ML020320188
| ML020320188 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 01/29/2002 |
| From: | Constellation Nuclear |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML020320050 | List: |
| References | |
| Download: ML020320188 (8) | |
Text
AnACHMENT (1)
DESCRIPTION OF CIRCUMSTANCES AND SAFETY BASIS Calvert Cliffs Nuclear Power Plant January 29, 2002
A1TACHMENT (1)
DESCRIPTION OF CIRCUMSTANCES AND SAFETY BASIS
Background
Calvert Cliffs Nuclear Power Plant (CCNPP) is a two-unit site. The Unit 2 EmergencySafety Features electrical system relies on two emergencydiesel generators(EDGs). Unit 1 also has two EDGs. In addition, there is a non-safety-related,augmentedquality, station blackout 5400 kW diesel generator (DG) available. The No. 2A EDG is a Fairbanks-Morsediesel generator,as are the Nos. IB and 2B EDGs. The No. lA EDG and No. OC DG are SocieteAlsacienneDe ConstructionsMecaniquesDe Mulhouse(SACM) dieselgenerators.
Plant Condition On January24, 2002, a biannual inspection of the No. 2A EDG was underway. Technical Specification3.8.1, Condition B, was entered for the inspection on No. 2A EDG at 3:00 a.m. on January24,2002. During the inspection,wear was notedon the flexible drive gear. This gear drives the auxiliary pumps necessaryfor DG operation. The amount of wear found was unexpectedbecausethe flexible drive gear only had about 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> of operation since the last biannual inspection. Unit 2 remained in Limiting Condition for Operation 3.8.1, Condition B, since taking No. 2A EDG out-of-service for inspection. Unit 2 is now in Limiting Condition for Operation 3.8.1, Condition H, and is operatingunderthe enforcementdiscretiongrantedon January27, 2002.
Apparent Canse The root causeinvestigationhas identified an apparentproblem within the pump flexible drive assembly (crosshead). The lube oil pump drive gear bearing bore was found out-of-round. We believe that this out-of-round condition causedthe lube oil pump drive shaft gear to improperly mesh with the flexible drive gear. This resulted in destructivepitting on the flexible drive gear. A vendor representativewas brought in to inspect the gear train. Vendor inspectionsupportsthe suspectedcauseat this time. The root causeinvestigationis continuing while repairsare underway. Disassemblyof the front end has been completedand reassemblystarted. The No. IB EDG has also been inspectedfor similar wear and this worn condition was not found. The No. 2B EDG will be inspectedafter the No. 2A EDG has been returnedto service. The vendor confinns that acceleratedwear of this type on the flexible drive gear is unexpected.A review of industry experiencefound no appropriatehistorical events.
Schedule A replacement flexible drive gear is being installed. Installation of this gear requires substantial disassemblyof the diesel engine, procurementof the parts, engine reassembly,and post-maintenance testing. Experiencedtechnical representativesfrom the EDG vendor are onsite assisting in the repair process. Partshave beendelivered. In addition, we have a spareEDG engineonsite that we can obtain partsfrom, if needed.A project managementschedulehasbeendevelopedand is as follows:
. Disassembleengine,cleanparts- 29 hours3.356481e-4 days <br />0.00806 hours <br />4.794974e-5 weeks <br />1.10345e-5 months <br />
. Repair and reassemblethe engine- 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> Activities associatedwith testingand inspectionof the EDG - 29 hours3.356481e-4 days <br />0.00806 hours <br />4.794974e-5 weeks <br />1.10345e-5 months <br /> Theseactivities beganat 7:00 a.m. on January26,2002, and are scheduledto be completeand the EDG declared operable by 11:00 p.m. on January31, 2002. To perform these activities, Calvert Cliffs is requestingenforcementdiscretion in the form of a one-time,6-day extensionto the 72-hour Completion Time. Although the scheduletime to completetheseactivities is lessthan six days,the additional time is requestedfor contingency activities beyond ones the schedule has already included. Without this
A1TACHMENT (1)
DESCRIPTION OF CIRCUMSTANCES AND SAFETY BASIS discretion,Unit 2 would havecommencedshutdownby 3:00 a.m. EST on January27, 2002. If additional problemsare discoveredduring the repair processthat cannotbe resolvedin the approvedtimeframe, we will shut down Unit 2 as soonasthat determinationis made.
