Transient thermal analysis and structural assessment of an ex-vessel LOCA event on the EU DEMO HCPB breeding blanket and the attachment system

In the framework of the EUROfusion Consortium the Helium Cooled Pebble Bed (HCPB) breeding blanket (BB) is being developed. A blanket attachment system is also under development, which allows the integration of the BB into the EU DEMO tokamak. The blanket attachment system is thereby responsible for the mechanical connection of the BB to the DEMO vacuum vessel (N). It transfers the mechanical loads between BB and W. The high mechanical and thermal loads on the blanket segments during normal and off-normal conditions especially pose strong requirements to the blanket attachment system. This article focuses on the off-normal event of an ex vessel Loss Of Coolant Accident (LOCA) in the HCPB BB. The performance of its blanket attachment system is assessed as this event will induce a large temperature increase and thus an additional thermal expansion in the blanket, posing big challenges for the blanket attachment system and the blanket supporting structure itself. A 3D transient thermal analysis under an ex-vessel LOCA condition of the HCPB BB is presented. Furthermore structural assessment of HCPB blanket segments and the current blanket attachment system with respect to RCC-MRx rules is reported, giving also an estimation of the resulting reaction loads to the W during such an accidental event. The Finite Element Method (FEM) software ANSYS 18.0 is used for the thermal and structural analysis.