ML20206B672

Safety Evaluation Re Concern Identified During Aug 1986 Safety Sys Functional Insp of Capability of Component Cooling Sys to Function After Seismic Event.Component Cooling Sys Does Not Meet Original Licensing Criterion

ML20206B672
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	04/02/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20206B671	List: ML20206B667 ML20206B672
References
TAC-65350, NUDOCS 8704100006
Download: ML20206B672 (2)

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[*g UNITED STATES NUCLEAR REGULATORY COMMISSION

, g g i a j ~ WA5HWGTON, D. C. 20555 OFFICE OF NUCLEAR REACTOR REGULATION SAFETY FVALUATION COMPONENT COOLING WATER SYSTEM TROJAN NUCLEAR PLANT INTRODUCTION During an August 1986 Safety System Functional Inspection (SSFI) of the Trojan Nuclear Plant by the NRC's Region V Office, the inspection team identified a potential safety concern associated with the component cooling water (CCW) system. This concern was described in Section 2.a of the Region V Inspection Report, 50-344/86-23, dated November 7, 1986. Specifically, the inspection team noted that a major break in the seismic Category II (nonseismic Category _I) portion of the CCW system could result in both safety trains blowing down,

> rendering them inoperable. Automatic isolation valves (interface valves) at the Category I/ Category II interface are intended to prevent the blowdown of the CCW system. However, tests and analyses conducted by the Portland General Electric Company (PGE) have shown that the interface valves do not close rapidly enough to prevent the blowdown of both trains.

DISCUSSION AND EVALUATION The CCW system consists of two seismic Category I flow paths, each of which serves a single train of identical engineered safety features (ESF) equipment, and a single seismic Category II, nonsafety-related flow path that connects the two seismic Category I paths. Interface isolation valves (one for each train) are provided to automatically isolate the seismic Category I portion from the seismic Category II portion of the system upon receipt of a safety in.iection signal or a low CCW surge tank level signal. One purpose of this automatic isolation capability is to ensure that the failure of seismic Category II equipment and components does not adversely affect the operation of ESF equipment essential to safe shutdown of the plant.

The inspection team found that PGE's design analysis (Calculation No. TM-051, "CCW System Loss of Inventory Following a Seismic Event," Rev. 0 (January 1, 1981) concluded that the CCW system was inadequately protected against a seismic event because the interface isolation valves'would not close quickly enough to prevent a major loss of CCW inventory. The analysis also noted that corrective action had been initiated by way of a request for a design change. However, PGE did not follow through on the corrective action.

During the inspection, PGE asserted that the calculation was too conservative, insofar as it was assumed the seismic event would initiate a complete double-ended guillotine rupture of the seismic Category II piping. PGE maintained that only i

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! a' moderate energy leakage crack needed to be postulated, which would give the isolation valves sufficient time.to close. The-staff disagrees with PGE's position since moderate energy leakage cracks are only postulated in seismic 3

Category I systems. The staff has no basis to support the contention that a j seismic Category II pipe will not catastrophically fail during a seismic

event. Flooding analyses and system failure modes and effects analyses that are performed by the staff are based on the assumption that a seismic event can

cause a complete double-ended guillotine rupture of any seismic Category II 4

piping system.

According to the Trojan Updated Final Safety Analysis Report (UFSAR), the CCW i . interface isolation valves (CV-3287 and CV-3288) are designed to protect the seismic Category I portion of the system. In addition, the UFSAR Failure

! Analysis for the CCW System (Table 9.2-15) states that any failure in the

! seismic Category II pressure boundary will not affect the seismic Category I portion of the system. It was the staff's position at the time of the original 1 FSAR review that a seismic Category 11 piping failure should be based on a j

double-ended rupture, and that the isolation valves should be protecting the i

CCW system against the blowdown of both trains (assuming a single failure). l I Moderate energy leakage crack criteria were issued by the staff in a July 12, 1973 letter; however, compliance to that guidance was not mandatory for Trojan l at that time. Furthermore, moderate energy leakage crack criteria were developed i only for the purpose of analyzing the effects of flooding and spray on surroundino j

equipment, not on the capability of the system itself to withstand a passive failure. It should be noted that Trojan's " Analyses of Pipe System Breaks Outside Containment " (PGE-1004) evaluated only high energy fluid systems, and

did not postulate a moderate energy system crack in the CCW system or any other j moderate energy fluid system as defined by the staff's July 12, 1973 letter.

CONCLUSION l

4 j Based on the foregoing discussion, the staff concludes that the capability of j . the present CCP system does not meet the original (and currenti licensing I - criterion in that the interface isolation valves, (CV-3287/3288) do not close i rapidly enough to protect the CCW system against the effects of a double ended j pipe rupture in the seismic Category II portion of the CCW system. In addition, although not reviewed at the time of the SSFI, this particular deficiency may also exist in the CCW system at interface isolation valves CV3303 and CV3304, j due to similarities in configuration. It is the staff's position that PGE

should take whatever actions are necessary to assure the CCW system meets the original licensing criterion; i.e., can withstand a seismic event that results '

in a complete double-ended guillotine rupture of a seismic Category II pipe. j l

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