NRC Generic Letter 1991-06
A wUNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D.C. 2OM5April 29, 1991TO: ALL HOLDERS OF OPERATING LICENSES
SUBJECT: RESOLUTION OF GENERIC ISSUE A-30, "ADEQUACY OF SAFETY-RELATED DCPOWER SUPPLIES," PURSUANT TO 10 CFR 50.54(f) (GENERIC LETTER 91-06)The staff of the U.S. Nuclear Regulatory Commission (NRC) has completed theevaluation of Generic Issue (GI) A-30 as part of the resolution of GI-128,"Electrical Power Reliability." GI A-30 focuses on safety-related dc systems.Enclosure 1ito this generic letter provides a brief description and history of..this GI. Additional details are provided in NUREG/CR-5414, "Technical Findingsfor Proposed Integrated Resolution of Generic Issue 128, 'Electrical PowerReliability."' As a result of its evaluation, the staff believes that certainmaintenance, surveillance, and monitoring provisions are appropriate forsafety-related dc systems. The staff believes that most plants have alreadyimplemented most of these provisions because of a number of actions takenpreviously by the staff and industry.In order for the NRC to determine whether any further staff action is requiredto modify, suspend or revoke your license, addressees are required, pursuant toSection 182 of The Atomic Energy Act of 1954, as amended, and 10 CFR 50.54(f),to provide written responses. to the questions in Enclosure 1 within 180 daysof the date of this letter. This information should be submitted to NRC, signedunder oath or affirmation.The actions requested in this generic letter are not considered a backfit inaccordance with NRC procedures and do not represent a change in staff positions.This generic letter is a request for information only to determine if licensee'splant specific maintenance, surveillance, and monitoring provisions are appropriateand that these provisions have been implemented. An evaluation of this letterwas performed in accordance with the charter of the Committee to Review GenericRequirements (CRGR) and 10 CFR 50.54(f) and will be made available in the PublicDocument Room with the minutes of the 163rd meeting of the CRGR.NRC has recognized that an "Individual Plant Examination (IPE) For SevereAccident Vulnerabilities" could enable licensees to address unresolved safetyand generic safety issues as outlined in generic letter 88-20, provided thatthe details defined in NUREG-1335 (Section 2.1.6, Subitem 7), "IndividualPlant Examination: Submittal Guidance", are included. Therefore, theenclosure to this letter gives licensees the option of providing certainsupporting information as part of the IPE instead of supplying it in responseTechnical Contacts:0. Chopra, NRR ._z==- Z2 I(301) 492-3265 j .-_D. Thatcher, RES7J(301) 492-3935 ( IE14756 UpJ&411 obxP& o5W0o 3 e I 0 Li aq Generic Letter 91-06 -2 -April 29, 1991to this letter. However, a decision to address this generic issue as providedin Enclosure 1 (i.e., by addressing questions 5 and 9) does not relieve licenseesfrom searching for other plant-specific vulnerabilities of dc systems as partof your IPE.This request is covered by Office of Management and Budget ClearanceNumber 3150-0011, which expires June 30, 1991. The estimated average number ofburden hours is 100 person hours per licensee response, including the timerequired to assess the questions, search data sources, gather and analyze thedata, and prepare the required reports. Comments on the accuracy of thisestimate and suggestions to reduce the burden may be directed to Ronald Minsk,Office of Information and Regulatory Affairs (3150-0011), NEOB-3019, Office ofManagement and Budget, Washington, D.C. 20503, and to the U. S. Nuclear RegulatoryCommission, Information and Records Management Branch, Division of InformationSupport Services, Office of Information and Resources Management,Washington, D.C. 20555.If you have any questions, please contact your project manager.
