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Nuclear Energy
Published in Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff, Radiation and Radioactivity on Earth and Beyond, 2020
Ivan G. Draganić, Zorica D. Draganić, Jean-Pierre Adloff
In this accident, it is true that the 3.7 meter high reactor core was at no time really uncovered in the same way as a dry kettle. But the water level had fallen to about 1 meter for probably 2 hours. Several more hours were needed to reestablish cooling by natural circulation after the core had been refilled with water. While the cooling was interrupted, radiogenic heat, mainly due to decay of fission products, accumulated and caused overheating of the fuel elements. At some points the temperature in the reactor core was close to 3000 degrees Celsius and some fuel elements melted; the melting point of uranium oxide is 2815 degrees celsius and that of its zirconium cladding is 1982 degrees celsius. The core’s container did not melt despite its much lower melting point, indicating that most of the intense heat was confined to the central region of the reaction core.
Cooling Reactors
Published in Geoffrey F. Hewitt, John G. Collier, Introduction to Nuclear Power, 2018
Geoffrey F. Hewitt, John G. Collier
The heat transfer processes in the reactor must be designed to prevent the system from exceeding two main temperature limits: Maximum temperature of the fuel. If the fuel is made from uranium metal, its maximum temperature is around 650°C, where volume swelling occurs due to a crystal structure change in the metal. For uranium oxide fuel, the maximum temperature is around 2800°C, the melting point of the oxide. Despite its much lower maximum temperature, metal fuel may release heat from its surface at a higher rate than oxide fuel because of its much higher thermal conductivity. However, in modem reactors metal fuel is rarely used, since it undergoes chemical reaction with the coolant if the cladding is ruptured.Maximum cladding temperature. The temperature of the cladding material is often the limiting factor. For instance, the commonly used Zircaloy cladding rapidly corrodes if its temperature is greater than about 500”C, and it reacts exothermically (i.e., generates heat, which can promote further reaction) with steam to form hydrogen at temperatures above 1000°C. Stainless steel cladding is used in AGRs and liquid metal-cooled fast reactors; it is compatible with carbon dioxide and sodium at normal operating conditions (700–750°C) but oxidizes rapidly at higher temperature, the short-term absolute limit being the stainless steel melting point of about 1400°C.
Overview
Published in Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde, Waste Production and Utilization in the Metal Extraction Industry, 2017
Sehliselo Ndlovu, Geoffrey S. Simate, Elias Matinde
The section on strategic metals looks at the hydrometallurgical processes for the production of uranium oxide and rare earth elements (REE). The hydrometallurgical process for the production of the uranium oxide involves a number of steps, such as leaching, ion exchange, solvent extraction and precipitation. In this process, a major portion of the radionuclides present in the ore remains in the tailings after uranium has been extracted and they can have a long-term impact on the environment due to the long half-lives and the ready availability of some of the toxic radionuclides (Weil, 2012). Current literature suggests that there is not much value or resource recovery from these tailings as they are generally dumped in special ponds or piles and covered by clay and topsoil with enough rock to resist erosion.
Using discrete simulations of compaction and sintering to predict final part geometry
Published in Powder Metallurgy, 2023
Gilmar Nogueira, Thierry Gervais, Véronique Peres, Estelle Marc, Christophe L. Martin
A uranium oxide powder was chosen to simulate the compaction and sintering process. The geometric relative density in the simulation (as if indented spherical discrete elements were dense) is multiplied by a factor 0.45 to obtain the relative density of the compact, thus considering the porosity of agglomerates. The 0.45 value is close to the value (0.41) of density measured by mercury porosimetry by [26]. It also has the advantage of leading to an initial geometrical density (0.4) with a realistic coordination number (2.5). The ceramic powder with an initial relative density of 0.18 and 40 000 particles representing agglomerates is introduced into a cylinder die of approximately 10 mm in diameter and 40 mm in height. Figure 4 summarises the process kinematics. The powder is pressed by two flat punches (double-action dry pressing, same force on the upper and lower punch) up to an axial stress of 600 MPa (1). The upper punch is then unloaded until the axial stress reaches 50 MPa (2). This accompanying stress is maintained during ejection, during which the cylinder slides out of the die (3). Finally, the upper punch is completely unloaded (4).
Aligning missions: nuclear technical assistance, the IAEA, and national ambitions in Pakistan
Published in History and Technology, 2020
Over the next several years, IAEA experts from North America and Europe oversaw Pakistan’s uranium prospecting. One major event was the identification, by another IAEA expert, the American geologist G. W. Chase, of a paleostream channel in the Baghal Chur basin, a key clue about where the uranium minerals may have distributed over long periods of time. Chase himself an American, having worked on uranium exploration in Oklahoma and elsewhere during the war, and worked for the AEC in the 1950s. Another discovery was the consistent finding of the ‘black’ oxide known as uraninite. Formerly known as pitchblende, the ore contained lead, rare earths, and a great deal of uranium. Although ‘yellow’ uranium oxide had been observed in the area for years, finding black uraninite in such quantities in 1973 was significant news for Pakistan’s uranium future. Project manager J. W. Hoadley (a Canadian geologist) guessed that two of the drilling sites in the Baghal Chur area would contain about 150 tons of uranium. He noted that a new phase of exploration ‘should be carried out with all possible energy and despatch’.43
Applications for Thorium in Multistage Fuel Cycles with Heavy Water Reactors
Published in Nuclear Technology, 2018
Timothy Ault, Steven Krahn, Andrew Worrall, Allen Croff
The system entails two stages. In Stage 1, enriched uranium oxide fuel is irradiated in a PWR. The used PWR fuel is sent to reprocessing, where the recovered uranium (RU) is reenriched and used to make new Stage 1 PWR fuel while the TRUs are sent to Stage 2. Stage 2 uses two fuel types in each fuel bundle in an HWR core. Fuel Type 1 incorporates the TRUs that are recovered from Stage 1 in a thorium matrix. Fuel Type 2 incorporates recycled 233U (including 233Pa that decays in near totality to 233U during interim storage) and the transuranics from reprocessing used Type 2 fuel in a thorium matrix. Type 2 fuel does not incorporate any recovered material from Stage 1. The two HWR fuel types are reprocessed and refabricated separately. In both cases, all the actinides, including thorium, uranium, plutonium, and the MAs (including protactinium), are recycled.