Regulatory Guide 1.160

Monitoring the Effectiveness of Maintenance at Nuclear Power Plants

ML12216A016
Person / Time
Issue date:	06/30/1993
From:	Office of Nuclear Regulatory Research
To:
References
DG-1020 RG-1.160
Download: ML12216A016 (7)

U.S. NUCLEAR REGULATORY COMMISSIONJune 1993REGULATORY GUIDEOFFICE OF NUCLEAR REGULATORY RESEARCHREGULATORY GUIDE 1.160(Draft was DG-1020)MONITORING THE EFFECTIVENESS OFMAINTENANCE AT NUCLEAR POWER PLANTSA. INTRODUCTIONThe NRC published the maintenance rule onJuly 10, 1991, as Section 50.65, "Requirements forMonitoring the Effectiveness of Maintenance at Nu-clear Power Plants," of 10 CFR Part 50, "DomesticLicensing of Production and Utilization Facilities."The Commission's determination that a maintenancerule was needed arose from the conclusion thatproper maintenance is essential to plant safety. Asdiscussed in the regulatory analysis for this rule,'there is a clear link between effective maintenanceand safety as it relates to such factors as the numberof transients and challenges to safety systems and theassociated need for operability, availability, and reli-ability of safety equipment. In addition, good mainte-nance is also important in providing assurance thatfailures of other than safety-related structures, sys-tems, and components (SSCs) that could initiate oradversely affect a transient or accident are mini-mized. Minimizing challenges to safety systems is con-sistent with the Commission's defense-in-depth phi-losophy. Maintenance is also important to ensure thatdesign assumptions and margins in the original designbasis are maintained and are not unacceptably de-1NRC Memorandum to All Commissioners from J. Taylor on"Maintenance Rulemaking," June 27, 1991. Copies areavailable for inspection or copying for a fee from the NRCPublic Document Room at 2120 L Street NW., Washington,DC; the PDR's mailing address is Mail Stop LL-6, Washing-ton, DC 20555; phone (202) 634-3273; fax (202) 634-3343.graded. Therefore, nuclear power plant maintenanceis clearly important in protecting the public healthand safety.Paragraph (a)(1) of 10 CFR 50.65 requires thatpower reactor licensees monitor the performance orcondition of SSCs against licensee-established goals ina manner sufficient to provide reasonable assurancethat such SSCs are capable of fulfilling their intendedfunctions. Such goals are to be established commen-surate with safety and, where practical, take into ac-count industry-wide operating experience. When theperformance or condition of an SSC does not meetestablished goals, appropriate corrective action mustbe taken.Paragraph (a)(2) of 10 CFR 50.65 states thatmonitoring as specified in paragraph (a) (1) is not re-quired where it has been demonstrated that the per-formance or condition of an SSC is being effectivelycontrolled through the performance of appropriatepreventive maintenance, such that the SSC remainscapable of performing its intended function.Paragraph (a)(3) of 10 CFR 50.65 requires thatperformance and condition monitoring activities andassociated goals and preventive maintenance activitiesmust be evaluated at least annually,2 taking into2As of the publication of this regulatory guide, a modificationto the maintenance rule is in preparation that would changethe evaluation interval to every refueling outage but not to ex-ceed 2 years.USNRC REGULATORY GUIDESRegulatory Guides are Issued to describe and make available to the pub-lic such information as methods acceptable to the NRC staff for imple-menting specific parts of the Commission's regulations, techniquesused by the staff in evaluating specific problems or postulated acci-dents, and data needed by the NRC staff in its review of applications forpermits and licenses. Regulatory Guides are not substitutes for regula-tions, and compliance with them is not required. Methods and solutionsdifferent from those set out in the guides will be acceptable if they pro-vide a basis for the findings requisite to the issuance or continuance of apermit or license by the Commission.This guide was issued after consideration of comments received fromthe public. Comments and suggestions for improvements in theseguides are encouraged at all times, and guides will be revised, as ap-propriate, to accommodate comments and to reflect new information orexperience.Written comments may be submitted to the Regulatory PublicationsBranch, DFIPS, ADM, U.S. Nuclear Regulatory Commission, Washing-ton, DC 20555.The guides are issued in the following ten broad divisions:1. Power Reactors2. Research and Test Reactors3. Fuels and Materials Facilities4. Environmental and Siting5. Materials and Plant