Patent Number: 047553502
Section: summary

BACKGROUND OF THE INVENTION The present invention relates generally to thermionic power conversion systems, and more specifically to modules for a nuclear energy powered thermionic reactor for space-based operation capable of providing large amounts of power in short pulses. In the operation of a thermionic converter, heat energy is converted directly to electrical current by heating a metallic emitter to sufficiently high temperatures so that electrons escape the emitter and flow to a cooler collector. The source of heat energy for conversion to electrical current may be any of several types, including exothermic chemical reactions and the heat of nuclear fission. In order to promote efficient operation of a thermionic system to generate useful amounts of electrical power, the system must not only generate large amounts of heat required for energizing the thermionic components, but must also provide for rejection of waste heat from the cold side of the thermionics. High power thermionic energy systems are proposed as power supplies for space-based beam or kinetic energy weapons. Those devices require substantial power, but only for short bursts. It is seen, therefore, that there is a need for a thermionic power system able to rapidily absorb very large amounts of waste heat during a high output power pulse, and then remove the absorbed waste heat energy to prepare for another pulsed output of power. It is, therefore, a principal object of the present invention to provide an efficient high power thermionic power system particularly adaptable to high powered pulsed operations in space. It is another object of the present invention to provide a nuclear fission powered thermionic system. These and other objects of the present invention are achieved by the following described nuclear energy powered thermionic reactor system. A unique discovery of the present invention is the use of a heat sink material contained within the core of each reactor module to absorb the waste heat of the thermionic conversion process. An advantage of the present invention is that the heat sink material may act as a neutron moderator, thereby reducing the amount of needed nuclear fuel. A further advantage of the present invention is that containing the heat sink material within the reactor core eliminates any need for an intermediate heat exchanger. Yet another advantage of the present invention is that the reactor radiation shield may be used as part of a heat sink for cooling the heat sink material in the reactor core. The reactor, unlike open-cycle turbine generators, emits no effluents, thereby avoiding problems with thrust cancellation, contamination, and so forth. Also unlike open-cycle power supplies, the reactor is completely reusable. Further, the reactor has no moving parts, eliminating any need in a space based system for torque cancellation and reducing or eliminating vibration. SUMMARY OF THE INVENTION The present invention is directed to a thermionic energy conversion system assembly comprising a heat source which surrounds a plurality of emitter electrodes which surround a plurality of corresponding collector electrodes which in turn surround a heat sink. The heat source may be fissionable nuclear fuel. The heat sink may be a container of heat sink material, which may be a lithium salt, such as lithium hydride. The heat sink material may also be a neutron moderator, such as lithium hydride enriched in the Li-7 isotope. The invention additionally includes a heat pipe, enclosed in the heat sink material, for transferring heat out of the heat sink material. The invention further includes a thermionic energy conversion system module comprising a plurality of stacked-in-series thermionic conversion assemblies. The heat sources and the heat sinks may be made continuous from one assembly to another, and a heat pipe enclosed in the heat sink material removes heat from the heat sink material. The invention further includes an array of thermionic energy conversion system modules to form a thermionic nuclear reactor. The invention additionally includes the method of thermionic energy conversion by using a heat sink positioned inside the thermionic converter assembly.