Systematic analysis of decay gamma-ray streaming through narrow gap in fusion experimental reactor

There exist a large number of void gaps (or slits) in a tokamak fusion reactor and streaming of decay-γ-ray from activated structure components through these gaps will cause serious problems after reactor shutdown. In this study, first, characteristics of decay-γ-ray source, i.e. spatial distribution and energy spectrum, were investigated for radiation shield with and without a void gap. Next, a series of streaming calculations were performed to clarify dependence of the amount of γ-ray streaming on gap size, γ-ray energy and source distribution using a simplified hypothetical shield model. Results of these calculations were summarized in the form of figures and tables, so that they are easily used for shield design. Further, an approximate method using these data was applied to streaming estimation and it was found that it has sufficient accuracy as compared with the detailed analysis. (author)