ML20084H796

AO BFAO-7426W:on 740505 & 06,Target Rock Main Steam Relief Valve PCV 1-19 Experienced Extended Blowdown.Caused by Leaking Pilot Seat & Burr on Second Stage Stem Insert Guide Sleeve Acting Together

ML20084H796
Person / Time
Site:	Browns Ferry
Issue date:	05/15/1974
From:	Eric Thomas TENNESSEE VALLEY AUTHORITY
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084H799	List: ML20084H796 ML20084H805
References
AO-BFAO-7426W, BFAO-7426W, NUDOCS 8305050358
Download: ML20084H796 (3)

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Mr. John F. O' Leary, Director .

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• Washington, DC 20545

Dear Mr. O' Leary:

TENNECSEE VALLEY AUTHORITY - BRO 1GS FEPRI NUCLEAR PLANT UNIT 1 -

DOCKET NO.-50-259 - FACILITY OPERATING LICENSE DPR M ORMAL OCCURRENCE REPCRT BFAO-7426W The enclosed report is to provide details concerning Target Rock rain steam relief valve (PCV 1-19) which experienced en extended blovdown on two occasions. This event occurred on Browns Ferry Nuclear Plant unit 1 on May 5 and 6, 197h, and is submitted in accordence with Appendix A to Regulatory Guide 1.16, Revision 1, October 1973.

Very truly yours, TENNESSEE VALLEY AUTHORITY E. F. Thomas -

Director of Power Production '

Enclosure CC (Enclosu p ,

Mr. "sb a Moseley, Director Reg n .' =tlatory Operations Office, USAEC 230 > eachtre. Streat, IFd. , Suite 618 Atlanta, Georgia 30303

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• ABHORMAL OCCURR12TCE REPORT '

Report No.: BFAO-7426W '

Report Date: May 15, 1974 Occurrence Date: May 5 and 6, 1974 Facility: Browns Ferry Nuclear Plant unit 1 Identification of Occurrence Target Rock main steca relief valve (PCV l-19) experienced an extended blowdown on two occasions.

Conditions Prior'to Occurrence On May 5,197h, the reacter tripped from 92-percent power and main steamline isolation occurred as a result of a feedwater system startup test which was in progress. -

on May 6, the reactor again tripped and isolation occurred while being returned to the 92-percent power level to continue the feedwater systen startup test.

Description of Occurrence On Tuesday, May 7, plant management co=oleted a thorough analysis of pressure end temperature traces following the two reactor isolations and scrans which occurred on May 5 and 6. Their analyses showed that relief valva 1 19 appavael;r enbeh occasions did not fully resent. This resulted in blowdown of the vessel to approximately 500 psi within approximately 10 uinutes. Uo excessive vessel stress was experienced. Upon identification of the valve malfunction, the decision was made to shut down the reactor and to replace and inspect the valve.

Designation of Atmarent Cauf:e of Occurrence There is no single apparent cause for the extended blowdown. The valve was completely disassembled and thoroughly inspected, and two abnormalities were found. Ucither abnormality, acting independently, could cause the extended blowdown. The first abno:"14ty found was a leaking pilot seat. Examination of the seat revealed that, in two opposite quadrants, there was evidence of very slight wire drawing across the seat. The second abnormality was a very small burr found on the second-ste6e stem insert guide sleeve. The burr was a result of deformed metal on the stem insert guide, probably caused by a hard lick during

~initici valve assembly. The additive effect of the first-stage seat leakege and the second-stage stem burr could create a condition which would result in an extended blowdown.

Analysis of Occurrence On May 5, PCV 1-19 was open approximately 7.5 minutes. The vessel pressure dropped from 1,062 p::ig to 550 psig which results in a coolant thermal transient of 73 F. This degree of thermal transient would not create any abnormal, unacceptable thermal stresses in the vessel.

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Analysis of Occurrence (continued)

On hay 6;PCV1-19wasopenapproximately9 minutes. The vessel pressure dropped from 1,03!+ psig to 525 psig, which resulted in a thermal transient of 76 F. This degree of ther::m.1 transient would not create any abnormal, unacceptable thermal stresses in the vessel.

Corrective Action l Administrative procedures are being changed to ensure that offsite plant mane 6ement is adecuately notified during off shift periods to enable informed judgments in returning the unit to service following significant events such cs these.

Failure Data Valve data: Target Rock Corporation - Podel 67F - Relief valve Size 6" inlet - 10" outlet Design pressure - 1,200 psi; setpoint 1,100 psig + 11 psi Capacity - 800,000 lb hr saturated steam; serial Ilo. 72 Failures - See BFAO-7 gu e g e

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