Study on the criticality monitoring method by measurements of short-half-life noble-gas fission products for the criticality monitoring of fuel debris inside a primary containment vessel of Fukushima Daiichi Nuclear Power Stations

Riyana, E. S.   ; 坂本 雅洋 ; 松村 太伊知 ; 寺島 顕一  ; 奥村 啓介 

Riyana, E. S.; Sakamoto, Masahiro; Matsumura, Taichi; Terashima, Kenichi; Okumura, Keisuke

We investigated the possibility of estimating the effective neutron multiplication factor (keff) of the fuel-debris inside the primary containment vessel (PCV) of unit-2 of Fukushima Daiichi Nuclear Power Station (1F) using remote gas-radioactivity measurement. Our calculation result demonstrates the correlation between keff and the activity ratio (AR) of Kr-to-Xe for various fuel debris compositions and geometry. We also show the time-dependent behavior of the AR of Kr-to-Xe when the keff changes suddenly in PCV.