Shutdown dose rates at ITER equatorial ports considering radiation cross-talk from torus cryopump lower port

Abstract

Shutdown dose rates for planned maintenance purposes is an active research field in ITER. In this work the radiation (neutron and gamma) cross-talk between ports in the most conservative case foreseen in ITER is investigated: the presence of a torus cryopump lower port, mostly empty for pumping efficiency reasons.There will be six of those ports: #4, #6, #10, #12, #16 and #18. The equatorial ports placed above them will receive a significant amount of additional radiation affecting the shutdown dose rates during in situ maintenance activities inside the cryostat, and particularly in the port interspace area. In this study a general situation to all the equatorial ports placed above torus cryopump lower ports is considered: a generic diagnostics equatorial port placed above the torus cryopump lower port (LP#4). In terms of shutdown dose rates at equatorial port interspace after 106s of cooling time, 405μSv/h has been obtained, of which 160μSv/h (40%) are exclusively due to radiation cross-talk from a torus cryopump lower port. Equatorial port activation due to only “local neutrons” contributes 166μSv/h at port interspace, showing that radiation cross-talk from such a lower port is a phenomenon comparable in magnitude to the neutron leakage though the equatorial port plug.