ML20035C471
| ML20035C471 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/05/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20035C467 | List: |
| References | |
| NUDOCS 9304080008 | |
| Download: ML20035C471 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION l
TEMPORARY EXEMPTION FROM 10 CFR PART 50. APPENDIX J TYPE B AND C LOCAL LEAK RATE TESTING OF CONTAINMENT PENETRATIONS NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION. UNIT 1 DOCKET NO. 50-245
1.0 INTRODUCTION
By letter dated January 18, 1993, as supplemented by letter dated March 22, 1993, Northeast Nuclear Energy Company (NNEC0/the licensee) requested a one-time schedular exemption from the requirements of 10 CFR Part 50, Appendix J, Sections III.D.2(a) and III.D.3. The temporary schedular exemption would extend the interval for Type B and C local leak rate testing (LLRT) of containment penetrations at the Millstone Nuclear Power Station, Unit I, beyond the 2-year limit of 10 CFR Part 50, Appendix J.
Appendix J requires these tests to be performed at every refueling outage, but with the interval not to exceed 2 years. NNECO commenced the most recent LLRT program at Millstone, Unit 1, on April 7,1991, during the cycle 13 refueling outage. NNEC0 experienced an unusually long refueling outage followed by a shutdown approximately 1 1/2 months after startup for licensed operator requalification. This second outage was, in turn, extended due to erosion / corrosion inspections. NNEC0 subsequently had another unplanned shutdown for service water system inspections and repair.
Due to this series of circumstances, NNEC0 has postponed the refueling outage for cycle 14 from February 1993, to February 1994. NNECO has requested an exemption from the 2-year interval requirement of 10 CFR Part 50, Appendix J, to allow them to perform the LLRTs during the cycle 14 refueling outage and avoid forcing the plant to have a mid-cycle shutdown solely to perform the Type B and C LLRTs.
I In their submittals and in a phone conference between the staff and NNECO on March 16, 1993, NNECO stated that they were unable to perform any of the LLRTs during the periods that the plant was shutdown due to the evolving nature of the unplanned shutdowns. The outages were unplanned and were expected to be of short duration when they began. The outages evolved into much longer than anticipated durations as the scope of the work to be done became more apparent to NNEC0 management. The work performed during these outages was extensive causing NNECO to involve the majority of their resources.
This left them with insufficient resources to plan and perfctm the LLRT program at the same time, which among other things, would require many test procedures to be modified due to the fuel being in the reactor vessel.
This testing is normally performed after the fuel has been off-loaded.
In addition, the outages DO P
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occurred early in the cycle and at first were not expected to substantially disrupt the refueling outage.chedule, and therefore, the LLRT schedule.
Later, when NNECO recognized that a schedular exemption for the LLRT program.
was needed, it was determined that an exemption to the Type A accelerated test frequency requirement of 10 CFR Part 50, Appendix J, was needed before they could consider requesting an exemption to the Type B and C test frequency requirement. Therefore, NNECO pursued the Type A exemption first. The Type A.
exemption was previously approved by the staff.
NNECO has committed to two compensatory measures in the interim until the refueling outage in order to demonstrate a good faith effort to comply with
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the regulations.
First, NNEC0 has identified 17 penetrations that they can reasonably test at power without placing the plant in inadvisable configurations or risking personnel safety.
These 17 penetrations include 16 cable penetrations and the control rod drive hatch. These tests will be completed prior to the expiration of the 2-year test interval for each penetration.
In addition, NNEC0 will also test penetration X-25/202D which has had recurring failures.
This penetration will be tested in late April 1993. NNEC0's second compensatory measure is to begin performing the LLRT program should they experience an unplanned outage of sufficient duration to i
begin testing penetrations. NNEC0 has determined that an outage of 2 weeks or longer will be sufficient to begin testing. The number of penetrations that can be tested during the unplanned outage will. depend on the length of the outage.
2.0 EVALUATION i
NNECO has addressed the following factors to justify the requested exemption:
2.1 Need For Extendina The Test Interval Until The Next Refuelino Outaae NNECO has stated that many of the components associated with this exemption request cannot be tested at power. There are two main reasons for this. The first is that some of the penetrations are not accessible during power operations and cannot, therefore, be tested. The second reason is that testing of certain penetrations would require operating the plant in an inadvisable configuration, such as with a safety system taken out of service.
