ML20129G777

Safety Evaluation Supporting Amends 116 & 114 to Licenses DPR-80 & DPR-82,respectively

ML20129G777
Person / Time
Site:	Diablo Canyon
Issue date:	10/25/1996
From:	NRC (Affiliation Not Assigned)
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ML20129G773	List: ML20129G777
References
NUDOCS 9610300199
Download: ML20129G777 (3)

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p24euqk UNITED STATES y

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g NUCLEAR REGULATORY COMMISSION a

WASHINGTON, D.C. 20086 4 001

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENIMENT NO. 116 TO FACILITY OPERATING LICENSE NO. DPR-80 AND AMENDMENT NO. 114 TO FACILITY OPERATING LICENSE NO. DPR-82 l

j PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER PLANT. UNITS 1 AND 2 l

l DOCKET NOS. 50-275 AND 50-323 l

l

1.0 INTRODUCTION

l By application dated June 7, 1996, Pacific Gas and Electric Company (or the licensee) requested changes to the Technical Specifications (Appendix A to Facility Operating License Nos. DPR-80 and DPR-82) for the Diablo Canyon l

Nuclear Power Plant, Units 1 and 2.

The proposed changes revise the combined Technical Specifications (TS) for the Diablo Canyon Nuclear Power Plant, Unit Nos. I and 2 to revise Technical Specifications 3/4.9.14.1, " Spent Fuel l

Assembly Storage - Spent Fuel Pool Region 2," and TS 3/4.9.14.3, " Spent Fuel Assembly Storage - Spent Fuel Pool Region 1," to allow storage of fuel l

assemblies in a checkerboard pattern in Region 2 of the spent fuel pool (SFP).

2.0 EVALUATION l

The licensee proposed to change TS 3/4.9.14.1 and 3/4.9.14.3 to allow the use of a checkerboard pattern with empty cells (i.e. cells filled only with water or non-fissile bearing material) in Region 2 of the SFP. The storage racks in l

the spent fuel pool are divided into two regions. Region 2 consists of 1034 storage cells and contains no Boraflex. The cells are stainless steel with an inside dimension of 8.85 inches arranged on a 10.929-inch center-to-center spacing, providing a 1.899-inch water gap between the walls of the storage i

cells. The spent fuel racks are normally fully flooded by water borated to at i

least 2000 ppe of boron as required by the plant TS. However, to meet the criterion stated in Standard Review Plan (SRP) Section 9.1.2, k,, must not exceed 0.95 with the racks fully loaded with fuel of the highesI anticipated reactivity and flooded with unborated water at a temperature corresponding to l

the highest reactivity. The maximum calculated reactivity must include a margin for uncertainties in reactivity calculations and in manufacturing tolerances such that the true k,,, will not exceed 0.95 at a 95/95 probability / confidence level.

t The Region 2 spent fuel storage racks were analyzed for storage of Westinghouse 17x17 fuel assemblies with nominal enrichments up to 5.0 weight percent (wt%) U-235 using the concept of burnup reactivity equivalencing.

For Region 2, the Westinghouse standard fuel assembly design gave a slightly higher reactivity than the optimized (OFA) fuel. The same initial assumptions, biases and uncertainties as used for the Region 1 analyses were l

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included, except for the design basis temperature and the effects of Boraflex shrinkage and gaps.

Since the Region 2 racks contain no Boraflex, the temperature coefficient of reactivity is positive and a temperature of 150'F l

was assumed. A depletion uncertainty of 0.0005 times the burnup in WD/KgU was assumed, resulting in an uncertainty of 0.02 Ak for fuel burned to 40 WO/KgU. This uncertainty is consistent with current practice and is 1

i acceptable. The equivalencing showed that fresh standard Westinghouse fuel i

enriched to 1.74 wtX U-235 yields the same rack reactivity (k 'sh fuelFor OFA assem i

5.0 wtX fuel irradiated to 40 WD/KgU.

i enriched to 1.79 wtX U-235 was equivalent to 5.0 wt% fuel irradiated to 38.75 l

WD/KgU, yielding a rack reactivity (k,,,) of 0.9462. These values meet the NRC acceptance criterion of 0.95 and are acceptable.

Fuel initially enriched i

to 5.0 wt% U-235 may be stored in a checkerboard pattern in Region 2, i

i alternating with cells filled with only water or non-fissile material.

For this case, the maximum calculated reactivity, including uncertainties, was

)

0.9392.

Most abnormal storage conditions will not result in an increase in the k,,, of the racks.

However, it is possible to postulate events, such as the i

misloading of an assembly with an enrichment and burnup (or integral fuel i

burnable absorber (IFBA)) combination outside of the acceptable area or pool i

temperatures exceeding 150*F, which could lead to an increase in reactivity for Region 2.

However, for such events credit may be taken for the presence of approximately 2000 ppe of boron in the pool water required by TS 3.9.14.2 i

since the staff does not require the assumption of two unlikely, independent, i

concurrent events to ensure protection against a criticality accident (Double Contingency Principle). The reduction in k caused by the boron more than l

offsets the reactivity addition caused by c,r,e,dible accidents.

In fact, the licensee has determined that only 400 ppe of boron is necessary to mitigate l

the worst postulated accident in any pool region. Therefore, the staff j

criterion of k no greater than 0.95 for any postulated accident is met.

l Therefore, the,,s,taff finds the TS changes acceptable to allow a checkerboard pattern in Region 2 of the SFP.

3.0 STATE CONSULTATION

i In accordance with the Commission's regulations, the California State official was notified of the proposed issuance of the amendments. The State official j

had no comments.

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4.0 ENVIR0 MENTAL CONSIDERATION These amendments change a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change a surveillance requirement.

The NRC staff has j!

determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative i

occupational radiation exposure. The Commission has previously issued a j

proposed finding that the amendments involve no significant hazards j

consideration, and there has been no public comment on such finding i

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. 4 (61 FR 50346). Accordingly, the amendments meet the eligibility criteria for i,

categorical exclusion set forth in 10 CFR 51.22(c)(9).

Pursuant to 10 CFR j

51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.

5.0 CONCLUSION

i The Commission has concluded, based on the considerations discussed above, 4

that (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, i

and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.

Principal Contributor:

S. Bloom Date:

October 25, 1996 4

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