Power distributions in the High Temperature Engineering Test Reactor (HTTR) by measuring gross gamma ray from the fuel assemblies

Nojiri, Naoki ; Shimakawa, Satoshi; Takamatsu, Kuniyoshi  ; Ishii, Yoshiki; Kawano, Shuichi; Kobayashi, Shoichi; Kawamoto, Taiki; Iyoku, Tatsuo

To provide a basis for determination of the actual core power distribution, The power distribution experiments by measuring gross gamma ray emitted from fission products in the fuel assemblies were performed. The fuel assemblies were not spent condition but in-service condition. The averaged burn up was about 4,400 MWD/t. The gamma ray of a fuel assembly was measured with a GM counter under a temporary fuel withdrawing situation from the core during shutdown state. Uncertainties of the determination were from 3 to 6 percent in axial distribution per one fuel compact and within about 4 percent in radial and axial distribution of the core per one fuel assembly. It was concluded that the power distribution of the HTTR is almost equivalent to the expected power-profile shaping. Calculation of gamma ray distribution was performed by ORIGEN-2 code based the power distribution obtained by the Monte Carlo MVP code. The calculation results show good agreement with the experimental ones. The method, procedure, analysis, correction, determination and comparison are described in this report.