Underwater analysis of (U,Zr)O using laser-induced breakdown spectroscopy (LIBS)

レーザー誘起ブレークダウン分光を用いた(U,Zr)Oの水中分析

大場 弘則  ; 佐伯 盛久; 伊藤 主税   ; 高野 公秀 ; 赤岡 克昭 ; Thornton, B.*; 作花 哲夫*; 若井田 育夫  

Oba, Hironori; Saeki, Morihisa; Ito, Chikara; Takano, Masahide; Akaoka, Katsuaki; Thornton, B.*; Sakka, Tetsuo*; Wakaida, Ikuo

福島第一原子力発電所の事故炉内部の、特に溶けた燃料の状態を調べることは、廃炉の作業を進めるうえで最重要課題のひとつになっている。本研究では、水没した燃料デブリを想定し、可搬型ファイバLIBS装置を用いて水中の模擬デブリ(U,Zr)Oからのレーザーブレークダウン発光を、放射線損傷を受けない波長範囲(730-1100nm)で計測した。その結果、750-870nmの波長域において、ウランとジルコニウムの発光スペクトルが干渉無しで観測できることを見出した。また、ジルコニウムとウランの混合比を変化させた試料を用意して発光強度比と混合比の関係を調べ良好な線形性を確認することができた。

In the post-accident nuclear core reactor of the TEPCO Fukushima Daiichi Nuclear Power Plants, melted fuel core, fuel cladding and construction material (corium debris) might drop in the lower part of the reactor, which filled with seawater that was injected for urgent cooling. The major components of the debris material are assumed to be uranium oxide (UO, fuel core), zirconium alloy (Zry, fuel cladding) and iron (Fe, construction material). In this presentation, we report underwater analysis of simulated corium debris, (U,Zr)O, by the transportable fiber-coupled LIBS instrument. The experiments were carried out using a wavelength region of 730-1100 nm for pulsed-lasers and plasma emission measurements, which shows no attenuation in the optical transmittance of the fiber optic cable by intense radiation dose. Based on the observed emission spectrum in the region of 750-870 nm, we determined candidates of the emission lines of Zr, U and Fe that are applicable to analyses of the debris without mutual interference. The LIBS spectra of five different concentration ratio samples for Zr/U were measured to obtain calibration data. We succeeded to obtain linear calibration data for emission intensity ratio versus concentration ratio of Zr/U.