ML20086K322

AO 74-47:on 741104,relief Valve Found Open Causing Reactor Depressurization.Caused by Pilot Valve Leakage.Leaking Valve Discs Machined & Seats Lapped to Eliminate Leakage

ML20086K322
Person / Time
Site:	Peach Bottom
Issue date:	11/14/1974
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
References
AO-74-47, NUDOCS 8401270027
Download: ML20086K322 (3)

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November 14, 1974 .

Mr. A. Giambusso Deputy Di rector of Reactor Projects United States Atomic Encrgy Commission Directorate of Licensing Washington, D.C. 20545

Subject:

Abnormal Occurrence The following occurrence was reported to Mr. Walt Baunack, A.E.C. Region 1 Regulatory Operations Office on November h, 1974.

Written notification was made to Mr. James P. O'Reilly, Region 1 Regulatory Operations Office on November 5,1974 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 Licensing as an Abnormal Occurrence:

Reference:

License Number DPR-44, Amendment Number 1 Technical Speci fication Reference 3.6.D.1 Report No.: 50-277-74-47 Report Date: November 14, 1974 Occurrence Date: November 4,1974 Faci li ty: Peach Bottom Atomic Power Station R.D. 1, Del ta, Pennsylvania 17314 4

Identi fication of Occurrence:

Relief valve opened causing reactor depressurization.

Conditions Prior to Occurrence:

Unit 2 operating at 100% power, 1090 MWe.

8401270027 741114 PDR ADOCK 05000 7 2t!

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Description of Occurrence:

Relief Valve 71L inadvertently opened during power operation at 100% power. Power was reduced and the plant shutdown is accordance with plant operating procedures. The valve reclosed at approxima ly 200 psi, approximately 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 5 minutes af ter i t had opened.

Decionation of Apparent Cause of Occurrence:

Pilot valve leakage pressurized the second stage piston thus opening the second stage valvo and the main valve. Refer to F.S.A.R.

Figure 4.4.3. .

Analysis of Occurrence:

When the transient occurred, plant procedures were proven adequate to shutdown the plant in a safe manner. All automatic actions were as-expected. Reactor temperature decreased 55 F during the first ,

ten minutes following the scram and 1020F during the subsequent two

~~R5-urs. This cooldown is conservative when compared to the reactor vessel design thermal cycle fatigue evaluation which assumed 1630F cooldown during the first ten minutes and 1000F per hour during the subsequent cooldown. Torus water temperature increase to approximately 120GF and was _ reduced using_t_orus cooling._to .lcss_than_1000F in about

, ~two~ .and ....

one-h'al f hours.

Since the temperature and pressure transient experienced by the reactor vessel was less severe than condi tions used in the reactor vessel design and since no radiation releases occurred as a result of the transient, minimal safety significance is associated with this occurrence.

Corrective Action:

All eleven Target Rock relief valves were inspected and pilot valve Icak rate tested. Relief valve 71L and four others had i pilot valve leakage. The leaking pilot valve discs were machined and the valve seats lapped to climinate the Icakage. The five valves were reset to the required Technical Specification values and re-installed. During the subsequent reactor startup, proper valve operation and rescating was verified by conducting the " Relief Valve Manual Actuation" surveillance test at approximately 150 psig.

An inspection of the torus internals was conducted by personnel from Philadelphia E1cetric,' Electric Production Department, Philadelphia El.cctric Engineering & Research Department and the Atomic Energy Commission.

The inspection indicated no coating or physical probicms caused by this blowdown.

The relief valve 71J bellows failure indication reported in Abnormal Occurrence Report No. 50-277-74-46 was corrected by replacing the Icaking bellows "0" ring.

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Mr. Giambusso Page 3 November 14,19)N

\, G('i Failure Data:

Previously reported Abnormal Occurrences concerning blowdowns by relief valves were report numbers:

50-277-74-12 50-277-74-44 Very truly yours, ,

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~H. /.' Coon'cy.[t Asp' t Gen'1 Superintendent ~

Generation Division cc: Mr. J. P. O'Reilly Director, Region 1 United States Atomic Energy Commission

. 631 Park Avenue King of Prussia, PA 19406 D

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