ML17212B434

Partial Safety Evaluation of Containment Purging & Venting During Normal Plant Operation.Licensee Should Commit to Use Purge Sys Only Specified Number of Times Per Yr.Debris Screens Should Be Provided for Purge Supply & Exhaust Lines

ML17212B434
Person / Time
Site:	Saint Lucie
Issue date:	02/23/1982
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML17212B433	List: ML17212B434 ML17212B435
References
NUDOCS 8203120082
Download: ML17212B434 (11)

Text

ENCLOSURE 2

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PART(AL SAFETY EVALUATION REPORT FOR CONTAINMENT PURGING AND VENTING DURING NORNAL OPERATION OF TOE ST -l UGIE PLANTi UNIT 1

( Docket No. 50-335)

I INTRODUCTION A number of events have occurred over the past severaL years which directly relate to the practice of containment purging and venting during normal plant operation.

These events have raised concerns relative to potentiaL failures affecting the purge penetrations which could Lead to degradation in containment integrity~

and~ for PWRs~ 'a degradation in ECCS performance.

By Letter~ dated November 28~

1978~ the Commission (NRC) requested aLL Licensees of operating reactors to respond to certain

.generic-concerns about containmemt purging or venting during normaL pant operation.

The generic concerns were

.twof o Ld:

(1).

Events had occurred where Li censees overrode or bypassed the safety actuation isolation signals to the containment isolation vaLves.

These events were determined to be abnorma L occurrences and were so characterized in our report to Congress in January 1979..

(2)

Recent Licensing reviews have required tests or analyses to show that containment pur ge or vent 8203i 20082 820223 PDR ADOCN 05000335 P

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Q vaLves would shut without. degrading containment integrity during the dynamic Loads of a design basis Loss of coolant accident (DBS-LOCA).

The NRC position of the November 1978 Letter requested Licenses to cease purging (or'enting) of containment or limit purging (or Licensees who ele venting) to an absolute-minimum.

cted to purge (or vent) the containment were requested to demonstrate t'hat the containment purge (or vent) system design met the criteria outlined in the NRC Standard Review P

associated Branch Revis.ion 1.

Lan. (SRP) 6.2.4~

Revision 1~

and the Techni ca L Posit i on (BTP)

CS8 6-4~

DISCUSSION AND EVALUATION

..The purge system at St., Luck.e PLant~ Unit 1. (St. Lucie 1) p consisting of two 48-inch Lines~

was designed to purge the containment atmosphere to improve working conditions for personneL.

In addition~

an iodine fi ltration system~

Located inside the;containment~

aids in removing airborne radioactivity that'ay be reLeased from the reactor coolant system during normaL operation.

The Licensee responded to the NRC position Letter of November 1978~

by indi cating (in a Letter dated February 1~ 1979) that they planned to justify unlimited purging of containment during operation.

Following

discussions with the NRC staff~ the Licensee reported (in a

letter dated May 25 1979) that they agreed to Limit containment purging in operationaL mdes 1

and 2 to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year.

Later~

by a Letter dated December 13~

1979~

the Licensee reported that they planned to continue to Limit containment purging to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year in operational modes 1

and 2 untiL a

50 degree modification to the purge isoLation valves was implemented.

A year Later the Licensee reported (in a Letter. dated Dec'ember 9~ 1980) that the 50 degree modification to the purge isolation valves had been P

compLeted.

The Licensee concluded that they had provided alL information and made aLL the evaluations requested by.

NRC to justify containment purging during norma l operations.

The Licensee provided an'naLysis of the mass of.air and steam released to the envi.ronmeng.prior to purge syst'm isolation following a LOCA.

The results of the analysis indi cated that the maximum total mass of containment II atmosphere released through the purge system to be 5224 LbM of saturated steam and air.

Me have reviewed the Licensee's assumptions used in the analysis~

and. concLude that the mass released has been conservatively calculated.

The Licensee reported that Combustion Engineering's ECCS perfor mance evaluation documenting the effect of containment purging using the above mass release clearly shows that the L

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'mpact of purging on ECCS performance is minimaL for St. Luci e 1.

Me have revi ewed the evaluation and find it to be acceptaUL'e.

The Licensee indicated that failure of the containment purge system to isolate the containment due to entrained debris in the exhausting f Luid (ai r and steam) i s highly unlike Ly~ and discussed the various paths of high and Low density materiaL wouLd h'ave to traveL to prevent the isolation of the system.

The licensee concLuded that there are adequate provisions to preclude the fai Lure 'of the containment purge isolation valves to close due to entrained debris in the f Luid steam.

Based on our revi ew of the Li censee's rationa Le~

we are not able to conc Lud'e that isolation va Lve closure wi L L not be prevented by debris which could potentialLy become entrained in the escaping

i r and steamy Me~ 'therefore~

recommend that debris screens be provided for the purge supply and exhaust Lines.

The debris screens shouLd be sei,smic Category I design and instaLled ab'out one pipe diameter away from t'e inner side of each inboard isolation valve.

The piping between the debris screen and the isolation vaLve shouLd also be seismic Category I design.

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0 The Li censee indi cated that no safety-related equipment is Located in the f Low.stream beyond the outboard isolation valves at the supply or exhaust penetrations.

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CONCLUSION We have reviewed the St.

Lucie 1

Purge System against the guide lines of BTP CSB 6>>4p Revision 1~ "Containment Purging During Normal Operations."

ALthough the Licensee provided information to justify unlimited purging during power operations, our view 'is that system use should be Limited.

The plant is inherently safer with closed purge valves than with open Lines which require valve action to provide, containment integrity.

We~ therefore~

recommend that the Licensee commit to Limit the use of the purge system to a'pecified annual time.th'at is-commensurate with identifigst,..

saf ety needs.

We recommend that debris screens be provided for the purge supply and exhaust Lines.

The debris screens should be sei smi c Category I design and insta L Led about

'one pipe diameter away from the inner side of each inboard isolation valve.

The piping between the debris screen and the isoLation P

valve should also meet seismic Category I design standards.

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In addition~

as a result of numerous reports'n the unsatisfactory performance of resilient seats in butterfly-type isolation valves due to seal deterioration~

periodic Leakage integrity tests of the 48"inch butterfly isolation valves in the purge system are necessary.

Therefore~

the Licensee should aLso propose a Technical Specification for testing the valves in accordance with the following testing frequency:

"The Leakage integrity tests of the isolation valves in the containment purge Lines shall be conducted at least once every three months."

The purpose of, the Leakage integrity tests of the isolation valves in the containment purge Lines is to identify excessive degradation of the resilient seats for these valves.

Therefore~

they need not be conducted 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 quantitative Type C tests required by Appendix J~

and would not relieve the Licensee of the responsibility to conform to the requirement's

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of Appendi x J.

GUIDELINES

FOP, USE IN ENLUATION OF PURGE AND VENT SYSTEM DEBRIS SCREEN DESIGN The debiis screen should satisfy the following criteria:

1.

The debris screen should be seismic Category I design. and installed about one pipe diameter away from the inner side of the inboard isolation valve.

2.

The piping between the '18bris screen and the isolation valve should also be seismic Category I design.

3.

The debris screen should be designed to withstand the LOCA differential pressure.

4.

The debris screen should be designed similar to that shown in the attached

~~ c Figures 1

and 2.

ENCLOSUPE 2

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