The 730 MW Krško nuclear power plant has cut generation after high temperatures on the Sava and low river flows limited available cooling capacity. The reduction extends the effect of summer hydrological stress into the Slovenian and Croatian electricity systems.
Initially, the operator reduced reactor output toward approximately 80% of capacity. The operator also warned that further reductions could be required if river conditions deteriorate further.
Krško’s cross-border role in Slovenia and Croatia
Krško’s operational impact extends beyond Slovenia due to its shared ownership and long-standing cross-border function. The plant supplies about 20% of Slovenian electricity demand and around 16% of Croatian demand.
A sustained derating would therefore affect two national electricity balances at the same time. The plant’s reduction removes a portion of low-variable-cost generation from the Slovenian-Croatian market.
Sava temperature limits and cooling-water constraints
Environmental restrictions are central to the operating decision. The daily average temperature of the Sava after cooling-water mixing is required to remain below 28°C, with additional limits applying to the permitted increase in river temperature caused by the plant.
When ambient temperatures are high and river flow is low, the river’s ability to absorb heat declines. That can force generation cuts even if the reactor remains technically available.
Comparison with Cernavoda and response in Romania
A similar cooling constraint has been reported for Romania’s Cernavoda nuclear station. Both 680 MW units were unavailable because exceptionally low Danube flows reduced cooling-water availability.
Romania restarted nearly 300 MW of coal-fired capacity at Rovinari. Krško has not faced a complete shutdown, but its reduction toward 80% removes meaningful output from the market.
Market timing effects during hot weather
At full 730 MW, an output level near 80% implies that roughly one fifth of potential generation is temporarily unavailable. The exact amount of energy not produced depends on how long and how the restriction is operated.
The impact is described as particularly relevant during hot weather because higher temperatures can increase air-conditioning demand while reducing cooling capability at thermal and nuclear plants. This combination can strengthen consumption at times when some conventional generators may be less able to run at full capacity.
Imports, dispatchable generation needs, and financial uncertainty
No estimate of lost revenue or the duration of the current derating has been provided in the information reviewed.
A reduced Krško contribution can increase reliance on imports, hydroelectric production, and other thermal generation. Solar output can offset part of daytime demand increases, but evening conditions remain more challenging once photovoltaic output falls, with Slovenia and Croatia showing day-ahead price profiles featuring sharp evening ramps.
The financial implications depend on market prices and how long derating lasts. Nuclear plants typically have high fixed costs but comparatively low marginal generation costs, so electricity not produced during higher-price periods can represent economically valuable lost output.
Cooling-system design under changing hydrology
The broader system issue is linked to conditions that can simultaneously lower river flows and raise water temperatures. Such factors challenge operating assumptions based on historical hydrological patterns.
This does not make nuclear generation unreliable, but it increases the importance of cooling-system design, environmental limits, and contingency planning for long-term generation adequacy.
Drought effects across Balkan power operations
Krško remains a key shared electricity asset for two southeastern European countries. Its 730 MW capacity anchors both systems, while stable nuclear output normally helps reduce exposure to volatile wholesale imports.
The current reduction indicates that even low-carbon baseload supply can become weather-sensitive during extreme summer conditions. Across the Balkans, drought conditions are affecting hydro production, nuclear cooling, thermal dispatch, electricity imports, and petroleum transport .
