Shut-down dose rate analysis for final design of shielding tent in port interspace of ITER UP#18

Abstract

Upper Port #18 (UP18) of ITER is one of the procurement items of the Korea Domestic Agency (KODA), and the final design is being carried out. UP18 as a diagnostics port is divided into 3 sections: port plug (PP), port interspace (PI), and port cell (PC) depending on the distance from the plasma. Because the PI and PC include diagnostics devices requiring maintenance such as valves and detectors, there is a design requirement for human access in a radiation environment. A separate shielding is necessary to satisfy the requirement. In the PI of UP18 the port interspace of UP18, a shielding tent concept was proposed to effectively mitigate the radiation cross-talk which is dose from neighboring ports as well as UP18 PP.Therefore, in this study, neutronics analysis was conducted to assess the shielding tent design. A parametric study for the shielding frame materials, design options, and shielding materials was performed. A shut-down dose rate (SDDR) in a maintenance region was evaluated using SRC-UNED v3.1.4 with FENDL 2.1 and 3.1 cross-section libraries. The analysis results show that the contribution of the shielding frames to SDDR is significantly high in the reference shielding tent design and especially the SDDR difference is attributed to the weight fraction of impurities such as cobalt (Co), niobium (Nb), and tantalum (Ta) within the frame. Borated heavy concrete (BHC) is the effective shielding material in the PI because it shields the neutrons and photons during operation and maintenance. Based on these results, the shielding tent material and design was optimized, considering both the manufacturing cost and the SDDR reduction. The calculated SDDR is 83.9 μSv/hr, which satisfies the design requirement.