EU-DEMO Breeding Blanket temperature evaluation before remote maintenance operation

In DEMO (the European proposal of demonstration fusion reactor) the Breeding Blanket (BB) segments shall be periodically replaced, at end of life or after failure. Any replacement of a BB segment shall be performed by Remote Handling Equipment (RHE) through the vertical upper port any active action is executed by RHE that clamps a BB segment in the upper portion using a BB transporter. A driving requirement of DEMO commercial technology for RHE is the maximum operating temperature at the BB-RHE interface during BB replacement the objective of this study is properly to assess this limit, being now the allowable value at 100 degrees C. This study deals with the Helium Cooled Pebble Bed (HCPB) concept. The initial configuration, with all sector segments (three in the outboard region and two in the inboard one) in their nominal position, has been considered; then the Finite Element model predicts if a natural convection cooling air flux inside vacuum vessel is adequate or if it is necessary a forced convection cooling system. The decay heat produced by the main blanket components (the BB modules caps and lateral walls, the backwalls, the supporting structures, the backplate manifolds, and so on) have been evaluated beforehand: the values applied as body loads in the thermal analyses have been selected within the set related to one month after shut-down. With the assumed geometrical and physical boundary conditions set for the natural and forced convection, the analyses indicate that a forced convection should be necessary to ensure compliance with the present RHE requirements. The obtained results, the analysis assumption and future analysis plan have been briefly discussed.