Remote maintenance scenario of the beam line components of the ITER neutral beam system

Abstract

The ITER neutral beam (NB) cell contains the neutral beam injectors (NBI) that provide heating power for fusion reaction in the tokamak machine. The NB cell is a radiation-controlled area where human worker access is strictly limited or prohibited depending on the NB cell configurations. Establishing the maintenance processes in the early design phase of a RH system is crucial in order to guarantee that the overall system configuration satisfies the maintenance requirements in given conditions and constraints. This paper describes the remote maintenance scenario of the beam line components (BLC) of the NB system by using the neutral beam remote handling system (NBRHS). This operation is a corrective maintenance operation that could happen multiple times during lifetime of ITER. If one of the BLCs fails, the failed NBI is isolated by closing the absolute valve to continue the tokamak operation. After that when the long-term maintenance campaign starts, the failed BLC needs to be replaced. The maintenance sequences involve human worker hands-on operations in the hot cell complex (HCC) and in the NB cell to prepare the RH operations, deployment operations of the NBRHS and the RH tools, removal/opening/transportation/storage operations to access to the failed component, and to remove and replace the failed component. Many RH tools are required during these processes such as unbolting/bolting, connector disconnection/connection, pipe cutting/welding/inspection, heavy and large component handling etc. Moreover, the operations need to be done without or minimizing spreading of contamination from the NBI vessels/components to the NB cell as the NB cell shall remain human accessible area during the long-term maintenance periods. The maintenance sequence study shows that the developed RH sequence is applicable in the current NB cell environment and is compatible with the defined interfaces in the plant systems. The developed scenario needs to be elaborated further detail in the next design phases together with the detail design of the RH equipment and the RH tools.