ML20148Q389

Summary of 781108 ANS-5.4 Meeting on Fission Gas Release. Encls Incl Correction to Error Statement of low-temp Release Model & Extension to Cover Cessium & Tellurium Fission Products

ML20148Q389
Person / Time
Issue date:	11/21/1978
From:	Meyer R Office of Nuclear Reactor Regulation
To:	Kniel K Office of Nuclear Reactor Regulation
References
NUDOCS 7811300026
Download: ML20148Q389 (25)

Text

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b*'*,,,*/ NOV 2 : 1975 MEMORANDUM FOR: K. Kniel, Chief, Core Performance Branch, DSS FROM: R. O. Meyer, Leader, Reactor Fuels Section, CPB, DSS

SUBJECT:

MEETING

SUMMARY

OF ANS FISSION GAS GROUP Enclosed is a meeting summary of the recent ANS-5.4 meeting on fission gas release. That summary is being sent to meeting e attendees as committee correspondence. Several items of interest are noted below.

(a) An error in the statement of the low-temperature release model has been identified and corrected. .

The correct expression is given in the enclosed detailed summary.

(b) The model has been extended to cover cesium and tellurium fission products. The model previously covered noble gases and iodine. Release predictions for non-noble gases are only approximate.

(c) - We hope to produce draf ts of tha standard and the supporting technical document at the committee's next meeting in February.

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Ralph 0. Meyer, Leader Reactor Fuels Section .

Core Performance Branch Division of Systems Safety

Enclosure:

As stated 78113060 2 C, L

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COMMITTEE CORRESPONDENCE SOCIETY /CL ilTTEE: ~ 'ORESS CORRESPONDENCE TO:

ANS-5.4 R. O. Meyer SUBJECT' U.S. NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 Fuel * .um Gas Activity AGEND A ITEM:

FILE NO.: N/A DATE: NOV 2 1 1978 TO: C. E. Beyer L. D. Noble Westinghouse Hanford A/59 General Electric Company, M/C 138 Hanford Engineering Development Lab. 175 Curtner Avenue P. O. Box 1260 San Jose, California 95125 Richland, Washington 99352 M. J. F. Notley B. J. Buescher Atomic Energy of Canada, Ltd.

The Babcock & Wilcox Company Chalk River, Ontario P. O. Box 1260 Canada, K0J1JO Lynchburg, Virginia 24505 Chang S. Rim R. J. Klotz Korea Atomic Energy Research Institute Department 9492 P. O. Box 7, Cheong Ryang Combustion Engineering, Inc. Seoul. Korea l I

Windsor, Connecticut 07085 R. L. Ritzman l R. A. Lorenz Science Applications, Inc. l Oak Ridge National Laboratory 2680 Hanover Street .

I P. O. Box Y Palo Alto, California 94304 Oak Ridge Tennessee S. E. Turner W. Leech Southern Science Applications, Inc.

Neclear Fuel Division, W Corp.

P. O. Box 10 P. O. Box 35b Dunedin, Florida 33528 Pittsburgh, Pennsylvania 15230

Dear Group Members:

l Enclosed are (1) a summary of the last Working Group Meeting, (2) an attendance list for the meeting, and (3) handouts presented at the meeting.

Sincerely, w

f 3, Ralph 0. Meyer

Enclosures:

cc: M. E. Remley, AI (As stated) M, Weber, ANS

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4 Enclosure 1

- Summary of ANS-5.4 Meeting ANS Working Group 5.4 met on Thursday, November 8,1978 at NRC Headquarters in Bethesda, Maryland.

1 An error in the statement of the low temperature release model L c been pointed out in Chang Rim's letter of September 4, 1978. The

. l derivation of this model was therefore reviewed in detail. The  ;

For stable isotopes,

, 'l correct statement of this model is as follows. l j

F = 8.5 x 10~ x Bu. (1) l For radioactive isotopes,

-12 x P/A, F = 2.0 x 10 (2) l where: i F is the release fraction. For radioactive ,

species, F is the frae. tion of the non-decayed inventory just as it had been defined in the Booth model. -

l l

1 Bu is burnup in megawatt-days per metric l

ton of heavy metal.

P is specific power in megawatts per metric ton of heavy metal

~

A is the decay constant in sec .

