Patent Number: 051065746
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION (BEST MODES FOR CARRYING OUT THE INVENTION) Reference is now made to FIG. 1 which illustrates a preferred embodiment of the invention. Gas cooled reactor 10 comprises three sectors 12, 14 and 16. Each sector has its own gas coolant inlet 12a, 14a, and 16a and its own outlet 12b, 14b and 16b. Each sector is structured to contain its own core separate and distinct from the cores of the other sectors and to be cooled independently from and in cooperation with other sectors. A representative core for use in any of the sectors of the FIG. 1 embodiment is illustrated in FIG. 2, to be hereinafter discussed. Although three sectors are shown for the preferred embodiment, more than three sectors can be used in practicing the invention. The use of a plurality of sectors provides redundancy and insurance of continued reactor operation even if one or more cores loses its active cooling. Adjacent sectors are capable of conducting heat from a malfunctioning sector and convecting that heat away using their own cooling system. The reactor can be made of refractory metals structure, such as Mo Re, W-Re, alloys with graphite pellets containing TRISO fuel particles, or the like, and can be of any suitable size such as from 80.times.130 cm to 100.times.170 cm. The gas coolant can comprise any suitable coolant such as hydrogen, helium, or helium-xenon. Individual components suitable for use in each sector are known to practitioners of the art and are a matter of design choice. Too, each sector can comprise any known suitable reactor design. Thus, specific sector structure is not disclosed herein. Nevertheless, the preferred embodiment is particularly suitable for use with cores 20 comprising fuel pellets 22, as seen in FIG. 2. Preferably the pellets are spherical in order to maximize surface area to mass ratio to optimize cooling. Those skilled in the art will recognize that pellets for use with the invention need not be spherical, but can be cylindrical (short or long), cubical, or of any other shape. Too, the fuel microspheres in the pellets can be contained in a solid medium, such as graphite, and spaced from one another therein. Alternatively, the pellets can be poured into each sector to provide the cores thereof, as seen in FIG. 3. The pellets can be those taught in "Pellet Bed Reactor Design for Space Power," M. S. El-Genk, et al., 22nd International Energy Conversion Engineering Conference, Paper No. 879360, Philadelphia, Pa. (1987) and "System Design Optimization for Multimegawatt Space Nuclear Power Applications," M. S. El-Genk, et al., Journal of Propulsion and Power, Vol. 6, No. 2 (1990), as well as others known to practitioners in the art. The reactor is particularly suitable to use in space where its unique refueling capability, the absence of single point failure, and low weight are advantageous. It can be fueled, emptied of fuel, and refueled in space using the vacuum of space, as seen in FIG. 3. Although it can be launched fueled, it can alternatively be launched empty and fueled in space. The pellets can be safely handled by skilled personnel wearing gloves since they only emit alpha radiation. The pellets are subjected only to low temperature gradients, hence, thermal stress is expected. Also, the microspheres 30 within the pellets 32 are preferably separated by a medium of graphite 34 to enhance heat conduction from microspheres to coolant and avoid stress which could occur had the microspheres been in direct contact, as seen in FIG. 4. To simplify the safety procedures at launch, the invention, in addition to providing similar redundancy in the reactor operating and safety systems, provides for the launching of a reactor empty of fuel, if so desired. This significantly simplifies launch procedures, particularly in manned shuttle launches. Thus, in accordance with the invention and as shown in FIG. 3, reactor fuel pellets 32 can be launched separately in containers 40, each container holding sufficient fuel pellets to fill out a sector of the core and being pressurized with an inert gas. Each container 40 is subcritical during launch, a great safety advantage. Therefore, a user of the invention has the option of either launching a reactor loaded with fuel elements, or launching an empty reactor and fueling and refueling the reactor core after it is successfully deployed in orbit. The refueling option, coupled with the sectioned core of the invention, provide for longer lifetime in a space platform operated with a nuclear reactor, resulting in significant cost saving and enhanced safety and redundancy. In addition to the economical advantages and safety during launch, the refueling option simplifies the final disposal of the used fuel elements 32'. In accordance with the invention, core refueling can be handled from a distance, or performed with robots or automatic mechanisms. The vacuum of space can be used to pull the used pellets 32' from core 20, using, for example, a porous disk 42. Also, sectioning the reactor enables the completion of the mission, even if one or more of the sections suffer a loss of coolant. Thermal radiation to outer space from the failed sections as well as conduction to the other operating sections will be sufficient to remove the heat from the failed core section. Such a unique feature provides not only redundancy in the design, but also safety by eliminating the likelihood of a single-point failure in the core. A reactor core, in accordance with the invention, is light in weight since the need for an auxiliary cooling system of the core in case of loss of coolant accident is eliminated. Also, since the pellets in the core are structurally self supported, the core requires no internal structure, resulting in lower reactor weight. The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the scope of the invention.