Analysis of standby and demand stress failures modes

This report describes work to develop and demonstrates methods for partitioning standby component failure modes into causes that fail the component while it is in standby, and when it changes state, during testing or from other demands. Failure of the component from standby stresses is modeled using a model that explicitly contains the length of the test interval. Failure of the component from demand stresses such as vibration, wind, etc., is modeled using the probability of failure on demand model. Misuse of these models in PRAS, could lead to PRAs that, give misleading results, or that are more useful for decision purposes. A method was developed and demonstrated to partition standby/demand stresses. The method was used on the work maintenance records from two Nuclear Power Plants (NPPs) to estimate reliability parameters for Motor Operated Valves And Emergency Diesel Generators (EDGs)