ML20138P502
| ML20138P502 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 10/24/1985 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20138P487 | List: |
| References | |
| NUDOCS 8511070205 | |
| Download: ML20138P502 (4) | |
Text
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UNITED STATES 8
N NUCLEAR REGULATORY COMMISSION E
WASHINGTON, D. C. 20555
\\...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS.69 AND 55 TO FACILITY OPERATING LICENSE NOS. NPF-4 AND NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY OLD DOMINION ELECTRIC COOPERATIVE NORTH ANNA POWER STATION, UNITS NO. 1 AND NO. 2 DOCKET NOS. 50-338 AND 50-339 INTRODUCTION:
l By letter dated February 14, 1985 (Ref. 1), Virginia Electric and Power Company (the licensee) requested an amendment to the Technical Specifications (TS) of North Anna Power Station, Units No. I and No. 2 (NA-182).
Specifically, the amendment would delete the rod bow penalty applied to the enthalpy rise hot channel factor specified in the Limiting Condition for Operation 3.2.3.
Our evaluation regarding this TS change follows.
DISCUSSION AND EVALUATION:
The Limiting Condition for Operation 3.2.3 of the NA-182 TS speciffes the allowable value of the nuclear enthalpy rise hot channel factor, F 4 as a 3
fgnction of thermal power level.
In the same specification, the allowable F
is further reduced by a penalty multiplier which is dependent on the 3y magnitude of the rod bow penalty. Figure 3.2-3 of the TS presently specifies the value of the rod bow penalty as a function of fuel exposure.
Fuel rod bowing reduces the channel gap size between adjacent fuel rods which results in reduction in the critical heat flux (CHF) as well as the departure Trom nucleate boiling ratio (DNBR). Thus a rod bow penalty is applied to the calculated DNBR.
i The NA-182 fuel design is the Westinghouse 17x17 standard fuel assembly with R-mixing vane grids. The grid spacing span is roughly 20 inches. The CHF and hence DNBR are calculated using the W-3 CHF correlation. W-3 was originally developed with the CHF data obtained with fluid flowing inside heater tubes and annuli. Based on the R-grid fuel rod bundle CHF data, Westinghouse later modified the W-3 correlation by applying a modified R-grid spacer factor and a c.orrelation multiplier.
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In the DNB design analysis, safety margin was increased by using a i
conservative correlation multiplier, DNBR limit, pitch reduction, and i
conservative values of therinal diffusion coefficient and axial grid spacing coefficient which affect the spacer factor.
For the 17x17 standard R-grid fuel design, a generic margin of 9.1% DNBR has been quantified (Ref. 2) which I
can be used to compensate for the rod bow penalty on DNBR reduction.
If the generic margin is nsufficient to cover the penalty, plant specific reduction in the allowable F is required to compensate for the DNBR reduction.
H The fuel rod bow penalty calculation is described in the Westinghouse topical report WCAP-8691, Revision 1, " Fuel Rod Bow Evaluation" (Ref. 3). Prior to i
the approval of this topical report, the rod bow penalty was calculated using the NRC interim method, which resulted in a higher rod bow penalty than the generic margin. The rod bow topical report has since been approved and the i
magnitude of rod bow penalty calculated with the approved method has been i
greatly reduced. For the Westinghouse 17x17 R-grid fuel assembly, the rod I
bow penalty is less than 3% at 33,000 MWD /MTU which is the maximum burnup of concern with respect to the rod bow penalty. This rod bow penalty of less than 3% is fully compensated by the generic margin of 9.1%. Tgerefore,no rod bow penalty is required on DNBR as well as the allowable FaYier on The N
j proposed removal of Figure 3.2-3 and the rod bow penalty multip i
from the current TS LCO 3.2.3 is therefore acceptable.
In our review of the proposed TS change, we requested that the licensee also j
revise the basis of TS 3/4.2.3 by including the magnitude and source of the 1
l generic margin and the rod bow penalty in the bases. This will provide a j
clear accounting of the margin and the penalty. The licensee has complied with our request and we find it acceptable.
In conclusion, based on the above, we find the proposed amendment request for removing the rod bow j
penalty to be acceptable.
l ENVIRONMENTAL CONSIDERATION i
j These amendments involve a change in the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.
The staff has 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 i
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in individual or cumulative occupational radiation exposure. The Comission has previously published a proposed finding that these amendments involve no significant hazards consideration and there has been no public coment on such finding. Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 951.22(c)(9).
l Pursuant to 10 CFR 551.22(b), no environmental impact statement or environmental j
assessment need be prepared in connection with the issuance of these amendments.
l
. CONCLUSION We have concluded, 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 the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Date: October 24, 1985 Principal Contributor:
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References:
1.
Letter from W. L. Stewart (VEPCO) to H. R. Denton (NRC), " Amendment to Operating Licenses NPF-4 and NPF-7, North Anna Power Station Unit Nos. I and 2, Proposed Technical Specification Change," Serial No. 731, 2.
Letter from E. P. Rahe, Jr. (Westinghouse) to J. R. Miller (NRC),
i
" Remaining Response to Request Number 1 for Additional Information on WCAP-8691, Revision 1", NS-EPR-2572, March 16, 1982.
3.
WCAP-8691, Revision 1, " Fuel Rod Bow Evaluation", July 1979.
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