Sincerely,J mes G. PartlowA sociate Director for ProjectsOffice of Nuclear Reactor Regulation
Enclosures:
1. 10 CFR 50.54(f) Request ForGI A-30 "Adequacy ofSafety-Related dc Power"2. List of Recently Issued genericletters ENCLOSURE 110 CFR 50.54(f) REQUEST -GENERIC ISSUE (GI) A-30 "ADEQUACY OFSAFETY-RELATED DC POWER SUPPLIES"BakgondThe specific area of concern of GI A-30 "Adequacy of Safety-Related DC PowerSupplies" is the adequacy of the safety-related dc power in operating nuclearpower plants, particularly with'regard to multiple and common cause failures.Risk analysis and past plant experience support conclusions that failure of thedc power supplies could represent a-significant contribution to the unreliabilityof shutdown cooling. Analysis indicates that inadequate maintenance andsurveillance and failure to detect battery unavailability are the prime contributorsto failure of the dc power systems.During the development of plans to resolve GI A-30 it was observed thatseveral previously issued regulatory notices (IENsj, bulletins (IEBs) andletters (GLs) submitted to licensees include recommendations similar to thosethat have been identified to resolve GI A-30. More specifically, it has beendetermined that recommendations contained in notifications IEN 85-74, "StationBattery Problems", IEB 79-27, "Loss of Non-Class 1E Instrumentation and ControlPower System Bus during Operation," and separate actions being taken to resolveGI 49, "Interlocks and LCOs for Class 1E Tie Breakers" include the elementsnecessary to resolve GI A-30. It is therefore concluded that licensees thathave implemented these recommendations and actions will have resolved GI A-30.The response to the questions that follow is necessary to provide the staffwith information to determine whether any further action is required for yourfacility.QuestionsThe following information is to be provided for each unit at each site:-1. Unit2. a. The number of independent redundant divisions of Class lE or safety-related dc power for this plant is .(Include anyseparate Class 1E or safety-related c, uc as any c dedicated tothe diesel generators.)b. The number of functional safety-related divisions of dc powernecessary to attain safe shutdown for this unit is _. -3. Does the control room at this unit have the following separate, independentlyannunciated alarms and indications for each division of dc power?a. alarms1. Battery disconnect or circuit breaker open?2. Battery charger disconnect or circuit breaker open (both inputac and output dc)?
-2 -3. dc system ground?4. dc bus undervoltage? ___ _5. dc bus overvoltage? _6. Battery charger failure?7. Battery discharge?b. Indications1. Battery float charge current?2. Battery circuit output current?3. Battery discharge?4. Bus voltage?c. Does the unit have written procedures for response to the above alarmsand indications?4. Does this unit have indication of bypassed and inoperable status ofcircuit breakers or other devices that can be used to disconnect thebattery and battery charger from its dc bus and the battery charger fromits ac power source during maintenance or testing?5. If the answer to any part of question 3 or 4 is no, then provide informationJustifying the existing design features of the facility's safety-relateddc systems. *See note below.6. (1) Have you conducted a review of maintenance and testing activities tominimize the potential for human error causing more than one dc divisionto be unavailable? and (2) do plant procedures prohibitmaintenance or testiig on reiufna-nt dc divisions at the same time?If the facility Technical Specifications have provisions equivalent to thosefound in the Westinghouse and Combustion Engineering Standard Technical Specificationsfor maintenance and surveillance, then question 7 may be skipped and a statementto that effect may be inserted here.7. Are maintenance, surveillance and test procedures regarding stationbatteries conducted routinely at this plant? Specifically:a. At least once per 7 days are the following verified to be withinacceptable limits:1. Pilot cell electrolyte level?
-3 -2. Specific gravity or charging current?3. Float voltage?4. Total bus voltage on float charge?5. Physical condition of all cells?b. At least once per 92 days, or within 7 days after a battery discharge,overcharge, or if the pilot cell readings are outside the 7-daysurveillance requirements are the following verified to be withinacceptable limits:1. Electrolyte level of each cell?2. The average specific gravity of all cells?3. The specific gravity of each cell?4. The average electrolyte temperature of a representativenumber of cells?5. The float voltage of each cell?6. Visually inspect or measure resistance of terminals andconnectors (including the connectors at the dc bus)?c. At least every 18 months are the following verified:1. Low resistance of each connection (by test)?2. Physical condition of the battery?3. Battery charger capability to deliver rated ampereoutput to the dc bus? _4. The capability of the battery to deliver its design dutycycle to the dc bus?5. Each individual cell voltage is within acceptable limitsduring the service test?d. At least every 60 months, is capacity of each battery verified byperformance of a discharge test?e. At least annually, is the battery capacity verified by performancedischarge test, if the battery shows signs of degradation or hasreached 85% of the expected service life? .
