LaBr -ray spectrometer for detecting B in debris of melted nuclear fuel

Koizumi, Mitsuo ; Tsuchiya, Harufumi ; Kitatani, Fumito  ; Harada, Hideo   ; Heyse, J.*; Kopecky, S.*; Mondelaers, W.*; Paradela, C.*; Schillebeeckx, P.*

Neutron Resonance Densitometry (NRD) has been proposed as a non-destructive analytical method for quantifying Special Nuclear Material (SNM) in the rock- and particle-like debris that is to be removed from the Fukushima Daiichi Nuclear Power Plant. The method is based on Neutron Resonance Transmission Analysis (NRTA) and Neutron Resonance Capture Analysis combined with Prompt Gamma Ray Analysis (NRCA/PGA). Although quantification of SNM will predominantly rely on NRTA, this will be hampered by the presence of strong neutron-absorbing matrix materials, in particular B. Results obtained with NRCA/PGA are used to improve the interpretation of NRTA data. Prompt -rays originating from the B(n, ) reaction are used to assess the amount of B. The 478 keV -rays from B, however, need to be measured under a high-radiation environment, especially from Cs. In order to meet this requirement, we have developed a well-shaped -ray spectrometer consisting of a cylindrical and four rectangular cuboid LaBr scintillators, and a fast data acquisition system.