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, , , _ . , . , - . , - , . , , - . . . . - - ~ . . . . , , . ~ , - . . , , , . . ,

s i,

4

In eq. (1) the uncert'ainty in the factor 8 5 is estimated to be I

~ +3.5 and -3.0. In Eq. (2) the uncertainty in the factor 2.0 is estimated to be +0.8 and -0.7.

< l 3 l

} The low temperature model was derived Erom the assumption of a 1 l

! knock-out mechanism. There is still some confusion as to whether i

a recoil mechanism is important. Larry Noble and the low-temperature * '

j subgroup will review this consideration. Since low-temperature ,

! releases arc small and relatively large errors can be toleratedt j

. s

! we will probably not get deadlocked over this issue.

4-1 Bob Ritzman has extended the consideration of non-noble gases to )

a l cesium and tellurium. His handout is enclosed. The important '

l i <

j equations in that handout ,are Eqs.1 and 5, which relate the i  !

diffusion parameters for cesium and tellurium to the diffusion i

i . parameter for the noble gases.

1 l

j Procedures for applying the high-temperature model were' discussed.

There was general agreement that enough radial nodes should be 1 1 l l used such that nodal temperature differences would not exceed 100 C.

This probably anounts to about 10 radial nodes as a minimum. No l cancensus was reached on axial noding, but one rather durable f suggestion was as follows. Enough axial nodes should be used 1

l such that nodal temperature differences would not exceed 100 C l with two exceptions: (1) this condition would not have to be met below 1000 C since releases would be too small to worry about i

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accuracy, and (2) any 5% axial section of the fuel (e.g., near a ,

control blade tip) could be exempted from fine subdivision since it could not cause a large error in the rod-averaged gas release.

As the meeting neared an end, assignments were discussed. Ralph Meyer 1

agreed to draft the (brief) standard. The (not-so-brief) support document would be similar to the April 1977 Status Report and l

organized as follows.

l l

l l

Section Author I Introduction B. O. Meyer II High Temperature Model A Data C. E. Beyer B bbthematica L. D. Noble and C, S. Rim C Model Fitting C. S. Rim D Non-Noble Isotopes R. L. Ritzman l

. l E . Isotopic Precursors M. J. F. Notley l

III Low Temperature Model I A Data R. A. Lorenz B Mathematics L. D. Noble C Model Fitting L. D. Noble D Non-Noble Isotopes M. J. F. Notley l

l Draft sections of the support document should be mailed to all I

members by the authors prior to the next meeting. The next )

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meeting is tentatively planned for~a central location (Dallas) in late i

j February.

l We worked until 9:00 p.m. without dinner and then adjourned.

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' 4-4 Enclosure 2 ANS-5.4 Meeting Attendees November 8, 1978 S. E. Turner So. Science Chariman C. E. Beyer HEDL B. J. Buescher B&W R. J. Klotz C-E R. A. Lorenz ORNL W. Leech W R. O. Meyer NRC-L. D. Noble GE M. J. F. Notley AECL R. L. Ritzman SAI R. E. Fbson INEL Guest J. C. Voglevede NRC Guest f

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4Y 8 November 1978 g

To: ANS 5.4 Subcommittee Members C.E. Beyer. B.O. Meyer Westinghouse Hanford A/59 U.S. Nuclear Regulatory Commission

, Hanford Engineering Development Lab. Washington, D.C. 20555 P.O. Box 1260 Richland, Wash. 09352 L.D. Noble General Electric Company, M/C 138 B.J. Buescher 175 Curtner Ave.

The Babcock & Wilcax Company San Jose, CA 95125 P.O. Box 1260 Lynchburg, VA 24505 M.J.F. Notley Atomic Energy of Canada, Ltd.

R.J. K3ot7 Chalk River, Ontario Department 9492 Canada, K0J1JO Combustion Engineering, Inc.

Windsor, CT 07085 Chang S. Rim Division Combustible l R.A. Lorenz FRAMATOME Oak Ridge National Laboratory Tour Fiat /Cedex 16/

t P.O. Box X 92084 Paris La Defense  !

, Oak Ridge, TN France W. Leech S.E. Turner Nuclear Fuel Division, W Corp. Southern Science Applications, Inc.

P.O. Box 355 P.O. Box 10 Pittsburgh, PA 15230 Dunedin, FL 33528

Dear Group Members:

Enclosed is a report of work done to extend the ANS 5.4 high temperature model to cesium and tellurium. Comments are welcome.

