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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.
35
Excellence
#72 of 94 ↑4
Bottom Quartile
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Days of continuous operation since the last outage ended. Clean run (no forced outages since last refueling).
196
Current Run
days ✔
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Longest recorded period of continuous operation between outages (1999-06-27 to 2001-02-03).
587
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.
7
B2B Runs
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Lifetime capacity factor: average power level across all recorded days (100% = always at full power).
90.1%
Capacity Factor
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Total number of scheduled refueling outages detected in the historical data.
17
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.
7
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.
91.7%
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
35/100
Bottom Quartile · #72/94
5-year window
Millstone 3 ranks #72 of 94 active US units on NukeWorker's Operational Excellence Score over the 5-year window. Strongest area: Scrams (5-year) (70th percentile). Weakest: Fuel Utilization (5th percentile).
Reliability
28
Capacity factor + Forced outages + B2B streaks
Efficiency
9
Fuel utilization + Refuel duration
Discipline
66
Startup duration + Scram count
Cohort Rankings
apples-to-apples comparison within each peer group
Reactor type:
#50 of 61
PWR
Containment:
#5 of 5
Dry Subatmospheric (PWR)
Cycle length:
#42 of 54
18-month cycle
Fleet rank above (72 of 94) compares all active US units; cohort ranks compare only against units sharing this property.
Per-dimension breakdown (7 metrics)
Capacity Factor
29th
89.1% (higher better, Reliability)
Forced Outage Days/yr
11th
16.0d (lower better, Reliability)
B2B Avg Streak
44th
512d (higher better, Reliability)
Fuel Utilization
5th
92.8% (higher better, Efficiency)
Refuel Duration
13th
41d (lower better, Efficiency)
Startup Duration
63th
3.9d (lower better, Discipline)
Scrams (5-year)
70th
0.2/yr (lower better, Discipline)
Each dimension's percentile is computed across the active US fleet (94 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 94 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:
↑ +2.0 pts vs 2025
Compare Millstone 3 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
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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
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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
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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 May 19, 2025
32.9% remaining
354 / 502 days
17.2 FPD margin
Avg refuel: 1.8%
Avg refuel (3yr): 8.3%
Deepest burn: 0.0% (2001-03 → 2002-09)
Most margin: 8.3% (2023-12 → 2025-04)
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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
| Type ⇅ | Actual Start ⇅ | Actual End ⇅ | Duration ⇅ | Days Online ⇅ | Scheduled | Delta |
|---|---|---|---|---|---|---|
|
Unscheduled
|
2025-10-17 | 2025-10-26 | 10 | 75d | - | - |
|
Unscheduled
|
2025-08-01 | 2025-08-03 | 3 | 76d | - | - |
|
Scheduled
|
2025-04-11 | 2025-05-17 | 37 | 207d | 2025-04-13 | -2d |
|
Unscheduled
|
2024-09-04 | 2024-09-16 | 13 | 231d | - | - |
|
Unscheduled
|
2024-01-09 | 2024-01-17 | 9 | 32d | - | - |
|
Unscheduled
|
2023-12-03 | 2023-12-08 | 6 | 3d | - | - |
|
Scheduled
|
2023-10-20 | 2023-11-30 | 42 | 114d | 2023-10-14 | +6d |
|
Scram
# 56544
|
2023-05-31 | 2023-06-28 | 29 | 363d | - | - |
|
Scheduled
|
2022-04-08 | 2022-06-02 | 56 | 295d | 2022-04-07 | +1d |
|
Unscheduled
|
2021-06-11 | 2021-06-17 | 7 | 159d | - | - |
|
Unscheduled
|
2020-12-31 | 2021-01-03 | 4 | 50d | - | - |
|
Scheduled
|
2020-10-02 | 2020-11-11 | 41 | 171d | 2020-10-19 | -17d |
|
Scram
# 54663
|
2020-04-14 | 2020-04-14 | 1 | 4d | - | - |
|
Scram
# 54631
|
2020-04-02 | 2020-04-10 | 9 | 102d | - | - |
|
Unscheduled
|
2019-12-18 | 2019-12-22 | 5 | 218d | - | - |
|
Scheduled
|
2019-04-12 | 2019-05-14 | 33 | 515d | 2019-04-13 | -1d |
|
Scheduled
|
2017-10-13 | 2017-11-13 | 32 | 477d | 2017-10-08 | +5d |
|
Scram
# 52000
|
2016-06-13 | 2016-06-23 | 11 | 27d | - | - |
|
Scram
# 51929
|
2016-05-16 | 2016-05-17 | 2 | 4d | - | - |
|
Scheduled
|
2016-04-10 | 2016-05-12 | 33 | 73d | 2016-04-10 | 0d |
|
Scram
# 51682
|
2016-01-25 | 2016-01-28 | 4 | 435d | - | - |
|
Scheduled
|
2014-10-12 | 2014-11-16 | 36 | 132d | 2014-10-12 | 0d |
|
Scram
# 50141
|
2014-05-26 | 2014-06-02 | 8 | 286d | - | - |
|
Scram
# 49260
|
2013-08-10 | 2013-08-13 | 4 | 85d | - | - |
|
Scheduled
|
2013-04-14 | 2013-05-17 | 34 | 509d | 2013-04-14 | 0d |
|
Scheduled
|
2011-10-09 | 2011-11-22 | 45 | 419d | 2011-10-09 | 0d |
|
Unscheduled
|
2010-08-15 | 2010-08-16 | 2 | 89d | - | - |
|
Unscheduled
|
2010-05-18 | 2010-05-18 | 1 | 2d | - | - |
|
Scheduled
|
2010-04-11 | 2010-05-16 | 36 | 96d | 2010-04-04 | +7d |
|
Unscheduled
|
2009-12-20 | 2010-01-05 | 17 | 392d | - | - |
|
Scheduled
|
2008-10-12 | 2008-11-23 | 43 | 513d | 2008-10-12 | 0d |
|
Scheduled
|
2007-04-07 | 2007-05-18 | 42 | 68d | 2007-04-07 | 0d |
|
Unscheduled
|
2007-01-29 | 2007-01-29 | 1 | 421d | - | - |
|
Unscheduled
|
2005-12-02 | 2005-12-04 | 3 | 36d | - | - |
|
Scheduled
|
2005-09-30 | 2005-10-27 | 28 | 153d | 2005-09-29 | +1d |
|
Unscheduled
|
2005-04-18 | 2005-04-30 | 13 | 347d | - | - |
|
Scheduled
|
2004-04-03 | 2004-05-06 | 34 | 461d | 2004-04-02 | +1d |
|
Unscheduled
|
2002-12-23 | 2002-12-29 | 7 | 80d | - | - |
|
Scheduled
|
2002-09-07 | 2002-10-04 | 28 | 527d | 2002-09-07 | 0d |
|
Scheduled
|
2001-02-03 | 2001-03-29 | 55 | 587d | 2001-02-03 | 0d |
|
Unscheduled
|
1999-05-02 | 1999-06-27 | 57 | - | - | - |
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