The properties of uranium
Natural uranium ore is chemically processed at the mine into uranium oxide yellowcake. Nuclear energy is produced from uranium-235 which is present in natural uranium at a concentration of only 0.7% by weight. This level must be increased to about 3-4% enrichment before it can be used in a typical commercial nuclear power station.
Uranium-235 has an almost unique ability both to easily absorb slow-speed thermal neutrons, called a high neutron cross section and then undergo nuclear fission, called a high fission cross section releasing energy and more neutrons as it breaks itself apart. Before it can be used in nuclear power stations, the yellowcake must be converted into gaseous uranium hexafluouride (hex conversion), lightly enriched with uranium-235 up to 4% concentration in a commercial enrichment plant, deconverted into uranium oxide and then crushed into cylindrical fuel pellets, which are inserted into hollow zirconium metal fuel rods.
Bundles of fuel rods are grouped together to form a single uranium fuel rod assembly which is then inserted into the nuclear reactor core to power the reactor.
Who developed uranium fuel?
Uranium oxide was initially discovered in 1789 by German chemist Martin Klaproth and was named after the newly discovered planet Uranus. However it was not until 1896 that French Nobel Prize-winning scientist Henri Becquerel discovered radioactivity that was being emitted from a sample of uranium stored near photographic equipment. Italian Physicist Enrico Fermi used uranium fuel to power the world's first experimental nuclear reactor called Chicago Pile 1, built under a tennis court at the University of Chicago in the United Sates. Pile 1 first went critical on 2nd December 1942 achieving a self-sustained nuclear chain reaction lasting 28 minutes.
Do we have enough uranium supplies?
The major economic advantage of nuclear power stations is their relatively cheap fuel and stable and predictable operating costs compared with fossil-fuelled generation. But global rising demand for nuclear power will inevitably drive uranium ore prices gradually upwards.
Prices spiked nearly ten-fold in 2007 on market fears of a uranium supply shortage, triggered by media expectations of a sudden global nuclear renaissance. Uranium ore prices have now dropped back again and are currently at a four-year low.
The 2007 uranium price bubble has caused some stakeholders to worry that there may be a serious supply shortage of uranium nuclear fuel in the future. Despite alarming headlines, these worries are not really very well founded. The price of reactor fuel is mainly determined by its manufacturing cost, not uranium ore prices. About 75% of the total price of a uranium fuel rod assembly comes from the industrial fabrication process; commercial hex conversion of uranium ore to gaseous hex, uranum-235 enrichment, deconversion and finally fuel rod fabrication.
The volatile price of uranium ore raw material is actually only a relatively small cost component of the overall manufacturing process, typically about 25%. Using nuclear fuel more efficiently by burning it for longer in the reactor is effectively driving this cost segment down even further to around 15-20%. In fact uranium fuel manufacturing capacity currently outweighs requirements by 40%. There is a supply glut. This means that it is economically very unlikely that commercial nuclear energy utilities will face a uranium fuel supply shortage anytime soon. Uranium supply probably will not become a bottleneck in any realistic nuclear renaissance in Britain.
Are there alternatives to uranium fuel?
Enriched uranium is the simplest and most well understood nuclear fuel. However despite its dominance of the nuclear fuel market, commercial reactors have also been powered with mixtures of recycled plutonium and uranium oxides.
The major alternative fuel to uranium is the thorium fuel cycle. It is possible to operate nuclear reactors using a hybrid mix of both thorium and uranium nuclear fuels.
The Radkowsky Thorium Reactor (RTR) core design comprises an inner seed core of 20% enriched uranium-235 fuel surrounded by an outer blanket core of natural thorium-232. The inner seed core of low-enriched uranium-235 fuel produces neutrons that react with the outer thorium-232 blanket fuel and then transmute and decay to breed uranium-233. The uranium-233 then burns (fissions) inside the reactor core in much the same way as conventional uranium-235 fuel. The US firm Lightbridge Corp. is presently undertaking experimental trials of thorium fuel in Russian reactors for global commercial deployment in Generation III+ pressurised water reactors.
Thorium is attractive as an alternative nuclear fuel for developing countries because large thorium reserves are known to exist and thorium reactor fuel is difficult to weaponise.