Material control and accountability aspects of safeguards for the United States uranium-233/thorium fuel recycle plant

The material control and accountability aspects of reprocessing and refabrication in a large-scale high-temperature gas-cooled reactor (HTGR) fuel recycle plant are discussed. Two fuel cycles are considered. The highly enriched uranium (HEU) cycle uses uranium enriched 93% in 235U as the initial fuel. The medium-enriched uranium (MEU) cycle uses uranium with a 235U enrichment less than 20% as its initial fuel. In both, 233U is bred from thorium. The HEU 235U and the 233U of both cycles are recycled. The MEU 235U is retired to waste after one reactor cycle. Typical heavy metal contents of spent fuel elements from both cycles are presented. The main functional areas of the recycle plant are shipping, receiving, and storage; reprocessing; refabrication; and waste treatment. A real-time materials accountability system will manage the data provided by measurements from all four areas. Simulations of material flow used in the HTGR development programme are forerunners of such a system. The material control and accountability aspects of reprocessing and refabrication only are discussed. The proposed accountability areas are identified and the measurement techniques appropriate to various streams crossing the boundaries of the areas are identified. Special emphasis is placed on novel non-destructive methods developed for assaying solid materials containing 233U-Th. The material form, total uranium and plutonium, and activity of selected reprocessing streams are listed. The isotopics and activity of the uranium input into refabrication are also presented. (author)