Under the Microscope: Nuclear power has been in decline worldwide since the nuclear accident at Chernobyl in 1986, writes Prof William Reville
Since then we have become acutely conscious of the dangers posed by the enhanced greenhouse effect, a primary driver of which are the gases released when fossil fuels are burned in conventional power stations to generate electricity.
Only radical measures will arrest the progress of the enhanced greenhouse effect and prevent its potentially disastrous consequences. One measure under investigation is a re-design of the nuclear industry to make it safe, environmentally tolerable and acceptable to the public.
The two biggest problems associated with the nuclear industry are (a) the possibility of catastrophic accident and (b) the generation of high-level nuclear waste. It is possible to design power stations that are inherently safe in operation. In a recent article I described a nuclear power station that automatically shuts down in a safe manner immediately any potentially dangerous surge is sensed. But, to my mind, the single biggest problem with nuclear power is the radioactive nuclear waste it generates.
This waste is so long-lived that it must be securely segregated from the environment for over 100,000 years. This is a ridiculous legacy to bequeath to future generations. But, if the high-level waste problem could be solved or greatly ameliorated, this, together with inherently safe reactor design, could well make nuclear power once again acceptable to the general public.
At the heart of nuclear power is the process called nuclear fission. In nuclear fission, atoms of the nuclear fuel uranium-235 (the mass of the uranium atom is 235 atomic mass units) each split into two fission fragments, most probably fragments of roughly equal size. In this fission process, a small amount of mass is converted into an enormous amount of energy in accordance with Einstein's equation E=MC2, where E is energy, M is mass and C is the speed of light. The energy is liberated as heat and is used to boil water to produce high pressure steam that is used to rotate a magnet in a coil of wire thereby causing electric current to flow in the wire.
The uranium-235 atom splits (fission) into two fragments when its central nucleus absorbs a free neutron. These fission fragments are themselves radioactive, and, in turn, decay through a series of radioactive daughters until a stable non-radioactive element is reached. When uranium nuclear fuel is "burned" in a nuclear reactor, several hundred of these fission fragments and products accumulate, making the fuel intensely radioactive.
Uranium atoms can also absorb neutrons without splitting, thereby being transformed into elements heavier than uranium (transuranic elements), for example plutonium-239, americium-241 and curium. Some of these elements have very long half-lives (for example plutonium-239 has a half life of 24,000 years) which means that spent nuclear fuel must be securely held for over 100,000 years before its activity has decayed sufficiently to allow it to be released to the environment.
The nuclear industry is now developing a new approach called partitioning and transmutation (PT) for handling high-level waste. In this approach, all nuclear waste is reprocessed chemically and the "un-burned" uranium and the transuranic elements are separated from the fission fragments and products.
The recovered uranium can be re-used in nuclear power plants. The transuranic elements are then bombarded with neutrons or with lasers, and thereby transmuted into other elements that are either non-radioactive or are radioactive but have short half-lives. Using this approach it is possible in principle to transform high-level waste into a form whose radioactivity decays to the level of natural uranium ore, present naturally in the earth's rocks, over a period of 1,000 years. It is quite feasible to design credible man-made containment for this waste.
The PT technology that would allow the benefits of this approach does not yet fully exist, but it can all be reasonably extrapolated from current knowledge and technology. PT would greatly reduce the amount of nuclear waste in the long term and would allow the industry to store the waste under demonstrably safe conditions. In a world increasingly beset by greenhouse warming and uncertainties over future oil supplies it is somewhat comforting to know that the nuclear industry is making strides at developing a process that could command considerable public acceptability if, as is not at all unlikely, circumstances force us to embrace it once again.
At the forefront of research into the transmutation of key radionuclides present in irradiated nuclear fuel is the Institute for Transuranium Elements, part of the Joint Research Centre (JRC) of the European Commission. The JRC provides scientific and technical support for the conception, development, implementation and monitoring of EU policies and has an annual operating budget of €340 million. The Director General of JRC since April 2001, Dr. Barry McSweeney, a UCC Biochemistry graduate, returns home to Ireland next month to take up the newly created position of chief science adviser to the Government. This is an exciting and important development in Irish science, of which, more anon.