Relative Rates of Krypton and Rubidium Release from Zeolite Getters

Abstract

Zeolites such as sodalite and zeolite A have been used for decades to encapsulate radioactive 85 Kr for long-term storage. However, recent reports of zeolite getters removed from hot cells after over 40 years showed corrosion of the containers, suggesting that 85 Kr had escaped the getter and decayed to 85 Rb, a potent corrosive agent. This study aims to determine whether it is more likely that 85 Kr escaped the sodalite cages, followed by decay, or that 85 Rb escaped the sodalite cage after decay. We answer this question by calculating the activation energies of krypton and rubidium traversing the six-membered rings of sodalite cages using density functional theory combined with the nudged elastic band method and classical transition state theory. We find that it is extremely unlikely that krypton would make the jump through the window, meaning it is more likely that the nonradioactive rubidium is what escapes the getter.