Non-destructive estimation of hydrogen concentration in pressure tube

Pressure tubes made of zirconium alloys form the major core components of Pressurised Heavy Water Reactors (PHWRs). During reactor operation, pressure tubes, which operate in an environment of high temperature and radiation, undergo corrosion reaction with the coolant and a part of the hydrogen (equivalent hydrogen) evolved during the process is picked up by it. As the presence of hydrogen has a detrimental effect on the integrity of the pressure tube due to the mechanism of delayed hydride cracking, it is necessary to estimate its concentration to ensure safe operation of the reactor. Presently, sliver scrape samples are removed from the inside surface of the pressure tube using a special tool and brought to post- irradiation examination laboratory for measurement of hydrogen using conventional techniques. The whole process consumes high man rem and requires considerable time for the results to be made available. It is a surface process, which gives average hydrogen concentration in the scraping area, and reconfirmation of the same in the event of any discrepancy in measurement is not possible. Considering these drawbacks, it is advantages to develop a non-destructive technique, which can be implemented for in-situ measurement of hydrogen concentration in operating reactors. This paper describes one such technique with the challenges involved in developing a system based on it and the associated limitations.