ML20024G558
| ML20024G558 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 12/05/1973 |
| From: | Skovholt D US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Mayer L NORTHERN STATES POWER CO. |
| References | |
| NUDOCS 9102120661 | |
| Download: ML20024G558 (7) | |
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D%TRIMTION Lb.ket File AEC PDR local PDR RP Reading Branch Reading JRBuchanan, ORNL DEC
. 1973 DJSkovholt s
TJCarter Incket !b. 50-263 ACRS (16)
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OcC DLZiemann Northern States Power Company JJShea.
ATE: Mr. L. O. liayer, Director of RMDiggs Nuclear Support Services 414 Nicollet Mill Minneapolis, Minnesota 5M 01 Gentlemen:
As you aru aware *.he General Electric Cocpany (CE) report NE10-20181, "GhGAP-III A tbdel for the Prediction of Pellet-Clad 1hermal Conductance in IMR Fuel Pods", November 1973, has been submitted to prmide a basis for further review of the effects of BWR fuel densificatlen. 'Due related proprietary information is pmvided in NEDC-20181 Suppicment 1 (Pro-prietary) November 1973.
Tne Regulatory staff considers that nodific.tions to the "GE bbdel for Fuel Lunsification" transmitted to you in our letter of July 16, 1973, are appropriate. The enclosure "Abdified GE Model for Fuel Densification",
represents the staff's current conclusions on BWR fuel densification.
We have requested, by separate letter, that GE supplemnt NEDO-20181 with calculations to determine the consequences of fuel densification, using the guidance provided in the enclosure. It is requested that you provide the necessary analyses and other relevant data for determining the effects of ruel densification on normal operation, anticipated transients, and accidents, incluling the postulated loss-of-coolant =cMamt, using the guidance in the enclosure.
If the analyses indicate that changes in operating conditions are warranted, you should submit proposed changes to your Technical Specifications with the analyses. We anticipate that the application of these changes should allow changes to the Technical Specifications which will be less restrictive to plant operations.
It is requested that you provide within fourteen days your schedule for sulnittal of your response to this request.
Sincerely,
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tonald J. Skovholt f /,
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Northern State Power Company
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Enclosure:
hbdified GE tbdel for Fuel Densification cc w/ enclosures:
Ibnald E. Nelson, Esquire VP and GC Northern States Ibwer Company 414 Nicollet Mall Minneapolis, Minnesota 55401 Gerald 01arnoff Shaw, Pittum, Ibtts, Trowbridge 6 Madden 910 - 17th Street, N. W.
Washington, D. C.
20006 lbward J. Vogel, Esquire Knittle 6 Vogel 814 Flour Exchange Building Minneapolis, Minnesota 55415 Steve Gadler, P. E.
2120 Carter Avenue At. Pat 0, Mir.nereta 55103 lbrriett Lansing, Esquire Assistant City Attorney City of St. Paul 63S City Ib11 S t. Paul, Minnesota 55102 Ken Drugan Minnesota Pollution Control Agency 717 Delaware Street, S. E.
Minneapolis, Minnesota 55440 Warren R. Lawson, M. D.
Secretary 6 Executive Officer State Department of licalth 717 Delaware Street, S. E.
Minneapolis, Minnesota 55440 Envirormental Library of Minnesota 1222 S. E. 4th Street Minneapolis, Minnesota 55414 Anthony Roismn, Equire Berlin, Roirman and Kessler 1712 N Street, N. W.
Washington, D. C.
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Decemb r 4,1973 ENCLOSlTRE MODIFIED CF M3 DEL F0P TUEL DENSIFICATION The General Electric fuel densification nodel is described in NEDC-20381, NEDM-10735 and Supplements 1, 2, 3, 4, and 5 to NEDM-10735 (see references 1 through 6).
Mee proprietary information regarding this matter is provided by NEDO-20181 (reference 9).
The GE model when modified as described below is considered to be suitably conservative for the evaluation of densification effects in BWR fuel.
Possible effects of fuel densification are:
(1) power spikes due t o axial gap forr.ation; (2) increase in LHGR because of pellet length shortening; (3) creep collapse of the cladding due to axial gap formation; (4) changes in s tored energy due to increased radial gap size.
rnd bitilarly, the GE model for fuel densification consists of four parts:
power spike model, linear heat generation model, clad creep collapse model, and stored energy model. The required modifications to each of these models are listed below.
