Regulatory Guide 1.160
| ML003740016 | |
| Person / Time | |
|---|---|
| Issue date: | 01/31/1995 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| RG-1.160 Rev 1 | |
| Download: ML003740016 (4) | |
U.S. NUCLEAR REGULATORY COMMISSION
Revision 1 January 1995 REGULATORY GUIDE
OFFICE OF NUCLEAR REGULATORY RESEARCH
REGULATORY GUIDE 1.160
(Draft Issued as DG-1031)
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 Nuclear 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, 1 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 reliability of. safety equipment. In addition, good maintenance is also important in providing assurance that failures of other than safety-related structures, systems, and components (SSCs) that could initiate or adversely affect a transient or accident are minimized.
Minimizing challenges to safety systems is consistent with the Commission's defense-in-depth philosophy.
Maintenance is also important to ensure that design INRC Memorandum to All Commissioners from J. Taylor on
"Maintenance Rulemaking," June 27, 1991. Copies are avail able 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 L-6, Washington, DC
20555; phone (202)634-3273; fax (202) 634-3343.
USNRC REGULATORY GUIDES
Regulatory Guides are Issued to describe and make available to the public such Information as methods acceptable to the NRC staff for Implement Ing specif1c parts of the Conmnission's regulations, techniques used by the staff in evaluating specific probiems or postulated accidents, and data needed by the NRO staff In Its review of appi*cations for permits and licenses. Regulatory Guides are not substitutes for regulations, and corn p=lance with them Is not required. Methods and solutions different from those set out In the guides will be acceptable If they provide a basis for the findings requisite to the Issuance or continuance of a permit or license by the Commlssion.
This guide was Issued after consideration of comments received from the public. Comnments and suggestions for Improvements In these guides are encouraged at all times, ard guides will be revised, as appropriate, to aoomrrnodate commnents and to reflect new information or experience.
Written iomments may be submitted to the Rules Review and Directives Branch, DFIPS, ADM, U.S. Nuclear Regulatory Commission, Washing ton, DO 20555-0001.
assumptions and margins in the original design basis are maintained and are not unacceptably degraded.
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 commensurate with safety and, where practical, take into account 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 required where it has been demonstrated that the performance 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 shall be evaluated at least every refueling cycle provided the interval between evaluations does not 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 S. Products
7. Transportation S. Occupational Health
9. Antitrust and Financial Review
1
0. General C
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Government Printing Office, P.O. Box 37082, Washington, DO
20402-0328, telephone (202)512-2249.
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. 628 Port Royal Road, Springfield, VA 22161.
Thle guides are Issued In -the following ton broad divisions:.
exceed 24 months. The evaluations shall be conducted taking into account, where practical, industry-wide operating experience." 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 maintenance. 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 performance 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 components that are relied upon to remain functional during and following design basis events to ensure the integrity of the reactor coolant pressure boundary, the capability to shut down the reactor and maintain it in a safe shutdown condition, and the capability to prevent or mitigate the consequences of accidents that could result in potential offsite exposure comparable to the 10 CFR Part 100
guidelines.
(2) Nonsafety-related structures, systems, or components T*(-hat 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.
The information collections mentioned in this regulatory guide are covered by the requirements in
10 CFR Part 50, which were approved by the Office of Management and Budget, approval number
3150-0011.
B. DISCUSSION
The objective of 10 CFR 50.65 (referred to hereafter 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 unnecessary actuations of safety-related systems are minimized.
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 systems, 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 required 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 unplanned 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 conducted by licensees, such as technical specification surýeillance testing, be used to the maximum extent practical to satisfy monitoring requirements. Such activities could be integrated with, and provide the basis for, the requisite level of monitoring. Consistent with the underlying purposes of the rule, maximum flexibility should be offered to licensees in establishing and modifying their monitoring activities.
Licensees are encouraged to consider the use of reliability-based methods for developing the preventive 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 understood 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 licensees to generate paperwork to document the basis for the design, fabrication, and construction of BOP
equipment (i.e., backfitting 10 CFR Part 50 Appendix B requirements to BOP equipment is not required).
Each licensee's maintenance efforts should minimize failures in both safety-related and BOP SSCs that affect safe operation of the plant. The effectiveness of maintenance programs should be maintained for the operational life of the facility.
