Low Sava River levels trim output at Slovenia’s Krško nuclear plant, not reactor performance

Electricity exports from Slovenia’s Krško Nuclear Power Plant (NEK) have edged lower in recent weeks, reflecting environmental and operational constraints tied to low water levels in the Sava River. While the change is noticeable at the grid connection point, the plant says it is not the result of any nuclear or mechanical fault.

Output down modestly at the grid connection

Under normal operating conditions, NEK delivers more than 700 MW to Slovenia’s transmission network. Data from the transmission system operator ELES shows that recent output at the grid connection point has decreased to around 690 MW.

Reactor stays at full capacity; cooling efficiency and internal load drive the reduction

The plant operator reports that the reactor continues to run at full 100% capacity. Instead of a technical problem, the lower exported electricity is attributed primarily to increased internal electricity consumption and reduced efficiency in the secondary cooling system.

Cooling depends on river water under strict thermal limits

The situation is linked to reduced river flow caused by limited rainfall. NEK uses river water in its tertiary cooling circuit to dissipate excess heat generated during power production: water is pumped through the condenser system, absorbs heat from steam, and is then returned to the river.

Environmental regulations impose strict thermal limits downstream from Brežice hydropower plant. The average daily temperature of the Sava at a designated monitoring point must not exceed 28°C, and the temperature increase attributable to the plant must remain below an average of 3°C.

Cooling towers and potential generation cuts when limits are approached

As river conditions move toward these thresholds, NEK progressively activates cooling towers to reduce thermal discharge into the river. If those measures are insufficient to keep within regulatory requirements, the facility must also reduce electricity delivered to the grid.

Plant officials emphasized that the current decline in exported power stems from environmental compliance and adjustments within the cooling system rather than any issue with reactor operation itself.