Reactor Status Timeline
Online NRC data, Mon to Fri ? Actual daily reactor status from NRC reports (Mon to Fri), the current state, and what is coming: the utility's published Scheduled outage plus, for subscribers, NukeWorker's model Projection. Colored by status. How far ahead you can see depends on your plan.OnlineCoastdownPower AscensionRefueling Outage
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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.
55
Excellence
#32 of 93 ↑11
Mid Quartile
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Days of continuous operation since the last outage ended. Clean run (no forced outages since last refueling).
80
Current Run
days ✔
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Longest recorded period of continuous operation between outages (2005-04-14 to 2006-10-01).
535
Record Run
days
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Breaker-to-Breaker runs — continuous operation exceeding the cycle-adjusted threshold (454 days for this 18-month cycle unit) with no trips to 0% power.
9
B2B Runs
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Lifetime capacity factor: average power level across all recorded days (100% = always at full power).
89.7%
Capacity Factor
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Net electricity actually generated over the most recent 12 months reported by the U.S. EIA (Form EIA-923), summed across every unit at this plant. Authoritative actuals, not an estimate.
20.59 TWh
Net Generation
EIA-923 · 12 mo to 2026-04 · plant total
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Total number of scheduled refueling outages detected in the historical data.
18
Outages
since 1999
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Average time from first power generation (>0%) to sustained full power (≥95% for 2+ days) across the last 3 scheduled outages. Click to compare against the fleet on the Operator Efficiency Leaderboard.
5.3
Avg Startup
days (last 3)
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Average fuel utilization — percent of the designed fuel cycle that this unit consumes before refueling, derived from the historical burn-down trajectory. Higher = more efficient operator (refuels with less margin remaining; closer to coastdown). Computed as 100% minus the unit's average refuel-point fuel %, using the last 3 years where available, otherwise lifetime average. Click to compare against the fleet on the Operator Efficiency Leaderboard.
99.7%
Fuel Utilization
3yr avg
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NukeWorker's Operational Excellence Score is a composite 0–100 ranking of every active US nuclear unit across 7 publicly observable performance metrics, grouped into three sub-scores:
• Reliability — capacity factor, forced outage days, B2B avg streak
• Efficiency — fuel utilization, refuel duration
• Discipline — startup duration, scram count
Each unit's metric is converted to a percentile across the active fleet. Sub-score = average of its components; composite = average of the three sub-scores. Use the time-window toggle below to switch between 3yr / 5yr / lifetime.
• Reliability — capacity factor, forced outage days, B2B avg streak
• Efficiency — fuel utilization, refuel duration
• Discipline — startup duration, scram count
Each unit's metric is converted to a percentile across the active fleet. Sub-score = average of its components; composite = average of the three sub-scores. Use the time-window toggle below to switch between 3yr / 5yr / lifetime.
Time window
— change how far back we look
NukeWorker's
Operational
Excellence Score
Operational
Excellence Score
55/100
Mid Quartile · #32/93
5-year window
South Texas 1 ranks #32 of 93 active US units on NukeWorker's Operational Excellence Score over the 5-year window. Strongest area: Scrams (5-year) (70th percentile). Weakest: Forced Outage Days/yr (37th percentile).
Reliability
41
Capacity factor + Forced outages + B2B streaks
Efficiency
54
Fuel utilization + Refuel duration
Discipline
70
Startup duration + Scram count
Cohort Rankings
apples-to-apples comparison within each peer group
Reactor type:
#19 of 61
PWR
Containment:
#17 of 47
Dry Ambient (PWR)
Cycle length:
#14 of 53
18-month cycle
Fleet rank above (32 of 93) compares all active US units; cohort ranks compare only against units sharing this property.
Per-dimension breakdown (7 metrics)
Capacity Factor
40th
90.7% (higher better, Reliability)
Forced Outage Days/yr
37th
4.8d (lower better, Reliability)
B2B Avg Streak
45th
513d (higher better, Reliability)
Refuel Duration
54th
32d (lower better, Efficiency)
Scrams (5-year)
70th
0.2/yr (lower better, Discipline)
Each dimension's percentile is computed across the active US fleet (93 units with sufficient history). Sub-score = average of its component percentiles. Composite = average of the three sub-scores. 5-year window. View full leaderboard →
Methodology
NukeWorker's Operational Excellence Score is a composite ranking that combines 7 publicly observable performance metrics into a single 0-100 number per US nuclear unit.
