ML18142A218

Forwards Safety Evaluation Re Removal of 7% DNBR Credit Associated W/Densification Power Spike from Retained DNBR Margin.Use of Improved Fuel Rod Bowing Evaluation Method Permits Reduction of Rod Bow Penalty on 15x15 L-grid Fuel

ML18142A218
Person / Time
Site:	Surry
Issue date:	03/21/1985
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Harold Denton, Varga S Office of Nuclear Reactor Regulation
References
85-064, 85-64, NUDOCS 8503270477
Download: ML18142A218 (6)

Text

Wfl.U4M L STEWART Vice President Nuclear Operations March 21, 1985 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation Attn:

Mr. Steven A. Varga, Chief Operating Reactors Branch No. 1 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.

20555 Gentlemen:

VIRGINIA POl1ER e

Nuclear Operations Department Post Office Box 26666 One James River Plaza Ricbmond, Virginia 23261 VIRGINIA POWER Serial No.85-064 PSE/RCA/mjp/2001N Docket Nos.

50-280 50-281 License Nos.

DPR-32 DPR-37 REDUCTION I*N ROD BOW DNBR PENAL TY FOR SURRY POWER STATION UNIT NOS. 1 AND 2 In a February 21, 1978 letter from Mr. C. M. Stallings of Virginia Power to Mr. E. G. Case of the NRC (Serial No. 095) Virginia Power proposed the elimination of a F~H penalty, due to rod bow, from the Surry Power Station Technical Specifications.

An enclosed safety evaluation noted that the appropriate DNBR penalty, then conservatively estimated to be 11.7%, was met by more than 18% retained DNBR margin.

The NRC subsequently approved the Technical Specification change.

Later, the NRC approved generic 11.4% full flow and 14.0% low flow penalties as applicable to all 15 x 15 fuel.

Through the use of an improved fuel rod bowing evaluation methodology, Westinghouse has since successfully demonstrated to the NRC that the existing rod bow penalty on 15x15 L-grid fuel can be further reduced.

Virginia Power has employed this benefit to reduce the rod bow penalty, allowing for an accompanying decrease in Surry Power Station's retained DNBR margin.

Specifically, the 7% DNBR credit associated with the densification power spike has been removed from the retained margin.

Implementation of these changes has no impact on the Technical Specifications or the conservatism of previous DNBR analyses. A safety evaluation is therefore provided in Enclosure 1 for your information only.

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Mr. Harold R. Denton Page 2 VIRGINIA POWER This change has been reviewed and approved by the Station Nuclear Safety and Operating Committee and the Safety Evaluation and Control Staff. It has been determined that this penalty reduction does not involve any unreviewed safety questions as defined in 10CFR50.59 or a significant hazards consideration as defined in 10CFR50.92.

Very truly yours, I \\*r--/

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W. L'. Stewart

Enclosure:

Safety Evaluation for proposed Rod Bow Penalty changes cc: Dr. J. Nelson Grace Regional Administrator Region II Mr. D. J. Burke NRC Resident Inspector Surry Power Station Mr. Charles Price Department of Health 109 Governor Street Richmond, Virginia 23219

I -

e PAGE 1

Safety Evaluation An improved Westinghouse methodology to analyze the effect of fuel rod bowing was presented in References 1, 2 and 3 and approved by the HRC in Reference

4. VEPCO intends to apply the results of these methods to determine the departure from nucleate boiling ratio CDNBR) effects of rod bow for the Surry Power Station Units 1 and 2, which are fueled with Westinghouse Standard 15 x 15 fuel assemblies.

VEPCO will continue to use a conservative design uncertainty CFQU) value of 1.0815 (1.05 x 1.03) for evaluation of the total overall peaking factor FQ, even though a smaller value can be justified based on the information piesented in Figure 6.1 of Reference 1.

The total retained DHBR Margin for 15 x 15 fuel has been quantified to be 18.1% (Ref. 5). The component parts of this margin are identified in the attached Table 1, taken from Reference 5. This retained margin has been used in the past to offset the previous (Ref

6)

DHBR rod bow penalties of 11.4% (full flow) and 14% Clow flow) associated with 85%

gap closure data. The new L-grid rod bow DHBR penalties given in Figure 6-4 of Reference 1 are substantially less than these values.

Therefore, the removal of the 7% DHBR credit associated with the densification power spike from the 18.1% retained DHBR margin is justifiable because adequate margin is available. The retained DHBR margin would be reduced to 11.1%, which is more than adequate to offset the Reference 1 L-grid rod bow penalties. The removal of the densification power spike will be seen directly as an increase in DHBR in any future Surry licensing submittals. This will

PAGE 2

offer two benefits:

1) allow the calculated DNBR numbers to more accurately reflect the true margin to the DNB limit and 2) simplify the procedure associated with performing a DNBR calculation.

As a

result of our evaluation, we have determined that the implementation of the updated rod bow penalty and the removal of the densi£ication power spike credit

£or Surry does not result in an unreviewed safety question as defined in 10CFR50.59.

In addition, the change does not involve a "significant hazards consideration".

There is a reduction of the retained DNBR margin due to the removal of the densification penalty; however, this is compensated for by implementation of the NRC~approved rod -bow penalties, which enable a commensurate level of safety to be maintained.

Table 1: Retained DNBR Ma~gin W Standa~d 15 x 15 Fuel 1.24 DNBR vs. 1.30 DNBR Pitch Reduction TDC.019 vs.. 038 Densification Spike Total Retained Ma~gin

4. 8?.

3. 3?.

3.0%

7.. 0%

18. 1 Yo PAGE 3

.fl' e

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Refe:cences

1.

J.

Ska:citka, et al., "Fuel Rod Bow Evaluation", WCAP-8691 Rev 1, CP:cop:cieta:cy) and WCAP-8692 Rev. 1 CNon-p:cop:cieta:cy), July 1979.

2.

Lette:c, E.

P.

Rahe, J:c.

CW) to J. R. Mille:c CNRC), "Pa:ctial

Response

to Request Numbe:c 1

fo:c Additional Info:cmation on WCAP-8691 Rev. 1," NS-EPR-2515, dated Octobe:c 9, 1981.

3.

Lette:c, E.

P.

Rahe, J:c. CW) to J. R. Mille:c CNRC), "Remaining

Response

to Request Numbe:c 1

fo:c Additional Info:cmation on WCAP-8691 Rev. 1," NS-EPR~2572, dated Ma:cch 16, 1982.

4. Lette:c, C. O. Thomas CNRC) to E. P. Rahe, J:c. CW), "Acceptance fo:c Refe:cencing of Licensing Topical Repo:ct WCAP-8691CP)

/

WCAP-8692CNP)," dated Decembe:c 29,1982.

5.

Lette:c, C. Eicheldinge:c CW) to V. Stello, J:c. CNRC), NS-CE-1161, August 13, 1976.

6.

Lette:c, T.

M.

Ande:cson CW) to J. F. Stolz CNRC), NS-TMA-2053, dated Ma:cch 16, 1979.

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