Vent exit device for condensing steam

In a boiling water nuclear reactor of the water moderated type having a dry well, a suppression chamber, and a vertically extending venting device extending from the dry well into the suppression chamber, for supplying steam to be condensed to said suppression chamber, the improvement comprising said venting device being formed of:

• a first elongated pipe,
• a second pipe, the diameter of which is larger than that of said first elongated pipe, and with respect to which an expansile ratio constituted by the ratio of the bore cross-sectional area of said second pipe to that of said first pipe is from 2:1 to 9:1,
• an upper cover plate, secured air-tightly to one end of said second pipe and one end of said first elongated pipe, for passing steam through said first elongated pipe to the inside of said second pipe,
• a lower cover plate secured air-tightly to the other end of said second pipe, and
• a plurality of openings formed on said second pipe, and wherein an area ratio is constituted by the ratio of the total cross-sectional area of all of said openings of said second pipe to the transverse cross-sectional area of the second pipe, the product of said expansile ratio and said area ratio being equal to or greater than 10.