An introductory course of the probabilistic safety assessment (PSA) for LWR. (1) The progress and fundamental philosophy of the application of PSA methodology

The probabilistic safety assessment (PSA) methodology has been well developed and in several countries risk information derived by the probabilistic assessment has been used for making nuclear safety assurance activities reasonable and efficient. The USA has developed risk informed regulation for the purposes of making the regulation more effective so as to provide appropriate allocation of regulatory resources, improvement of plant maintenance rules, reactor oversight process, etc., which leads to current high performance of nuclear power plants in USA. In Japan risk informed approach has been positively studied and then an introductory course of the PSA methodology as its basis was prepared in serial form. This is the first issue showing its progress and fundamental philosophy. (T. Tanaka)