Utilization of Cs/Cs in the environment to identify the reactor units that caused atmospheric releases during the Fukushima Daiichi accident

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

This paper investigates the reactor units of Fukushima Daiichi Nuclear Power Station which generated large amounts of atmospheric releases during the period from 12 to 21 March 2011. The Cs/Cs ratio measured in the environment can be used to determine which reactor unit contaminated specific areas. Meanwhile, atmospheric dispersion model simulation can predict the area contaminated by each dominant release. Thus, by comparing both results, the reactor units which contributed to dominant atmospheric releases was determined. The major source reactor units from the afternoon of 12 March to the morning of 15 March corresponded to those assumed in our previous source term estimation studies. A new possibility found in this study was that the major source reactor from the evening to the night on 15 March was Units 2 and 3 and the source on 20 March temporally changed from Unit 3 to Unit 2.