ML20235Z387

Safety Evaluation Supporting Amends 136 & 117 to Licenses DPR-53 & DPR-69,respectively

ML20235Z387
Person / Time
Site:	Calvert Cliffs
Issue date:	03/07/1989
From:	Office of Nuclear Reactor Regulation
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Shared Package
ML20235Z380	List: ML20235Z378 ML20235Z387 ML20235Z390
References
NUDOCS 8903150408
Download: ML20235Z387 (3)

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T UNITED STATES NUCLEAR REGULATORY COMMISSION l

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WASHINGTON, D. C. 20555 l' Af& '

m SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l

RELATED TO AMENDMENT NO.

TO FACILITY OPERATING LICENSE NO. DPR-53 AND AMENDMENT NO.

TO FACILITY OPERATING LICENSE NO. DPR-69 BALTIMORE GAS AND ELECTRIC COMPANY

_CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 DOCKET NOS. 50-317 AND 50-318 U-235 ENRICHMENT INCREASE FOR THE SPENT FUEL POOL

1.0 INTRODUCTION

z-By its letter dated ilune 9,1988, Baltimore Gas and Electric Company (BG&Ef the licensee) requested that the Calvert Cliffs Units I and 2 Technical 3

Specifications (TS) 5.6.1, " Criticality - Spent Fuel," be modified by

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increasing the enrichment limit for fuel which may be stored in the spent fuel storage racks from 4.1 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 wallandanexternal0.060inchthickstainlesssteelgheet.i ) loading of 0.020 The Boraflex sheet 1s 0.90 inches thick with a nominal boron-10 (8 2

gm/cm. The average distance between the centers of these cells is 10.09 inches. Spent fuel is normally stored in pool water containing about 2300 ppm of soluble boron. This normal storage arrangement would result in extremely guberitical configurations. However, for conservatism, the spent fuel rack (ere calculated assuming no soluble horon in the water, s

s Jeterminetheeffectivemultiplicati8n)transporttheorycoda imensional discrete ordinates (S The DOT-!

factor (k Neutron cross section data ib) of the was used spent fuet pool storage arrays.

the ENDF/B-IV library was generated for input to this code using the CEPAK code. This madel has been benchmarked against experimental data and has been found to adequately reproduce the critical values.

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 890315040s e90307

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. placement of fuel assemblies and poison boxes, 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 squa " root of the sum was taken. This result was then added to the cal! elational bias of -0.00138 and the nominal K of 0.93678 giving a K

of0.946includingalluncertaintiesata9N5 probability / confidence 1$N1 This meets the NRC limiting acceptance criterion of k no greater than 0.95.

Consequently, the NRC staff concludes that the sp$k fuel storage racks at Calvert Cliffs Units 1 and 2 can accommodate, with respect to criticality, fuel having a maximum enrichment of 5.0 eight percent U-235.

Recently the NRC staff has expressed concerns regarding the possibility of gaps developing in Boraflex sheets due to irradiation induced axial shrinkage. This concern was documented in NRC Information Notice No. 87-43.

In response, the licensee has performed an analysis to determine the reactivity effects of Boraflex gap formation in the Calvert Cliffs spent fuel pool. The results indicate that, even with the assumption of a complete loss of soluble boron in the pool water, sufficient margin is available to accomodate nearly a 4 inch vertical gap in every Boraflex sheet at the active fuel centerline without exceeding the NRC limiting criterion of a maximum k of 0.95.

Although the licensee has no surveillance requirements fn place for detecting degradation of the full f

length Boraflex sheets, it has a poison coupon monitoring program to detect degraded Roraflex specimens which would indicate any extreme shrinkage or loss of neutron absorption properties.

In addition, since the installation process for the Boraflex assemblies involved only single sheets, that are not fastened or permanently glued onto any surface or structure, gap formation due to Boraflex shrinkage would not be expected. Based on the above and on normal spent fuel pool conditions, that it contains sufficient soluble boron to more than offset any reactivity increase due to Boraflex degradation, the NRC staff finds the use of Boraflex in the Calvert Cliffs spent fuel pool design to be an acceptable means of meeting the required ccceptance criteria.

In the December 28, 1988 letter, BG&E comitted to considering the fuel handling accident in each Unit 1 or 2 core reload analysis to ensure that the accident analysis would bound all possible U-235 enrichment and fuel burnup levels for each specific-fuel assembly in the reactor core or the spc)i fuel pool. The NRC staff finds this analytical approach to be acceptable.

However, until final completion of the NRC generic fuel handling accident analysis for 5.0 weight percent U-235 enriched fuel with burnup levels up to 60,000 MWD /MT, TS 5.6.1, " Criticality - Spent Fuel," cannot be modified to permit the storage of irradiated fuel with U-235 enrichment levels above that currently pemitted at Calvert Cliffs, specifically 4.1 weight percent U-235.

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Consequently, the NRC staff has determined that an increase in the enrichment limit of TS 5.6.1 for unirradiated fuel stored in the spent fuel storage racks, to a value up to and including 5.0 weight percent U-235 is acceptable.

Furthermore, the staff has determined that an increase in-the TS 5.6.1 enrichment limit up to and including 5.0 weight percent U-235 for irradiated fuel is acceptable, contingent upon the acceptability of the NRC generic fuel handling accident analysis, but that the TS 5.6.1 enrichment limit shall not be modified for irradiated fuel until this contingency is satisfied.

3.0 INTENT The intent of the proposed change is to permit the storage of fuel, that is not irradiated, with enrichment levels up to and including 5.0 weight percent U-235, in the spent fuel storage racks.

Irradiated fuel is fuel that has experienced criticality (i.e., k8ff greater than or equal to 1.0).

4.0 STATE CONSULTATION

S A Notice of Consideration of Issuance of Amendment to Facility Operating License and Opportunity for Prior Hearing was published in the Federal Register on August 8, 1988 (53 FR 28791). No hearing requests or intervention petitions were received. The State of Maryland was consulted on this matter and had no comments on the determination.

5.0 ENVIRONMENTAL CONSIDERATION

Pursuant to 10 CFR 51.21, 51.32 and 51.35, an environmental assessment and finding of no significant impact was published in the Federal Register on January 30, 1989 (53 FR 4352).

Accordingly, based upon the environmental assessment, the Commission has determined that issuance of this amendment will not have a significant effect on the quality of tne human environment.

6.0 CONCLUSION

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We have conclided, based on the considerations discussed above, that:

(1) there is reasonable: assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and (3) the issuance of these amendments will not be inimical to the conraon defense and security or to the health and safety of the public.

PRINCIPAL CONTRIBUTORS:

L. Kopp. S. McNeil Dated: March 7, 1989

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