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Scanning European outage signalsFrance's outage book totals an estimated 35 GW of event-MW — 7× the 11-country median and larger than Spain and Germany combined — driven by nuclear refuelling season. Normalized for fleet size, however, Sweden leads at 266 MW offline per installed GW, 2.1× the median, concentrated in just three nuclear units.
Data source notice: This analysis is based on publicly available ENTSO-E Transparency Platform data. Latency patterns described here are observations from public disclosure records and do not constitute regulatory findings or determinations of wrongdoing.
France’s outage book is dominated by its nuclear refuelling season, with multiple large reactors offline. Normalised for fleet size, Sweden’s concentration of a few long‑duration nuclear outages pushes it to the top of the density ranking.
In absolute terms, the raw outage volume varies widely across the 11 markets examined, with France among the highest due to its many large nuclear units.
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| 2.4× |
| 11.6% |
| 4 | Sweden (SE) | ~8,500 | 1.7× | 8.2% |
| 5 | Italy (IT) | ~5,000 | 1.0× | 4.8% |
| 6 | Netherlands (NL) | ~5,000 | 1.0× | 4.8% |
| 7 | Norway (NO) | ~5,000 | 1.0× | 4.8% |
| 8 | Belgium (BE) | ~4,500 | 0.9× | 4.3% |
| 9 | Poland (PL) | ~4,000 | 0.8× | 3.9% |
| 10 | Czechia (CZ) | ~3,500 | 0.7× | 3.4% |
| 11 | Finland (FI) | ~1,100 | 0.2× | 1.1% |
Normalising for installed capacity changes the ranking significantly. The density measure — event-MW offline per GW of installed capacity — highlights countries where a few large outages weigh heavily relative to fleet size. Sweden appears at the top, reflecting its concentrated nuclear outages, while France, despite its large absolute volume, ranks lower when fleet size is taken into account.
France’s outage book stems from its 56‑reactor nuclear fleet entering its programmed summer refuelling and maintenance window. Multiple units each rated above 1,000 MW are in planned outages that drive the aggregate: a 1,500 MW unit is scheduled to return on 24 June, a 1,498 MW unit on the same date, a 1,273 MW unit on 29 June, a 1,220 MW unit on 4 July, and a 1,080 MW unit on 31 August.
These outages are driven by the seasonal calendar — nuclear refuelling is routine summer work, not a crisis. The long durations are designed, and the coincidence of so many reactors docking at once reflects fleet‑wide scheduling rather than unexpected failures. This structural feature means the large volume is not a distress signal, but it does remove enough flexible nuclear supply that residual‑load tightness becomes a genuine risk if demand spikes while the outage corridor remains open.
A 31.9 GW installed fleet sees a significant share of event‑MW from just three nuclear reactors: the largest contributor is a 1,065 MW unit that has been offline since 4 May and is not due back until 30 August — a planned outage spanning 118 days. A 1,121 MW unit, Oskarshamn 3, was down for 75 days between 12 April and 26 June, and a 1,172 MW Ringhals unit began a shorter maintenance stint on 1 June.
Together these three concentrate roughly 3,400 MW on a modest fleet. This concentration of a few large, long‑duration nuclear outages means the Swedish system is unusually sensitised to any delay in those return dates, because a small extension — especially for the August‑end Forsmark unit — would cascade through autumn‑winter readiness.
Normalising by installed capacity inverts the leaderboard. Countries with large fleets but spread‑out outages, like Spain and Germany, fall in the density ranking relative to their absolute position, because their large absolute books are spread over large fleets. Conversely, smaller fleets with high outage volumes rise. The structural insight is clear: outage‑book magnitude tracks installed capacity until you control for it, and the countries that look heavily offline in raw league tables are often just the countries with the most generation assets in the first place.
For anyone measuring system tightness, the density ranking is the more relevant metric because it directly indicates the share of capacity that is unavailable — and therefore the proportion that must be met by other sources if demand rises.
The composition of each country’s outage book reveals why these patterns persist. France’s returned outage rows are overwhelmingly nuclear, with a single pumped‑storage exception, confirming the planned, seasonal nature of the refuelling window. Spain’s book is dominated by hydro reservoir and hydro pumped‑storage units, though it also includes some nuclear and fossil gas outages — operating limits often dictated by reservoir levels rather than mechanical work, and typically shorter in duration. Germany’s outages are concentrated in lignite and hard‑coal plants, with some fossil gas units also offline, tending to be smaller unit sizes that dilute the density. Sweden’s key outages are nuclear with long durations (75–118 days), amplifying the overall impact.
Because nuclear refuelling is a routine summer activity across Europe, the French and Swedish numbers do not signal a behavioural anomaly. But the fuel‑mix difference matters for market participants: a hydro‑driven outage in Spain will resolve as water levels change, often with less market‑notice rigidity, while a nuclear long‑duration outage in Sweden creates a fixed, multi‑month supply reduction that traders and system operators must schedule around.
Track whether France’s largest units clear on schedule — the 1,500 MW unit due 24 June, the 1,498 MW unit the same day, the 1,220 MW unit due 4 July, and the 1,080 MW unit due 31 August. Any extension of these planned returns would immediately increase the residual‑load burden during a period when cooling demand can spike.
Track Sweden’s 1,065 MW Forsmark outage, currently slated to end 30 August. If that 118‑day outage extends beyond August, Sweden’s outage concentration widens further, and the Nordic balance tightens into autumn, a period when hydro resources typically ebb and nuclear availability becomes critical. For traders, a delay here would alter the shape of the Nordic prompt spread and firm‑capacity margins; for regulators, it would concentrate scrutiny on the remaining dispatchable capacity.