Enclosure 3 to E-53126

Patram 80 Paper

DO f',JOT ~\~ ICROFI LM COVER

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6th INTERNATIONAL SYMPOSIUM

PACKAGING AND TRANSPORTATION OF RADIOACTIVE MATERIALS

PATRAM '80 \IS"ffi\

PROCEEDINGS

CONF-801115--Vol.l

DE86 012663

VOLUME I

INTERNATIONAL CONGRESS CENTER

BERLIN (WEST) NOVEMBER 10-14, 1980

Editor: H.W. HObner, BAM Berlin

D1STRIBUTION OF THIS DOCUMENT IS UNUlffll _

Paper No. Title, Author(s) Page

202 Risk Assessment Applied to Transportation of Tritiated Heavy Water G. J . Dicke . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419

027 Radioactive Materials Packages and the British Railway Accident Environment A. R, Taig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428

Session VII - Leakage, Leakrate and Seals (Chairmen: C.B.G. Taylor, The Radiochemical Centre, United Kingdom / R. Trapp, BAM, FR Germany)

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7 Importance of Leak Flow Mode Assumptions for Interpretation of Package

~~;~~Yr~~::r: ;et~,~~ '.~~,~~~~~-~f-:~~~ ~~~~i.t'.~~~ ~.n. ~~.~~,~~'.~~~ ... .. . 089 Leak Testing and Activity Leakage Rate Evaluation - Practical Experiences,

First Approaches to some Systemization and Outstanding Problems

437

H. Kowalewsky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446

006 An Assessment of the Containment of the UK 250 Litre Plutonium Nitrate Package R. S. Butterfield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454

065 Leakage of Radioactive Powders from Containers W. D. Curren, R. D. Bond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463

088 Investigation of Gas leakage from Sealing Constructions at Containments tor Radioactive Materials K. Heumos, H. Kowafewsky, H.·P. Weise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472

126 Vacuum Drying and Leakage Testing of Irradiated Fuel Packagings K. Goldmann, H. Bernard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 479

180 Pressurized Powder Releases through Micro-Openings in Faulted Containers J. Mishima, S. L Sutter, P. C. Owzarski, l. C. Schwendiman . . . . . . . . . . . . . . . . . 488

Poster Session A (Chairman: M. Bauschke, BAM, FR Germany) 001 Conceptual Design of a 85Kr Transportation System

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H. BrOcher, D. Niephaus, 0 . Nommensen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495

A Handy Calculation Method of Transport Index and Radiation Spectrum out­side of Cask H. Yamakoshi, M. Nakata, K. Ueki, A. Sekiguchi . . . . . . . . . . . . . . . . . . . . . . . . . . 501

Impact Test of Truck with Nuclear Fuel Shipping Cask S. Kikuchi, M. Kubo. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512

Studies of Physical Properties of Plutonium Dioxide Powders C. Cuillerdier, M. Germain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517

VII

LEAKAGE OY RADIOACTIVE POWDERS FROM CONTAINERS

W.D. CURREN and R.D. BOND UKA.EA, ATOMIC ENERGY ESTABLISHMENT WINFRITH

I. INTRODUCTION • This study has been directed at determining an appropriate standard of leak tightness for containment of plutonium oxide powder during shipment. The IAEA regulations specify an allowable leakrate in terms of mass of Pu02 escaping in unit time; the experimental work described in this paper has been carried out in order to interpret the IAEA requirement in terms of a flowrate of gas, which is more easily measured in practice.

2. REGULATORY REQUIP.EMENTS

The allowable leakrate for plutonium oxide under normal transport conditions is defined by the IAEA Regulations (Safety Series No 6) as 10- 6 x A2 value per hour. Each isotope of plutonium has its individual A2 value. In the UK the plutonium transported originates mainly from reprocessing of fuel from MJ\GNOX reactors, and a typical isotopic analysis is given in table I .

Table I: Composition of Magnox Plutonium

Pu 238

d. 1%

l'u 239

76. 9%

Pu 240

19.3%

Pu 241

3.2%

Pu 242

0.5%

The speci f ic activity of this material is 3.63 Ci/g, dominated by che contri­bution from Pu 241. Using the prescribed A2 values, calculation shows that the allowed l eakrate for Pu02 of this composition is 2. 8 x 10-8 g/hr, equivalent to 7.8 x 10-12 g/sec.

J. PACKAGING SYSTEM

In the UK, PuOz is packed for transport into a sealed metal can of about 2 litres capacity. Several varieties of can are in use, ranging from tin-place with crimped lids to stainless steel cans sealed by welding. Inside the can there is usually a PVC bag, enc l osing an inner screw- cap container into which Pu02 is loaded in a glove-box. The safety case f or the package depends on the leak tight­ness of the outer metal can .

