Hydrogen permeation through heat transfer pipes made of Hastelloy XR during the initial 950 °C operation of the HTTR

The permeation of hydrogen isotopes through the Hastelloy XR high-temperature alloy adopted for the heat transfer pipes of the intermediate heat exchanger in the HTTR, is one of the concerns in the hydrogen production system, which will be connected to the HTTR in the near future. The hydrogen permeation between the primary and secondary coolants through the Hastelloy XR was evaluated using the actual hydrogen concentrations observed during the initial 950 °C operation of the HTTR. The hydrogen permeability of the Hastelloy XR was estimated conservatively high as follows. The activation energy E0 and pre-exponential factor F0 of the permeability of hydrogen were E0 = 65.8 kJ/mol and F0 = 7.8 × 10−9 m3(STP)/(m s Pa0.5), respectively, in the temperature range from 707 to 900 K.