An approach toward evaluation of long-term fission product distributions in the Fukushima Daiichi nuclear power plant after the severe accident

Abstract

The safe completion of the Fukushima Daiichi Nuclear Power Plant decommissioning projects requires that the long-term distributions of fission products (FPs) as well as fuel debris for the entire plant be understood. The fuel debris is going to be removed from the plant under the severe conditions of FPs being scattered during major decommissioning work, and then, the decommissioning projects are going to be terminated by storing safely the removed debris as recovered fertile materials or as materials for final radioactive waste disposal.In order to determine the FP distribution in the plant for the long period from the accident occurrence to the termination of the plant decommissioning, procedures for analyzing short-, medium- and long-term FP behaviors has been proposed. The proposed procedures should be improved by applying the FP data measured in the plant and validated based on the fed-back data. Then, the accuracy-improved procedures should be applied to estimate FP distributions during each phase of the decommissioning projects.First the paper outlines the short-, medium- and long-term FP transfer analyses. Then, their applicability and some examples of their validations based on dose rate data of the containment atmosphere monitoring system (CAMS) of Unit 1 are introduced.(195 words)