[3K01-05] Criticality Analysis of Fuel Debris 1

[3K02] 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

*Eka Sapta Riyana¹, Masahiro Sakamoto¹, Taichi Matsumura¹, Kenichi Terashima¹, Keisuke Okumura¹ (1. JAEA)

Keywords:Fuel Debris, Subcritical System, Neutron Multiplication Factor, Monte Carlo Calculation, Short Half-life Fission Products

We investigated the possibility of estimating the effective neutron multiplication factor (k_eff) 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 k_eff and the activity ratio (AR) of ⁸⁸Kr-to-¹³⁵Xe for various fuel debris compositions and geometry. We also show the time-dependent behavior of the AR of ⁸⁸Kr-to-¹³⁵Xe when the k_eff changes suddenly in PCV.