Very truly yours,

/ .4 i

,4v A'

!' Robert L. Rit~.an RLR/ imp Enc '

Science Applications, InC. 5 Palo Alto Square, Suite 200, Palo Alto, CA 94304 (415) 4934328

CESIUM AND TELLURIUM RELEASE FROM UO 2

R.L. Ritzman The AMS-5.4 Working Group has made a considerable effort to formulate a method for calculating the release of fission product xenon and krypton from UO reactor fuel (1) ,

An earlier paper described efforts to extend the procedure to fission product iodine (2) . The present paper outlines the results of further work to provide a procedure for the fis-sion products, cesium and tellurium.

The procedure for cesium and tellurium corresponds exactly with the procedure that was used for lodine; i.e.,

! specific data from the literature were used to develop dif- $

fusivity ratios for cesium relative to xenon and for tellur-ium relative to xenon. Then reference noble gas diffusion parameters (D') were multiplied by the ratio to obtain D' values for either cesium or tellurium for use in the ANS-5.4 model. The same four data sources were used to derive cesium / xenon and tellurium / xenon diffusivity ratios as were used to develop the iodine / xenon diffusivity ratios. These are essentially the only sets of experiments in which the release of all of the species were measured under the same conditions for each particular set. The next section pre-sents the data analysis for the cesium / xenon diffusivity ratios. This is followed by a similar section for the tel-lurium/ xenon diffusivity ratios. The last section summarizes all the fission product diffusivity ratio results and tabu-lates the D' values that are indicated by the applied method.

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. _. . _ _ . _. -_ __ . _ . . ~ . _ _ ,

l Cesium / Xenon Diffusivity Ratios 1

i The first data source used was the work of Davies,

{ Long, and Stanaway(3) who measured D'Cs/ Xe ratios for a series of UO 2 sintered compacts, sintered spheroids, and fused spheroids of various densities at temperatures ranging from ,

i 1000 C to 2150 C. A total of 19 determinations of use to 4

this ptudy, as reported by the investigators, are tabulated in

Table 1. A similar set of measurements were performed by Parker, Creek, Barton, Martin, and Lorenz(4) with 93-94fo dense

] UO 2 at temperatures ranging from 1400 C to 1980 C.

The D'Cs/

l D'Xe ratios obtained from 12 separate '"periments given in this source are listed along with other pertinent data in

) Table 2. The other two data sources come from investigators 4

j who used diffusion theory to interpret their experimental work, and thus obtained values for the limiting diffusion coefficient and the activation energy in the classical Arrhenius equa-tion. The parameter values given by 01 and Takagi(5,6) and by Parker (7) in his analysis of old ORNL data are given in Table 3.

i i The 31 data points given in Tables 1 and 2 were sub-jected to a least squares analysis in which in (D' Cs/D' Xe) was i assumed to vary linearly as the recriprocal of the absolute temperature in accordance with a form of the Arrhenius equation.

The derivation of the appropriate relationship as given in Reference (2) shows this line will have a slope corresponding to (Q Xe- Cs)/R and an intercept value at 1/T = 0 corresponding The result of the least squares analysis is to In(D'Cs/D'OXe).

displayed in Figure 1 along with the 31 experimental diffusivity ratio values and two other lines which correspond to the ratio

! of Arrhenius expressions published by 01 and Takagi and by Par-ker.

4 2

Table 1. Diffusivity Ratios Obtained for UO 2

in Reference (3)

Sample Density Surface Area Temperature Type 2 D'Cs/D'z*

g/cm 3 cm /3 OC Sintered 10.3 140 1000 5.76 Compact 10.3 140 1000 26.0 Compact 10.3 140 1200 1.96 Compact 10.3 140 1400 1.96 Compact -

4100 3600 5.29 Compact 10.3 10 1600 39.7 Compact 10.8 5 1600 0.64 Compact 10.7 7 2000 4.84 Compact 10.7 7 2050 0.83 Compact 10.7 7, 2150 0.141 Sintered -

25 1200 1.0 Spheroids -

25 1400 21.2 Spheroids -

25 1600 0.36 Spheroids -

25 1600 6.25 Spheroids -

25 1600 0.64 Spheroids -

25 1600 0.36 Spheroids -

25 1400 6.25 Fused 10.6 77 1200 1.0 Spheroids 10.6 77 1600 3.24 3

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_ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ \

