Transfer Cask, a key System for Nuclear Maintenanceand Operational Availability of Iter

The operational availability of Iter is strongly dependent on the duration of the maintenance of internal components as divertor cassettes, blanket modules or plugs (diagnostics, heating systems). These plasma facing components will be highly activated by neutrons and/or contaminated with tritium so will have to be moved using the Cask and Plug Remote Handling System (CPRHS) from/to Port Cell (PC) to/from Hot Cell (HC) to be repaired or replaced. The Casks being not shielded, human access will be forbidden in the trajectory zones and, in the event of a failure of CPRHS functions, all rescue operations will have to be remotely conducted.The Iter maintenance systems shall be able of processing, in a six-month maintenance period, several tasks in both parallel and series. The time to perform online CPRHS operations for 2 equatorial plugs maintenance has been estimated at half of the total time allocated to the long term maintenance activities. The remaining time for PC preparation and cleaning, refurbishment and testing of 2 plugs in HC might be too short especially as the duration of online operations has been estimated assuming 100% availability of CPRHS and without taking into account all the regulatory operations (control, test) to do because of the nuclear environment.Insofar as the potential failure modes of CPRHS functions could be severe in terms of time to repair, an inventory of function outages and an analysis of conventional and nuclear risks have been made at each stage of the diagnostic plug maintenance process using CPRHS. Finally, based on the probability of occurrence of abnormal events and the estimated time for potential rescue operations, the CPRHS availability (RAMI approach) and the duration for the transfer of a plug using a probabilistic approach (Monte Carlo analysis) have been assessed to verify that the time for maintaining two diagnostic plugs is in line with the Iter operational availability requirement.