Development of a site release category model and its application

Abstract

Unmanageable numbers of single-unit source term categories (STCs) and multiple-unit STCs (STC combinations) are generally derived from the level 1·2 site risk assessment (SRA). Hence it is practically impossible to evaluate the consequence for all STCs in the level 3 SRA process. Also, the representative source terms may cause an optimistic or too conservative results compared to the reference case derived by analyzing the consequences of all STCs in a site. To make the level 3 SRA possible considering these limitations, a site release category (SRC) model based on dose-estimates has been developed only for the multi-unit STCs. By introducing the early and overall dose-estimates as new grouping variables, the SRC model could generate the manageable numbers of SRCs and show the reasonable results with a little conservativeness. As a result of applying the SRC model to the three-unit SRA model, 228 STC combinations are grouped into 22 SRCs and the site risk from the SRC model is about 1% higher than the reference site risk derived by analyzing the consequences of all single and multiple-unit STCs. Hence, from the SRC model, SRA can be performed with the manageable numbers of consequence analyses and the reasonable conservativeness of results.