Protection6. Products7. Transportation8. Occupational Health9. Antitrust and Financial Review10. GeneralCopies of issued guides may be purchased from the Government PrintingOffice at the current GPO price. Information on current GPO prices maybe obtained by contacting the Superintendent of Documents, U.S.Government Printing Office, Post Office Box 37082, Washington, DC20013-7082, telephone (202)512-2249 or (202)512-2171.Issued guides may also be purchased from the National Technical Infor-mation Service on a standing order basis. Details on this service may beobtained by writing NTIS, 5285 Port Royal Road, Springfield, VA 2216 account, where practical, industry-wide operating ex-perience. Adjustments must be made where necessaryto ensure that the objective of. preventing failures ofSSCs through maintenance is appropriately balancedagainst the objective of minimizing unavailability ofSSCs because of monitoring or preventive mainte-nance. In performing monitoring and preventivemaintenance activities, an assessment of the totalplant equipment that is out of service should be takeninto account to determine the overall effect on per-formance of safety functions. Paragraph (b) of10 CFR 50.65 states that the scope of the monitoringprogram specified in paragraph (a) (1) is to includesafety-related and nonsafety-related SSCs, as follows:(1) Safety-related structures, systems, or compo-nents that are relied upon to remain functionalduring and following design basis events to en-sure the integrity of the reactor coolant pressureboundary, the capability to shut down the reac-tor and maintain it in a safe shutdown condition,and the capability to prevent or mitigate the con-sequences of accidents that could result in po-tential offsite exposure comparable to the10 CFR Part 100 guidelines.(2) Nonsafety-related structures, systems, orcomponents(i) That are relied upon to mitigate accidentsor transients or are used in plant emergencyoperating procedures (EOPs); or(ii) Whose failure could prevent safety-relatedstructures, systems, and components fromfulfilling their safety-related function; or(iii) Whose failure could cause a reactor scramor actuation of a safety-related system.Paragraph (c) of 10 CFR 50.65 states that therule provisions are to be implemented by licensees nolater than July 10, 1996.Any information collection activities mentionedin this regulatory guide are contained as requirementsin 10 CFR Part 50, which provides the regulatory ba-sis for this guide. The information collection require-ments in 10 CFR Part 50 have been approved by theOffice of Management and Budget, Approval No.3150-0011.B. DISCUSSIONThe objective of 10 CFR 50.65 (referred to here-after as the maintenance rule or the rule) is to requiremonitoring of the overall continuing effectiveness oflicensee maintenance programs to ensure that:(1) safety-related and certain nonsafety-related SSCsare capable of performing their intended functionsand (2) for nonsafety-related equipment, failures willnot occur that prevent the fulfillment of safety-relatedfunctions, and failures resulting in scrams and unnec-essary actuations of safety-related systems are mini-mized.The extent of monitoring may vary from systemto system depending on the system's importance torisk. Some monitoring at the component level may benecessary; however, it is envisioned that most of themonitoring could be done at the plant, system, ortrain level. For example, for less risk-significant sys-tems, indicators of system reliability (where sufficientperformance data exist) and availability may be allthat is necessary. For more risk-significant systems,some parameter trending, beyond that already re-quired by NRC requirements to provide early warningof degradation, may also be necessary for criticalcomponents whose unavailability causes a systemtrain to be unavailable or whose failure is otherwiseunacceptable. Rather than monitoring the many SSCsthat could cause plant scrams, the licensee maychoose to establish a performance indicator for un-planned automatic scrams and, where scrams causedby equipment failures have been problematic orwhere such scrams are anticipated, the licensee maychoose to monitor those initiators most likely to causescrams.It is intended that activities currently being con-ducted by licensees, such as technical specificationsurveillance testing, can satisfy monitoring require-ments. Such activities could be integrated with, andprovide the basis for, the requisite level of monitor-ing. Consistent with the underlying purposes of therule, maximum flexibility should be offered to licen-sees in establishing and modifying their monitoringactivities.Licensees are encouraged