Nuclear fission works by firing neutrons at an atomic nucleus making it unstable then decaying. As the nucleus decays it releases energy and more neutrons – which in turn hits other nuclei near them creating a chain reaction. This only works with certain isotopes called fissle isotopes: Plutonium-239, Plutonium-241, Urainium-233 and Uranium-235.
U-235 occurs in natural uranium (0.72%) and enriched uranium (2.5-5%), these are the two main fuels used in nuclear power plants. Usually natural isn’t enough on it’s own and it has to be enriched, but in the Canada Deuterium Uranium (CANDU) pressurised heavy water reactor only natural is needed.
Weapons-grade plutonium has over 93% of the fissile isotope, Pu-239, and can be used, like reactor-grade Plutonium, in fuel for electricity production via:
- Fabrication with uranium oxide as a MOX fuel for burning in existing reactors,
- Fabrication with thorium as a fuel for existing Russian reactors,
- Fuelling fast-neutron reactors.
Fast neutron reactors produce about 60 times as much energy as the normal reactors, but are very expensive. As of now China (1), India (1), Japan (2) and Russia (1) have the only active ones. The USA and UK have stopped all research and development into fast reactors and the only work being carried out is related to decommissioning them.
Thorium and even safer reactors
At about three times the amount of naturally occuring uranium, thorium is quite abundant. Although thorium isn’t fissle, after absorbing slow neutrons and decaying twice, Th-232 will produce U-233. At the moment CANDU reactors can use thorium as a fuel, but The Liquid Fluoride Thorium Reactor (LFTR) gets the most out of thorium because it uses a molten salt reactors which aren’t pressurised so cannot explode and it cannot have a meltdown because the fuel is already in a molten state. Unbelievably almost all of the thorium is used up in the thorium-cycle and the excess consists of less than 0.1% transuranic elements.
Although nuclear power is portrayed in the media as basically kicking a nuke, it is reasonably safe. Infact given the technological advancements in the industry, it could well be safer than (and definitely greener than) the coal and oil industries. Even so, nuclear scientists are looking for safer more efficient ways to generate power and the LFTR looks like the new clear way of generating nuclear power.
I was delighted to find the House of Lords discussing thorium pros and cons so reasonably and was glad to hear mention of the zero fatalities from Fukushima.