Patent Number: 062597604
Section: claims

1. A nuclear steam supply system with a life of at least 10 years, comprising: an upright pressure vessel containing a pool of light water;  a fast or epithermal spectrum reactor core immersed in said pool of light water;  a plurality of steam generators immersed in said pool of light water within said pressure vessel and each having a secondary circuit extending outside said pressure vessel, said plurality of steam generators exceeding a predetermined number of said steam generators needed to operate said reactor core at full power and selected from among said plurality of steam generators; and  means within said pressure vessel inducing a flow within said pool of light water through said reactor core and said at least one steam generator and back to said reactor core. 2. The nuclear steam supply system of claim 1 wherein said means inducing a flow within said pool of reactor coolant includes a certain number of reactor coolant pumps immersed in said pool of reactor coolant and of which a smaller maximum number of reactor coolant pumps operate simultaneously to induce said flow within said pool of reactor coolant while remaining reactor coolant pumps are inactive but available as spares so that no more than said smaller maximum number of reactor coolant pumps are active simultaneously. 3. The nuclear steam supply system of claim 1 wherein said means inducing a flow in said pool of light water comprises a certain number of reactor coolant pumps immersed in said pool of light water and of which a smaller maximum number of reactor coolant pumps operate simultaneously to induce said flow of light water while the remaining reactor coolant pumps are inactive but available as spares such that no more than said smaller maximum required number of reactor coolant pumps are active simultaneously. 4. The nuclear steam supply system of claim 3 wherein said upright pressure vessel is generally cylindrical with a lower section and upper section, said reactor core is positioned generally centrally in said lower section of said pressure vessel and said means inducing a flow within said pool of reactor coolant includes a core chimney extending upward from said reactor core toward said upper section forming a central passage above said reactor core and annular passage adjacent an inner surface of said pressure vessel, said steam generators being located in said upper section of said pressure vessel and said reactor coolant pumps being positioned to draw said reactor coolant down through said annular passage. 5. The nuclear steam supply system of claim 4 wherein said reactor coolant pumps have impellers immersed in said pool of reactor coolant within said pressure vessel, and motors driving said impellers mounted outside said pressure vessel. 6. The nuclear steam supply system of claim 1 wherein said reactor core produces approximately 5-20% steam in the light water exiting said reactor core. 7. The nuclear steam supply system of claim 6 wherein said reactor core produces approximately 10% steam in the light water exiting said reactor core. 8. The nuclear steam supply system of claim 7 wherein said at least one steam generator comprises a plurality of steam generators immersed in said pool of light water within said pressure vessel and each has a secondary circuit extending outside said pressure vessel, said plurality of steam generators exceeding a predetermined number of steam generators needed to operate said reactor core at full power and selected from among said plurality of steam generators. 9. The nuclear steam supply system of claim 1 wherein said fast or epithermal spectrum reactor core has fuel rods with a pitch to diameter ratio of no more than about 1.1 and with a surface area which is more than a surface area of a cylindrical rod of the same diameter. 10. The nuclear steam supply system of claim 9 wherein said fuel rods have an annular cross section. 11. The nuclear steam supply system of claim 9 wherein said fuel rods have stainless steel cladding. 12. The nuclear steam supply system of claim 1 wherein said upright pressure vessel is generally cylindrical with a lower section and an upper section, said reactor core is positioned generally centrally in said lower section of said pressure vessel and said means inducing flow within said pool of reactor coolant includes a core chimney extending upward from said reactor core toward said upper section of said pressure vessel and forming a central passage above said reactor core and an annular passage adjacent an inner surface of said pressure vessel, said steam generators being; located in said upper section where at least some of said steam generators extend into said annular passage. 13. The nuclear steam supply system of claim 12 wherein all of said steam generators extend into said annular passage and said reactor core has control rods inserted by drivelines extending downward through a top of said pressure vessel and said central passage. 14. The nuclear steam supply system of claim 12 wherein others of said steam generators are located in said upper section of said pressure vessel and aligned with said central passage. 15. The nuclear steam supply system of claim 14 wherein said reactor core has control rods inserted by drivelines inserted through a bottom of said pressure vessel. 16. The nuclear steam supply system of claim 1 wherein said upright pressure vessel is generally cylindrical and has a lower section and an upper section, said reactor core is positioned generally centrally in said lower section of said pressure vessel and said means inducing said flow in said pool of light water comprises a core chimney extending upward from said reactor core toward said upper section of said pressure vessel creating a central passage above said reactor core and an annular passage between said chimney and an inner surface of said pressure vessel and extending down below said reactor core, said steam generator comprising a plurality of steam generators in said upper section of said pressure vessel with sufficient capacity to produce a .DELTA.T across said reactor core of at least approximately 75 degrees C. 17. The nuclear steam supply system of claim 16 wherein said plurality of steam generators exceeds a predetermined number of steam generators needed to operate said reactor core at full power and selected from said plurality of steam generators. 18. The nuclear steam supply system of claim 16 wherein said reactor core produces partial boiling of said light water and said steam generators have sufficient capacity to produce a .DELTA.T across said reactor core of at least 100 degrees C. 19. The nuclear steam supply system of claim 18 wherein said reactor core produces about 5-20% steam in light water exiting said reactor core and said chimney comprises a plurality of chimney channels extending across said reactor core and upward within said central passage to raise the level at which light water containing steam exiting the reactor core mixes with said pool of light water.