Materials optimisation for fusion power plants waste management from neutronics and activation assessment

Materials-related issues in the safety and licensing of nuclear fusion facilities

“…Focusing attention on the materials used in the cooling system, it should be pointed out that the gamma dose rate is generated by the deposition of the activated corrosion products (ACPs) on the pipe, valve, pump and heat exchanger walls and by the direct activation of the pipe walls induced by the delayed neutron emitted by the decay of 17 N, an activation product of 16 O [9]. In a water-cooled DEMO or power plant, such as the water-cooled lithium lead (WCLL) concept, the same problem arises, while the contribution of the cooling system to the worker dose is less significant in a helium cooled plant such as the helium-cooled pebble bed (HCPB), helium-cooled lithium lead (HCLL) or dual-coolant lithium lead (DCLL).…”

“…Engineering alloys for use in fusion, such as austenitic or ferriticmartensitic stainless steels, have been studied for optimization by reducing the composition of impurities, which reduces the overall radioactivity of the material at the end of its service life. An example is reducing the silver impurity in stainless steel [16] and Nb and Mo impurities in RAFM [17]. With good planning, low activation materials and optimized engineering alloys will reduce the waste burden during decommissioning, perhaps even leading to free release of portions of the decommissioning debris for use in commercial industry.…”

“…Neutron and gamma-ray shielding is required to reduce radiation fluxes originating from the plasma as well as other sources, principally materials that have become activated by neutrons. For example, neutron activation of oxygen in water coolant yields 16 N which is a powerful gamma emitter and may lead to a need to shield parts of the cooling circuit to minimize personnel exposure. Apart from reducing dose rates in ORE, the shielding function is necessary to reduce materials damage by neutrons (particularly at the VV), to protect electronic components including those in safety equipment, and to minimize nuclear heating in cryogenically-cooled superconducting coils.…”