Nuclear energy is an intermittent source of electricity

Unlike renewables such as solar and wind, nuclear power plants can operate continuously, providing stable and predictable electricity generation. Reactor shutdowns are events that occur several times a year and cause nuclear production to vary, but this is nothing like the intermittence experienced by wind turbines and photovoltaic panels.

Nuclear power is often considered a reliable and non-intermittent source of electricity. Nuclear power plants can operate at baseload, which means that they are capable of generating electricity continuously and at a constant level, 24 hours a day, 7 days a week [1].

This distinguishes them from renewable energy sources such as wind and solar, which depend on weather conditions and are therefore considered intermittent. The electricity generation of a nuclear power plant does not fluctuate according to external factors such as wind or sun, which ensures a stable and predictable power supply. This prevents problems of balancing electricity supply and demand on the grid, which can be particularly important for countries that rely heavily on electricity for their energy supply.

Generally predictable shutdowns

However, it should be noted that nuclear power plants can sometimes be shut down for maintenance or repairs [2]. This can lead to a temporary drop in electricity production, but these shutdowns are usually scheduled and grid operators are informed in advance so they can make the necessary arrangements to compensate for this drop in production.

Load and availability factors

In order to compare the intermittent nature of the various sources of electricity, the "load factor" is generally used. It is equal to the ratio between electricity actually produced and the energy produced if the source were constantly operating at maximum power. In France, this coefficient was respectively 24% and 14% for wind and solar power plants in 2024 [3]. The load factor of the French nuclear fleet was about 67% in 2024. In the United States, the load factor of all nuclear power plants exceeds 90% [1]. 

French nuclear power plants, because they perform load following to adapt to demand (often forced because intermittent renewable sources take priority on the electricity grid), do not produce as many kWh as they could. Therefore, in France, the availability coefficient (Kd) is often used to assess the capacity of the fleet to meet demand. This coefficient corresponds to the load factor of the plants if they produced at the maximum power actually available, at all times. The latter is between 70 and 80% depending on the year, with a low point in 2022 at 58% following the discovery of corrosion phenomena on some reactors [4].