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

Yanagibashi, Katsumi; Kanamori, Masashi; Okamoto, Naritoshi

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.