Patent Number: 055704018
Section: claims

1. A boiling water reactor comprising: a containment vessel;  a reactor pressure vessel arranged inside said containment vessel;  a nuclear fuel core arranged inside said reactor pressure vessel;  wetwell means arranged inside said containment vessel, said wetwell means comprising first and second wetwell airspace chambers and first and second pools of water arranged such that said first wetwell airspace chamber overlies said first pool and said second wetwell airspace chamber overlies said second pool, said first and second pools of water being connected to allow free flow of water therebetween, and said first and second wetwell airspace chambers being separated such that gas cannot flow freely therebetween;  a drywell comprising a space inside said containment vessel and outside said reactor pressure vessel and said wetwell;  a condenser pool of water arranged above said drywell;  first and second condensers in heat transfer relationship with the water in said condenser pool;  first and second condenser inlet flow paths for coupling steam from said drywell into said first and second condensers respectively;  first and second condenser outlet flow paths for coupling gas from said first and second condensers respectively into said first and second pools of said wetwell respectively; and  first and second venting means for respectively venting gas from said first and second wetwell airspace chambers to said drywell, each of said first and second venting means having a first state in which said respective venting means is closed and a second state in which said respective venting means is at least partially open.  a containment vessel;  a reactor pressure vessel arranged inside said containment vessel;  a nuclear fuel core arranged inside said reactor pressure vessel;  wetwell means arranged inside said containment vessel, said wetwell means comprising first and second wetwell airspace chambers and first and second pools of water arranged such that said first wetwell airspace chamber overlies said first pool and said second wetwell airspace chamber overlies said second pool, said first and second pools of water being connected to allow free flow of water therebetween, and said first and second wetwell airspace chambers being separated such that gas cannot flow freely therebetween;  a drywell comprising a space inside said containment vessel and outside said reactor pressure vessel and said wetwell;  a condenser pool of water arranged above said drywell;  heat exchange means in heat transfer relationship with the water in said condenser pool;  inlet flow path means for coupling steam from said drywell into said heat exchange means;  first and second outlet flow paths for coupling gas from said heat exchange means into said first and second pools of said wetwell respectively; and  first and second venting means for respectively venting gas from said first and second wetwell airspace chambers to said drywell, each of said first and second venting means having a first state in which said respective venting means is closed and a second state in which said respective venting means is at least partially open. 2. The boiling water reactor as defined in claim 1, wherein said wetwell means comprise a diaphragm floor and a partition attached to and extending downward from said diaphragm floor, a first portion of said diaphragm floor and said partition forming part of said first wetwell airspace chamber, and a second portion of said diaphragm floor and said partition forming part of said second wetwell airspace chamber. 3. The boiling water reactor as defined in claim 2, wherein said partition is configured to block flow communication across said partition at elevations above the water level of the one of said first and second pools having a lower level than the level of said other of said first and second pools. 4. The boiling water reactor as defined in claim 1, wherein each of said first and second venting means comprises a vacuum breaker. 5. The boiling water reactor as defined in claim 2, wherein said first venting means comprises a first vacuum breaker which penetrates said first portion of said diaphragm floor and said second venting means comprises a second vacuum breaker which penetrates said second portion of said diaphragm floor. 6. A boiling water reactor comprising a containment vessel, a reactor pressure vessel surrounded by said containment vessel with a drywell therebetween, a nuclear fuel core arranged inside said reactor pressure vessel, a wetwell arranged inside said containment vessel and partly filled with water to form a suppression pool of water and a wetwell airspace of gas overlying the water in said suppression pool, a condenser pool of water arranged above said drywell, first and second condensers in heat transfer relationship with the water in said condenser pool, first and second condenser inlet flow paths for coupling steam from said drywell into said first and second condensers respectively, first and second condenser outlet flow paths for coupling gas from said first and second condensers respectively into said suppression pool, and first and second vacuum breakers for venting gas from said wetwell airspace to said drywell, the improvement wherein said wetwell airspace is divided into first and second gas-filled chambers by a partition arranged such that gas exiting said first and second condenser outlet flow paths rises into said first and second gas-filled chambers respectively, said first gas-filled chamber communicates and said second gas-filled chamber does not communicate with said drywell via said first vacuum breaker when said first vacuum breaker is open and said second vacuum breaker is closed, and said second gas-filled chamber communicates and said first gas-filled chamber does not communicate with said drywell via said second vacuum breaker when said first vacuum breaker is closed and said second vacuum breaker is open. 7. The boiling water reactor as defined in claim 6, wherein said partition comprises a vertical wall having a bottom boundary which is submerged in said suppression pool along the entire length of said vertical wall. 8. A boiling water reactor comprising: 9. The boiling water reactor as defined in claim 8, wherein said wetwell means comprise a diaphragm floor and a partition attached to and extending downward from said diaphragm floor, a first portion of said diaphragm floor and said partition forming part of said first wetwell airspace chamber, and a second portion of said diaphragm floor and said partition forming part of said second wetwell airspace chamber. 10. The boiling water reactor as defined in claim 9, wherein said partition is configured to block flow communication across said partition at elevations above the water level of the one of said first and second pools having a lower level than the level of said other of said first and second pools. 11. The boiling water reactor as defined in claim 8, wherein each of said first and second venting means comprises a vacuum breaker. 12. The boiling water reactor as defined in claim 9, wherein said first venting means comprises a first vacuum breaker which penetrates said first portion of said diaphragm floor and said second venting means comprises a second vacuum breaker which penetrates said second portion of said diaphragm floor.