Patent Number: 053316746
Section: claims

1. In a nozzle dam for hermetically sealing against a wall of a nozzle of the steam generator bowl of a water cooled nuclear reactor primary coolant system against passage of fluids between said nozzle and said bowl, said nozzle dam comprising: passage means completely through said nozzle dam for releasing gas from the nozzle in the region below the nozzle dam, through the dam, to said bowl when said nozzle dam is mounted sealingly in said nozzle.  said passage means comprising a hole through said dam, and  said dam further comprising valve means connected to said hole for controlling flow of fluids through said hole in said dam.  pipe means connected to said valve means, said pipe means being positioned for directing said fluids out of said bowl.  after the reactor coolant system water general level is raised to a level that is higher than the nozzle dam, and  before completion of a later step of lowering of the reactor coolant system water general level to bring it to a level that is below the nozzle dam wherein taking of the general level below the nozzle dam is not yet attained,  the intermediate step of opening a passage exiting the nozzle for release of trapped gas through said passage from the nozzle from the region immediately below the nozzle dam.  said intermediate step being carried out before said later step of lowering the reactor coolant system water general level is started.  said passage for said release of said gas from said nozzle being through said nozzle dam.  said passage for said release of said gas from said nozzle being through a wall of said bowl.  said passage for said release of said gas from said nozzle being through said nozzle dam.  said opening of said passage being by opening a valve in a pipe line of said passage until gas flow ceases.  said opening of said passage being by opening a valve in a pipe line of said passage until gas flow ceases.  in preparation for removing said nozzle dam from said nozzle,  before completion of the step of lowering of the reactor coolant system water general level to bring it to a level that is below the nozzle dam, wherein taking of the general level below the nozzle dam is not yet attained,  the step of opening a passage exiting the nozzle for release of trapped gas from the nozzle in the region immediately below the nozzle dam, and keeping the passage open until the trapped gas is released and water in the nozzle rises to the dam. 2. The nozzle dam described in claim 1, further comprising: 3. The nozzle dam described in claim 2, further comprising 4. In a water cooled nuclear reactor primary coolant system in which a nozzle dam is in place for hermetically sealing a nozzle of the steam generator bowl, a method for reducing the chance of uncontrolled drop of reactor coolant system inventory level below mid loop level when a hermetic seal between the nozzle and steam generator bowl is broken, said method comprising: 5. The method described in claim 4, further comprising: 6. The method described in claim 4, further comprising: 7. The method described in claim 4 further comprising: 8. The method described in claim 5, further comprising: 9. The method described in claim 5 further comprising said passage for said release of said gas from said nozzle being through a wall of said bowl. 10. The method described in claim 6 further comprising: 11. The method described in claim 7, further comprising: 12. In a water cooled nuclear reactor primary coolant system in which a nozzle dam is in place for hermetically sealing a nozzle of the steam generator bowl, a method for reducing the chance of uncontrolled drop of reactor coolant system inventory level below mid loop level when a hermetic seal between the nozzle and steam generator bowl is broken, said method comprising: