European development of He-cooled divertors for fusion power plants

Abstract

Helium-cooled divertor concepts are considered suitable for use in fusion power plants for safety reasons, as they enable the use of a coolant compatible with any blanket concept, since water would not be acceptable, e.g. in connection with ceramic breeder blankets using large amounts of beryllium. Moreover, they allow for a high coolant exit temperature for increasing the efficiency of the power conversion system. Within the framework of the European power plant conceptual study, different helium-cooled divertor concepts based on different heat transfer mechanisms are being investigated at ENEA Frascati, Italy, and Forschungszentrum Karlsruhe, Germany. They are based on a modular design which helps reduce thermal stresses. The design goal is to withstand a high heat flux of about 10–15 MW m−2, a value which is considered relevant to future fusion power plants to be built after ITER. The development and optimization of the divertor concepts require an iterative design approach with analyses, studies of materials and fabrication technologies and the execution of experiments. These issues and the state of the art of divertor development shall be the subject of this report.

Surface morphology changes of tungsten exposed to high heat loading with mixed hydrogen/helium beams

“…A high thermal efficiency of a power plant requires a hot coolant which results in high temperatures of the plasma-facing material, limited by recrystallization and grain growth of W. During normal operation, the divertor PFCs have to withstand 10-15 MW/m 2 steady state heat load and expected particle fluxes of $10 24 atom/m 2 s À1 [1], a few per cent of this amount consist of He from the D-T fusion reaction. The typical surface temperature of the highest heat loaded divertor plasma-facing material will be in the range between 1000 and 1700°C [2]. Excursions up to >2000°C are possible.…”

Recent US activities on advanced He-cooled W-alloy divertor concepts for fusion power plants

“…This concept, named HEMP (Helium cooled Modular divertor with Pin array), and a modification of it based on flow through parallel slots (HEMS) became the reference concept for the divertor development at the Forschungszentrum Karlsruhe (FZK) [10].…”

Consistent integration in preparing the helium cooled lithium lead DEMO-2007 reactor

“…It uses EUROFER (a low activation ferritic/martensitic steel) as structural material, the eutectic Pb-15.7Li [9] enriched at 90% in 6 Li as breeder, neutron multiplier and tritium carrier and He as coolant with inlet/outlet temperature of 300/500 • C and 8 MPa pressure. To simplify the balance of plant a helium-cooled divertor has been chosen [10]. It uses W as armour material, W-alloy as pressure retaining boundary and He as coolant with inlet/outlet temperature of 541/717 • C and 10 MPa pressure.…”