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Bentonite Pellet Thermal ConductivityTechniques and Measurements
POSIVA OY
Olki luoto
FI-27160 EURAJOKI, F INLAND
Phone (02) 8372 31 (nat. ) , (+358-2-) 8372 31 ( int. )
Fax (02) 8372 3809 (nat. ) , (+358-2-) 8372 3809 ( int. )
May 2015
Working Report 2015-09
Harri Kivikoski, Ismo Heimonen, Hannu Hyttinen
May 2015
Working Reports contain information on work in progress
or pending completion.
Harri Kivikoski, Ismo Heimonen, Hannu Hyttinen
VTT
Working Report 2015-09
Bentonite Pellet Thermal ConductivityTechniques and Measurements
BENTONITE PELLET THERMAL CONDUCTIVITY TECHNIQUES AND MEASUREMENTS
ABSTRACT
The goal of the project was to specify and define how to get accurate thermal conductivity values from bentonite pellets. The pellets are used in a nuclear repository for filling the gap between bentonite buffer and rock in the deposition hole. The main objective of this research was to develop the Hot Box device (standards ISO 8990 (1994) and SFS-EN ISO 12567-1 (2000) to measure thermal conductivity of the gap filling pellets.
Thermal conductivity of the bentonite pellets is depending on the water content, density and degree of saturation 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.
Thermal conductivity of the pellet filling can be measured by either the stationary heat flow method or the transient method. In the stationary heat flow method steady-state techniques perform a measurement when the temperature of the material measured does not change with time. The constant thermal gradient is caused over the bentonite pellet filling. Stationary heat flow devices for the thermal conductivity measurements are a heat flow meter and Hot Box. The transient techniques perform a measurement during the process of heating up. The advantage is that measurements can be made relatively quickly. The transient method is less accurate than stationary heat flow method. Transient methods are usually carried out by heated probes or planes.
A Hot box device was used for the thermal conductivity measurements. A Hot Box consists of three chambers: the cold chamber, the warm chamber and the metering chamber which is located inside the warm chamber. The insulated metering chamber reduces the heat loss through the metering chamber to a minimum as the metering chamber and the warm chamber temperatures are kept the same. The dimensions of the Hot Box device are: length of 3.3 m, width of 2.7 m and height of 3.3 m.
A polycarbonate mould was built to hold the bentonite pellets during measurements. The outside dimensions of the mould were 1.19 m x 1.19 m and the width of the gap was 50 mm. The thermal conductivity of the bentonite pellets was measured for two pellet types. The chosen pellet types were the Buffer Test Pellets Batch 2 and the VTT Extruded MX-80 pellets. The Buffer Test Pellets Batch 2 was made by Hosokawa Bepex in Germany. The raw material for these pellets was also MX-80 bentonite. The pellets were pillow shaped and the dimensions were 12 x 12 x 6 mm. The water content was 16.6% and the bulk density was 1075 kg/m3. One test was carried out with dried pellets. The water content of the VTT Extruded MX-80 pellets was 15.25% and the bulk density was 986 kg/m3. The pellets were cylinder shaped and the diameter of the individual pellet was 8 mm and the average length was 12 mm. The pellets were poured into the mould.
The temperature gradients over the gap filling in the thermal conductivity tests were chosen to be between 2.0–4.1 °C/cm.
After all thermal conductivity tests, samples were taken from the cold and warm sides of the pellet filling and the redistribution of the water content was determined. The measured thermal conductivities of the Buffer Test Pellets Batch 2 were either 0.17 W/Km (dry) or 0.19 W/Km (water containing). The used temperature gradient did not have a significant effect on the thermal conductivity values. The thermal conductivity of the VTT Extruded pellets was 0.17 W/Km which was 0.02 W/Km lower than with the Buffer Test Pellets Batch 2 at nearly the same water content.
Keywords: KBS-3V, spent fuel repository, buffer, gap filling, bentonite pellets, thermal conductivity.
Bentoniittipellettien lämmönjohtavuuden määritysmenetelmät ja mittaukset
TIIVISTELMÄ
Työn tavoitteena oli määrittää menetelmät, joilla saadaan mitattua luotettavasti ja tar-kasti loppusijoitusreiässä kallion ja bentoniittilohkojen väliseen rakoon asennettujen bentoniittipellettien lämmönjohtavuus. Tutkimuksen päätavoitteena oli kehittää Hot Box laitetta bentoniittipellettien lämmönjohtavuusmääritykseen.
Bentoniittipellettien lämmönjohtavuus on riippuvainen pellettien vesipitoisuudesta, tiheydestä, kyllästysasteesta, yksittäisten pellettien koosta ja muodosta sekä raon geo-metriasta ja mitoista bentoniittipuskurissa. Bentoniittipellettien lämmönjohtavuuden tarkkaan määrittämiseen vaikuttavat tutkittavan näytteen koko ja mittalaitteiston tarkkuus.
Bentoniittipellettien lämmönjohtavuus voidaan määrittää joko stationaari- tai transient-timenetelmällä. Stationaarimenetelmässä bentoniittipellettitäytön yli aiheutetaan vakio-lämpötilagradientti. Lämmönjohtavuuden määrityksen käytettäviä stationaarimenetel-miä ovat lämpövirtalevylaitteisto ja Hot Box-laitteisto. Transienttimenetelmässä tutkit-tavaan näytteeseen aiheutetaan lämpöpulssi syöttämällä vakiovirta sondin lämmitys-vastukseen. Sondissa olevalla lämpötila-anturilla seurataan lämmityksen seurauksena näytteessä syntyvää lämpötilan nousua ajan suhteen. Transienttimenetelmä ei ole yhtä tarkka kuin stationaarimenetelmä. Tyypillisiä Transienttimenetelmiä lämmönjohtavuus-määritykseen ovat lämmönjohtosondi- ja hot disk-menetelmä.
Hot Box- laitteistoa käytettiin bentoniittipellettien lämmönjohtavuuden määrittämiseen. Hot Box- laitteisto koostuu kolmesta kammiosta: kylmäkammiosta, lämpökammiosta ja mittauskammiosta, joka sijaitsee lämpökammion sisällä. Lämmöneristetty mittauskam-mio vähentää lämpöhäviön mittauskammiosta minimiin kun mittauskammion ja lämpö-kammion lämpötilat pidetään samana. Hot Box- laitteiston mitat ovat: pituus 3,3 m, leveys 2,7 m ja korkeus 3,3 m.
Bentoniittipellettien lämmönjohtavuusmäärityksiin rakennettiin polykarbonaattimuotti, jonka ulkomitat olivat 1,19 m x 1,19 m ja raon paksuus oli 50 mm. Bentoniittipellettien lämmönjohtavuusmääritykset tehtiin kahdelle pellettityypille Buffer Test Pellets Batch 2 pelleteille ja VTT Extruded MX-80 pelleteille. Buffer Test Pellets Batch 2 pelletit oli valmistanut Hosokawa Bepex Saksassa. Pellettien raaka-aineena oli MX-80 bentoniitti. Pelletit olivat tyynyn muotoisia ja yksittäisen pelletin mitat olivat 12 x 12 x 6 mm. Pel-lettien vesipitoisuus oli 16,6 % ja tilavuuspaino 1075 kg/m3. Yksi lämmönjohtavuus-määritys tehtiin kuivatuilla pelleteillä. VTT Extruded MX-80 pellettien vesipitoisuus oli 15,25 % ja tilavuuspaino 986 kg/m3. Pelletit olivat muodoltaan sylinterimäisiä ja yksit-täisen pelletin halkaisija oli 8 mm. Pelletit kaadettiin rakoon.
