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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,045 records · Page 58

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NASA NTRS1973

Uranium dioxide fuel cladding strain investigation with the use of CYGRO-2 computer program

Previously irradiated UO2 thermionic fuel pins in which gross fuel-cladding strain occurred were modeled with the use of a computer program to define controlling parameters which may contribute to cladding strain. The computed strain was compared with measured strain, and the computer input data were studied in an attempt to get agreement with measured strain. Because of the limitations of the program and uncertainties in input data, good agreement with measured cladding strain was not attained. A discussion of these limitations is presented.

Smith, J. R.↗

NASA NTRS1973

Hollow cathodes with BaO impregnated, porous tungsten inserts and tips

The technology of impregnated materials is described and some inherently advantageous characteristics of impregnated cathodes are discussed. Thermionic emission measurements are presented for oxide coated and impregnated cathodes. Five cathode configurations with barium oxide impregnated porous tungsten inserts and/or tips have been fabricated and tested. Reliability, durability, and stability of operation are characterized. One of the cathodes has accumulated over 9000 operational hours, another has been cycled on and off more than 800 times.

Hudson, W. R.↗

NASA NTRS1972

Planetary exploration with electrically propelled vehicles.

The characteristics of propulsion systems required for carrying out flight missions within the solar system, as desired by planetary physicists and astronomers, are reviewed. It is shown that an encouraging answer to these requirements is available in the form of electrostatic or ion propulsion systems. The design and performance characteristics of an electrostatic thrustor employing an ion source, accelerating electrode, beam neutralizer, and power source are discussed, together with those of the Kaufmann engine (electrostatic thrustor employing bombardment type ionization). More demanding missions which will become feasible with the advent of nuclear-electric power sources (such as the incore thermionic reactor) may include close orbiters around all the planets, and asteroid and cometary missions.

Stuhlinger, E.↗

NASA NTRS1973

CdS-metal contact at higher current densities.

An investigation is conducted concerning the mechanisms by which a steady flow of current proceeds through the contact when an external voltage is applied. The main characteristics of current mechanisms are examined, giving attention to photoemission from the cathode, thermionic emission, minority-carrier extraction, and the tunneling of electrons. A high-field domain analysis is conducted together with experimental studies. Particular attention is given to the range in which tunneling predominates.

Stirn, R. J.↗

NASA NTRS1973

Development costs for a nuclear electric propulsion stage.

Development costs are presented for an unmanned nuclear electric propulsion (NEP) stage based upon a liquid metal cooled, in-core thermionic reactor. A total of 120 kWe are delivered to the thrust subsystem which employs mercury ion engines for electric propulsion. This study represents the most recent cost evaluation of the development of a reactor power system for a wide range of nuclear space power applications. These include geocentric, and outer planet and other deep space missions. The development program is described for the total NEP stage, based upon specific development programs for key NEP stage components and subsystems.

Mondt, J. F.↗

NASA NTRS1974

Improved control for nuclear/thermionic power source: A concept

Variable-gain power regulator is used to maintain constant load voltage. There are two feedback loops. One is tied directly with regulator to feed error voltage, which is sum of reference and load voltages. Second loop is tied with reactor, where output current of thermionic fuel elements is fed back to signal generator.

Sawyer, C. D.↗

NASA NTRS1973

Computer acquired performance data from a chemically vapor-deposited-rhenium, niobium planar diode

Performance data from a chemically vapor-deposited-rhenium, niobium thermionic converter are presented. The planar converter has a guard-ringed collector and a nominal fixed spacing of 0.25 mm (10 mils). The data were obtained by using a computerized acquisition system and are available on request to one of the authors on microfiche as individual and composite parametric current, voltage curves. The parameters are the temperatures of the emitter T sub E collector T sub C, and cesium reservoir T sub R. The composite plots have constant T sub E and varying T sub C or T sub R, or both. Current, voltage envelopes having constant T sub E with and without fixed T sub C appear in the present report. The diode was tested at increments between 1600 and 2000 K for the emitter Hohlraum, 800 to 1100 K for the collector, and 540 and 650 K for the reservoir. A total of 312 current, voltage curves were obtained in the present performance evaluation. Current, voltage envelopes from three rhenium emitter converters evaluated in the present program are also given. The data are compared at commom emitter Hohlraum temperatures.

Manista, E. J.↗

NASA NTRS1973

Effect of reactor coolant radioactivity upon configuration feasibility for a nuclear electric propulsion vehicle

A preliminary shielding analysis was carried out for a conceptual nuclear electric propulsion vehicle designed to transport payloads from low earth orbit to synchronous orbit. The vehicle employed a thermionic nuclear reactor operating at 1575 kilowatts and generated 120 kilowatts of electricity for a round-trip mission time of 2000 hours. Propulsion was via axially directed ion engines employing 3300 pounds of mercury as a propellant. The vehicle configuration permitted a reactor shadow shield geometry using LiH and the mercury propellant for shielding. However, much of the radioactive NaK reactor coolant was unshielded and in close proximity to the power conditioning electronics. An estimate of the radioactivity of the NaK coolant was made and its unshielded dose rate to the power conditioning equipment calculated. It was found that the activated NaK contributed about three-fourths of the gamma dose constraint. The NaK dose was considered a sufficiently high fraction of the allowable gamma dose to necessitate modifications in configuration.

