ML20063P962
| ML20063P962 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 08/09/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20063P961 | List: |
| References | |
| NUDOCS 9008160056 | |
| Download: ML20063P962 (5) | |
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A UNITED STATES NUCLEAR REGULATORY COMMISSION n
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J SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 112 TO PROVISIONAL OPERATING LICENSE NO. DPR-19 AND AMENDMENT NO. 108 TO FACILITY OPERATING LICENSE NO. DPR-25 COMMONWEALTH EDIS0N COMPANY DRESDEN NUCLEAR POWER STATION. UNITS 2 AND 3 l
DOCKET NOS. 50-237 AND 50-249
1.0 INTRODUCTION
By letter dated July 31, 1990, comonwealth Edison Company (Ceco) submitted' i
emergency Technical Specification (TS) changes for the Dresden Nuclear Power Station, Units 2 and 3.
The proposed change excludes the Reactor Building Closed Cooling Water (RBCCW)) system inlet pathway to the primary containmentforeachunit(twovalves from Appendix J, Type C leak rate testing requirements until the next refueling outage for each u, nit (approximately 2 months of continued operation for Dresden Unit 2 and 10 months of continued operation for Dresden Unit 3).
In addition to not being Type C tested, the two valves in the RBCCW inlet pathway for each unit were not properly included as part of the tested containment boundary during the last containment integrated leak rate test (Type A test). Thus, e
i neither the sum of local leak rates (Type B and Type C) nor the overall i
integrated containment leak rate (Type A) is known.
Because the valves cannot be tested with the plant at power, nor can the lines be isolated by other barriers with the plant at power, the requestod changes to the Technical Specifications were needed to allow continued plant operation, 2.0 DISCUSSION AND EVALUATION l
The existing RBCCW system has design features-that function to inhibit L
poteatial release paths. The RBCCW system consists of'two 6 inch lines that penetrate primary containment. The supply (inlet) line is normally isolated using a check valve inside and a motor-operated gate valve l
outside of conteinment.- The return line contains two remotely operated
-valves, one inside and one outside of the drywell.
In additioa to the two containment isolation valves on each line other barriers exist.
Insideofthecontainment,thepipingformsaclosed loop. Outside of containment, the piping is configured such that loop water seals are created.
The system is filled with water during normal operation. The water serves as a seal in the event the valves leak.
Additionally, any through-wall water leaks would be easily detected either
-inside or outside of the drywell through sump level alarms, system pressures, or tank levels.
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l l The piping outside of containment is connected to a vented surge tank.
l This tank receives makeup water that is supplied by multiple pumps connected to a comon header, which provides suction from a 100,000 gallon storage tank. This configuration provides substantial assurance that the system would remain water-filled in )ost-accident conditions. Containment leakage, then, would have to enter tie closed system inside containment, pass through two valves and a loop seal, and the system would have to be depressurized, before leakage could enter the environment.
In addition to the above, the licensee performed a probabilistic risk assessment (PRA) to further demonstrate that the probability of an event resulting in a loss of containment function coincident with a LOCA during the remainder of the current Dresden-(Unit 2 and 3) operating cycles is.
insignificant.
Based on this evaluation, CECO concluded that the fission product barriers remain intact unless an extreme combination of highly improbable coincident failures occurred. The probabilities calculated for
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the event in which containment functio tions were found to be less than IX10'y failure would occur under LOCA condi-A recirculation piping failure (or any high energy line break), RBCCW pipe failure inside containment, and a failure of the loop seal would have to. occur in order to result in the failure of the containment function. The probability of a failure of the RBCCW 1X10'pscontainmentfunctioncoincidentwithaLOCAwasdeterminedtobe syste i
and is therefore considered to be insignificant.
CECO has also implemented administrative controls that direct the operators to close the remotely operated valves on the RBCCW systems when the Reactor Recirculation Pumps trip during a postulated Loss of Coolant Accident (LOCA). The RBCCW pumps will be kept on, if possible, to ensure the system is filled with water and pressurized above containment pressure.
If the RBCCW expansion tank HI/LO level alarm is received during a LOCA event, field teams will be sent, as conditions permit, to check RBCCW piping outside containment to ensura integrity. The Station Director will be informed to take the n ecessary actions to further isolate the system.
The staff has evaluateo the licensee's submittal and concludes, based on the system design, the administrative controls that have been implemented and the low probability of the combination of failures that would have to occur to breach containment integrity, that operation until the next refuel-ing outage with the two valves in the inlet pathway of the RBCCW of each unit untested will not add significantly to the risk to the public health and safety and therefore, the proposed TS chenges are acceptable.
In addi-tion, a similar TS change was issued to Quad Cities Unit 1 on June 27, 1990.
3.0 FINDINGS OF EMERGENCY WARRANTING AN AMENDMENT WITHOUT NOTICE In the fourth quarter of 1989, the licensee assessed the leak rate testing program at Quad Cities and identified 29 containment pathways that were not being local leak rate tested.
