Hexafluoride mining

The raw material for nuclear reactor fuel, uranium, exits the mining—milling sequence as uranium oxide. Because of its color, it is called yellow cake. The yellow cake is converted to uranium hexafluoride and enriched in 235u... 

Nuclear power is now the only substantial use for uranium. But before uranium can be used in a nuclear reactor, it must undergo several processes. After uranium is mined from geological mineral deposits, it is purified and converted into uranium hexafluoride (UF,). The UF, is next enriched, increasing the concentration of U-235 by separating out UF,5 made with U-238 atoms. The enriched UF, is then converted into uranium dioxide (UO,), and pressed into fuel pellets for use in the nuclear reactor. 

Development efforts in the nuclear industry are focusing on the fuel cycle (Figure 6.12). The front end of the cycle includes mining, milling, and conversion of ore to uranium hexafluoride enrichment of the uranium-235 isotope conversion of the enriched product to uranium oxides and fabrication into reactor fuel elements. Because there is at present a moratorium on reprocessing spent fuel, the back end of the cycle consists only of management and disposal of spent fuel. 

Fuel. The nuclear fuel cycle starts with mining of the uranium ore, chemical leaching to extract the uranium, and solvent extraction with tributyl phosphate to produce eventually pure uranium oxide. If enriched uranium is required, the uranium is converted to the gaseous uranitim hexafluoride for enrichment by gaseous diffusion or gas centrifuge techniques, after which it is reconverted to uranium oxide. Since the CANDU system uses natural uranium, I will say no more about uranium enrichment although, as I m sure you appreciate, it is a major chemical industry in its own right. 

Fuel costs are composed of the cost of mining uranium, the cost of converting it into uranium hexafluoride, the cost of enriching the uranium hexafluoride, the cost of converting the enriched material to UO2, and the cost of manufacturing the fuel assembly. 

The mined uranium ore is crushed and ground into a fine powder. After ore dressing, the concentrate is leached with sulfuric acid. The solution is treated in a Hq-uid-Hquid extraction, in which uranium is transferred to an organic phase. It is extracted from that with ammonia, and ammonium uranate is precipitated. At 1000°C it is decomposed to yellow uranium oxide UOj. Uranium hexafluoride is prepared by treating the oxide with hydrogen fluoride to make uranium tetrafluoride. This in turn is treated with elemental fluorine to prepare the gaseous hexafluoride UF (sub-Hmation point 56°C). 

Mill Wastes. The uranium-containing wastes from milling are mounded and covered with earth. This earth cover prevents erosion and delays for decay the 14-hour radon gas, the gaseous decay product of uranium. These mill waste repositories are located near the mines and mills and are not a very different hazard from the original naturally occurring uranium deposits. The depleted uranium from the enrichment operations is stored in cylinders as uranium hexafluoride for future use in the uranium-plutonium breeding cycle. Other uranium wastes from enrichment and fuel fabrication go to the low-level repositories. 

The fuel cycle begins with mining and milling operations that produce uranium ore concentrate. This ore is converted to UaOg that is then dissolved with nitric acid to form uranyl nitrate, which is then purified for the production of UO3. UO3 is a starting point for the manufacture of various forms of uranium fuel it may be used to produce UO2 containing natural uranium (0.71% it might be used to produce uranium hexafluoride for processes that... 

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