Sample thickness effect on nuclear material quantification with NRTA for particle like debris of melted fuel

Tsuchiya, Harufumi ; Harada, Hideo   ; Koizumi, Mitsuo ; Kitatani, Fumito  ; Takamine, Jun ; Kureta, Masatoshi   ; Iimura, Hideki  ; Becker, B.*; Kopecky, S.*; Kauwenberghs, K.*; Moens, A.*; Mondelaers, W.*; Schillebeeckx, P.*

Neutron resonance densitometry (NRD) is based on a combination of neutron resonance transmission analysis (NRTA) and neutron resonance capture analysis (NRCA). This non-destructive technique is considered for the quantification of nuclear materials in samples of melted fuel that will be removed from the Fukushima Daiichi Nuclear Power Plant. However, NRD has never been applied for measurements of melted fuel, and the measurements are considered to be difficult because of the characteristics of the samples. To verify the effectiveness of NRD, all components having an impact on the results have to be investigated. The uncertainty of the result is strongly influenced by the characteristics of the sample, in particular the sample inhomogeneity, particle size, presence of neutron absorbing impurities, radioactivity and temperature. To estimate the impact of the sample characteristics, JAEA and JRC-IRMM have started a collaboration. Within this collaboration experiments are in progress at the Time-Of-Flight facility of the EC-JRC-IRMM. In this presentation, results of neutron transmission measurements on Cu samples with different thicknesses at a 25-m flight path are reported. The data, which are analyzed with a resonance shape analysis code REFIT, are used to verify the effect of the particle size and the presence of neutron absorbing impurities. Some of the results are also used to validate data obtained by Monte Carlo simulations.