Byron 1
Online · 100% powerConstellation Energy·Byron, IL·PWR·1,164 MWe
?
Composite Operational Excellence Score (0-100) — average percentile rank across 7 dimensions in three sub-scores: Reliability (capacity factor, forced outage days, B2B avg streak), Efficiency (fuel utilization, refuel duration), and Discipline (startup duration, scram count). 5-year window. Higher = more operationally excellent. Click to see the full breakdown.
Excellence
Rank locked · 93 units
Subscribers
?
Current reactor power level from the most recent NRC daily report.
100%
Power
ONLINE
?
Days of continuous operation since the last outage ended. Ranked against all operating units.
211
Current Run
days
#33 of 95
Mid Quartile
?
Longest recorded period of continuous operation between outages.
543
Record Run
days
#73 of 95
Bottom Quartile
?
Breaker-to-Breaker runs — continuous operation exceeding the cycle-adjusted threshold (459 days for this 18-month cycle unit) with no trips to 0% power.
14
B2B Runs
#1 of 86
Top Quartile
?
Lifetime capacity factor: average power level across all recorded days (100% = always at full power). Ranked against all NRC-tracked units.
94.3%
Capacity Factor
#6 of 95
Top Quartile
?
Net electricity actually generated over the most recent 12 months reported by the U.S. Energy Information Administration (Form EIA-923), summed across every unit at this plant. These are authoritative actuals, not an estimate.
19.65 TWh
Net Generation
EIA-923 · 12 mo to 2026-07 · plant total
?
Total NRC-reported scram events (emergency reactor shutdowns). Ranked fleet-wide — fewer scrams = better rank.
1
Scrams
#4 of 94
Top Quartile
?
Years since commercial operation began. License remaining: 18 years.
41.1
Operating Age
years
18 yrs remaining
Excellence Score, Records & Plant Facts
ELITE B2B CHAMPION
5+ RUNS CLEAN
4,252 days without a trip
·
14 Career Runs · 7 since last trip
Champion since Jan 4, 2017
Breaker-to-Breaker Runs 14 runs
Breaker-to-breaker runs measure continuous operation between refueling outages using a cycle-adjusted threshold (90% of cycle length minus RFO duration). An active streak means the unit has been running continuously since the last refueling with no trips to 0% power.
Byron 1 has logged 14 breaker-to-breaker runs, continuous stretches from one refueling to the next with no trip to zero power. Its longest ran 535 days, and its runs average 521 days.
535
Best Run (days)
B1R23 (2020-03-27) → B1R24 (2021-09-13)
521
Avg Run (days)
★ 7-run breaker-to-breaker
B1R20 → B1R21 → B1R22 → B1R23 → B1R24 → B1R25 → B1R26 → B1R27
All Runs
| 2024-09-30 | 2026-03-02 | 518 days | B1R26 → B1R27 |
| 2023-03-25 | 2024-09-09 | 534 days | B1R25 → B1R26 |
| 2021-10-01 | 2023-03-06 | 521 days | B1R24 → B1R25 |
| 2020-03-27 | 2021-09-13 | 535 days | B1R23 → B1R24 |
| 2018-09-25 | 2020-03-09 | 531 days | B1R22 → B1R23 |
| 2017-03-27 | 2018-09-10 | 532 days | B1R21 → B1R22 |
| 2015-10-03 | 2017-02-27 | 513 days | B1R20 → B1R21 |
| 2012-10-08 | 2014-03-10 | 518 days | B1R18 → B1R19 |
| 2009-10-09 | 2011-03-14 | 521 days | B1R16 → B1R17 |
| 2008-04-15 | 2009-09-14 | 517 days | B1R15 → B1R16 |
| 2005-03-26 | 2006-09-11 | 534 days | B1R13 → B1R14 |
| 2003-10-14 | 2005-02-28 | 503 days | B1R12 → B1R13 |
| 2000-10-11 | 2002-03-12 | 517 days | B1R10 → B1R11 |
| 1999-05-18 | 2000-09-23 | 494 days | B1R9 → B1R10 |
About This Site
Written by NukeWorker from public records: facts that do not change. Operator, status and capacity come from the live data elsewhere on this page. Sources: Wikipedia: Byron Nuclear Generating Station.
Byron Station is a two-unit nuclear plant in Rockvale Township, Ogle County, Illinois, near the town of Byron and about two miles east of the Rock River. It lies about 17 miles southwest of Rockford.
