Estimation of TBR on the gap between neighboring blanket modules in the DEMO reactor

Someya, Yoji; Tobita, Kenji

When one wants to simply estimate Tritium Breeding Ratio (TBR) using 1D analysis, the TBR may be reduced from a "local" TBR for the breeding zone of a blanket module by multiplying the breeder coverage. The gap between adjoining modules and the frames of the modules are regarded as non-breeding zones. Based on the methodology, the width of the blanket modules gap was determined to be 5 mm or less in the SlimCS DEMO reactor. Contrary to this, recent study revealed that neutrons scattered in the non-breeding zones can enter breeding zones, contributing to tritium production. This means that the estimation method mentioned above tends to underestimate TBR. In order to assess the scattering effect quantitatively, we carried out the 3D Monte Carlo code MCNP-5 calculation. When a values of the TBR compare the MCNP to the previous method, indicating little decrease in TBR for the gap of less than 2 cm. The allowance of the gap will facilitate access of remote handling systems for replacement of the blanket modules.