5.4.4.1 Pellet crush strength tests (AECL and 2nd VTT extrusion)

In total 12 different pellet types were tested. These included five extruded pellet types made by VTT (from extrusion test session 2), five roller pressed pellet types made by AECL, commercial Cebogel pellets, and the reference Buffer Test pellets. The materials and pellet sizes are presented in Table 13 and Table 14. 10 individual pellets of each type were tested, except for Cebogel and MX-80 extruded by VTT which had 20 pellets tested.

Table 13. List of diameters for extruded pellets made by VTT, except for Cebogel which is a commercial product, used in these crush strength tests.

Sample name Bentonite type Pellet diameter (mm)

Cebogel QSE Cebogel 6,3MX-80 (VTT2.6) MX-80 (failed # 1) 8,0MX-80 (VTT2.5) 75% MX-80 + 25% Sand 8,0MX-80 (VTT2.2) 75% MX-80 + 25% Illite 8,0MX-80 (VTT2.3) 100% Milos A 8,0MX-80 (VTT2.4) 100% Milos B 8,0

46

Table 14. Roller pressed pillow-shaped pellets made by AECL, except for reference Buffer Test pellets which were made by Hosokawa Bebex, used in these crush strength tests.

The water contents of the crushed pellets are presented in the Figure 43. It shows the trend that extruded pellets have higher water content than roller pressed ones. There are two batches of MX-80 pellets designated as failed. These were done with the small extrusion machine in the second extrusion session and the pelleting process was observed to have too high temperatures. These pellets were included in the crush strength test to see how they perform against other extruded pellets.

Figure 43. Water content summary of the crushed pellets.

Sample name Pellet size

(mm)100% Wyoming, large (AECL) 23 x 15 x 9100% Wyoming, small (AECL) 10 x 10 x 6

75% Wyom. + 25% Sand (AECL) 10 x 10 x 675% Wyom. + 25% Illite (AECL) 10 x 10 x 6

Buffer Test 12 x 12 x 5.5

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During the pellet crush strength tests the maximum force and also displacement at maximum force was recorded. For the extruded type of pellets, the individual pellet lengths were taken into account by normalising the data to N/mm units. An example of a data set of 20 pellets from VTT extruded MX-80 is shown in the Figure 44. These kinds of plots show graphically the possible spread of the data. Also it can be noted that in some cases while the maximum force varies, also the displacement values can vary, resulting in deviation in that direction too.

The next two figures show more detailed graphs of this same issue. In Figure 45 the maximum values for each pellet type is plotted with the maximum displacement. In Figure 46 the crush strength test average values are plotted with error bars to visualize the spreads. From this figure it can be seen that, for example, Milos B VTT extruded pellets have an even variation in both directions. Also in the same figure the MX-80 VTT extruded pellets show a large variation over the displacement value. This would indicate that some of the MX-80 extruded pellets were softer than other. Possible reasons for this could be for example unevenly distributed initial water content within the raw material or the pelleting process caused this deviation.

Figure 44. Example of an actual data plot from MX-80 pellet crush strength test.

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Figure 45. Normalised pellet crushing data (maximum values) showing the displacement diversity.

Figure 46. Normalised crushing data with error bar analysis.

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The pellet crush strength results from VTT’s 2nd extrusion pellet manufacturing session, with Cebogel as the reference, are shown as a bar chart in Figure 47. All the pellets in that test were 8 mm in diameter except Cebogel, which had a nominal diameter of 6.3 mm. Note that the force numbers are shown as un-normalised actual measured values. In the Figure 48 the same results are shown as normalised by the actual length of each pellet. In the same figure there is also the average value of the hand screw measurements, which were made at the same time as extrusion for MX-80 pellets. The hand screw values show good agreement when compared to material test machine values. Based on these results the hand screw can be valuable aid during the pelleting process for quick assessments of the pellets. In the Figure 49 the crush strength measurements made by AECL with their equipment in Canada and the measurements made by VTT in Finland for the same pellets can be seen. The results show fairly good agreement with each other. Also the shipping of the pellets and their possible water content change can affect the results.

Figure 47. Pellet crush strength test results from 2nd extrusion pellet manufacturing session.

