A Study on Methods for Establishing Surrogate Safety Goals for Nuclear Power

Quantitative risk values for nuclear power plants (NPPs) can be obtained by conducting a probabilistic safety assessment (PSA). However, people cannot judge the risk level without comparing the risk values from PSA with the standards of acceptable risk in society. Acceptable risk standards are affected by many factors, and those factors are preferentially considered in specified applications. There are many methods used to establish acceptable risk, and a comparative method is easily understood and accepted by the public. In the United States, both qualitative safety goals and quantitative health objectives (QHOs) for the current generation of light water reactors are established by a comparative method and are described in the Safety Goals Policy Statement published by the U.S. Nuclear Regulatory Commission. The evaluations of Level 1 PSA or Level 2 PSA are enough for most regulatory decisions and engineering practices.

In order to use PSA as a useful tool for regulation, establishing surrogate safety goals based on QHOs is necessary. But, there is no clear derivation process. First, this paper introduces the process of how to derive QHOs from qualitative safety goals and a model of quantitative health risk. Then, models using core damage frequency (CDF) and large early release frequency (LERF) based on the QHOs are introduced. The situations of nuclear power for each country—the number of plants, the types of reactors, the weather conditions, the population distribution, and the off-site emergency response plan—are different for each country. This paper considers two representative situations. The first situation is that a society has only a single NPP. The maximum consequence method is used to determine the surrogate safety goals for this situation. The second situation is that a society has multiple types of NPPs and the off-site environments of the plants are different from each other. The statistical tolerance intervals method is used to determine the surrogate safety goals for this situation. Data of individual early fatality and cancer fatality risk in China from 2004 to 2013 are collected and analyzed, and then, Chinese, U.S., Korean, and Japanese QHOs are compared. Chinese QHOs and some data from the reference are used to establish surrogate safety goals for the two situations, which are compared with existing surrogate safety goals CDF = 1E-04 per reactor and LERF = 1E-05/reactor-year.