Nuclear Availability Index
NAI, last 3 months
Availability distribution
How many days the fleet ran at each availability level, 2026 to 2026Daily availability heatmap
Every day, colored by fleet availability, 2026 to 2026By ISO / region, today
generation as a percent of capacity, lowest first| ISO / Region | Availability | MW offline | Nuclear capacity | Units |
|---|---|---|---|---|
| CAISO | 49.9 | 1,122 | 2,240 | 2 |
| SPP | 60.4 | 771 | 1,948 | 2 |
| IESO (Ontario) Canada | 62.0 | 4,619 | 12,160 | 16 |
| ISO-NE | 62.9 | 1,243 | 3,352 | 3 |
| SRP | 66.7 | 1,311 | 3,937 | 3 |
| Duke Progress | 78.9 | 759 | 3,593 | 4 |
| MISO | 79.2 | 2,398 | 11,512 | 13 |
| PJM | 80.3 | 6,430 | 32,692 | 31 |
| Southern | 81.1 | 1,530 | 8,080 | 8 |
| TVA | 86.2 | 1,126 | 8,181 | 7 |
| ERCOT | 97.8 | 109 | 4,986 | 4 |
| Duke Carolinas | 100.0 | 0 | 7,226 | 7 |
| BPA | 100.0 | 0 | 1,151 | 1 |
| NYISO | 100.0 | 0 | 3,329 | 4 |
| FPL | 100.0 | 0 | 3,649 | 4 |
| Dominion SC | 100.0 | 0 | 977 | 1 |
Ontario sits low because several Bruce and Pickering units are in multi-year refurbishment, a planned programme rather than an outage. Its megawatts come from IESO market data, not the NRC status report, and are never added into the U.S. figures on this site. Ontario in detail.
Methodology & citation
The NAI is U.S. nuclear generation divided by available nuclear capacity, expressed as a percent, summed over every operating unit reporting that day. It is the positive framing of "MW offline": an NAI of 96.0 means 4% of the fleet's capacity is offline for refueling, maintenance or a forced outage. Source data is the NRC Daily Power Reactor Status Report and EIA net-summer capacity, updated every morning. It is an availability measure, not a forecast.
The NAI itself is the national U.S. number at the top of this page, and that is what the citation below refers to. The Availability column in the by-market table is the same calculation applied to each fleet separately, so the rows are comparable with one another but none of them is the NAI.
Ontario (IESO) is listed as its own row because it is a market like the others and every column applies to it. Its megawatts come from the IESO Generator Output & Capability Report (MW delivered against rated capability), not the NRC status report, and it is never added into the U.S. figures anywhere on this site. Its availability also runs structurally lower than the U.S. fleet's: several Bruce and Pickering units are in multi-year refurbishment, which is a planned programme rather than a bad day. Ontario in detail.