Impact of fuel type and discharge burnup on source term

Knowledge of spent nuclear fuel (SNF) source term (decay heat, reactivity, nuclide inventory, other relevant properties of SNF) is essential in the safe handling and final disposal of SNF. For example, decay heat power is one of the key limiting factors to determine how densely the fuel canisters can be packed in the final disposal tunnels. The fuel type and burnup affect the nuclide inventory of the SNF and therefore have an essential impact on the source term. Fuel discharge burnup has increased over time and new types of fuel typically enable higher burnups than before. In Finland, two different reactor types have been operated (VVER-440 and BWR) and two others (EPR and VVER-1200) are planned to be operated in the near future. The fuel assembly design used in these types of reactors varies in many parameters such as e.g. geometric shape, axial enrichment zoning and nuclide content (VVER-1200). Also, several different fuel assembly types can be used in one type of a reactor. The possible differences include e.g. average enrichment, enrichment zoning, number of burnable absorber rods and geometric parameters, such as fuel pellet dimensions and cladding thickness. The operating parameters such as power and boron concentration also depend on the reactor and fuel assembly types and have an effect on the SNF source term. In this work, the source term of different VVER-440 and VVER-1200 fuel assemblies are calculated as a function of fuel burnup using the Monte Carlo particle transport code Serpent 2. The effect of burnup and fuel type to different components of the source term such as decay heat, activity and the nuclide inventory will be examined.