The computer code COSMO (containment spray model) is prepared to provide information on radio iodine removal by the containment spray of boiling water reactors and pressurized water reactors involv ing an ice-condenser-type reactor in the event of a loss-of-coolant accident (LOCA). The code considers the removal of inorganic iodine, organic iodide, and particulate iodine in multiple compartments, taking into consideration natural deposition onto the con tainment wall, spray washout, liquid-film absorption, filtration, and leakage to the environment. The code is also developed by adding many abilities such as the gas convection flow between multicompartment rooms due to fluid disturbance and spray covering onto the inner structures involving the wall in the containment vessels. The calculated results are com pared with the iodine removal tests of the Japan Atomic Energy Research Institute model contain ment, and the iodine removal for light water reactors of 1000 MW(electric) in the postulated LOCA con ditions is evaluated.