Possible use of the DEMO-S ceramic blanket for neptunium transmutation

Abstract

The DEMO-S steady-state demonstration fusion reactor uses a ceramic blanket for energy generation and tritium breeding. The possible transmutation of minor actinides of spent nuclear fuel in the helium-cooled ceramic blanket is examined. The reactor tritium breeding ratio, reaction rates and heat deposition in the module materials were analysed. These values were estimated as a function of the fuel element diameter with neptunium, the number of fuel elements in the cassette, and the presence or absence of a moderator around the cassettes. A three-dimensional Monte Carlo calculation using the MCNP code was performed for the full heterogeneous model of the blanket and fuel assemblies. After six years of reactor operation, for the cassette containing 19 fuel elements with NpN, 82% of the neptunium burnt out in the case of the water-cooled cassette and 72% in the case of the lead-cooled cassette. This corresponds to a transmutation of ∼100 kg neptunium in one module.