Pellettien lämmönjohtavuus määritettiin lämpötilagradienteilla 2,0–4,1 °C/cm. Kaikkien lämmönjohtavuusmääritysten jälkeen otettiin vesipitoisuusnäytteet pellettitäytön kyl-mältä ja lämpimältä pinnalta eri korkeuksilta rakotäyttöä. Buffer Test Pellets Batch 2 pelleteillä mitatut lämmönjohtavuudet vaihtelivat välillä 0,17–0,19 W/Km. Alhaisimmat lämmönjohtavuudet mitattiin kuivatuilla pelleteillä. Kokeissa käytetyillä lämpötila-gradienteilla ei ollut merkittävää vaikutusta lämmönjohtavuusarvoihin. VTT Extruded pelleteillä mitattiin lämmönjohtavuudeksi 0,17 W/Km.
Avainsanat: KBS-3V, loppusijoituspaikka, puskuri, bentoniittipelletti, rakotäyttö, läm-mönjohtavuus.
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TABLE OF CONTENTS
1. OBJECTIVE .......................................................................................................... 3
2. BACKGROUND ..................................................................................................... 5
3. LITERATURE REVIEW ......................................................................................... 7 3.1 Measuring Methods ...................................................................................... 7
3.1.1 Heat flow meter method .................................................................... 7 3.1.2 Thermal probe method ...................................................................... 7 3.1.3 Hot disk method ................................................................................ 8 3.1.4 Thermal conductivity assessment from the full scale Prototype
Repository test .................................................................................. 9 3.2 Calculation Methods ................................................................................... 14
3.2.1 Beziat Method /Beziat et al. 1988/ .................................................. 14 3.2.2 Knutsson and Johansen Method /Knutsson 1983/.......................... 15
3.3 Thermal Conductivity Values ..................................................................... 15 3.3.1 Sugita Conductivity Values /Sugita et al. 2003/ .............................. 16 3.3.2 Masuda Conductivity Values /Masuda et al. 2006/ ......................... 16 3.3.3 Hökmark Conductivity Values /Hökmark et al. 2010/ ...................... 16 3.3.4 Kim Conductivity Values /Kim et al. 2012/ ...................................... 17 3.3.5 Marjavaara Conductivity Values /Marjavaara et al. 2013/ ............... 18
4. VTT HOT BOX METHOD .................................................................................... 19
5. PROPERTIES OF THE PELLETS ...................................................................... 25
6. VTT HOT BOX RESULTS ................................................................................... 26 6.1 Test Parameters ......................................................................................... 26 6.2 Measured Values ....................................................................................... 26 6.3 Observations After Thermal Conductivity Tests ......................................... 27
7. CONCLUSIONS .................................................................................................. 33
8. REFERENCES .................................................................................................... 35
APPENDIX 1: MATERIAL DATA SHEET ..................................................................... 37
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3
1. OBJECTIVE
The goal of the project was to specify and define how to get accurate thermal conductivity values from bentonite pellets. The pellets are used in a nuclear repository for filling the gap between bentonite buffer and rock in the deposition hole and also for filling the gap between backfill blocks and tunnel wall. The thermal conductivity values may be later employed as key parameters in thermal modelling of the repository site. A main objective of this research was also to develop the Hot Box device to measure thermal conductivity of the gap filling pellets.
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5
2. BACKGROUND
The thermal conductivity of the pellet filling in the gap between the deposition hole rock surface and the bentonite buffer 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.
The maximum temperature of the canister surface and the buffer takes place in about 15 years after the disposal of the canister. The dimensioning temperature of the bentonite buffer is +100 °C. In the dry condition, in the dimensioning calculation, the nominal temperature is set to +95 °C. The 5 °C margin is showed to be enough for variation of thermal properties. In normal water saturation conditions the conductivity of bentonite is much higher and the nominal maximum temperature is about +75 °C. The nominal temperature is controlled by adjusting the space between adjacent canisters, adjacent tunnels and the pre-cooling time affecting on the decay power of the canisters /Ikonen et al. 2012/.
The hottest surface temperatures of the canisters will be those deposited in dry deposition holes in central parts of the deposition areas and where the thermal conductivity of the rock is lowest. The average thermal conductivity of the rock in ONKALO at +60 °C is 2.82 W/m/K. The analysis report for rock thermal properties gives the standard deviation in thermal conductivity at +25 °C as ±0.51 W/m/K /Kukkonen et al. 2011/.
Heat transport in materials like clay takes place in several ways /Pusch 2003/:
1. By conduction through interconnected minerals. 2. By conduction through water in continuous voids. 3. By convection in flowing porewater. 4. By vapor transport in unsaturated soil under the influence of a thermal gradient.
The thermal conductivity of a given soil with a given moisture content does not have a unique value because it depends on the boundary conditions, which may cause a moisture redistribution.
In soils, convection through air or water is usually negligible. Heat transfer by convection increases rapidly with an increase in soil pore diameter above a few millimetres, with an increase in ground temperature above 30 °C and with an increase in temperature gradient above about 1 °C/cm /Farouki 1986/.
The porosity of a soil has a strong influence on its thermal conductivity. The dry density γd of a soil is related to its porosity n by
γd = (1-n)γs
where γs is the unit weight of the solid grains. An increase in the porosity means a decrease in the dry density and more space between the solid particles. In the case of
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dry soils this means more air present and hence a lower thermal conductivity especially if the air is still.
The pore spaces in soils are available for movement of air, water vapour and liquid water, the result being the transfer of both mass and heat.
Heat transport across the porous pellet filling is a combination of conduction, radiation and convection and cannot easily be determined in laboratory – scale experiments.
Thermal conductivity of the bentonite pellets is depending on the water content, density and degree of saturation 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.
The most commonly used technique for determining the thermal conductivity of materials is to apply stationary heat flow through the sample. This technique is very accurate but difficult in the sense that it requires a constant thermal gradient in the sample. This is a problem in partially water saturated materials since the heat gradient will cause moisture redistribution in the sample. For this reason, a transient method that requires a very short measuring time should be used although it is less accurate /Börgesson et al. 1994/. On the other hand in a dry deposition hole the circumstance corresponds to a constant thermal gradient where moisture redistribution of the pellet filling is possible.
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3. LITERATURE REVIEW
3.1 Measuring Methods
A literature review was made from the available and published measurement methods of the bentonite pellets’ thermal conductivity. In the following subsections more detailed descriptions are given for three different laboratory measurement techniques and for one in-situ back calculating technique.
3.1.1 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 the standard (EN 12667:2001).
During the tests the bentonite pellets are hand compacted into an insulated frame with dimensions of 450 mm * 450 mm * 80 mm (Figure 3-1). The frame is then inserted to a machine for measuring over 48 hours period.
Figure 3-1. Thermal conductivity measurement of the bentonite pellets with heat flow meter method.
