Plutonia-Thoria Fuel Cycle as Starting Solution for a Wider Thorium Use

This paper is focused on a description of thoria fuel option. Our opinion is that this option, beyond being a valuable way to exploit the energy content of plutonium without further breeding it, may be a starting point for introducing an Uranium-Thorium fuel cycle, based on a different strategic context with respect to past proposals. The option is based on the adoption of current or advanced PWRs, the latter characterised by a reduced fuel power density, always adopting conventional fuel rods and assemblies. A three-batches full core loading scheme is assumed. The thoria-plutonia composition is determined by the constraints to obtain at Beginning Of Life (BOL) a non positive void coefficient, and to reach a burnup as high as possible. Different fuel compositions and pellet radius are considered. The plutonium content is in the range of 4.5˜15%, mainly depending on the plutonium quality, namely Weapon Grade (WG) or Reactor Grade (RG). The results are in terms of dynamic coefficients, life duration, plutonium consumption and final isotopic compositions. These fuels show the capability to destroy about 40˜60% of total plutonium for RG, while this figure rises to 65˜70% for WG. These values are well above those obtained by MOX option.