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

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

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.