Impact of fusion neutrons on helium production in beryllium and tungsten, and tritium breeding in ITER and DEMO

Abstract

The project studies blanket designs of ITER and DEMO for neutron shielding, helium production and tritium breeding. On the one hand, a comparison has been made between beryllium and tungsten as first wall materials. On the other hand, tritium breeding blanket models have been studied, focus on the European test blanket module (TBM) concepts, the helium-cooled pebble bed (HCPB) and the helium-cooled lithium-lead (HCLL).The choice of plasma facing materials and the tritium breeding technology are key issues in the technological development of future fusion power plants. Whereas the ITER design includes beryllium as the first wall material of the blanket and tungsten in the divertor, DEMO will possibly use tungsten for both surfaces, due to beneficial characteristics of this material related to lower tritium retention and lower erosion rates. As future DEMO-type reactors are intended to be tritium self-sufficient, the reactors would dedicate most of the blanket to tritium breeding.Both analytical (multigroup diffusion theory) and Monte-Carlo methods were utilized to calculate the neutron fluxes and neutron induced reactions. The Serpent code is used to run Monte-Carlo simulations.The results for the Be-W comparison indicate that W is a better first wall material in terms of blanket shielding capability for high-energy neutrons and showing lower helium production in the first wall. However, the simulations for the HCPB and HCLL models show that the use of a Be first wall instead of W leads to a substantial increment of the tritium breeding ratio (TBR), allowing the use of lithium with lower enrichment.The assessment of the European tritium breeding blanket concepts indicated that HCPB models have a higher TBR and better shielding capability than HCLL models, being the HCPB with Be as first wall the most efficient breeding blanket.Finally, lithium depletion simulations for the HCPB and HCLL models showed that these blankets can be easily designed to work without recharging lithium during their estimated lifespan of 5 years.