Thermal Diffusion of Hydrogen and Hydride Precipitation in Zr–Nb Pressure Tube Alloys

Abstract

AbstractThe thermal diffusion of hydrogen in a Zr–2.5 wt % Nb pressure tube alloy has been studied in the H range from 28 to 108 ppm as a function of specimen orientation. The heat of transport Q*, lay between 4.1 and 5.1 kcal/mol, and no effect of either H concentration or specimen orientation was detected in the range studied. A number of experimental runs (with the cold zone below the solubility limit for precipitation) were done to study hydride precipitation effects. The position at which coarse hydrides precipitated within the cold zone was determined by the thermal gradient. Stress reorientation was observed in circumferentially oriented specimens, associated with stresses induced by the specimen clamping procedure. A I.D. finite difference computer program, together with the concept of two solid solubilities (one for precipitation, the other for dissolution), was used to explain the experimental results.