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- Jul 2, 4:07pm
- Uranium Resources
Uranium is a resource that is as common as tin or zinc. Some analysts argue that the production processes of the uranium mining industry, and the nuclear industry's use of uranium, mean that we should evaluate the supply of uranium in a similar manner to the evaluation of metal resources [MacDonald 2003]. It is the quality, not the quantity, of the resource that we must concentrate upon.
According to the 'Red Book' [NEA 2004], the OECD Nuclear Energy Agency's statistical study of world uranium resources and demand, in 2002 the world consumed 67,000 tonnes of uranium. Only 36,000 tonnes of this was produced from primary sources. The balance came from a variety of secondary sources, in particular the ex-military inventory of uranium which is being released as nuclear weapons systems are run down. The availability of cheap uranium from the military has been one of the contributing factors to the shrinkage of capacity within the uranium mining sector over the last decade [Combs 2004]. It also entails that at some point between 2010 and 2020 the uranium mining industry must dramatically expand to meet future demand [Bertel 2002].
Estimating the available reserves of uranium is a little difficult as various agencies interpret the availability of uranium resources using different methodologies. If we add together all potential sources of uranium, including 'unconventional' sources such as sea water, the amount of uranium that is accessible around the globe is in excess of 17 million tonnes [Price, 2002]. Most estimates, which consider known reserves and reasonable estimates of other high grade sources of uranium ore, put the figure at around 4 to 5 million tonnes. Some authorities take a more sceptical view. For example the European Commission's Green Paper on Energy [EC 2001] discounts speculative sources and quotes only the known uranium resource (2 to 3 million tonnes).
Generally uranium reserves are classified according to the cost of recovery as a dollar value. Clearly this is an imprecise measure given that it does not reflect the net value of the energy produced from uranium less the energy used in its mining and processing and in the generation of power. Below a certain concentration the recovery of uranium will take more energy than it produces. The most productive uranium ores contain 1,000 to 20,000 parts per million of uranium (ppmU) [WNA 2004]. Other potential sources, such as igneous rocks, have concentrations of uranium of around 4ppmU. Sea water, also quoted as a future source of uranium, has an average uranium content of 0.003ppmU. In the 1970s Peter Chapman [Chapman 1975] calculated the cut-off value, at which the energy used to extract uranium from the ore exceeds the energy produced from the nuclear plant, at around 20ppmU. Even with advances in processing and reactor design this is unlikely to fall far below 10ppmU. This puts a limitation on the theoretical size of the uranium resource because a number of the potential sources fall below this level.
Fuel Cycles and Uranium Consumption
The world's nuclear capacity is based upon 'thermal' fission reactors that split uranium atoms and produce heat. The problem with this type of reactor is that it can only split atoms of one isotope of uranium - uranium-235 (235U). As 235U only constitutes around 0.7% of the uranium resource the amount of energy that nuclear energy systems can generate, using current technologies, is very limited.
The bulk of the uranium resource, made up of the isotope uranium-238 (238U), does not take part directly in nuclear fission. However some of the 238U is converted to plutonium-239 (239Pu) whilst inside the reactor and this is also fissioned to produce additional energy. The only way it is possible to use the majority of the uranium resource is to adopt a different reactor technology - the 'fast breeder' or 'fast' reactor. This exploits the conversion of 238U into 239Pu by 'fast' neutrons in order to produce 239Pu, and following reprocessing of the nuclear fuel the 239Pu can be substituted for the 235U for future energy production.
The primary difference between the thermal reactor system and the fast breeder reactor system is the way that the nuclear fuel cycle operates. Thermal reactors operate a 'once through' cycle. Nuclear fuel is used to generate energy and then it is put into indefinite storage. Some nuclear fuel is reprocessed in order to recover the plutonium, but at the moment the recycling of plutonium back into the fuel cycle operates at a minimal level - through the production of 'mixed oxide' (or MOX) fuel. Switching to a system where fast reactors are used more widely, in order to operate a more 'closed' cycle, would allow a greater proportion of the uranium resource to be utilised. However, it would also require that the world's nuclear reprocessing capacity were dramatically increased as the closed cycle cannot operate without these reprocessing facilities. Th
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