ML20055H827
| ML20055H827 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 07/25/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20055H826 | List: |
| References | |
| NUDOCS 9007300148 | |
| Download: ML20055H827 (4) | |
Text
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SAFETY EVALUATION BY THE'0FFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 111 T0-PROVISIONAL OPERATING LICENSE NO. DPR-19 AND AMENDMENT NO. 107 TO FACILITY-OPERATING LICENSE NO. DPR-25 COMONWEALTH EDISON = COMPANY DRESDEN-NUCLEAR POWER STATION, UNITS 2 AND 3 1
DOCKET NOS. 50-237 AND 50-249
1.0 INTRODUCTION
D By letter dated: April 18,1990, Comonwealth Edison (the;1icensee) provided a request for a license amendment to change the. Appendix A Technical.Specifica-.
tions(TS). The proposed change would modify the surveillance interval require-ments'forfunctionaltestingoftheReactorProtectionSystem(RPS) Electrical Protective Assemblies (EPAs).
The test interval for EPAs would be changed i
from once every six months, which is also specified in the Boiling Water Reactor (BWR) Standard Technical Specifications (STS), to every cold shutdown of more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> unless performed in the previous six. months.
2.0 EVALUATION Redundant EPAs are provided that monitor the output of each RPS motor-generator
{MG)setpowersource.
Breakers located between the MG sets and the RPS are tripped upon sensing an abnormal MG set output voltage or frequency.
.This protects the the RPS from'the effects of continuous operation with a degraded-power source. Because the RPS is not qualified for operation under degraded oower source conditions, the EPAs preclude-the potential.for RPS system failures that could preclude the capability for initiating a scram or other safety actions due to. abnormal MG set electrical output conditions.
Operating experience has shown that the EPAs are highly reliable devices and that the potential for MG failures resulting in~ degraded out)ut voltage or frequency, are low probability events.
The licensee noted t1at no failures of EPAs have occurred in over 336 tests at Dresden, Units 2 and 3.
In; addition.
the combined experience at the Quad Cities and LaSalle units is only one failure in over 500 tests. Therefore, it was proposed that the test interval for EPAs be changed from every six months to during cold shutdowns of more than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> duration if not performed in the previous six months on the' basis of this experience.
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The incentive for this change is to reduce the number of tests required to be performed during power operation where the unit is placed in a half-scram or half-isolation condition. The Dresden units have experienced unnecessary j
reactor-scrams and grou) isolations while testing EPAs due to inadvertent trips on tha remaining salf of the RPS logic when in a half-trip condition.
FinallyffasanupdatefortheLaSalle, Unit 1TSinordertobeconsistentwith the licensee noted that this change was also proposed and accepted by the sta the TS proposed for issuance with the LaSalle, Unit 2 operating license.
How-ever, whatever basis that may have been set forth for this change could not be located in a search of the LaSalle docket files or the licensee's letter Report (posed this change for the LaSalle units.SER) for Amendment 11 to the LaSal that pro The staff's Safety Evaluation this change in with a group of TS changes that were judged to be more conservative than those which they replaced and, therefore, acceptable on this basis.
3 The SER did not elaborate on the basis for this conclusion.
There are a number of considerations which would lead to a qualitative conclu-sion that plant safety is insensitive to the proposed TS change.
They include the low probability of a failure of the redundant EPAs. The low probability of MG set failures could produce a sustained abnormal voltage or frequency l
that could pose a threat to the protection systems components that are supplied power from the MG sets. The low probability that even if the protection systems were damaged due to an abnormal MG set electrical output, assuming the EPAs failed, such would not be detected by other on-line testing of the protection systems before the occurrence of a valid scram or isolation demand.
Also, the low probability that these independent events would occur in the required sequence could result in a challenge to plant safety.
Finally, sny significant threat to safety would also require the failure of ATWS mitigation systems and operator action. However, because the licensee had not attempted to quantify the impact on safety of changing the surveillance interval for EPAs, the staff requested that such analysis be performed to support the proposed TS change.
In response, the licensee quantified the reliability of the EPAs based upon-operating experience at Dresden, Qcad Cities, LaSalle and Grand Gulf. This experience included four failures cf EPAs over a time interval of 311 EPA-years.
However, no attempt was made to quantify experience with MG set failures or the probability of events that could lead to a potential threat to safety.
It was, however, noted that other BWR TS had requirements as proposed for Dresden, Units 2 and 3.
A review was, therefore, made of the BWR operating licenses '. hat had been issued in the past 10 years.
It was found.that nine units (I.aSalle 1 and 2, Nine Mile Point 2, Perry, River Bend, Shoreham, Susquehanna 1 and 2, and Washington Nuclear Power 2) have TS as proposed for the Dresden units while only five units (Clinton, Grand Gulf, Hope Creek, Fermi 2, und Limerick) i have the six months. test interval as included in the currert BWR STS.
Because i
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- the Tb change for Nine Mile Point-2 ('4MP) had been implemented following the issuance of the operating license, an evaluation had been provided by the licensee to support the license amendment for the proposed change in the EPA surveillance interval.
The impact of the change in the EPA surveillance interval was evaluated for NMP-2 using the methodology included in the BWR Owners Group Topical Reports NEDC-30844 and -30851P.
These reports provided the justification for an exten-sion of on-line test intervals and allowable out-of-service times for BWR Reactor Protection Systems (RPS). The staff had )reviously approved the use of these Topical Reports to support proposed TS c1anges for the RPS on an individual plant basis. The results of the NMP-2 analysis was provided by Niagara Mohawk Power Cor) oration in support of the TS change for the EPA sur-veillance intervals by t1eir letter dated December 15, 1988.
The results of the NMP-2 analysis showed that the change in failure probability of the RPS scram solenoids increased by 4.'7 x 10 E-8 failures per year due to the increase in EPA surveillance interval. The change in core damage frequency was 6.2 x 10 E-12 per year when failure probabilities for the alternate rod insertion and standby liquid control system were considered. The reduction in inadvertent scrams by eliminating the testing of EPAs during power operation was determined to be 1.8 x 10 E-3 scrams per year which was determined to I
result in a decrease in core damage frequency of 1 x 10 E-10 per year.
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These results confirm the qualitative judgement that safety is insensitive to the proposed increase in EPA surveillance intervals.
In fact, the result is a net benefit to safety, yet negligibly small by any relevant standard. We find that NMP-2 quantitative analysis of the impact on safety of the change in EPA-surveillance interval provides a suitable basis for acceptance of this TS change and confirms the acceptability of the prusosed surveillance interval-as included in the TS of those plants licensed in tie past 10 years as noted above. Therefore, we find the proposed TS change to be acceptable for Dresden, Units 2 and 3.
3.0 ENVIRONMENTAL CONSIDERATION
These amendments involve changes to a requirement with respect-to the instal-lation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendments i'-
involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is -
i no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued-a proposed finding that these amendments involve no significant hazards consideration and there has been no public comment on such finding. Accordingly, these amendments meet 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 nor environmental assessment need be prepared in connection with the issuance of these amendments.
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4.0 CONCLUSION
The staff has concluded, based on the considerations discussed above that: (1)thereisreasonableassurancethatthehealthandsafetyofthe-ublic will not be endangered by operation.in the proposed manner, and-p(2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of these amendments will not be inimical to the common defense and security nor to the health and safety of the public.
Principal Contributor: Thomas G. Dunning Dated: _
July 25,1990 J
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