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
graded. Therefore, nuclear power plant maintenance is clearly important in protecting the public health The NRC published the maintenance rule on and safety.
July 10, 1991, as Section 50.65, "Requirements for Monitoring the Effectiveness of Maintenance at Nu- Paragraph (a)(1) of 10 CFR 50.65 requires that clear Power Plants," of 10 CFR Part 50, "Domestic power reactor licensees monitor the performance or Licensing of Production and Utilization Facilities." condition of SSCs against licensee-established goals in The Commission's determination that a maintenance a manner sufficient to provide reasonable assurance rule was needed arose from the conclusion that that such SSCs are capable of fulfilling their intended proper maintenance is essential to plant safety. As functions. Such goals are to be established commen- discussed in the regulatory analysis for this rule,' surate with safety and, where practical, take into ac- there is a clear link between effective maintenance count industry-wide operating experience. When the and safety as it relates to such factors as the number performance or condition of an SSC does not meet of transients and challenges to safety systems and the established goals, appropriate corrective action must associated need for operability, availability, and reli- be taken.
ability of safety equipment. In addition, good mainte- nance is also important in providing assurance that Paragraph (a)(2) of 10 CFR 50.65 states that failures of other than safety-related structures, sys- monitoring as specified in paragraph (a) (1) is not re- tems, and components (SSCs) that could initiate or quired where it has been demonstrated that the per- adversely affect a transient or accident are mini- formance or condition of an SSC is being effectively mized. Minimizing challenges to safety systems is con- controlled through the performance of appropriate sistent with the Commission's defense-in-depth phi- preventive maintenance, such that the SSC remains losophy. Maintenance is also important to ensure that capable of performing its intended function.
design assumptions and margins in the original design Paragraph (a)(3) of 10 CFR 50.65 requires that basis are maintained and are not unacceptably de- performance and condition monitoring activities and associated goals and preventive maintenance activities
1 NRC Memorandum to All Commissioners from J. Taylor on must be evaluated at least annually, 2 taking into
"Maintenance Rulemaking," June 27, 1991. Copies are 2 available for inspection or copying for a fee from the NRC As of the publication of this regulatory guide, a modification Public Document Room at 2120 L Street NW., Washington, to the maintenance rule is in preparation that would change DC; the PDR's mailing address is Mail Stop LL-6, Washing- the evaluation interval to every refueling outage but not to ex- ton, DC 20555; phone (202) 634-3273; fax (202) 634-3343. ceed 2 years.
USNRC REGULATORY GUIDES Written comments may be submitted to the Regulatory Publications Branch, DFIPS, ADM, U.S. Nuclear Regulatory Commission, Washing- Regulatory Guides are Issued to describe and make available to the pub- ton, DC 20555.
lic such information as methods acceptable to the NRC staff for imple- menting specific parts of the Commission's regulations, techniques The guides are issued in the following ten broad divisions:
used by the staff in evaluating specific problems or postulated acci- 1. Power Reactors 6. Products dents, and data needed by the NRC staff in its review of applications for 2. Research and Test Reactors 7. Transportation permits and licenses. Regulatory Guides are not substitutes for regula- 3. Fuels and Materials Facilities 8. Occupational Health tions, and compliance with them is not required. Methods and solutions 4. Environmental and Siting 9. Antitrust and Financial Review different from those set out in the guides will be acceptable if they pro- 5. Materials and Plant Protection 10. General vide a basis for the findings requisite to the issuance or continuance of a permit or license by the Commission. 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.
This guide was issued after consideration of comments received from Government Printing Office, Post Office Box 37082, Washington, DC
20013-7082, telephone (202)512-2249 or (202)512-2171.
the public. Comments and suggestions for improvements in these guides are encouraged at all times, and guides will be revised, as ap- Issued guides may also be purchased from the National Technical Infor- propriate, to accommodate comments and to reflect new information or mation Service on a standing order basis. Details on this service may be experience. obtained by writing NTIS, 5285 Port Royal Road, Springfield, VA 22161.
account, where practical, industry-wide operating ex- essary actuations of safety-related systems are mini- perience. Adjustments must be made where necessary mized.
to ensure that the objective of. preventing failures of SSCs through maintenance is appropriately balanced The extent of monitoring may vary from system against the objective of minimizing unavailability of to system depending on the system's importance to SSCs because of monitoring or preventive mainte- risk. Some monitoring at the component level may be nance. In performing monitoring and preventive necessary; however, it is envisioned that most of the maintenance activities, an assessment of the total monitoring could be done at the plant, system, or plant equipment that is out of service should be taken train level. For example, for less risk-significant sys- into account to determine the overall effect on per- tems, indicators of system reliability (where sufficient formance of safety functions. Paragraph (b) of performance data exist) and availability may be all
10 CFR 50.65 states that the scope of the monitoring that is necessary. For more risk-significant systems, program specified in paragraph (a) (1) is to include some parameter trending, beyond that already re- safety-related and nonsafety-related SSCs, as follows: quired by NRC requirements to provide early warning of degradation, may also be necessary for critical
(1) Safety-related structures, systems, or compo- components whose unavailability causes a system nents that are relied upon to remain functional train to be unavailable or whose failure is otherwise during and following design basis events to en- unacceptable. Rather than monitoring the many SSCs sure the integrity of the reactor coolant pressure that could cause plant scrams, the licensee may boundary, the capability to shut down the reac- choose to establish a performance indicator for un- tor and maintain it in a safe shutdown condition, planned automatic scrams and, where scrams caused and the capability to prevent or mitigate the con- by equipment failures have been problematic or sequences of accidents that could result in po- where such scrams are anticipated, the licensee may tential offsite exposure comparable to the choose to monitor those initiators most likely to cause
