A conceptual methodology for site exclusion boundary and site large early release frequency for multi-unit nuclear power plants site

Abstract

Probabilistic Safety Assessment (PSA) risk metrics Core Damage Frequency (CDF) and Large Early Release Frequency (LERF) are currently applied for single NPP unit. The purpose of the work is to arrive at quantitative value for LERF for a site consisting of many NPPs. For this objective, the work proposes to define an exclusion boundary for the whole site (site exclusion boundary) which is different from exclusion boundary for one NPP. At a site, the exclusion boundaries of the individual NPPs may overlap or can be separate. In the present research, various concepts of total exclusion boundary length for the site are delineated upon using the exclusion radius/boundary of individual NPPs. A case study for a hypothetical site consisting of three NPP units was considered for the demonstration of the proposed methodology. The NPPs have same power level and equal radius of exclusion boundary. LERF results are available for individual NPPs and those accident sequences are relevant that (initiating events are independent events or common cause events) that cause release of more than 4% of core I-131 radioactive nuclide within 10 h of accident. The radionuclide dispersion was calculated using Gaussian plume model for dose at various locations on the site exclusion boundary for the multiple NPP site. The calculation of site LERF was carried out for various locations on the site exclusion boundary for a specific configuration of NPPs at site.