Archive for the ‘Nuclear power’ Category

We need nuclear power in order to help reduce our carbon emissions. That is the key motive given for the government’s agreement to the building of new nuclear capacity. This view, however, is based upon highly erroneous judgements about the power-producing capacity of nuclear power.

A recent announcement that it would be optimistic to expect to have on stream a new nuclear power plant by 2017 looks anything but impressive given the scale of the climate change challenges and the need for urgent action. A closer look at the background parameters of the nuclear industry reveals how fundamental the obstacles are.

It would in fact, because of the laws of physics and limited fuel reserves, be impossible for nuclear power to make more than a small contribution to Britain’s or the world’s energy needs. It is possible, however, for it to create immense quantities of long-lived dangerous waste and serious security problems, a big price for a small gain

The maximal potential yield of energy from nuclear power can only be accessed if both thermal and fast-breeder reactors are used. Uranium is mined then expended in thermal reactors which yield plutonium as a by-product. This plutonium can be used in fast-breeder reactors to produce energy while creating yet more plutonium from uranium.

A full exploitation of the potential of fast-breeder reactors would yield, according to generally accepted estimates, approximately 50 times as much energy as could be produced from using only thermal reactors to their full potential. Key to this, however, is the doubling time, the time it takes a fast-breeder reactor to produce as much plutonium as has been loaded into it as fuel. Because of the complexities, estimates for the doubling time are between 20 and 30 years.

The overall size of this timescale is dictated by nuclear physics. The first doubling of energy produced comes after about 30 years, the second after a further 30. Only in stages, over about 1500 years could the capacity of fast-breeder reactors be tapped.

This is why, given that action to combat climate change by reducing carbon emissions must take place now, fast-breeder reactors can play only a minor part in this. Any contribution from nuclear power to the energy strategy will have to be largely confined to the use of thermal reactors.

Consider, then, the potential contribution of the uranium that fuels thermal reactors.

Take a nuclear power station in Britain in the standard size range, one that produces one giga-watt of power and uses fissile uranium enriched to five times the concentration in natural uranium. As it operates it produces both heat and plutonium by nuclear fission of the uranium. The plutonium then contributes through further fission a large proportion – typically some 40 per cent – of the heat output. The energy in the electricity finally generated is at about on third the level of the heat output, due to wastage. The total amount of uranium oxide required includes both the fuel fed into the reactor and that from which the fissile uranium is extracted during enrichment.

The net effect is that the reactor will produce, for every tonne of fuel used, energy as electricity equivalent to the heat obtained from burning 3850 tonnes of oil. Multiplying this figure by the joint OECD and International Atomic Energy Agency estimate for the world’s uranium reserves, a total of 3.11 million tonnes, gives a figure for the amount of energy potentially produceable in thermal nuclear reactors. It comes to about 11.5 million tonnes of oil equivalent.

With this figure the scale of the realistic potential contribution of nuclear power to the world’s energy needs becomes clear. The world’s annual primary energy consumption stands at about 11,000 million tonnes of oil equivalent (m.t.o.e.), of which about 77 per cent comes from fossil fuels. This means that the energy available in the uranium reserves would be enough to replace our fossil fuel usage only for about a year and half.

In practice, it would be necessary, if nuclear power were to be used as much as possible to replace fossil fuels, to deploy it over a longer time-scale than this, since plants would have to be built and its use would only mesh with the electricity infrastructure that the move to renewables for all sectors including road transport will also require. Given that Britain uses some 2.6 per cent of the world’s fossil fuels it would seem fair that it should build a proportionate number of these new power plants. It would be about 32. Britain now has 20 plants, with 10 in operation

At present, nuclear supplies 18 per cent of Britain’s electricity from 10 power stations.  This amounts to just three per cent of energy consumption. On the generous assumption that 20 new plants could be put into operation, to triple power output, we could perhaps get about 10 per cent of our energy from nuclear power. Only by constructing a great many more power stations could Britain get the nuclear proportion significantly higher and even then the overwhelmingly greater contribution would still be coming from renewables and, for some time, from fossil fuels also.

It is often said that nuclear could provide flexibility of power supply and back-up for renewables, given that those are subject to fluctuations in wind and sunlight. However, the government (DTI) paper of May 2007 stresses that nuclear specifically, because of the operational complexities, is not suitable for this.

It is indisputable that nuclear, while causing serious long-lived environmental damage and major security difficulties, remains inescapably a comparatively feeble energy source.