Analysis of Pu isotopes in melted fuel by neutron resonance transmission; Examination by linear absorption model

溶融燃料中の中性子透過法によるPu同位体分析;線形吸収モデルによる検討

北谷 文人  ; 原田 秀郎   ; 高峰 潤 ; 呉田 昌俊   ; 瀬谷 道夫

Kitatani, Fumito; Harada, Hideo; Takamine, Jun; Kureta, Masatoshi; Seya, Michio

ホウ素等の核燃料物質以外の物質が含まれた試料についてNRTAでどの程度の精度で測定可能か検討した。試料は、使用済み核燃料に不純物としてホウ素と鉄が含まれるもの仮定した。測定は、中性子源から5mの位置でTOF測定を行う。吸収スペクトルを、JENDL-4.0での総中性子吸収断面積を使用して線形吸収を仮定して生成する。これに、統計からくる誤差を計算し加えることによって誤差を考慮した吸収スペクトルを求めた。このスペクトルを使用して中性子強度,不純物濃度等を変化させた場合の、NRTAによるPu同位体分析の精度について検討を行った。

Feasibility study of neutron resonance transmission analysis (NRTA) has been started to quantify nuclear materials in particle-like debris of melted fuel formed in severe accidents of nuclear reactor such as Fukushima Daiichi Nuclear Power Plants. The achievable measurement accuracy was examined by NRTA using a linear absorption model for the sample in which substances other than nuclear fuel materials, such as boron, were contained. In this study, boron and iron were considered to be contained in spent nuclear fuel as impurities. The neutron flight path is 5 m, that is the length between the neutron source and a neutron detector. Neutron absorption spectra were calculated using the total neutron absorption cross-section by JENDL-4.0. The absorption spectra together with their errors were evaluated. The achievable accuracy of Pu isotopic density was deduced as a function of neutron intensity and impurity density. This research was supported by JSGO/MEXT.