When excess pressure and temperature are added to a containment vessel of a nuclear power plant during a severe accident, damage of the containment vessel and the release of radioactive materials into the environment are expected. Filtered containment venting systems (FCVS) installed in exhaust systems reduce the release of radioactive materials by the use of multistage filters. In actual FCVS, several types of alkaline solution are used in the scrubbing stage to capture the radioactive iodine (I₂). Therefore, it is difficult to remove CH₃I by the alkaline solution, and molecular sieves such as silver zeolites installed downstream of the scrubbing stage are used to capture the organic iodide (CH₃I). Silver nitrate aqueous solution (AgNO₃ aq.) is highly reactive against iodine; hence, by using AgNO₃ aq., the removal of organic iodide in the scrubbing stage can be expected. We have conducted basic evaluations of the removal properties of iodine and organic iodide by AgNO₃ aq. using small-scale and pool-scrubbing (inner diameter: 300 mm) test sections at ambient temperature and pressure. The small-scale test results show that AgNO₃ aq. has the same I₂ removal performance as sodium hydroxide aqueous solution (NaOH aq.). Moreover, the pool-scrubbing test results show that a CH₃I decontamination factor (DF) of over 50 can be expected under the conditions of a AgNO₃ concentration ≥ 10 wt％ and submergence ≥ 1.14 m.