Retention of very high levels of helium and hydrogen generated in variousstructural alloys by 800 MeV protons and spallation neutrons

摘要

A series of irradiations were conducted in the Los Alamos Neutron Science Centeras part of the test program supporting the Accelerator Production of Tritium Program sponsored by US-DOE. In this irradiation campaign, a variety of candidate structural alloys were placed in various particle spectra, ranging from 800 MeV protons, to mixed energy distributions of both protons and spallation neutrons, and to primarily high energy neutrons. At proton energies on the order of hundreds of MeV, exceptionally high levels of gas atoms are generated in all elemental constituents of typical structural alloys, with helium typically at -150 appm per dpa and hydrogen at approximately an order of magnitude greater. Since neither of these gases are considered to have a good effect on structural properties of interest, their retention after both recoil and diffusional losses is of strong interest. Helium is essentially immobile at all temperatures of interest, but hydrogen has some limited temperature-dependent mobility. To assess the degree of retention, each gas was measured in a number of highly irradiated specimens of different alloy compositions and dpa levels. The results show that helium production is relatively insensitive to composition and its retention is nearly total. The retained hydrogen levels, however, are somewhat sensitive to composition, reflecting different levels of diffusional loss, but are still at very large concentrations. There is some speculation that co-generation of helium and hydrogen assists in the trapping of hydrogen, and results in relatively high levels of hydrogen retention even at higher irradiation temperatures.