Evaluation of uranium thorium and plutonium thorium fuel cycles in a very high temperature hybrid system

•A conceptual design of a hybrid system composed by a VHTR and two ADSs is analyzed.•U + Th and Pu + Th fuel cycles are evaluated in the proposed hybrid system.•Notable reduction of the Pu isotopes and MA stockpile is obtained in the U + Th cycle.•Considering U233 recycling, the U + Th cycle in the hybrid system is advantageous.•Pu + Th cycle reaches a better performance than the U + Th cycle with the same burnup.

In recent times, there is a renewed and additional interest in thorium because of its interesting benefits. Thorium fuel cycle is an attractive way to produce long term nuclear energy with low radiotoxicity waste. In addition, the transition to thorium could be done through the incineration of weapons grade plutonium or civilian plutonium. Th-based fuel cycles have intrinsic proliferation-resistance and thorium is 3–4 times more abundant than uranium. Therefore, thorium fuels can complement uranium fuels and ensure long term sustainability of nuclear power.In this paper, the main advantages of the use of fuel cycles based on uranium-thorium and plutonium-thorium fuel mixtures are evaluated in a hybrid system to reach the deep burn of the fuel. To reach this goal, the preliminary conceptual design of a hybrid system composed of a critical reactor and two Accelerated Driven Systems, of the type of very high temperature pebble-bed systems, moderated by graphite and cooled by gas, is analyzed.Uranium-thorium and plutonium-thorium once-through and two stages fuel cycles are evaluated. Several parameters describing fuel behaviour and minor actinide stockpile are compared for the analyzed cycles.