-4 -8. Does this plant have operational features such that following loss of onesafety-related dc power supply or bus:a. Capability Is maintained for ensuring continued and adequatereactor cooling? _b. Reactor coolant system integrity and isolation capability are maintained?c. Operating procedures, instrumentation (including indicators andannunciators), and control functions are adequate to Initiatesystems as required to maintain adequate core cooling? _9. If the answer to any part of question 6, 7 or 8 is no, then provide yourbasis for not performing the maintenance, surveillance and testprocedures described and/or the bases for not including the operationalfeatures cited. *See note below.*Note: For questions involving supporting type information (question numbers 5and 9) instead of developing and supplying the information in response tothis letter, you may commit to further evaluate the need for such provisionsduring the performance of your individual plant examination for severe accidentvulnerabilities (IPE). If you select this option, you are requiredto:(1) So state in response to these questions, and(2) Commit to explicitly address questions 5 and 9 in your IPE submittalper the guidelines outlined in NUREG-1335 (Section 2.1.6, Subitem 7),"Individual Plant Examination: Submittal Guidance."
., IEnclosureLIST OF RECENTLY ISSUED GENERIC LETTERSGenericLetter No.Date ofIssuanceSubjectIssued To91-05LICENSEE COMMERCIAL-GRADEPROCUREMENT AND DEDICATIONPROGRAMS04/09/9191-04CHANGES IN TECHNICAL SPECIFI- 04/02/91CATION SURVEILLANCE INTERVALSTO ACCOMMODATE A 24-MONTH FUELCYCLE91-0391-0291-01REPORTING OF SAFEGUARDSEVENTSREPORTING MISHAPS INVOLVINGLLW FORMS PREPARED FORDISPOSALREMOVAL OF THE SCHEDULE FORTHE WITHDRAWAL OF REACTORVESSEL MATERIAL SPECIMENSFROM TECHNICAL SPECIFICATIONSALTERNATIVE REQUIREMENTS FORSNUBBER VISUAL INSPECTIONINTERVALS AND CORRECTIVEACTIONSCONSIDERATION OF THE RESULTSOF NRC-SPONSORED TESTS OFMOTOR-OPERATED VALVESSIMULATION FACILITYEXEMPTIONS03/06/9112/28/9001/04/9112/11/9010/25/9008/10/90ALL HOLDERS OF OLsAND CPs FOR NUCLEARPOWER REACTORSALL HOLDERS OF OLsOR CPs FOR NUCLEARPOWER REACTORSALL HOLDERS OF OLsOR CPs FOR NUCLEARPOWER REACTORS ANDALL OTHER LICENSEDACTIVITIES INVOLVINGA FORMULA QUANTITYOF SPECIAL NUCLEARMATERIAL (SNM)ALL OPERATORS OFLOW-LEVEL RADIO-ACTIVE WASTE (LLW)DISPOSAL SITES,WASTE PROCESSORS,& ALL HOLDERS OFLICENSES FOR NUCLEARFUELS, NUCLEARMATERIALS & NUCLEARPOWER REACTORSALL HOLDERS OF OLsOR CPs FOR NUCLEARPOWER PLANTSALL LIGHT-WATERREACTOR LICENSEESAND APPLICANTSALL LICENSEES OFOPERATING NUCLEARPOWER PLANTS ANDHOLDERS OF CONSTRUC-TION PERMITS FORNUCLEAR POWER PLANTSALL HOLDERS OFOPERATING LICENSESOR CONSTRUCTIONPERMITS FOR NUCLEARPOWER REACTORS90-0989-10SUPP. 390-08