加速器駆動未臨界炉に対する炉雑音解析研究の現状と課題

摘要

This report presents a current status of the research and development of reactor noise analyses applicable to accelerator-driven subcritical reactor system. These research activities have been concentrated on the Feynman-α neutron correlation analysis on time domain and the power spectral analysis on frequency domain. At present, the latter power spectral analysis is of greater advantage than the former Feynman-α one, for periodic and pulsed neutron source. While Feynman-α formula for pulsed neutron source is too complicated to be fitted directly to variance-to-mean ratio data, the power spectral analysis has a simpler formula based on the first-order reactor transfer function. The Feynman-α should be improved to consider spatial effect of deeply subcritical system and instability of accelerator operation. Further subject of reactor noise analyses is an improvement for high power operation.%加速器駆動未臨界炉システム(Accelerator-Driven Subcritical System)は、超ウラン元素を含む超寿命放射性廃棄物の核変換処理の観点から注目され、我が国と欧州を中心に開発が精力的に進められている。Np,Cm,Am等のマイナーアクチニド(Minor Actinide)が燃料として装荷されるADSは、反応度事故のリスクを回避するため、未臨界状態で運転される。