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Figure 48. Normalised pellet crush strength test results from 2nd extrusion pellet manufacturing session with hand screw measurements.

Figure 49. AECL and VTT measured pellet crush strength results.

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5.4.4.1 Pellet crush strength tests (3rd VTT extrusion) results

Figure 50. Pellet crush strength test results from 3rd extrusion pellet manufacturing session.

Figure 51. Normalised pellet crush strength test results from 3rd extrusion pellet manufacturing session.

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Table 15. The extruded pellets used in crush tests summary table.

Figure 52. Normalised pellet crushing data (maximum values) showing the displacement diversity.

Bentonite typeAverage

crush strength (N)

Standard deviation

(N)

Average strength /

length (N/mm)

Standard deviation (N/mm)

Displacement at crushing

(mm)

Standard deviation

(mm)

MX-80, 6mm, 17% (VTT3.5) 241 29 14,19 1,65 0,2 0,068MX-80, 6mm, 21% (VTT3.4) 244 29 14,09 1,57 0,195 0,025MX-80, 8mm, 17% (VTT3.3) 169 35 11,88 2,34 0,208 0,053MX-80, 8mm, 21% (VTT3.1) 238 39 14,72 2,27 0,27 0,095

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Figure 53. Normalised crushing data with error bar analysis.

5.4.4.2 Thermal conductivity tests of the Buffer Test pellets

Thermal conductivity measurement of the reference Buffer Test pellets were first measured with thermal probe method. The bentonite pellets were hand compacted into the plastic cylinder and the calculated bulk density was 1045 kg/m3.The thermal conductivity tests were performed three times. The measured thermal conductivity values varied between 0.21-0.24 W/Km and the average thermal conductivity was 0.22 W/Km. The second set of Buffer Test thermal conductivity measurements were done with heat flow meter method. The bentonite pellets were hand compacted into insulated frame and the calculated bulk density was 1257 kg/m3. The measured average thermal conductivity value was 0.19 W/Km.

5.4.4.3 Water filtration

Small laboratory glass filtration tests

The water absorption and swelling of bentonite pellets were tested prior to the artificial wetting tests. The tests were performed in glass decanters. The amount of pellets used was 4000ml unless stated otherwise. Total of 11 different scenarios of pellets were tested. Pellets were poured in and tap water was added until all pellets were covered. Water was added during the tests at all times when the surface was dry and capable of absorbing more water. Tests were ended when the surface was no longer capable of absorbing water. Photographic images were taken throughout the tests (Figure 54). Measurements during tests were done on the amount of water that could be added and

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how much swelling of the bentonite pellets was happening. After tests, water contents were measured for samples from next to the glass and middle of the mass at top, centre and bottom of the glass decanter. Results and information on tested pellets can be found from Table 16. Water content sampling is represented in Figure 55. Water content results for post-test samples are presented in Table 17 and in Figure 56.

Figure 54. Photographic documentation taken during small-scale glass filtration tests.

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Table 16. Results and information on tested pellets.

Figure 55. Post-test water content sampling locations.

Table 17. Post-test water contents results.

Sample nameBentonite Mass (g)

Initial Added

Water (g)

Final Added

Water (g)

Initial Added Water Ratio

(%)

Final Added Water Ratio

(%)

Total Swelling (ml)

Total Swelling (%)

Buffer Test (2000ml) 2345.0 881.4 1010.2 37.6 43.1 367.4 18.4Buffer Test 4554.7 1798.8 2114.5 39.5 46.4 718.0 18.0100% Wyoming, large (AECL) 4685.4 1694.4 2040.4 36.2 43.5 1024.6 25.6100% Wyoming, small (AECL) 4661.8 1782.9 2222.1 38.2 47.7 1025.6 25.675% Wyom. + 25% Sand (AECL) 5018.2 1730.7 2103.4 34.5 41.9 1148.5 28.775% Wyom. + 25% Illite (AECL) 4871.3 1794.4 2291.5 36.8 47.0 1073.2 26.8100% Milos A (AECL) 4532.7 1756.9 2292.4 38.8 50.6 1077.7 26.9100% Milos B (AECL) 4560.1 1989.9 3007.5 43.6 66.0 1561.0 39.0MX-80 (VTT3.1) 4550.0 1733.5 1964.2 38.1 43.2 895.8 22.4Cebogel 2000ml 2230.6 858.6 1018.0 38.5 45.6 345.0 17.0Cebogel 4307.8 1908.5 2144.4 44.3 49.8 - -

