The issue of radioactive waste management is becoming increasingly important. To provide a safe and acceptable environmental load for disposal of high-level radioactive waste (HLW), it is necessary to examine the future fuel cycle system that intends to use the mixed oxide (MOX) fuel based on plutonium. This approach has not been considered until now from the viewpoint of establishing an acceptable disposal method. If such fuels are reprocessed and vitrified in the near future, the thermal properties of the vitrified waste will have significant impact on disposal strategies including an increase in the disposal area of HLW deep underground. &nbsp;In addition to the thermal properties of the waste, the number of vitrified waste packages is also a major influencing factor that determines the disposal area of the repository. The impact of disposal of MOX fuel from light water reactors (LWRs) has been considered for both the number and the thermal properties of the vitrified waste for various conditions of the nuclear fuel cycle.To reduce the thermal properties of the vitrified waste, a UO2-MOX mixed vitrified waste can be assumed given that previous research has suggested diluting MOX dissolution liquid waste with a U solution or a UOX liquid waste as a possible option also from the viewpoint of MOX dissolution condition. In this study, the evaluation of effects of mixing two type of fuels were performed. Furthermore, heat transfer calculation was carried out to evaluate the temperature of buffer material in a geological repository. As the results, it was confirmed that the buffer material temperature was kept below 100°C for the following conditions: a cooling period for the SF of 15 years for UO2 fuels and 50 years for MOX fuels, a waste loading ratio of 20 wt%, an occupied area per waste package of 44.4 m2/glass unit, and a mixture ratio of UO2/MOX = 95:5. It is evident from the results that the heat generation of the MOX-LWR fuel are high if a technical option such as mixing both fuels is not introduced for the disposal of the spent MOX-LWR fuel. The nuclear fuel cycle conditions, technical options, waste occupied area per waste package are strongly relevant to the thermal properties of the vitrified waste, and it is necessary to consider the combination of these factors together with the number of waste packages to progress the feasibility studies for geological disposal of MOX-LWR spent fuel.

Thermal Impact on Geological Disposal of Mixed Uo2-Mox Vitrified Waste Associated With Mox Reprocessing

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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