Hydrogen permeability over the joint weld of the steel parts of fusion reactor with magnet confinement of plasma

Hydrogen and its isotopes diffusion and permeability over the laser joint weld of low-activation 10Cr9WVA ferritic steels have been studied. Welding of steel sheets were produced with the help of Russian gas laser TL-5M type (l=10.6 mm, P=2.5 kW) in He atmosphere with the rate of 66 mm/s. Hydrogen diffusion over the joint welds was detected by the conventional method of electrical resistance measurement. By this way, the kinetics of resistance changes during hydrogenation of specimens engraved from weld metal, neighboring zone of thermal effect as well as basic metal have been determined. Coefficients of hydrogen diffusion were measured in the temperature range from 773 to 1073 K. So, for 10Cr9WVA steel at 873 K it was established that the hydrogen diffusion coefficient in the weld metal is approximately 10 times higher than in the basic metal, and three times higher than that in the zone of thermal effect. Hydrogen permeability over the joint weld specimens was measured by the Dines–Barrer method on the volummetric setup. It was established that the hydrogen flux over the laser joint weld is significantly (up to two orders) more than that over the basic metal. Using the data on the hydrogen permeability and diffusion coefficient, the hydrogen solubility in the weld metal was estimated, which is several ten times higher than that in the basic metal of the steel investigated. As a result, it was concluded that welding the steel parts of the first wall of thermonuclear reactors with magnet confinement of plasma is undesirable due to possible tritium leaking into the environment. A possible way of decreasing the joint welds hydrogen permeability, including application of protective impermeable for hydrogen coatings, is considered.