How it's computed: Each unit's raw value is converted to a percentile (0-100) within the 93 active US units that have at least 2 completed refueling cycles. The 7 percentiles are averaged into 3 sub-scores (Reliability, Efficiency, Discipline), and those are averaged into the final composite.
Active window — 5-year:
- Reliability — Capacity factor (5yr), forced outage days/yr (5yr), B2B avg streak (lifetime)
- Efficiency — in-cycle fuel utilization (3yr), median refuel duration (5yr)
- Discipline — robust mean startup duration, scrams/yr (5yr, annualised)
Cohort rankings: alongside the fleet rank, each unit gets ranked within its reactor type (PWR/BWR), containment design (Ice Condenser, Mark I, etc.), and cycle length (12/18/24-month). Useful for apples-to-apples comparisons.
What's excluded: subjective community ratings, confidential INPO ratings, financial metrics. We only use publicly available NRC + cycle data.
Why three windows? 5yr (default) is the industry standard. 3yr captures recent operational changes and post-pandemic recovery. Lifetime gives newer units a fair comparison and reveals long-term consistency.
Edge cases: units with fewer than 2 cycles (e.g., Vogtle 4) show "Provisional". Decommissioned units excluded.
Refresh cadence: recomputed daily. Each window cached separately.
A data-derived proxy for operational performance; not affiliated with INPO. INPO ratings are confidential and qualitative — ours is public and quantitative.
5-yr trend:
↑ +4.8 pts vs 2025
Compare South Texas 1 head-to-head with up to 3 other units.
Compare now
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Duration of each outage in days, shown chronologically. Green bars are scheduled refueling outages, red bars are forced/unscheduled. The orange dashed line marks the average duration. Extended outages (>180 days) and D&D periods are excluded.
Outage Duration Trend
South Texas 1 has 40 outages plotted here, averaging 23 days each. The most recent, in Mar 2026, was a scheduled refueling outage lasting 33 days.
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Days between consecutive scheduled refueling outage starts, showing operating cycle regularity. The purple dashed line marks the average cycle length. Most U.S. reactors operate on 18-month (547 day) or 24-month (730 day) cycles.
Cycle Length History
Between refueling outages, South Texas 1 runs about 560 days, or roughly 18 months, per cycle. That average comes from 17 completed cycles, the most recent lasting 532 days.
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Time in days from first power generation (>0%) to sustained full power (≥95% for 2+ consecutive days) after each scheduled refueling outage. The dashed line marks the average. Includes startup testing holds and power dips.
Startup Duration Trend
After a refueling outage, South Texas 1 takes about 5 days to climb from first power back to full power. That average is drawn from 18 startups on record, and the most recent took 3 days.
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Estimated fuel remaining in the current cycle, expressed as a percentage of the unit's typical cycle. Starts at 100% when the unit returns to power post-refuel and drops as full-power-days are burned. Days at reduced power burn fuel proportionally — so a unit with significant downtime (high burn deficit) drops slower and ends up with MORE fuel left than its calendar position would suggest. Coastdown threshold around 15%. Toggle to overlay past cycles on a normalized "days into cycle" axis to see how aggressively this unit historically burns down before refuel.
Fuel Burn Down Cycle since Apr 23, 2026
84.3% remaining
78 / 494 days
0.7 FPD margin
South Texas 1 is 78 days into its current fuel cycle with an estimated 84.3% of its fuel left. This cycle is set up to run about 494 days. Across its last 17 cycles, it has refueled with an average of 1.5% remaining.
Avg refuel: 1.5%
Avg refuel (3yr): 0.3%
Deepest burn: 0.0% (2000-05 → 2001-10)
Most margin: 11.4% (2015-12 → 2017-03)
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Monthly capacity factor with outage events overlaid as red bands. Green bars show average power level per month. Toggle to Daily view for raw daily data.
Power History
Over its operating life, South Texas 1 has run at about 89.7% of its rated capacity. Across the last 12 reported months it averaged 90.0%. On the chart, flat stretches near the top are full-power running and drops to zero are outages.
