Assessment of occupational radiation exposure (ORE) for hands-on assistance to the remote handling at ITER ports and waste treatment

The occupational radiation exposure (ORE) assessment for ITER systems is evolving as design makes progress. This paper deals with the ORE assessments for two important ITER activities: those in the assistance to the remote handling on a port plug hosting diagnostics and those carried out in the Waste Treatment System. For the former a software tool has been developed to handle the large amount of data processed and to allow user friendly updating of data as design or maintenance procedures evolves, and, know-how on maintenance activities improves. A systematic approach was adopted to evaluate work efforts (WE) needed to execute specific tasks. The so-called "elementary works" were identified and classified and the time required to perform the operation and involved people were estimated. The elementary works were then aggregated in the so-called main operations (e.g. window replacement, pipe removal, etc.). For each of them, on the base of expected maintenance frequency and dose rate fields, total WE and worker doses were calculated. It was assessed that hands-on activities in the Equatorial Port No. I require 472 person h of WE leading to a collective dose of similar to 7.4 person mSv/year. The most critical operation in terms of worker doses is the sealing/unsealing of port plug, which weights for about the 23% of the total. The second ORE assessment was related to the management of ITER operational radioactive wastes. These wastes include streams originated in the plant from the experimental and maintenance activities, with exclusion of those generated inside the Tokamak that will be highly activated and will be managed inside the Hot Cell Processing System. The estimated collective annual dose related to the Waste Treatment System ranges between similar to 4.3 and similar to 4.9 person mSv. The two values depend on the assumptions made for the exposure levels in the operative areas. Both studies have to be considered as preliminary as far as the results are concerned due to the quite rough input data (on dose rates and design details), while the approach might be considered sound and up to date. (C) 2007 Elsevier B.V. All rights reserved.