The licensee determined the Appendix J Type C testing was not required for these 29 pathways.
However,theNRCstaff questionr1 this determination and on May 18, 1990, concluded that these 29 l
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3-pathwayswere,infact,subjecttoAppendixJ,TypeCtesting. Once informed of the NRC's position on these pathways, the licensee requested a l
temporary waiver of compliance. The NRC staff orally granted this waiver on May 18, 1990.
Upon completion of the Quad Cities review in December 1989, these pathways were reviewed against the Dresden local leak rate test (LLRT) program. The RBCCW system was one of the systems identified at Quad Cities, however, it was not identified as a Dresden concern in the December 1989 comparison I
review with Quad Cities because the RBCCW system had been included in the Dresden LLRT programs since 1984.
Subsequent to the December 1989 review, the Corporate General Office Support Services Staff proceeded to conduct a detailed review of the entire Dresden LLRT program and identified five additional pathways of potential concern which were communicated to Dresden Station on July 18, 1990. These pathways were validated by station personnel after further review and walkdowns on July 20, 1390 ani a waiver of compliance was orally approved by the staff on the same Qta, (Three of the pathways identified were leak rate tested within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> and did not require an emergency TS amendment).
Ceco on July 31, 1990 proposed a TS amendment which deferred the testing of the two remaining RBCCW inlet pathways (one for each unit) until the next refueling outage for each unit.
The staff finds that Ceco acted as quickly as possible once informed of the requirement to test these pathways.
Furthermore, the staff finds that failure to grant the proposed changes in a timely manner would have required a shutdown of both Dresden units. Accordingly, the staff concludes that the licenseehassatisfiedtherequirementsof10CFR50.91(a)(5),andthata i
valid emergency exists,
4.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The NRC staff has reviewed the Ceco's amendment application and determined, in accordance with the criteria of 50.92(c), that operation of Dresden, Units 2 and 3, according to the proposed amendment will not:
(1)
Involve a significant increase in the probability or consequences of an accident p W iously evaluated.
Leakage through the associated valves does not a' Iter the initiating aspects of the events. The continued operation in the existing RBCCW configuration does not present a sign.ificant increase in the probability of a larger release of radioactivity than described in the FSAR.
The existing RBCCW system designfeatures(i.e.waterfilledsystem)inhibitpotentialrelease paths.
In addition, the PRA performed by CECO demonstrated that the probabilityofcontainmentfunctjonfailurecoincidentwithaLOCAis notsignificant(lessthan1X10-).
CECO has also implemented administrative controls to direct operators to close remotely operated valves on the RBCCW systems when a reactor recirculation pump trip occurs during a postulated LOCA. On this bases it is concluded that continued operation will not result in a signifIcant increase in risk with regards to accident probabilities or consequences, i
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... s 4-(2) Create the possibility of a new or different kind of accident from any accident previously evaluated. The emergency TS amendment does not result in any physical plant changes during the period of interest.
If the valves in the RBCCW system inlet pathway should leak, the severity of the accident would at worst be affected, but not the type I
of accident.
(3) Involve a significant reduction in the margin of safety. Dose calcu-lations described in the TS Bases suggest that the accident leak rate could be allowed to increase to about 3.2%/ day before the guideline thyroid dose value given in 10 CFR 100 would be exceeded.
- However, 1.6f/ day provides an additional margin of safety to assure the health i
and safety of the general public. Additional margin is further achieved by establishing the allowable operational leak rate at 75% of the maxi-mum allowable leak rate. Despite the lack of rigorous leak testing, substantial barriers to fission product release are provided by the intact system piping and associated valves.
These barriers provide mitigating capability such that the potential impact on the margin of safety is insignificant. Additionally, the PRA provided by CECO further demonstrates that the probability of containment function failure coin-cident with LOCA conditions is also acceptably small.
Accordingly, the Commission has determined that this request does not involve a significant hazards consideration.
5.0 STATE NSULTATION The State :n Illinois was informed by telephone on August 2,1990, of the staff's final no significant hazards consideration determination and intent to issue a license amendment. The state contact had no comment.
6.0 ENVIRONMENTAL CONSIDERATION
These aitandments involve changes to a requirement with respect to the instal-lation or un of a facility component located within the restricted area as defined in 10 CFR Part 20. The staff has determined that-the amendments 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 no significant increase in individual or cumulative occupational radiation-exposure.. The Commission has determined that these amendments involve no significant hazards consideration. 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 l
assessment need be prepared in connection with the issuance of these amendments.
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7.0 CONCLUSION
l The staff has concluded, based on the considerations discussed above,'that:
l (1) there is reasonable assurance that the health and safety of the will not be endangered by operation in the proposed menner, and (2) public 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: Byron Siegel Dated:
August 9, 1990 1
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