Improvement of exchanging method of neutron startup source of high temperature engineering test reactor

Sawahata, Hiroaki ; Shimazaki, Yosuke ; Ishitsuka, Etsuo   ; Yamazaki, Kazunori; Yanagida, Yoshinori; Fujiwara, Yusuke ; Takada, Shoji; Shinozaki, Masayuki; Hamamoto, Shimpei  ; Tochio, Daisuke 

In the HTTR, Cf is loaded in the reactor core as a neutron startup source and changed at frequency. In this exchange work, there were two technical issues; slightly higher radiation exposure of workers by neutron leakage and reliability of neutron source transportation container in handling. To reduce the radiation dose by neutron leakage, detail numerical evaluations using PHITS code were carried out, the effective shielding method for fuel handling machine was proposed. Easily removable polyethylene blocks and particles were used as the neutron shielding, and installed in the cooling paths of the fuel handling machine. As a result, the collective effective dose by neutron was reduced from about 700 man-microSv to about 300 man-microSv. As to the neutron source transportation container, the handling performance was improved and the handling work was safety accomplished by downsizing.