JCO臨界事故に関するサイクル機構とJCOとの関係について-改訂第2版-

The Relationship of JNC and JCO in the Uranium Processing Plant Criticality Accident -The second version edition-

柳橋 勝美; 金盛 正至; 岡本 成利

Yanagibashi, Katsumi; Kanamori, Masashi; Okamoto, Naritoshi

平成11年9月30日、JCOにおいて臨界事故が発生した。この事故はJNCがJCOに発注した高速実験炉「常陽」燃料用としてウラン濃縮度約18.8%、約60kgUの八酸化三ウラン(U3O8)を硝酸ウラニル溶液(UNH)へ再転換加工する作業中に発生したものである。本報告書は、JNCとJCOとの「常陽」燃料用濃縮ウランの再転換加工の契約に関して、原子力開発が開始された当時のウラン加工事業に関する国の方針、JCOへの発注の経緯、契約内容等について記述した先の調査報告書(JNC TN8420 2002-004、JNC TN8420 2003-003)の発行後も継続して事実関係の再調査や再確認を行ってきており、これらを反映して改訂第2版としてまとめ直したものである。

On September 30 1999, the criticality accident occurred at JCO's uranium conversion building in Tokai. The accident occurred during reconversion from UO to uranium nitrate solution (UNH) with uranium enriched 18.8% and about 60 kgU. JCO contracted with JNC to supply UNH that is fuel material for the experimental fast breeder reactor "JOYO". JNC has contracted with JCO that had started nuclear fuel material processing business following a definite policy of Japanese government and developed "SUMITOMO ADU PROCESS". JNC made the first contract with JCO in 1985 and has made a contact every year. There had never been a problem in their products. JNC inspected products based on contract. JNC discharge our duty as customer inspecting products based on contract. As for safety control, JCO had taken licensing safety review and had been permitted to be "a processing facility". Therefore JNC understood that JCO produced following this license. "The Uranium Processing Plant Criticality Accident Investigation" showed that JCO had been taking a different method from the permit and violating the license. However JNC had never been explained about that and JCO's operation procedures had never described about that. Therefore the Criticality Accident couldn't be avoided. The reports is the revision of former JNC TN8420 2003-003.