A hydrogen leak in one of the heat exchangers of the Loviisa nuclear power plant’s second unit has led to a reduction in generation capacity, forcing operator Fortum to cut output to 50%.
While the fault has been isolated and repair work is underway, the incident underscores the operational challenges of aging nuclear infrastructure undergoing life-extension upgrades.
The leak was detected on Saturday evening after an increase in the generator’s hydrogen consumption—an early indicator of system abnormality in power plant cooling systems. Hydrogen is used to cool the generator due to its high thermal conductivity, but leaks can present both technical and safety risks if not promptly contained. In this case, the leak was traced to one of the unit’s four heat exchangers and was swiftly isolated. Fortum estimates the repair will take two days.
Although Fortum emphasized that the incident poses no danger to personnel, the environment, or the facility, the event occurs during a broader modernization program that aims to extend the plant’s lifespan to 2050. The €1 billion investment plan covers critical system upgrades, including aging mechanical infrastructure like the 43-year-old second unit, commissioned in 1980.
The temporary derating of Unit 2 has immediate implications for Finland’s electricity grid. Loviisa contributes approximately 10% of the country’s total electricity supply. Although Unit 1 remains unaffected and is operating normally, any reduction in base-load nuclear power—particularly during periods of high demand or constrained supply—can pressure spot prices in the Nord Pool market and trigger greater reliance on fossil backup or imports. Fortum has stated that it will continue to update the electricity market in line with regulatory obligations.
The operator noted that a similar hydrogen-related issue last occurred in 2015, highlighting the long maintenance intervals typically associated with nuclear facilities. However, such incidents—though infrequent—serve as a reminder of the fine operational margins in nuclear power plants, where minor component failures can have disproportionately large effects on generation.
The Loviisa nuclear plant is among the few in Europe still planning for long-term operation beyond the 2040s, bucking a broader trend of decommissioning. However, life extension comes with inherent technical debt, particularly in systems like hydrogen-cooled generators where component aging may outpace maintenance schedules. Continuous upgrades and real-time monitoring will be essential to avoid further capacity disruptions, especially as Finland’s energy system undergoes decarbonization and increased electrification.
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