3.1.2 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 are hand compacted into the plastic cylinder with a diameter of 150 mm and a height of 200 mm (Figure 3-2). The length of the thermal probe is 160 mm. Typically the duration of the test will be for half an hour.
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Figure 3-2. Thermal conductivity measurement of the bentonite pellets with thermal probe method.
3.1.3 Hot disk method
In the hot disk method, a disk sensor is placed between two pieces of the sample material and is then heated by a constant electrical current for a short period of time (1 to 30 minutes). The generated heat dissipates from the sensor into the surrounding unknown sample material, causing a rise in temperature of the sensor and surrounding sample material. The average transient temperature increase of the sensor, of the order 0.5–5 °C, is simultaneously measured by monitoring the change in electrical resistance. The Temperature Coefficient of Resistivity of the sensor material correlates the change in resistivity with the corresponding change in temperature.
Figure 3-3. Hot Disk Sensor /Thermal-Instruments Ltd./
The time duration of the heating current is normally limited by the size of the sample, in order to avoid influence from the outside (lateral) boundaries of the sample. In addition, if the sample is much larger than the sensor diameter, the probing depth of the heating (thermal penetration depth) should be of the same magnitude as the radius of the Hot Disk sensor, ensuring stable values of both thermal conductivity and diffusivity.
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Sugita et al. 2003 measured thermal conductivity and thermal diffusivity of bentonite pellets by the hot disk method. A sensor sheet was installed at the center of the test cell filled with pellets, as shown in Figure 3-4.
Figure 3-4. Measurement of thermal properties /Sugita et al. 2003/.
A Hot Disk Thermal Constants Analyzer was used by C-S. Kim et al. 2012 to measure thermal conductivity of bentonite pellets. The system operates by supplying a pulse of constant heat to a sample sensor, which acts as both a heat source for increasing the temperature of the sample and a resistance thermometer to monitor the change in temperature after the heat pulse. The test configuration shown in Figure 3-5 is known as a one-sided test. It is performed by taking measurements with the test material in contact with only one side of the sensor. The other side of the sensor is in contact with an insulating material with pre-determined thermal properties. In this test series, rigid foam insulating material was used as the backing material. The material being tested was first poured into the container (of known volume) and then thermal properties were measured.
Figure 3-5. Measuring Thermal Conductivity of Pellet Fill using a One-sided Test Configuration /C-S. Kim et al. 2012/.
3.1.4 Thermal conductivity assessment from the full scale Prototype Repository test
The Prototype Repository test is a full scale field test carried out in Äspö, Sweden. Six full scale copper-shielded iron canisters with electrical heaters were placed in bentonite buffer. The planning of the test started in 1998 and the installation was completed in 2003.
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The effective thermal conductivity of the gap filling pellets was estimated from the Prototype Repository temperature profile measurements in the buffer. The measurement was made from the canister to deposition hole rock surface and from the radial heat flow of the canister /IPR-07-22 and R-09-04/.
The temperature at the block/pellets interface was calculated using Equation (1):
, (1)
where qr is the radial heat flux, W/m2 r0 is the canister radius, m r1 and r2 are radial positions of the temperature sensors, m.
The assumed bentonite block thermal conductivity was λb = 1.2 W/Km, which is an estimate for the initial bentonite block conductivity based on the experimental findings.
The radial heat flux was calculated using Equation (2):
(2)
where A is the total canister surface area, m2 Q(t) is the canister power, W ϕ is the surface flux ratio.
The measured and calculated temperatures from the Prototype Repository test are presented in Figure 3-6.
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Figure 3-6. Temperature profiles in the buffer at canister mid-height in hole #5 in the orientations 80°–85° (top) and 170°–180° (mid) and in hole #6 in the orientation 270° (bottom). The values at r = 0.825 are calculated and the rest are measured. The time indicates number of days since the heater in the corresponding hole was started /IPR-07-22/.
Using Equation (1) once more, the thermal conductivity of the gap filling was estimated.
In Figure 3-7 the obtained thermal conductivity ratio (λs/λb) and estimated pellet gap filling thermal conductivity are shown as a function of time since the corresponding heater was started. λs is the calculated thermal conductivity of the pellet filling (Equation 1).
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Figure 3-7. Conductivity ratio and estimated pellet gap filling thermal conductivity at canister mid-height in hole #5 in the orientations 80°–85° (top) and 170°–180° (mid) and in hole #6 in the orientation 270° (bottom). Unrealistic results (ratio > 1) are indicated with a shaded area. Note that the time indicates number of days since the heater in the corresponding hole was started (2003-05-08 for hole #5 and 2003-05-23 for hole #6) /IPR-07-22/.
Figure 3-8 shows buffer temperatures as a function of radial distance from the canister axis measured in a particularly dry deposition hole #6 after 50 days from the start. /Goudarzi and Johannesson 2006/.
The surface heat flux of the canister is not evenly distributed over the surface. The heat flux at mid-height of the canister has been reduced such that the slope of the temperature curves in the bentonite block section agrees with typical laboratory values of the bentonite block thermal conductivity /Hökmark et al. 2009/.
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Figure 3-8. Thermocouple readings compared with theoretical distance-temperature relation obtained assuming mid-height heat flux being 74% of average surface heat flux. Best match is for the dotted line (Bentonite block 1.29 W/Km and Pellets 0.4 W/Km) /Hökmark et al. 2009/.
The effective buffer thermal conductivity as a function of gap filling pellets thermal conductivity for a number of bentonite block thermal conductivity assumptions is presented in Figure 3-9.
The effective buffer thermal conductivity was calculated using Equation (3)
∙ ∙
∙ ∙ (3)
λb(eff) is the effective buffer thermal conductivity, W/Km λpellets the thermal conductivity of bentonite pellets, W/Km λblock the thermal conductivity of bentonite block, W/Km R1 the radius from the centre of the canister to the bentonite block, R1 = 0.535 m R2 the radius from the centre of the canister to the rock surface of deposition
hole, R2 = 0.875 m Rbp the radius of the block/pellets interface, Rbp = 0.825 m.
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Figure 3-9. Effective buffer thermal conductivity as a function of gap filling pellets thermal conductivity for a number of bentonite block thermal conductivity assumptions /Hökmark et al. 2009/.
3.2 Calculation Methods
A literature review was made from the available and published calculating methods of the bentonite thermal conductivity. In the following subsections more detailed descriptions are given for two different calculation methods.
3.2.1 Beziat Method /Beziat et al. 1988/
One thermal conductivity calculation method is described by Beziat et al. 1988. They investigated theoretical formulas for calculations of thermal conductivity of the French natural clay Fo-Ca. It was found that geometric mean model for porous media (Woodside and Messmer 1961) according to Equation (4) gave values that agreed fairly well with measured ones. The accuracy in this investigation was about ±0.2 W/Km.
∙ ∙ ∙ ∙ (4)
where λs = thermal conductivity of solids = 2.6 W/Km λw = thermal conductivity of water = 0.6 W/Km λa = thermal conductivity of air = 0.024 W/Km n = porosity (pore volume divided to total volume) n = e/(1+e) e = void ratio Sr = degree of saturation %.
