Patent Number: 050874128
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, it is seen that the invention is generally referred to by the numeral 10. Nuclear reactor 10 is formed from reactor vessel 12 having primary coolant outlet plenum 14, core barrel 16, fuel elements 18, safety rods 20, and control drums 22. Drives 24 are also provided for safety rods 20 and control drums 22. Instrumentation and power leads enter reactor 10 through head penetration nozzle 26. Nuclear reactor 10 is essentially a conventional nuclear reactor relative to the use of a reactor vessel, fuel elements, safety rods, and control drums with improvements directed toward nuclear reactors intended for applications in outer space. Primary coolant inlet passage 28 is provided on the outer wall of primary coolant outlet plenum 14. As seen in the detail view of FIG. 4A, passage 28 is of a general torus or semicircular shape in the preferred embodiment. As best seen in FIG. 4 and the detail view of FIG. 4B, inlet passage 28 directs the primary coolant to inlet plenum 30 adjacent to distributor plate 32. During auxiliary heat removal gaseous coolant flows into plenum 28 through nozzles 46. As seen in FIG. 1 and 4B, distributor plate 32 is bolted to core barrel 16 and extends across the lower portion of reactor vessel 12 above primary coolant outlet plenum 14. As best seen in the detail views of FIG. 4B and 4C, distributor plate 32 is provided with passageways 34 which direct the primary coolant to a gap 38 between each fuel element housing thimble 36 and the fuel element 18 it surrounds. As seen in FIG. 4C, fuel element housing thimbles 36 and fuel elements 18 are mounted in distributor plate 32 to form gap 38. Fuel elements 18 also extend below distributor plate 32 into primary coolant outlet plenum 14 as seen in FIG. 1, 3, and 4 so that the interior of each fuel element 18 is in fluid communication therewith. The primary coolant flows from gap 38 through porous material 40 as indicated by the arrow in FIG. 4C into center 42 of fuel element 18 and then flows downwardly through fuel element 18 into primary coolant outlet plenum 14. Reactor vessel 12 is provided with nozzles 44 used to insert or drain liquid from the reactor core. During reactor operation the liquid is circulated up through the moderator region bounded by the inside of core barrel 16 and the outside of fuel element housing thimbles 36. As seen in FIG. 3 and indicated by arrows, the liquid then enters circulation pumps 45, is discharged by the pumps into the upper head, and then flows down around and through the control drums 22 in the reflector region bounded by the reactor vessel 12 and the core barrel 16. As seen in FIG. 3A, and indicated by arrows, the liquid then completes its circulation loop by flowing into the moderator region through the passages provided in core barrel 16 at the lower end. As seen in FIG. 3A, fuel element housing thimbles 36 are provided with fins which extend from the thimble outer circumference into the liquid and which serve to conduct heat from the liquid to the primary gaseous coolant flowing inside the thimbles 36. This is accomplished by using a primary coolant that is at a temperature cooler than the liquid moderator when the coolant enters annular gap 38. The primary coolant (cold relative to the moderator) is heated by conduction/convection from the warmer liquid moderator through housing thimble 36. The moderator is heated by absorbed radiation to a dynamic equilibrium temperature higher than that of the coolant. Direct heating of the primary coolant by the fuel elements does not occur until radial passage of the coolant through porous material 40. In conventional terrestrial water moderator reactors, for useful energy production the heat flow is into the liquid moderator at the fuel elements rather than from the liquid as in the reactor of the invention. The liquid moderator/reflector is not in place during manufacture, ground transportation, launch, and disposal, thus enhancing reactor safety since the reactor is kept subcritical. When operation begins, the liquid moderator/reflector is added to reactor vessel 12 through fill/drain nozzles 44 for circulation in the core as described above. The liquid moderator/reflector enables the relatively small amount of fissile material in fuel elements 18 to go critical (become a self-sustaining reaction) in the core and cools the control drums and other system components. In the preferred embodiment, the primary coolant is a gas suitable for such use and the liquid moderator/reflector is water. A gas coolant that is in a cryogenic state, such as hydrogen at minus 400 degrees F., when it enters the inlet of gap 38 is well suited to the heat transfer process of the invention. Other suitable liquid moderator/reflector such as various organic liquids may also be used. An alternative to the preferred approach is shown in FIG. 5 wherein a heat exchanger external to the reactor is provided for supplemental heat removal from the liquid moderator. The liquid moderator circulates through the core from the bottom fill nozzles up through the moderator and reflector regions and into the upper head. From the upper reactor head the liquid exits the core, passes through pump 47, and flows into heat exchanger 48 where it is cooled by the coolant gas before the gas enters the reactor. The liquid moderator then flows from the heat exchanger into the core through the fill/drain nozzles 44. Cooling of the liquid moderator is provided in the core as described in the preferred approach.