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Applications of Isotope Separation


Uranium Enrichment  
   

The enrichment of uranium is a critical step in the nuclear fuel cycle as depicted below. Natural uranium exists as two isotopes: U-238, 99.3% and U-235, 0.7%. Uranium deposits are mined and refined, producing Uranium Oxide (U3O8), more commonly referred to as 'yellowcake'. The 'yellowcake' is then converted to Uranium Hexafluoride (UF6). Enrichment increases the concentration of U-235 to up to 5%, for use as nuclear reactor fuel. In a fuel fabrication plant enriched UF6 gas is converted to uranium dioxide (UO2), which is formed into ceramic fuel pellets. The pellets are then encased in Zircalloy or stainless steel tubes to form fuel rods, which in turn are assembled in clusters to form fuel assemblies for use in the core of a nuclear reactor. In a nuclear reactor steam is produced that drives turbines that generate electricity. The used fuel from a nuclear reactor is first stored and then reprocessed. Nuclear waste not destined for reprocessing, ranging from low level to high level wastes are either treated in waste facilities or end up in specially engineered underground repositories. Nuclear facilities are decommissioned after the end of their operating lives.

Nuclear Fuel Cycle

The global nuclear energy capacity is expected to increase from 373GWe (439 reactors) in 2008 to a projected 748GWe (815 reactors) in 2030 [Source: OECD Nuclear Energy Agency, 2008]. As the new nuclear reactors are being constructed, and many more being planned, it is evident that the bottleneck in the industry will soon be enrichment capacity.

The capacity of enrichment plants is measured in terms of 'separative work units' or SWU. The SWU is a complex unit measuring the quantity of separative work performed to enrich a given amount of uranium to a certain degree of enrichment and a corresponding level of depletion of the waste stream. Of the present world capacity of 49 million SWU's, about 21 million SWU's need to be replaced because of aging and uneconomical facilities. In addition to this, there will be a new capacity demand by 2015 for another 14 million SWU's, and by 2030 this demand is likely to grow by another 29 million SWU's. This implies a new enrichment plant of about 5 million SWU capacity being commissioned globally nearly every second year.

This sharp increase in demand for enrichment capacity creates opportunities for new enrichment technologies. Any company deciding to enter the uranium enrichment market on the back of new technology, will find that the barrier to market entry is lower simply because the company is free from the commercial licensing stronghold of the dominant industry players.

Albeit a number of uranium enrichment processes have been demonstrated historically or in the laboratory, only two, the gaseous diffusion process and the gas centrifuge process are presently operating on a commercial scale. In both cases, UF6 gas is used as the feed material. Both processes make use of the slight difference in mass between U-235 and U-238 and attain the required concentration of U-235 through a series of enrichment stages (called a cascade). Large commercial enrichment plants are in operation in France, Germany, Netherlands, UK, USA, and Russia, with smaller plants elsewhere. New centrifuge plants are being built in France and the USA.

At present the gaseous diffusion process accounts for about 40% of world enrichment capacity. Though they have proved durable and reliable, most gaseous diffusion plants are now nearing the end of their design life. The running costs of this process are very high due to the large amount of electricity it requires. The trend in enrichment technology is to retire obsolete diffusion plants and the focus is on centrifuge enrichment technology.

The gas centrifuge process proved to be the reference technology in the industry since the early 1970's. There are several variants of this technology in the world, the most well known ones being the Urenco centrifuge, the Russian Centrifuge, and the American Centrifuge designs. The gas centrifuge process is capital intensive.

Many countries have attempted to develop variations of laser-based isotope separation (e.g. AVLIS, SILVA, MLIS, CHEMLIS), but most of these programs have been stopped. The one known survivor that can compete as a third-generation technology is the Silex technology being developed by the GE-Hitachi program in the USA. The commercial efficacy is still to be determined.

Klydon operates in a highly regulated environment with technologies classified as "dual-use technologies" in terms of the Nuclear Non-proliferation Treaty (NPT) and is following due process to apply for the required licenses to work with Uranium. Klydon has to date not done any work directly on Uranium. However, based on test results of isotopes of comparable characteristics, Klydon is confident that the ASP technology can be applied to the enrichment of uranium.

As depicted above, based on 2006 market prices, the enrichment step contributes a significant 34% to the operating cost (value add) of producing nuclear fuel and about 5% of the total generation cost of nuclear energy. The envisaged lower-than-benchmark total enrichment operating cost of the ASP process will result in a decrease of the total generation cost of nuclear energy.

The ASP process can also be applied to opportunities beyond conventional uranium enrichment. Two examples are the cases of 're-processing of depleted uranium' and 'complimentary enrichment'.

Depleted uranium - commonly referred to as "tails" - is historically considered as a waste product of conventional uranium enrichment, because considerable enrichment processing is required to further extract the remaining useful quantities of uranium-235. Due to its capital intensive nature, conventional enrichment processes cannot be applied economically to further process the "tails". Uranium hexafluoride is however radioactive and forms extremely corrosive and potentially lethal compounds if it contacts water and is therefore considered a threat to human health and the environment. In the USA alone, the DOE still maintains approximately 700,000 metric tons of depleted uranium tails in about 63,000 metal cylinders in storage yards at the Paducah and Portsmouth enrichment plants, a burden on the tax-payer [Source: GAO-08-606R March 31, 2008]. A big advantage of the ASP process is that the smaller economy of scale and the lower total operation cost (that includes the cost of construction capital) provide a compelling argument to build and operate enrichment plants economically to re-circulate depleted uranium, resulting in two principle products, namely enriched UF6 (4-5% U-235) and uranium "tails" with a safe concentration of U-235 of 0.1%.

The ASP process can also be applied to a business case of complimentary enrichment. The case is considered complimentary to the existing enrichment capacity in the industry (and less threatening to existing operators), because UF6 is only partially enriched to approximately 2% U-235 and then fed to existing 'secondary' enrichment plants. The "tails" are depleted directly to a safe 0.1% U-235 content or fed to "tails" re-processing plants.

Uranium
Depleted uranium (“tails”) stored in large steel cylinders, located at Portsmouth, OH
[Source: ANL: Environmental Science Division]

 

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