Gabor Miskolczy

Design and preliminary testing of a thermionic AMTEC cascade

This paper describes the design of an experiment to demonstrate the feasibly of operating a cascade of a Thermionic Energy Converter (TEC) with an Alkali Metal Thermo Electric Converter (AMTEC). Both of these devices convert heat to electricity without moving mechanical parts and lend themselves to be incorporated into a cascade. Typically, the TEC operates from a hot temperature of 2000 K to 1700 K, rejecting heat at 1100 K to 700 K, while the AMTEC operates from a hot temperature of 1100 K to 900 K and a cold temperature of about 400 K. These temperature ranges form almost ideal cascade.

Radioisotope Thermionic Converters for Space Applications

The recent history of radioisotope thermionics is reviewed, with emphasis on the U.S. programs, and the prospects for the future are assessed. In radioisotope thermionic converters the emitter heat is generated by the decay of a radioactive isotope. The thermionic converter emitter is mounted directly on a capsule containing the isotope. The rest of the capsule is generally insulated to reduce thermal loss. The development of isotope-fueled thermionic power systems for space application has been pursued since the late 1960s. The U.S. effort was concentrated on modular systems with alpha emitters as the isotope heat source. In the SNAP-13 program, the heat sources were Cerium isotopes and each module produced about 100 watts. The converters were planar diodes and the capsule was insulated with Multi-Foil insulation. Unlike nuclear reactors, the isotope heat source cannot be turned off. Thus the isotope must be handled in a hot cell, and furthermore, once the isotope is inserted into the thermionic converter, the refractory metals must be protected from oxidation with either vacuum or inert atmosphere. With the advent of DC-to-DC converters which operate with low input voltage and high efficiency, radioisotope thermionic converters are attractive.

Design of Cesium Reservoir Critical Component Experiment for S‐PRIME

The purpose of this experiment is to confirm the operating temperatures and pressures of the cesium graphite integral reservoir design for the Space Power Reactor In‐Core Multicell Evolutionary (S‐PRIME) thermionic reactor. The test will verify the reservoir performance under both steady state and transient situations. The special cylindrical TFE (Thermionic Fuel Element) cell used for this test has a prototypic reservoir design and electrical heating for the emitter. It is similar to cylindrical converters designed in the past such as CC‐1X (General Atomics 1988) built under the TFE verification program, except for the reservoir details. The S‐PRIME TFE has six cells and one graphite reservoir. The reservoir is integral to one of the end cells and is thermally coupled to both of the emitters via the emitter sleeve and the collector via a section of a sheath insulator.

Design of a planar thermionic converter to measure the effect of diffusion of uranium oxide on performance

A plane parallel variable‐spaced research converter was designed to investigate the effect of diffusion of uranium oxide fuel through the tungsten emitter. This work is part of the Thermionic Fuel Element (TFE) verification program. In the TFE program the cylindrical emitter is made of Chemical Vapor Deposited (CVD) tungsten from tungsten fluoride, which is over coated with CVD tungsten, from the chloride, resulting in a 〈110〉 crystal orientation. The planar converter has a similar emitter construction. This paper describes the design and preliminary testing of this converter.

Application of chemical vapor composites (CVC) to terrestrial thermionics

Terrestrial flame fired thermionics took a great leap forward in the earlier 1980’s with the development of reliable long‐lived hot shells. These results were presented by Goodale (1981). The hot shell protects the fractory emitter from oxidizing in the combustion environment. In earlier efforts with supralloys emitters it was found that superalloys were poor thermionic emitters since they operated at too low a temperature for practical and economical use as discussed by Huffman (1978). With the development of Chemical Vapor Deposited (CVD) silicon carbide and CVD tungsten, it became possible to fabricate long‐lived thermionic converters. These results were shown by Goodale (1980). Further improvements were achieved with the use of oxygen additives on the electrodes. These developments made thermionics attractive for topping a power plant or as the energy conversion part of a cogeneration plant as described by Miskolczy (1982) and Goodale (1983). The feasibility of a thermonic steam boiler and a thermioni...

Modeling of a cesium‐graphite reservoir critical component experiment for S‐prime

The S‐PRIME (Space Power Reactor, In‐core, Multi‐cell, Evolutionary) program has identified the cesium reservoir as a critical component requiring experimental validation. A test vehicle to measure the response of the cesium‐intercalated graphite reservoir has been designed. The geometric design of the test device parallels that of the in‐core, fueled device to the extent possible. Heat loss is through a gas gap to a water‐cooled jacket rather than to a molten metal loop. Auxiliary heaters were added to the collector and cesium reservoir heat sink region in order to provide flexibility to achieve the wide range of temperatures proscribed in the test protocol. The thermal finite difference computer model developed for the nuclear device was adapted to reflect the required modifications in the design of the experimental apparatus.This computer model indicated that the single test device is capable of simulating both types of cesium reservoirs required in the S‐PRIME system. The nominal operating conditions ...

Heat pipe design for sheath insulator reactor test

A reactor experiment was designed to test the sheath insulator component of the thermionic fuel element (TFE) of a space power reactor. In this fully instrumented reactor test, two gas‐controlled sodium heat pipes will be used to control the temperature of the sheath insulator specimens to which an external voltage will be applied. The heat pipes were designed with the aid of a computer program, which predicted performance. A demonstrator heat pipe was built and electrically tested. The test results agreed with the prediction as modeled by the computer program.