Optimization of periodic testing frequency of a reactor protection system based on a risk-cost model and public risk perception

Techniques for optimizing the frequency of periodic surveillance testing of nuclear power plant (NPP) safety systems have been receiving increased attention and growing importance because of the need to reduce system unavailability and maintenance cost. Economic losses from maintenance human errors should be included in estimating periodic testing and maintenance costs because the losses increase with maintenance human errors. This paper proposes a method for optimizing periodic testing intervals of a digital reactor protection system by balancing risk and cost of periodic surveillance tests, in which maintenance human error and public risk perception have been reflected. The risk and costs were estimated from both plant operator and socio-economic standpoints. This model determines the optimal testing frequency for the minimum value of an objective function that consists of all costs, including the monetary values of the consequence of maintenance human errors and reactor core damage. We present a case study using our model for the OPR1000 plant. The study results show the significance of reducing human errors in periodic testing and maintenance. The proposed method is expected to be useful to NPP operators as well as regulators for evaluating the optimal periodic testing frequency of a nuclear reactor protection system and for obtaining information needed in decision making processes.

Research highlights
► Risk, cost, and public risk perception are incorporated to optimize test frequency.
► Protection system unavailability decreases with an increasing test frequency.
► CDF and spurious trip rate increase with human errors.
► Shorter interval tests are notably beneficial when the human error level is very low.
► Test error, moderator temperature coefficient, trip cost are key factors.