Recently discovered safety system problems resulting from air system deficiencies

In March 1987, the US Nuclear Regulatory Commission's (NRC's) Office for Analysis and Evaluation of Operational Data (AEOD) issued a case study report on air systems problems. The case study report highlighted 29 significant events involving safety-related systems in US plants that resulted from degraded or malfunctioning non-safety-grade air systems. The case study noted that air systems are not safety-grade systems at most operating plants. As a result, plant accident analyses assume that safety-related equipment dependent on air systems will either fail safe upon loss of air or perform its intended function with the assistance of backup accumulators. The failures have shown that in many instances safety-related equipment dependent on air systems did not fail safe upon loss of air or perform its intended function with the assistance of backup accumulators. The root causes of most of those failures were traceable to design and/or maintenance deficiencies. In August 1988, the NRC issued a generic letter to all licensees. The generic letter requested that licensees review their plant air systems in accordance and perform design and operations verifications of the instrument air systems. Numerous air systems deficiencies were found by the licensees in the course of responding to generic letter 88-14. Many of the deficiencies that could have seriously hampered plant responses to design-basis events had existed for many years