to consider the use ofreliability-based methods for developing the preven-tive maintenance programs covered under paragraph(a) (2) of the rule; however, the use of such methodsis not required.With regard to the scope of the maintenancerule, as stated in paragraph (b) of the rule, it is un-derstood that balance of plant (BOP) SSCs may havebeen designed and built with normal industrial qualityand may not meet the standards in Appendix B to10 CFR Part 50. It is not the intent to require licen-sees to generate paperwork to document the basis forthe design, fabrication, and construction of BOPequipment.Each licensee's maintenance efforts should mini-mize failures in both safety-related and BOP SSCsthat affect safe operation of the plant. The effective-ness of maintenance programs should be maintainedfor the operational life of the facility.As noted in the Regulatory Position, there maybe a need to address maintenance activities that occurin the switchyards that could directly affect plant op-erations. Plant management should be aware of andhave the ability to control these activities.1.160-2 The regulatory guidance is intended to provideflexibility for a licensee to structure its maintenanceprogram in accordance with the safety significance ofS those SSCs within the scope of the rule.The nuclear industry has developed a documentthat provides guidance to licensees regardingimplementation of the maintenance rule. This docu-ment has been prepared by NUMARC. A verificationand validation (V&V) effort was conducted byNUMARC, with NRC staff observation, to test theguidance document on several representative systems.A number of changes were made to the NUMARCguidance document based on the results of the V&Veffort. The NRC staff reviewed this document andfound that it provides acceptable guidance tolicensees.Certain requirements for a renewed license under10 CFR Part 54 may be satisfied by taking credit foractivities required by the maintenance rule. However,the renewal rule requires (10 CFR 54.21(a)(6)(iii)),among other provisions, that an effective programmust be implemented by the facility operating pro-cedures and reviewed by the on-site review commit-tee. The maintenance rule does not have theserequirements.Industry and NRC-sponsored probabilistic riskanalyses (PRAs) have shown the risk significance ofS emergency ac power sources. The station blackoutrule (10 CFR 50.63) required plant-specific copinganalyses to ensure that a plant could withstand a totalloss of ac power for a specified duration and to deter-mine appropriate actions to mitigate the effects of atotal loss of ac power. During the station blackout re-views, most licensees (1) made a commitment to im-plement an emergency diesel generator (EDG) reli-ability program in accordance with NRC regulatoryguidance but reserved the option to later adopt theoutcome of Generic Issue B-56 resolution, (2) statedthat they had or will implement an equivalent pro-gram, or (3) endorsed the program embodied inNUMARC 87-00, Revision 1, August 1991, "Guide-lines and Technical Bases for NUMARC InitiativesAddressing Station Blackout at Light Water Reactors"(i.e., maintain the emergency diesel generator targetreliability of 0.95 or 0.975). Subsequently, utilitiesdocketed commitments to maintain their selected tar-get reliability values. Those values could be used as agoal or as a performance criterion for emergency die-sel generator reliability under the maintenance rule.When utilities were performing their plant-specific coping analyses, they were allowed to useplant-specific data concerning unavailability due tomaintenance. Therefore, emergency diesel generatorS unavailability due to maintenance, as assumed in aplant-specific individual plant examination (IPE)analysis, could also be used as the basis for a goal orperformance criterion under the maintenance rule.Section (a) (3) of the maintenance rule requiresthat adjustments be made where necessary to ensurethat the objective of preventing failures of SSCsthrough maintenance is appropriately balancedagainst the objective of minimizing unavailability ofSSCs due to monitoring or preventive maintenance.Therefore, plant-specific emergency diesel generatorreliability and unavailability should be monitored asgoals under 10 CFR 50.65(a)(1) or established asperformance criteria under the plant's preventivemaintenance program under 10 CFR 50.65(a)(2),taking into account the objectives of 10 CFR50. 