ML20086H995

AO 75-24:on 750401,stem on Hpsw/Rhr HX Discharge Valve MO-2-1089D Failed.Caused by High Valve Vibration Due to Throttling Mode of Valve Causing Disc Lock Nut Tack Welds to Fracture & Nut to Back Off

ML20086H995
Person / Time
Site:	Peach Bottom
Issue date:	04/11/1975
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Giambusso A Office of Nuclear Reactor Regulation
Shared Package
ML20086H997	List: ML20086H995 ML20086J004
References
AO-75-24, NUDOCS 8401230034
Download: ML20086H995 (2)

Text

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PHILADELPHIA ELECTRIC COMPANY 2301 M ARKET STREET PHILADELPHI A. PA.19101 g (215)841 4o00

• Apri1 11, 1975 Mr. A. Giambusso .~

Director Of fice of Nuclear Reactor Regulations United States Nuclear Regulatory Commission Wasington, DC 20555

Dear Mr. Giambusso:

I

Subject:

Abnormal Occurrence The following occurrence was reported to Mr. Eldon Brunner, Region 1, Office of Inspection and Enforcement, United States Nuclear Ro$alatory Commi ssion on Apri l 1, 1975 Written notification was made to Mr. James P. O'Reilly, Director, Region 1, Office of Inspection and Enforcement, United States Nuclear Regulatory Commission on April 2, 1975 In accordance with Section 6 7 2.A of.the Technical Specifications, Appendix A of DPR-44 for Unit 2 Peach Bottom Atomic Power Station, the following report is being submitted to the Directorate of Reactor Licensing as an Abnormal Occurrence.

Re fere~nce : License Number DPR-56 Technical Specification

Reference:

358 Report No.: 50-277-75-24 Report Date: April 11, 1975 Occurrence Date: Apri1 1, 1975 Facility: Peach Bottom Atomic Power Station R.D. 1, Delta, Pennsylvania 17314 Identification of Occurrence:

, Failure of the stem on HPSW/RHR heat exchanger discharge valve h0-2-10-89D.

Conditions Prior to Occurrence:

Reactor at approximately full power. O c Description of Occurrence:

During routine surveillance testing of the RHR system, it was noted that with the HPSW/RHR. heat exchanger discharge valve indicating full closed, the HPSW flow was still appreciabic.

8401230034 750411 .*

PDR ADOCK 05000277 C -~i Q

S pyg COPY SENT REGION / a f

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U, 50-277-75-24 Mr. A. Girmbusa P:ge 2

" April 11, IS75 Designation of Apparent Cause of Occurrence:

High valve vibration, due to the throttling mode of the valve, caused the disc lock nut tack welds to fracture allowing the -

nut to back off. The loosening of the valve disc increased stem vibra-tion, and resulted in a fatigue failure of the stem in the yoke bushing  ;

area. The valve seat had backed out and was found to be loose in the The threads in the valve body had been completely cbstroyed.

valve body.  ;

Analysis of Occurrence: '

The safety significance of this occurrence is considered ,

minimal, since no cooling capability of the RHR/HPSW was lost. t 1

i C_orrective Action:

Until repairs can be made, HPSW will not be available to the j

'D' RHR heat exchanger. However, all four LPCI loops are availabic, as are all four HPSW pumps. Phi.1adelphia Electric Compar,y's Enginecr-ing Department is actively pursuing other mechanisms to reduce vibra-tiras in this area which are seat The valve believed to be is being the cause replaced of this and by stainless steel similar failurcs. Following deposi tion of weld metal, the valve scating weld overlay.

surface will be completed by machining. The valve stem will be re-placed with tighter clearances between the stem and the disc, yoke, bushing and key. This is being done in an effort to minimize vibration of the assembly while the valve is in the throttled condition.

l Failure Data:

9 No previous stem failure has been experienced, but vibration induced problems have been reported as Abnormal Occurrences on these reports:

A0-50-277-74-53, A0-50-278-74-28, A0-50-278-74-35, A0 '

278-74-36, and A0-50-278-75-5. f, Very truly yours, t H. . Cooney I

As t. Gent. Superintendent Generation Divi sion i t

cc: Mr. J. P. O'Reilly, Director i Region 1 Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 H.