Improvement of the RIMS detection sensitivity for application to failed fuel detection and location system of the fast reactor

高速炉の破損燃料位置検出システムへの適用に向けたRIMS検出感度の向上

岩田 圭弘   ; 原野 英樹*; 伊藤 主税   ; 青山 卓史*

Iwata, Yoshihiro; Harano, Hideki*; Ito, Chikara; Aoyama, Takafumi*

高速炉の破損燃料位置検出(FFDL)システムへの適用に向けて、レーザー共鳴イオン化質量分析法(RIMS)を用いたAr中の極微量Kr, Xe同位体分析を行っている。Kr, Xeの正確な分析には光電子により生成する, の検出量を低減することが必要不可欠である。光電子生成量の低減を目的とした除電器とBrewster窓、及びKr, Xeの損失なく生成した, の引き出し量低減を目的としたスリット型電極孔の2種類の改善方策により, の影響を1-2桁抑制し、の目立った影響なく核種濃度pptレベルのを検出できた。今後は、同位体比分析にかかわる統計誤差の抑制を目的としたRIMS分析装置の検出効率向上策について検討していく。

In the fast reactors, rapid and accurate detection of fuel failures as well as subsequent identification of failed fuel location are essential to achieve their safety operation and high plant availability. The gas tagging method, currently employed in the prototype fast breeder reactor Monju, is one of the efficient ways for the failed fuel detection and location (FFDL) technique, the principle of which is the isotope analysis of the argon (Ar) cover gas that includes, in case of fuel failure, a partial amount of leaked krypton (Kr) and xenon (Xe) originally loaded into each fuel pin. We propose a new type of FFDL technique using laser resonance ionization mass spectrometry (RIMS) for the isotope analysis of the cover gas in view of selective ionization of a specific element to obtain high S/N ratio. Nevertheless, the actual experimental data shows the existence of Ar and Ar non-resonant ionization by the photoelectron generated in the vacuum chamber to hinder precise measurement of Kr and Xe. We could successfully decrease the effect of these ions by one to two orders of magnitude by applying both a set of a neutralization apparatus and a Brewster window, and an electrode with a slit-type hole in the ion acceleration region, resulting in reliability improvement of RIMS in the FFDL system.