Resolution of Generic Safety Issues: Issue 4: End-of-Life and Maintenance Criteria ( NUREG-0933, Main Report with Supplements 1–34 )
The exact scope of this issue is unclear and SPEB has used the following interpretation in its evaluation. Based on an ACRS-sponsored review of LERs,4 it was concluded that the criteria used for setting up equipment maintenance intervals and determining equipment life expectancy required further review and evaluation. It was believed that these factors were significant contributors to the component failures in equipment such as valves, pumps, etc.
The failure of safety-related components can lead to loss of reactor coolant pressure boundary integrity or loss of safety functions. Such failures possibly could be reduced by using end-of-life data and improved periodic maintenance criteria.
Available material aging information, coupled with actual plant operating and maintenance experience, could be factored into the process of determining the end-of-life for various components as well as determining appropriate maintenance periodicity.
This issue has been addressed as part of the NRC overall equipment qualification program. Existing and proposed requirements include both end-of-life and maintenance considerations.
Specifically, NUREG-058819 and the DOR Guidelines118 (both endorsed by Commission Order CLI-80-2146) require that qualification programs for electrical equipment should identify materials susceptible to aging effects and establish a schedule for periodically replacing the equipment and/or materials.
IEEE 323-1974,90 the industry standard upon which the above requirements are based, includes a number of paragraphs addressing this issue. For example, paragraph 6.4.2 on "Operating History" states that, in order to use operating history information for establishing qualification, the designer must have documentation which includes recording and analysis of all failures and trends that occurred during the operating period and a log of all periodic maintenance and inspections.
The proposed Revision 1 to Regulatory Guide 1.8991 (which is to provide guidelines for meeting the Equipment Qualification Rule and endorses IEEE 323-197490) was drafted in February 1982 and includes a number of specific positions on the subject of equipment end-of-life and maintenance. The Regulatory Guide positions are:
|7.g.||The qualified life of the equipment (or component, as applicable) and the basis for its selection be defined and documented.|
|7.h.||Qualified life should be established on the basis of the severity of the testing performed, the conservatisms employed in the extrapolation of data, the operating history, and the other methods that may reasonably be used. All assumptions should be documented.|
|7.i.||An ongoing program to review surveillance and maintenance records to identify age-related degradations should be established.|
|7.j.||A component maintenance and replacement schedule that includes consideration of aging characteristics of the installed components should be established.|
|8.||Sections 6.4 and 6.5 of IEEE 323-197490 discuss qualification by operating experience and by analysis, respectively. The adequacy of these methods should be evaluated on the basis of the quality and detail of the information available in support of the assumptions made. Operating experience and analysis based on test data may be used where testing is precluded by the physical size of the equipment or the state of the art of testing. When the analysis method is employed because of the physical size of the equipment, tests on vital components of the equipment should be provided.|
The NRC is in the process of codifying (via rulemaking) similar requirements for mechanical equipment.
The NRC Standard Review Plan,11 Section 3.11, "Environmental Qualification of Mechanical and Electrical Equipment," includes requirements for maintenance/ surveillance programs for equipment located in mild environments. Specifically,it is required that "the maintenance/surveillance program data shall be reviewed periodically (not more than every 18 months) to ensure that the design qualified life has not suffered thermal or cyclic degradation resulting from the accumulated stresses triggered by the abnormal environmental conditions and the normal wear due to its service condition. Engineering judgment shall be used to modify the replacement program and/or replace the equipment as deemed necessary."
Therefore, SPEB believes that present NRC criteria require that each licensee have a comprehensive equipment qualification program including a maintenance program which is based on both qualified life and operating history.
Based on the above cited requirements and the overall Equipment Qualification Program Plan in SECY-81-504,92 SPEB concludes that this issue has been adequately addressed. Regulatory Guides 1.33225 and 1.89,91 Revision 1, contain criteria for maintenance and surveillance programs to ensure operability throughout the life of the plant for safety-related mechanical and electrical equipment located in harsh or mild environments.384 Thus, this issued has been RESOLVED.