Surface, middle

Surface, next to glass

Center, middle

Center, next to glass

Bottom, middle

Bottom, next to glass

Buffer Test (2000ml) 79,9 77,6 56,9 70,0 68,9 71,1Buffer Test - - 67,7 68,9 72,2 71,7100% Wyoming, large (AECL) 85,5 110,8 48,1 67,5 52,5 58,2

100% Wyoming, small (AECL) 120,6 138,7 54,1 54,5 52,9 55,075% Wyom. + 25% Sand (AECL) 90,7 81,2 43,7 44,9 46,2 46,2

75% Wyom. + 25% Illite (AECL) 132,4 108,8 55,1 58,2 60,2 58,2100% Milos A (AECL) 124,2 129,2 57,7 60,5 62,5 62,8100% Milos B (AECL) 97,6 106,4 75,9 83,0 67,6 81,3MX-80 (VTT3.1) 123,1 111,5 58,6 66,5 57,2 55,5

Water Content (%) atSample name

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Figure 56. Post-test water content results in graphical form.

Long tube filtration test

The reference commercial roller-compacted MX-80 Buffer Test bentonite pellets were tested in the laboratory for their water filtration behaviour in longer test tube setup (Figure 57). The tube was 2020 mm in height and had an inner diameter of 88 mm. The pellets were installed by pouring them up to 1600 mm level in smaller batches, without any compaction method. The bentonite pellet mass was 11 kg, giving a bulk density of 1087 kg/m3. The pellets were watered with tap water from a pump capable of delivering about 500 kPa of pressure. The exact pumping pressure was not monitored in the initial laboratory test. The amount of water used in the first wetting phase was 4.76 kg. Then the water level was about 10.0 mm over the pellets (equalling 0.06 kg of water). About 34 minutes later more water (+1.54 kg) was added to the system totalling 5.36 kg. Then the water level was 80.0 mm over the top pellets (equalling 0.487 kg of water). The mass ratio between water and pellets was 44 % after the first phase and 55 % after the second. The flow rate in the laboratory test was 3.3 litres per minute. The water first reached the bottom of the tube and then the water level rose to the top. Air was coming out from the top but some of the air stayed trapped in the pockets between pellets. During the second water addition time, more air moved up towards the top along water paths. When the pump was stopped there were still bubbles coming out of the water sitting above the pellets. The test was stopped after 50 minutes from the start and the total uplift at that time was 20.0 mm.

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It was noted that the pellet filling lifted upwards very little when compared to earlier small tube laboratory tests. The reason for this may be the higher height of the filling, different packing ratio and the smaller inside diameter of the tube which may create more friction forces. After half an hour the filling had an uplift of 12.0 mm indicating that it would be manageable during the first phase test of bentonite buffer in ONKALO. Based on these results it was estimated that the initial watering of the 266 kg pellet filling in ONKALO with 120 litres will last about 9 minutes when done with four nozzles. After the initial water is absorbed by the pellet filling there should be some time when more water can still be added with the current pump setup.

Figure 57. a) MX-80 Buffer Test pellets inside the test tube before starting the long tube filtration test.

Figure 58. b) A captured frame from video just after the water front has passed the water nozzle.

Figure 59. c) The MX-80 Buffer Test pellets 20 minutes after watering.

