JOYO MK-III Heat Transport System Renovation Operation; Primary Heat Transport Mechanical System (IHXs (Intermediate Heat Exchangers))

Oshima, Jun; Ashida, Takashi ; Isozaki, Kazunori ; Sumino, Kozo ; Yamaguchi, Akira; Sakaba, Hideo; Ozawa, Kenji; Tomita, Naoki

The MK-III project to improve the irradiation capability of the experimental fast reactor JOYO have been carried out since 1987.The increase of fast neutron flux and the enlargement of irradiation field increase the reactor thermal power from 100MWt to 140MWt. To accommodate the increased thermal power,the IHXs and the IHX connecting piping were replaced. The IHXs were replaced with securing cooling system boundary in high dose rate surroundings and very limited operation space of the radiation controlled area in the containment vessel. Primary sodium contains radioactive 22Na,24Na and radioactive CPs such as 60Co and 54Mn,and this sodium adhered to the inner surface of IHXs and pipe. Therefore, the renovation procedure and method were carefully examined based on the JOYO operation and maintenance experiences and research and development results on the sodium handling technique.The major results obtained in the primary heat transport mechanical system (IHXs) renovation operation were shown as follows;