Application of fracture mechanical assessment to in-wall shield ribs in ITER vacuum vessel

•Structural analysis of IWS rib assembly was performed and verified via RCC-MR.•Systematic crack initiation assessment was conducted by using weight function method.•Conservatism of the weight function method was verified by detailed X-FEM analyses. In-wall shield ribs are installed between double walls of vacuum vessel and their role is to hold neutron shielding blocks. Since one of key issues on these structures is to sustain integrity during entire ITER operation without any in-service inspection or maintenance, fracture behavior shall be evaluated in design stage. In the present study, a weight function method was employed for crack initiation assessment. The most critical structure was selected as a representative one and its structural integrity was evaluated. In order to check validity of this method, an extended finite element method was adopted for bounding cases. As a result, not only structural safety but also quite conservatism were observed comparing to those of extended finite element analysis with similar tendency. It means that the weight function method could be a conservatively practical approach for fracture mechanical assessment of in-wall shield ribs.