Approach to the lifetime assessment of the bayonet back plate for IFMIF target

Agostini, P.*; Ida, Mizuho; Miccich, G.*; Nakamura, Hiroo; Turroni, P.*

Fusion Engineering and Design, 84(2-6), p.364 - 368, 2009/06

https://doi.org/10.1016/j.fusengdes.2008.11.083

In the International Fusion Materials Irradiation Facility (IFMIF), a back-plate of liquid lithium (Li) target is most severely irradiated by high flux of neutrons. The conceptual configuration of the IFMIF target, based on the bayonet back plate, has been developed. The life time analysis of the back-plate has to be made carefully, in order to credibly estimate its expected replacement frequency. The various interconnections between the main damaging causes were discussed in order to evidence the most plausible reasons of the back-plate malfunctioning. The results were as follows. Under IFMIF Li condition with nitrogen content of 10 wppm or less, the erosion/corrosion rate of the back-plate made of the reduced activation ferritic steel is 0.003 mm/year or less. Even in case that the Bragg peak of heat deposition by deuterons approaches to the back-plate by 1 mm, temperature of the back-plate increases by only 12 degrees or less, and induced fatigue load is well low. Thermal stress due to the neutron irradiation is 93 MPa at the back-plate center, which is well below the plastic limit. The positive shift in the ductile brittle transition temperature (DBTT), the most effective factor, reduces the back-plate lifetime to three months or shorter under irradiation damage rate of 60 dpa/year. However, the lifetime can be recovered by the post irradiation annealing heat treatment.