Thermo-structural analysis and design consideration of the replaceable backwall in IFMIF liquid lithium target

The IFMIF is an accelerator-based intense neutron source for testing candidate materials for fusion reactors. Intense neutrons are emitted inside the Li flow through a backwall. The backwall made of 316L stainless steel or RAFM is attached to the target assembly with a lip seal welded by a YAG laser. Since the backwall is operating under a severe neutron irradiation of 50 dpa/year and a maximum nuclear heating rate of 25 W/cm3, thermo-structural design is one of critical issues in a target design. Thermal stress was calculated using the ABAQUS code. As a permissible stress, yield strength at 300 °C was used. In the case of the 316 stainless steel backwall, the maximum thermal stress was more than the permissible stress (164 MPa). On the other hand, in case of the F82H backwall, a maximum thermal stress was below the permissible stress (455 MPa). Therefore, F82H is recommended as the backwall material.