05000397/LER-2015-006

LER-2015-006, Postulated Multiple Spurious Operations Scenario That Could Adversely Impact Post-Fire Safe Shutdown

Columbia Generating Station
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
3972015006R01 - NRC Website

Plant Conditions

At the time of discovery, the plant was in Mode 1 at approximately 64% Power No inoperable structures, components or systems contributed to this event Eiient Description A self-assessment of the Columbia Generating Station (CGS) Fire Protection (FP) and Post Fire Safe Shutdown (PFSS) programs identified a potential issue with MSO Scenario 2x MSO Scenario 2x postulates the spurious opening (due to fire-induced circuit damage) of High Pressure Core Spray (HPCS)[BGFValve (V)[V]-15, HPCS-V-10; and HPCS-V-11, causing a flow diversion from the Suppression Pool (SP) to the Condensate StorageTanks (CSTs)[KA], with a resulting loss of SP inventory.

MSO Scenario 2x was investigated further, and on July 6,2015 it was- determined that this was a tredible unanalyzed PFSS condition. The review of MSO Scenario 2x relative to the circuit designs for HPCS-V-15, HPCS-V-10, and HPCSAPI 1 identified that the postulated fire-induced circuit failures (hot shorts) strategically placed in the open function control circuits for each valve would create a flow path that results in a loss of SP inventory- This resulted in an unanalyzed PFSS condition, and was reported to the NRC in an 8-hour report (Event Notification No. 51201) in accordance with 10 CFR 50:72(b)(3)(11)(B)-.

Apparent Cause Invalid assumptions and an inadequate review of MSO Scenario 2x did not identify that, with HPCS-P-3 (HPCS keepfill pump) running; hot shorts on HPCS-V-10, HPCS-V-1 1-, and HPCS-V-15 could result in suppression pool flow diversion and inventory loss to theCSts.

As part of the focused self-assessment, the PFSS analysisto M$0, Was, reviewed by two industry PFSS. subject matter experte. The review identified only the evaluation for MSO Scenario 2x as a potential technically incomplete analysis Immediate Corrective Action' The calculation was reVised to include a: re-evaluation of :MSO 'Scenario. X.. The rribtor-operatorfOr HOCS4- 11 WAS deactivated through alempdrary modification on June 12, 2015 due to unrelated maintenance issues during the refueling outage, which isolated the return line to the Condensate Storage Tanks and prevented this from being a credible scenario. The motor-operator for HPCS-V-1t'will remain deactivated maintaining the:

affected line isolated until a permanent solution for MSO Scenerip.2x.,10 developed' Further Corrective Actions Procedure changes will be implemented to provide more techniddigUidanCefOr evaluation of further PFSS' MSO. scenarios.: A plant design change will be developed to permanently resolve :MSO Scenario 2x

• ,E)ctent of ConditiOn, 28158A R3 We FORW366A (01-2014) tiliC'FORM 356A.

P14014 LICENSEE EVENT REPORT (LER) CONTINUATION SHEET tis,auCLEAwsseuLATOsvcommissio,rt,' 1. FACILJTY NAME.

Columbia Generating Station . DOCKET 16. LER NUMBER 3 PAGE.

05000 397 2016- 006 Operating Experience & Previous Occurrences An extent of condition and cause was performed for all similar LEFIs where inadequate design review was found. There were no LERs in recent history with the same:cause.

Assessment of Safety Consequences

A did not occur at CGS. There were no actual_ afety consequences of the event. There was no equipinent damage injOrieS, or doSe exposilre toStatiOn'personneL There was no-Change in plant status' or operating condition andtherdwaSno risk-to the public at any time &la to this event. However, had the postulated event occurred prior to.haVingJaken corrective, actions, thisloondition.wouid,:haveohallenged the plant's ability to aOhleVe and maintain safeshutdown in: accordance witilthe :requirements of 10 cm- 50, APpendix At all times the specified safety functions as &Scribed in postulated Design BaSit Accidents were ableto be fUlfilled as fires are

• not postUlated to. occur simbitaneousiy with atherdesign baSisadcidents. ReqUiremeritSfor PFSS were not fully however_ here were no: actual, safetyoonsequences of this event ascnofire

• octurred.

Energy Industry Identification SysteM Information EnergyIndintry identification System Information codes from 'IEEE Standards 805-1984: and 803-1983 are represented in brackets as (XI and [XX] thrOughout the body otthenarrative.

26I5BA Ri ';NRC:FORM'3064 (01-2914),