Design of a lip seal-replaceable backwall for IFMIF liquid lithium target

IFMIF is an accelerator-based intense neutron source for testing candidate materials for fusion reactors. Neutrons are emitted inside liquid Li flowing on a so-called backplate or backwall made of reduced activation ferritic/martensitic (RAFM) steel. The backwall is joined to a target assembly by means of a lip seal welded by a remote handling system. Since the backwall is operating under severe neutron irradiation conditions, such as a damage rate of 50 dpa/year and a maximum nuclear heating rate of 25 W/cm3, thermo-structural design is one of the critical issues for target design. To reduce thermal stress in the lip seal region, a stress mitigation structure was provided. Thermal stresses were calculated by using the ABAQUS code. The analysis of the lip seal with the stress mitigation structure showed that the maximum von Mises stresses of the backwall core (RAFM) and the lip seal (316L) were 93 and 335 MPa, respectively. Considering the existing weld technique, a modified-improved model to be realized by using the TIG and YAG welding is proposed. R and D on the lip seal weld is currently under way