2015 Nov

Uranium as a Nuclear Fuel

November 5, 2015

Physics of Nuclear Energy

History of nuclear energy

Uranium was first discovered in 1789 by Martin Klaproth. However, ionising radiation, discovered by Wilhelm Rontgen, was used to further the research in beta radiation. Pierre and Marie later went on to name the phenomenon, demonstrated by subsequent experiments of Rontgen, Villard and Henri Becquerel, radioactivity. In 1939, Hahn and Strassmann demonstrated that nuclear fission released neutrons which can result in the fission in other uranium nuclei, causing a self-sustaining chain reaction which releases large amounts of energy.

Niels Bohr suggested that it is more likely for fission to occur in the uranium-235 isotope, due to it containing neutrons with slower speeds. However, U-235 was found to be difficult to extract since natural uranium contains 99.3% U-238. Thus U-235 has to be increased by a process known as enrichment.

Later, it was explained that the critical mass of uranium is required to produce a self-sustaining energy release. This concept, along with the fact that a chain reaction can be sustained in a uranium-water mixture, is what made Francis Perrin and Rudolf Peierls, and their theories, important in the development of nuclear reactors and the atomic bomb.

Uranium as a source of energy

Due to the nature of uranium atoms, they are relatively easy to split. Therefore, uranium is heavily mined to produce energy. While Nuclear Physics is taught as an academic topic in our A level Physics tuition classes, it’s social impact is far-reaching. Only certain nations are allowed to import uranium, or other nuclear fuel, as established by the Nuclear Non-Proliferation Treaty. This treaty ensures that nuclear fuel is used peacefully; without malevolence.

After uranium ore is mined, the ore is crushed and then dissolved by an acid. The resulting uranium oxide is converted to a gas, uranium hexafluoride – enabling it to be processed for “enrichment”. After it is enriched, the gas is converted to uranium dioxide to be formed into fuel pellets. The pellets are then used as fuel elements for the reactor core. Nuclear reactors use approximately 200 tons of uranium per annum and, if used efficiently, can be partly recycled – which reduces the amounts mining and extracting necessary.

Uranium pressurized water reactor

Uranium fuel in a reactor needs to be assembled in a way to ensure a stable and controlled fission chain reaction. One of the most effective ways to do this is by splitting the U-235 atoms to produce steam, which spins a turbine to drive a generator – ultimately resulting in electricity. Water is used as a moderator to stabilize the emitted neutrons, in turn, controlling the chain reaction. Hence, the uranium pressurized water reactor is currently the best method to produce nuclear energy.

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