ML20080R813
| ML20080R813 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 03/06/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20080R794 | List: |
| References | |
| NUDOCS 9503100088 | |
| Download: ML20080R813 (4) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20mo001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 97 TO FACILITY OPERATING LICENSE NO. NPF-62 ILLIN0IS POWER COMPANY. ET AL.
CLINTON POWER STATION. UNIT NO. 1 DOCKET NO. 50-461
1.0 INTRODUCTION
The Clinton Power Station (CPS) Containment Building Ventilation and Purge.
System consists of a 36-inch primary containment building ventilation system and a 12-inch containment purge system. The 36-inch ventilation system isolation valves are butterfly valves equipped with resilient seals.
System operation is typically restricted to shutdown conditions. The 12-inch purge system is normally in operation when the plant is at power.
l The CPS technical specifications for the 36-inch ventilation system isolation valves were originally written to reflect operating experience of resilient seals.
Resilient seals have been known to degrade more rapidly than valves without such seals.
Therefore, increased testing of these valves was considered necessary in order to detect signs of degradation. The staff's original Safety Evaluation Report required periodic testing of once every three months for active valves and once every six months for inactive valves.
Since the licensee was planning to perform ASME stroke testing every three l
months, the CPS technical specifications were originally written to require leak tests at least once every 92 days with an upper leakage limit of 0.01 L,.
Operating experience at the Clinton Station has subsequently demonstrated that there is no need to operate the 36-inch ventilation system during operating Modes 1, 2, and 3.
In addition, by letter dated September 27, 1950, the licensee requested to defer stroke testing of the 36-inch isolation valves from quarterly to once every cold shutdown. These actions have significantly reduced the number of times that the valves are being cycled. The net result of valve testing during the last two operating cycles has been that resilient seal degradation is not occurring when the valves remain closed.
By letter dated June 13, 1994, the licensee stated that the current technical specifications requiring leak testing once every 92 days are overly conservative.
(It should be noted that in Amendment No. 95 issued on De ember 2, 1994, the staff changed the frequency of testing these valves to once every 184 days.) Based on plant operating experience, the licensee proposed a test frequency in accordance with 10 CFR 50, Appendix J.
In addition, in the event that the valves would be cycled during plant operation, the licensee proposed that the valves would be locally leak-tested within 92 days.
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. 2.0 EVALUATION When the CPS technical: specifications were being developed,.the, staff was.
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-concerned about the durability of resilient seals.on large purge system isolation valves.
In addition, it'was not known how frequently.the Mark III j
containment plants would need to operate the 36-inch purge system. -Due to the significant post-LOCA radiological consequences that could' occur due to excessive leakage from these valves, the staff determined that it~ was.
j important to monitor for any degradation.- As stated above, the staff's SER' stated th:1 appropriate leak testing of there valves would be once every six.
months for inactive valves, and once.every three months for active valves.
i Therefore, the CPS technical specifications were written to permit some.
R limited use of the 36-inch ventilation system at power, provided that the
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valves were leak-tested once every 92 days, and that the individual. valve leakage did not exceed 0.01 L,.
The 36-inch supply and exhaust isolation valves (IVR001A & B and IVQ004A & B)'
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are associated with containment penetrations IMC-101 and IMC-102,.
'i respectively.
Prior to startup from a refueling outage, the valves are. leak-tested and caution-tagged closed for the duration of the operating cycle.
l Since the second refueling outage when the ASME stroke testing.was deferred to l
cold shutdown conditions, these valves have not been cycled during plant i
operation. However, the licensee has continued to perform leak tests once-every 92 days, as required by the technical specifications.
j Operating experience at CPS has shown that if the. valves are not cycled, no.
~i mechanism is introduced to significantly change the valve leakage rate. This i
is evidenced by the "as-found" local leak rate tests performed for these two containment penetrations.
(This test is separate from that described above and assists maintenance staff in determining potential outage work.) During cycle 3, the measured leak rate for penetration IMC-101 did not change at all, except for the test performed just prior to the third refueling outage when the leak rate decreased. During cycle 4, the measured leak rate for penetration IMC-101 did not vary more than 250 sccm (approximately 8%) from-the leak rate measured at the end of the third refueling outage. Regarding penetration.lMC-102, the leak rate did not vary more than 50 scem (approximately 15%) during cycle 3.
In addition, during cycle 4, the measured leak rate from penetration IMC-102 remained below the value measured at the j
end of the third refueling outage, and was measured to be exactly the same for three consecutive test intervals.
j Based on the test data discussed above, the licensee has demonstrated that the leakage characteristics for these valves remain basically unchanged, provided that the valves are not cycled. Since cycling the valves provides a mechanism for seal degradation, the licensee has proposed leak testing within 92 days following the opening of a 36-inch supply or exhaust isolation valve.
The licensee has no preventive maintenance plans for periodic replacement of the resilient seals.
The valves are located indoors in mild environments, and will not be subject to harsh temperatures or radiation fields. Due to this mild environment, the licensee's equipment qualification manual, which is
7 based on vendor recommendations, lists the lifetime of the resilient seals for the full 40-yekr duration of the plant.. In actual practice, the licensee I
trends leakage rates for these 36" valves and, as a result of this information, the licensee previously replaced the seal of one valve.
The technical specifications originally had an individual leakage limit of 0.01 L for each valve. While the improved technical specifications, which were i,ssued in Amendment No. 95 on December 2,1994, no longer list an individual leakage limit,-the licensee still-maintains this limit in owner controlled documents. Discussions with the licensee indicate that they have no plans to modify or delete this limit.
l The staff concurs with the licensee's assessment that the leakage characteristics of the valves will not significantly change once the valves are known to be leak-tight and they remain in the closed position. The licensee's proposal does not change the safety function of these valves or the individual leakage limits. While the frequency of testing will be decreased from once every 92 days to once every refueling cycle, this would appear to be sufficient to identify long-term seal degradation provided the valves are not opened. As previously discussed, if the valves are opened, a separate leakage test will be conducted within 92 days. Therefore, based on the above information, the staff finds the licensee's proposal to be acceptable.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance of the amendment.
The State official had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
This amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR
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Part 20 and changes surveillance requirements. The NRC staff has determined i
that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released i
offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a
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proposed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding
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(59 FR 49427). Accordingly, the amendment 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 enyt onmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
The staff has concluded, based on the considerations discussed above, that:
(1) there is 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 compliance with the Commission's regulations,
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.h and (3) the issuance of the. amendment will not' beLinimical to the comon.
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'defenseLand ' security or to the health and safety of the public.
-Principal: Contributor:
Douglas V. Pickett ~
i Date: March 6, 1995 i
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