Corrosion behavior of new nuclear shielding Ni–Cr–W–Gd alloys in simulated spent nuclear fuel pool water

Abstract

The novel Ni–Cr–W–Gd alloy have the gadolinium neutron absorption unit and the tungsten gamma ray shielding unit, which can be used for thermal neutron and gamma ray co-shielding. This Ni–Cr–W–Gd alloy have good strength and fracture elongation, however, its corrosion performance has not been reported yet. In this work, the corrosion behavior for Ni–Cr–W–Gd alloys was studied in the boric acid solution at 40 °C. Electrochemical measurement techniques, long-term immersion tests, corrosion morphology and composition analysis, and first principles calculation have been used. After 4000 h immersing, the maximum steady state corrosion rate among all alloys is only 0.3221 μm/yr. The increasing Gd promotes the increase in corrosion current density and make the weight loss of alloys more serve. Both the results of relative potential test and first principles calculation demonstrate the NiCrW matrix is the anode and Ni5Gd is the cathode in micro galvanic corrosion. The matrix around the interface of matrix/Ni5Gd suffer preferential anodic dissolution, resulting in the detachment of the Ni5Gd phase and formation of pores on the surfaces. The passive films are composed of Cr2O3 and WO3, moreover, the intensity of Gd2O3 increases with Gd content. This work contributes to the promotion of the novel alloys in spent fuel storage environments.