Pin and cermet hybrid bimodal reactor

Abstract

A bimodal propulsion and power nuclear reactor with coaxial power and propulsion cores, each with its own primary propellant/coolant. An inner core region provides electrical power while an outer annular core region surrounding the inner core region has, passageways for heating a gaseous propellant.

We claim: 
     
       1. A nuclear reactor that will provide heat for conversion to electricity and direct nuclear thermal propulsion by heating a propellant, having first and second separate reactor core regions, coupled thermally and neutronically, the first core region being a central power core region having a nuclear fuel and coolant for generating electrical power, and   the second core region being an annular propulsion core region surrounding the first core region and having a nuclear fuel capable of heating a gaseous propellant, with passageways for the gaseous propellant, said passageways being separate from the coolant path in the first core region.   
     
     
       2. The nuclear reactor of claim 1 wherein the nuclear fuel in said first core region is an array of fuel pins, each fuel pin comprising a compound of uranium encased in metallic cladding, and the nuclear fuel in said second core region is a cermet material containing a compound of uranium. 
     
     
       3. The nuclear reactor of claim 2 wherein said cermet material and said passageways for gaseous propellant in said second core region have refractory metallic cladding. 
     
     
       4. The nuclear reactor of claim 3 wherein said refractory metallic cladding is selected from the group consisting of tungsten, molybdenum-rhenium alloy, and tungsten-molybdenum-rhenium alloy. 
     
     
       5. The nuclear reactor of claim 3 wherein said passageways are refractory metallic tubes within the cermet fuel elements, opening on the ends of said cermet fuel elements. 
     
     
       6. The nuclear reactor of claim 2 wherein-the first core region is cooled by a coolant that is liquid at reactor operating temperatures. 
     
     
       7. The nuclear reactor of claim 6 wherein the coolant is lithium. 
     
     
       8. The nuclear reactor of claim 2 wherein said compound of uranium in said fuel pins is uranium nitride. 
     
     
       9. The nuclear reactor of claim 8 wherein said uranium nitride is alloyed with titanium or zirconium. 
     
     
       10. The nuclear reactor of claim 2 wherein said metallic cladding on said fuel pins is an alloy of niobium containing over 90% niobium. 
     
     
       11. The nuclear reactor of claim 10 wherein said alloy of niobium contains zirconium. 
     
     
       12. The nuclear reactor of claim 10 wherein said niobium cladding alloy has an inner liner of rhenium. 
     
     
       13. The nuclear reactor of claim 2, further comprising (a) a closed reactor vessel containing said first core region and (b) an outer propellant containment vessel surrounding said second core region and having at least one thrust nozzle for conducting said gaseous propellant to space. 
     
     
       14. The nuclear reactor of claim 13, further comprising reflector elements outside of said propellant vessel. 
     
     
       15. The nuclear reactor of claim 2, further comprising control rods contained in reentrant thimbles in said first core region. 
     
     
       16. The nuclear reactor of claim 2 wherein said compound of uranium in said cermet material is uranium dioxide (UO 2 ) or uranium nitride (UN). 
     
     
       17. The nuclear reactor of claim 2 wherein said gaseous propellant is hydrogen. 
     
     
       18. The nuclear reactor of claim 2 further containing thermal insulation at the part of the interface between said first and second core regions closer to the nozzle for exhausting the propellant. 
     
     
       19. The nuclear reactor of claim 18 further having a vacuum gap in the noninsulated area of to interface for channeling any diffused propellant to space. 
     
     
       20. The nuclear reactor of claim 18 wherein said thermal insulation is molybdenum-zirconium oxide multifoil insulation. 
     
     
       21. A nuclear reactor that will provide heat for conversion to electricity and direct nuclear thermal propulsion by heating a gaseous propellant, having first and second separate reactor core regions, coupled thermally and neutronically, the first core region being a central power core region having an array of nuclear fuel pins and lithium coolant for circulation to an electrical power generating means, each fuel pin comprising uranium nitride nuclear fuel encased in metallic cladding consisting essentially of an alloy of niobium and zirconium, and   the second core region being an annular propulsion core region surrounding the first core region and having a cermet nuclear fuel containing uranium nitride or uranium oxide capable of heating a gaseous propellant, with passageways for the gaseous propellant, said passageways being separate from the coolant path in the first core region, said cermet being encased in a refractory metal cladding.   
     
     
       22. A bimodal nuclear reactor for providing electrical power and propulsion for space applications having (a) an inner core region containing a coolant that is liquid at reactor operating temperatures and can be circulated to electrical power generating means and   (b) an annular outer core region surrounding the inner core region and having passageways for a gaseous propellant that is heated in said annular core and expelled into space through at least one nozzle, both inner and annular outer core regions containing fissile nuclear fuel and being separated by the walls of a metal vessel that contains the inner core region, there being a vacuum gap at the interface of said walls and said annular outer core region on the reactor end distant from said nozzle(s) and thermal insulation at said interface on the reactor end near to said nozzle(s).   
     
     
       23. The reactor of claim 22 wherein said gaseous propellant is selected from the group consisting of hydrogen, ammonia, steam, and carbon dioxide. 
     
     
       24. The reactor of claim 22 wherein said inner core region is capable of heating coolant for electrical power generation for seven years and said annular outer core region is capable of heating a gaseous propellant to a temperature of more than 2000 degrees Kelvin for 250 hours.