In Japan, the burnup of nuclear fuel is being promoted to improve the operating rate of nuclear power plants and reduce fuel costs. In addition, the use of MOX fuel is expected to increase due to the promotion of the nuclear fuel cycle. Therefore, it is expected that reprocessing of high burnup fuel and MOX fuel will be carried out in the future. When reprocessing fuels with properties different from those of current nuclear fuels, the composition of High-level radioactive Liquid Waste (HLW) generated in the reprocessing process changes, and further technological development including treatment and disposal methods is required. Therefore, from 2019, in the project commissioned by Ministry of Economy, Trade and Industry “vitrification technology for waste volume reduction”, we are developing vitrification technology that can stably vitrify HLW generated by reprocessing of high burnup fuel and MOX fuel. In this project, we are studying scenarios related to nuclear power generation, developing glass materials, and operating control methods for glass melters. In this presentation, we will report on the progress of research on the development of glass materials by 2022.
In the vitrification of radioactive waste in Japan, the generation of a low-viscosity fluid mainly composed of molybdenum called the yellow phase (YP) is an issue. In HLW generated by reprocessing of high burnup fuel and MOX fuel, a glass material for processing high burnup fuel and MOX fuel without generating YP is required.
In this project, we aim to process high burnup fuel and MOX fuel without generating YP by two methods of changing the composition and shape of the glass material. Borosilicate glass is used in vitrification in Japan. In changing the composition of the glass material, glass with a different ratio of network-former (NWF) and network-modifier (NWM) is produced, and YP inhibitory properties and chemical durability are evaluated. We are also investigating a method of adding rare earth element oxides and the like to borosilicate glass to improve YP inhibitory properties.
Glass beads are used in vitrification in Japan and are mixed with HLW in a melter. In order to improve the reactivity with waste liquid when changing the shape of glass materials, we are studying materials such as glass fiber cartridges and briquettes, which are formed from fibers and powdered glass.
Until 2022, we mainly examined glass materials for vitrifying HLW generated by reprocessing of high burnup fuel. As a result of the examination, a candidate composition that can achieve the target waste-loading without generating YP by changing the composition of the glass material was obtained. The properties such as chemical durability, viscosity, electrical conductivity were evaluated. Also, the effects of changing the glass shape(glass fiber cartridge and/or briquette) on generating YP by vertical gradient furnace tests.
This work was carried out as a part of the basic research programs of vitrification technology for waste volume reduction（JPJ010599）supported by the Ministry of Economy, Trade and Industry, Japan.