Utilization of (134)Cs/(137)Cs in the environment to identify the reactor units that caused atmospheric releases during the Fukushima Daiichi accident.

Masamichi Chino,Tatsuo Torii,Yukiyasu Nishizawa,Hiroaki Terada,Kimiaki Saito,Genki Katata,Satoshi Mikami,Haruyasu Nagai

doi:10.1038/srep31376

Abstract

The Fukushima Daiichi nuclear power reactor units that generated large amounts of airborne discharges during the period of March 12–21, 2011 were identified individually by analyzing the combination of measured 134Cs/137Cs depositions on ground surfaces and atmospheric transport and deposition simulations. Because the values of 134Cs/137Cs are different in reactor units owing to fuel burnup differences, the 134Cs/137Cs ratio measured in the environment was used to determine which reactor unit ultimately contaminated a specific area. Atmospheric dispersion model simulations were used for predicting specific areas contaminated by each dominant release. Finally, by comparing the results from both sources, the specific reactor units that yielded the most dominant atmospheric release quantities could be determined. The major source reactor units were Unit 1 in the afternoon of March 12, 2011, Unit 2 during the period from the late night of March 14 to the morning of March 15, 2011. These results corresponded to those assumed in our previous source term estimation studies. Furthermore, new findings suggested that the major source reactors from the evening of March 15, 2011 were Units 2 and 3 and that the dominant source reactor on March 20, 2011 temporally changed from Unit 3 to Unit 2.

Highlights

The Fukushima Daiichi nuclear power reactor units that generated large amounts of airborne discharges during the period of March 12–21, 2011 were identified individually by analyzing the combination of measured 134Cs/137Cs depositions on ground surfaces and atmospheric transport and deposition simulations
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) summarized sixteen results on source term estimation (Table B2 of UNSCEAR 2013 Report[6]). It described that the source term estimated by Terada et al.[3] provided a sound basis for estimation of the levels of radioactive material in the terrestrial environment where prior measurements did not exist and the dispersion and deposition of released material modeled by the World Meteorological Organization (WMO) based on the source term by Terada et al.[3] could replicate the broad pattern of deposition density of 137Cs over the Japanese land mass
We summarized a number of international papers lately that have carried out the source term estimation and numerical analysis of atmospheric dispersion process of radionuclides released during the accidents (Table 1 of Katata et al.5)

Summary

Introduction

The Fukushima Daiichi nuclear power reactor units that generated large amounts of airborne discharges during the period of March 12–21, 2011 were identified individually by analyzing the combination of measured 134Cs/137Cs depositions on ground surfaces and atmospheric transport and deposition simulations. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) summarized sixteen results on source term estimation (Table B2 of UNSCEAR 2013 Report[6]) It described that the source term estimated by Terada et al.[3] (which is the one from our previous study) provided a sound basis for estimation of the levels of radioactive material in the terrestrial environment where prior measurements did not exist and the dispersion and deposition of released material modeled by the World Meteorological Organization (WMO) based on the source term by Terada et al.[3] could replicate the broad pattern of deposition density of 137Cs over the Japanese land mass. This paper focuses on the reactor units that generated large 137Cs atmospheric releases during the period of March 12–21, 2011

Methods

Results

Conclusion