Diablo Canyon 1 - Status & History

Comprehensive reactor performance metrics, cycle analysis, and historical outage data.

Plant Info Outage History Daily Power Log
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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.
48
Excellence
#52 of 94 ↑1
Mid Quartile
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Days of continuous operation since the last outage ended. Clean run (no forced outages since last refueling).
147
Current Run
days ✔
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Longest recorded period of continuous operation between outages (2017-06-21 to 2019-02-10).
599
Record Run
days
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Breaker-to-Breaker runs — continuous operation exceeding the cycle-adjusted threshold (451 days for this 18-month cycle unit) with no trips to 0% power.
12
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.
6.3
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.
96.9%
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.
Time window — change how far back we look
NukeWorker's
Operational
Excellence Score
48/100
Mid Quartile · #52/94
5-year window

Diablo Canyon 1 ranks #52 of 94 active US units on NukeWorker's Operational Excellence Score over the 5-year window. Strongest area: Scrams (5-year) (70th percentile). Weakest: Startup Duration (23th percentile).

Reliability
61
Capacity factor + Forced outages + B2B streaks
Efficiency
36
Fuel utilization + Refuel duration
Discipline
46
Startup duration + Scram count
Cohort Rankings apples-to-apples comparison within each peer group
Reactor type: #36 of 61 PWR
Containment: #32 of 48 Dry Ambient (PWR)
Cycle length: #29 of 54 18-month cycle
Fleet rank above (52 of 94) compares all active US units; cohort ranks compare only against units sharing this property.
Per-dimension breakdown (7 metrics)
Capacity Factor 67th
93.1% (higher better, Reliability)
Forced Outage Days/yr 63th
2.6d (lower better, Reliability)
B2B Avg Streak 53th
520d (higher better, Reliability)
Fuel Utilization 30th
97.1% (higher better, Efficiency)
Refuel Duration 42th
34d (lower better, Efficiency)
Startup Duration 23th
6.1d (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: 2021: 65/100 (#26/93)2022: 73/100 (#15/92)2023: 55/100 (#36/92)2024: 62/100 (#24/93)2025: 55/100 (#30/94)2026: 58/100 (#29/94) ↑ +2.6 pts vs 2025
Compare Diablo Canyon 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

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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

31.4% remaining 359 / 514 days 6.2 FPD margin
Avg refuel: 1.5% Avg refuel (3yr): 3.1% Deepest burn: 0.0% (1999-03 → 2000-10) Most margin: 12.3% (2002-12 → 2004-03)
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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

Type ⇅ Actual Start ⇅ Actual End ⇅ Duration ⇅ Days Online ⇅ Scheduled Delta
Unscheduled
2025-12-17 2025-12-18 2 214d - -
Scheduled
2025-04-13 2025-05-17 35 484d 2025-04-13 0d
Unscheduled
2023-12-09 2023-12-16 8 27d - -
Scheduled
2023-10-01 2023-11-12 43 528d 2023-10-04 -3d
Scheduled
2022-03-27 2022-04-21 26 511d 2022-03-27 0d
Scheduled
2020-10-04 2020-11-01 29 568d 2020-10-04 0d
Scheduled
2019-02-10 2019-03-16 35 599d 2019-02-10 0d
Unscheduled
2017-06-21 2017-06-21 1 2d - -
Scheduled
2017-04-23 2017-06-19 58 533d 2017-04-30 -7d
Scheduled
2015-10-04 2015-11-07 35 273d 2015-09-27 +7d
Unscheduled
2015-01-01 2015-01-04 4 281d - -
Unscheduled
2014-03-17 2014-03-26 10 5d - -
Scheduled
2014-02-09 2014-03-12 32 223d 2014-02-09 0d
Unscheduled
2013-06-27 2013-07-01 5 377d - -
Scheduled
2012-04-23 2012-06-15 54 530d 2012-04-22 +1d
Scheduled
2010-10-03 2010-11-10 39 377d 2010-10-04 -1d
Unscheduled
2009-09-20 2009-09-21 2 181d - -
Scheduled
2009-01-26 2009-03-23 57 530d 2009-01-26 0d
Unscheduled
2007-08-11 2007-08-15 5 75d - -
Scheduled
2007-05-01 2007-05-28 28 518d 2007-04-30 +1d
Scheduled
2005-10-24 2005-11-29 37 458d 2005-10-23 +1d
Unscheduled
2004-07-22 2004-07-23 2 49d - -
Scheduled
2004-03-23 2004-06-03 73 468d 2004-10-20 (Enhanced) -211d (Enhanced)
Scheduled
2002-10-21 2002-12-11 52 139d 2002-10-21 0d
Unscheduled
2002-06-04 2002-06-04 1 9d - -
Unscheduled
2002-04-29 2002-05-26 28 524d - -
Unscheduled
2000-11-21 2000-11-21 1 8d - -
Scheduled
2000-10-08 2000-11-13 37 135d 2000-10-08 0d
Unscheduled
2000-05-15 2000-05-26 12 177d - -
Unscheduled
1999-11-20 1999-11-20 1 21d - -
Unscheduled
1999-10-29 1999-10-30 2 36d - -
Unscheduled
1999-09-23 1999-09-23 1 193d - -
Scheduled
1999-02-08 1999-03-14 35 - 1999-02-08 0d
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