This table logs every recorded outage for South Texas 1, 40 in all since 1999. Of those, 18 were scheduled refueling outages and 22 were unplanned or forced. The typical outage lasted about 23 days. Where the Scheduled column shows (Model), the date is a NukeWorker projection because the utility had not published one.
| Type ⇅ | Actual Start ⇅ | Actual End ⇅ | Duration ⇅ | Days Online ⇅ | Scheduled | Delta |
|---|---|---|---|---|---|---|
|
Scheduled
|
2026-03-21 | 2026-04-22 | 33 | 498d | 2026-03-20 | +1d |
|
Scheduled
|
2024-10-05 | 2024-11-08 | 35 | 66d | 2024-10-04 | +1d |
|
Scram
# 57237
|
2024-07-25 | 2024-07-31 | 7 | 143d | - | - |
|
Unscheduled
|
2024-03-01 | 2024-03-04 | 4 | 31d | - | - |
|
Unscheduled
|
2024-01-22 | 2024-01-30 | 9 | 278d | - | - |
|
Scheduled
|
2023-03-18 | 2023-04-19 | 33 | 497d | 2023-03-17 | +1d |
|
Scheduled
|
2021-10-09 | 2021-11-06 | 29 | 105d | 2021-09-11 | +28d |
|
Unscheduled
|
2021-06-24 | 2021-06-26 | 3 | 127d | - | - |
|
Scram
# 55104
|
2021-02-16 | 2021-02-17 | 2 | 306d | - | - |
|
Scheduled
|
2020-03-14 | 2020-04-16 | 34 | 491d | 2020-03-13 | +1d |
|
Scheduled
|
2018-10-06 | 2018-11-09 | 35 | 528d | 2018-10-06 | 0d |
|
Scheduled
|
2017-03-18 | 2017-04-26 | 40 | 317d | 2017-03-18 | 0d |
|
Scram
# 51897
|
2016-05-02 | 2016-05-05 | 4 | 94d | - | - |
|
Scram
# 51687
|
2016-01-27 | 2016-01-29 | 3 | 34d | - | - |
|
Scram
# 51615
|
2015-12-22 | 2015-12-24 | 3 | 3d | - | - |
|
Scheduled
|
2015-10-18 | 2015-12-19 | 63 | 505d | 2015-10-03 | +15d |
|
Unscheduled
|
2014-05-30 | 2014-05-31 | 2 | 5d | - | - |
|
Scheduled
SGR/Major
|
2014-03-16 | 2014-05-25 | 71 | 152d | 2014-03-15 | +1d |
|
Unscheduled
|
2013-10-02 | 2013-10-15 | 14 | 140d | - | - |
|
Unscheduled
|
2013-05-12 | 2013-05-15 | 4 | 167d | - | - |
|
Scheduled
|
2012-10-21 | 2012-11-26 | 37 | 534d | 2012-10-20 | +1d |
|
Scheduled
|
2011-04-03 | 2011-05-06 | 34 | 225d | 2011-04-03 | 0d |
|
Unscheduled
|
2010-08-21 | 2010-08-21 | 1 | 194d | - | - |
|
Unscheduled
|
2010-02-04 | 2010-02-08 | 5 | 78d | - | - |
|
Scheduled
|
2009-10-01 | 2009-11-18 | 49 | 524d | 2009-10-04 | -3d |
|
Scheduled
|
2008-03-30 | 2008-04-25 | 27 | 513d | 2008-03-30 | 0d |
|
Scheduled
|
2006-10-01 | 2006-11-03 | 34 | 535d | 2006-09-30 | +1d |
|
Scheduled
|
2005-03-09 | 2005-04-14 | 37 | 409d | 2005-03-08 | +1d |
|
Unscheduled
|
2004-01-24 | 2004-01-25 | 2 | 170d | - | - |
|
Scheduled
SGR/Major
|
2003-03-26 | 2003-08-07 | 135 | 24d | 2003-03-26 | 0d |
|
Unscheduled
|
2003-03-01 | 2003-03-02 | 2 | 97d | - | - |
|
Unscheduled
|
2002-11-17 | 2002-11-24 | 8 | 390d | - | - |
|
Scheduled
|
2001-10-03 | 2001-10-23 | 21 | 288d | 2001-10-03 | 0d |
|
Unscheduled
|
2000-12-17 | 2000-12-19 | 3 | 218d | - | - |
|
Unscheduled
|
2000-05-13 | 2000-05-13 | 1 | 2d | - | - |
|
Scheduled
SGR/Major
|
2000-03-01 | 2000-05-11 | 72 | 170d | 2000-03-01 | 0d |
|
Unscheduled
|
1999-09-12 | 1999-09-13 | 2 | 76d | - | - |
|
Unscheduled
|
1999-06-28 | 1999-06-28 | 1 | 43d | - | - |
|
Unscheduled
|
1999-05-16 | 1999-05-16 | 1 | 18d | - | - |
|
Unscheduled
|
1999-03-27 | 1999-04-28 | 33 | - | - | - |
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