The efficient capture of volatile iodine species (I2, CH3I) potentially released from nuclear facilities is a major issue to improve the nuclear safety. In that respect, activated carbons (AC) have been used for the removal of iodine within ventilation networks of nuclear facilities. More particularly, the commonly used nuclear grade AC are co-impregnated with potassium iodide (KI, 1 wt%) and triethylenediamine (TEDA, < 5 wt%) [1]. However, uncertainties remain about the contribution of the involved retention mechanisms (more particularly, the isotopic exchange for KI-impregnated AC). Hence, the present study aims to gain insights into the importance of this reaction as a comparison with other adsorption mechanisms (physisorption and chemisorption). A specific methodology has been implemented (Fig. 1 (A)). In a first part, the behavior of characterized AC towards the retention of methyl iodide under a large panel of configurations (Fig. 1 (A)) was explored. Preliminary experiments using standardized test methodologies for nuclear grade AC have shown the importance of isotopic exchange phenomenon for the capture of γ-labeled CH3I under humid conditions (T = 20°C, R.H. = 90%, Fig. 1 (B)). The quantification of this reaction has to be assessed by comparing the breakthrough curves obtained in both cases (radioactive and not-radioactive CH3I). Accordingly, a test bench is under development and validation. This talk will describe the used strategies to obtain the first data relevant to the quantification of isotopic exchange phenomena. More precisely, the methodologies, the different test benches as well as the first results showing the importance of this phenomena in the retention of radioactive iodine will be presented.