Advanced Evaluation of Radiation Effects on Fusion Materials

59 IMR KINKEN Research Highlights 2012 IMR KINKEN Research Highlights 2012 A new framework of bidirectional collaborative research program has been started in 2010 for the study of nuclear fusion reactor materials. By utilizing the environment of the research center at each university, joint research is conducted interactively between the centers and the National Institute of Fusion Science (NIFS). Two topics that were conducted in this framework are described in this paper. The first topic is a study of a trapping mechanism of hydrogen Isotopes in neutron-irradiated plasmafacing materials [1]. One feature of fusion reactor environments is that helium and hydrogen are produced by nuclear transmutation, and the transport and retention of hydrogen isotopes and helium from the core plasma and tritium generated at the blanket occur under neutron irradiation. It is hence indispensable to clarify the effects of neutron irradiation on the behavior of hydrogen isotopes and helium in the candidate materials to assess the feasibility of their use in fusion reactors. For this, in 2010 a thermal desorption spectrometer (TDS) apparatus (Fig. 1) was installed in a radiation-controlled laboratory at the International Research Center for Nuclear Materials Science (IRCNMS). This apparatus allows us to obtain thermal desorption spectra, thereby enabling the identification and quantification of hydrogen isotopes and helium contained in radioactive materials following reactor or accelerator irradiation. In 2011, the TDS apparatus was equipped with an ion gun to inject hydrogen isotopes or helium into neutronirradiated specimens. By using this apparatus, the emission and retention behavior of D was measured in recrystallized tungsten (W) specimens that were first irradiated with 2.8 MeV Fe ions to 3 dpa (displacement per atom) and then exposed to D atoms with very low energy and low flux (fluence: 6.2×1022 Dm-2); the result is shown in Fig. 2. For comparison, the results for W specimens irradiated with neutrons or Fe ions and then exposed to TPE (tritium plasma experiment: high energy, high fluence 1025 D m-2) are included. In the case of TPE exposure, neutron irradiated specimens exhibit D desorption from relatively low temperatures to as high as above 1000 K, whereas Fe-ion-irradiated specimens exhibit the completion of D desorption at around 700 K. In the case of specimens with Fe-ion irradiation and D atom exposure, D desorption starts at around 500 K and continues even above 1000 K. The D desorption behavior suggests the existence of trapping sites for Advanced Evaluation of Radiation Effects on Fusion Materials International Research Center for Nuclear Materials Science