ML20141M540
| ML20141M540 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 08/27/1992 |
| From: | Burski R ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| W3F192-0317, W3F192-317, NUDOCS 9209010100 | |
| Download: ML20141M540 (2) | |
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m 71; F, Durski W3F192-0317 A4.05 QA August 27, 1992
-U.S.
Nuclear Regulatory Commission Attn:
Document Control Desk Washington, D.C.
20555
Subject:
Waterford 3 SI:S
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Docket No. 50-382 License No.- NPF-38 Technical Specification Change Request (TSCR)
NPF-38-123 Arlditional Information Gentlemen:
This letter serves to' document key aspects of a discussion between members of the U.S.N.R.C. -and Waterford 3 staf f concerning improved -
Main Steam Isolation Valve (MSIV) reliability and provide additional information regarding the subject TSCR.
Waterford 3 submittal (W3F192-0020)- dated April 24, 1992 justifies a proposed Technical Specification Change to increase the maximum MSIV closure time from 3.0 seconds to 4.0-seconds.
In the past the Waterford 3 MSIV's - have experienced serious
. material failures that have reduced the valves reliability and
-threatened plant oparability.
A principal failure which has occurred involved fatigue cracking and fracture at the stem to stem head connection on the valve stem.
The root cause of the crack'ing in the stem head was determined to be fatigue failure induced by a hydraulic system instability which produced excessive pressure pulsation stress cycles.
Replacement of the valve stems and improvements to the hydraulic system performance have-been accomplished as described.in LER-89-023-00.
- The intent of the subject TSCR is to slow the closing speed of the MSIV. actuators, thereby reducing the inertial impact force on the valve-stem and surrounding components during valve seating.
Ultimately, it-is hoped that this will contribute to alleviating future valve material problems and increase stem and-valve component lifetime.
This action is being taken based on engineering judgement related to experience at San Onofre Nuclear Generatinc Station (SONGS) which has the same type of MSIV's as Waterford 3.
The MSIV.'s at SONGS have not experienced the same 9209010100 920827
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,s U.S. Nuclear. Regulatory Commission Technical Specificatic n Change Request TSCR NPF-38-123 Additional Information W3F192-0317 Page 2 August 27, 1992-magnitude of problems as the valves at Waterford 3 and it is believed that this is primarily due to the difference in stroke times.
Their closure time was initially 5.0 seconds and has been increased to 8.0 seconds.
SONGS replac3d an MSIV stem for reasons other than cracking and sent the removed stem to the same laboratory that Waterford 3 used in its root cause analysis for destructive testing.
The testing revealed no evidence of stem cracking even though this stem was believed to have been exposed to a similar cyclic fatigue history as the Waterford 3 stem.
As indicated in our TSCR submittal, ABB/CE has reanalyzed the mass and energy released to containment for the most limiting MSLB cases with a longer MSIV closure time.
These analyses use the same code / method as used in the original analysis, however, credit is taken for flow choking during MS'.V closure.
Waterford 3 feels that this small reduction in conservatism is justified by the potential increase in ' component reliability due to reduced high cycle fatigue.
Ve truly yours,
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R.F. surski Director, Nuclear Safety RFB/PLC/dc cc:
J.L. Milhoan, NRC Region IV D.L. 1:.,inten, NRC-NRR R.B. h-uehee N.S.
Reynolds NRC Resident Inspectors Office i
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