Handling of off-gas produced in the mercury target of spallation neutron source in J-PARC

Kai, Tetsuya   ; Seki, Masakazu; Ueno, Hideki; Kinoshita, Hidetaka   ; Otsu, Kiichi; Teshigawara, Makoto   ; Kogawa, Hiroyuki  ; Kasugai, Yoshimi  

Various radioactive nuclei are produced in the mercury circulation system of J-PARC spallation neutron source. It is required to minimize release of such volatile radioactivity as tritium (half-life of 12 years) and xenon-127 (half-life of 36 days) during works opening the mercury system to the atmosphere to replace a mercury target chamber, etc. Although a depuration process by helium-gas flushing is carried out to the mercury system, a disposal of large amount of produced gas would be an issue. Thus a test was performed to remove xenon-127 from the disposal gas. As a result the concentration of xenon-127 was successfully reduced down to one-hundredth after a 6-hour operation of a charcoal trap cooled by liquid-nitrogen. In addition desorption of xenon-127 was confirmed by heating the charcoal trap to 100 degree in Celsius. These test indicated that xenon-127 in off-gas can be well removed by using the cooled charcoal trap.