Application of NDA technique for Pu/U solid waste at Rokkasho Reprocessing Plant

In order to implement accurate material accountancy at large reprocessing plant like Rokkasho Reprocessing Plant (RRP), it is necessary to introduce accurate measurement systems not only for mainstream material, but also need appropriate measurement systems for solid waste materials, even very small nuclear material contained. RRP has generated various solid wastes for instance leached hulls, vitrified waste for high-level liquid waste and low-level solid waste. The plutonium quantity in these wastes cannot be measured directly nondestructive assay (NDA) techniques because the waste contains curium so that the neutron from spontaneous fissions is obscured by curium or plutonium. The most practical NDA technique is neutron counts emitted from curium in the wastes. In this sense, RRP has introduced several NDA systems in order to provide effective and efficient the material accountancy. Key NDA system for waste measurement is Waste Crate Assay System (WCAS). WCAS measures plutonium and Uranium quantity in the solidified waste based on Add- a-source method and curium versus plutonium ratio method. This paper describes the evaluation results for optimization of parameters. (author)