[en] Purpose: To maintain the inside of the dry well at a low humidity condition and prevent the reduction of the water level in the suppression pool of BWR type reactors. Constitution: Air curtains are formed at the side of the deflector provided to the inlet on the dry well side of a vent tube. The air curtain comprises an air blowing header, an air suction header, an air circulating fan, a dehumidifier for removing humidity from airs, a drain pipe for returning condensates to the suppression pool and the like. Steams going to flow from the down comer to the dry well is sucked and dehumidified by the air curtains, whereby the inside of the dry well is kept at low humidity condition. (Ikeda, J.)