This prescribed regularity may seem mundane, but it is quite an accomplishment that operating reactors are as reliable and predictable as they are. This leaves some big shoes to fill for the next generation of technology expected to join fleets in the next few years.
Normally, nuclear reactors operate at steady levels, as close to full capacity as possible. In 2024, for commercial reactors worldwide, the average capacity factor – the ratio of actual energy output to the theoretical maximum – was 83%. North America contributed an average of about 90%.
(I will note here that it is not always fair to look at this number to compare different types of power plants – natural-gas plants may have lower capacity factors, but that is mostly because they are more likely to be intentionally turned on and off to help meet uneven demand.)
Those high capacity factors also underestimate the true reliability of the fleet – there’s a lot of scheduled downtime. The reactors require refueling every 18 to 24 months, and operators schedule those outages for the spring and fall, when power demand is not as high as when we are all running our air conditioners or heaters at full blast.
Take a look at this chart of nuclear disruptions from the U.S. Energy Information Administration. There are some days, especially at the height of summer, when power outages are rare, and almost all commercial reactors in the US are operating at nearly full capacity. On July 28 this year, the fleet was operating at 99.6%. Compare this to 77.6% capacity on October 18, as the reactors were taken offline for refueling and maintenance. Now we’re headed into another busy season, with reactors coming back online and shutdowns entering another low point.
This does not mean that all outages are planned. At the Sequoyah Nuclear Power Plant in Tennessee, one of two reactors shut down due to generator failure in July 2024, an outage that lasted nearly a year. (The utility also performed some maintenance during that time extend plant life.) Then, just days after that reactor was restarted, the entire plant had to be shut down Due to low water level,
And who can forget the incident earlier this year when jellyfish wreaked havoc on not one but two nuclear power plants in France? In second exampleThe squishy creatures got into the filters of equipment that draws water from the English Channel for cooling at the Pallu nuclear plant. They forced the plant to cut production by nearly half, although it was restored within a few days.