Read more
Commonwealth Edison began construction on April 1, 1975, and built two Westinghouse four-loop pressurized water reactors. In 1984 a licensing board refused permission to start operation over contractor quality-control concerns, then reversed itself in October 1984. Unit 1 received its operating license on February 14, 1985, was connected to the grid on March 1, 1985, and entered commercial service on September 16, 1985. Unit 2 was licensed on January 30, 1987, connected on February 6, 1987, and entered commercial operation on August 2, 1987. Elevated groundwater tritium was reported in 2006.
Facility Statistics
Key performance and lifecycle metrics calculated from NRC operational data. Includes operating age, construction timeline, capacity factor, efficiency, generation totals, and reliability records.
Byron 1 has operated for about 41.1 years and averaged a 94.3% lifetime capacity factor, generating roughly 270.2 TWh of electricity. Its longest unbroken run reached 543 days.
Lifecycle & Tenure
Operating Age: 41.1 Yrs
Build Time: 9.7 Yrs
Lic. Remaining: 18 Yrs
Production & Power
Lifetime CF: 94.3%
Efficiency: 31.9%
Generated: 270.2 TWh
Reliability & Outages
Record Run: 543 Days
Refuelings: 19
Avg Startup: 4.1 Days
Ownership & Construction
The utility or company that owns and operates the facility, the architect-engineer responsible for plant design, and the primary construction contractor. Click names to view all facilities by that entity on the map.
Ownership, operation and management history
| Date | Change | From | To |
|---|---|---|---|
| Oct 20, 2000 | Merger | Commonwealth Edison (Unicom) | Exelon |
| Feb 1, 2022 | Spin-off | Exelon | Constellation Energy |
CEG
Constellation Energy Corporation
NasdaqGS
$258.08
▼ -0.90 (-0.35%)
Previous Close
258.98
Day's Range
254.45 – 261.88
52-Week Range
228.63 – 406.04
Volume
2,392,730
Delayed quote as of Oct 28, 2026 4:00 PM ET.
Source: Yahoo Finance.
Full quote on Yahoo Finance
Operational Excellence Score Subscribers
Byron 1 is rated 0 to 100 on how well it actually runs, scored against every other operating reactor in the US fleet from its own operating record. Subscribers see the score, the three sub-scores behind it, and each of the seven measured inputs.
- This unit's composite score and fleet rank
- Reliability, Efficiency and Discipline sub-scores
- All seven measured inputs, with fleet percentiles
- Rank against comparable units, not just the fleet
- Three-year, five-year and lifetime windows
- Five-year trend, and every other operating US reactor
Included with every outage subscription and with NukeWorker Gold membership. Trading the outage rather than working it? The same record, cut by power market, is on NukeGryd.
Scram History 1 events since 2011
Automatic and manual reactor scram (emergency shutdown) events reported to the NRC since 2011. Includes event dates, trip type, and average recovery time. Click the title to view the full fleet scram dashboard.
Byron 1 has recorded 1 reactor scram, or emergency shutdown, since 2011 (1 automatic, 0 manual). On average the unit was back to full power about 8 days after each trip.
Technical Specs
Reactor design specifications including type (PWR/BWR), containment design, nuclear steam supply system manufacturer, thermal and electrical power ratings, and current operational status.
Reactor Type:
PWR
Containment:
PWR-DRYAMB
NSS Supplier:
WEST 4LP
Turbine Supplier:
WESTINGHOUSE ELECTRIC CORPORATION IAEA
Thermal Power:
3645 MWt
Net Capacity:
1164 MWe
Gross Capacity:
1,242 MWe IAEA
Design Capacity:
1,120 MWe IAEA
Efficiency:
31.9%
Status:
Operating
Lifetime Output:
359.8 TWh through 2025 IAEA
Licensing
NRC licensing history including docket number, license type and number, construction permit date, operating license issuance, commercial operation date, license renewal, and expiration date.
Docket #:
05000454
License #:
NPF-37
License Type:
OL-FP
Const. Permit:
1975-12-31
Construction Start:
1975-04-01 IAEA
Operating Lic:
1985-02-14
First Criticality:
1985-02-02 IAEA
Grid Connection:
1985-03-01 IAEA
Commercial Op:
1985-09-16
License Renewed:
2015-11-19
License Exp:
2044-10-31
Market & Region
EIA market and grid-region classifications: NERC reliability region, U.S. Census region, balancing authority responsible for grid operations, and whether the unit operates as a rate-regulated utility or a competitive merchant generator. Hover any value for the full name.
NERC Region:
RFC
— Reliability First Corporation
Census Region:
ENC
— East North Central
Balancing Authority:
PJM
— PJM Interconnection (ISO/RTO)
Market Structure:
Merchant
— Competitive generator selling into wholesale markets