Shielding analysis at the upper section of accelerator-driven system

鉛ビスマスターゲット/冷却ADS上部構造の遮蔽解析

佐々 敏信   ; 大井川 宏之 

Sasa, Toshinobu; Oigawa, Hiroyuki

マイナーアクチニドの核変換を行う鉛ビスマスターゲット/冷却ADSでは、陽子ビームを鉛直方向から導入する。この構成では、ビームダクトは炉上部へのストリーミングパスとなるため、遮蔽解析を行った。炉上部の陽子ビーム制御用マグネットの放射化解析を行い、日本の法令に基づく作業者の作業時間が10分程度となること,延長するためには追加遮蔽が必要であることを明らかにした。また、タンク型炉心で挿入される蒸気発生器内の水の放射化解析を行い、二次冷却系への遮蔽対策が不要であることを示した。

A lead-bismuth target/cooled ADS for transmutation of minor actinides adopts a vertical injection of proton beam. In this configuration, the beam duct acts a streaming path toward the upper section of subcritical core. In this analysis, two issues for radiation shielding related to ADS beam transport are discussed. Several magnets to control the proton beam are located above the subcritical core and the workmen might access the high-dose area. We determined the allowable maintenance time and obtained the several tens minutes for maintenance per person can be allowable according to the Japanese regulations. To enhance the maintenance time, additional shield must be located. Our proposed ADS are designed as a tank-type layout of the subcritical core because of the usage of heavy liquid metal coolant. So, the steam generators which are located beside the beam duct have a potential of heavy irradiation by escaped neutron through the beam duct space. We investigated the activation of secondary coolant and found that no specific addition of shields was required.