Hydrogen ingress through the rolled joints of CANDU pressure tubes

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Laker Energy Products Ltd and Carleton University are collaborating to develop experiments and models that simulate hydrogen movement through the rolled joints used to couple end fittings to pressure tubes in CANDU fuel channels. Hydrogen in pressure tubes can lead to a time-dependent mechanism of fracture called delayed hydride cracking (DHC) that has been responsible for several failures of zirconium components in nuclear reactors and chemical plants. In CANDU reactors, hydrogen levels are kept low by design, however, during operation hydrogen ingress happens across the rolled joints at the end of each pressure tube. Surveillance campaigns and predictive models with large safety margins are used to guarantee hydrogen levels in the pressure tubes stay well below the levels where DHC can occur. Margins are currently employed that reflect our level of understanding of the mechanism of ingress across the rolled joints. Arguably these margins could be safely reduced with better understanding, and save millions of dollars of avoided costs by prematurely replacing good pressure tubes. Laker Energy Products Ltd is one of only two suppliers of end fittings for rolled joints in CANDU reactors. They wish to collaborate with Carleton University to understand the rolled-joint ingress mechanism and ultimately to develop a better end-fitting design.