Effect of high-temperature neutron irradiation on fracture toughness of ITERspecification tungsten

The effect of neutron irradiation on the fracture toughness of two commercially pure tungsten materials processed according to ITER specifications has been investigated for three doses: 0.08 dpa, 0.44 dpa, and 0.67 dpa at 600 °C. The choice of this temperature was motivated by its technological importance due to the risk of irradiation-induced embrittlement. The temperature of 600 °C is below the void swelling peak temperature (∼800 °C) and, at the same time, well above the ductile to brittle transition temperature (DBTT) of the reference material (∼300 °C). Neutron irradiation was performed in the BR2 material test reactor inside the fuel channel in order to limit the transmutation of rhenium and osmium close to the rates expected in a fusion environment. The results of the mechanical tests performed up to 600 °C show that the fracture toughness decreases with the increase in the irradiation dose for both tungsten products. The fracture surfaces of the non- and irradiated specimens were systematically analysed to determine the evolution of the failure mechanisms.