Evolution of requirements for in-service inspection of pressure tubes of PHWR coolant channels

Zirconium base alloys are used for pressure tubes of PHWR coolant channels because of their unique characteristics namely low neutron absorption cross-section, good mechanical strength, adequate creep resistance and corrosion resistance. On account of the necessity to use minimum amount of structural material in the core region for the sake of neutron economy, the design margin for pressure tube is kept to a minimum. Hence it becomes essential to ensure the in-service integrity of the pressure tubes through a comprehensive in-service integrity of the pressure tubes through a comprehensive in-service inspection (ISI) programme. Unlike several other conventional reactor components, full life-time operating experience with pressure tubes is not available at present. Therefore ISI requirements have to keep changing as and when any new phenomenon having potential to affect the integrity of pressure tubes comes to light. In this paper, the stage wise evolution of coolant channel in-service inspection programme for Canadian and Indian PHWRs ash been described. Requirements of different tools needed to carry out in-service inspection are also discussed. The current and planned activities towards the development of ISI tools for PHWR coolant channels being done are presented. (author). 19 refs., 3 figs., 2 tabs