Modelling of oxidation and hydriding behaviour of pressure tubes in PHWR

A computer model named DOCTOR (Deuteriding Of Coolant Tubes during Operation of Reactor) has been developed for predicting the axial profile of oxide thickness and hydrogen (deuterium) concentration in PHWR pressure tubes. This model is applicable to single channel or full core analysis. The main source of hydrogen is considered to be oxidation of pressure tube on the inner surface by high temperature coolant water. Three stages of oxidation is considered namely, pre-transition, post-transition and accelerated. The oxidation rate is considered to be dependent on channel power, axial power/flux distribution, coolant temperature and pre-existing oxide thickness at the location. The kinetics parameters for oxidation model are derived from the actual measurement of oxide thickness on a number of pressure tubes examined in PIE Division. The model has been validated with PIE data of Hydrogen equivalent measurement on a number of irradiated Zircaloy-2 pressure tubes of various PHWRs. (author)