ML18086B124
| ML18086B124 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 11/06/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18086B123 | List: |
| References | |
| NUDOCS 8112090495 | |
| Download: ML18086B124 (7) | |
Text
DRAFT SAFETY EVALUATION REPORT FOR CONTAINMENT PURGING AN? VENTING DURING NORMAL OPERATION OF THE SALEM NUCLEAR GENERATING STATION, UNIT 1 (Docket No. 50-272>
I.
INTRODUCTION A number of events have occurred over the past several years which directly relate to the pracfice 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 CNRC) requested all licensees of operating reactors to respond to ce'rtain gener.ic concerns about containment purging or venting during normal plant**
operationm The generic concerns were twofold:
(1)
Events had occurred where licensees overrode or bypassed the safety actuation isolation signals to the containment isolat~on valves. These events were determined to be abnormal 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 purge or vent valves would shut without degrading containment integrity during the dynamic loads of a design basis loss of coolant accident CDBA-LOCA).
I 8112090495 811106 PDR ADOCK 05000272 P
PDR!
ENCLOSURE Z.
The NRC position of the November 1978 letter requested licensees to cease purging. Cor venting) of contai.nment. o~* limit purging Cor venting> to an absolute minimum.
Licensees who elected to purge Cor vent) the containment were requested to demonstrate that the containment purge Cor. vent>. system.
design met the.criteria outlined in the NRC Standard Review Plan CSRP) 6.2.4, Revision 1,
- and the associated Branch Technical Position CSTP). CSB 6-4, Revision 1.
II DISCUSSION AND EVALUATION The purge/vent system at the Salem.Nuclear Generating Station, Unit 1 (Salem 1) consists of a purge system and a pressure-vacuum relief system.
The purge system, consisting of two 36-inch diameter lines, is* designe~ to purge the containment atmosphere to improve internal atmospheric.conditions for personnel access. The pressure-vacuum relief system, consis.ting of one ten-in.ch diameter line, is designed to maintain the containment pressure within a prescribed range.
The licensee responded to 'the NRC position _letter 6f November 1978, by indicattng that they plan to justify unlimited venting through the 10~inch pressure vacuum relief system. It has been the licensee's ~xperience,
~specially during the warmer months. of changing ambien~ barometric pressure, that.pressure relief is required ~o maintain the containment pressure within Technical Specification limitsa. Further, the licensee indicated that administrative controls will be implemented to keep the 36-inch purge valves closed during operating modes 1 through 4.
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The licensee indicated that analyses of the radiolgical consequences and the effect on the containment backpressure'.due to the release of containment atmosphere to the environment performed for.Salem 2 are applicable to Salem 1.
We have reviewed the above cited analyses for.Salem 2 and found them to be acceptable and applicable to Salem 1.
The licensee has not provided sufficient information concerning the provisions made to ensure that isolation valve closure will not be prevented by *decris 111hich could potentially become entrained in the escaping air and steam.
III CONCLUSIONS We have reviewed the Salem 1 purge/vent system against the guidelines of BTP CSB 6-4, Revision 1, "Containment Purging During Normal Operation." *Although
. the licensee has provided justification for unlimited purging/ventingrthrough
- the 10*inch pressure-vacuum relief sys.tem during power operation, purging/"
venting should be Limited because the plant is inherently safer with closed purge/vent valv~s than with open lines which require valve action to provide containment integrity. We,*therefore, recommend that the licensee be requested to comm\\t to Limit usage of the 10-inch pressure-vacuum relief system commensurate with identified plant safety needs.
'The ~icensee has not provfded sufficient. information concerning the provisions made to ensure that isolation valve closure wi LL not be prevented by debris which could potentially become entrained in the escaping air and steam.
We recommend that a debris screen be provided for the 10-inch pressure-vacuum relief system.
The debris ~creen should be designed to seismic Category I criteria and installed about one-pipe-diam~ter away froni the inner side of the inboard isolation valve.
The piping between the debris screen and the isolation valve should also be designed to seismic Category I criteria.
We recommen~ that the licensee propose a change to their Technical Specifi-cations which would require that the 36-inch purge isolation valves be maintained in the locked closed position during plant operating modes 1 through 4. Maintaining these valves closed will preclude the release of radioactivity to the environment via the containment purge system, should a loss-of-coolant accident occur.
In addition, as a result 'of numerous reports on the unsatifactory performance of resilient seats in butterfly-type isolation valves due to' seal deterioration perioqic leakage integrity tests of butterfly isolation valves in purge/vent systems are necessary. Therefore1 the licensee should als6 propose a Technical Specification for testing these valves in accordance with the following testing frequencies:
a)
The leakage integrity tests of the 36-inch isolation valves in the containment purge Lin~s shall be conducted at least ante every six months.
b)
"The leakage integrity tests of the 10~inch isolation valves in the
. containment pressure-vacuum relief Line shall be conducted at least once
- every three months.. "
The purpose of the leakage integrity tests of the isolation valves in the containment purge and pressure-vacuum relief lines is to identify excessive --- --*--.:...--... -.. -*--------.. --*-... *. -.
degradation of the resilient seats for these valves. Therefor.e, they need *not be conducted with the precision required for the Type c isolation valve tests in 10 CFR Part SO, Appendix J. These tests would be performed in addition to the quantitative Type C tests required by Appendix J and would not relieve the applicant of the responsibility to conform to the requirements of Appendix J.
Subject to successful implementation of the above recommended actions, we find
- A the purge/vent system design and oeprating practices for Salem, Unit 1 to be acceptable.
SAFETY EVALUATION SALEM GENERATING STATION UNITS 1 & 2
- OVERRIDE OF CONTAINMENT PURGE ISOLATION AND OTHER ENGINEERED SAFETY FEATURE ACTUATION SIGNALS INTRODUCTION As a result of Abnormal Occurrence #78-5, the NRC issued a generic letter requesting each licensee to take certain actions.
EVALUATION
- The attached interim report was prepared for use by EG&G Idaho, as part of our technical assistance program.* This report provides a technical evaluation of the electrical instrumentation and control design aspects of the override of containment purge valves isolation and other engineered safety feature actuation s 1gna1 s
- and i's b.ased upon review of the design aspects against the 6*staff review criteria provided for the review.
The isolation valves for venting and purging satisfy the staff review criteria cited above, with three exceptions. The exceptions are that:
1.. Inadequate physical protection is provided for the.containment ventilation isolation reset push button switches located in*
the control room, *
- 2.
The b,Ypas*sing of a Safety Injection (SI) signal at the contain..;
ment ventilation isolation (CVI) retentive*memory is not annunciated, and
- 3.
The radiation monitors that initiate CVI are not safety grade.
CONCLUSION Based upon our reviewof the consultant's technical evaluation, we conclude that the electrical, instrumentation and control design aspects of the override of containment purge valve isolation-and other engineered safety feature actuation signals are.acceptable with the exception of the three items identified above.
We also consider the contractor's interim report to be a final report because there is to. t>e no further contractor effort on this subject for this. plant.
The licensee should be required to provide:
- 1. Spring loaded covers over the existing safety related containment ventilation isolation reset push buttons that are mounted on the control panels within 30 days,
- 2.
System level annunciation of the bypassed status of contain-ment ventilation isolation within 90' days, and
- 3.
Radiation monitors that are safety grade and satisfy the requirements of IEEE Std. 279-1971. This requirement has been incorporated into Regulatory Guide 1.141, Revision l; 11Containment Isolation Provisions for Fluid Systems.
11 This revision has been endorsed by ACRS and will be required after final Commission approval.