Friday, April 11, 2014
Deconstructing the myths about nuclear power
Peter Bunyard disposes of the argument for nuclear power: it is highly uneconomical, and the saving on greenhouse gas emissions negligible, if any, compared to a gas-fired electricity generating plant
Peter Bunyard will be speaking at Sustainable World Conference, 14-15 July 2005.
A critical point about the practicability of nuclear power to provide clean energy under global warming is the quality and grade of the uranium ore. The quality of uranium ore varies inversely with their availability on a logarithmic scale. The ores used at present, such as the carnotite ores in the United States have an uranium content of up to 0.2 per cent, and vast quantities of overlying rocks and subsoil have to be shifted to get to the 96,000 tonnes of uranium-containing rock and shale that will provide the fresh fuel for a one gigawatt reactor .
In addition, most of the ore is left behind as tailings with considerable quantities of radioactivity from thorium-230, a daughter product of the radioactive decay of uranium. Thorium has a half-life of 77 000 years and decays into radium-226, which decays into the gas radon-222. All are potent carcinogens.
Fresh fuel for one reactor contains about 10 curies of radioactivity (27 curies equal 1012 becquerels, each of the latter being one radiation event per second.) The tailings corresponding to that contain 67 curies of radioactive material, much of it exposed to weathering and rain run-off. Radon gas has been found 1 000 miles from the mine tailings from where it originated. Uranium extraction has resulted in more than 6 billion tonnes of radioactive tailings, with significant impact on human health .
Once the fuel is used in a reactor, it becomes highly radioactive primarily because of fission products and the generation of the ‘transuranics’ such as neptunium and americium. At discharge from the reactor, a tonne of irradiated fuel from a PWR (pressurized water reactor such as in use at Sizewell) will contain more than 177 million curies of radioactive substances, some admittedly short-lived, but all the more potent in the short term. Ten years later, the radioactivity has died away to about 405 000 curies and 100 years on to 42 000 curies, therefore still 600 times more radioactive than the original material from which the fuel was derived .
Today’s reactors, totalling 350 GW and providing about 3 per cent of the total energy used in the world, consume 60 000 tonnes of equivalent natural uranium, prior to enrichment. At that rate, economically recoverable reserves of uranium — about 10 million tonnes — would last less than 100 years. A worldwide nuclear programme of 1 000 nuclear reactors would consume the uranium within 50 years, and if all the world’s electricity, currently 60 exajoules (1018Joules) were generated by nuclear reactors, the uranium would last three years . The prospect that the amount of economically recoverable uranium would limit a worldwide nuclear power programme was certainly appreciated by the United Kingdom Atomic Energy in its advocacy for the fast breeder reactor, which theoretically could increase the quantity of energy to be derived from uranium by a factor of 70 through converting non-fissile uranium-238 into plutonium-239.
In the Authority’s journal , Donaldson, D.M., and Betteridge, G.E. stated that, “for a nuclear contribution that expands continuously to about 50 per cent of demand, uranium resources are only adequate for about 45 years.”
The earth’s crust and oceans contain millions upon millions of tonnes of uranium. The average in the crust is 0.0004 per cent and in seawater 2 000 times more dilute. One identified resource, the Tennessee shales in the United States, have uranium concentrations of between 10 and 100 parts per million, therefore between 0.1 and 0.01 per cent. Such low grade ore has little effective energy content as measured by the amount of electricity per unit mass of mined ore .
Below 50 parts per million, the energy extracted is no better than mining coal, assuming that the uranium is used in a once-through fuel cycle, and is not reprocessed, but is dumped in some long-term repository. Apart from the self-evident dangers of dissolving spent fuel in acid and keeping the bulk of radioactive waste in stainless steel tanks until a final disposal is found, reprocessing offers very little if at all in terms of energy gained through the extraction and re-use of uranium and plutonium in mixed oxide fuel (MOX) .