Power Spike Model i
The GL power spike model is acceptable ao it is described in NEDM-10735
- r.. Supplerent 1 to NEDM-10735 and modified in Supplement 5 of NEDM-10735 ce long as it is used in conjunction with a maximum axial gap size given by the following equation:
AL = (.965 - p1 F 0.0025)L where AL = maximum axial gap length L = fuel column length
- . - t.... G us W w a ul G.... tic.1 Whet d a._.. t y (geowtriy 0.0025 - allowance for irradiation induced cladding growth and axial strain caused by fuel-clad mechanical interaction
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Lir. ear Heat Ceneration M 'i t
lhe following expression should be used to calculate the decrease in fuel column length in determinations of the linear heat generation rate:
i 0.965 - oi R=
L 2
where:
al = decrease in fuel column length L = fuel column length pi = mean value of measured initial pellet density (geometric)
Credit can Le taken for fuci column length increase due to thermal expansion, and for the actual measured length of the fuel column.
_ Clad Creep Collcose "odel Examination of exposed BWR fuel rods (Ref. 5) and Regulatory staff calculations shcw that clad collapse will not occur in typical BWi; fuel ouring tne nrs. cycle et operation.
rnncequently, n.
additicr.al :.rt: p collapse calculations are required for the first cycle of typical BWR fuel.
For reactors in subsequent cycles of operation the GE creep collapse model described in NEDO-10735 should be used with the following modifications:
1.
The equation used to calculate the change in ovality due to the increasing creep strain should account for the ovality change due to change in curvature as well as for the ovality change due to change in rod circumference.
2.
A conservative value should be used for the clad temperature.
Axial temperature variations in the vicinity of a fuel gap as affected by thermal radiation from the ends of the pellets and by axial heat conduction should be taken into account.
Effects M'
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fron any buildup of oxide and crud on the cled surfc:ts should also be considered.
3.
The calculations should be made for the fuel rod having the worst combination of fast neutron flux and clad temperature.
4.
No credit should be taken for fission gas pressure buildup.
5.
No credit should be taken for end effects.
An infinitely long, unsupported length of cladding should be assumed.
6.
Conservative values for clad wall thickness and initial ovality should be used.
An acceptable approach is to use the two standard deviation limit of as fabricated dimensions.
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(1) _Densification The densification-kinetics expressien as described in tlEDC-201El it accept:ble subject. Lu the restriction that the rate constants (M,A and D[
are adjusted such that a specified density increase occurs at a burnup no greater than 4,000 mwd /tU.
The specified density increase will correspond to the density increase experienced by like fuel during an out-of-reactor resintering anneal at 1700 C for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
This density increase may be considered to give the maximum density in the model, and no further density increase need be predicted.
Resintering tests already performed by G.E. and reported in NEDC-20181 on archive and current producticn pellets raay be used es a basis for obtaining the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> resintering dtta.
A linear interpolation to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> will De acceptable on a plot of density increase vs log (time) between the measured points at 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br />.
The 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> and 100 hour0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> points to
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correspond to a 9 % tolerance on the measured density-increase distributions for the resintered pellets at each time period.
(2) for purpcTes of calculating the densitication effect on gap conductance and stored energy the change in fuel pellet radius should be calculated from density change in (1) above and from the assumption that shrinkage is isotropic, i.e.
{
!L " l/3 & where r
p
= change in density from densification-kinetics expression op described in NtDC-20181 r = radius (3) Creep Clad creepdce.n a H ef fect:. g;p ccc.Judonce may be calculated with the CREEP-1 code, as described in NEDC-20181, provided that the resultent creep strains are multiplied by 0.31.
(4)
Since the assembly average stored energy is one of the most important inputs to EWR LOCA evaliacion, a Technical Specification limit should be imposed on ma ix mum permitted assembly power.
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i IITLI.L NCL 3 1.
"GEGAP-3 A Model for the Prediction of Pellet-Clad Thermal Conductance in BWR Tuci Rods," Supplement I (Proprietary), NEDC-20181 (Proprietary)
November 1973, 2.
D. C. Ditmore and R. B. Elkins:
"Densification Considerations in BWR Fuel Design and Performance" NEDM-10735, December 1972.
" Responses to AEC Questions - NEDH-10735," NEDH-10735 Supplement 1 3.
April 1973.
4.
" Responses to AEC Questions NEDM-10735 Supplement 1," NEDM-10735 Supplement 2, May 1973.
5.
" Responses to AEC Questions NEDM-10735 Supplement 1," NEDH-10735 Supplement 3 June 1973.
" Responses to AEC Ques tion NEDM-10735," NEDM-10735 Supplement 4, 6.
{
July 1973.
"Densification Considerations in BWR Fuel," NEDM-10735 Supplettent 5, 7.
July 1973.
8 l'. C. Elif cr cr.d J. E. !!cr.ch, "1.06 A-Of-Cuvian t Accident 6 itergency Core Cooling Modeln for General Electric Boiling Water Reactors,"
NEDO-10329, April 1971.
9.
NEDO-201El, "GEGAP-III A Model for the Prediction of Pellet-Clad Thermal Conductance in BWR Fuel Rods," November 1973.
.