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RECENT ACTIVITIES AT THE CENTER FOR SPACE NUCLEAR RESEARCH FOR DEVELOPING NUCLEAR THERMAL ROCKETS

Description: Nuclear power has been considered for space applications since the 1960s. Between 1955 and 1972 the US built and tested over twenty nuclear reactors/ rocket-engines in the Rover/NERVA programs. However, changes in environmental laws may make the redevelopment of the nuclear rocket more difficult. Recent advances in fuel fabrication and testing options indicate that a nuclear rocket with a fuel form significantly different from NERVA may be needed to ensure public support. The Center for Space Nuclear Research (CSNR) is pursuing development of tungsten based fuels for use in a NTR, for a surface power reactor, and to encapsulate radioisotope power sources. The CSNR Summer Fellows program has investigated the feasibility of several missions enabled by the NTR. The potential mission benefits of a nuclear rocket, historical achievements of the previous programs, and recent investigations into alternatives in design and materials for future systems will be discussed.
Date: September 1, 2001
Creator: O'Brien, Robert C.
Partner: UNT Libraries Government Documents Department

Multi Megawatt Power System Analysis Report

Description: Missions to the outer planets or to near-by planets requiring short times and/or increased payload carrying capability will benefit from nuclear power. A concept study was undertaken to evaluate options for a multi-megawatt power source for nuclear electric propulsion. The nominal electric power requirement was set at 15 MWe with an assumed mission profile of 120 days at full power, 60 days in hot standby, and another 120 days of full power, repeated several times for 7 years of service. Of the numerous options considered, two that appeared to have the greatest promise were a gas-cooled reactor based on the NERVA Derivative design, operating a closed cycle Brayton power conversion system; and a molten lithium-cooled reactor based on SP-100 technology, driving a boiling potassium Rankine power conversion system. This study examined the relative merits of these two systems, seeking to optimize the specific mass. Conclusions were that either concept appeared capable of approaching the specific mass goal of 3-5 kg/kWe estimated to be needed for this class of mission, though neither could be realized without substantial development in reactor fuels technology, thermal radiator mass efficiency, and power conversion and distribution electronics and systems capable of operating at high temperatures. Though the gas-Brayton systems showed an apparent advantage in specific mass, differences in the degree of conservatism inherent in the models used suggests expectations for the two approaches may be similar. Brayton systems eliminate the need to deal with two-phase flows in the microgravity environment of space.
Date: November 1, 2001
Creator: Longhurst, Glen Reed; Harvego, Edwin Allan; Schnitzler, Bruce Gordon; Seifert, Gary Dean; Sharpe, John Phillip; Verrill, Donald Alan et al.
Partner: UNT Libraries Government Documents Department

Thermoacoustic power systems for space applications

Description: Future NASA deep-space missions will require radioisotope-powered electric generators that are just as reliable as current RTGs, but more efficient and of higher specific power (W/kg). Thermoacoustic engines can convert high-temperature heat into acoustic, or PV, power without moving parts at 30% efficiency. Consisting of only tubes and a few heat exchangers, these engines are low mass and promise to be highly reliable. Coupling a thermoacoustic engine to a low-mass, highly reliable and efficient linear alternator will create a heat-driven electric generator suitable for deep-space applications. Data will be presented on the first tests of a demonstration thermoacoustic engine designed for the 100-Watt power range.
Date: January 1, 2001
Creator: Backhaus, S. N. (Scott N.); Tward, E. (Emanual) & Pedach, M. (Michael)
Partner: UNT Libraries Government Documents Department

Directed reflectivity, long life AMTEC condenser (DRC). Final report of Phase II SBIR program[Alkali Metal ThermoElectric Converter]