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4 Table 2. Diffusivity Ratios Calculated From ,

Release Data for UO 2 in Reference (4) i e

i Fraction Released 4 Sample  % Theo. Temperature in 5.5 Hours 1 Type Density OC cs he D'Cs/D'Xe I

! PWR-UO 2

93-94 1515 0.014 0.013 1.16 l PWR-UO 2

93-94 1610 0.017 0.027 0.396 t

PWR-UO 2

93-94 1710 0.027 0.026 1.08 PWR-UO 2

93-04 1800 0.032 0.037 0.748 l

PWR-UO 2

93-94 1900 0.086 0.097 0.786 PWR-UO 2

93-94 1980 0.15 0.12 1.56 1

i EGCR-UO 2

97 1400 0.026 0.008 10.6 PWR-UO.j 93-94 1400 0.005 0.005 1.0 j PWR-UO 2

93-94 1400 0.21 0.061 11.9 t

EGCR-UO 2

97 1610 0.12 0.026 21.3 PWR-UO 2

93-94 1610 0.20 0.060 11.1 l

PWR-UO 2

93-94 1780 0.032 0.037 0.748 1

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F Table 3. Arrhenius Equation Parameters for Cesium and Xenon from References (5), (6), and (7)

Pre-Exponential Activation Reference Specie Factor Energy (5) Xe 3.0 x 10~ cm /sec 63.0 Kcal/g-atom 2

(6) Cs 8.5 x 10~ cm /sec 6.1 Kcal/g-atom

-1 (7)* Xe 2.32 x 10~ sec 79.6 Kcal/g-atom 0 ~

Cs 1.37 x 10 sec 52.3 Kcal/g-atom i

l l

Parameters taken from values uncorrected for the " burst effect".

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, Oi & Takagi '

6Q = 56.9 Kcal Parker (WASH-1400)

/ 6Q = 27.3 Kcal

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Least Squares

. , - il ,/ AQ = 12.1 Kcal

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7 Figure 1. D1"fusivity Hatio Data and Curves for Cesium / Xenon

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1 Inspection of Figure 1 reveals considerable scatter in the 31 data points. The least squares analysis resulted in a positive value for AQ = (Q f 12.1 Kcal/g-atom Xe -9Cs)  ;

which is considerably less than the value of 56.9 Kcal/g-atom obtained from the 01 and Takagi expressions and the value of 27,3 Kcal/g-atom obtained from the Parker expressions. The ,

i complete equation for the least squares line is:

' .58 x 10 -2 e12100/RT (1)

(D'Cs / Xe) =

lI Likewise the complete equations for the 01 and Takagi line and tPo Parker line are respectively:

1

)

(D ' Cs /D ' gg ) = 2. 8 3 x 10 -6 e56900/RT (2) and

~0e27300/RT (3)

(D'Cs/D'Xe) = 5.89 x 10 It is noteworthy that all three lines indicate a posi-tive value for the difference in activation energies, but the wide range of values is rather disappointing. It does appear that neither the 01 and Takagi line nor the Parker line pro-vide a very good fit to the data points in Figure 1. On this basis, and to maintain consistency with the approach used for lodine, it was decided to rely on the least squares fit to indiente the diffusivity of cesium relative to xenon in UO '

2 The data scatter and the disagreement in AQ values diminish the confidence that can be attached to applications involving this approach, but it represents the best that can be done with presently available information. Multiplying Equation (1) above by the reference equation for xenon diffusion in UO 2' 7

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a the following equation, which estimates cesium diffusion, is

obtained.

1

-4 e-37600/RT 4) l D'Cs = 1.63 x 10 l '

l Use of this equation in conjunction with the diffusion model and acceptable fuel thermal performance models thus provides a means to estimate high-temperature release of cesium from l 1 l operating reactor fuel.

l Tellurium / Xenon Diffusivity Ratios From the work of Davies, Long, and Stanaway( ) , a set of 17 determinations of D'Te/D'Xe ratios useful to the present

! study were made. These ratios and associated data are listed in Table 4. The fission product release studies of parker, Creek, Barton, Martin, and Lorenz(4) provide 10 additional f D'Te/D'Xe ratio values which are listed along with other rele-

! vant data in Table 5. In Table 6 the Arrhenius equation para-f meters as determined by Oi and Takagi(5,6) and by Parker (7) s for xenon and tellurium diffusion from UO 2 are given. The i values in these three tables constitutes the body of data used j here to obtain a diffusivity ratio expression for the tellurium / ,

, xenon combination.

