from uranium to the plug, step by step

Do you remember Homer Simpson asleep in front of the control panel? For years, that has been the most popular image of a nuclear power plant: glowing bars, red buttons and donuts. Others, however, may think of sirens, black smoke, protective suits and names that continue to weigh: Chernobyl or Fukushima.

Between fiction and collective fear, there is a much more normal story—and at the same time more amazing—that usually goes unnoticed: that of giant factories that produce electricity from the power of atoms.

If you approach one, you will see towers that seem to breathe water vapor. And inside, hidden behind a heart of steel, millions of atoms splitting in two, releasing energy so enormous that a handful of uranium is enough to power a city for days.

Although the debate is served with this type of fontthe truth is that it continues to be one more piece of the energetic present. So, leaving prejudices aside, let’s take a look inside a nuclear power plant: to discover how it works, how it differs from a thermal one, how many are still active in Spain and why it remains at the center of the energy debate.

What is a nuclear power plant?

A nuclear power plant is an industrial facility designed to produce electricity. At its core—literally—is the nuclear reactor, the place where the magic happens: the fission of atoms.

Inside each atom there are protons and neutrons that remain united. When that nucleus breaks—when hit by a neutron—an enormous amount of energy is released in the form of heat. That’s where nuclear energy comes in: the same energy that holds those tiny particles together.

Nuclear power plants take advantage of this nuclear fission process to obtain heat, heat water, produce steam and move turbines that generate electricity. It’s that simple. Or, if you look closely, that impressive.

Difference between a nuclear power plant and a thermal power plant

Confusion is common: “Aren’t a nuclear power plant and a thermal power plant the same thing?” In part, yes. Both use heat to drive a turbine and produce electricity. But the big difference is in the origin of that heat.

In a thermal power plantthe heat comes from burning fossil fuels (coal, gas or fuel oil). This releases carbon dioxide (CO₂) and other polluting gases. While, in a nuclear power plant, heat is obtained from the fission of uranium atoms, without combustion or CO₂ emissions during electricity generation.

Therefore, nuclear They are considered clean energy in emissionsalthough they leave a different challenge: what to do with radioactive waste? We could say that it is a smokeless energy, but not without questions and I will stop here because we will talk about it at the end.

How it works: the process to generate electricity

It may sound complicated, but the operation of a nuclear power plant can be explained in a simple way: Imagine a big kettle, like a teapot, only inside there are atoms splitting and releasing energy.

1. Uranium fission. It all starts inside the reactor. Uranium-235 atoms break apart when hit by neutrons. Each fission releases heat and more neutrons, which continue colliding with other atoms, creating a controlled chain reaction.
2. Water heating. The heat produced is used to heat water. This water circulates through pipes under enormous pressure or is transformed directly into steam, depending on the type of reactor.
3. The steam drives the turbine. The force of the steam rotates the blades of a turbine connected to an electrical generator. That movement is what is finally converted into electricity.
4. The electricity is sent to the grid. The generator converts the mechanical energy of rotation into electrical energy, which is transported to homes and industries.
5. Cooling and recirculation. The steam condenses, cools, transforms back into water and returns to the circuit, repeating the cycle.

It seems simple, and it is in concept. But behind it there are decades of engineering, thousands of security measures and constant surveillance so that this invisible and powerful energy is always kept under control.

In Spain There are two types in operation: the pressurized water reactors (PWR)where water is heated inside the reactor and converted to steam outside, and the boiling water reactors (BWR)where steam is generated directly inside the reactor.

How many nuclear power plants are there in Spain?

According to the Ministry for the Ecological Transition and Demographic Challenge (MITECO)Spain has seven nuclear reactors spread over five sites:

• Almaraz I and II (Cáceres). In operation since 1981 and 1983, with a combined power of about 2,000 MW. It is one of the first that is on the list for closure: Almaraz I in 2027 and Almaraz II in 2028.
• Ascó I and II (Tarragona). Connected to the grid in 1983 and 1985, they total about 2,000 MW. Its closure is scheduled for 2030 Ascó I and 2032 Ascó II.
• Chests (Valencia). In operation since 1984; It is the only one with a boiling water reactor (BWR), with 1,092 MW of power. Its closure is scheduled for 2030.
• threshing (Guadalajara). In operation since 1988, with a power of 1,066 MW. It is scheduled to close in 2035.
• Vandellós II (Tarragona). In service since 1988, with a power of 1,087 MW. It is scheduled to close in 2035.

In addition, there were three others that are already closed:

• Jose Cabrera (Guadalajara), the first Spanish nuclear power plant.
• Santa María de Garona (Burgos).
• Vandellós I (Tarragona), closed after a fire in 1989.

In total, Spanish operational reactors generate around 20% of the country’s electricity, according to data from Nuclear Forum. And they do it constantly, 24 hours a day, without depending on the sun or the wind.

What is the largest nuclear power plant in the world?

If nuclear power plants had their own world ranking, Japan would be in first place. The central Kashiwazaki-Kariwa It has seven reactors and a power that exceeds 8,000 megawatts. Today it is stopped for revisions, but it is still the largest on the planet. The center follows Bruce in Canada with 6,234 MW and eight pressurized heavy water reactors (PHWR). Closing the podium we go to Europe, specifically, to the Nuclear Power Plant of Zaporozhyein Ukraine with a power that is close to 6,000 MW. In these moments It is closed due to the Ukrainian War.

On a global scale, the International Atomic Energy Agency (IAEA) predicts that nuclear capacity could increase up to 80% before 2050, driven by the climate challenge and the search for constant electricity without CO₂.

What happens if a nuclear power plant runs out of electricity?

Although it may seem like a paradox, a nuclear power plant also needs electricity to operate safely. Even when the reactor is stopped, the fuel continues to generate waste heat, and cooling systems must remain active to dissipate it. If that power is interrupted, the risk increases: Heat could build up and damage the reactor core.

If a plant completely loses electricity—both external and emergency—the cooling systems stop working. In that case, the nuclear fuel begins to heat uncontrollably, which can cause partial or complete melting of the core. That was exactly what It happened in Fukushima in 2011when a tsunami destroyed the diesel generators and the batteries were not enough.

For this reason, nuclear facilities have multiple electrical backup systems, designed to go into action immediately if the main grid fails:

• Redundant connections to the external network.
• Emergency diesel generators.
• Batteries that ensure hours of operation even if everything fails.

These layers of safety reduce the possibility of an accident to a minimum, and each plant conducts periodic drills to check that everything is working as it should.

nuclear waste

When a nuclear power plant finishes its work, something remains that cannot be seen, but that matters as much as the electricity it produces: radioactive waste. A material that will continue to be dangerous no matter how many centuries – or even millennia – pass, which is why it needs controlled and safe storage.

In Spain, Enresa (the National Radioactive Waste Company) is responsible for collecting and storing them. Those with low and medium activity rest in the Center of El Cabrilin Córdoba. However, the great challenge is in the high-activity fuels—the used fuel—which requires a stable place for thousands of years.

That is why the country works on a centralized temporary warehouse (ATC)an intermediate point before making the leap to deep geological storage (AGP): sealed caverns underground like those that already exist in Finland or Sweden.

Ultimately, waste is a reminder that even the cleanest energies leave their mark. The challenge is not only technical, but a long-distance race that mixes physics, geology and political consensus.

Image | Nuclear Forum

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