Energy & Climate Change

Illustration: Ferry

The most advanced way to boil water

The basic idea of nuclear power is simple. It's boiling water. The current generation of light water reactors, and even more the new generations being built now, can be said to be the most advanced and safe ways to boil water to make electricity.

Nearly all electricity in the world is produced by turbines that spin generators . Most of this spinning is generated by boiling water in a power plant , where roughly one third of the energy used to boil the water can be turned in to electricity. There are two main ways to boil water . The first is by burning fuels, such as coal, wood or oil. The second is by splitting certain atoms in a controlled chain reaction in a nuclear reactor.

Nuclear energy is our most recently discovered way to produce energy. There was a big push to develop electricity producing civilian reactors after the Second World War. Back then, there were many different types of reactors being tested. In the United States, there was even a reactor-project that aimed to power aeroplanes . Due to various developments and even some chance, the world ended up building mostly two types of reactors. The Pressurized Water Reactor (PWR) was originally designed to run nuclear submarines and was simply scaled to a bigger size, and the simpler Boiling Water Reactor (BWR) that was developed from the PWR a few years later. We have both of these types in Finland. Olkiluoto 1 and 2 are BWR’s, while the OL3 being built is a PWR. Both reactors in Loviisa nuclear power plant are PWR’s, as is the Hanhikivi 1 now being prepared by Fennovoima. There are other reactor types around the world, but they are currently not very common.

What makes nuclear power plant a different way to boil water is the amazing energy density of the fuel it uses. In a reactor, a small amount of mass is turned in to energy (heat), with the well-known formula  that Einstein is most known for: e=mc2. The scale is hard to grasp, but let’s take a few examples. Nuclear energy is several million times denser than the chemical energy in coal, oil or wood. There is so much energy stored in uranium that roughly a coffee cup full of it would be enough to produce all the energy a human with a western lifestyle uses in her entire lifetime . How far can one drive with a coffee cup of gasoline?

How far can one drive with a coffee cup of gasoline?

In a nuclear reaction an unstable (fissile) atom, like Uranium isotope U235, splits, releasing a large amount of heat and a couple of neutrons from the nucleus. Some of these neutrons hit other unstable atoms nearby, splitting them. More heat and neutrons are released, and the chain reaction continues. We can then use various neutron catchers, like the control rods placed inside the nuclear reactor, to control the amount of neutrons hitting and splitting new atoms, and make the amount of reactions happening stable. Water boils, turbine spins the generator and at home we can turn on the lights, keep the fridge cool and the electric stove hot. Animated picture of PWR

Nuclear power plant is also different from other ways to boil water for electricity in another important way. This is the release of pollution to the environment. More precisely, it is the lack of pollution released. When we burn fuels (other than natural gas), there is always some small particles and other toxic substances released to the environment, as well as greenhouse gases such as carbon dioxide, which also get released from natural gas. Sure, a nuclear reaction releases lots of dangerous and radioactive isotopes, but they and their radioactivity remain mainly inside the reactor. The amount of radiation released to people from nuclear reactors amounts to roughly the same dose one can get from eating a few bananas  every year.

Nuclear reaction does not release any greenhouse gases. This means that it has a very low carbon footprint . Spent nuclear fuel is of course dangerous due to its radioactivity. After it has been cooled down however, it is not much more dangerous than many other everyday substances. It is in a solid form, so it is also relatively easy to store in a safe and secure way.

The current generation of light water reactors, and even more the new generations being built now, can be said to be the most advanced and safe ways to boil water to make electricity. But at the end of the day, there is not that much mystique about nuclear power. It is just a way to boil water. 

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