Progress in nuclear analyses of the ITER TBM Port Plug with Dummy TBMs

To achieve the validation and testing of tritium breeding blanket concepts, mock-ups of breeding blankets, called Test Blanket Modules (TBMs), are tested in three equatorial ports of the ITER tokamak. The TBM Port Plugs consist of Frame and TBM-Sets, which will be tested sequentially, each one tailored to the specific plasma operation scenario and test objective. In case a TBM-Set is not available, it can be replaced by a Dummy TBM at any time. TBM Frame and Dummy TBM are made of stainless steel and also need to meet ITER requirements on shielding, heat removal and safety, including activation. The maintenance operations for the TBM Port Plug include various activities in the Port Cell as well in the Hot Cell. In order to assess the requirements, a detailed MCNP model of the TBM Port Plug (PP), the Pipe Forest (PF) inside the Port Interspace (PI) and the Bioshield Plug (BP) was developed and integrated into the ITER neutronics C-Model. This analysis concerns the neutronic behaviour of the TBM PP with two Dummy TBMs by means of activation and shut-down dose rate (SDDR) calculations. The analysis includes the evaluation of the radiation fields around the TBM PP inside the ITER tokamak at several cooling times. Two configuration scenarios have been considered, one with a PF and PF structure inside the PI and one without this structure. The results show that the contribution to the SDDR from the TBM PP at 12 days after reactor shut down is small compared to the contribution originating from the PF structure.