Synergistic Effects of Plasma and Neutron Irradiations in High-Z Plasma Facing Materials

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A part of helium generated by D-T reaction arrives at the first wall and diverter and cause not only irradiation effect at the surface. Some of them spread in the matrix will cause synergistic irradiation effects together with defects formed by neutron irradiation. The purpose of the present work is to clarify a damage phenomenon under helium irradiation and the synergistic irradiation effects.Understanding meeting and parting processes and a diffusion process of injected helium in W and Fe-Cr alloy at high temperatures was deepened from a helium irradiation experiment. Low energy helium irradiation experiments performed at high temperatures more than 1,000℃ revealed that binding energy of helium and a vacancy, and movement and coalescence of a helium bubbles played an important role for damage accumulation. Density and size of a helium bubble are decided by these elements. The formation of helium bubbles plays an essential role for surface mechanical strength and deformation behavior.Accumulation processes of defects by simultaneous irradiations of helium and neutrons was calculated by the reaction rate theory. It was revealed that reaction of helium with point defects formed by the neutron irradiation determine the accumulation of radiation induce defects.