The 27 tellurium / xenon diffusivity ratio data points given in Tables 4 and 5 were subjected to a least squares analysis of the same type that was performed for the cesium /

xenon and the iodine / xenon data. The result of the analysis is shown by the solid line in Figure 2 along with the 27 experi-mental data points and two other dashed lines which correspond l

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i I Tab? e 4. Diffusivity Ratios Obtained for UO 2

, in Reference (3)

I l

t Sample Density Surfaee g

Area Temperature D'Te/D'Xe Type g/cm 3 cm /g OC l

. l 1

Sintered 10.3 140 1000 7.84 l Compacts 10.3 140 1000 24.0 Compacts 10.3 140 1200 15.2 Compacts 10.3 140 1400 7.29

! Compacts 10.3 19 1600 100.

Compacts 10.8 5 1600 121.

! Compacts 10.16 4 1300 44.9 Compacts 10.7 7 2000 13.0 Sintered -

25 1200 6.76 Spheroids -

25 1400 39.7 Spheroids -

25 1600 110.3 Spheroids -

25 1600 196.

Spheroids -

25 1600 441.  !

Spheroids -

25 1600 441. l Spheroids -

103 1400 10.9 -

Fused 10.6 77 1200 32.5 Spheroids 10.6 77 1600 259.

9 i

0 Table 5. Diffusivity Ratios Calculated from Release Data for UO 2 in Reference (4) s

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Fraction Released l Sample  % Theo. Temperature in 5.5 Hours '

Type Density OC Te Xe D'Te/D'Xe PWR-UO 2

93-94 1515 'O.029 0.013 4.98 PWR-UO 2

93-94 1610 0.12 0.027 19.75 PWR-UO 2

93-94 1710 0.20 0.026 59.2 PWR-UO 2

93-94 1800 0.21 0.037 32.2 f

PWR-UO 2

93-94 1400 0.039 0.008 23.8 j EGCR-UO 2

97 1400 0.008 0.008 1.0 l

l PWR-UO 2

93-94 1400 0.013 0.005 5.76 PWR-UO 2

93-94 1400 0.16 0.061 6.88 EGCR-UO 2

97 1610 0.12 0.026 21.3 PWR-UO 2

93-94 1780 0.21 0.037 32.2 10

Table 6. Arrhenius Equation Parameters for Tellurium and Xenon from References (5), (6), and (7) s 4

j ..

I Pre-Exponential Activation Reference Specie Factor Energy

-3 (5) Xe 3.0 x 10 cm /sec 63.0 Kcal/g-atom (6) Te 6.6 x 10' cm /sec 70.0 Kcal/g-atom (7)# Xe 2.32 x 102sec- 79.6 Kcal/g-atom 1 -1 Te 5.33 x 10 sec 66.6 Kcal/g-atom

+

Parameters taken from values uncorrected for the " burst effect".

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1 -  : o AERE R-4342 i . x OANL-3981 i -

N-4 100 --

. Parker (WASH-1400) ';

i ,  : 6Q = 13.0 Kcal i f i e a /

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) Figure 2. Diffusivity Ratio Data and Curves for Tellurium / Xenon 1

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4 to the ratio of Arrhenius expressions published by 01 and Takagi and by Parker. Inspection of Figure 2 reveals consider-able scatter in the 27 data points. The least squares analysis resulted in a negative value for AQ = (Q -9Te); i.e., -12.5 Xe Kcal/g-atom in contrast to the positive values which had been The ratio of Arrhe-obtained for both (QXe-9Cs) and (QXe -9 I ). ,

nius expressions from 01 and Takagi also yielded a negative AQ but the value was only -7.0 Kcal/g-atom. However, the ratio of A$rhenius expressions from Parker gave a positive AQ value of 13.0 Kcal/g-atom. The complete equation for the least squares line is:

l 3 -12500/RT (5)

(D'Te/D'Xe) = 1.10 x'10 e ,

l l

Likewise'the complete equations for the 01 and Takagi line and '

the Parker line are respectively:

-7000/RT (6) l (D'Te/U'Xe) = 2.2e 1 and

-l 13000/RT e (7)

(D'Te/E'Xo) = 2.29 x 10 The conf 41derable disagreement between oQ values and the wide distances between equation lines in Figure 2 indicate that tel'lurium behavior in UO is not very well defined. In 2

any case, however, it is apparent that the 01 and Takagi line is a poor fit for the data points in Figure 2. The positive slope of the Parker line is probably due to the fact that it was derived from a collection of data which did not include ,

the measurements of Davies, Long, and Stanaway. Therefore, it  !