Soffer, L.↗

NASA NTRS1973

Nuclear electric propulsion reactor control systems status

The thermionic reactor control system design studies conducted over the past several years for a nuclear electric propulsion system are described and summarized. The relevant reactor control system studies are discussed in qualitative terms, pointing out the significant advantages and disadvantages including the impact that the various control systems would have on the nuclear electric propulsion system design. A recommendation for the reference control system is made, and a program for future work leading to an engineering model is described.

Ferg, D. A.↗

NASA NTRS1974

Electrical heating tests of uranium dioxide external fuel configuration at emitter temperature of 1900 K

Testing of two fuel clad specimens for thermionic reactor application is described. The annular UO2 fuel was clad on both sides with tungsten; heat rejection was radially inward. The tests were intended to study inner clad stability, fuel redistribution, and fuel melting problems. The specimens were tested in a vacuum chamber using electron bombardment heating. Fuel structural changes were studied using periodic gammagraphs and posttest metallography. The first specimen test was terminated at 50 hours because of a braze failure. The second specimen was tested for 240 hours when an outer clad leak developed due to a tungsten-water reaction. The fuel developed numerous cracks on cooldown but the inner clad remained dimensionally stable. The fuel cover gas did not impede the rate of fuel redistribution. Posttest examination showed the fuel had not melted during operation.

Diianni, D. C.↗

NASA NTRS1974

Advanced design concepts in nuclear electric propulsion

Conceptual designs of the nuclear propulsion programs are reported. Major areas of investigation were (1) design efforts on spacecraft configuration and heat rejection subsystem, (2) high-voltage thermionic reactor concepts, and (3) dual-mode spacecraft configuration study.

Peelgren, M. L.↗

NASA NTRS1974

Nuclear electric propulsion stage requirements and description

The application of a nuclear electric propulsion (NEP) stage in the exploration of near-earth, cometary, and planetary space was discussed. The NEP stage is powered by a liquid-metal-cooled, fast spectrum thermionic reactor capable of providing 120 kWe for 20,000 hours. This power is used to drive a number of mercury ion bombardment thrusters with specific impulse in the range of 4000-5000 seconds. The NEP description, characteristics, and functional requirements are discussed. These requirements are based on a set of five coordinate missions, which are described in detail. These five missions are a representative part of a larger set of missions used as a basic for an advanced propulsion comparison study. Additionally, the NEP stage development plan and test program is outlined and a schedule presented.

Mondt, J. F.↗

NASA NTRS1973

Hollow cathodes with BaO impregnated, porous tungsten inserts and tips

Hudson, W. R.↗

NASA NTRS1974

Energy-conversion research and development with diminiodes

Diminiodes are variable-gap cesium diodes with plane emitters and guarded collectors a few millimeters in diameter. This miniaturization allows the electrodes to be made of little pieces of rare materials like single crystals of unusual metals or metallides. In addition to smallness, diminiode advantages include simplicity, precision, fabrication ease, parts interchangeability, cleanliness, full instrumentation, ruggedness, and economy. The diminiode design also stresses effective, economical use with computers that control, collect, and correlate thermionic current and voltage data. Such diminiode tests completed recently for ultrapure metal electrodes produced relatively low, sharply defined ultimate power outputs.

Morris, J. F.↗

NASA NTRS1975

Inhibiting Kirkendall void growth in welded bimetallic structures

Technique employs pre-aged, void-free junction composed of parent materials. Basic process for Kirkendall void inhibition can be applied to thermionic power systems, high temperature seals, high temperature junctions between any two metals of differing melting points where Kirkendall void formation would be detrimental.

Arcella, F. G.↗

NASA NTRS1974

Isotopic composition of lithium, potassium, rubidium, and strontium in lunar surface material

The isotopic composition of alkali and alkaline earth elements in the Luna 16 regolith was investigated by the method of thermionic emission, without chemical separation. The isotopic composition of the lithium in two regolith samples did not differ (within the limits 0.5 percent) from the mean of the terrestrial reference standard. At the same time, the observed difference (1 percent) in the isotopic composition of lithium between the samples requires further investigation and confirmation. The isotopic compositions of K and Rb did not differ within the limits of experimental error from the isotopic composition of the reference standard.

Zaslavskiy, V. G.↗

NASA NTRS1975

Radioactive waste disposal via electric propulsion

It is shown that space transportation is a feasible method of removal of radioactive wastes from the biosphere. The high decay heat of the isotopes powers a thermionic generator which provides electrical power for ion thrust engines. The massive shields (used to protect ground and flight personnel) are removed in orbit for subsequent reuse; the metallic fuel provides a shield for the avionics that guides the orbital stage to solar system escape. Performance calculations indicate that 4000 kg. of actinides may be removed per Shuttle flight. Subsidiary problems - such as cooling during ascent - are discussed.

Burns, R. E.↗

NASA NTRS1975

The UF6 Breeder - A solution to the problems of nuclear power

One of the major advantages of uranium hexafluoride reactors for power generation is the simplified fuel reprocessing scheme which the gaseous fuel makes possible. Critical experiments related to the development of the reactors for electric power generation are discussed along with UF6 breeder reactor studies. Previous energy conversion studies are reported, taking into account gas turbine power plants, thermionic conversion, and MHD conversion. Thermodynamic cycle analyses show that high efficiencies can be achieved using UF6 as the working fluid for Rankine or Brayton cycles without requiring excessive temperatures.

Williams, J. R.↗