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Development of accident tolerant control rod for light water reactors

軽水炉用事故耐性制御棒の開発

太田 宏一*; 中村 勤也*; 尾形 孝成*; 永瀬 文久

Ota, Hirokazu*; Nakamura, Kinya*; Ogata, Takanari*; Nagase, Fumihisa

軽水炉のシビアアクシデントにおいては、大規模な燃料破損に先行して制御棒の破損が生じ中性子吸収材が炉心領域から離脱して、制御不能な再臨界となる危険性がある。本研究では、(1)十分に高い融点および共晶反応温度を有する、(2)溶融、再固化燃料物質の高い混和性を有する、(3)十分な制御棒価値を有する事故耐性の高い制御棒(ATCR)の概念を検討している。今回、希土類酸化物が制御棒構造材の融点以上の高温まで鉄と高い共存性があること、Sm$$_{2}$$O$$_{3}$$やEu$$_{2}$$O$$_{3}$$、Gd$$_{2}$$O$$_{3}$$、Dy$$_{2}$$O$$_{3}$$及びそれらとHfO$$_{2}$$との混合物の利用により、現行のAg-In-Cd制御材と同等以上の制御棒価値が得られることを明らかにした。

Control rods can be disintegrated and neutron absorber would be removed from the core region before most of the fuel pins are still not damaged seriously in severe accidents of LWRs. The present study investigates a concept of accident tolerant control rod (ATCR) with the following characteristics; (1) sufficiently-high melting and eutectic temperatures, (2) high miscibility with molten and solidified fuel materials, and (3) enough control rod worth. It has been shown that rare-earth sesqui-oxides are expected to be compatible with iron up to higher temperatures than the melting points of structure materials of control rods, and that Sm$$_{2}$$O$$_{3}$$, Eu$$_{2}$$O$$_{3}$$, Gd$$_{2}$$O$$_{3}$$, Dy$$_{2}$$O$$_{3}$$ or their mixtures with HfO$$_{2}$$ are available as alternative neutron absorbers to conventional Ag-In-Cd alloy.

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