Development of web based offsite consequence analysis program and periodic risk assessments for ILRT extension

PSA is generally used to assess the relative risks posed by various types of operations and facilities, to understand the relative importance of the risk contributors, and to obtain insights on potential safety improvements. There is usually no pass fail criterion that must be met to allow operations to continue. A major goal of PSA is to gain insights that can be used to either minimize the probability of accidents or to minimize the consequences of accidents that might occur. According to NUREG 1493 which applies the PSA concept to an ILRT interval extension, an ILRT interval was extended from three in ten years to one in ten years in almost all US nuclear power plants. In addition, NUREG 1493 stated that there is an imperceptible increase in risk associated with ILRT intervals up to twenty years. Since then, many licensees began to submit requests for one-time ILRT interval extensions of 15 years. To permit permanent 15 year ILRT intervals under the existing NRC guidance, it was necessary to develop a standard method for supporting the risk impact assessment. Thus, NEI performed a project to develop a generic methodology for the risk impact assessment for ILRT interval extensions to 15 years using current performance data and risk informed guidance. The risk impact assessment is generally performed by MACCS II code, which was included in an international collaborative effort to compare predictions obtained from seven consequence codes: ARANO (Finland), CONDOR (UK), COSYMA (EU), LENA (Sweden), MACCS (United States), MECA2 (Spain), and OSCAAR (Japan). However, it costs lots of man power and efforts on using the MACCS II code, especially on collecting raw data for input files and on converting the raw data format. Accordingly, the web based OSCAP based on MACCS II code was developed to focus on automatic processing algorithm for handling the main input files with meteorological data, population distribution data and source term data. It is considered that the web-based OSCAP could make man-powers required for the risk impact assessment considerably reduced, and could provide an advantage of analyzing CCDF (Complementary Cumulative Distribute Function), Early Fatality (EF), Latent Cancer Fatality (LF), average individual risk, etc. for Level 3 PSA. In addition, the web based OSCAP was designed to have a function of 'Documentation Assistance' according to the methodologies of NUREG 1493 and NEI Interim Guidance