Abstract: A method of inhibiting or reducing contamination of out-of-core components of the primary coolant circuit of a pressurized water reactor due to absorption by oxide films of such components of cobalt and other radioactive contaminants generated by neutron irradiation of coolant impurities while in the reactor core. The method consisting of intermittently (e.g. at reactor shutdown for maintenance purposes), and/or once-off during commissioning of the reactor, holding the temperature of the circulating coolant within a suitable range below normal operating temperature for an extended period while maintaining its boric acid concentration substantially higher than during normal operation. Inhibition of absorpotion by component oxide films persists long-term and predisposes to preferential and improved removal of contamination by the usual purification equipment which operates continuously during normal operation of the reactor.