10 CFR Part 100 guidelines. scrams.
(2) Nonsafety-related structures, systems, or It is intended that activities currently being con- components ducted by licensees, such as technical specification surveillance testing, can satisfy monitoring require- (i) That are relied upon to mitigate accidents ments. Such activities could be integrated with, and or transients or are used in plant emergency provide the basis for, the requisite level of monitor- operating procedures (EOPs); or ing. Consistent with the underlying purposes of the rule, maximum flexibility should be offered to licen- (ii) Whose failure could prevent safety-related sees in establishing and modifying their monitoring structures, systems, and components from activities.
fulfilling their safety-related function; or Licensees are encouraged to consider the use of (iii) Whose failure could cause a reactor scram reliability-based methods for developing the preven- or actuation of a safety-related system. tive maintenance programs covered under paragraph (a) (2) of the rule; however, the use of such methods Paragraph (c) of 10 CFR 50.65 states that the is not required.
rule provisions are to be implemented by licensees no later than July 10, 1996. With regard to the scope of the maintenance rule, as stated in paragraph (b) of the rule, it is un- Any information collection activities mentioned derstood that balance of plant (BOP) SSCs may have in this regulatory guide are contained as requirements been designed and built with normal industrial quality in 10 CFR Part 50, which provides the regulatory ba- and may not meet the standards in Appendix B to sis for this guide. The information collection require- 10 CFR Part 50. It is not the intent to require licen- ments in 10 CFR Part 50 have been approved by the sees to generate paperwork to document the basis for Office of Management and Budget, Approval No. the design, fabrication, and construction of BOP
3150-0011. equipment.
B. DISCUSSION
Each licensee's maintenance efforts should mini- mize failures in both safety-related and BOP SSCs The objective of 10 CFR 50.65 (referred to here- that affect safe operation of the plant. The effective- after as the maintenance rule or the rule) is to require ness of maintenance programs should be maintained monitoring of the overall continuing effectiveness of for the operational life of the facility.
licensee maintenance programs to ensure that:
(1) safety-related and certain nonsafety-related SSCs As noted in the Regulatory Position, there may are capable of performing their intended functions be a need to address maintenance activities that occur and (2) for nonsafety-related equipment, failures will in the switchyards that could directly affect plant op- not occur that prevent the fulfillment of safety-related erations. Plant management should be aware of and functions, and failures resulting in scrams and unnec- have the ability to control these activities.
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The regulatory guidance is intended to provide Section (a) (3) of the maintenance rule requires flexibility for a licensee to structure its maintenance that adjustments be made where necessary to ensure S program in accordance with the safety significance of those SSCs within the scope of the rule.
that the objective of preventing failures of SSCs through maintenance is appropriately balanced against the objective of minimizing unavailability of The nuclear industry has developed a document SSCs due to monitoring or preventive maintenance.
Therefore, plant-specific emergency diesel generator that provides guidance to licensees regarding reliability and unavailability should be monitored as implementation of the maintenance rule. This docu- ment has been prepared by NUMARC. A verification goals under 10 CFR 50.65(a)(1) or established as performance criteria under the plant's preventive and validation (V&V) effort was conducted by maintenance program under 10 CFR 50.65(a)(2),
NUMARC, with NRC staff observation, to test the taking into account the objectives of 10 CFR
guidance document on several representative systems.
50. 65 (a) (3).
A number of changes were made to the NUMARC
guidance document based on the results of the V&V Under 10 CFR 50.65(a)(2), the utility would es- effort. The NRC staff reviewed this document and tablish performance criteria for both emergency die- found that it provides acceptable guidance to sel generator reliability and unavailability. Emergency licensees. diesel generator performance criteria for reliability would be met by the absence of a maintenance- Certain requirements for a renewed license under preventable failure or the occurrence of a single
10 CFR Part 54 may be satisfied by taking credit for maintenance-preventable failure followed by appro- activities required by the maintenance rule. However, priate root cause determination and corrective action.
the renewal rule requires (10 CFR 54.21(a)(6)(iii)), Performance criteria for unavailability would be met among other provisions, that an effective program by having fewer unavailable hours, on a rolling 1-year must be implemented by the facility operating pro- basis, than required by the established performance cedures and reviewed by the on-site review commit- criteria.
