Residual carbon impurities in Zr–2.5Nb and their effect on deuterium pickup

Abstract

The presence of residual carbon in Zr–2.5Nb at parts per million (ppm) levels affects the alloy's rates of oxide film growth and deuterium absorption (in 573 K lithiated heavy-water). Pickup rates increase with increasing carbon concentrations between 40 and 300 ppm with a possible inflection in the kinetic curves in the vicinity of 120 ppm. Increased rates are likely due to enhanced development of an inter-connected, large-scale, pore network within the oxide film. Oxides on Zr–2.5Nb containing 145 ppm carbon appear to be fully stoichiometric with a well developed network of large pores, while the oxide on the 85 ppm C alloy contains a high density of fine pores and is likely sub-stoichiometric.