Iodine is considered as one of the most harmful radioactive fission products due to its high volatility and mobility. Activated carbons (ACs) were first used for the adsorption of iodine due to their low production cost, fairly large specific surface area as well as good adsorption capacities of radioactive iodine compounds. ACs co-impregnated with potassium iodide (KI) and triethylenediamine (TEDA) were later developed to perform extremely high affinity with gaseous iodine and organic iodine compounds. However, impregnated ACs have flaws including low autoignition temperature, volatility of TEDA and high sensitivity to nitric oxides (NOx), made it unsuitable for the capture of radioactive iodine during a severe nuclear accident. Considering the high temperature of the airflow during accident, the inorganic adsorbent material, such as zeolite molecular sieves is a better choice.

CIRP research team studied the feasibility of zeolite molecular sieves applied under severe accident conditions using Ag loaded 13X molecular sieve with a low Si/Al (1.2) ratio prepared by ion exchange method. The performance of iodine removal of the silver-loaded 13X molecular sieve and texture properties of Ag/13X were systematically investigated.

The research reveals that Ag/13X had a high specific surface area, well-developed micropores, and a typical H4-type isotherm. There was no significant change in the crystalline structure before and after Ag ion exchange. The adsorption capacity and adsorption efficiency of I2 and CH3I were measured by testing the static and dynamic adsorption curves. Results show that the static adsorption capacity of I2 reached 700 mg/g at 100 ℃ and the decontamination factor over dynamic testing reached 1000 and 4677 with a bed depth of only 16 and 20 mm respectively; the adsorption capacity of CH3I at 1‰ and 1% penetration is 104.4 mg/g and 131 mg/g respectively. Additionally, the adsorption efficiency of CH3I was more than 99.9% under dry conditions with a layer thickness of 30 mm. Above experimental data indicates the applicability of Ag-13X in severe nuclear accidents.

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