To provide structural material design data for the Accelerator Production of Tritium (APT) project, a 1 mA, 800 MeV proton beam at the Los Alamos Neutron Science Center (LANSCE) was used to irradiate a large number of metal samples, including a tungsten target similar to that being considered as the neutron source for the tritium production. The maximum proton fluence to the tungsten target was ∼1021 protons/cm2. An unavoidable byproduct of spallation reactions is the formation of large amounts of hydrogen and helium. Postulated off normal conditions for APT would result in target temperatures approaching 1200°C. The use of tungsten target rods clad with Alloy 718 raises concerns as to the amount and rate of release of these gases under such off normal conditions, with the major concern being pressurization and possible failure of the cladding. To address these issues, portions of the LANSCE tungsten rods were heated to temperatures up to 1200°C, and the time-dependent evolution of helium and hydrogen gas was measured.
Stepped-anneal and total helium/hydrogen measurements were conducted at Pacific Northwest National Laboratory (PNNL) on multiple samples of the tungsten material. Helium measurements were conducted using a high-sensitivity magnetic-sector isotope-dilution helium analysis system. Stepped-anneal measurements were conducted at temperatures from 25°C to 1600°C in ∼100°C steps. Total helium measurements were conducted by rapid vaporization after completion of the stepped-anneal process, and are compared with Monte Carlo calculations performed at Los Alamos National Laboratory (LANL) using the LAHET code system.
Hydrogen measurements were conducted between 750°C and 1200°C using a high-temperature furnace that had been extensively modified for the application. Hydrogen detection was accomplished by periodic sampling of the furnace gas using a separate quadrupole analyzer. Hydrogen measurements are also compared with LANL calculations.