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6 DISCUSSION

6.1 Discussion and conclusions

The goal of this work was to provide knowledge about how to manufacture customized bentonite pellets and how customized bentonite pellets perform in practice during the nuclear repository construction process. The project was mainly focused on laboratory experimental tests to optimize the pellet filling by customizing the raw materials and pellet manufacturing. Bentonite pellets were made using both extrusion and roller compaction methods. The pellets were intended for use in gaps between compacted bentonite and the rock walls in both buffer deposition holes and tunnel backfilling. Performance of different types of custom-made pellets were evaluated with regard to their ease of manufacturing, density, crush strength, abrasion resistance, water holding capacity, free swelling and also their thermal conductivity. These evaluations were done in both Finland (by VTT) and Canada (by AECL). Over 50 different varieties of pellets were roller-compaction manufactured at AECL in Canada and 20 types of extrusion pellets at VTT in Finland. The parameters that were varied during manufacturing included: bentonite raw material type, water content, pellet sizes, bentonite compaction machine parameters, use of recycled pellets, and addition of two different types of filler (illite or granitic sand) at varying addition percentages. By examining the pellets produced by these methods and materials the performance and behaviour were evaluated in laboratory with selected tests. The roller-compacted pellets having the best performance in placement trials were the smallest size (~9 mm diameter and 6 mm thick). The gravimetric water content of these pellets was limited to 7-15 % for manufacturing reasons. There was a good correlation between crush strength and abrasion resistance of the pellets. The water holding capacity of this size of pellet, which is desired during tunnel backfilling, was improved when using lower quality bentonite Milos B (Ibeco RWC-BF) compared to MX-80 or Milos AC200 in the case of poured pellets. It should be noted that in the case of tunnel backfilling, spraying the pellets in place with slight moisture addition may alter the results. The work done using extrusion pellets showed that it was possible to manufacture pellets with higher water contents, up to 21 % from MX-80. This water content value was higher than what was typically possible using roller-compaction method in this study. Higher water content values allow closer compatibility with the designed bentonite buffer water content. The extrusion tests also showed that the required production simulation runs could be made successfully with reference type of MX-80 bentonite raw material at 17 % water content for 6 mm and 8 mm sizes of bentonite pellet diameters. This means that it is possible to produce in house customized extruded pellets for future tests domestically.

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6.2 Future work recommendations

To gain more knowledge how to optimize the utilization, manufacturing or installation process of bentonite pellets needed in the repository construction process more studies could be commissioned. A few possible focus areas are drafted here in the next paragraphs. The thermal conductivity of the pellet filling in the gap between the deposition hole rock surface and the bentonite block is one of the key parameters in thermal behaviour of the bentonite buffer. The disposed copper canister produces residual heat due to decay of radioactive products. The decay heat is conducted through the bentonite buffer and the pellet filling to the surrounding rock mass. If the thermal conductivity of the pellet filling is too low the surface temperature of the canister will rise too high and the spacing between adjacent canisters should be increased. To have more accurate parameters for models more detailed laboratory tests could be commissioned. Most of the tests are usually done in quite small scale and the actual tall and narrow geometry (8000 mm height, 50 mm wide) of the vertical repository is not taken in account in the test setups. More accurate testing equipment and methods could be planned and manufactured in separate continuation studies. The placeability of the bentonite pellets by various technical installation methods could be further optimized by adjusting the bentonite raw material properties. Also the pellet’s shape and size distribution, surface texture and other external features could be fine-tuned while having the actual installation methods in mind. The packing and filling behaviours should be studied together laboratory tests and with Discrete Element Method (DEM) computer simulations. For example there could be a vertical density gradient in the pellet filling which depends on the actual filling method and pellet behaviour. If the lowest part of the pellet filling has higher density which exceeds design variation tolerances this may then lead to a need to lower an individual bentonite buffer block density by increasing its water content or by lowering compression pressure. Pellet manufacturing processes and techniques could be enhanced to take other possible raw material flows and sources such as using rejected bentonite buffer blocks better into account. Also the sieving, sorting and classification procedures of pellets could be improved at factory level to be more suitable for bentonite pellets intended to be used in repositories.

