Radioiodine is one of the primary source terms released during severe nuclear power plant accidents. Due to its high fission yield, volatility, and significant threat to human thyroid health, it is a critical parameter in severe accident management. Containment spray systems play a vital role in mitigating the release of gaseous iodine by controlling its migration and chemical behavior within the containment. The effects of different spray solution com-positions and operating parameters on iodine removal efficiency remain in-sufficiently studied. Additionally, the chemical transformation of gaseous iodine into various species upon entering the sump pool is not fully under-stood. This study experimentally investigates the performance of spray systems in reducing gaseous iodine emissions under simulated severe accident conditions. Ultraviolet-visible spectroscopy and inductively coupled plasma mass spectrometry (ICP-MS) were employed to measure iodine species in the liquid phase and iodine concentrations in the gas phase. The results indicate that gaseous iodine concentrations decrease rapidly during the initial stages of spraying, with a removal half-life of approximately 20–30 min. In the sump pool, iodine primarily exists in the forms of I2, I ⁻ , I3⁻, and IO3⁻. Increasing the pH of the spray solution significantly enhances the reduction of I2 to I⁻. In addition, temperature changes have a significant effect on the volatility of the iodine captured in the spray solution, leading to the re-evaporation of dissolved I₂ in the aqueous film, resulting in fluctuations in the local concentration. These findings provide a scientific basis for optimizing containment spray system designs and strategies for severe accident management, offering valuable insights into mitigating environmental impacts.