On the radiation resistance and thermal durability of silver-exchanged zeolites for trapping radioxenon

Abstract

The radioxenon releases from civilian nuclear installations are significantly affecting the International Monitoring System (IMS), which is being deployed for the verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). These civilian radioxenon releases are disturbing and limiting the detection capability of the noble gas component of the IMS for CTBT-related events. Substantial reductions of civilian radioxenon releases would significantly improve the detection capability of the noble gas component of the IMS. Recently, it was demonstrated that silver-exchanged zeolites or zeolite-like frameworks (AgZs), in particular Ag-ETS-10 and Ag-ZSM-5, had unprecedented Xe adsorption capacities at room temperature for Xe concentrations relevant for radioxenon releases at Medical Isotope Production Facilities (MIPFs). Depending on the actual gas composition and conditions of the gas streams containing radioxenon in these facilities, the use of the current best performing AgZ can increase the radioxenon retention time by a factor 20 to 200 compared to the same volume of activated carbon at room temperature. However, knowledge on the radiation resistance and thermal durability of these AgZs in relevant conditions for MIPFs is still insufficient. Accordingly, Ag-ETS-10 and Ag-ZSM-5 were directly irradiated by adsorbing Xe-133 for about seven days to reach an estimated absorbed dose in the range of 10 to 100 MGy. In addition, the thermal durability of both AgZs was investigated by performing about 40 adsorption/thermal desorption cycles in relevant conditions. Each thermal desorption was performed at about 200°C under nitrogen. The AgZs were characterized before and after irradiation or cycling by Xe breakthrough measurements, SEM/EDX, PXRD, 27Al- and 29Si solid-state NMR, and by N2 adsorption-desorption at 77 K and CO2 adsorption at 273 K. The results on the radiation resistance and thermal durability of Ag-ETS-10 and Ag-ZSM-5 will be presented and discussed.