Regulatory Guide 1.160
| 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
COMMISSION
June 1993 REGULATORY
GUIDE OFFICE OF NUCLEAR REGULATORY
RESEARCH REGULATORY
GUIDE 1.160 (Draft was DG-1020)MONITORING
THE EFFECTIVENESS
OF MAINTENANCE
AT NUCLEAR POWER PLANTS
A. INTRODUCTION
The NRC published the maintenance rule on July 10, 1991, as Section 50.65, "Requirements for Monitoring the Effectiveness of Maintenance at Nu-clear Power Plants," of 10 CFR Part 50, "Domestic Licensing of Production and Utilization Facilities." The Commission's determination that a maintenance rule was needed arose from the conclusion that proper maintenance is essential to plant safety. As discussed in the regulatory analysis for this rule,'there is a clear link between effective maintenance and safety as it relates to such factors as the number of transients and challenges to safety systems and the associated need for operability, availability, and reli-ability of safety equipment.
In addition, good mainte-nance is also important in providing assurance that failures of other than safety-related structures, sys-tems, and components (SSCs) that could initiate or adversely 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 that design assumptions and margins in the original design basis are maintained and are not unacceptably de-1 NRC Memorandum to All Commissioners from J. Taylor on"Maintenance Rulemaking," June 27, 1991. Copies are available for inspection or copying for a fee from the NRC Public 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 maintenance is clearly important in protecting the public health and safety.Paragraph (a)(1) of 10 CFR 50.65 requires that power reactor licensees monitor the performance or condition of SSCs against licensee-established goals in a manner sufficient to provide reasonable assurance that such SSCs are capable of fulfilling their intended functions.
Such goals are to be established commen-surate with safety and, where practical, take into ac-count industry-wide operating experience.
When the performance or condition of an SSC does not meet established goals, appropriate corrective action must be taken.Paragraph (a)(2) of 10 CFR 50.65 states that monitoring 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 effectively controlled through the performance of appropriate preventive maintenance, such that the SSC remains capable of performing its intended function.Paragraph (a)(3) of 10 CFR 50.65 requires that performance and condition monitoring activities and associated goals and preventive maintenance activities must be evaluated at least annually, 2 taking into 2 As of the publication of this regulatory guide, a modification to the maintenance rule is in preparation that would change the evaluation interval to every refueling outage but not to ex-ceed 2 year
s. USNRC REGULATORY
GUIDES Regulatory 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, techniques used by the staff in evaluating specific problems or postulated acci-dents, and data needed by the NRC staff in its review of applications for permits and licenses.
Regulatory Guides are not substitutes for regula-tions, and compliance with them is not required.
Methods and solutions different 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 a permit or license by the Commission.
This guide was issued after consideration of comments received from the public. Comments and suggestions for improvements in these guides are encouraged at all times, and guides will be revised, as ap-propriate, to accommodate comments and to reflect new information or experience.
Written comments may be submitted to the Regulatory Publications Branch, DFIPS, ADM, U.S. Nuclear Regulatory Commission, Washing-ton, DC 20555.The guides are issued in the following ten broad divisions:
1. Power Reactors 2. Research and Test Reactors 3. Fuels and Materials Facilities
4. Environmental and Siting 5. Materials and Plant Protection
6. Products
7. Transportation
8. Occupational Health 9. Antitrust and Financial Review 10. General Copies of issued guides may be purchased from the Government Printing Office at the current GPO price. Information on current GPO prices may be obtained by contacting the Superintendent of Documents, U.S.Government Printing Office, Post Office Box 37082, Washington, DC 20013-7082, 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 be obtained by writing NTIS, 5285 Port Royal Road, Springfield, VA 22161.
account, where practical, industry-wide operating ex-perience.
Adjustments must be made where necessary to ensure that the objective of. preventing failures of SSCs through maintenance is appropriately balanced against the objective of minimizing unavailability of SSCs because of monitoring or preventive mainte-nance. In performing monitoring and preventive maintenance activities, an assessment of the total plant equipment that is out of service should be taken into account to determine the overall effect on per-formance of safety functions.
Paragraph (b) of 10 CFR 50.65 states that the scope of the monitoring program specified in paragraph (a) (1) is to include safety-related and nonsafety-related SSCs, as follows: (1) Safety-related structures, systems, or compo-nents that are relied upon to remain functional during and following design basis events to en-sure the integrity of the reactor coolant pressure boundary, 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 the 10 CFR Part 100 guidelines.