Other Plant Equipment The other EDGs onsite have been tested recently at full load for an hour. The No. 2B EDG was tested on January 13,2002, the No. IB EDG was tested on January 6, 2002, the No. lA EDG was tested on January 20, 2002, and the No. OC DG was tested on January 9, 2002. Equipment required for feed and bleed operations in the Reactor Coolant System is operable (e.g., high pressure safety injection pumps, charging pumps, power-operated relief valves [FORVs]). The auxiliary feedwater pumps are also operable. The condition of the reactor coolant pump seals is normal. There are no significant operator work-around issues on Unit 2, and particularly on the systems mentioned above.
Risk Insights Preventing plant challenges during shutdown conditions has been, and continues to be, an important aspect of ensuring safe operation on the plant. Entry into and operation of shutdown cooling is not without risk including the risk associated with increased radioactive waste streams from the operation of the shutdown cooling system. These risks must be considered when the plant is required to shut down.
Continuing to use the steam generators to remove heat from the core and to provide steam for the turbine-driven auxiliary feedwater pumps is preferable for this time. In addition, the Reactor Coolant System remains in a steady-state mode with the reactor coolant pumps in operation. Pressure and temperature transients are avoided.
The effect of remaining in Mode 1 for this extendedtime was evaluatedusing risk insights. Calvert Cliffs has evaluated the risk associatedwith remaining in Mode 1 in this degradedcondition and comparedit to the risk associatedwith unit shutdownand startup.
The Unit 2 risk of operatingfor six dayswith the No. 2A EDG out-of-servicewas determinedby:
. Using a Seismic, Fire, and Internal Events probabilistic risk assessmentwith average unavailabilities(Unit 2 impactsfor externaleventsestimatedusingthe Unit 1 Model).
. Screeninghigh wind events(tornadoesand hurricanes)as out-or-season.
Improving the operatoractionsto start and refuel the No. OC00. Operatoraction is requiredto refuel the No. OCfuel oil day tank when it is depleted.
Given theseconditions,the quantified risk was determinedto be approximately3E-7.
The risk of shuttingdown with the No. 2A EDG out-of-servicewas detenninedby:
. Reviewing the shutdowns and startups since 1980 and determining the number of plant challenges (plant trips) that occurred during these transients. Each plant trip was then qualitatively reviewedto determineif it would be applicablegiven the improvementsmadeto the plant since these events and the plant conditions (e.g., time in fuel cycle) that exist for this potential Unit 2 shutdown.
. Trips that occurredduring a nonnal shutdownwere evaluatedas having the samerisk impact as if they occurredat 100%power.
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A1TACHMENT (1)
DESCRlPnONOF CIRCUMSTANCES AND SAFETY BASIS
. Trips that occurredduring nonnal startupswere evaluatedas having 50% of the risk of the same transientoccurring at 100%power.
The shutdownperiod (after nonnal shutdownbut beforenonnal startup)was evaluatedas having 20% of the risk of the at-powercondition.
Given theseconditions,the quantifiedrisk was determinedto be approximatelyIE- 7.
The following qualitative issueswere not consideredin the aboveanalysis:
. There is a benefit to providing a dedicatedoperatorto cross-connectkey motor control centers (MCCs) following a loss of non-safety-relatedpower to 4 kV Bus 21. Cross-tying the MCCs ensuresthat both PORV block valves are available, both PORVs can be opened, the safety injection MOVs are powered,etc. Due to fIre concerns,the PORV and PORV block valve are powered from opposite facility MCCs. In some accident sequencesa single PORV spuriously opens. With both MCCs energized,the open PORV can be readily isolated. Motor control center cross-connectionalso improves the ability to achieve once-through-core-cooling(RCS feed-and-bleed). Calvert Cliffs Nuclear Power Plant requires both PORVs to open for once-through-core-coolingduring scenarioswhen feedwater(auxiliary and main) is lost at the plant trip. The MCC cross-tieaction was identified as important through a review of key probabilistic risk assessment contributorsgiven No. 2A EDG is out-of-service. Improved operatoractionsdue to understandingthe importanceof this action, and by having a dedicatedoperator to perform theseactions,resultsin a reductionin risk.
