ML20116E217
| ML20116E217 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 11/10/1988 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20116D885 | List:
|
| References | |
| FOIA-96-237 NUDOCS 9608050150 | |
| Download: ML20116E217 (4) | |
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j NUCLEAR REGULATORY COMMISSION o
R*ese*}j wasmwarow, o.c. noses ENCLOSURE 1 l
I SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO THE U-235 ENRIClMENT INCREASE FOR FUEL STORAGE BALTIMORE GAS AND ELECTRIC COMPANY CALVERT CLIFFS UNITS 1 AND 2 DOCKET NOS. 50-317 and 50-318
1.0 INTRODUCTION
By letter dated June 9, 1988 Baltimore Gas and Electric Company (BGE), the licensee, requested an Amendpent to Facility Operating License Nos. DPR-53 and DPR-69 for Calvert Cliffs Unit Nos. I and 2, respectively. The proposed change would revise Technical Specification 5.6.1 and 5.6.2 to increase the cnrichment limit of fuel which may be stored in the new and spent fuel storage racks from 4.1 weight percent U-235 to 5.0 weight percent U-235.
2.0 EVALUATION The Calvert Cliffs spent fuel storage racks consist of square stainless steel cells having an inside dimension of 8-9/16 inches. The inner wall of each storage cell is made of a 0.060 inch thick sheet of 304L stainless steel. A Boraflex sheet 6-1/2 inches wide is sandwiched between this inner wall and an external 0.060 inch thick stainless steel sheet. The Boraflex sheet is 0.090 2
inches thick with a nominal boron-10 (BIO) loading of 0.020 gm/cm. The average distance between the centers of these cells is 10.09 inches. The new (unirradiated) fuel storage racks consist of 144 storage locations with a nominal 18 inch center-to-center distance between new fuel assemblies. The spent fuel is normally stored in pool water containing about 2300 ppm of soluble boron whereas the new fuel is normally stored in a dry (air) cnvironment. Both of these normal storage arrangements result in extremely suberitical configurations. However, for conservatism, the spent fuel racks 9608050150 960731
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l are calculated assuming no soluble boron in the water and the new fuel is i
assumed to be stored under various amounts of water moderation.
The 00T-IV two-dimensional discrete ordinates (S,) transport theory code was l
used to determine the effective multiplication factor (k,ff) of the spent fuel pool storage arrays while the KENO-IV Monte Carlo code was used for the new fuel storage racks. Neutron cross section data from the ENDF/B-IV ISbrary was generated for input to these codes using the CEPAK code. These modets have l
been benchmarked against experimental data and have been found to adeouately 1
reproduce the critical values.
l The new (unirradiated) fuel storage rack was analyzed for varying degreet, of moderation, assuming no burpable poison or control rods and 5.0 weight percent U-235 in unirradiated fuel. The maximum k,ff was found to occur for full flooding at a water density of 1.0 gm/cc. Therefore, this is also the optimum moderation condition. The nominal k,ff calculated was 0.89, well below the NRC j
limiting criterion of 0.95 for fully flooded conditions and 0.98 for optimum moderation conditions. An uncertainty analysis, therefore, was not required since typical uncertainties have previously been found to be less than 3.0% for similar storage configurations.
The spent fuel pool criticality calculations were also based on no burnable poison or control rods in the fuel assemblies, unirradiated fuel with 5.0 weight percent U-235, and, as previously mentioned, no soluble boron in the water.
In addition, the most adverse effects of temperature, eccentric placement of fuel assemblies and poison bpxes, changes in steel thickness, change in center to center spacing, boron' poison loss possible over the life of the Boraflex, and the calculational uncertainty were included in the following manner. The squares of each delta-k change were added and the square root of the sum was taken. This result was then added to the calculational bias of
+0.00138 and the nominal k,ff of 0.93678 giving a k,ff of 0.946 including all l
uncertainties at a 95/95 probability / confidence level. This meets the NRC limiting acceptance criterion of k,ff no greater than 0.95.
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3 The staff has recently expressed concerns regarding the possibility of gaps developing in Boraflex sheets due to irradiation induced axial shrinkage as documented in NRC Information Notice No. 87-43. Based on this, the licensee has performed analyses to determine the reactivity effects of Boraflex gap formation on the Calvert Cliffs spent fuel pool. The results indicate that t
even with the assumption of a complete loss of soluble boron in the pool tater, sufficient margin is available to acconnodate nearly a 4 inch vertical gap in every Boraflex sheet at the active fuel centerline without exceeding the NRC limiting criterion of 0.95. Although no surveillance requirements are in place for detecting degradation of the full length Boraflex sheets, there are measuring techniques for detecting degraded Boraflex specimens in the inservice surveillance program which would indicate any extreme shrinkage or l
loss of neutron absorption properties.
In addition, since the fabrication process for the Boraflex assemblies involved only single sheets which are not fastened or permanently glued onto any surface or structure, gap formation due to Boraflex shrinkage would not be expected. Based on this and on the fact that the spent fuel pool normally contains sufficient soluble boron to more l
than offset any reactivity increase due to Boraflex degradation, the staff finds the reliance on Boraflex in the Calvert Cliffs spent fuel pool design as a means to meet the required staff acceptance criteria acceptable.
3.0 CONCLUSION
i Based on the above evaluation, the s f concludes that the spent fuel and fresh fuel storage racks at Calvert Cliffs Units 1 and 2 can accommodate fuel from the Units having a maximum enrichment of 5.0 weight percent,U-235. The requested change in Technical Specification 5.6.1 and 5.6.2 to increase the enrichment limit of the new and spent fuel storage racks from the current 4.1 weight percent U-P35 to a maximum of 5.0 weight percent U-235 is acceptable.
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ENCLOSURE 2 i
SYSiEMATIC ASSESSMENT OF LICENSEE PERFORMANCE FACILITY NAME Calvert Cliffs Units 1 and 2
SUMMARY
OF REVIEW The Reactor Systems Branch, DEST, reviewed the request by Baltimore Gas &
Electric Company to increase the enrichment limit of fuel which way be stored in the new and spent fuel sforage racks. Based on our evaluation, we conclude that the new and spent fuel storage racks at Calvert Cliffs Units 1 and 2 can accommodate fuel having a maximum enrichment of 5.0 weight percent U-235.
NARRATIVE DISCUSSION OF LICENSEE PERFORMANCE - FUNCTION AREA Review of the submittal indicated that the licensee adequately addressed most of the technical aspects of the issue. However, additional information was required. The licensee was very responsive to the staff questions and was sensitive to the safety significance placed on the issues.
AUTHOR:
L. I. Kopp DATE:
11/8/88