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.

概率安全评估（PSA）风险度量标准目前已将核损害频率（CDF）和大提前释放频率（LERF）应用于单个NPP单元。该工作的目的是为包含许多NPP的站点得出LERF的定量值。为实现这一目标，工作提出了为整个场所定义一个排除边界（场所排除边界），该边界不同于一个NPP的排除边界。在一个站点上，各个NPP的排除边界可能重叠或可以分开。在本研究中，使用单个NPP的排除半径/边界来描述该站点的总排除边界长度的各种概念。考虑了一个由三个NPP单元组成的假想场所的案例研究，以论证所提出的方法。NPP具有相同的功率水平和相等的排除边界半径。LERF结果可用于单个NPP，并且那些事故序列与（引发事件是独立事件或共同原因事件）相关，这些事件序列导致事故10小时内释放了4％以上的核心I-131放射性核素。使用高斯羽流模型针对多个NPP站点在站点排斥边界上各个位置的剂量计算放射性核素弥散。针对站点上特定的NPP配置，在站点排除边界上的各个位置进行了站点LERF的计算。LERF结果可用于单个NPP，并且那些事故序列与（引发事件是独立事件或共同原因事件）相关，这些事件序列导致事故10小时内释放了4％以上的核心I-131放射性核素。使用高斯羽流模型针对多个NPP站点在站点排斥边界上各个位置的剂量计算放射性核素弥散。针对站点上特定的NPP配置，在站点排除边界上的各个位置进行了站点LERF的计算。LERF结果可用于单个NPP，并且那些事故序列与（引发事件是独立事件或共同原因事件）相关，这些事件序列导致事故10小时内释放了4％以上的核心I-131放射性核素。使用高斯羽流模型针对多个NPP站点在站点排斥边界上各个位置的剂量计算放射性核素弥散。针对站点上特定的NPP配置，在站点排除边界上的各个位置进行了站点LERF的计算。