Understanding silver structural rearrangement on zeolite Y for methyl iodide capture in nuclear safety system

Abstract

To enhance nuclear power safety, the adsorptive passive capture of emitted radioactive organic iodine under harsh conditions is essential. Silver states and CH₃I reactive adsorption on silver zeolite Y were studied under simulated accident conditions (10 ppm CH₃I at 7 bar, 0–80 % RH, and 150 °C). The roles of Ag⁺ ions, silver clusters, and external silver aggregates in silver zeolite Y during CH₃I capture were analyzed. Ag⁺ ions enabled near-complete CH₃I removal (<0.1 ppm), while silver clusters and external silver aggregates enhanced the overall adsorption capacity. It was also noted that the formation of ${\mathrm{Ag}}_n^{Y+}$ clusters within sodalite cages could potentially block pores, leading to immediate breakthrough. Pelletized silver zeolite Y adsorbents demonstrated optimal CH₃I capture capacity at sufficiently auto-reduced states. Under dry conditions, Ag⁺ ions primarily promoted light hydrocarbon by-products, whereas silver clusters contributed to the formation of heavier hydrocarbons. Humid conditions led to the weakening of adsorption affinity and rate of CH₃I, along with oxygenated by-products. The findings, including silver structural rearrangement by auto-reduction, provide critical guidance for understanding the adsorption mechanism and improving the design efficiency of a nuclear containment system.