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REFERENCES

Holt, E., Marjavaara, P., Löijä, M., Artificial Wetting of Buffer Material – Small Scale. Posiva Working Report 2011-53. Juvankoski, M., Jalonen, T., Ikonen, K. 2012. Buffer Production Line Report: Design, Production and Initial State of the Buffer, Posiva Oy, Eurajoki, Report 2012-17. ISBN 978-951-652-198-8. Keto, P. (ed.), Hassan, Md. M., Karttunen, P., Kiviranta, L., Kumpulainen, S., Sievänen, U., Korkiala-Tanttu, L., Koskinen, V., Koho, P. & Jalonen,T. 2012. Backfill Production Line Report: Design, production and initial state of the deposition tunnel backfill and plug., Posiva Oy, Eurajoki, Report 2012-18. ISBN 978-951-652-199-5. Kim. C.S., Man, A., Dixon, D. Holt, E., Fritzell, A. 2012. Clay-Based Pellets for Use in Tunnel Backfill and as Gap Fill in a Deep Geological Repository: Characterisation of Thermal-Mechanical Properties. 2012. TR 2012-05, NWMO, Canada. Marjavaara, P., Kivikoski, H., Filling the Gap between Buffer and Rock in the Deposition Hole. Posiva Working Report 2011-23.

Standards

ASTM D5334 – 08. Standard Test Method for Determination of Thermal Conductivity of Soil and Soft Rock by Thermal Needle Probe Procedure. EN 1097-1:2001 Tests for mechanical and physical properties of aggregates. Part 1: Determination of the resistance to wear (micro-Deval). EN 12667:2001 Thermal performance of building materials and products- Determination of thermal resistance by means of guarded hot plate and heat flow meter methods - Products of high and medium thermal resistance. Vuorinen, Jarmo. 1999. Papers of Road Office in Finland 30/1999. The comparability of Nordic abrasion test and Micro-Deval test. Finnish Road Administration. 2000. 28 pp. in Finnish.

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APPENDIX 1: INDIVIDUAL WETTING TEST DETAILS

Individual test details: Test #10 Buffer test pellets

Figure 60. A group of Buffer test pellets and sample after artificial wetting test.

Wetting test #10 was done 26.10-2.11.2011 Material: Buffer test pellets Water content before testing: 16,2 % Bulk density (from gap filling test): 1067 kg/m3 Mass of pellets: 16,4 kg Water added: 11,5 kg Watering method: top Duration time: 6,5 days Average water content after test: 59,9 % Average bulk density after test: 994,7 kg/m3 Preload force to lid: 12 kN Lid force in the end of test: 10,5 kN Radial pressure average after 6,5 days: 57,8 kPa

Individual test details: Test #11 Cebogel pellets

Figure 61. A group of Cebogel pellets and sample after artificial wetting test.

Wetting test #11 was done 9.11-25.11.2011 Material: Cebogel pellets Water content before testing: 20,1 % Bulk density (from gap filling test): 1107 kg/m3

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Mass of pellets: 15 kg Water added: 7,4 kg Watering method: bottom Duration time: 15,8 days Average water content after test: 69,6 % Average bulk density after test: 906 kg/m3 Preload force to lid: 1 kN Lid force in the end of test: 0,2 kN Radial pressure average after 15,8 days: 29,8 kPa

Individual test details: Test #12 100% Wyoming, small (AECL) pellets

Figure 62. A group of 100 % Wyoming, small (AECL) pellets and sample after artificial wetting test.

Wetting test #12 was done 28.11-14.12.2011 Material: 100 % Wyoming, small (AECL) pellets Water content before testing: 9,2 % Bulk density (from gap filling test): 1112 kg/m3 Mass of pellets: 17 kg Water added: 9,2 kg Watering method: bottom Duration time: 14,7 days Average water content after test: 50,5 % Average bulk density after test: 1079 kg/m3 Preload force to lid: 1 kN Lid force in the end of test: 3,9 kN Radial pressure average after 14,7 days: 119,3 kPa

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Individual test details: Test #13 Buffer test pellets

Figure 63. A group of Buffer test pellets and sample after artificial wetting test.

Wetting test #13 was done 16.12.2011-3.1.2012 Material: Buffer test pellets Water content before testing: 16,4 % Bulk density (from gap filling test): 1067 kg/m3 Mass of pellets: 14 kg Water added: 6,3 kg Watering method: bottom Duration time: 17,9 days Average water content after test: 69,5 % Average bulk density after test: 952 kg/m3 Preload force to lid: 0,5 kN Lid force in the end of test: 1,3 kN Radial pressure average after 17,9 days: 42,7 kPa

Individual test details: Test #14 100% Wyoming, large (AECL) pellets

Figure 64. A group of 100% Wyoming, large (AECL) pellets and sample after artificial wetting test.