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3.2.1.1 Calculation results of the Buffer Test Pellets Batch 2
Juvankoski et al. 2012 presented the following material properties for the Buffer Test Pellets Batch 2 (Posiva’s gap filling reference pellets):
Bulk density of pellet filling 1075 kg/m3 Water content of pellet filling 17% Void ratio of pellet filling 1.993 Porosity of pellet filling 66.6% Degree of pellet saturation 23.5%.
Using Equation (4) gives the thermal conductivity of Posiva’s gap filling reference pellets:
2.6 . ∙ 0.6 . ∙ 0.024 . = 0.19 W/Km.
3.2.2 Knutsson and Johansen Method /Knutsson 1983/
Knutsson /1983/ found that Johansen’s method (Johansen & Frivik 1980) for calculating the thermal conductivity was applicable to highly compacted bentonite. The thermal conductivity λ was calculated by equations (5) to (8):
λ = λ0 + Ke (λ1 - λ0) (5)
where
0.034 ∙ . (6)
0.56 ∙ 2 (7)
Ke = 1+logSr (8)
where λ0 = thermal conductivity at Sr = 0, W/Km λ1 = thermal conductivity at Sr = 100%, W/Km Ke = influence of the degree of saturation Sr n = porosity.
3.2.2.1 Calculation results of the Buffer Test Pellets Batch 2
Using Equations (5) to (8) gives thermal conductivity of the Posiva’s gap filling pellets:
λPellets = 0.07986 + 0.371 ( 0.8568 - 0.07986) = 0.368 W/Km
The calculation method of Beziat et al. gave the same result as the measured thermal conductivity values in this project.
3.3 Thermal Conductivity Values
A literature review was made from the published bentonite pellets thermal conductivity values. In the following subsections more detailed descriptions are given for measured and calculated thermal conductivities.
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3.3.1 Sugita Conductivity Values /Sugita et al. 2003/
/Sugita et al. 2003/ measured thermal conductivity of Kunigel sodium bentonite pellets with a dry density of 1000 kg/m3. The measured values are presented in Figure 3-10.
Figure 3-10. Thermal conductivity of bentonite block and pellets /Sugita et al. 2003/.
3.3.2 Masuda Conductivity Values /Masuda et al. 2006/
Masuda et al. 2006 measured thermal conductivities of different types of bentonite pellets. The measured thermal conductivity values and other properties of the tested bentonite pellets are presented in Figure 3-11.
Figure 3-11. The properties of tested bentonite pellets /Masuda et al. 2006/.
The measured thermal conductivities varied between 0.129–0.33 W/Km. The water content of the pellets was 7.5%.
3.3.3 Hökmark Conductivity Values /Hökmark et al. 2010/
The calculated thermal conductivity values of the gap filling pellets from the Prototype Repository test were 0.27 W/Km (at day 5, Hole #5) in the 80°–85° orientation and 0.32 W/Km, Hole #5) in the 170°–180° orientation. For hole #6 the initial (at day 5) thermal conductivity of the gap filling pellets was 0.42 W/Km, but it decreased down to 0.35 W/Km at day 50 /Hökmark et al. 2010/ (Figure 3-7).
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3.3.4 Kim Conductivity Values /Kim et al. 2012/
Kim et al. 2012 measured thermal conductivities of pellet fillings by using a Hot Disk Thermal Constants Analyzer which is a transient method. Three different sizes of pellets were made for buffer-rock gap fill applications. These were identified as small (S), medium (M) and large (L). The small pellets were discshaped, with a diameter of 9 mm and a thickness of 6 mm. The medium pellets were oblongshaped, measuring 22 mm long by 11 mm wide by 7 mm thick. The large pellets were also oblong-shaped, measuring 22 mm long by 14 mm wide by 8 mm thick. The measured thermal conductivities of the gap filling pellets are presented in Table 3-1.
Table 3-1. Thermal Conductivity of pellet fills /Kim et al. 2012/.
Thermal Conductivity (W/(m·K))
(for various pellet sizes) Pellet Composition Densification Small Medium Large
Wyoming bentonite
Poured: Vibrated: Vibrated with 20% fines: Vibrated with 30% fines:
0.34–0.45 0.52–0.61
- 0.62–0.69
0.41 0.59
- -
0.48 0.56 0.65 0.67
Asha bentonite Poured: Vibrated:
0.43 0.49
- -
0.43 0.54
Milos AC200 bentonite Poured: Vibrated:
0.44 0.54
- -
0.45 0.61
Milos B bentonite Poured: 0.47 - 0.43 Vibrated: 0.58 - 0.63
Cebogel pellets Poured: 0.46 - - Vibrated: 0.53 - -
Buffer Test Pellets Batch 1, MX-80 bentonite
Poured: 0.52 - -
Vibrated: 0.56 - -
10% Silica Sand + Wyoming bentonite
Poured: - 0.45 - Vibrated: - 0.61 - Vibrated with 30% fines: - 0.52 -
25% Silica Sand + Wyoming bentonite
Poured: 0.44 0.45 0.56 Vibrated: 0.52 0.59 0.56
50% Silica Sand + Wyoming bentonite
Poured: 0.44 - - Vibrated: 0.52 - -
10% Illite + Wyoming bentonite
Poured: - 0.49 0.39 Vibrated: - 0.56 0.49
25% Illite + Wyoming bentonite
Poured: 0.42 0.41 0.38 Vibrated: 0.48 0.53 0.49 Vibrated with 30% fines: - - 0.54
50% Illite + Wyoming bentonite
Poured: 0.46 0.51 - Vibrated: 0.51 0.52 -
Note: “fines” consist of 80 mesh Wyoming bentonite granules (similar to MX-80).
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3.3.5 Marjavaara Conductivity Values /Marjavaara et al. 2013/
The thermal conductivity of the Buffer Test Pellets Batch 1 was earlier determined with thermal probe and heat flow meter methods. The measured average values are presented in Table 3-2.
Table 3-2. Thermal conductivity values of the gap filling pellets.
Pellet composition Measurement method Thermal conductivity, W/Km
Buffer Test Pellets Batch 1 Thermal probe 0.22 Buffer Test Pellets Batch 1 Heat flow meter 0.19
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4. VTT HOT BOX METHOD
Hot Box devices are commonly used to test window structures and to measure U-values of different building elements with a composition of different materials.
A Hot Box consists of three chambers: the cold chamber, the warm chamber and the metering chamber which is located inside the warm chamber (Figure 4-1). The insulated metering chamber reduces the heat loss through the metering chamber to a minimum as the metering chamber and the warm chamber temperatures are kept at constant temperature. The middle frame is located in the middle of the Hot Box. The test specimen is installed to the middle frame.
The dimensions of the VTT Hot Box device are: length of 3.3 m, width of 2.7 m and height of 3.3 m.
Both chamber walls are made of thick polyurethane foam with a thermal resistance of 4.0 m2K/W.
Fans are used to circulate the air inside the chambers during the test. The velocity of the moving air is 0.5 m/s.
The size of the bentonite pellet test specimen that the hot box can accommodate is 1.2 m x 1.2 m x 0.32 m. The cold side temperature can be adjusted from -20 °C to +20 °C. The metering chamber has a maximum temperature of about +40 °C.