1.160-2
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 operations. Plant management should be aware of and have the ability to control these activities.
The regulatory guidance is intended to provide flexibility for a licensee to structure its maintenance program in accordance with the safety significance of 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, NUMARC
93-01, "Industry Guideline for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants" (May 1993).2 This document 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. Licensees may use methods other than those provided in NUMARC
93-01 to meet the intent of the maintenance rule.
However, the NRC will determine acceptability of other methods on a case-by-case basis.
Industry and NRC-sponsored probabilistic risk analyses (PRAs)_ have shown the risk significance ol 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 tota:
loss of ac power for a specified duration and tc determine appropriate actions to mitigate the effects o, a total loss of ac power. During the station blackoul reviews, most licensees (1) made a commitment tc implement an emergency diesel generator (EDG
reliability program in accordance with NRC regulator.
guidance but reserved the option to later adopt thi outcome of Generic Issue B-56 resolution and (2 stated that they had or will implement an equivalen program.
Subsequently, utilities docketei commitments to maintain their selected targe reliability values (i.e., maintain the emergency diese generator target reliability of 0.95 or 0.975). Thos values could be used as a goal or as a performanc criterion for emergency diesel generator reliabilit under the maintenance rule.
Additionally, emergency diesel generatc unavailability values were assumed in plant-specifi individual plant examination (IPE) analyse
s. Thes
2Coples 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.
values should be compared to the plant-specific emergency diesel generator unavailability data regularly monitored and reported as industry-wide plant performance information. These values could also be used as the basis for a goal or performance criterion under the maintenance rule.
All SSCs within the scope of the maintenance rule, including the emergency diesel generators, are required to be handled under either 10 CFR
50.65(a)(1) where they are subject to monitoring against licensee-establishect goals or under 10 CFR
50.65(a)(2) where they are subject to monitoring against licensee-established performance criteria as described in NUMARC 93-01. Additionally, periodic evaluations under 10 CFR 50.56(a) (3) that balance reliability and unavailability and assess the impact of removing SSCs from service on overall plant safety must be performed.
Performance criteria for emergency diesel generators (and the support systems vital to their functioning) would be met by the absence of a repetitive maintenance-preventable functional failure (MPFF), by not exceeding the established reliability or unavailability criterion, or by the occurrence of a single maintenance-preventable failure followed by appropriate cause determination and corrective action. SSCs being handled under 10
CFR 50.65(a)(2) would be dispositioned to 10 CFR
50.65 (a) (1) if the performance criteria are not met or if a repetitive maintenance-preventable functional failure occurs. Once under 10 CFR -50.65(a)(1), the SSCs would be subject to goal setting and monitoring.
All SSCs within the scope of the rule (i.e., those under
10 CFR 50.65(a)(1) and (a)(2)) are subject to the requirements of 10 CFR 50.65(a)(3), including (1)
f periodic evaluation,
(2) balancing reliability and t
unavailability, and (3) assessing the impact on plant
)
safety of taking equipment out of service for maintenance.
C. REGULATORY POSITION
)
The' scope of monitoring efforts under the maintenance rule, as defined in 10 CFR 50.65(b),
- t encompasses those SSCs that directly and significantly
,I
affect plant operations, regardless of what organization e
actually performs the maintenance activities.
e Maintenance activities that occur in the switchyard can y
directly affect plant operations; and as a result, electrical distribution equipment out to the first inter-tie with the off-site distribution system (i.e.,
ir equipment in the switchyard) should be included as ic defined in 10 CFR 50.65(b).
NUMARC 93-01 provides methods acceptable to the NRC staff for complying with the provisions of
10 CFR 50.65. NUMARC 93-01 references other documents, but NRC's endorsement of NUMARC
93-01 should not be considered as endorsement of the referenced documents.
1.160-3
D. IMPLEMENTATION
The purpose of this section is to provide information to applicants and licensees regarding the NRC staff's plans for using this regulatory guide.
Except in those cases in which an applicant or licensee proposes an acceptable alternative method for complying with specified portions of the Commission's regulations, the methods described in this guide will be used in the evaluation of the effectiveness of maintenance activities of licensees who are required to comply with 10 CFR 50.65. The guide will also be used to evaluate the effectiveness of emergency diesel generator maintenance activities associated with compliance with 10 CFR 50.63.
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.
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