Swiss Nuclear Plant Reduces Output Amid Heatwave

Switzerland’s energy infrastructure is grappling with a critical disruption as the relentless summer heatwave claims its first major industrial victim. The Beznau nuclear power plant, a cornerstone of the Canton Aargau energy grid, has been forced to slash its operations dramatically. In a move that underscores the fragility of our power systems, operator Axpo confirmed on Wednesday that one of its two reactors has been completely disconnected from the grid. The second unit is barely holding on, currently running at a throttled 50% capacity.

This is not a mechanical failure or a safety malfunction; it is a direct consequence of the soaring temperatures gripping the nation. As of July 2, 2025, the plant is effectively operating at a fraction of its potential, sending a stark warning signal across the Swiss energy sector. The reduction began last Sunday when output was halved, but the intensifying heat has now necessitated a full shutdown of one unit. This dramatic curtailment highlights an uncomfortable truth: our energy security is inextricably linked to the whims of the weather, and right now, the weather is winning.

The culprit behind this energy squeeze is the River Aare, which has surged past critical thermal limits. Federal directives are clear and uncompromising: once the river water approaches the 25-degree Celsius threshold, nuclear operations must yield. Axpo is strictly complying with these mandates, which are designed to prevent the ecological collapse of the river system. The plant draws water for cooling and releases it back into the river; discharging hot water into an already feverish river would be catastrophic for local flora and fauna.

The stakes for the environment are incredibly high. Pushing past this temperature limit risks "excessive pollution"—in this case, thermal pollution—that could decimate fish populations and disrupt the delicate aquatic ecosystem near Döttingen. While the lights must stay on, the Swiss Federal Office of Energy (SFOE) has drawn a line in the sand. The protection of biodiversity is taking precedence over maximum energy output, creating a tense standoff between ecological preservation and industrial necessity.

Why is Beznau faltering while other plants remain resilient? The answer lies in a critical design distinction that leaves Beznau uniquely exposed to climate extremes. Unlike its counterparts in Gösgen and Leibstadt, the Beznau facility does not possess cooling towers. It relies entirely on a direct-cycle cooling system using the River Aare. This architectural decision, made decades ago, has become a significant liability in the face of modern climate realities.

Plants with cooling towers can release excess heat into the atmosphere via steam, buffering them against rising river temperatures. Beznau has no such luxury. It must return its cooling water directly to the river, meaning its operational capacity is strictly tethered to the water's ambient temperature. As the Aare warms up, Beznau's ability to generate power plummets. This structural vulnerability exposes a glaring weakness in Switzerland's aging nuclear fleet, proving that infrastructure built for the climate of the past is struggling to survive the climate of the present.