Samples of irradiated graphite from a uranium-graphite reactor contaminated with fuel debris from loss-of-flow accidents, are investigated. Peculiarities of spatial distribution, speciation, and kinetics of leaching by aqueous solution of actinides and fission products are studied at scales from the whole reactor stack down to sub-mm graphite fragments. The main fraction of fuel debris is associated with aluminosilicate-based phases decorating cracks and other defects of damaged graphite details. Elemental composition of actinides and fission products depends on both irradiation and leaching conditions. Significant differences are observed between leach kinetics of various radionuclides; integral leached fraction varies between ~5% for 244Сm to ~90% for 134,137Cs. For some radionuclides sudden massive release due to uneven dissolution of the carrier phases is observed. Disposal of irradiated graphite with significant fraction of fuel debris requires dedicated treatment aimed either at decontamination or at conversion of the radionuclides to insoluble well-fixed form.
The article is dedicated to the safety assessment of mixed storage of irradiated graphite and other types of radioactive waste accumulated during the operation of uranium-graphite reactors. The analysis of heat release processes inside storages containing irradiated nuclear graphite, representing a potential hazard due to the possible heating and, accordingly, the release of long-lived radionuclides during oxidation was carried out. The following factors were considered as the main factors that can lead to an increase in the temperature inside the storage facility: corrosion of metallic radioactive waste, the presence of fuel fragments, and also the random exposure of irradiated graphite to local sources of thermal energy (spark, etc.). It was noted in the work that the combined or separate influence of some factors can lead to an increase in the temperature of the onset of the initiation of Wigner energy release in graphite radwaste (Tin ≈ 90–100°C for the “Worst-case” graphite). The model of heat generation in the storage was developed based on the analysis of the features of graphite radioactive waste storage and Wigner energy release. The layered location of different types of waste (graphite and aluminum) and the local character of the distribution of heat sources were adopted in this model. The greatest heating is achieved if graphite radioactive waste is located near the concrete walls of the storage facility, as well as in direct contact with irradiated aluminum radioactive waste, which was shown in this paper.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.