Analysis of Radionuclide Deposition Ratios from the Fukushima-Daiichi Incident

Abstract:

Consequence management radiological dose assessors make several assumptions in dose projections regarding radionuclide depositions following a radiological release from a nuclear power plant. During trainings and exercises these coordinators and dose assessors make assumptions that the radionuclide deposition ratios will remain constant, only varying in terms of radioactive decay and weathering. This assumption is sometimes made regardless of large spatial and terrain variations. Following the Fukushima-Daiichi accident, the National Nuclear Security Administration\’s Consequence Management Response Teams (CMRT) assisted in consequence management operations in Japan. Part of their work included taking air samples and in-situ measurements using high purity germanium detectors throughout certain areas of the country. The validity of the aforementioned assumption was examined by analysis of the in-situ measurements that were obtained by the U.S. response teams and the Japan Atomic Energy Agency (JAEA). Using isotopic ratios for a LWR core-damage accident, from FRMAC Manual Volume 3, a comparison was made with the collected in-situ measurement data to determine how the FRMAC values compare against actual measured data. The main radionuclides considered in this evaluation were 134Cs, 136Cs, 137Cs and 131I. The goal of this comparison was to determine how valid training and exercise assumptions are pertaining to an actual incident.