Description: The Alkali Metal Thermal to Electric Converter (AMTEC) is a static energy conversion device that operates at high thermal to electric conversion efficiencies that are essentially independent of size, have reached 19% and are expected to reach 25% to 30% in 1997. AMTEC systems have been chosen by NASA and DOE for spacecraft applications and have considerable promise for a wide variety of terrestrial applications. Reduction of parasitic heat losses in AMTEC systems related to radiative heat transfer from the hot side to the condenser can make a substantial contribution to system efficiency. Through design, analysis and the fabrication and testing of cells and systems, the proposed program to develop a Directed Reflectivity Condenser (DRC) has investigated the feasibility of an improved AMTEC condenser component. Phase 1 work showed the potential for adding from 4% to 7% to overall system efficiency for identical operating conditions using the concept. A detailed thermal analysis of several DRC capped cell designs was carried out and some of the conditions under which a DRC, used as the condenser at an end cap of a cylindrical converter, can reduce thermal radiation related losses were determined. A model experimental converter was built and tested to compare DRC and planar condenser surfaces. The results of both analysis and experiment indicate that for moderate aspect ratios of a cylindrical, end condensed converter, the DRC can reduce overall thermal losses by up to 4%. The initial effort in Phase 2 extended the analysis to a novel 150 watt radial AMTEC cell design. This analysis indicated that for the effective aspect ratio of this new converter design, the system performance at the 100+ watt level was not significantly improved by use of a DRC type condenser surface. Further analyses however showed that for cylindrical, end-condensed converters, optimized for use with ...
Date: September 10, 2001
Creator: Hunt, Thomas K.
Partner: UNT Libraries Government Documents Department

The Oxidation of Hydrazine by Nitric Acid

Description: Hydrazine nitrate-nitric acid solutions are used in the ion exchange process for separating Pu-238 and Np-237 and have been found to dissolve plutonium metal in a manner advantageous to SRP metal recovery operations. Laboratory tests on the stability of hydrazine in nitric acid solutions were performed to obtain accurate data, and the results of these tests are reported here. These tests provide sufficient information to specify temperature control for hydrazine-nitric acid solutions in plant processes.
Date: July 2, 2001
Creator: Karraker, D.G.
Partner: UNT Libraries Government Documents Department

Semi-Annual Technical Progress Report of the Radioisotope Power System Materials Production and Technology Program Tasks for September 2000 through March 2001

Description: The Office of Space and Defense Power Systems of the Department of Energy (DOE) provides Radioisotope Power Systems (RPS) for applications where conventional power systems are not feasible. For example, radioisotope thermoelectric generators were supplied by the DOE to the National Aeronautics and Space Administration for deep space missions including the Cassini Mission launched in October of 1997 to study the planet Saturn. The Oak Ridge National Laboratory (ORNL) has been involved in developing materials and technology and producing components for the DOE for more than three decades. For the Cassini Mission, for example, ORNL was involved in the production of carbon-bonded carbon fiber (CBCF) insulator sets, iridium alloy blanks and foil, and clad vent sets (CVS) and weld shields (WS). This report has been divided into three sections to reflect program guidance from the Office of Space and Defense Power Systems for fiscal year (FY) 2001. The first section deals primarily with maintenance of the capability to produce flight quality (FQ) CBCF insulator sets, iridium alloy blanks and foil, CVS, and WS. In all three cases, production maintenance is assured by the manufacture of limited quantities of FQ components. The second section deals with several technology activities to improve the manufacturing processes, characterize materials. or to develop technologies for new radioisotope power systems. The last section is dedicated to studies related to the production of {sup 238}Pu.
Date: May 22, 2001
Creator: Moore, J.P.
Partner: UNT Libraries Government Documents Department

Advanced Ultrasonic Inspection Techniques for General Purpose Heat Source Fueled Clad Closure Welds

Description: A radioisotope thermoelectric generator is used to provide a power source for long-term deep space missions. This General Purpose Heat Source (GPHS) is fabricated using iridium clad vent sets to contain the plutonium oxide fuel pellets. Integrity of the closure weld is essential to ensure containment of the plutonium. The Oak Ridge Y-12 Plant took the lead role in developing the ultrasonic inspection for the closure weld and transferring the inspection to Los Alamos National Laboratory for use in fueled clad inspection for the Cassini mission. Initially only amplitude and time-of-flight data were recorded. However, a number of benign geometric conditions produced signals that were larger than the acceptance threshold. To identify these conditions, a B-scan inspection was developed that acquired full ultrasonic waveforms. Using a test protocol the B-scan inspection was able to identify benign conditions such as weld shield fusion and internal mismatch. Tangential radiography was used to confirm the ultrasonic results. All but two of 29 fueled clads for which ultrasonic B-scan data was evaluated appeared to have signals that could be attributed to benign geometric conditions. This report describes the ultrasonic inspection developed at Y-12 for the Cassini mission.
Date: January 11, 2001
Creator: Moyer, M.W.
Partner: UNT Libraries Government Documents Department

