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Nuclear heat sources for cryogenic refrigerator applications

Description: Spacecraft cryogenic refrigerators require thermal inputs on the order of 1000 W. First, the characteristics of solar-electric and radioisotope heat source systems for supplying this thermal input are compared. Then the design of a $sup 238$Pu heat source for this application is described, and equipment for shipping and handling the heat source is discussed. (LCL)
Date: June 1, 1975
Creator: Raab, B.; Schock, A.; King, W.G.; Kline, T. & Russo, F.A.
Partner: UNT Libraries Government Documents Department

Nuclear Rocket Facility Decommissioning Project: Controlled Explosive Demolition of Neutron-Activated Shield Wall

Description: Located in Area 25 of the Nevada Test Site (NTS), the Test Cell A (TCA) Facility (Figure 1) was used in the early to mid-1960s for testing of nuclear rocket engines, as part of the Nuclear Rocket Development Program, to further space travel. Nuclear rocket testing resulted in the activation of materials around the reactors and the release of fission products and fuel particles. The TCA facility, known as Corrective Action Unit 115, was decontaminated and decommissioned (D&D) from December 2004 to July 2005 using the Streamlined Approach for Environmental Restoration (SAFER) process, under the Federal Facility Agreement and Consent Order. The SAFER process allows environmental remediation and facility closure activities (i.e., decommissioning) to occur simultaneously, provided technical decisions are made by an experienced decision maker within the site conceptual site model. Facility closure involved a seven-step decommissioning strategy. First, preliminary investigation activities were performed, including review of process knowledge documentation, targeted facility radiological and hazardous material surveys, concrete core drilling and analysis, shield wall radiological characterization, and discrete sampling, which proved to be very useful and cost-effective in subsequent decommissioning planning and execution and worker safety. Second, site setup and mobilization of equipment and personnel were completed. Third, early removal of hazardous materials, including asbestos, lead, cadmium, and oil, was performed ensuring worker safety during more invasive demolition activities. Process piping was to be verified void of contents. Electrical systems were de-energized and other systems were rendered free of residual energy. Fourth, areas of high radiological contamination were decontaminated using multiple methods. Contamination levels varied across the facility. Fixed beta/gamma contamination levels ranged up to 2 million disintegrations per minute (dpm)/100 centimeters squared (cm2) beta/gamma. Removable beta/gamma contamination levels seldom exceeded 1,000 dpm/100 cm2, but, in railroad trenches on the reactor pad containing soil on the concrete pad in ...
Date: June 1, 2008
Creator: Kruzic, Michael R.
Partner: UNT Libraries Government Documents Department

Effective Pu-238 and Np-237 neutron absorption cross sections in N and K Reactors

Description: The efficiency of producing Pu-238 from Np-238 depends on the relative absorption cross sections of the target, Np-237, and the product, Pu-238. A lowering of the Pu-238/Np-237 cross section ratio reduces the destruction of Pu-238 formed during reactor operation. The absorption cross sections of both these isotopes are strongly neutron energy dependent; the absorption cross section of Pu-238 decreases more rapidly with thermal neutron temperature increases than the conventional v{sup {minus}1} dependency and exhibits negligible resonance absorption. On the other hand, Np-237 is a very nearly v{sup {minus}1} thermal neutron absorber and has dominant low level resonance cross sections. Thus, for higher thermal neutron temperatures and a more epithermal neutron spectrum, depletion of the Pu-238 product is reduced relative to Np-237 burnout. The relative absorption cross sections of these two isotopes were calculated for the K and N Reactors as a function of graphite temperature for two linear densitie of neptunium in the target elements for each.reactor type. The method of calculation was as follows: The HAMMER integral transport code was used to obtain region and cell averaged four-group cross sections for both the fuel and target cells. These cross sections were then used in the HFN diffusion theory code to obtain reactor-effective cross sections.
Date: June 10, 1968
Creator: Roblyer, S.P.
Partner: UNT Libraries Government Documents Department

High Temperature Integrated Thermoelectric System and Materials

Description: The final goal of this project is to produce, by the end of Phase II, an all ceramic high temperature thermoelectric module. Such a module design integrates oxide ceramic n-type, oxide ceramic p-type materials as thermoelectric legs and oxide ceramic conductive material as metalizing connection between n-type and p-type legs. The benefits of this all ceramic module are that it can function at higher temperatures (> 700 C), it is mechanically and functionally more reliable and it can be scaled up to production at lower cost. With this all ceramic module, millions of dollars in savings or in new opportunities recovering waste heat from high temperature processes could be made available. A very attractive application will be to convert exhaust heat from a vehicle to reusable electric energy by a thermoelectric generator (TEG). Phase I activities were focused on evaluating potential n-type and p-type oxide compositions as the thermoelectric legs. More than 40 oxide ceramic powder compositions were made and studied in the laboratory. The compositions were divided into 6 groups representing different material systems. Basic ceramic properties and thermoelectric properties of discs sintered from these powders were measured. Powders with different particles sizes were made to evaluate the effects of particle size reduction on thermoelectric properties. Several powders were submitted to a leading thermoelectric company for complete thermoelectric evaluation. Initial evaluation showed that when samples were sintered by conventional method, they had reasonable values of Seebeck coefficient but very low values of electrical conductivity. Therefore, their power factors (PF) and figure of merits (ZT) were too low to be useful for high temperature thermoelectric applications. An unconventional sintering method, Spark Plasma Sintering (SPS) was determined to produce better thermoelectric properties. Particle size reduction of powders also was found to have some positive benefits. Two composition systems, specifically 1.0 SrO ...
Date: June 6, 2011
Creator: Chu, Mike S. H.
Partner: UNT Libraries Government Documents Department