Nuclear: Filling the energy gap

Plans to build a new nuclear power station at Hinkley Point, already the site of an operational nuclear reactor, were finalised recently in an attempt to plug the “energy gap” created by declining fossil fuel reserves, the decommissioning of older power stations, and escalating costs.

Hinkley Point

Hinkley Point

As expected, these proposals have been met with some opposition – with the Fukushima incident still within recent memory, this is no surprise. Stories like Chernobyl haven’t helped the reputation of nuclear power, and, for some people, the word nuclear conjures up unpleasant images of mushroom clouds over Hiroshima.

Nuclear fission, the splitting of a single uranium-235 nucleus into two smaller nuclei, currently accounts for 18% of the UK’s total power supply, a percentage likely to increase as supplies of coal and natural gas (which still account for 70% of our energy supply) fall below requirements in the next couple of decades. Uranium supplies, meanwhile, could last for more than 200 years, and that figure could be extended by an order of magnitude with advances such as breeder reactors.

With such an abundant fuel source under our feet, nuclear fission sounds like the perfect solution, but how likely is a meltdown, and is it worth the risk? To answer questions like those, it helps to begin by understanding how nuclear power works.

A typical commercial fission reactor works by giving a uranium-235 nucleus an extra neutron, causing it to become highly unstable and split into smaller nuclei. The combined mass of these “daughter nuclei” is slightly lower than that of the original nucleus, and this mass deficit is compensated for by a release of energy – this is the meaning of the famous equation E = mc² simply, ‘E’ refers to the energy released, ‘m’ represents the change in mass, and ‘c’ is the speed of light.

Because c² is a very large number, even a small change in mass can result in large energy output: Around 24,000,000 kWh of heat can be generated from 1 kg of uranium-235, compared to around 8 kWh for 1 kg of coal.

The energy released heats up water, turning it into steam and driving a turbine to generate electricity. This process is used for all fossil fuels, and the turbine itself is very similar to a wind turbine or the dynamo powering a bicycle light.

It works on the principle of electromagnetic induction: moving a magnet near a coil of wire will generate an electric current in the wire, a principle discovered by British scientist Michael Faraday in 1831.

Of course, we now have a lot of daughter nuclei left over, and they’re of no use to us in terms of power generation. Getting rid of them isn’t simple, since many of them are highly radioactive and can cause serious health problems if not disposed of correctly.

The storage and disposal of radioactive nuclear waste is very strictly regulated, and a lot of spent nuclear fuel will remain unsafe to biological organisms for millions of years – this is inconvenient, to say the least, but when disposed of correctly the risk from nuclear waste is negligible.

Fosmark horizontal silo for nuclear waste storage

Fosmark horizontal silo for nuclear waste storage

There’s also the possibility of things going wrong with the reaction itself. Accidents like Chernobyl are the result of uncontrolled chain reactions, a phenomenon deliberately invoked in nuclear bombs like that dropped on Hiroshima, but such accidents are freak occurrences caused by human error, and adequate safety controls (such as control rods) can prevent this under normal conditions.

It’s more difficult, however, to defend against natural disasters, as Fukushima taught us recently, or possible terrorist attacks. Either of these could be devastating, and making the process as safe as possible is a major concern for engineers working on nuclear power stations.

Luckily, fission isn’t the only type of nuclear reaction. Fusion, the combining of small nuclei like hydrogen into heavier elements like helium, is the power source used in stars, and a promising candidate for the “fuel of the future”, which could avoid all of these problems. It works using a very similar principle to fission, by converting a small mass defect into thermal energy.

While not currently a practical source of power, fusion is virtually non-polluting and could generate huge amounts of power using little more than water, with no risk of a meltdown and few radioactive waste products. It’s unsurprising that this is the subject of a lot of current research, including here at York; the university is heavily involved in fusion research through the York Plasma Institute and the multinational ITER project.

With a lot of kinks to iron out, however, viable fusion reactors are still decades away – too late to plug the energy gap. So for the moment, at least until renewable sources can catch up, fission may have to suffice. With proper safety procedures, the risk from nuclear power is very low, and, for the time being, our need to plug the energy gap outweighs this risk; that’s where Hinkley Point comes in.

One comment

  1. Unsure if it’s standard practice still. But on the topic of defending nuclear plants from Terrorist attack. Someone I know worked at one that had an RAF Bomber stationed nearby with specific instructions to destroy the complex and bury it in rubble if it was attacked.

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