Resolution of Generic Safety Issues: Issue 166: Adequacy of Fatigue Life of Metal Components (Rev. 2) ( NUREG-0933, Main Report with Supplements 1–34 )
The issue of fatigue of metal components was identified in SECY-93-049380 following the staff's senior management review of key license renewal issues. The recommendation to treat fatigue of metal components as a generic safety issue was approved1097 by the Commission in June 1993.
Select portions of the STS contain requirements to monitor cumulative fatigue usage for critical components associated with the safety injection systems. In addition, STS Section 5.0, "Design Features," requires the tracking of certain transients to ensure that design bases are not exceeded. However, many plants do not have the STS or any requirement to monitor for fatigue limits. The resolution of Issue 78 was expected to determine the degree to which fatigue limit monitoring was necessary, address fatigue adequacy in general, and recommend actions, if any, to be taken by the staff. However, during the Commission meetings on promulgating requirements for license renewal, it became increasingly apparent that the adequacy of fatigue life of metal components should not be conducted solely for license renewal but should also be conducted for existing operating plants. Therefore, NRR took1517 the lead responsibility for addressing this issue for operating plants. The resolution of Issue 78 was expected to provide essential technical information for the resolution of Issue 166.
This issue was considered nearly-resolved based on Commission approval1097 of the staff's recommendation to pursue its resolution. 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; however, Issue 190 was established to address this subject separately.1517
In resolving the issue, consideration was given to the staff's work under the Fatigue Action Plan (FAP), the completion of which was documented in SECY-95-245.547 In an assessment of FAP issues for a plant design life of 40 years, it was concluded that no immediate staff or licensee actions were required. The staff obtained available records of transient monitoring from 7 plants selected for the FAP sampling. On the basis of this sample and considering the available transient monitoring records and the conservatism identified in the component analyses, the staff did not believe that the CLB fatigue criteria were exceeded at operating plants. Thus, this issue was RESOLVED with no new requirements.629