Replacement of nitrogen gas evaporator of JOYO

Sumino, Kozo ; Oshima, Jun; not registered; not registered; not registered; Ozawa, Kenji

The nitrogen gas evaporator using steam heating is a main component of the nitrogen gas supply system of JOYO and had been operated without the maintenance in order to supply nitrogen gas to the plant continuously. However, the necessity of replacing the nitrogen gas evaporator occurred due to the corrosion of the tank which involved water and steam for the heating in the recent years. Therefore, the nitrogen gas evaporator using steam was replaced with a new one that has a tank made of stainless steel, and the nitrogen gas evaporator using air heating was newly installed in order to supply the nitrogen gas during the maintenance of the nitrogen gas evaporator using steam heating. In addition, thermometers were installed at water in a tank and supply nitrogen gas in order to monitor these temperatures from the main control room. The main results of a preoperation function test were as follows; (1)It was confirmed that the performance of the new nitrogen gas evaporator using steam heating was more than it of the old one. (2)The nitrogen gas evaporator using air heating could successfully maintain the nitrogen gas atmosphere (within 4% oxygen concentration) in the lower part of the reactor containment vessel. (3)The correlation between the water temperature in a tank and the supply nitrogen gas temperature were confirmed for the normal and maximum operations.