ITER Vacuum Vessel materials: impact of Cobalt content on the clearance index and contact dose rate

0.05 wt% is the reference value of Cobalt content in the ITER Inboard and Outboard Vacuum Vessel materials. Different Co contents have been considered and the effects on the corresponding waste management policy and maintenance Occupational Radiation Exposure are presented and discussed. The analyses hughlighted the impact of the cobalt content (from 0.01 up to 0.25 wt%) into the different Vacuum Vessel steels on the material clearance index of the Inboard and Outboard Vacuum Vessel zones (inner and outer shells and shielding plates) and on the material contact dose rate of the inner and outer shell of the Outboard Vacuum Vessel. The ANITA-2000 activation code package, with the EAF-2003 neutron activation library, has been used for the calculations. The same operating conditions used for the ITER GSSR reference calculation have been assumed. The following conclusions have been outlined from the results analysis: • the increasing of cobalt content on all the VV materials (both inboard and outboard VV zones) from 0.01 to 0.25 wt% does not change significantly their behavior from a waste management policy point of view, i.e. if a material containing 0.05 wt% Co (ITER reference) is clearable within 100 years from the final plant shut down it remains clearable within 100 years also with a 0.25 wt% Co content. • the time needed to reach a material contact dose lower than 100 microSv/h at the Outboard Vacuum Vessel Front and Rear Walls depends clearly on the cobalt content in the 316L(N)-IG material of the corresponding zones. This is significant mainly for the Rear Wall: the time increases from about 4 months to about 8 years if Cobalt content increases from 0.01 to 0.25 wt%. For the Front Wall that time increases correspondingly from about 67 to about 82 years. Detailed results of the activation calculation are given in appendix.