Evaluation of surveillance test interval from risk viewpoint

The paper presents the application of the probabilistic risk assessment (PRA) technique for surveillance test interval (STI) evaluation. Assessment was performed for the reactor protection system (RPS) and based upon the living PRA model of the Taipower's Maanshan power plant. A fault tree was developed and analyzed to find the most proper subsystem for test interval relaxation. Comparisons were made for generic data and plant specific data sets; approaches of staggered test versus sequential test were also compared. Sensitivity studies were made to evaluate the uncertainty of human error and common cause failure factors. Event tree analyses were made to calculate core melt down frequencies for test induced transients and anticipated transient without scram (ATWS) events and to evaluate the effect of STI relaxation. Results indicated that an extension of three times of the current RPS test interval has no significant risk impact for the Maanshan plant.