Uranium Tailings – Heap

nuclear fuel cycle
Nuclear Fuel Cycle. Source: Nuclear Regulatory Commission from US. License: CC BY 2.0

Uranium tailings are a waste byproduct (tailings) of uranium mining. Uranium is commonly found  at low levels (a few ppm – parts per million) in all rocks, soil, water, plants, and animals (including humans). Uranium occurs also in seawater, and can be recovered from the ocean water. But only a few of the uranium ores known contain sufficient uranium (greater than 0.1%) to extract commercially. Significant concentrations of uranium occur in some substances such as uraninite (the most common uranium ore), phosphate rock deposits, and other minerals. The valuable uranium-bearing minerals are then removed via heap leaching with the use of acids or bases, and the remaining radioactive sludge, called “uranium tailings”, is stored in huge impoundments.  In case of uranium mining, it strongly depends on the concentration of uranium in the ore.  For example, the ore extracted from the Australian Olympic Dam Mine has a concentration of 0.05 %. Most reserves have uranium with a concentration of between 0.1 bis 0.2 %. Noteworthy, in Canadian Saskatchewan ore is mined that contains more than 20 % uranium. A short ton (907 kg) of ore yield one to five pounds (0.45 to 2.3 kg) of uranium depending on the uranium content of the mineral.

It must be noted, uranium tailings can retain up to 85% of the ore’s original radioactivity.  Uranium tailings contains almost all the descendants of radioactive cascades, that have been in radioactive equilibrium for millions of years. For example, pure uranium-238, from uranium series, is weakly radioactive (proportional to its long half-life), but a uranium ore is about 13 times more radioactive than the pure uranium-238 metal because of its daughter isotopes (e.g. radon, radium etc.) it contains. Not only are unstable radium isotopes significant radioactivity emitters, but as the next stage in the decay chain they also generate radon, a heavy, inert, naturally occurring radioactive gas. At this place, we are discussing natural facts, it must be noted, the decay heat of uranium and its decay products (e.g. radon, radium etc.) contributes to heating of Earth’s core. Together with thorium and potassium-40 in the Earth’s mantle is thought that these elements are the main source of heat that keeps the Earth’s core liquid. But uranium tailings need to be isolated from the environment because they are concentrated and they contain these long-lived radioactive materials from radioactive decay chain.

References:
Nuclear and Reactor Physics:
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Advanced Reactor Physics:

      1. K. O. Ott, W. A. Bezella, Introductory Nuclear Reactor Statics, American Nuclear Society, Revised edition (1989), 1989, ISBN: 0-894-48033-2.
      2. K. O. Ott, R. J. Neuhold, Introductory Nuclear Reactor Dynamics, American Nuclear Society, 1985, ISBN: 0-894-48029-4.
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      4. E. E. Lewis, W. F. Miller, Computational Methods of Neutron Transport, American Nuclear Society, 1993, ISBN: 0-894-48452-4.

See above:

Nuclear Fuel Cycle