12インチNTD-Si照射実験装置に関する概念設計,1; 核解析による大口径NTD-Si均一照射条件の検討

Conceptual design about the 12-inch NTD-Si irradiation experimental device, 1; Study of uniform irradiation condition in NTD-Si ingot with large-diameter by nuclear analyses

八木 理公 ; 加島 洋一; 渡邊 雅範; 山本 和喜 

Yagi, Masahiro; Kashima, Yoichi; Watanabe, Masanori; Yamamoto, Kazuyoshi

最大12インチ径までの大口径シリコンの中性子照射技術を開発のため、中性子輸送計算モンテカルロ計算コードMCNP5を用いて12インチ径のNTD-Siの径方向の中性子束分布を改善する照射条件を解析的に見いだすことにより照射実験装置を設計する。この設計手法の妥当性を確証するため、JRR-4で照射実験を行う。12インチNTD-Si照射実験装置は、炉心タンク外壁脇に設置し、中性子束の増大を目的とした反射体カバー内で直径12インチ,高さ60cmのシリコンを回転させることにより周方向に均一照射することとし、熱中性子フィルタを周囲に覆ったシリコンを回転させながら上下移動させるスルー法に関する均一照射条件を検討した。検討の結果、厚さ2mmの天然ボロン濃度1.5%含有アルミニウムを用いた熱中性子フィルタをシリコンに覆い、シリコン上下移動範囲を炉心中心-42+22cmにした場合、ダミー領域の上下10cmを除いてSi中性子吸収反応率の偏差が-3.2% +5.3%、シリコン中心に対する外周のSi中性子吸収反応率の比(O/C比)が1.09となり、目標値であるO/C比1.1を満足することができた。

The irradiation experimental device is designed by surveying analytically an irradiation condition to improve the neutron flux distribution of the diameter direction on NTD-Si by using Monte Carlo calculation code MCNP5 in order to develop neutron irradiation technology for the large-diameter silicon to 12 inches diameter at the maximum. Some irradiation experiment will be performed to confirm validity of the design technique in JRR-4 by using the experimental device for the 12 inches NTD-Si ingot. The experimental device is installed in the No.1 reactor pool side of the core tank outer wall. The 12 inches silicon of 60 cm in height is irradiated in a reflector cover which surrounds the silicon for increasing the flux. The silicon also is irradiated with rotating in order to require the condition of uniformly distributed thermal neutron flux over whole circumferences. A uniform irradiation condition was achieved by the pass-through core method with adding the thermal neutron filter which covers the silicon surface and is able to move up and down with rotating. The condition was satisfied when silicon was covered with the thermal neutron filter, which is made from aluminum alloy of 2 mm thickness with natural boron element ratio of 1.5%, and was run in the range from -42 mm to 22 mm for the center of the reactor core. The deviation of the Si-30 neutron absorption reaction rate was range from -3.22% to +5.27% in the intermediate volume of 40 cm height and the neutron absorption reaction ratio of the circumference to the center was within 1.09 in the volume.