Tritium migration and trapping in neutron damaged materials

Deuterium-tritium fusion reactions produce 14.1 MeV neutrons that create radiation damages and transmutation elements in fusion reactor materials.  A significant amount of solid transmutation elements such as rhenium and osmium will be produced in tungsten (W), one of the candidate plasma-facing component (PFC) materials.  A series of thermal-neutron shielded and unshielded neutron-irradiation campaigns was carried out with polycrystalline W and W alloys in High Flux Isotope Reactor (HFIR) under the US-Japan PHENIX and FRONITER projects to advance the understanding of irradiation response of tungsten on thermo-mechanical properties and tritium behavior. Not only the abovementioned solid transmutation elements but also material surfaces and grain structures play critical roles in tritium behavior in neutron-irradiated tungsten as it determines a boundary condition for diffusing tritium.  Defect characterization by positron annihilation lifetime spectroscopy and coincidence Doppler broadening measurements, surface compositions, and depth profiles of elements by scanning Auger microscope are being studied prior to prior plasma exposure experiments in thermal-neutron shielded and unshielded neutron-irradiated tungsten. We report defect characterization, surface compositions and depth profiles of elements from unshielded polycrystalline W irradiated at 1073K and 1373K as well as from shielded polycrystalline W irradiated at 873K, 1073K and 1373K.