The World of Nuclear Science

Reactors - Electricity Generation

Nuclear power reactors, that is, nuclear reactors used for electricity generation use the energy released from the nuclear reactions to boil water. The energy comes from the heat produced in nuclear reactions, which boils water. The steam then drives a turbine which generates electricity from an attached generator - similar to any other power station.

Nuclear power reactors are large reactors. A typical power reactor generating 1000 MW of electricity will use several tons of uranium per year. This amount of fuel is less than what a coal power plant would use in terms of mass and volume.

Nuclear power reactors do not have a long lifespan - they must be decommissioned after about 30 years operation. This is because of the build up of radiioactivity in the plant, as well as the structural components of the reactor being worn out due to wear and tear, from the intense radioactive and hot conditions.

Nuclear energy is several thousand times more efficient in terms of fuel mass to energy ratio than any other energy source we have today. This is because the atomic region from which nuclear energy is obtained - the nucleus - contains a huge amount of energy compared to relatively tiny amount of energy stored outside the nucleus to do with electrons (used in fossil fuel energy).

The world's reserves of fossil fuels are running out, and efforts have and are being made to find viable alternatives to fossil fuel energy. About 18% of the world's electricty today is generated by nuclear reactors. If this capacity were to be generated from coal, over one billion tonnes of coal would have to be burnt - releasing hundreds of billions of tonnes of greenhouse gases, as well as many toxic heavy metals and causing acid rain. Thus in this sense, nuclear energy is much more cleaner. In fact, the capacity today generated by nuclear means is more than the electricity produced by all methods combined in the early 1960s.

Consequently, already nuclear electricity generation is very important in terms of trying to lower greenhouse gas emissions and acid rain. However, the main problem of nuclear power to which many remain opposed is the radioactive waste that is produced. Waste disposal is the most difficult part of nuclear power generation.

Nuclear electricity generation is also not a renewable source of energy. The world's supply of uranium is limited just like its supplies of fossil fuels. Eventually there will be little uranium left, and yet another way of generating power must be found. Breeder reactors have been proposed as one way to work around this problem. These reactors have the ability to "generate their own fuel". When the fission of uranium-235 releases a neutron, a uranium-238 atom may absorb it and eventually form plutonium-239. This plutonium is fissionable, and so can be used as fuel in the reactor. Overall the process makes the uranium-238 isotope useful for electricity generation (since it is difficult to fission it as-is). Theoretically, therefore the 99.3% of uranium that exists, being of the uranium-238 isotope, would be able to be used for electricity. However, breeder reactors generate the plutonium which can pose a health hazard, partly due to its long half-life of 24,000 years (although the uranium-238 isotope has a half-life of 4.5 billion years). Additionally, many people maintain that terrorists could easily steal the plutonium and make it into a nuclear weapon.

Nuclear fusion reactors have been proposed as an alternative - they leave almost no radioactive waste behind, and can use normal water as a raw form of their fuel (the hydrogen-1 isotope). However, nuclear fusion requires a very high temperature (about 10 billion ° c) before it proceeds. There is no controlled way that we can attain these temperatures, and even if we could, we do not know of any material that can sustain these temperatures to hold the fuel. Experiments are being done by using magnetic bottles to contain the fuel via massive magnetic fields. One example is a tokamak, shaped like a round, circular tube.

schematic of a tokamak. An electrical current is passed around the outside, and this creates a magnetic field within the tube. (Electric fields create magnetic fields.) The plasma (heated fusion fuel, consisting of charged particles) is moving around the tube shape, which also constitutes another current has its own magnetic field, and these two combine to keep the plasma confined.

Experiments are being conducted using strong focused laser beams to generate the high enough temperatures controllably so that fusion can be started. There are some experimental fusion reactors, but none have been built large enough to generate useful electricity. However, many scientists speculate that fusion will be a successful way of creating electricity in the future although this speculation did start at least 40 years ago. Nevertheless, nuclear fusion shows considerable promise.