Grouping of reprocessed nuclides in spent fuel to reduce the overall repository impact by simple analyses of thermal load and nuclide migration

Repository is designed from aspects such as mechanical stability, thermal load, and chemical environment. The volume of the high-level radioactive waste (HLW) repository is mainly governed by the interval of the emplacement between two wastes. Dense disposal may cause high temperature field around the disposal pit thus the interval must be expanded due to the thermal stability of buffer material. Partitioning is therefore considered to reduce the thermal load in the repository by separating the heat generation nuclides such as Sr-90 and Cs-137 from HLW. Some partitioning processes classify the nuclides into several groups from the point of process viability and not fully investigated from the impact to the HLW repository so far. The long half-lived nuclides such as Cs-135 need long migration distance, say depth, but deep disposal can not be accepted due to high geothermal condition. This contradiction implies the grouping of Cs and Sr is not available from both thermal and migration points of view. The report indicated the appropriate grouping of the reprocessed nuclides is investigated to reduce the overall impact of the repository from both thermal impacts and migration impacts. The impact factor was assigned for each nuclide by the simple analyses of thermal load and migration then grouping of the nuclides in Spent Fuel is examined by using the impact factor. According to the total impact factors in each group, availability of separate disposal is discussed. For example, the group without heat generation can be disposed in shallow repository when the migration impact is extremely low. The calculation indicated the key is the separation of alkaline earth metals from alkaline metals. The comparison of the total volume of the repository of HLW and that for repositories of partitioned groups of nuclides, were made and the results indicated that the volume reduction will be achieved by the introduction of the appropriate grouping of nuclides