Direct disposal concepts of spent mixed oxide fuel from light water reactors based on heat transfer calculations

Direct disposal concepts of mixed oxide spent fuel (MOXSF) consumed in light water reactors were investigated via heat transfer calculation. The temperature of the buffer material surrounding the waste is the most stringent limitation on the direct disposal of MOXSF. Therefore, the effects on the maximum temperature of the buffer material were examined by changing the occupied area, cooling term of MOXSF, disposal depth, and buffer material thickness referring to the direct disposal concepts of uranium spent fuel. Moreover, some possible disposal concepts for MOXSF were obtained based on the examination. The examination results showed that it is necessary to change the cooling term and disposal depth in addition to the change of the occupied area. The obtained disposal concepts with a combination of these changes needed the occupied area per unit waste of the MOXSF was three to five times that of uranium spent fuel.