Can Nuclear Energy Reduce CO2 Emissions?
Photo by Brian R. Marshall
There is considerable doubt as to whether nuclear energy could reduce carbon dioxide (CO2) emissions in the longer term. Nuclear power stations themselves do not emit CO2, but the nuclear fuel cycle is a complex process with the following steps, some of which are large users of fossil energy:
- mining and milling to produce an oxide of uranium known as 'yellow-cake', U3O8;
- conversion into the gas, uranium hexafluoride, UF6;
- enrichment to increase the concentration of the isotope U-235;
- fuel fabrication, where enriched UF6 is converted into uranium oxide (UO2) powder and pressed into small pellets which are inserted into fuel rods;
- power station construction;
- operation and maintenance of power station;
- interim storage of spent fuel *(optional) reprocessing of spent fuel;
- long-term waste management (which only exists in theory); and
- power station decommissioning (which has never been done for a large nuclear power station).
The energy inputs to these steps have been investigated by authors who are independent of the nuclear industry, namely Nigel Mortimer (1991), Energy Policy 19:76-8, Jan-Feb., and in more detail by Jan Willem Storm Van Leeuwin and Philip Smith (2003). These researchers find that the energy inputs depend sensitively on the grade of uranium used.
For high-grade ores the energy inputs are less than the energy outputs. But even then the nuclear power station must operate for 7-10 years to generate its energy inputs (compare 3-5 months for wind power). For a nuclear power station with lifetime 35 years, this may be acceptable, although it introduces a limitation on the rate of growth of the nuclear industry in a carbon constrained situation.
The quantity of known uranium reserves with high-grade ore grades is very limited. Under the current circumstances where 16% of the world's current electricity production comes from nuclear energy, these reserves would only last about 20 years. Even a doubling of the reserves, as a result of further exploration, would only provide enough fuel for one generation of nuclear power stations at the existing level of electricity generation. This would be hardly sufficient for a 'sustainable' substitute for coal.
For low-grade ores, Van Leeuwin and Smith find that the fossil energy consumption in mining, milling and enrichment becomes so large that the nuclear fuel cycle emits the same or more CO2 than an equivalent gas-fired power station. Although there are vast quantities of uranium oxide in the Earth's crust, almost all exist at at low or very low concentrations.
A theoretical solution would be to go to fast breeder reactors, which produce so much plutonium that in theory they can multiply the original uranium fuel by 50. Large-scale reprocessing of spent fuel is necessary to extract the plutonium from intensely radioactive wastes, and this has high hazards and costs. At present only a small percentage of spent nuclear fuel is reprocessed, most in France. All non-military reprocessing plants in the USA and UK have been shut down. In addition fast breeders use liquid sodium as a coolant and so are more dangerous than ordinary nuclear reactors. So far, fast breeders have all been technical and economic failures. The largest that ever operated, the French 1200 megawatt Superphénix, was shut down at the end of 1998 after a history of coolant leaks and other accidents and total costs of about A$15 billion..
So, on the basis of present technology and the small amounts of high-grade uranium reserves, the potential contribution of nuclear power to the reduction of CO2 emissions is quite limited in quantity and could only be further implemented slowly, if it is to decrease CO2 emissions. That's why a sustainable energy future, based on efficient energy use, renewable sources of energy and, as a transitional fuel, natural gas, is the best solution to the greenhouse problem. (See the Clean Energy Future studies at www.wwf.org.au.)
Dr Mark Diesendorf teaches in the Institute of Environmental Studies, University of New South Wales.