Nuclear power plants in blackout: solution or risk?

The debate about phasing out nuclear energy continues unabated – in Germany as well as currently in Spain. Critics such as opposition leader Alberto Núñez Feijóo warn that the planned shutdown of Spain's nuclear power plants starting in 2027 could endanger the stability of the power grid. But what really happens if a widespread power outage – a so-called blackout – occurs? Can nuclear power plants help in such a situation? Or do they themselves pose a risk?

A closer look shows that nuclear power plants are more of a threat than a solution in the event of a blackout.

Nuclear power plants are not a flexible energy source

Nuclear power plants reliably supply a so-called base load—a constant amount of electricity regardless of the time of day or the weather. This property used to be a great advantage when our electricity demand was also relatively constant. However, in an energy system that increasingly relies on solar and wind power and requires flexible control, this inertia becomes a problem.

Especially in the case of sudden, unforeseen events – like the one Spain just experienced – the weaknesses of nuclear power become clear: A technical error there took a huge amount of power off the grid in one fell swoop. Such disruptions occur within seconds – and this is precisely where power grids need extremely fast balancing mechanisms.

Why nuclear power plants cannot help in the event of sudden outages

Nuclear power plants are designed for continuous operation. They react very slowly to changes in the power grid. If a high level of power suddenly fails—be it due to a technical defect, the sudden shutdown of a large power plant, or a fault in the transmission grid—only systems that can intervene immediately can help:

• Battery storage that delivers energy within milliseconds,

• Pumped storage power plants that switch on quickly,

• Fast-start gas power plants that start up within minutes,

• Load management that reduces power consumption in the short term.

Nuclear power plants, on the other hand, can neither ramp up quickly nor increase their output in the short term. They are simply unsuitable for such rapid interventions.

On the contrary: If the grid becomes unstable or collapses, the continued operation of a nuclear power plant can even be dangerous. Nuclear power plants require a stable grid connection to operate or shut down safely.

What happens in the event of a blackout?

If a widespread power outage occurs, nuclear power plants rely on emergency power supplies. Even after an emergency shutdown—the so-called "SCRAM"—a reactor must be actively cooled. Although the chain reaction has been stopped, the reactor core still produces considerable residual heat, which can be dangerous without active cooling.

Diesel generators typically perform this task. However, they aren't designed to run indefinitely. If the blackout lasts a very long time or other problems arise, the situation can become critical – as the 2011 Fukushima disaster dramatically demonstrated.

In short: nuclear power plants need a stable grid – and cannot help in an acute crisis situation, but instead become an additional source of danger themselves.

Spain as a current example: Challenge recognized

The current situation in Spain clearly shows what is important: The problem is not the abandonment of nuclear power – but the lack of preparation for sudden major disruptions. A modern power grid needs:

• Large battery storage,

• Fast reserve power plants,

• Intelligent grid management and automation,

• Load management and decentralized structures.

With its high shares of solar and wind power, Spain actually has very good prospects. The key now will be to draw the right conclusions and consistently invest in flexible and resilient grid infrastructure.

Conclusion: The real challenge lies not in the nuclear phase-out, but in the restructuring of the energy system

Abandoning nuclear power plants does not automatically make the grid unsafe. The risk arises when there are insufficient systems in place to compensate for sudden outages.

Flexibility, speed and decentralization – these are the requirements for the energy system of the future.

Nuclear power plants no longer fit this picture. Instead, modern, responsive technologies that can ensure stability in real time are needed.