By limiting the performanceof discretionarymaintenanceor testing, there is improved defense-in-depth. This resultsin a reductionin risk.
Review of the operatoractionsto be taken on a loss of off site power improvesthe likelihood of successof theseactions. This resultsin a reductionin risk.
The presenceof all four offsite circuits maximizesthe reliability of off site power. The Calvert Cliffs key probabilistic risk assessmentdoes not explicitly provide credit for the benefit of the third high-line. A more detailed analysisof the benefit of the additional high-line results in a reduction in risk.
Limiting the conductof maintenanceor testingon the off site power systemreducesthe likelihood of losing offsite power. This specifically appliesto switchyard maintenance. This impact was not explicitly included in the risk analysis.
. The benefit of providing an assignedoperator,to control auxiliary feedwatercontrol valves in the event that flow control is lost following a loss of offsite power, was also identified through a review of important risk contributors. Local control of auxiliary feedwaterdue to the loss of instrumentair or due to degradedinstrumentationis more important when No. 2A EDG is not available. Improved operatoractionsdue to understandingthe importanceof this action and by having an assignedoperatorto perform theseactionsresultsin a reduction in risk.
. Low magnitudeseismicevent impactson No. OCDG were not considered,since these impacts affect non-critical ventilation, especiallyin light of the current low outsidetemperatures.
The abovequalitative actionswere not quantified.
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AtTACHMENT (1)
DESCRIPTION OF CIRCUMSTANCES AND SAFETY BASIS The qualitative portion of our risk assessmentincluded multiple compensatorymeasuresthat were not included in our quantitative risk assessment.We believe that the qualitative risk reduction offsets the quantitative risk assessment,such that this Notice of EnforcementDiscretion requestis safety and risk neutral.
Compensatory Measures During the period that we are in non-compliancewith the Technical Specifications, we have implementeda numberof risk-managementmeasures.
. We will not perform electivemaintenanceon the No. 2B EDG.
. Calvert Cliffs has a high quality, non-safety-related5400 kW No. OCDG installed that can be aligned to either Unit 2 4 kV vital bus. The No. OCDG would be available if the No. 2B EDG were to fail during an event where emergencyelectrical power was required. A dedicated operatorin the Control Room hasbeenassignedand trained to utilize No. OCDG. This operator is in addition to the normal shift crew complementto ensurethat there is no conflict in resources if the actionsare required.
The same dedicatedoperator has also been assignedto cross-connectkey MCCs to provide power to necessaryequipmentin the eventof a loss of off site power.
. During the period that we are in non-compliancewith the Technical Specifications,we will not perform any discretionary maintenanceor testing on any Unit 2 safety-related equipment.
Requiredsurveillancetestingwill be performed.
. We have reviewedwith the plant operatorsthe actionsto be taken should a loss of offsite power occur while No. 2A EDG is not available.
If the plant is threatenedby severeweatherwith the potential to interrupt otIsite power during the period that we are in non-compliancewith the Technical Specifications, we will shut down Unit 2.
. All four off site circuits are available, though only two are required to be operable by the Technical Specifications.
. During the period that we are in non-compliancewith the Technical Specifications,Calvert Cliffs will not conductmaintenanceor testing on the off site power system.
. An operatorhas beenassignedto control the auxiliary feedwaterflow control valves in the event that flow control is lost following a lossof offsite power.
Conclusion We have consideredthe possibility of significant hazardsassociatedwith this period of non-compliance with the Technical Specifications(see Attachment 2) and determinedthat there are none. We have determinedthat the requestedperiod of non-compliancewith the TechnicalSpecificationswill not present an undue risk to the plant or to the health and safety of the public. Additionally, operation of Calvert Cliffs Unit 2 during the period of non-compliancewith the Technical Specificationswill result in no adverseconsequencesto the environment in that there will be no significant change in the types or significant increasesin the amountsof any eff1uentsthat may be releasedoff site, and in no significant increasein individual or cumulativeoccupationalradiationexposure.Therefore,we requestthat the NRC grant the requestedNotice of EnforcementDiscretion.