Design of a Pu-238 Waste Incineration Process

Description: Combustible Pu-238 waste is generated as a result of normal operation and decommissioning activity at the Savannah River Plant and is being retrievably stored there. As part of the long-term plan to process the stored waste and current waste in preparation for future disposition, a Pu-238 incineration process is being cold-tested at Savannah River Laboratory (SRL). The incineration process consists of a continuous-feed preparation system, a two-stage, electrically fired incinerator, and a filtration off-gas system. Process equipment has been designed, fabricated, and installed for nonradioactive testing and cold run-in. Design features to maximize the ability to remotely maintain the equipment were incorporated into the process. Interlock, alarm, and control functions are provided by a programmable controller. Cold testing is scheduled to be completed in 1986.
Date: May 29, 2001
Creator: Charlesworth, D.L.
Partner: UNT Libraries Government Documents Department

Toroidal Plasma Thruster for Interplanetary and Interstellar Space Flights

Description: This work involves a conceptual assessment for using the toroidal fusion reactor for deep space interplanetary and interstellar missions. Toroidal thermonuclear fusion reactors, such as tokamaks and stellarators, are unique for space propulsion, allowing for a design with the magnetic configuration localized inside toroidal magnetic field coils. Plasma energetic ions, including charged fusion products, can escape such a closed configuration at certain conditions, a result of the vertical drift in toroidal rippled magnetic field. Escaping particles can be used for direct propulsion (since toroidal drift is directed one way vertically) or to create and heat externally confined plasma, so that the latter can be used for propulsion. Deuterium-tritium fusion neutrons with an energy of 14.1 MeV also can be used for direct propulsion. A special design allows neutrons to escape the shield and the blanket of the tokamak. This provides a direct (partial) conversion of the fusion energy into the directed motion of the propellant. In contrast to other fusion concepts proposed for space propulsion, this concept utilizes the natural drift motion of charged particles out of the closed magnetic field configuration.
Date: July 11, 2001
Creator: Gorelenkov, N.N.; Zakharov, L.E. & Gorelenkova, and M.V.
Partner: UNT Libraries Government Documents Department

Thermoelectric Development at Hi-Z Technology

Description: An improved Thermoelectric Generator (TEG) for the Heavy Duty Class Eight Diesel Trucks is under development at Hi-Z Technology. The current TEG is equipped with the improved HZ-14 Thermoelectric module, which features better mechanical properties as well as higher electric power output. Also, the modules are held in place more securely. The TEG is comprised of 72 TE modules, which are capable of producing 1kW of electrical power at 30 V DC during nominal engine operation. Currently the upgraded generator has completed testing in a test cell and starting from August 2001 will be tested on a Diesel truck under typical road and environmental conditions. It is expected that the TEG will be able to supplement the existing shaft driven alternator, resulting in significant fuel saving, generating additional power required by the truckļæ½s accessories. The electronic and thermal properties of bulk materials are altered when they are incorporated into quantum wells. Two-dimensional quantum wells have been synthesized by alternating layers of B4C and B9C in one system and alternating layers of Si and Si0.8Ge0.2 in another system. Such nanostructures are being investigated as candidate thermoelectric materials with high figures of merit (Z). The predicted enhancement is attributed to the confined motion of charge carriers and phonons in the two dimensions and separating them from the ion scattering centers. Multilayer quantum well materials development continues with the fabrication of thicker films, evaluation of various substrates to minimize bypass heat loss, and bonding techniques to minimize high contact resistance. Quantum well thermoelectric devices with N-type Si/Si0.8Ge0.2 and P-type B4C/B9C have been fabricated from these films. The test results generated continue to indicate that much higher thermoelectric efficiencies can be achieved in the quantum wells compared to the bulk materials.
Date: August 5, 2001
Creator: Kushch, Aleksandr
Partner: UNT Libraries Government Documents Department