ML20029B349
| ML20029B349 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 03/05/1991 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20029B348 | List: |
| References | |
| NUDOCS 9103070082 | |
| Download: ML20029B349 (3) | |
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UNITED STATES
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WAsHiNoToN. D, c. 2o55s SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMEN 0 MENT NO.160 TO FACILITY OPERATING LICENSE NO. OPR-50 METROPOLITAN EDIS0N COMPANY JERSEY CENTRAL POWER & LIGHT COMPANr PENNSYLVANIA ELECTRIC COMPANY CPU NUCLEAR CORPORATION THREE MILE ISLAND NUCLEAR STATION, UNIT NO. 1 DOCKET NO. 50-289
1.0 INTRODUCTION
By letter dated September 25, 1990, GPU Nuclear Corporation (the licensee) requested an amendment to the Technical Specifications (TS) for Three Mile Island Nuclear Station, Unit No. 1 (TMI-1),
The proposed TS changes would delete the existing requirement to replace Reactor Guilding (RB) purge valve seats at the first refueling interval following 5 years servic9, and add the requirement to durometer test RB purge valve seats as part of the refueling surveillance.
The seats of the four 48" RB purge valves are made of molded ethylene propylert terpolymer (EPT) and form part of the containment isolation barrier.
The purge valve seats were last replaced in February and March of 1985, and are currently scheduled for replacement during the 9R refueling outage scheduled to commence the third quarter of 1991.
The proposed TS amendment was submitted to change the basis of purge valve seat replacement from calendar age to physical condition as monitored by surveillances associated with the purge valves.
2.0 BACKGROUND
The issue of excessive leakage of con inment isolation valves with resilient seats was initially raised in IE Circ
- 77-11, dated September 6, 1977.
Examination of valve seat material from valves which failed leakage tests under 10 CFR 50, Appendix J indicated that the material had lost resiliency and showed signs of wear due to valve cycling.
The circular reported that licensees-have taken actions such as seat replacement, testing seat materials for resiliency and increasing the frequency of local leak rate tests.
The circular also recommended certain steps be taken to minimize the possibility of excessive valve leakage and to quickly detect leakage paths which develop.
These steps included a comparison of material history and manufacturer's recommendations with testing frequency and maintenance schedules to determine if a schedt'e for valve seat re;>lacement should be developed.
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2-This issue evolved into Generic Issue (GI) B-20. " Containment Leakage due to Seal Deterioration." Resolution of this GI involved incorporating specific requirements for local leak rate testing into GI B-24. " Containment Purging during Normal Plant Operation." This requirement for-increased local leak rate tests is based on guidance contained in Branch Technical Position CSB 6-4.
The increased frequency of local leak rate tests provides assurance that gross deterioration _ of resilient valve seats _would be quickly detected.
Technical Specifications proposed as part of GI B-24 included a surveillance requirement to periodically replace the resilient seals in containment purge valves for plants which continued to purge during plant operation.
This requirement was incorporated into the THI-1 TS.
The basis for this requirement was expected wear.to the valve seats due to repeated valve operation and a loss of resiliency due to exposure to an adverse environment. These proposed GI 8-24 Technical Specifications did not include surveillance requirements to inspect the condition of the resilient valve seats at specific intervals.
A requirement for periodic purge valve seat replacement is not included in the proposed revision to the Standard Technical Specifications.
Generic Issue B-24 4
is now closed.
A reexamination of policy with regard to the operational usage of large purge system valves was conducted by the Office of Nuclear Reac'e Regulation in 1990. This analysis concluded that the staff's current policy as prc,ented in Standard Review Plan 6.2.4 and Branch Technical Position CSB 6-4 is adequate.
l 3.A EVALUATION
.The licensee has proposed adding the requirement to conduct a durometer test in addition to a visual inspection of purge valve seats as part of the refueling surveillance under TS 4.4.1.7.2.
The durometer test will provide an indicatio~
of. seat degradation by measuring the hardness of the seat material.
The visual inspection provides timely detection of excessive seat wear.
l The addition of a durometer test to the surveillance requirements provides I
added assurance that RB purge valve seat degradation will be detected and seat replacement will be performed in a timely manner.
Dased on this evaluation, l
the staff finds this proposed change to TS 4.4.1.7.2 acceptable.
The bases were ' changed to reflect this additional testing requirement.
- The licensee has proposed deleting the existing requirement to replace purge
- valve seats at the first refueling interval following 5 years of valve seat
. service.
This requirement'was added via License Amendment 108 dated May 8,-
1985.
The basis for this periodicity is the manufacturer's recommended shelf
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life for;the seat of 5 years.
The manufacturer has since revised this recom-mendation to allow installation after 5 yrds "provided the material is properly
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stored, durometer hardness checked, and.hally inspected for ozone cre.cking prior-to use." (Henry Pratt Company memor edue dated January 16, 1990; B.R.
- Cummins-to P.E. Boucher).
se
.. ' e licensee has calculated a service life for the seat aaterial based en hermal aging and integrated radiation dose. This computed service life is much greater than 5 years; however, the actual rate of degradation of the seat material will depend on the specific environment to which the material is exposed. Specifying periodicity for seat replacement does not nect:ssarily assure the valve will perform its containment isniat
- function with a greater degree of certainty.
All detected leakage whic. nn developed past the currently installed seats has been corrected by minor adjustments of seat alignment, not seat replacement.
The requirements of 10 CFR Part 50 and guidance conteined in U.S. Nuclear Regulatory Comission Regulatory Guides do not directly address a maximum service life for containment isolation valve seats. However, 10 CFR 50 Appendix J and Technical Position CSB 6-4 require periodic leak tests of the RB purge valves.
This provides a direct indication of the ability of the valve seat to perform its design function. The required quarterly leak tests of the purge valves under TS 4.4.1.2 and the refueling surveillance under TS 4.4.1.7.2 were found to provide sufficient confidence in the integrity of the purge valves as containment isolation barriers. The deletion of the requirement to replace the purge valve seats at the first refueling interval following 5 years service from TS 4.4.1.7.2 is therefore acceptable.
4.0 EllVIRONMENTAL CONSIDERATION The amendment changes a requirement with respect to installation or use of a facility component located within the restricted areas as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types of any effluents that may be released offsite, and that d are is no significant increase in individual or cumulative occtgational radiation sxposure. The. Comission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public coment on such finding.
Accordingly, the ameNment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
The Comission has concluded, based on the considerations discussed above, that (1) there ic reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in comp'iance with the Comission's regulations, and (3) the issuance of the a;nendment will not be inimical to the comnion defense and security or to the health and safety of the public.
Principal Contributor:
S. Jones Date:
March 5, 1991 i
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