Hydrogen Corrosion-uptake Analysis and Modeling for Heavy Water Reactor Zr-2.5Nb Pressure Tubes

Zr-2.5Nb pressure tubes would take in hydrogen (or deuterium) under heavy water operating conditions. Once the hydroge uptake exceeded the corresponding limit, it would have a negative impact on delayed hydride cracking for the pressure tubes. In-service inspection data for pressure tube body hydrogen equivalent concentration was analyzed and it was noted that the concentration for each fuel channel increased along the axial from inlet to outlet. A hydrogen absorption model according to Arrhenius relationship was developed based on the fact of deuterium being the major concern of pressure tube body hydrogen uptake. The deuterium concentration of the pressure tube body was lower than that observed in design-referred plant. According to the modeling results for upper prediction limit of hydrogen uptake, the hydrogen equivalent concentration of pressure tube body would still keep far from the terminal solid solubility of hydrogen for dissolution at 210 kEFPH while the deuterium uptake rate would keep below the standard limit thus it would not be a concern for life extension of pressure tube.