Patent Number: 050911449
Section: summary

BACKGROUND OF THE IVNENTION The present invention relates to nuclear system Boiling Water Reactor (BWR) containments and, refers more particularly to such a reactor containment in which a suppression pool wetwell space is continuously ventilated, as well as a method for ventilating such containment, to remove non-condensable gases from the wetwell space so that during a loss-of-coolant-accident, drywell space pressure can be maintained at not above about one atmosphere gauge pressure thereby allowing use of lighter weight containment structures, as well as enclosure of more components within the containment. Nuclear system nuclear reactors are housed in containment enclosures as accident mitigation structures. These structures generally are designed as high pressure buildings surrounding the reactor system to function to contain all fluid and fission products which release upon occurrence of a reactor loss-of-coolant-accident (LOCA). Efforts to improve these containment designs have been ongoing and in recent years system improvements proposed include, inter alia, addition of a high-pressure relief line with a filter system to trap particulate fission products as non-condensable gases are released to relieve pressure. Still, all past containment designs require a high pressure enclosure around the reactor system to collect the energy, fluids and fission products released incident a LOCA. These containment buildings in turn require isolation systems for process lines and penetrations through the containment boundary, and they are complex and expensive mandating use of as compact a structure as possible. OBJECTS AND SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide a continuously ventilated reactor containment and a method for ventilating the containment which overcomes the drawbacks of the prior art. It is a further object of the invention to provide a continuously ventilated reactor containment which can be significantly reduced in containment structure weight to lightweight values since the containment even during a LOCA, will be exposed to a pressure of not above about one atmosphere gauge. It is a still further object of the invention to provide a nuclear reactor containment which because it is continuously ventilated and thus of lighter weight than prior containments, can be used to contain in addition to the reactor vessel, other system components inclusive of a turbine unit and associated equipment. Briefly stated, there is provided a nuclear reactor containment wherein the wetwell space above a suppression pool of a nuclear reactor containment is continuously ventilated by exhausting gas therefrom, while at the same time during a normal operation, atmospheric air from a source of same is admitted to the wetwell, but such admission being blocked during a LOCA. All exhaust flow from the wetwell is conveyed through a conduit that outlets at a remote elevated location in the atmosphere. All exhaust flow through the conduit is before outletting therefrom, passed through a gas treatment operation wherein any particulate, particularly fission material, in the gas mixture are removed. Further treatment of the gas with charcoal to adsorb noble gases can be carried out. In normal reactor operation the ventilation flow rate is at minimal level. However on occurrence of a loss-of-coolant-accident, highly heated gases from the containment drywell are passed into the suppression pool where condensables condense, while non-condensable gases are cooled and vent to the wetwell. Fission products are scrubbed in the pool and much of same are retained therein. The ventilation rate increases during LOCA to carry off the increased non-condensable gas mixture volume created by the LOCA and, because this conduit is such sized, containment drywell pressure during LOCA is maintaineed at a level not to exceed about one atmosphere gauge. This allows that containment structures can be of lighter weight and different shapes than heretofore, and enclose more components such as turbine units and condensers. In accordance with these and other ojects of the invention, there is provided a method of operating a reactor system having a vented wetwell, comprising continuously venting the wetwell during normal operation so as to maintain a substantially constant pressure differential between the wetwell and the atmosphere with the vented gases being filtered to remove entrained particles. In this way, the integrity of an incorporating containment can be better preserved during a pressurization. In accordance with a feature of the invention, there is further provided in the operation of a nuclear reactor system, which system includes a containment defining a drywell space wherein a nuclear reactor is disposed, there being a suppression pool in the containment with the suppression pool having a wetwell space above a level of the pool to which any non-condensable gases entering the suppression pool can vent, a method of continuously ventilating the containment. By this method, continuous exhausting of the wetwell space to remove gas therefrom is carried out, while concurrently an inflow of air from an atmospheric source thereof is admitted to the wetwell during normal opertion but blocking off said inflow during a loss-of-coolant-accident whenever a pressure in the wetwell space is above a predetermined value. The gas exhausted from the wetwell space is subjected subsequent to its removal from that space, to a treatment operation to separate any particulate material entrained therein from the gas. In accordance with a further feature of the invention, there is still further provided in a nuclear system comprising a nuclear reactor which includes a reactor pressure vessel, and a reactor core situated in the pressure vessel, means enclosing space defining a containment in which the nuclear reactor is disposed. The containment includes a drywell space, structure therein for holding a suppression pool of water and which defines a wetwell space above a level of the water, with the wetwell space separated from the drywell space. Means are provided for maintaining a continuous exhaust flow of gas mixture from the wetwell space to remove gas therefrom, as is means for continuously admitting air from an atmospheric source thereof to the wetwell space during normal opertion but such means being operable to block air admission to the wetwell space during a loss-of-coolant-accident whenever a pressure in the wetwell is above a predetermined value. Conduit means communicate an entry end of the conduit with the wetwell space and this conduit means extends to an opposite outlet end located exteriorly remote from the containment and elevated above the containment. Gas treatment means is disposed in the conduit means for treating the gas to separate any particulate matter entrained therein from the gas. A still further invention feature provides a nuclear system comprising an array of operating components including, a nuclear reactor having a reactor pressure vessel and a reactor core in the vessel, a turbine unit, a condenser receiving an exhaust of steam from the turbine unit and converting it to a condensate, and means for feeding a flow of condensate to the reactor vessel, all disposed in common containment drywell space defined by an enclosure structure. The enclosure structure includes a structure part comprising a suppression pool housing separated from the drywell space, with this housing containing a pool of water, there being a wetwell space in the housing above a level of the water pool. Means define a flow connection between the drywell space and a submerged location in the water pool, with means being provided for maintaining a continuous exhaust flow of gas mixture from the wetwell space to remove gas mixture. Means continuously admit atmospheric air from a source thereof to the wetwell space during normal operation but such means being operable to block air admission to the wetwell space during a loss-of-coolant-accident whenever pressure within the wetwell space is above a predetermined value, and a conduit communicates at an entry end thereof with the wetwell space and extends to an outlet end located exteriorly of the containment. Gas treatment means are disposed in the conduit for treating the gas to separate any particulate matter entrained therein from the gas. The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.