Assessing the performance of a novel Fe-based material for replacement of Co-based alloy Stellite in CANDU reactor components

Abstract

Activation of ⁵⁹Co to form radioactive ⁶⁰Co in the primary heat transport system (PHTS) of CANDU reactors has been identified as one of the main source terms of gamma radiation to workers. In the CANDU PHTS, ⁵⁹Co is present as particulates and dissolved species resulting from wear and corrosion of Co-containing components, such as valves as for light water reactors but also fueling machine bearing balls made of Co-based alloys like Stellite. Therefore, replacing Co-based alloy components in the PHTS with Co-free materials has been proposed as one of the strategies to reduce worker dose. A novel Fe-based alloy with a composition of Fe-25Cr-4Ni-2Mo-0.4N manufactured by hot-isostatic-press is a promising candidate for Stellite replacement. Corrosion and mechanical testing of the Fe-based alloy under conditions relevant to the operation of CANDU fueling machine was performed. Potentiodynamic polarization and long-term immersion tests in refreshed autoclaves showed that the Fe-based alloy exhibited corrosion resistance equivalent to or better than Stellite 6 in aerated lithiated water at temperatures up to 300 °C. Additionally, the performance of the Fe-based alloy in uniaxial compression tests conducted on ball samples in air at room temperature, 150 °C, and 300 °C showed similar behavior to Stellite 6.