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A1TACHMENT (2)
DETERMINA nON OF NO SIGNIFICANT HAZARDS Calvert Cliffs Nuclear Power Plant January 29, 2002
AtTACHMENT (1)
DETERMINADON OF NO SIGNIFICANT HAZARDS Calvert Cliffs Nuclear Power Plant is requesting regional enforcement discretion from certain requirementsof the Calvert Cliffs Technical Specifications. The Technical Specificationsrequire that, when in Modes 1-4 with one of the separateand independentdiesel generatorsinoperable,the inoperable diesel generatormust be restoredto operablestatuswithin 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If the inoperablediesel generatoris not restoredto operablestatus,the unit must be placed in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />. 11risrequestfor regional enforcementdiscretion is being madeto avoid an unnecessaryplant transientas the result of full compliancewith the TechnicalSpecifications. Calvert Cliffs Nuclear Power Plant wishes to extendthe 72-hour CompletionTime by 6 days. Therefore,Calvert Cliffs is requesting Enforcement Discretion from the Nuclear Regulatory Commissionto allow the one emergencydiesel generator to be inoperable for 6 days longer than the Technical Specification Completion Time of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> without exiting Mode 1. The additionaltime is neededto repair and test the EDG.
The proposedenforcementdiscretion has beenevaluatedagainstthe standardsin 10 CFR 50.92 and has beendeterminedto not involve a significant hazardsconsideration,in that operationof the facility during the period of the enforcementdiscretion:
Would not involve a significant increase in the probability or consequencesof an accident previously evaluated The emergencydiesel generators(EDGs) provide onsite electrical power to vital systemsshould offsite electrical power be intemlpted. Calvert Cliffs Unit 2 has two safety-relatedEDGs. The EDGs are not an initiator to any accidentpreviously evaluated. Therefore,this extendedperiod of operation with the EDG out-of-service will not increase the probability of an accident previously evaluated.
The EDGs act to mitigate the consequences of designbasisaccidentsthat assumea loss of offsite power. For that purpose, redundantEDGs are provided to protect against a single failure.
During the TechnicalSpecification72-hourCompletionTime, an operatingunit is allowed by the Technical Specificationsto remove one of the EDGs from service, thereby losing this single failure protection. This operating condition is consideredacceptable. The consequencesof a design basis accident coincident with a failure of the redundant EDG during the period of Technical Specification non-complianceare the sameas those during the 72-hour Completion Time. Furthermore,as a compensatoryaction, Calvert Cliffs will not perform any discretionary maintenanceor testing on any Unit 2 safety-relatedequipment during the period of non-compliance with the Technical Specifications. This will reduce the risk that other mitigating equipmentwould not be available in the event of a designbasisaccident. Therefore,during the period of non-compliance,there is no significant increase in consequencesof an accident previously evaluated.
Therefore, the proposedchange does not involve a significant increasein the probability or consequences of an accidentpreviouslyevaluated.
- 2. Would not create the possibility of a new or different type of accident from any accident previously evaluated.
During the period of non-compliancewith the TechnicalSpecifications,the plant will not be in a new configuration nor will any unusual operator actions be required. The EDGs are not an initiator to any accident,but are designedto respondshouldan accidentoccur.
AnACBMENT (2)
DETERMINATIONOF NO SIGNIFICANT HAZARDS Therefore, the proposedchangedoes not create the possibility of a new or different type of accidentfrom any accidentpreviouslyevaluated.
3 Wouldnot involve a significant reduction in a margin of safety.
During the period of the 72-hour Technical Specification Completion Time when one EDG is out-of-serviceduring power operation,the margin of safety is allowed to be reduced. This time period is a temporary relaxation of the single failure criteria, which, consistent with overall system reliability considerations,provides a limited time to repair the equipment and conduct testing. Calvert Cliffs is requestingan extensionto this limited time. Calvert Cliffs has also instituted a numberof compensatorymeasuresthat reducethe possibility of a plant transientor a loss of offsite power. Calvert Cliffs concludesthat the period of non-compliancewith the Technical Specifications beyond that allowed by the Completion Time does not result in a significant further reduction in the margin of safety,basedon our managementof plant risk, the availability of the an alternatediesel generator,the reliability of the redundantEDG, and other compensatorymeasures.
Therefore,the proposedchangedoesnot involve a significant reduction in a margin of safety.
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