Uranium mining

Uranium is best known as a fuel for nuclear power plants. To prepare this fuel, uranium ores are processed to extract and enrich the uranium. The process begins by mining uranium-rich ores and then crushing the rock. The ore is mixed with water and thickened to form a slurry. The slurry is treated with sulfuric acid and the product reacted with amines in a series of reactions to give ammonium diuranate, (NH4)2U20 . Ammonium diuranate is heated to yield an enriched uranium oxide solid known as yellow cake. Yellow cake contains from 70—90% U3Og in the form of a mixture of U02 and U03. The yellow cake is then shipped to a conversion plant where it can be enriched. 

Uranium was useless as long as the nuclear fuel energy cycle was not closed via uranium mining, uranium chemistry, uranium enrichment technologies, fuel rod production, nuclear reactors, to final storage or plutonium extraction of spent fuel rods. 

The Straz deposit in the Hamr District of the Czech Republic provides a good example of this problem (Slezak, 1997). Starting in 1968, more than 4 Mt of sulfuric acid, 3 X 10 t of nitric acid, and 1.2 X 10 t of ammonia were injected into the subsurface to mine uranium ore. Now, —266 Mm in the North Bohemian Cretaceous Cenomanian and Turonian aquifers are contaminated with uranium, radium, and manganese and other solutes. The contaminated area is more than 24 km and threatens the watershed of the Plucnice River. 

High quality requirements particularly as regards uranium concentration and the maximum quantities of undesirable ions such as Mo, V and P are stipulated by the processors for the end product, so-called yellow cake produced by the uranium ore mines. Uranium is generally precipitated as diuranates from the aqueous solutions produced by the ion exchange and solvent extraction processes under precise conditions. 

The quantity of natural uranium to be mined for the production of the heavy metal reprocessed. This type of reference has already been used in Chap. 8 because it is the most general one with no special assumption about the form of the natural uranium involved. Its disadvantage is the strong dependence on fuel-cycle type. With an equilibrium LMFBR fuel cycle, for instance, the quantity of uranium to be mined becomes close to zero and, consequently, the period of significance of the waste hazard becomes extremely long. To maintain its applicability, the uranium equivalent must always be calculated on the virtual basis that all power has been generated from freshly mined uranium. 

In production of fuel for a fast reactor, uranium — natural or depleted — is only needed to make up for the fission products separated during reprocessing of irradiated nuclear fuel (INF), which accounts for about 10% of the fresh fuel mass. For a thermal reactor, natural uranium is enriched to a required level, with roughly 10% of the mined uranium going into fuel, while its remaining 90% ends up in the tails of enrichment processes and is not involved in energy generation. 

The short, simple fuel assemblies for the HWR, called fuel bundles, are easily produced, and Korea, India, Argentina, Romania, and China all have independent fuel fabricafion facilities sufficient to meet their demand. Furthermore, HWR fuel-cycle costs are low because natural uranium is relatively inexpensive, the uranium utilization (amount of energy produced from the mined uranium) is good, and the fuel bundle design and manufacture is simple. 

The already high uranium utilization (in terms of electrical energy derived from the mined uranium) is increased by 32% and 36% compared with natural uranium fuel, for 0.9% and 1.2% SEU, respectively (Table 15.2). As lower enrichment plant tails become economical through advances in enrichment technology, the improvements in uranium utilization with SEU will become even larger 43% for 0.9% SEU, and 56% for 1.2% SEU with 0.1% enrichment plant tails, relative to natural uranium. Lower enrichment-plant tails pushes the optimal enrichment level higher. 

The inverse of uranium utilization is uranium consumption. Relative to a PWR, natural uranium requirements in an HWR are 30% lower with natural uranium fuel. Enrichments to 0.9% SEU and 1.2% SEU would increase the fuel bumup by a factor of 2 and 3, respectively, relative to natural uranium fuel. This amounts to 45% lower uranium consumption with 0.9% SEU. The reduction in mined uranium requirements also has environmental benefits at the front end of the cycle, which will become even more important in the coming decades as cheaper, higher-grade uranium ore resources are depleted, requiring the mining of greater volumes of lower-grade ores. 

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 current once through, open fuel cycle results in actually fissioning only about 1% of the uranium mined. Approximately 93% of the mined uranium currently exists as low-enriched tails from the enrichment process, and 7% consists of low-enriched material in the spent fuel assembly, which are currently being stored at the plant s (in the United States). 

Mr. Allan further noted that presently spent Candu-fiiel contains half the amount of plutonium as could be separated from LWR fuel and would, if separated, be significantly more expensive than freshly mined uranium. However, the Candu reactor system is flexible direct recycle of LWR fuel and LWR plutonium is possible. If Canada should at some future date begin to reprocess spent fuel, it could even decide to retrieve Candu fuel from the rq)ository and convert its strategy to high-level waste di sal. The in rtant point fix>m waste management perspective is that both options exist, both are feasible and both meet the objective of protecting human health and die environment. 

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). 

MDS Nordion began in 1946 as the radium sales department of Eldorado Mining and Refining (1944) Ltd., an Ottawa-based crown corporation that mined uranium ore, from which radium, a naturally occurring radioactive element, was extracted and refined. Radium was employed extensively in cancer therapy at the time, and Eldorado sold it around the world. In 1947 the Canadian government s nuclear research establishment at Chalk River, Ontario completed a nuclear reactor that began to produce radioisotopes. Since there was a potential market in the medical field for many... 

Uranium ores vary dramatically from one site to another. In certain areas (for example, Saskatchewan, Canada, Wyoming, U.S.A., and South Australia, Australia), the ore is rich. In other areas (for example the mineral sands of Egypt, or the South African gold/uranium mines), uranium is essentially a by-product. 

Several wastes important to DOE are excluded from the RCRA definition of solid wastes (40 CFR 261.2). They include source, special nuclear, or byproduct material as defined by the AEA [Section 11(e), (z), (aa)] waste from extraction, beneficiation, and processing of ores and minerals, including overburden from mining uranium ores utility wastes oil and gas drilling muds and brines and some wastes that are reused or recycled. 

The uraniimi fuel cycle for the uranium-plutonium system is a multicomponent system of chemical process operations that begins with mining uranium ore from the earth as... 

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