A water wall type containment cooling system, which has a cooling pool outside the suppression pool, is one of the passive containment cooling systems (PCCSs). To improve its heat removal capability, we have proposed a divided wetwell (gas phase space in the suppression chamber), which separates the wetwell space into a high steam partial pressure region (first wetwell) and high noncondensable gas partial pressure region (second wetwell). We experimentally examined the thermal hydraulic behavior of the water wall type PCCS which applies the divided wetwell.By cooling the second wetwell and condensing the steam which flowed from the first wetwell into the second wetwell, noncondensable gas in the first wetwell was discharged to the second wetwell. In the first wetwell, the saturated steam partial pressure increased. After the noncondensable gas was fully discharged to the second wetwell, the first wetwell temperature came within 1°C of the suppression pool surface temperature. Therefore, attainable temperatures of the first wetwell and the suppression pool water increased for the same pressure of the primary containment vessel. Consequently, the time-integrated released heat to the outer pool was 70% larger than the non-divided case due to increase of the temperature difference between the suppression pool and outer pool.
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