Hydrogen estimation in zirconium alloys using thermo analytical techniques

Zirconium based alloys are used for reactor structural components (mainly fuel clad, pressure tube, garter spring, etc) in water cooled thermal nuclear reactors because of their low neutron absorption cross section, good corrosion resistance in water and good mechanical strength. The pressure tubes, made of Zr-2.5%Nb alloy, are used in Indian pressurized heavy water reactor (PHWR) and are exposed to high temperature (300° C) water and high pressure (100 kg/cm2) during reactor operation. The oxidation of zirconium (in any component) at higher temperature with light/heavy water produces hydrogen/deuterium which, in turn, are picked up by the component. Since the solid solubility of hydrogen in the zirconium is quite low (1 ppm at room temperature and 60 ppm at 300° C, hydrogen precipitates as zirconium hydride. Zirconium hydrides, being brittle, cause embrittlement of the component during service. In view of this, periodic measurement of hydrogen concentration in some components (particularly pressure tubes in service) is essential to assess the hydrogen/deuterium pick-up. The estimation of hydrogen/deuterium, in the samples taken from reactor components, is carried out using several thermal analytical techniques