Patent Number: 053533208
Section: claims

1. In a water-cooled nuclear reactor comprising: a core of nuclear fuel;  a reactor pressure vessel containing said nuclear fuel core therein and comprising an inlet;  containment spaced outwardly from and surrounding said reactor pressure vessel;  a pool of water located within said containment and outside said reactor pressure vessel at an elevation which is higher than an elevation of said nuclear fuel core; and  means for channeling water from said pool to said inlet of said reactor pressure vessel by the force of gravity in response to a predetermined condition inside said reactor, said water channeling means comprising a supply pipe having a flow passage of first diameter extending from a first end to a second end thereof, said second end of said supply pipe flow passage being in flow communication with said pool via said first end of said supply pipe flow passage; and a nozzle having a flow passage extending from a first end to a second end, said first end of said nozzle flow passage being in flow communication with said first end of said supply pipe flow passage via said second end of said supply pipe flow passage and being in flow communication with said inlet of said reactor pressure vessel via said second end of said nozzle flow passage, the improvement wherein:  a core of nuclear fuel;  a reactor pressure vessel containing said nuclear fuel core therein and comprising an inlet;  containment spaced outwardly from and surrounding said reactor pressure vessel;  a pool of water located within said containment and outside said reactor pressure vessel at an elevation which is higher than an elevation of said nuclear fuel core; and  means for channeling water from said pool to said inlet of said reactor pressure vessel by the force of gravity in response to a predetermined condition inside said reactor, said water channeling means comprising a supply pipe having a flow passage of first diameter extending from a first end to a second end thereof, said second end of said supply pipe flow passage being in flow communication with said pool via said first end of said supply pipe flow passage; and a nozzle having a flow passage extending from a first end to a second end, said first end of said nozzle flow passage being in flow communication with said first end of said supply pipe flow passage via said second end of said supply pipe flow passage and being in flow communication with said inlet of said reactor pressure vessel via said second end of said nozzle flow passage, the improvement wherein: 2. The nuclear reactor as defined in claim 1, wherein said throat has said second diameter for a length of at least 10 cm. 3. The nuclear reactor as defined in claim 1, wherein said second section has a maximum diameter which is less than a diameter of said inlet, and said nozzle flow passage further comprises a third section situated between said second section and said inlet, said third section having the shape of a bell mouth which changes gradually in diameter from said maximum diameter of said second section to said inlet diameter. 4. The nuclear reactor as defined in claim 3, wherein said nozzle flow passage further comprises a fourth section situated between said throat and said supply pipe, said fourth section having the shape of a circular cylinder of said first diameter. 5. The nuclear reactor as defined in claim 1, wherein said second section has a half-angle of about 4.degree.. 6. In a water-cooled nuclear reactor comprising: 7. The nuclear reactor as defined in claim 6, wherein said nozzle flow passage comprises a throat and first and second sections in flow communication with said throat, said throat having a second diameter which is smaller than said first diameter, said first section having the shape of a bell mouth which changes gradually in diameter from said first diameter to said second diameter, and said second section having the shape of a truncated cone having a minimum diameter substantially equal to said second diameter, said first section being situated between said throat and said supply pipe and said second section being situated between said throat and said inlet of said reactor pressure vessel. 8. The nuclear reactor as defined in claim 7, wherein said throat has said second diameter for a length of at least 10 cm. 9. The nuclear reactor as defined in claim 7, wherein said second section has a maximum diameter which is less than a diameter of said inlet, and said nozzle flow passage further comprises a third section situated between said second section and said inlet, said third section having the shape of a bell mouth which changes gradually in diameter from said maximum diameter of said second section to said inlet diameter. 10. The nuclear reactor as defined in claim 9, wherein said nozzle flow passage further comprises a fourth section situated between said throat and said supply pipe, said fourth section having the shape of a circular cylinder of said first diameter. 11. The nuclear reactor as defined in claim 7, wherein said second section has a half-angle of about 4.degree.. 12. A reactor pressure vessel comprising an inlet in flow communication with a nozzle, said nozzle having a flow passage extending from a first end to a second end, said first end of said nozzle flow passage being in flow communication with said inlet of said reactor pressure vessel via said second end of said nozzle flow passage, wherein said nozzle flow passage comprises a throat and first and second sections in flow communication with said throat, said throat having a predetermined diameter, said first section having the shape of a bell mouth which gradually decreases in diameter from a first diameter to said predetermined diameter, and said second section having the shape of a truncated cone having a minimum diameter substantially equal to said predetermined diameter, said first section being situated between said throat and said first end of said nozzle flow passage and said second section being situated between said throat and said inlet. 13. The reactor pressure vessel as defined in claim 12, wherein said throat has said predetermined diameter for a length of at least 10 cm. 14. The reactor pressure vessel as defined in claim 12, wherein said second section has a maximum diameter which is less than a diameter of said inlet, and said nozzle flow passage further comprises a third section situated between said second section and said inlet, said third section having the shape of a bell mouth which changes gradually in diameter from said maximum diameter of said second section to said inlet diameter. 15. The reactor pressure vessel as defined in claim 14, wherein said nozzle flow passage further comprises a fourth section situated between said throat and said first end of said nozzle flow passage, said fourth section having the shape of a circular cylinder of said first diameter. 16. The reactor pressure vessel as defined in claim 12, wherein said second section has a half-angle of about 4.degree..