• 4. ENVIRONMENTAL CONDITIONS

Cans are sealed containing air at room temperature and standard pressure. After sealing, self-heating by Pu02 can cause a modest temperature rise of say sooc, with an associated pressure rise of about 0.2 atmospheres. The pressure developed is the driving force for leakage of PuOz from the can.

Other factors, which can arise as a result of accident conditions, will in-

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-crease this driving force. Metal cans containing Pu02 are transported in the UK in a variety of wood cadmium containers, and fire tests of specimen containers at soooc for 30 minutes have resulted in an increase of temperature in the can of a further 100c. The pressure outside the can is normally I atmosphere; this can fal l to 0.5 atmospheres in an aircraft depressurisation accident, increasing the differential pressure by 0.5 atmospheres.

It is clear that the maximum differential pressure across a leak-path in a can will not exceed I atmosphere in normal or accident conditions; the experimental work reported in this paper has been restricted therefore to this pressure range.

5. MECHANISM OF POWDER LEAKAGE

It is postulated that PuOz can be carried through an aperture by a gas strea. For a given leak-path and differential pressure, the mass transfer of powder shou be proportional to the air flowrate, and the constant of proportionality will be the density of the aerosol.

6. GASEOUS LEAK-.RATES

If the pressure of a gas on one side of an orifice is Pl, and the pressure on the other, P2, is progressively reduced, the flowrate through the orifice in­creases up to an equilibrium value, at which the linear flowrate reaches the velo­city of sound. Ic can be shown theoretically that the maximum gas flow through a circular orifice can be related simply to the orifice diameter. In practice, measured gas flows reach equilibrium at about 60-80? of the theoretical maximum.

Flowrates of air through the orifice plates used in the experimental progra!!lllle have been measured for a range of differential pressures up co I atmosphere, and ~he resvlts ~re shown in figure I.

7

~ 20011m

v .. ~

6

"' E 5 ~

w !c u:

~ u.

4

u: 3

c ..J 4 2 t-z w ~ ~ ~ • >< w

0

t.p mm Hg Fig. J

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I

7. EXPERIMENTAL PROGRAMME

An experimental programme has been carried out to establish a correlation be­tween mass transfer and gas flowrate for a range of orifice sizes. In the experi­ments reported here , U02 powder with a particle size range of 1- 20 µm has been used to simulate Pu02. The apparatus used is shown in figure 2 .

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fig. 2

•It consists of a metal container 100 mm diameter and 200 mm high, mounted on a

rating table. At the top of the container is a pipe through wh i ch nitrogen or air can be admitted to pressurise the can. There is also an adaptor to which a thin metal orifice plate 10 mm diameter can be fitted , and a mixing chamber.

These items are shown in more detail in figure J.

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THIM COll- DISC

R.f(A ""'"

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fig. 3

uo2 particles emerging from the orifice plate enter a mixing chamber connected to a vacuum pump. Air, drawn into the mixing chamber through radial holes, sweeps the U02 particles onto a 0. 2 um filter , which retains them. The mixing chamber has undergone a series of modifications, and in its present form it has been shown that 75-80% of the U02 emerging from t he orifice is col lected by the filter. Orifice plates are available in the range 200 pm to S JJm diameter .

To carry out an experiment , about SO g U02 powder is loaded into the can, and the pressure inside the can is adjusted to an appropriate value. The can is attached to the vibrating table, and this is energised. At the end of the run, the filter paper is removed, and the amount of U02 collected is assayed by alpha­counting.

An electron microscope is used to assess particle sizes.

The amount of U02 transferred through orifices of 200 }'rn and 100 )Im diameter as a function of differential pressure is shown in figure 4.

The curves obtained are similar in form to those shown in figure I, which showed variation of air flowrate with pressure. Once choked flow conditions ar. established, both air flowrate and U02 flowrate become constant.

Using a constant differential pressure of I atmosphere across the orifice , the amount of uo2 collected is proportional to time . This is illustrated in figure S for orifices of 200 pm and 100 pm diameter .

Similar information for smaller orifices of 50 ;m and shown in figure 6.

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25 pm diameter is

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....... • ....... JO '--'

2001'• • 1J ,.......

10 C

¥ II '--'

. 16 •

g 14

It

....... 10 ,........ .--,

..___., 100/"e

........