(2) Nonsafety-related structures, systems, or components (i) That are relied upon to mitigate accidents or transients or are used in plant emergency operating procedures (EOPs); or (ii) Whose failure could prevent safety-related structures, systems, and components from fulfilling their safety-related function;
or (iii) Whose failure could cause a reactor scram or actuation of a safety-related system.Paragraph (c) of 10 CFR 50.65 states that the rule provisions are to be implemented by licensees no later than July 10, 1996.Any information collection activities mentioned in this regulatory guide are contained as requirements in 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 the Office of Management and Budget, Approval No.3150-0011.
B. DISCUSSION
The objective of 10 CFR 50.65 (referred to here-after as the maintenance rule or the rule) is to require monitoring of the overall continuing effectiveness of licensee maintenance programs to ensure that: (1) safety-related and certain nonsafety-related SSCs are capable of performing their intended functions and (2) for nonsafety-related equipment, failures will not occur that prevent the fulfillment of safety-related functions, and failures resulting in scrams and unnec-essary actuations of safety-related systems are mini-mized.The extent of monitoring may vary from system to system depending on the system's importance to risk. Some monitoring at the component level may be necessary;
however, it is envisioned that most of the monitoring could be done at the plant, system, or train level. For example, for less risk-significant sys-tems, indicators of system reliability (where sufficient performance data exist) and availability may be all that is necessary.
For more risk-significant systems, some parameter trending, beyond that already re-quired by NRC requirements to provide early warning of degradation, may also be necessary for critical components whose unavailability causes a system train to be unavailable or whose failure is otherwise unacceptable.
Rather than monitoring the many SSCs that could cause plant scrams, the licensee may choose to establish a performance indicator for un-planned automatic scrams and, where scrams caused by equipment failures have been problematic or where such scrams are anticipated, the licensee may choose to monitor those initiators most likely to cause scrams.It is intended that activities currently being con-ducted by licensees, such as technical specification surveillance testing, can satisfy monitoring require-ments. Such activities could be integrated with, and provide the basis for, the requisite level of monitor-ing. Consistent with the underlying purposes of the rule, maximum flexibility should be offered to licen-sees in establishing and modifying their monitoring activities.
Licensees are encouraged to consider the use of reliability-based methods for developing the preven-tive maintenance programs covered under paragraph (a) (2) of the rule; however, the use of such methods is not required.With regard to the scope of the maintenance rule, as stated in paragraph (b) of the rule, it is un-derstood that balance of plant (BOP) SSCs may have been designed and built with normal industrial quality and may not meet the standards in Appendix B to 10 CFR Part 50. It is not the intent to require licen-sees to generate paperwork to document the basis for the design, fabrication, and construction of BOP equipment.
Each licensee's maintenance efforts should mini-mize failures in both safety-related and BOP SSCs that affect safe operation of the plant. The effective- ness of maintenance programs should be maintained for the operational life of the facility.As noted in the Regulatory Position, there may be a need to address maintenance activities that occur in the switchyards that could directly affect plant op-erations.
Plant management should be aware of and have the ability to control these activities.
1.160-2 The regulatory guidance is intended to provide flexibility for a licensee to structure its maintenance program in accordance with the safety significance of S those SSCs within the scope of the rule.The nuclear industry has developed a document that provides guidance to licensees regarding implementation of the maintenance rule. This docu-ment has been prepared by NUMARC. A verification and validation (V&V) effort was conducted by NUMARC, with NRC staff observation, to test the guidance document on several representative systems.A number of changes were made to the NUMARC guidance document based on the results of the V&V effort. The NRC staff reviewed this document and found that it provides acceptable guidance to licensees.
Certain requirements for a renewed license under 10 CFR Part 54 may be satisfied by taking credit for activities required by the maintenance rule. However, the renewal rule requires (10 CFR 54.21(a)(6)(iii)), among other provisions, that an effective program must be implemented by the facility operating pro-cedures and reviewed by the on-site review commit-tee. The maintenance rule does not have these requirements.
Industry and NRC-sponsored probabilistic risk analyses (PRAs) have shown the risk significance of S emergency ac power sources. The station blackout rule (10 CFR 50.63) required plant-specific coping analyses to ensure that a plant could withstand a total loss of ac power for a specified duration and to deter-mine appropriate actions to mitigate the effects of a total 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 regulatory guidance but reserved the option to later adopt the outcome of Generic Issue B-56 resolution, (2) stated that they had or will implement an equivalent pro-gram, or (3) endorsed the program embodied in NUMARC 87-00, Revision 1, August 1991, "Guide-lines and Technical Bases for NUMARC Initiatives Addressing Station Blackout at Light Water Reactors" (i.e., maintain the emergency diesel generator target reliability of 0.95 or 0.975). Subsequently, utilities docketed commitments to maintain their selected tar-get reliability values. Those values could be used as a goal 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 use plant-specific data concerning unavailability due to maintenance.
