Corrosion behavior of zirconium alloy fuel assembly cladding tubes in the pressurized water reactor’s primary circuit

The corrosion behavior of fuel assembly cladding tubes made of E-110 niobium-containing zirconium alloy is described.Experimental data were obtained during operation and postoperation examination of the KLT-40S reactor.This type of reactor is employed in nuclearpowered icebreakers and the Academic Lomonosov floating nuclear power plant.The data show that the fuel assembly cladding tube material underwent a local (nodular) corrosion in the same way as corrosion of fuel cladding made of E-110 alloy.However, the rate of corrosion of the fuel assembly tubes was significantly lower than that of the cladding of fuel pins, which is explained by a lower heat flux through their surface.A short period of an increase in the rate of corrosion of the fuel assembly tubes was observed during operation of the nuclear propulsion reactor, which was due to a mechanical damage of the protective oxide film on the E-110 alloy surface.As a result, increased concentrations of insoluble zirconium-containing particles, hydrogen and ammonia in the primary coolant were observed during reactor power operation.After the reactor was shut down and the coolant was partially replaced, intense corrosion of the zirconium alloy stopped, indicating self-healing of the protective oxide film on E-110 alloy under the primary coolant conditions.