Hydrogen release from 800-MeV proton-irradiated tungsten rods

For the Accelerator Production of Tritium Project (APT), spallation neutron s will be moderated and then absorbed in He-3 gas to produce tritium. The s pallation neutrons mill be generated by the interaction of high energy (sim ilar to1 GeV) protons with solid tungsten rods or cylinders. A byproduct of the spallation reactions is large amounts of helium and hydrogen gas gener ated in the rods and other structural materials. The release kinetics of th ese gases during various proposed off-normal scenarios involving loss of co olant and afterheat-induced rises in temperature is of particular interest to the APT Project. In addition, however, this data is of interest for fusi on reactors where tungsten used in a tokamak divertor will also be exposed to neutrons. In this case, the generated protium will be accompanied by deu terium and tritium diffusing in from the plasma-facing surface. Tungsten ro ds irradiated with 800 MeV protons in the Los Alamos Neutron Science Center (LANCE) to high exposures have been sectioned to produce small specimens s uitable for measurement of both hydrogen and helium. Hydrogen evolution was measured by subjecting the specimens to a simulated temperature ramp from similar to 200 to similar to 1200 degreesC, similar to that expected due to a loss of coolant and subsequent afterheat. The release measurements were conducted using mass spectrometric techniques. Four release peaks at temper atures of approximately 550, 850, 1100 and 1200 degreesC were observed, ini tially suggesting a number of trapping sites with different binding energie s. Subsequent analysis, however, showed that the observed peaks were artifa cts of the temperature heating profile, and that the release curve could be duplicated using a single trap energy of 1.4 eV.