PHWRs use natural uranium as fuel and consequently the burn-up coefficient is relatively small compared to PWRs or other existing power reactors. The small burn-up coefficient results in a high volume of irradiated fuel to be disposed, with a high concentration of plutonium and minor actinides. In Romania the irradiated fuel from the existing CANDU 6 spent fuel pool is currently transferred in the Dry Intermediate Fuel Storage Facility existing at the NPP site. Partitioning and Transmutation (P&T) techniques could contribute to reduce the radioactive inventory and its associated radio-toxicity. The use for this purpose of ADS and FBR was more studied, but HWR were not. Therefore, the paper presents different theoretical possibilities to transmute/burn the Plutonium and minor actinides in two different PHWRs — CANDU and ACR, using WIMSD code. Different types of MOX alternative fuel, with variable initial Pu content are analyzed. The results present the reactivity effects along with the isotopes concentration in spent alternative fuel and determine the optimal solution for the fuel type/composition. Thus is indicated the most suitable PHWR type of reactor for possible Plutonium and minor actinides transmutation. The simulations showed that Pu content for an irradiation period of 200 days decreases from the initial value up to 11% in a CANDU reactor and 29% in an ACR. Thus ACR can reduce the plutonium inventory from MOX fuel and could be a transmutation solution. From the economic/technical point of view this analysis also provides input for a study yet to be conducted.

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