0 -------t---------:;---------'-,b-------.:

,-.nsi.11! , ,u,

fig. 4

These results were obtained with the test container tn the upright position, and the orifice I 90 mm over the U02 layer. Under these conditions the aeroso 1 density, for a range of orifice diameters and differential pressures, can be calculated to be between J.7 x 10-7 g/ml and 4.5 x 10-7 g/ml. If the container is tilted, to bring the orifice closer to the U02 surface, the aerosol density in­creases by a factor of about 5. Under these conditions, blockage of the orifice with U02 frequently occurs during the experiment. With the orifice below the U02 layer , blockage always occurred before any escape of U02 was detected .

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~ :. ~ r g

17-

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1r

I l l

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Ji

I I lOOJ,•

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I I

I I

I I

I I

I ...... , I

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----'40 ---50 -- ---+.:,--JJOio'"' IIHE (HINU,11)

fig . 5

468

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MASS UO, VERSUS VIBRATION TIME

2 VERTICAL POSITION

2·

~jlm

I 2

/

• / 1-

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/ 1-<I /

/ >, .. 1·2 .. .. ..

}.lil'm ~ f H)

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0·8 .---, /

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0·6

04

~ 0 ·2 y~ 0 10 20 30 40 50

TIME (minutes)

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469

8. DISCUSSION

A series of experiments has been carried out which has demonstrated that, for di fferential pressures up to I atmosphere , the rate of transmission of U02 t hrough an aperture is di rectly pr opor t ional to the rate of air flow.

The density of the U02 aerosol transmi tted through the ori fice wa s found to be constant , within an order of magnitude, for orifice diameters in the r ange 10 -200 um, for different ial pressure up to I atmosphere, and for experiments lasting up to I hour. In order to promote maximum flow of U02, the UOz container was vibrated far more energetically than would be conceivable i n normal transport. The maximum value of aerosol density found , with the orifice 20 mm above the uo2 surface, was 9 x 10-6 g/ml .

Assumi ng that similar aerosol densities can be achieved using PuOz, the IAEA regulations wi ll be satisfi ed by a leak tightness standard of 10-6 ml/sec at I atmosphere; a fiBure which is readily achievable using conventional engineered cl osures .

Clearly, this calculat i on contains several factors of pessimism. A leakrate of 10-6 ml/sec corresponds t o a circular orifice less than O. I um in diameter; only the smal lest particles coul d be transmitted, and blockage would occur quickly .

It is pl anned that experiments wi th Pu02 will be carried out and correlated with the resul t s of UOz experiments reported here .

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DISCUSSION

Question gv J . A. Andersen, USA: 1 . To what condition do you assign the 10- ml/s leak rate - the normal conditions of transport, which ar5 required to limit the ~oss of radioactive material to A2 x 10- , or the B(U) (A2 x 10-) or B(M) (A" x 1) post- accident condition? 2. What do you believe to be a practical or engineered leakage rate for an actual cask or cont ainment vessel for plutonium, post-accident? (e . g. what are yourfindings regarding an allowable post-accident leak rate for a practical plutonium containment vessel?).

Answer: 1 . To the normal cond1t1ons of t ransport . 2 . The ex­periment al work described 1n this paper provides results measured under steady state conditions; 1t is not easy therefore to calculate a target figure for post- accident l eakrate. I would expect, however, tha6 the target figure, post- accident, should be more relaxed than 10- ml/s. •

Question by T. Tamberg, FR Germany : Could the intense vibrat1 you use prevent plugging of the pores to a certain extent?

Answer: I think that this 1s very likely. In spite of the in­tense vibration used, blockage often occurs during experiments using 25/m and 10/m diameter holes.

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Comment by J. Draulans, Belgium: Our experience indicates that ther8 is a quick decomposition of P . V.C. at a temperature even below 120 c . Such a decomposition produces highly corrosive gases, able to attack metal containers (aluminium and stainless steel) and silicon gaskets.

Answer: Under normal, i.e. accident-free cond6tions of trans­port, the temperature of the can does not exceed 70 C. At this tenp-

~~~t~~~du~~V~~~r~=~~:P~:~!~~~w~sp~~~u~tfr~~l~;ooc~ agree that P.V.C.

Question by c. B. G. Taylor, United Kingdom: You said the aero-

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ol density is higher by an order of magnitude, 20 mm above the powder urface, compared to that at the top of the can. Did you establish

the details of this density gradient; and which figures did you use for your final statements of radioactive leak rate?

Answer: The aerosol density increased by a factor of 5 in re­ducing the distance between orifice and powder bed from 200 mm to 20 nun. In making the final statement of permissible leak rate, I used the highest vglue of aerosol density found in a single experi­ment, viz: 9 x 10- g/ml .

• 471