Replacement of the proton beam window at Material and Life Science Experimental Facility

Oi, Motoki ; Hosokawa, Hidemitsu*; Nishikawa, Masaaki*; Fukuda, Shimpei; Teshigawara, Makoto   ; Meigo, Shinichiro   ; Takada, Hiroshi   

At J-PARC, a neutron production target is installed in the helium vessel, and 3-GeV proton beams are delivered from a 3-GeV synchrotron to the target through a beamline with high vacuum environment. A proton beam window (PBW) is installed to isolate the helium vessel from the proton beamline. Since the PBW is degraded by radiation damage, it is scheduled to be replaced every 2 or 3 years under the 1-MW operation. In the summer outage in 2017, the PBW #2 was replaced to #3. A shielding cask was used for transferring the activated PBW, while hands-on works were done to remove the cooling water pipes at the top of the shielding plug of PBW. Since the cooling water contains 510 Bq/cc of tritium, it was drained from the pipes and the pipes were dried before removing PBW. The hands-on work was carried out in a green-house with a local exhaust device to prevent scattering of radioactive materials. In this presentation, we report the replacement work of the PBW including safety measures.