Effect of Gd on neutron absorption properties and electrochemical corrosion behavior of Zr-Gd alloy in boiling concentrated HNO3

A Zr-Gd alloy with neutron poisoning properties and resistance to boiling concentrated HNO3 corrosion was developed based on a corrosion-resistant Zr-702 alloy to meet the demand for neutron shielding in the closed-loop treatment of spent fuel and the nuclear chemical industry. In this study, 1 wt.%, 3 wt.%, 5 wt.%, 7 wt.%, and 9 wt.% Zr-Gd alloys were designed and fabricated with Zr-702 as the control element. The electrochemical behavior of the Zr-Gd alloys in boiling concentrated HNO3 was investigated, and the neutron shielding effect on plate thickness and Gd content was simulated. The experimental results demonstrate that the corrosion resistance of the alloy decreased slightly before similar to 7- 9 wt.% with increasing Gd content; this is the inflection point of its corrosion resistance. The alloy uniformly dissolved the Gd content that could not be dissolved in the Zr lattice, resulting in numerous micropores on the passivation coating, which deteriorated and accelerated the corrosion rate. The MCNP simulation demonstrated that when the Gd content was increased to 5 wt.%, a 2-mm-thick plate can shield 99.9% neutrons; an alloy with a Gd content >= 7 wt.% required only a 1-mm-thick plate, thereby showing that the addition of Gd provides an excellent neutron poisoning effect. Thus, the corrosion resistance and neutron shielding performance of the Zr-Gd alloy can meet the harsh service requirements of the nuclear industry.

Automated summary

A Zr-Gd alloy with neutron poisoning properties and resistance to boiling concentrated HNO3 corrosion was developed to meet the demand for neutron shielding in the nuclear industry. The corrosion resistance of the alloy decreased slightly before 7-9 wt.% Gd content, and the addition of Gd resulted in numerous micropores on the passivation coating, accelerating the corrosion rate. Simulation showed that a 2-mm-thick plate with 5 wt.% Gd content can shield 99.9% neutrons, while a 1-mm-thick plate with >= 7 wt.% Gd content is sufficient, indicating excellent neutron poisoning effect. The Zr-Gd alloy can meet the harsh service requirements of the nuclear industry.