Wetting test #14 was done 4.1-19.1.2012 Material: 100 % Wyoming, large (AECL)pellets Water content before testing: 17 % Bulk density (from gap filling test): 1092 kg/m3 Mass of pellets: 17 kg

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Water added: 6,7 kg Watering method: bottom Duration time: 14,8 days Average water content after test: 56,2 % Average bulk density after test: 1083 kg/m3 Preload force to lid: 0,5 kN Lid force in the end of test: 3,1 kN Radial pressure average after 14,8 days: 73,0 kPa

Individual test details: Test #15 100% Milos A (AECL)

Figure 65. A group of 100 % Milos A (AECL) pellets and sample after artificial wetting test.

Wetting test #15 was done 20.1-3.2.2012 Material: 100 % Milos A (AECL) pellets Water content before testing: 11,6 % Bulk density (from gap filling test): 1047 kg/m3 Mass of pellets: 15,8 kg Water added: 7,2 kg Watering method: bottom Duration time: 13,7 days Average water content after test: 67,6 % Average bulk density after test: 945 kg/m3 Preload force to lid: 0,5 kN Lid force in the end of test: 0,8 kN Radial pressure average after 15,8 days: 76,6 kPa

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Individual test details: Test #16 100% Milos B (AECL)

Figure 66. A group of 100 % Milos B (AECL) pellets and sample after artificial wetting test.

Wetting test #16 was done 6.2-22.2.2012 Material: 100 % Milos B (AECL) pellets Water content before testing: 13,1 % Mass of pellets: 16,2 kg Water added: 7,2 kg Watering method: bottom Duration time: 15,9 days Average water content after test: 65,6 % Average bulk density after test: 967 kg/m3 Preload force to lid: 0,5 kN Lid force in the end of test: 0,6 kN Radial pressure average after 15,9 days: 30,9 kPa

Individual test details: Test #17 75% Wyom. + 25% illite (AECL)

Figure 67. A group of 75 % Wyom.+25 % Illite (AECL) pellets and sample after artificial wetting test.

Wetting test #17 was done 28.2-15.3.2012 Material: 75 % Wyom. + 25 % Illite (AECL) pellets Water content before testing: 10 % Mass of pellets: 17,4 kg Water added: 7,0 kg

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Watering method: bottom Duration time: 15,9 days Average water content after test: 52,2 % Average bulk density after test: 1085 kg/m3 Preload force to lid: 0,5 kN Lid force in the end of test: 1,6 kN Radial pressure average after 15,9 days: 62,6 kPa

Individual test details: Test #18 MX-80, 8mm extruded (VTT)

Figure 68. A group of MX-80, 8mm (VTT) extruded pellets and sample after artificial wetting test.

Wetting test #18 was done 21.3-5.4.2012 Material: MX-80 (VTT) pellets Water content before testing: 23,6 % Mass of pellets: 15,7 kg Water added: 6,9 kg Watering method: bottom Duration time: 15,9 days Average water content after test: 76,1 % Average bulk density after test: 870 kg/m3 Preload force to lid: 0,5 kN Lid force in the end of test: 0,9 kN Radial pressure average after 15,9 days: 47,3 kPa

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Individual test details: Test #19 75% Wyom. + 25% sand (AECL)

Figure 69. A group of 75 % Wyom. +25 % Sand (AECL) pellets and sample after artificial wetting test.

Wetting test #19 was done 11.4-27.4.2012 Material: 75 % Wyom. + 25 % Sand (AECL) pellets Water content before testing: 7,4 % Mass of pellets: 17,9 kg Water added: 7,2 kg Watering method: bottom Duration time: 15,9 days Average water content after test: 46,4 % Average bulk density after test: 1137 kg/m3 Preload force to lid: 0,5 kN Lid force in the end of test: 1,9 kN Radial pressure average after 15,9 days: 85,6 kPa

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Documents

Customized Bentonite Pellets: Manufacturing, Performance