tee. The maintenance rule does not have these If any performance criterion is not met, or a requirements.
second emergency diesel generator maintenance- preventable failure occurs, it is expected that the li- Industry and NRC-sponsored probabilistic risk censee would establish goals and monitor subsequent S analyses (PRAs) have shown the risk significance of emergency ac power sources. The station blackout rule (10 CFR 50.63) required plant-specific coping emergency diesel generator performance under
10 CFR 50.65(a)(1), consistent with an appropriate balance between emergency diesel generator reliabil- analyses to ensure that a plant could withstand a total ity and unavailability.
loss of ac power for a specified duration and to deter- mine appropriate actions to mitigate the effects of a The emergency diesel generator reliability per- total loss of ac power. During the station blackout re- formance criteria or goals selected for implementing views, most licensees (1) made a commitment to im- the intent of 10 CFR 50.63 for coping with station plement an emergency diesel generator (EDG) reli- blackout could be monitored through the use of the ability program in accordance with NRC regulatory triggers3 and the monitoring methods described in guidance but reserved the option to later adopt the Appendix D of NUMARC 87-00, Revision 1, outcome of Generic Issue B-56 resolution, (2) stated "Guidelines and Technical Bases for NUMARC In- that they had or will implement an equivalent pro- itiatives Addressing Station Blackout at LWRs,"
gram, or (3) endorsed the program embodied in August 1991 (except for triggers and testing for
"problem diesels" as described in paragraph D.2.4.4 NUMARC 87-00, Revision 1, August 1991, "Guide- lines and Technical Bases for NUMARC Initiatives of NUMARC 87-00, which will be addressed sepa- Addressing Station Blackout at Light Water Reactors" rately by the NRC). An acceptable unavailability goal (i.e., maintain the emergency diesel generator target could be to have fewer hours unavailable (on a rolling reliability of 0.95 or 0.975). Subsequently, utilities 1-year basis) than the number of hours established as docketed commitments to maintain their selected tar- acceptable by the licensee.
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 rul
e.
C. REGULATORY POSITION
The scope of monitoring efforts under the main- When utilities were performing their plant- tenance rule, as defined in 10 CFR 50.65(b), encom- specific coping analyses, they were allowed to use passes those SSCs that directly and significantly affect plant-specific data concerning unavailability due to S
3 The triggers are intended to indicate when emergency diesel maintenance. Therefore, emergency diesel generator generator performance problems exist such that additional unavailability due to maintenance, as assumed in a monitoring or corrective action is necessary. It is recognized plant-specific individual plant examination (IPE) that it is not practical to demonstrate by statistical analysis that conformance to the trigger values will ensure the attain- analysis, could also be used as the basis for a goal or ment of high reliability, with a reasonable degree of confi- performance criterion under the maintenance rule. dence, of individual EDG units.
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plant operations, regardless of what organization actu- diesel generator reliability and availability, describes ally performs the maintenance activities. Mainte- an acceptable method to establish emergency diesel nance activities that occur in the switchyard can di- generator performance criteria and/or goals and sub- rectly affect plant operations, and as a result electrical sequently monitor emergency diesel generator per- distribution equipment out to the first inter-tie with formance.
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
D. IMPLEMENTATION
maintenance rule.
The purpose of this section is to provide informa- NUMARC 93-01, dated May 1993, "Industry tion to applicants and licensees regarding the NRC
Guideline for Monitoring the Effectiveness of Mainte- staff's plans for using this regulatory guide.
nance at Nuclear Power Plants," 4 provides methods acceptable to the NRC staff for complying with the Except in those cases in which the applicant or provisions of 10 CFR 50.65. NUMARC 93-01 refer- licensee proposes an acceptable alternative method ences other documents, but NRC's endorsement of for complying with specified portions of the Commis- NUMARC 93-01 should not be considered as en- sion's regulations, the methods described in the guide dorsement of the referenced documents.
will be used in the evaluation of submittals for The example in NUMARC 93-01, Sec- construction permits and operating licenses (as appro- tion 12.2.4, which refers to optimizing emergency priate) and will be used to evaluate the effectiveness of maintenance activities of licensees who are re-
4 Copies are available for inspection or copying for a fee from quired to comply with 10 CFR 50.65. The guide will the NRC Public Document Room at 2120 L Street NW., also be used to evaluate the effectiveness of emer- Washington, DC; the PDR's mailing address is Mail Stop LL-6, Washington, DC 20555; phone (202) 634-3273; fax gency diesel generator maintenance activities associ-
(202) 634-3343. ated with compliance with 10 CFR 50.63.
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REGULATORY AND BACKFIT ANALYSES
Separate regulatory and backfit analyses were Public Document Room, 2120 L Street NW.,
prepared for this Regulatory Guide 1.160. They are Washington, DC; the PDR's mailing address is Mail available, in the file for Regulatory Guide 1.160, for Stop LL-6, Washington, DC 20555; phone inspection or copying for a fee in the Commission's (202)634-3273; fax (202)634-3343.
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