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Figure 4-1. VTT Hot Box device for measuring thermal conductivity of bentonite pellets.
Polycarbonate mould
A polycarbonate mould was built for holding the bentonite pellets. The outside dimensions of the mould were 1.19 m x 1.19 m and the width of the gap was 50 mm (Figure 4-2 and 4-5). The thickness of the polycarbonate sheet was 8 mm. The volume of tested pellet filling was 70 litres. Two polycarbonate sheets were anchored with cable ties so that the width of the gap would be maintained at 50 mm after pouring the pellets into the mould.
21
Figure 4-2. The polycarbonate mould for the bentonite pellets.
Instrumentation of the Hot Box setup
Thermal radiation shielded thermocouples and surface thermocouples were installed on the baffles in the cold chamber and in the metering chamber (Figure 4-3). Also two thermal radiation shielded thermocouples were installed on the warm chamber wall.
Additional T-type thermocouples were installed on the warm and cold sides of the polycarbonate mould walls (Figure 4-4). One thermocouple was installed in the middle of the pellet filling.
Figure 4-3. The locations of the Hot Box thermocouples. Thermal radiation shielded thermocouples and surface thermocouples are installed on the baffle.
22
Figure 4-4. The locations of the additional thermocouples on the polycarbonate mould.
Figure 4-5. Pellet filling installed into the Hot Box.
Thermal performance of the test specimen
The thermal performance of the test specimen was determined using a guarded Hot Box according to the standard ISO 8990 (1994). The test was carried out according to the standard SFS-EN ISO12567-1 (2000): “Thermal performance of windows and doors –
23
Determination of thermal transmittance by hot box method – Part 1: Complete windows and doors”.
The following corrections (1–4) for heat losses of the specimen were done due to the test arrangements:
1. Edge heat losses according to the standard ISO 8990.
The edge heat losses edge were calculated from Equation (9) based on the temperature difference in edge area Tvi-Tve and calibrated edge heat loss coefficient Hedge.
∅ (9)
where Hedge is edge heat loss coefficient (based on calibration, W/K Tvi edge inner surface temperarure, °C Tve edge external surface temperature, °C.
2. Heat losses of polycarbonate frame according to the standard EN ISO 9646.
3. Heat losses of wool insulated gap at upper edge of the specimen, according to the standard EN ISO 9646.
∅ (10)
where U is the thermal transmittance of the calculated area, W/m2K A area, m2 Ti inner (warm side) temperature, °C Te outer (cold side) temperature, °C.
4. Losses of mechanical fasteners according to the standard EN ISO 9646.
The correction to the thermal transmittance U is given by Equation (11).
∆
, (11)
where
is 0.8 when the fastener penetrates the insulation layer f thermal conductivity of the fastener, W/mK nf number of fasteners per area, 1/m2 Af cross section of one fastener, m2 d0 thickness of the insulation layer containing the fastener, m R1 thermal resistance of the insulation layer penetrated by the fasteners,
m2K/W RT,h total thermal resistance of the component ignoring any thermal bridging,
m2K/W.
24
The thermal transmittance (U-value) of the central area of the specimen was calculated. The thermal resistance for the central area was calculated. When taking into account the surface resistances due to internal and external surface heat transfer coefficients and resistances of two 8 mm polycarbonate layers in internal and external surfaces, the thermal resistance of the specimen filling material was determined. The thermal conductivity was calculated using Equation (12):
/ (12)
where λ is thermal conductivity of the pellet filling, W/Km d thickness of the pellet filling, m R R = 1/U, thermal resistance of the pellet filling, W/m2K.
25
5. PROPERTIES OF THE PELLETS
The thermal conductivity was measured for two bentonite pellet types. The chosen pellet types were roller compacted Buffer Test Pellets Batch 2 and the VTT Extruded MX-80 2012 pellets.
The roller compacted Buffer Test Pellets Batch 2 were made by Hosokawa Bepex in Germany. The raw material for these pellets was MX-80 bentonite. The pellets were pillow shaped and the dimensions were 12 x 12 x 6 mm. The water content was 16.6% and the target bulk density for filling was 1075 kg/m3. One test was carried out with oven dried pellets with 0.65% water content.
The other type of tested pellets was VTT Extruded MX-80 2012 pellets. The water content was 15.25% and the target bulk density for filling was 986 kg/m3. The pellets were cylinder shaped and the diameter of the individual pellet was 8 mm and the average length was 12 mm.
The pellets were poured into the mould. No compaction or vibration was used.
The realized bulk densities were measured after the thermal conductivity tests. The bulk densities of the Buffer Test Pellets Batch 2 varied between 1085 to 1160 kg/m3 and the bulk density of the VTT Extruded MX-80 2012 pellets was 1140 kg/m3. The measured bulk densities were larger than in the earlier investigations /Marjavaara et al. 2011/, where the widths of the gap were 25 mm and 35 mm. Some gap filling tests were performed with the gap width of 50 mm and the densities were about 50 kg/m3 higher than presented target bulk densities.
26
6. VTT HOT BOX RESULTS
6.1 Test Parameters
The temperature gradients over the gap filling in the present thermal conductivity tests were chosen to be between 2.0–4.1 °C/cm. This meant that the temperature difference over the 50 mm pellet filling was from 10 °C to 20 °C in different tests. Respectively the measured temperature gradients over the outer gap filling in the Prototype Repository test varied between 0.5–1.5 °C/cm (hole #5) during the first year of the test /Hökmark et al. 2010/.
The temperatures in the cold and warm chambers were adjusted so that the desired temperature gradient over the pellet filling was reached.
Table 6-1. The temperature gradients during the thermal conductivity tests.
Test Number Pellet type Thermal gradient, °C/cm 1 Buffer Test Pellets Batch 2 4.1 2 Buffer Test Pellets Batch 2 2.8 3 Buffer Test Pellets Batch 2 2.1 4 Dried Buffer Test Pellets Batch 2 2.1 5 VTT Extruded MX-80 pellets 2.0
6.2 Measured Values
At first the thermal conductivity of the polycarbonate sheet was determined to be 0.186 W/Km.
The bentonite pellets were poured into the mould and the mould was installed into the Hot Box. The Hot Box chambers were closed and the planned temperatures of the cold and warm side of the test specimen and the heating power were adjusted. The temperatures and the heating power were continuously measured. The thermal conductivity of the pellet filling was calculated after the temperatures and the heating power were stabilized. The test was typically left to measure over the weekend. The measuring time duration varied from 25 hours to 122 hours.
Table 6-2 presents the thermal transmittances of the specimen central area, the thermal resistance of the material layer and thermal conductivity of the material in the central area.
27
Table 6-2. The thermal transmittances of the specimen central area, the thermal resistance of the material layer and thermal conductivity of the material in the central area.
