Krsko output restored to 680 MW as Sava cools; southern Europe's nuclear squeeze eases
Slovenia's Krsko plant returns to 90% capacity after heat-driven cuts, as river temperature restrictions prove a recurring summer constraint on European nuclear supply.
Slovenia's 700 MW Krsko nuclear plant raised output from 560 MW to 680 MW, or 90% of capacity, on Friday (2026-08-14) as the Sava river cooled, operator Nek said. The plant had been running at a 20% reduction since the week of 2026-08-03, when exceptional river temperatures and low water levels forced the operator to comply with environmental restrictions on water use.6
The restoration illustrates a pattern that complicated power supply across southern Europe this summer. Krsko was one of several nuclear units throttled or shut by heat, a vulnerability grid operators are now pricing into power markets during peak demand periods. The unit returned just as the regional system emerged from a stretch of forced outages that tested balancing reserves.6
The heat-induced cut was severe enough that Slovenia's government ordered the plant to remain online at minimum safe output until Wednesday (2026-08-12) to support grid stability. That order, reported by Montel, came after Nek announced the 20% reduction. Hourly output stood at around 520 MW at the time, according to TSO Eles data. The government chose minimum operation over a full shutdown, keeping some power flowing while the grid ran short of normal baseload.4
The pattern is not isolated to Krsko. Romania's Cernavoda plant lost 1.3 GW of stable generation when a faulty transformer forced the shutdown of the 650 MW Unit 2 on Monday (2026-05-18), coinciding with scheduled maintenance on the 650 MW Unit 1 that started on 10 May and was slated to last until 7 July. Analysts said the double outage pushed Romania's system "to its limits" and produced significant morning and evening price spikes. Entso-E data showed the Unit 2 outage would last until 1 June.1
Hungary faced a similar problem weeks later. The Paks nuclear plant, the country's only nuclear facility, was expected to resume production as early as Monday evening (2026-08-10) after rain lifted Danube water levels, Prime Minister Peter Magyar said. One turbine was being switched back on after the plant was throttled amid low river flows.5
What all three episodes share is the mechanism: river temperature and water level restrictions, not equipment failure, are the binding constraint on nuclear output during summer. The plants are technically available but environmentally limited. That distinction matters for traders because it changes how quickly output can return. A transformer fault takes weeks to fix; a river that cools can restore capacity in days. Krsko's rapid return from 560 MW to 680 MW, just two days after the government's minimum-output order expired, shows how fast conditions can shift.4,6
The timing of these constraints is also shifting. European nuclear plants have traditionally scheduled refuelling and maintenance for summer, when demand is lower. But the 2026 season has shown that heat now strikes during what should be the shoulder period, compressing both maintenance windows and thermal limits simultaneously. Cernavoda's Unit 2 failure arrived right as Unit 1 was in its scheduled outage, leaving Romania with no room to manoeuvre.1
ICE Endex TTF front-month gas stood at €63.41/MWh in the European morning session on Thursday (2026-08-20), flat on the day. The absence of a sharp move following Krsko's restoration suggests the market had already discounted the return before it was confirmed.6
Beyond the immediate restoration, fuel supply adds a longer-run layer of uncertainty. US regulators approved license renewals for the 759 MW Robinson Unit 2 in South Carolina through 2050, according to ZeroHedge. Urenco is privately building a new enrichment plant amid a widening supply gap, having signed contracts with EDF's French and UK fleets, described by Urenco as its largest ever. A LucidCatalyst study commissioned by Urenco, published at COP30 in November 2025, found small modular reactors could serve up to 700 GW of industrial demand in Europe and North America by 2050, worth $0.5 trillion annually. The top five sectors alone represent more than 75% of that opportunity, led by synthetic aviation fuels at 203 GW. The study's authors concede the 700 GW figure is a ceiling, achievable only with mass manufacturing rather than bespoke construction.2,3
Krsko is back at 680 MW. The next heatwave will reimpose the same environmental limits. Whether 2026 proves an outlier for summer nuclear output in river-dependent southern Europe or an early signal of a more persistent constraint is what traders will be watching as the season extends.3,6