Calculation of hydrogen and helium concentrations for CSNS target

The China Spallation Neutron Source (CSNS) is driven by protons whose energies are about 1.6 GeV. At such high energies, the spallation neutrons lead to the formation of large amounts of helium, hydrogen and new heavier species in the form of transmutation products. These hydrogen, helium and transmutation products have a critical effect on the mechanical properties on the one hand and exacerbate the displacement radiation damage on the other hand. In this paper, the background hydrogen/helium concentrations and the maximum hydrogen/helium concentrations near cracks in a tungsten target for CSNS have been calculated at temperatures of 100 °C and 300 °C by applying a theoretical model. For the CSNS tungsten target plate, we find the maximum hydrogen concentration near the tips of cracks ranges from 3.0 × 10^-2-2 × 10^-1, which exceeds the hydrogen background concentration by 1.2-1.8 times; the maximum helium concentration near the tips of cracks ranges from 3.0 × 10^-4-1.2 × 10^-3, which exceeds the helium background concentration by 2-4 times; the maximum hydrogen/helium concentration increases with the increase of the transfer length across the surfaces of the target and it decreases with the increase of temperature. (authors)