In the event of a nuclear accident, it is imperative to ensure the integrity of the containment. One concept is to vent the containment using the filtered containment venting system (FCVS), which uses different filtration stages to ensure the removal of radioactive material. A filtration stage being investigated and implemented worldwide uses silver-doped zeolite material to mitigate the release of the iodine source term. This filter allows the silver to react with the different iodine compounds, forming silver-iodine compounds. However, depending on other gases present, such as hydrogen and/or steam, other reactions or different physical phenomena may affect the retention. Hence, it is important to verify the operational capability of such silver-doped zeolite materials under different conditions expected during a venting phase of an FCVS.

In this work, the focus has been on the hydrogen and steam effect on the methyl iodide removal by two silver-doped zeolites, AgX and AgR (RASA Industries Ltd., Japan). The main differences between the two zeolites are the structure and silver content. The general test conditions investigated were nitrogen or air atmosphere (10 vol.% to 30 vol.%) with different contents of steam (65 vol.% to 83 vol.%) and variation of hydrogen content (2.5 vol.% or 5 vol.%). The methyl iodide concentration was between 100-200 ppm.

The results have shown that both zeolites are efficient in retaining methyl iodide under the conditions investigated in this work. The effect of the test conditions, i.e., temperature, steam, and gas composition, on the removal is reported.