Test number 1 2 3 4 5
Pellet type Symbol Unit Buffer Test Pellets Batch 2
Buffer Test Pellets Batch 2
Buffer Test Pellets Batch 2
Buffer Test Pellets Batch 2
VTT Extruded MX-80
Initial water content
% 16.6 16.6 16.6 0.65 15.25
Cold side temperature
Tne °C 0.519 7.056 8.546 7.833 8.628
Warm side temperature
Tni °C 20.809 21.218 18.976 18.458 18.461
Thermal transmittance central area
Uc W/m2K 1.890 1.900 1.869 1.810 1.771
Total thermal resistance
Rtot m2K/W 0.529 0.526 0.535 0.553 0.565
Thermal resistance surface to surface
Rs-s m2K/W 0.359 0.356 0.365 0.383 0.395
Material thermal resistance
Rmaterial m2K/W 0.275 0.272 0.281 0.298 0.310
Thermal conductivity of material
material W/mK 0.19 0.19 0.19 0.17 0.17
The measured thermal conductivities of the Buffer Test Pellets Batch 2 were either 0.17 W/Km (dry) or 0.19 W/Km (water containing). The used temperature gradient did not have a significant effect on the thermal conductivity values. The thermal conductivity of the VTT Extruded pellets was 0.17 W/Km, which was 0.02 W/Km lower than with the Buffer Test Pellets Batch 2 at nearly the same water content.
6.3 Observations After Thermal Conductivity Tests
The initial water contents of the pellets were measured before the thermal conductivity tests. After the thermal conductivity measurements the mould was opened and three samples were taken from the warm and could side of the pellet filling from different heights. The pellets were dried at 105 °C for 48 hours and the water content was determined.
Test 1. The Buffer Test Pellets Batch 2 with thermal gradient of 4.1 °C/cm
The temperatures of the cold and warm side of the pellet filling were and 0.5 °C and 20.8 °C and the thermal gradient was 4.1 °C/cm. The duration of the test was 66 hours. The initial water content of the Buffer Test Pellets Batch 2 was 16.6%. The water content distribution of the pellet filling after the thermal conductivity measurement is shown in Figure 6-1.
28
Figure 6-1. The water content distribution of the Buffer Test Pellets Batch 2 after the thermal conductivity measurement. The temperatures of the cold and warm side of the pellet filling were and 0.5 °C and 20.8 °C and the thermal gradient was 4.1 °C/cm.
The water content had mainly increased on the cold side of the upper part of the pellet filling.
Test 2. The Buffer Test Pellets Batch 2 with thermal gradient of 2.8 °C/cm
The temperatures of the cold and warm side of the pellet filling were 7.1 °C and 21.2 °C and the thermal gradient was 2.8 °C/cm. The duration of the test was 122 hours. The initial water content of the Buffer Test Pellets Batch 2 was 16.6%. The water content distribution of the pellet filling after the thermal conductivity measurement is shown in Figure 6-2.
29
Figure 6-2. The water content distribution of the Buffer Test Pellets Batch 2 after the thermal conductivity measurement. The temperatures of the cold and warm side of the pellet filling were 7.1 °C and 21.2 °C and the thermal gradient was 2.8 °C/cm.
The water content had increased on the cold side of the pellet filling but also on the upper part of the warm side. The duration of the test was nearly double compared to test 1.
Test 3. The Buffer Test Pellets Batch 2 with thermal gradient of 2.1 °C/cm
The temperatures of the cold and warm side of the filling were 8.5 °C and 19.0 °C and the thermal gradient was 2.1 °C/cm. The duration of the test was 29 hours. The initial water content of the Buffer Test Pellets Batch 2 was 16.6%. The water content distribution of the pellet filling after the thermal conductivity measurement is shown in Figure 6-3.
30
Figure 6-3. The water content distribution of the Buffer Test Pellets Batch 2 after the thermal conductivity measurement. The temperatures of the cold and warm side of the pellet filling were 8.5 °C and 19.0 °C and the thermal gradient was 2.1 °C/cm.
The water content had increased on the cold side of the pellet filling but also on the upper part of the warm side. The duration of the test was shorter than in the tests 1 and 2.
Test 4. Dried Buffer Test Pellets Batch 2 with thermal gradient of 2.1 °C/cm
The temperatures of the cold and warm side of the filling were 7.8 °C and 18.5 °C and the thermal gradient was 2.1 °C/cm. The pellets were dried at 105 °C for 72 hours before thermal conductivity measurement. The initial water content of the Buffer Test Pellets Batch 2 was 0.65% before thermal conductivity measurement. The duration of the test was 72 hours. The water content distribution of the pellet filling after the thermal conductivity measurement is shown in Figure 6-4.
31
Figure 6-4. The water content distribution of the dried Buffer Test Pellets Batch 2 after the thermal conductivity measurement. The temperatures of the cold and warm side of the pellet filling were 7.8 °C and 18.5 °C and the thermal gradient was 2.1 °C/cm.
The initial water content of the dried pellets was very low so the water content distribution after thermal conductivity measurement was inaccurate.
Test 5. VTT Extruded MX-80 pellets with thermal gradient of 2.0 °C/cm
The temperatures of the cold and warm side of the filling were 8.6 °C and 18.5 °C and the thermal gradient was 2.0 °C/cm. The duration of the test was 25 hours. The initial water content of the VTT Extruded pellets was 15.2%. The water content distribution of the pellet filling after the thermal conductivity measurement is shown in Figure 6-5.
32
Figure 6-5. The water content distribution of the VTT Extruded pellet filling after the thermal conductivity measurement. The temperatures of the cold and warm side of the pellet filling were 8.6 °C and 18.5 °C and the thermal gradient was 2.0 °C/cm.
Any significant transition of the moisture was not observed with VTT Extruded pellets. This may have been caused by the used low thermal gradient and by the short testing time or by the properties of pellet type.
In all tests of the Buffer Test Pellets Batch 2 containing significant amount of water, there was an observed redistribution of the water content mainly in the upper part of the pellet filling. A more pronounced redistribution of the water content was found with higher thermal gradients and longer test times. Only one test was carried out with VTT Extruded pellets and similar water content redistribution was not observed.
33
7. CONCLUSIONS
A Hot-Box device was used for measuring the thermal conductivity of two types of bentonite pellets. The chosen pellet types were roller compacted Buffer Test Pellets Batch 2 and the VTT Extruded MX-80 2012 pellets.
The Buffer Test Pellets Batch 2 was made by Hosokawa Bepex in Germany. The raw material for these pellets was MX-80 bentonite. The pellets were pillow shaped and the dimensions were 12 x 12 x 6 mm. The water content was 16.6% and the target bulk density was 1075 kg/m3. One test was carried out with dried pellets.
The other type of tested pellets was VTT Extruded MX-80 pellets. The water content was 15.25% and the target bulk density was 986 kg/m3. The pellets were cylinder shaped and the diameter of the individual pellet was 8 mm and the average length was 12 mm.
The temperature gradients over the gap filling in the present thermal conductivity tests were chosen to be between 2.0–4.1 °C/cm. The used thermal gradients were higher than what were measured over the outer gap filling in the Prototype Repository test (between 0.5–1.5 °C/cm (hole #5) during the first year of the test).
The measured thermal conductivities of the Buffer Test Pellets Batch 2 were either 0.17 W/Km (dry) or 0.19 W/Km (water containing). The used temperature gradients did not have a significant effect on the thermal conductivity values. The thermal conductivity of the VTT Extruded pellets was 0.17 W/Km, which was 0.02 W/Km lower than with the Buffer Test Pellets Batch 2 at nearly the same water content.
