The Extremes

Record Tracker

The all-time marks of the U.S. nuclear fleet, from the daily status of every reactor since 1999. Recomputed every morning; a mark set in the last 90 days is flagged.

National supply records

as of Oct 9, 2026

Most nuclear capacity offline in a day

#1 36,428 MW Apr 24, 1999

#2 30,002 MW May 2, 2011

#3 26,274 MW Oct 30, 2012

Least nuclear capacity offline in a day

#1 50 MW Aug 4, 2015

#2 88 MW Jul 24, 2026 new

#3 94 MW Aug 10, 2019

Highest fleet availability

#1 99.95% Aug 4, 2015

#2 99.91% Jul 24, 2026 new

#3 99.90% Aug 10, 2019

Largest one-day loss of supply

#1 6,394 MW Oct 4, 2025

#2 6,260 MW Mar 27, 1999

#3 6,066 MW Jan 1, 2000

Ranks are at least 30 days apart (7 for the one-day loss), so #1, #2 and #3 are three separate episodes and not three consecutive days of one refuelling season. The series follows the reactors that are operating today back through their own history, at today's ratings, so a record from 1999 and one from this year are measured on the same fleet.

Worst day on record, by market

the most nuclear capacity each market has had offline at once

Market	Most MW offline	Date
PJM	14,854 MW	Apr 24, 1999
MISO	7,062 MW	Apr 27, 2013
TVA	5,259 MW	May 23, 2011
Southern	4,045 MW	Mar 31, 2025
SRP	3,942 MW	Apr 12, 2006
ERCOT	3,790 MW	Nov 24, 2002
ISO-NE	3,361 MW	Apr 30, 2005
Duke Carolinas	3,276 MW	Apr 7, 2012
NYISO	3,199 MW	Aug 17, 2003
FPL	3,064 MW	Oct 27, 2005
Duke Progress	2,530 MW	Oct 9, 2016
CAISO	2,240 MW	Nov 1, 2020
SPP	2,027 MW	Nov 13, 2022
BPA	1,177 MW	Aug 31, 2017
Dominion SC	994 MW	Apr 9, 2026

Each unit is attributed to the balancing authority it sits in today, across the whole record, so a market's figure for an early year counts units that had not yet joined it.

Operating records

Individual

The longest runs on line, the longest stretches without a trip and the fastest refuelling outages in the record, by unit. These come from the per-unit operating record, which is what the Individual plan is.

Unlock with Individual $165/mo