65 (a) (3).Under 10 CFR 50.65(a)(2), the utility would es-tablish performance criteria for both emergency die-sel generator reliability and unavailability. Emergencydiesel generator performance criteria for reliabilitywould be met by the absence of a maintenance-preventable failure or the occurrence of a singlemaintenance-preventable failure followed by appro-priate root cause determination and corrective action.Performance criteria for unavailability would be metby having fewer unavailable hours, on a rolling 1-yearbasis, than required by the established performancecriteria.If any performance criterion is not met, or asecond emergency diesel generator maintenance-preventable failure occurs, it is expected that the li-censee would establish goals and monitor subsequentemergency diesel generator performance under10 CFR 50.65(a)(1), consistent with an appropriatebalance between emergency diesel generator reliabil-ity and unavailability.The emergency diesel generator reliability per-formance criteria or goals selected for implementingthe intent of 10 CFR 50.63 for coping with stationblackout could be monitored through the use of thetriggers3 and the monitoring methods described inAppendix D of NUMARC 87-00, Revision 1,"Guidelines and Technical Bases for NUMARC In-itiatives Addressing Station Blackout at LWRs,"August 1991 (except for triggers and testing for"problem diesels" as described in paragraph D.2.4.4of NUMARC 87-00, which will be addressed sepa-rately by the NRC). An acceptable unavailability goalcould be to have fewer hours unavailable (on a rolling1-year basis) than the number of hours established asacceptable by the licensee.C. REGULATORY POSITIONThe scope of monitoring efforts under the main-tenance rule, as defined in 10 CFR 50.65(b), encom-passes those SSCs that directly and significantly affect3The triggers are intended to indicate when emergency dieselgenerator performance problems exist such that additionalmonitoring or corrective action is necessary. It is recognizedthat it is not practical to demonstrate by statistical analysisthat conformance to the trigger values will ensure the attain-ment of high reliability, with a reasonable degree of confi-dence, of individual EDG units.1.160-3 plant operations, regardless of what organization actu-ally performs the maintenance activities. Mainte-nance activities that occur in the switchyard can di-rectly affect plant operations, and as a result electricaldistribution equipment out to the first inter-tie withthe off-site distribution system (i.e., equipment in theswitchyard) should be considered for comparison with10 CFR 50.65(b) for inclusion under the scope of themaintenance rule.NUMARC 93-01, dated May 1993, "IndustryGuideline for Monitoring the Effectiveness of Mainte-nance at Nuclear Power Plants,"4 provides methodsacceptable to the NRC staff for complying with theprovisions of 10 CFR 50.65. NUMARC 93-01 refer-ences other documents, but NRC's endorsement ofNUMARC 93-01 should not be considered as en-dorsement of the referenced documents.The example in NUMARC 93-01, Sec-tion 12.2.4, which refers to optimizing emergency4Copies are available for inspection or copying for a fee fromthe NRC Public Document Room at 2120 L Street NW.,Washington, DC; the PDR's mailing address is Mail StopLL-6, Washington, DC 20555; phone (202) 634-3273; fax(202) 634-3343.diesel generator reliability and availability, describesan acceptable method to establish emergency dieselgenerator performance criteria and/or goals and sub-sequently monitor emergency diesel generator per-formance.D. IMPLEMENTATIONThe purpose of this section is to provide informa-tion to applicants and licensees regarding the NRCstaff's plans for using this regulatory guide.Except in those cases in which the applicant orlicensee proposes an acceptable alternative methodfor complying with specified portions of the Commis-sion's regulations, the methods described in the guidewill be used in the evaluation of submittals forconstruction permits and operating licenses (as appro-priate) and will be used to evaluate the effectivenessof maintenance activities of licensees who are re-quired to comply with 10 CFR 50.65. The guide willalso be used to evaluate the effectiveness of emer-gency diesel generator maintenance activities associ-ated with compliance with 10 CFR 50.63.1.160-4 REGULATORY AND BACKFIT ANALYSESSeparate regulatory and backfit analyses wereprepared for this Regulatory Guide 1.160. They areavailable, in the file for Regulatory Guide 1.160, forinspection or copying for a fee in the Commission'sPublic Document Room, 2120 L Street NW.,Washington, DC; the PDR's mailing address is MailStop LL-6, Washington, DC 20555; phone(202)634-3273; fax (202)634-3343.1.160-5 Federal Recycling Program I-0 FIRST CLASS MAILPOSTAGE AND FEES PAIDUSNRCPERMIT NO. G-67OFFICIAL BUSINESSPENALTY FOR PRIVATE USE, $300