The measured thermal conductivity values were of the same order as the values measured by Sugita et al. 2003 (0.10 W/Km, Pellet (initial), Figure 3-10), Masuda et al. 2006 (0.129 W/Km, briquette type) and Marjavaara et al. 2012 0.19 W/Km with Heat flow meter method and 0.22 W/Km with Thermal probe method.
The effect of convection was not observed in the Hot Box thermal conductivity tests. The durations of the tests were too short to estimate the possible convection in the pellet filling.
In all tests of the Buffer Test Pellets Batch 2 containing significant amount of water, there was an observed redistribution of the water content mainly in the upper part of the pellet filling. A more pronounced redistribution of the water content was found with higher thermal gradients and longer test times. Only one test was carried out with VTT Extruded pellets and the significant transition of the moisture was not observed.
Two thermal conductivity calculation methods were tested with actual material properties of the bentonite pellets. The calculation method of Beziat et al. gave the same result as the measured thermal conductivity values in this project. The measured thermal conductivity values were from 0.17 W/Km to 0.19 W/Km and the calculated value was 0.19 W/Km.
34
The measurements proved that the thermal conductivity of the bentonite pellet filling in the deposition hole will be low, if the pellet filling does not get additional water from the surrounding rock.
In future work thermal conductivity of the pellet filling should be measured in the laboratory with higher gap filling mould and longer testing time so that the effect of the possible convection on the thermal conductivity could be determined.
35
8. REFERENCES
Beziat, A., Dardaine, M., Gabis, V. 1988. Effect of compaction pressure and water content on the thermal conductivity of some natural clays. Clays & Clay Minerals 36 (5).
Börgesson, L., Fredrikson, A., Johannesson, L.-E. 1994. Heat conductivity of buffer materials, SKB TR-94-29, Svensk Kärnbränslehantering AB, Stockholm, Sweden.
Börgesson, L. and Hernelind, J. 1999. Coupled thermo-hydro-mechanical calculations of the water saturation phase of a KBS-3 deposition hole. Influence of hydraulic rock properties on the water saturation phase. SKB TR-99-41.
Design, production and initial state of the buffer, 2010. TR-10-15. Svensk Kärnbränslehantering AB, Stockholm, Sweden.
Farouki, O.T. 1986. Thermal Properties of Soils. Trans Tech Publications.
Gustafsson, S.E. 1991. Transient plane source techniques for thermal conductivity and thermal diffusivity measurements of solid materials, Rev. Sci. Instrum. 63 (3), pp. 794-804.
Hot Disk Constants Analyzer, TPS2500, manufactured by Hot Disk AB, Chalmers Science Park, Chalmers University of Technology, Sven Hultins gata 9 A, SE-412 88 Gothenberg, Sweden.
Hökmark, H., Sundberg, J., Lönnqvist, M., Hellström, G., Kristensson, O. 2009. Strategy for thermal dimensioning of the final repository for spent nuclear fuel. SKB R-09-04, Svensk Kärnbränslehantering AB.
Hökmark, H., Kristensson, O. 2010. Äspö Hard Rock Laboratory, Prototype Repository. THM modelling of the bentonite buffer. Canister mid-height 1D radial models, holes #1 and #3. IPR-07-22, Svensk Kärnbränslehantering AB, Stockholm, Sweden.
Ikonen, K., Raiko, H. 2012. Thermal Dimensioning of Olkiluoto Repository for Spent Fuel. Posiva Oy, Olkiluoto. Working Report 2012-56.
Juvankoski, M., Jalonen, T., Ikonen, K. 2012. Buffer Production Line Report. Posiva Report 2012-17, Eurajoki.
Kim, C-S., Man, A., Dixon, D., Holt, E., Fritzell, E. 2012. Clay-Based Pellets for Use in Tunnel Backfill and as Gap Fill in a Deep Geological Repository: Characterisation of Thermal-Mechanical Properties. Nuclear Waste Management Organization NWMO TR-2012-05, Canada.
Knutsson, S. 1983. On the thermal conductivity and thermal diffusivity of highly compacted bentonite. SKB Technical Report 83-72, Svensk Kärnbränslehantering AB, Stockholm, Sweden.
36
Kukkonen, I., Kivekäs, L., Vuoriainen, S., Kääriä, M. 2011. Thermal properties of rocks in Olkiluoto: Results of laboratory measurements 1994-2010. Posiva Oy, Olkiluoto. Working Report 2011-17. 96 p.
Marjavaara, P., Kivikoski, H. 2011. Filling the Gap Between Buffer and Rock in the Deposition Hole. Posiva Working Report 2011-33. Eurajoki.
Marjavaara, P., Holt, E., Sjöblom, V. 2013. Customized Bentonite Pellets: Manufacturing, Performance and Gap Filling Properties. Eurajoki.
Masuda, R., Asano, H., Toguri, S., Mori, T., Shimura, T., Matsuda, T., Uyama, M. and Noda, M. 2006. Buffer Construction Technique Using Granular Bentonite. Radioactive Waste Management Funding and Research Center No. 15 Tokyo.
Pusch, R. 2003. The Buffer and Backfill Handbook, Part 3: Models for calculation of processes and behaviour. SKB Technical Report TR-03-07, Svensk Kärnbränslehantering AB, Stockholm, Sweden.
Rautionaho, E., Korkiala-Tanttu, L. 2009. Bentomap: Survey of bentonite and tunnel backfill knowledge, State-of-the-art. VTT, Working papers 133. Espoo.
Sugita, Y., Chijimatsu, M., Suzuki, H. 2003. Fundamental properties of bentonite pellets for Prototype Repository Project. In: Alonso and Ledesma (Eds.): Advances in understanding engineered clay barriers. Proceedings of the international symposium on large scale field test in granite. Sitges, Barcelona Spain, 12th–14th November, 2003. Balkema Publishers.
Thermal-Instruments Ltd. http:/www.thermal-instruments.co.uk. 31.10.2013.
Woodside, W., Messmer, J.M. 1961. Thermal conductivity of porous media. Journal of Applied Physics, Vol. 32, No. 9. pp 1688–1699.
Standards:
ISO 8990 (1994). Thermal insulation – Determination of steady-state thermal transmission properties. Calibrated and guarded hot box.
SFS-EN ISO 12567-1 (2000). Thermal performance of windows and doors – Determination of thermal transmittance by hot box method – Part 1: Complete windows and doors.
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.
ASTM D5334 – 08. Standard Test Method for Determination of Thermal Conductivity of Soil and Soft Rock by Thermal Needle Probe Procedure.
EN ISO 9646. Information technology – Open Systems Interconnection – Conformance testing methodology and framework.
37
APPENDIX 1: MATERIAL DATA SHEET
Characterization results
Authors: Leena Kiviranta, B+Tech Oy Sirpa Kumpulainen, B+Tech Oy Date: 08.07.2013 Last updated: 12.1.2015 Characterized in project: 197/CHARMA4 Material ID: Be-Wy-BT0020-3-Sa-R Alternative (project) ID: Material received at B+Tech Oy: 1.3.2013 The methods used in characterization are described in Posiva working report 2011-84, unless otherwise indicated. Visual descriptions
Figure 1. Photo of characterized material.
