PNO-V-87-067, on 871007,licensee Reported That Recently Completed Single Failure Analyses Had Identified Potential Single Failures Which Had Not Previously Been Known.Lists Potential Single Failures Associated W/Esfs

PNO-V-87-067:on 871007,licensee Reported That Recently Completed Single Failure Analyses Had Identified Potential Single Failures Which Had Not Previously Been Known.Lists Potential Single Failures Associated W/Esfs

ML20235U508
Person / Time
Site:	San Onofre
Issue date:	10/08/1987
From:	Andrew Hon, Johnson P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
To:
References
PNO-V-87-067, PNO-V-87-67, NUDOCS 8710140116
Download: ML20235U508 (2)

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PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-V -67 Date 10/08/87 l This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. The information presented is as initially received without verification or evaluation and is basically all that is known by Region V staff ,

on this date.

FACILITY: SOUTHERN CALIFORNIA EDIS0N Emergency Classification l SONGS UNIT 1 Notification of Unusual Event l DOCKET N0. 50-206 Alert l SAN CLEMENTE, CA Site Area Emergency j General Emergency )

X Not Applicable j

{

SUBJECT:

IDENTIFICATION OF POTENTIAL SINGLE FAILURES j l

1 The licensee reported via the Emergency Notification System and separately in phone discussions l with Region V and NRR personnel on October 7 that recently completed single failure analyses had '

identified potential single failures which had not previously been known. These newly identified potential single failures are associated with engineered safety features, and are summarized as follows:

(1) Failure of a main feedwater pump (also used as safety injection pump) discharge valve to the steam generators to close on a safety injection signal following a main steam line break (MSLB) could divert safety injection flow and cause continued feeding of the steam generators for up to 90 seconds.

(2) Failure of a sequencer or a vital DC bus could cause continued feeding of steam generators by one feedwater pump following a safety injection signal, possibly filling main steam lines with water (an unanalyzed condition).

(3) The harsh environment resulting from an MSLB outside containment could lead to failure of feedwater flow control valves and isolation valves (not environmentally qualified).

(4) Failure of a vital DC bus accompanied (in a specified sequence) by a loss of offsite power could prevent opening of both charging pump suction valves and two of three charging pump injection valves (with the third assumed to be connected to a broken loop), preventing remote initiation of the recirculation phase and creating the potential for charging pump damage due to loss of suction.

(5) Failure of a vital DC bus accompanied (in a specified sequence) by a loss of offsite power could cause loss of two operating component cooling water (CCW) pumps while the third is out of service (as permitted by technical specifications). CCW is used to cool the heat exchanger used during the recirculation phase.

(6) Loss of the IC 4160V bus under certain conditions could cause both charging pumps to pump the volume control tank dry and lose suction, leading to possible damage. Two of the three loop injection valves could also fail to open.

(7) An undetectable failure accompanied by an additional active failure could render the overpressure mitigation system inoperable, causing a loss of low temperature overpressure protection for the reactor coolant system.

8710140116 871000 PDR I&E PNO-V-87-87-887PDR gl v i l

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1 4 PRELIMINARY MODIFICATION OF EVENT OR UNUSUAL OCCURRENCE--PNO-V-87-87-67 Date 10/08/87 -

} Southern California Edison M SONGS' Unit 11.50-206.

, The licensee has administrative controls or procedures in effect which address conditions (5) and (6).;fCondition (7) is a concern only in Mode 5 and is not a consideration in continued plant

-operation.: 10ther conditions are considered. by the : licensee' to have a.very low probability of Loccurrence, consistent with sin

' Systematic Evaluation Program (gleThe SEP). failures analyzed licensee. and.foundother has implemented acceptable by NRC compensatory during the measures including. pre-shift briefings and a special order addressing the single failure concerns, aThe'above concerns were discussed with Region V and NRR management on October 7. Licensee representatives will be in Bethesda on October. 9,1987 to discuss the results of their single

~

failure. analyses in more detail with NRR representatives.

This informatio is current as of 8:00 a.m. PDT on October 8,1987.

Contact:

P.hJ on A. Hon

,(PT 463-3745' (714).492-2641

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DISTRIBUTION BY 5520: FAX T0:

Date Time Date Time Chairman Zech EDO RI INPO Comm. Roberts AE00 RII NSAC ,

.Comm.~Bernthal PA0 RIII LICENSEE

-Comm. Carr SLITP RIV RESIDENT INSPECTOR Comm.-Rogers NRR HQS. OPERATIONS OFFIC' SECY NMSS CA ARM MAIL T0:

PDR' 01 DCS (Original)

OGC OIA DOT:(Trans. Only, Applicable Stat Q

' 'ACRS- RES

'GPA l RV FORM 211 Revised: 8/19/87 i

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