Resolution of Generic Safety Issues: Issue 168: Environmental Qualification of Electrical Equipment (Rev. 3) ( NUREG-0933, Main Report with Supplements 1–34 )
As discussed in SECY-93-049,380 the staff reviewed significant license renewal issues and found that several related to environmental qualification (EQ). A key aspect of these issues was whether the licensing bases, particularly for older plants whose licensing bases differ from newer plants, should be reassessed or enhanced in connection with license renewal or whether they should be reassessed for the current license term. The staff concluded that differences in EQ requirements constituted a potential generic issue which should be evaluated for backfit independent of license renewal.1518
In the staff's development of an interoffice action plan to address upgrading EQ requirements for older plants during the current licensing term, the staff evaluated the technical adequacy of EQ requirements. As part of this evaluation, the staff reviewed tests of qualified cables performed by SNL, under contract with the NRC. The purpose of these tests was to determine the effects of aging on cable products used in nuclear power plants. After accelerated aging, some of the environmentally-qualified cables either failed or exhibited marginal insulation resistance during accident testing, indicating that qualification of some electric cables may have been non-conservative. Although the SNL tests may have been more severe than required by NRC regulations, the test results raised questions with respect to the EQ and accident performance capability of certain artificially-aged cables. Depending on the application, failure of these cables during or following design basis events could affect the performance of safety functions in nuclear power plants.
Based on the existence of an ongoing action plan to address the safety concern and the NRR decision1517 to pursue its resolution, the issue was considered nearly-resolved in April 1993. It was later given a HIGH priority ranking in SECY-98-166.1718 In accordance with an RES evaluation,1564 the impact of a license renewal period of 20 years was to be considered in the resolution of the issue.
Accelerated aging tests on electrical equipment showed that some environmentally qualified cables either failed or exhibited marginal insulation resistance. Failure of these cables during or following a design-basis event could affect the performance of safety functions. After review and analysis of six LOCA tests, condition-monitoring tests on I&C cables, and information provided by the nuclear industry, the staff concluded that the existing equipment qualification process was adequate to ensure that I&C cables would perform their intended function. Regulatory Issue Summary 2003-091852 was issued in May 2003, and the issue was RESOLVED with no new requirements for licensees.1853