Nuclear technology considerations and neutronics for the ST-E1 fusion power plant

Abstract This paper presents Tokamak Energy’s pre-concept design of ST-E1, a low aspect ratio tokamak fusion reactor. Efficacy of radiation shielding in protecting the high temperature superconducting magnets systems is a major driver dictating tokamak size, plant lifetime, and balance of plant. It is crucial that neutronics and material considerations are incorporated into plant design from the earliest design stages and comprehensively taken into account across all areas through the systems engineering framework. At Tokamak Energy, a dedicated workflow for plant-scale neutronics simulations has been developed using G4Tokamak, an in-house application based on the Geant4 toolkit. This workflow enabled faster and more efficient design iterations, and its results were verified through benchmarking against MCNP. A four-part shielding architecture, comprising of the centre column, vacuum vessel, outboard horizontal and vertical elements, was designed to balance neutronics performance, thermal management, structural demands, and cost. The shielding system, at this pre-concept stage, demonstrates the feasibility of limiting the neutron flux to the magnet systems to support a full power life of 30 years, and limiting the nuclear heating of the cold mass within cryogenic cooling capacity. Activation studies highlight maintenance and long-term waste management challenges, with non-reduced activation ferritic martensitic steels and plasma facing components showing the highest activation. Collectively, these results establish a comprehensive neutronics and materials framework, baseline core shielding design for ST-E1, and demonstrate its readiness for progression to detailed concept development.