How does nuclear energy work? Where does its fuel come from?
Uranium is an ore found in the ground. There is a lot of it in certain areas in Australia, itself possessing only one nuclear reactor for research and medical purposes only.
How does nuclear energy work? Who uses it?
There are a number of countries that have used nuclear energy for power generation for decades, notably France, the United Kingdom and the United States.
These countries, as others have, have developed nuclear weapons too. When you have a nuclear reactor for peaceful purposes, weapons-grade plutonium can also be produced. Therefore opposition to nuclear energy has long been connected to concerns held by the nuclear disarmament movement
How does nuclear energy work? The process
All nuclear reactors now in operation use nuclear fission (link to advantages of nuclear energy). Nuclear fission is the process where the nucleus (hence 'nuclear' energy) of a 'heavy', fissionable atom is split. Enormous amounts of energy are released in this process.
This energy, in the form of heat is transferred to steam turbines to generate electricity. So, apart from the source of energy, a nuclear energy plant is in essence no different from any fossil fuel power plant. Both use the energy source to generate heat to drive turbines that generate electricity. Electricity is then fed into a grid for domestic and industrial use.
An atom’s nucleus can only split if it is ‘fissionable’. Only the nuclear isotopes Uranium 235 (U235), Plutonium 239 and Uranium 238 are of this type. Only U235 occurs naturally. The other isotopes are created in the U235’s fission process.
This transformation occurs as in the fission process neutrons bombard the U235 at high speed and penetrate its atoms. Fission happens when a nucleus absorbs a neutron and splits into two nuclei that now have a different composition.
Uranium as it is found contains only about 0.7% of U235 and much of the rest is uranium 238 with which it is much more difficult to achieve fission. It can be achieved with ‘fast breeder reactors’, which can blast neutrons at speeds high enough to penetrate and spit the U238’s nucleus.
Therefore fast breeder reactors are more efficient users of uranium than the common thermal reactors—in fact 60 times more so—and leave far less radioactive waste. They can reuse the current nuclear waste stockpiles. Such reactors can also use thorium, a far more abundant material than uranium but containing mostly U238. There is now only one fast breeder reactor in service but scientists hope that in about 15 years more will come on stream.
How does nuclear energy work? Its fuel
The uranium is produced into pellets, which are in turn cast into rods. These rods are placed in the reactor core for neutron bombardment.
How does nuclear energy work? Chain reaction.
The common expression a ‘chain reaction’ of events comes from the nuclear fission process. The nuclei of split atoms also release one or two neutrons during fission. These hit other U235 or other isotopes which split in turn, and so on.
How does nuclear energy work? Heat transfer.
But how is the heat from a radioactive nuclear process safely transferred to the steam turbines that make electricity? You were going to ask, weren’t you?
A liquid or gas circulates through the reactor core to transfer the heat from it to the turbines. In some reactors this gas or liquid is also used as a coolant for the reactor core.
How does nuclear energy work and how can a chain reaction be stopped?
When a nuclear chain is uncontrolled it overheats, causes damage to the reactor and radioactivity may spill into the environment. That’s what happened at Chernobyl where there was no separate protective building around the reactor’s housing.
Essentially the chain reaction is slowed, stopped or sped up by addition of rods into the reactor core. These rods absorb neutrons, thereby affecting the nuclear process. These control rods are made of cadmium, hafnium or boron.
To shut a reactor down if this system fails neutron-absorbing fluid can be added. Usually this is water, or heavy water or graphite.
How does nuclear energy work and what if all safeguards fail
Around the reactor core is a strong structure to prevent any intrusion from outside and to prevent any radioactive material escaping into the environment in case of a nuclear accident. Commonly this is a one meter-thick concrete and steel structure
How does nuclear energy work if fuel needs to be replaced?
Nuclear fuel needs to be replaced as the fissionable material is used up. The reactor core, its pressure vessel that contains the fuel rods needs to be opened for this to happen. For most reactors this happens every one to two years. A third or a quarter of the fuel rods are replaced at such times.
How does nuclear energy work? Is it unnatural?
Well, that’s an interesting question. U235 occurs naturally but the technology to release its nuclear energy is highly complex. And plutonium and E238 do not occur naturally.