Hydrogen release from 800-MeV proton-irradiated tungsten rods

For the Accelerator Production of Tritium Project (APT), spallation neutrons will be moderated and then absorbed in He-3 gas to produce tritium. The spallation neutrons mill be generated by the interaction of high energy (similar to1 GeV) protons with solid tungsten rods or cylinders. A byproduct of the spallation reactions is large amounts of helium and hydrogen gas generated in the rods and other structural materials. The release kinetics of these gases during various proposed off-normal scenarios involving loss of coolant and afterheat-induced rises in temperature is of particular interest to the APT Project. In addition, however, this data is of interest for fusion reactors where tungsten used in a tokamak divertor will also be exposed to neutrons. In this case, the generated protium will be accompanied by deuterium and tritium diffusing in from the plasma-facing surface. Tungsten rods irradiated with 800 MeV protons in the Los Alamos Neutron Science Center (LANCE) to high exposures have been sectioned to produce small specimens suitable 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 temperatures of approximately 550, 850, 1100 and 1200 degreesC were observed, initially suggesting a number of trapping sites with different binding energies. Subsequent analysis, however, showed that the observed peaks were artifacts of the temperature heating profile, and that the release curve could be duplicated using a single trap energy of 1.4 eV.