Study on source of radioactive material in primary coolant of HTTR

Ishii, Toshiaki ; Shimazaki, Yosuke ; Ono, Masato ; Fujiwara, Yusuke ; Ishitsuka, Etsuo   ; Hamamoto, Shimpei  

In the primary cooling system of the High-Temperature Engineering Test Reactor, the highest dose rate was observed at the Helium Gas Circulator filter areas. To find the origin of the radioactive material, the radiation dose rates, and ray spectrums were measured. From these results, it is clear that the main radioactive nuclide at the filter is Co after 6 years reactor shutdown, and the in-core materials are a low possibility as the candidates of radioactive materials. It is also clear that the mixtures of materials, the contained low-level impurities and other new candidate materials must be considered.