JRR-4における12インチNTD-Si照射実験装置に関する概念設計(受託研究)

Conceptual design of irradiation experimental device for 12 inch NTD-Si ingot in JRR-4 (Contract research)

八木 理公 ; 渡邊 雅範; 大山 光樹; 米田 政夫   ; 山本 和喜 ; 加島 洋一

Yagi, Masahiro; Watanabe, Masanori; Oyama, Koji; Komeda, Masao; Yamamoto, Kazuyoshi; Kashima, Yoichi

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し、JRR-4で照射実験を行う。これによって、照射装置の設計手法の妥当性を確証する。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、本実験装置における12インチNTD-Siの最適な均一照射条件を導くことができた。

The irradiation experimental device is designed by surveying analytically an irradiation condition to improve the neutron flux distribution of the radial direction on NTD-Si by using neutron transportation calculation Monte Carlo calculation code MCNP5 in order to develop neutron irradiation technology for the large-diameter silicon to 12 inches diameter at the maximum and an irradiation experiment will be performed in JRR-4. Thus the validity of the design technique of the irradiation device will be confirmed by this experiment. The irradiation experimental device is installed in the side of the core tank outer wall. A 12 inches silicon ingot of 60cm in height is irradiated in a reflector cover which surrounds the silicon ingot for increasing the flux. The silicon ingot is rotated during irradiation 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, in which silicon ingot moved 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 thickness of 2mm with natural boron element ratio of 1.5%, and was moved in the range from -42mm to 22mm for the center of the reactor core. The deviation of the Si-30 neutron absorption reaction rate was range from -3.2% to +5.3% in the intermediate volume of 40cm height and the neutron absorption reaction ratio of the circumference to the center was within 1.09 in the volume.