An ab initio study of Cobalt(II) complexes as possible corrosion products in a CANDU supercritical water-cooled reactor (SCWR)

Abstract

Atomic Energy of Canada Limited and CANDU are currently developing a Gen-IV Supercritical Water-cooled Reactor (SCWR). The SCWR offers advantages of increased thermal efficiency and sustainability, but at the cost of operating under extreme conditions (650°C and 25 MPa). Under these conditions, transition metals from the construction materials could dissolve and form complexes with surrounding anions and reprecipitate on the pipes and valves of the reactor, causing corrosion. Cobalt is one transition metal of interest because it exists in small quantities in many metal alloys and becomes highly reactive when bombarded with neutrons. Comprehensive ab initio computational studies were performed on cobalt(II) complexes containing water, chloride, hydroxide and ammonia ligands. For all molecules studied, optimized geometries were obtained as well as vibrational stretching frequencies, which were compared to experimental data, where possible, so that the most likely species to exist inside the reactor could be predicted.