How to read U.S. nuclear outages
The U.S. has the world’s largest nuclear fleet: about 94 reactors at 54 plants with roughly 97 gigawatts of capacity. Reactors are the grid’s most reliable generators, running above 90% of the time, so the capacity that is not running is the number to watch.
Refueling seasons
Each reactor shuts down every 18 to 24 months to replace about a third of its fuel and carry out maintenance the plant cannot do while running. Operators schedule these outages for spring (March–May) and autumn (September–November), when mild weather keeps power demand low, and avoid summer and midwinter peaks. The day-of-year chart shows the pattern clearly: offline capacity peaks near 20–25% in April and October and falls to a few percent in July and January.
Why it matters for energy markets
Nuclear plants run at almost no marginal cost, so when a reactor goes offline its output is usually replaced by natural gas. A heavy refueling season, or an unexpected outage during a heat wave, adds to gas burn and can lift both power and natural gas prices — which is why traders watch the daily outage numbers.
Planned and unplanned outages
EIA’s data, compiled from the Nuclear Regulatory Commission’s daily reactor status reports, gives each unit’s capacity and how much of it is offline, but not why. A unit that drops to zero for a month in spring or autumn is almost always refueling. A partial reduction is often a planned “coastdown” at the end of a fuel cycle. Sudden outages outside the refueling seasons are more likely to be forced — equipment trips or repairs.
Frequently asked questions
How many U.S. nuclear reactors are offline today?
This page shows the number of reactors with any capacity out of service on the latest reported day, how many are fully shut down, and the total gigawatts offline, from the EIA's daily nuclear outage data.
When is nuclear refueling season?
Spring, roughly March to May, and autumn, roughly September to November. Operators schedule refueling for these mild-weather months when electricity demand is lowest, so offline capacity typically peaks in April and October.
How long does a nuclear refueling outage last?
Most refueling outages last three to five weeks, though longer ones happen when major maintenance or equipment replacement is done at the same time. Each reactor refuels every 18 to 24 months.
Why do nuclear outages affect natural gas prices?
Nuclear plants produce power at very low running cost, so their output is used first. When reactors go offline, the lost output is mostly replaced by natural gas-fired plants, raising gas demand. Heavy outage seasons, or unplanned outages during hot weather, can therefore push up gas and power prices.
Where does this nuclear outage data come from?
From the U.S. Energy Information Administration, which compiles daily outage data for every U.S. reactor from the Nuclear Regulatory Commission's power reactor status reports. Plant locations and operators come from EIA's monthly generator inventory.