Practical Method of Risk-Informed Decision Making in Nuclear Power Plant Operation and Its Safety Effect

Before the Fukushima-Daiichi Accident, Japanese nuclear power plants （ NPPs ） were utilized with a capacity factor of around 70 ％ , 20 ％ lower than the US capacity factor of around 90 ％ , which is a consequence of Japanese NPPs being operated with a shorter fuel cycle and longer outage period. One reason for this situation is that Japanese decision making is strongly focused on equipment reli-ability. In a typical pressurized-water reactor, however, core damage frequency （ CDF ） during refueling outage is higher than that during operation, that is, a short fuel cycle could possibly increase the total CDF of NPPs. In this paper, a decision-making rule using an index representing CDF par power generation is firstly proposed. Secondly, using this rule, a decision process is simulated to optimize the fuel cycle and refueling outage period while showing the effects on CDF reduction in each plant. Thirdly, by applying this decision process to all Japanese NPPs, the total CDF reduction in Japan is indicated. This simulation shows that the change of decision-making rule will bring about an 18 ％ CDF reduction or 16 ％ increase in power generation in total in Japan. At the same time, each NPP gains strong incentive to improve its own safety because this new rule permits a higher capacity factor operation only for the NPPs that are safer than the average.