Therefore, emergency diesel generator S unavailability due to maintenance, as assumed in a plant-specific individual plant examination (IPE)analysis, could also be used as the basis for a goal or performance criterion under the maintenance rule.Section (a) (3) of the maintenance rule requires that adjustments be made where necessary to ensure that the objective of preventing failures of SSCs through maintenance is appropriately balanced against the objective of minimizing unavailability of SSCs due to monitoring or preventive maintenance.
Therefore, plant-specific emergency diesel generator reliability and unavailability should be monitored as goals under 10 CFR 50.65(a)(1)
or established as performance criteria under the plant's preventive maintenance program under 10 CFR 50.65(a)(2), taking into account the objectives of 10 CFR 50. 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.
Emergency diesel generator performance criteria for reliability would be met by the absence of a maintenance- preventable failure or the occurrence of a single maintenance-preventable failure followed by appro-priate root cause determination and corrective action.Performance criteria for unavailability would be met by having fewer unavailable hours, on a rolling 1-year basis, than required by the established performance criteria.If any performance criterion is not met, or a second emergency diesel generator maintenance- preventable failure occurs, it is expected that the li-censee would establish goals and monitor subsequent emergency diesel generator performance under 10 CFR 50.65(a)(1), consistent with an appropriate balance between emergency diesel generator reliabil-ity and unavailability.
The emergency diesel generator reliability per-formance criteria or goals selected for implementing the intent of 10 CFR 50.63 for coping with station blackout could be monitored through the use of the triggers 3 and the monitoring methods described in Appendix 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.2.4.4 of NUMARC 87-00, which will be addressed sepa-rately by the NRC). An acceptable unavailability goal could be to have fewer hours unavailable (on a rolling 1-year basis) than the number of hours established as acceptable by the licensee.C. REGULATORY
POSITION The 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 affect 3 The triggers are intended to indicate when emergency diesel generator performance problems exist such that additional monitoring or corrective action is necessary.
It is recognized that it is not practical to demonstrate by statistical analysis that 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 electrical distribution equipment out to the first inter-tie with the off-site distribution system (i.e., equipment in the switchyard)
should be considered for comparison with 10 CFR 50.65(b) for inclusion under the scope of the maintenance rule.NUMARC 93-01, dated May 1993, "Industry Guideline for Monitoring the Effectiveness of Mainte-nance at Nuclear Power Plants," 4 provides methods acceptable to the NRC staff for complying with the provisions of 10 CFR 50.65. NUMARC 93-01 refer-ences other documents, but NRC's endorsement of NUMARC 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 emergency 4 Copies are available for inspection or copying for a fee from the NRC Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing address is Mail Stop LL-6, Washington, DC 20555; phone (202) 634-3273;
fax (202) 634-3343.diesel generator reliability and availability, describes an acceptable method to establish emergency diesel generator performance criteria and/or goals and sub-sequently monitor emergency diesel generator per-formance.
D. IMPLEMENTATION
The purpose of this section is to provide informa-tion to applicants and licensees regarding the NRC staff's plans for using this regulatory guide.Except in those cases in which the applicant or licensee proposes an acceptable alternative method for complying with specified portions of the Commis-sion's regulations, the methods described in the guide will be used in the evaluation of submittals for construction permits and operating licenses (as appro-priate) and will be used to evaluate the effectiveness of maintenance activities of licensees who are re-quired to comply with 10 CFR 50.65. The guide will also 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 ANALYSES Separate regulatory and backfit analyses were prepared for this Regulatory Guide 1.160. They are available, in the file for Regulatory Guide 1.160, for inspection or copying for a fee in the Commission's Public Document Room, 2120 L Street NW., Washington, DC; the PDR's mailing address is Mail Stop LL-6, Washington, DC 20555; phone (202)634-3273;
fax (202)634-3343.
1.160-5 Federal Recycling Program I-0 UNITED STATES NUCLEAR REGULATORY
COMMISSION
WASHINGTON, D.C. 20555-0001 FIRST CLASS MAIL POSTAGE AND FEES PAID USNRC PERMIT NO. G-67 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE, $300