Therefore, a shutdown would be required in order to completely test all penetrations in the LLRT program.
NNECO has stated that conducting a mid-cycle outage solely for the purpose of performing the LLRT program in its entirety is not advisable for four main reasons.
First, performing LLRTs on the emergency core cooling systems (ECCS) t would pose challenges to the management of shutdown risk since the ECCS systems would need to be drained to perform the tests. Typically, LLRTs for the ECCS systems are not done with fuel in the core although NNECO notes that they can still be tested. Moreover, additional challenges to the management of shutdown risk would be posed since the shutdown cooling system would have to be removed from service to be tested. Second, NNECO would have to rewrite many of their LLRT and system operating procedures to accommodate unusual
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system configurations that would be required due to performance of the tests I
while fuel is in the core. Third, NNECO would have to remove the drywell head shield plugs and drywell insulation in order to test a single 2-inch check valve in the head spray system which is normally not operated during the cycle. This evolution is normally only performed during refueling outages.
Fourth, the shutdown would add an unnecessary cooldown and heatup cycle to the plant increasing the probability of undesirable events which have a higher i
probability of occurrence during shutdown and startup than during power operation. NNECO does not feel that an outage of this type is the best utilization of their resources since the tests would be performed again during the cycle 14 refueling outage in order to put the LLRT program schedule back in phase with the refueling cycle.
In addition, the cost of a shutdown solely to perform the LLRT program would be high in terms of radiological exposure and personnel safety.
For the reasons stated above, the staff concurs that the LLRT program cannot be completed at power, and that a shutdown solely to perform the tests should not be required.
2.2 Good Leak Rate History For Components NNECO performed a detailed analysis of the past leak rate history of the 98 penetrations in question. NNEC0 reviewed the results of their last six tests-and found that of the QR penetrations tested each time, a total of 18 different penetrations had failed. The review showed that the majority of the.
penetrations were historically " good performers." NNEC0 has worked to improve the leak tightness of their containment penetrations.
The success of these efforts is demonstrated by the fact that only two penetrations during the last six tests have had recurring failures. One (penetration X-14) was successfully fixed by NNECO in 1989, as is demonstrated by its passing the 1991 "as found" LLRT. The other is penetration X-25/202D on which NNECO has committed to performing a mid-cycle test prior to the end of the 2-year test interval.
NNECO has implemented a corrective action plan to address the problems with this penetration. The mid-cycle test of penetration X-25/202D will demonstrate whether or not this corrective action plan has'been successful. NNECO also has further corrective actions scheduled for this penetration during the next refueling outage. NNEC0's efforts to improve overall containment integrity have been successful. This is demonstrated by the fact that NNECO has shown continuous improvement in the "as left" integrated leak rate test (ILRT) results. Leak rates in weight percent per day (wt %/ day) have been consistently reduced from 0.779 in 1984 to 0.441'in 1987 te 0.4077 wt %/ day in 1991. The allowable operational leak rate specified in the regulations is 0.9 wt %/ day and the maximum leak rate assumed in the Millstone Unit I accident analysis is 1.2 wt %/ day. This improvement-in the overall leak tight condition of the containment at the start of the operating cycle combined with the consistently good performance of the containment penetrations in the LLRT program provides reasonable assurance that the requested test interval extension will not result in the overall leakage rate exceeding the 10 CFR Part 50, Appendix J limits.
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e i I 2.3 Intent Of Accendix J The staff notes that the 2-year interval requirement for Type B and C components is intended to be often enough to prevent significant deterioration from occurring and long enough to permit the tests to be performed during plant outages.
Leak rate testing of the penetrations during plant shutdown is preferable because of the lower _ radiation exposures to plant personnel.
Moreover, as noted before, some penetrations cannot be tested at power.
For penetrations that cannot be tested during power operation, or for which testing at power is inadvisable as discussed above, the increase in confidence in containment integrity following a successful test is not signi', cant enough to justify a plant shutdown specifically to perform the tests within the 2-year time period.
3.0 CONCLUSION
Based on the above evaluation, the staff finds the requested temporary exemption, to allow the Type B and C test intervals to be extended to the refueling outage which will begin no later than February 28, 1994, to be acceptable.
Principal Contributor:
R. Elliott Date:
April 5,1993
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