ML13330A184

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Forwards Westinghouse WCAP-9832 & WCAP-9808 Re Main Steam Line Integrity Evaluation.Crack Appearing Instantaneously Would Be Stable Both Globally & Locally.Initial Circumferential Flaw Would Show Negligible Growth
ML13330A184
Person / Time
Site: San Onofre 
Issue date: 01/14/1981
From: Baskin K
Southern California Edison Co
To: Crutchfield D
Office of Nuclear Reactor Regulation
Shared Package
ML13316A523 List:
References
TAC-44652 NUDOCS 8101160465
Download: ML13330A184 (2)


Text

Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 K. P. BASKIN TELEPHONE MANAGER OF NUCLEAR ENGINEERING, (213) 572-1401 SAFETY, AND LICENSING January 14, 1981 Director, Office of Nuclear Reactor Regulation Attention:

D. M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.

20555 t)

Gentlemen :

2D5~I

Subject:

Docket No. 50-206 Main Steam Line Piping Integrity Evaluation

-4 San Onofre Nuclear Generating Station Unit 1 By letter dated October 9, 1980, it was committed that the NRC staff would be provided by January 15, 1981 with the final results of the Main Steam Line Integrity Evaluation to complete the review of this subject which was initiated during a meeting with the Regulatory staff held on May 13, 1980, and documented in our letter dated June 10, 1980. Accordingly, two Westinghouse reports are enclosed: (1) WCAP-9832, "Mechanistic Fracture Evaluation of San Onofre Unit 1 Main Steam Line Pipe Containing a Postulated Through-Wall Crack," dated November, 1980, (2) WCAP-9808, "Fatigue Crack Growth Evaluation for San Onofre Unit 1 Main Steam Line Pipe," dated October, 1980.

The objective of the analysis performed in WCAP-9832 is to examine mechanistically whether a crack which is assumed to appear instantaneously, in the main steam line, would become unstable and lead to a circumferential break when subjected to the worst possible combination of plant loadings. The results of the analysis indicate that the crack would be stable both globally and locally so that assuming the worst loading combination, the postulated flaw will not propagate around the circumference of the pipe and cause a guillotine break.

The fatigue crack growth analysis presented in WCAP-9808 was conducted as suggested by Section XI Appendix A of the ASME Boiler and Pressure Vessel Code. The analysis procedure involves postulating an initial circumferential flaw and predicting the growth of that flaw due to an imposed series of stress transients. The results of the analysis indicate that growth of the postulated flaw by fatigue is negligible.

D.

January 14, 1981 Based on the information summarized above, in conjunction with the main steam line Inservice Inspection and leak detection capabilities as described in the enclosure to our letter dated June 10, 1980, it is concluded that there is reasonable assurance that a double-ended guillotine rupture of the main steam line is not credible. The additional considerations associated with the review of the Main Steam Line Break Accident will be provided in our submittal of the impact on the safety analysis of the automation of the auxiliary feedwater system as required by the TMI Lessons Learned Requirements.

The submittal will be provided to the NRC by February 1, 1981, as indicated in our letter dated October 9, 1980.

If you have any questions or desire additional information, please contact me.

Very truly yours, Enclosures