I is not really applicable to the present analysis. This leaves l l

l 13

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the least squares line as the best available indicator of the l

.diffusivity of tellurium relative to xenon in UO Multiply-l 2 )

l.

1 ing Equation (5) above by the reference equation for xenon )

diffusion in UO2 pr duces the following equation for tellurium:

i l

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D'Te = 2.43e- 2200/RT (8) j i , l l Use of this equation in conjunction with the diffusion model i

and acceptable fuel thermal performance models provides a means

for estimating the high-temperature release of tellurium from I operating reactor fuel.

[ Summary,of Diffusivity Ratio Results The diffusivity ratio approach has been used to derive diffusion parameter expressions for fission products iodine,

! cesium, and tellurium from a limited body of experimental data.

I Each analysis censidered approximately 30 data points obtained

from two principal sources. Although the data were quite scat-l tered, least squares analyses were performed to obtain Arrhenius type expressions for D' Fission product /D' Xenon which were then j

i multiplied by the ANS-5.4 reference equation for D' Xenon n UO 2 fuel to yield the diffusion parameter expressions for. the other .I 1

fission products. The complete set of diffusion parameter l expressions are:

4 D'Xe = 2.21 x 10-3 exp(-49700/RT) l (9)

~

D'y = 1.26 x 10 exp(-40800/RT) (10)

D'Cs = 1.68 x 10'4 exp(-37600/RT) (11)

D'Te = 2.43 exp(-62200/RT) (12) 4 14

3 , .

8 Thetemperaturerangeofapplicabilityfortheseekpressions extends from about 1000 C to about 2200 C. The expression for xenon is that developed by the ANS-5.4 ilorking Group as described in Reference,(1).

A plot of the four diffus1'on parameter expressions ic ,

given in Figure 3 to provide a visual comparison of the results of the study. Except at rather high temperatures the indicated i D' values for the different fission products lie within roughly a factor of 20 of one another. It should be noted again that these results are based on a limited set of data and a parti-cular interpretation of those data. VIhile the results probably represent the best that can be done with the currently avail-able information, they should be applied with caution. On this j basis it would be advisable to pursue verification studies if

)

the results are considered for incorporation in a standard pro-

! cedure for predicting volatile fission product release from operating reactor fuel.

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Diffusion Parameters as a 4

Figure 3.

Function of 1/T for Xenon, Iodine, Cesium, and Tellurium a

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9

i REFE RENCES

1. " Status Report - ANS 5.4 Fuel Plenum Gas Activity", ( 218)

(Fission Product Release from UO, Fuel), S.E. Turner, l

Chairman , April,1977.

2. R.L. Ritaman, "The Release of Iodine from UO 2", ANS 5.4  !

Subcommittee Report, April 25, 1977.

1

3. D. Davies, G. Long, and W.P. Stanaway, "The Emission of Volatile Fission Products form Uranium Dioxide", British Report AERE-R-4342, June, 1963.

4. G.W. Parker, C.E. Creek, C.J. Barton, W.J. Martin, and l R.A. Lorenz, "Out-of-Pile Studies of Fission-Product l Release from Overheated Reactor Fuels at ORNL, 1955-1965",

ORNL-3981, July, 1967.

I

5. N. Oi, "Xe Dif. fusion in UO 2 Single Crystals", Z. Natur-forsch, 20a, 1566 (1965)

6. N. 01 and J. Takagi, " Diffusion of Non-Gaseous Fission Products in UO 2 Single Crystals", Z. Naturforsch, 19a, 1331 (1964).

7. G.W. Parker, " Calculation of Gap Release of Radioactive Fission Products", Appendix C of Appendix VII of WASH-1400, October, 1975.

9 l'

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