Dynamic PRA with component aging and degradation modeled utilizing plant risk monitoring data

In the nuclear industry, risk monitors are intended to provide a point-in-time estimate of system risk given current plant configurations. Current risk monitors are limited in that they do not properly take into account the deteriorating states of plant systems, structures, and components (SSCs), which are unit-specific. Current approaches to computing risk monitors use probabilistic risk assessment (PRA) techniques, but the assessment is typically a snapshot in time. Living PRA models attempt to address limitations of traditional PRA models in a limited sense by including temporary changes in plant and system configurations. However, information on plant component health is not considered. This often leaves risk monitors using living PRA models incapable of conducting evaluations with dynamic degradation scenarios evolving over time. There is a need to develop enabling approaches to solidify risk monitors to provide time and condition-dependent risk by integrating traditional PRA models with condition monitoring and prognostic techniques. This paper presents a novel hazard-rate based model of incorporating degradation of SSCs into an existing PRA model. Time-varying instantaneous hazard-rate of component is used to model degradation based on time-varying performance measure. The instantaneous hazard-rate is used to determine and update time-varying failure probability of the components in their PRA models. The method is applied to estimate the evolution of failure probability of an in-service pump using vibration measurements taken while the pump undergoes degradation.