ML20236A068

Safety Evaluation Re Containment Purging & Venting During Normal Operation of Plant.Purge/Vent Sys Design & Operating Practices for Facility Acceptable Subj to Implementation of Recommended Actions

ML20236A068
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	12/04/1981
From:	NRC
To:
Shared Package
ML20236A072	List: ML20236A068
References
TAC-08291, TAC-42594, TAC-44892, TAC-8291, NUDOCS 8710220001
Download: ML20236A068 (4)

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i SAFETY EVALUATION REPORT FOR CONTAINMENT PURGING AND VENTING DURING y

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' NORMAL OPERATION OF THE TROJAN NUCLEAR PLANT (Docket No. 50-344)'

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INTRODUCTION A number of events have occurred over the past several' years which directly relate to the practice of containment purging and venting 'during norma'l plant operation. These. events have raised concerns relative to potential failures affecting the purge penetrations which could lead to degradation in containmen.t integrity, and, for PWRs, a degradation in ECCS performance. By letter dated November 28, 1978, the Commission i

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(NRC) requested all Licensees of operating reactor's to respond to certain generic concerns about containment purging or venting during normal plant operation. The generic concerns were twofold:

(1)

Events had occurred where licensees ' overrode-or bypassed

• 1 the safety actuation isolation signals to the containment isolation valves..These events were determined to be abnormal occurences and were characterized in our report to Congress in January 1979.

(2)

Recent Licensing reviews have required tests or analyses.to show that containment purge or vent valves would shut without degrading containment integr'ity' during the dynamic loads of a design basis loss of coolant accident kDBA-LOCA).

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Pd.The NRC position of the Novembdr 1978 ~ Letter requested Licensees to cease.

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purging ' for venting) of containme'nt or, Limit purging (or venting) to an.

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{j absolute. minimum.. Licensees who elected 'to purge (or; vent) the. containment.

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'. Aere requested to.' demonstrate thac'ty containment purge (or! vent), system?

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[O ' design met the criteria outlined.in :the MC Standard Review Plan '(SRP)' 6.2.4,

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. h '/ Revision 1, andthe associated Br:anch Technical Position (BTP); CS8'6-$

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. e Revision 1.

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,,f(13CUS$100 AND EV ALUATiW.

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T'.5 ref ge and vent systems at the' Trojan plant konsist of. a" 54-inch purge a

, f. srstem f or purging.the containment atmosphere to allow personnel access, y,

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s1d a 8-inch vent system for maintaining the ebntainment pressure within a

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I' fphreribed range during normal operation and for oost-accident a'tmosphere I

In addition, two 4000 s,fm iodir e, filtration units are provided-

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insicie the containment to aic in ruoving airborne radioactivity-that may it1

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r be released f rom the reactor coolant system;during normal operation.

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f The Licensee i:esponded to the NRC positio,n letter of November 1978 by 4

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, stating that the 54-inch containment purge-system isolation' valves would be n

, i a,aintained in the closed position (uring operation.(Modes.1, 2, 3' and 4).

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s The 8-inch vent system isolation valves wiLL be used for purging the containmerw atmosphere. to attd6 perso el access and to maintain.the containment pressure > within a prescribed range during normal operation..The:

7 Vice isee ind4 hated that an inab'itity to purge would. Lead to. significant -

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incre$ des in pLbnt unavailability, increase tha airborne activity levels in

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1 the contai e'nt, and increase personnet exposures.

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The closure time for the 6-inch vent system isolation valves,, including instrumentation-delays, wiLL not exceed 5 seconds. Therefore, containment purging concurrent with a LOCA wiLL not result in a decrease in the containment pressure to the extent that ECCS performance would be adversely -

affected.

A debris screen will be provided inboard of each ~of the inside containment isolation valves. This wiLL provide added assurance that the vent system isolstion valves will not be prevented from ' closing, should they be in the open position at the onset of a LOCA.

l III CONCLUSIONS f.

We have reviewed the Trojan plant purge and vent systems against the provisions of BTP CSB 6-4, Revision 1, " Containment Purging During Power Operation." Although the Licensee provided information to justify purging /

venting without limitation through the 8". hydrogen vent'aystem during power

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~operation, purging / venting should be limited, because the plant is inherently safer with closed purge / vent valves than with open lines which require valve.

action to provide containment integrity.

We, therefore, have concluded that the licensee should limit usage of the vent sys' tem for safety purposes.

Also, we have concluded that the licensee should propose a change to.their Technical Specifications which would require that the 54-inch purge isolation valves 4

be maintained in the Locked closed position during plant operating Modes 1 J

through 4.

Maintaining these valves closed wiLL preclude the release of radioactivity to the environment via the containthent purge system, should a LOCA occur.,

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IIn addition, as.a result-of numerous. reports on the unsatisfactory

.a performance of resilient. seats in butterfly-type _. isolation. valves:due.to' seal deterioration, periodic leakage integrity tests of butterfly. isolation' 4

valves-in purge / vent systems. are necessary. - Th'erefore, tha licensee s'hould' also propose a Technical Specification for testing these ' alves in accordance-v with the.following testing frequencies:.

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i a)

"The leakage jntegrity' test's: of the 54-inch isolation valves in the J

j containment purge ines shaLL be conducted at - Least once every 'six 1

months."

b)

"The Leakage integrity tests of the 8-inch isolation valves in the.

vent Lines shaLL be conducted at least once every three months."

1 The purpose of the. Leakage integrity' tests of the isolation valves in the l

i containment purge and vent lines is to identify excessive degradation of.

1 the resilient seats for these vales. Therefore,- they need not be conducted -

l with the precision required for the Type C isolation valve tests in 10 CFR Part 50, Appendix J.

These tests would be performed in addition to the-q 4

quantitative Type C tests required by Appendix J and would not relieve the.

licensee of the responsibility,to. conform to the requirements of Appendix J.

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Subject to successful implementation of the above re' commended actions,' we find the purge / vent system design and operating practices for the Trojan plant to be acceptable.

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