ML20050B447
| ML20050B447 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 03/30/1982 |
| From: | Kay J YANKEE ATOMIC ELECTRIC CO. |
| To: | Speis T Office of Nuclear Reactor Regulation |
| References | |
| FYR-82-35, NUDOCS 8204050344 | |
| Download: ML20050B447 (2) | |
Text
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YANKEE ATOMIC ELECTRIC COMPANY g
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2.C.2.1 FYR 82-35 j
1671 Worcester Road, Framingham Massachu etts 01701 Qq __
dANKEE W'A/
March 30, 1982 x\\'
1.C.2.1 O
4 hg*g United States Nuclear Regulatory Commission
/g Wa shi ng ton, D. C.
20555
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Attention:
Mr. Themis P. Speis Assistant Director for Reactor Safety co
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N Division of Systems Integration
References:
(a)
License No. DPR-3 (Docket No. 50-29)
(b) Letter, T. Speis (USNRC) to D. E. Vandenburgh (YAEC),
dated January 26, 1982
Subject:
Single Failure Assumptions in ECCS Analyses
Dear Sir:
Reference (b) informed Yankee of a Westinghouse concern regarding single failure assumptions used in large break loss-of-coolant accident analyses.
Specifically, Westinghouse concluded that for some plants, the loss of a single Low Head Safety Injection (LHSI) pump may not be the worst single failure assumption and that the effect of maximum LHSI is to produce higher calculated peak clad temperatures via the effects of additional LHSI spillage on containment backpressure.
Based on this information, Yankee was requested to address certain questions related to this issue.
The manner in which higher peak clad temperatures are produced f rom the result of maximun LHSI is purely artificial.
ECC spillage for containment backpre ssu re calculations is assumed to act as an equivalent spray flow with 100% efficiency.
This assumption is consistent with the CSB.6.1 guidelines and Appendix K requirements for containment backpressure calculations.
However, this assumption regarding the handling of ECC spillage is too conservative.
Realistically, a majority of the ECC spillage would be directed to the sump (or liquid region).
This would render the Westinghouse concern a non problem.
Moreover, Yankee's ECCS consists of three trains of ECC injection and the e f f ec t o f ha vi ng the third train available is to further reduce calculated peak clad temperatures.
This is due to two important factors.
First, the refill period would be shortened. Second, since the current calculations show PCT's occurring before the downcomer region is filled, higher flood rates would result.
Both of these are positive effects and would more than offset the negative effect of a slightly reduced containment backpressure.
Additionally, a best estimate analysis for Yankee would show that peak clad temperatures would not be affected by the maximum LHSI assumption, since experimental data has shown that peak cladding temperature occur during the 80 8204050344 820330 PDR ADOCK 05000029 P
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United States Nuclear Regulatory Commission March 30, 1982 Attention:
Mr. Themis P. Spels Page 2 1
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blowdown phase.
LOFT test L2-3 results confirmed that maximum clad temperatures occur during the blowdown phase of a large break 10CA.
No significant cladding temperature excursions occurred during reflood.
La rge break calculations performed in accordance with Appendix K have been shown conservative with respect to best estimate calculations by several hundreds of deg ree s.
Based on the conservatisms in Appendix K, the LOFT L2-3 experimental results and the two train large break performance analysis at Yankee, we feel that the ef fect of maximum LIISI is of no real safety significance and has no im pac t whatsoever on current operating limits.
We trust that the above information is satisfactory.
If there are any questions, please contact us.
Very truly yours, J. A.
Kay Senior Engineer - Licensing JAK: dad
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