Studies on diffusion of hydrogen in PWR clad material

Zr-1%Nb alloy is used as cladding material in pressurised water reactors (PWR). Diffusion of hydrogen in this material is one of the important input parameters required for simulating the kinetics of hydrogen embrittlement. For this purpose, one end of cut piece of Zr-1%Nb alloy clad tube of PWR was polished, electrochemically charged with hydrogen and then annealed at required temperatures and time. Hydrogen content was determined in cut pieces of clad tube in axial direction employing hot vacuum extraction quadrupole mass spectrometry (HVE-QMS) technique. From the hydrogen profile in axial direction, diffusion coefficient of hydrogen was estimated employing the solution of Fick's second law of diffusion with semi-infinite system boundary conditions. Activation energy (E-a) for diffusion of hydrogen in Zr-1%Nb was calculated from the slope of the Arrhenius plot between Log D-H and 1/T. The obtained D-0 and E-a are well in the range of expectations based on the literature data in various Zr based materials by considering micro-constituents in these materials.