38
Basic/Index testing results
Table 1. Basic/Index testing results. Sample Water
ratio
(%)
Swelling
index
(ml/2g)
Liquid
limit
(%)
Plastic
limit
(%)
Plasticity
index
(%)
Specific
surface
area
EGME
(m2/g)
Water
absorption
capacity
(%)
Methylene
blue index
mg/g
16.9 27.6 528
Chemistry & Mineralogy
Table 2. pH and electrical conductivity (EC) of clay suspensions. Sample
pH
T
(°C)
EC
(µS/cm)
8.45 25.9 386
Table 3. Water soluble anions (SO4 and Cl) are determined with ion chromatography (IC), and water soluble cations (Al, Si, Fe, Ca, Mg, Na and K) with ICP-AES from 1:100 solid:solution extracts. Sample IC ICP‐AES
SO4
(mg/g)
Cl
(mg/g)
Al
(mg/g)
Si
(mg/g)
Fe
(mg/g)
Ca
(mg/g)
Mg
(mg/g)
Na
(mg/g)
K
(mg/g)
3.27 0.09 0.00 0.37 0.00 0.03 0.00 5.38 0.14
Table 4. Total chemical composition of bulk material: major elements. Sample SiO2
(wt.%) Al2O3
(wt.%) Fe2O3 (wt.%)
FeO (wt.%)
TiO2 (wt.%)
MgO (wt.%)
CaO (wt.%)
Na2O (wt.%)
K2O (wt.%)
P2O5 (wt.%)
SUM
55.58 18.65 2.96 0.69 0.15 2.25 1.25 1.96 0.51 0.04 99.92
Table 5. Total chemical composition (continued) of bulk material: selected trace elements. Sample
Mn (ppm)
Cr
(ppm) Cu
(ppm) La
(ppm) Mo
(ppm) Sr
(ppm) Zn
(ppm) 77 27 4 49 3 237 78
Table 6. Total chemical composition (continued) of bulk material: volatile elements and their speciation. Sample
C-Total (wt.%)
C-CO3 (wt.%)
C-Organic (wt.%)
S-Total (wt.%)
S-SO4 (wt.%)
S-Sulphidic (wt.%)
LOI (wt.%)
0.69 0.11 0.58 0.23 0.19 0.04 15.7
39
Table 7. Total chemical composition of clay fraction: major elements. Sample SiO2
(wt.%) Al2O3
(wt.%) Fe2O3 (wt.%)
FeO (wt.%)
TiO2 (wt.%)
MgO (wt.%)
CaO (wt.%)
Na2O (wt.%)
K2O (wt.%)
P2O5 (wt.%)
SUM
56.73 20.75 3.28 0.41 0.12 2.29 0.02 2.61 0.03 0.04 99.94
Table 8. Total chemical composition (continued) of clay fraction: selected trace elements. Sample
Mn (ppm)
Cr
(ppm) Cu
(ppm) La
(ppm) Mo
(ppm) Sr
(ppm) Zn
(ppm) <77 <14 20 42 <1 7 11
Table 9. Total chemical composition (continued) of clay fraction: volatile elements and their speciation. Sample
C-Total (wt.%)
C-CO3 (wt.%)
C-Organic (wt.%)
S-Total (wt.%)
S-SO4 (wt.%)
S-Sulphidic (wt.%)
LOI (wt.%)
0.21 0.00 0.21 <0.02 <0.02 <0.02 13.6
Table 10. The contents of CBD-extractable Fe, Al, Si and Mg phases in clay fraction. Fe2O3 (wt.%) SiO2 (wt.%) Al2O3 (wt.%) MgO (wt.%) 0.13 0.33 0.17 0.04
Table 11. Exchangeable cations and CEC of bulk materials measured with NH4Cl- and Cu(II)-triethylenetetramine-methods. Sample Saturation of exchangeable sites Exchangeable cations (in dry (105°C) weight) CEC Ca
(%) K
(%) Mg (%)
Na (%)
Ca (eq/kg)
K (eq/kg)
Mg (eq/kg)
Na (eq/kg)
Sum (eq/kg)
Cu-trien (eq/kg)
20 1 9 70 0.18 0.01 0.08 0.63 0.89 0.94
40
Table 12. Mineralogical composition (wt.%). Qualitative data is marked as x (XRD) or o (optical microscopy), quantitative (Rietveld) data as values. Mineral or mineral group Specification wt.% Clay minerals and mica -Smectite -Illite -Kaolin -Serpentine -Biotite -Chlorite -Muscovite -Glauconite -Vermiculite -Zeolite -Palygorskite -Sepiolite -Talc -Pyrophyllite
86.0 0.3
2.7
Feldspar -Plagioclase -K-feldspar
2.5 0.9
Olivine Pyroxene Amphibole Silica - Quartz -Cristobalite - Tridymite/opal
3.2 0.3
Aluminium hydroxide -Gibbsite -Boehmite -Diaspore
Hydroxyaluminosilicate -Allophane -Imogolite
Iron oxide and hydroxide -Hematite -Goethite -Lepidocrocite -Maghemite -Magnetite
0.1
Sulphide -Pyrite
1.0
Titanium oxide -Anatase -Rutile
Gypsum 1.7 Soda (hydrated) Carbonate -Calcite -Dolomite -Siderite -Magnesite -Ankerite
0.8
0.5 Apatite tr Zircon
Note: tr=trace amounts
41
Table 13. Structural composition of Na-converted smectite. Tetrahedral positions -Si4+ 7.801 -Al3+ 0.199 -Sum 8.000 Octahedral positions -Al3+ 3.160 -Fe3+ 0.328 -Fe2+ 0.047 -Mg2+ 0.469 -Sum 4.004 Interlayer positions -Ca2+ 0.003 -Mg2+ 0.000 -K+ 0.000 -Na+ 0.698 -Sum 0.701 O 24 H 4 Unit cell weight 746 Charges -Tetrahedral charge -0.199 -Octahedral charge -0.506 -Total charge -0.704 -Beidellite content (%) from structural composition 28 -Beidellite content (%) from Greene-Kelly test CEC (for smectite) calculated from structural composition (eq/kg) 0.94 CEC (for clay fraction) measured (eq/kg) 0.97
Physical properties
Table 14. Percentages of different granule sizes (from dry sieving). Granule size wt. %
> 2 mm 0.4 1-2 mm 2.0 0.5-1 mm 46.7 0.25-0.5 mm 32.8 0.125-0.25 mm 12.6 0.063-0.125 mm 4.2 < 0.063 mm 1.3
42
Figure 2. Plot of granule size vs. percent passing different size sieves. Table 15. Grain density, swelling pressure, hydraulic conductivity, dry density and bulk density of bulk materials.
Sample Grain density (g/cm3)
SP (MPa)
HC at 20 °C
(m/s)
Ratio of non-
swelling material
w (%)
Calculated from w Immersion method ρd
(g/cm3) ρb
(g/cm3) EMDD (g/cm3)
ρd (g/cm3)
ρb (g/cm3)
EMDD (g/cm3)
2.78 5.17 3.65*10-14 0.14 28.96 1.54 1.99 1.44 1.53 1.97 1.42
0
20
40
60
80
100
0 0,5 1 1,5 2
f n%
Granule size [mm]
Be‐Wy‐‐BT0020‐3‐Sa‐R
