IN Brief:
- Both 650MWe Cernavodă reactors remained in a safe shutdown state on 29 October.
- An approximately 10cm rise at the cooling-water intake has not satisfied restart criteria.
- Nuclearelectrica requires sustained higher water levels and favourable forecasts before either unit reconnects.
Nuclearelectrica is keeping both reactors at Romania’s Cernavodă nuclear power station in a safe shutdown state after a modest improvement in Danube water levels failed to satisfy the conditions required for restarting generation. The operator recorded an increase of approximately 10cm in the level measured at the plant’s pump intake basin, but its 29 October assessment found that the rise was localised and had not yet developed into a sustained improvement across the upstream river basin.
The water level at the intake remains below the threshold regarded as necessary to reconnect either unit. Nuclearelectrica requires the appropriate level to persist for several days and show an upward trend before it can make a restart decision. Forecasts available to the operator on 29 October did not indicate that all those conditions would be met, leaving the two units disconnected from Romania’s national electricity system while hydrological monitoring continues.
Cernavodă is Romania’s only nuclear generating station, with two CANDU reactors each rated at approximately 650MWe. Together they normally account for around one-fifth of the country’s electricity generation. Unit 1 was shut down in a controlled operation on 28 July as the Danube fell to unusually low levels during severe drought. Unit 2 followed in mid-August after the river continued to recede, removing the station’s normal contribution to the national power balance.
Cooling water availability affects the ability to reject the large quantities of waste heat associated with electricity generation. When a reactor is producing power, steam generation and conversion to electricity depend on a thermal cycle in which heat must eventually be removed through the station’s cooling arrangements. Intake pumps, hydraulic conditions and the temperature and availability of the water supply all form part of the operating envelope. A temporary rise at one measurement point therefore does not, by itself, establish conditions for sustained full-power operation.
The controlled shutdown preserves the reactor safety functions that remain necessary when electricity generation has stopped. Cernavodă has multiple cooling systems designed to work at different cooling-water levels, with arrangements selected according to their technical parameters. The station’s redundant cooling provisions and operating procedures therefore need to be considered separately from the river conditions required to resume power production. Nuclearelectrica says the units remain in a safe state while its technical teams monitor the intake and cooling systems.
Romania’s nuclear regulator, CNCAN, has monitored the prolonged low-water conditions and confirmed that the reactors were shut down preventively in accordance with operating procedures. The regulator recorded the controlled shutdown of Unit 1 on 28 July and Unit 2 on 13 August, with no radiological consequences for the population or environment. The station’s operating limits protect safety margins while generation remains suspended below the river-water threshold.
The 10cm intake-level increase improves the latest local measurement, but upstream conditions and forecasts still do not indicate a sustained recovery. Nuclearelectrica has said it will request reconnection as a priority once the necessary water level has been maintained for several days and is trending upwards. That decision will be based on continued observations at the intake and the wider river basin, alongside the technical criteria governing each unit’s safe return to generation.
The lengthy absence of nuclear generation has increased Romania’s dependence on other power sources and cross-border trade. Net electricity imports accounted for around 16.3% of national demand in October to 26 October, compared with 1.7% in the corresponding period a year earlier, according to electricity market figures. Nuclear generation ordinarily supplies a substantial, relatively steady share of Romania’s electricity, so restoring Cernavodă would reduce the volume that must be obtained from other domestic generators and imports. Until reconnection, grid planners must retain replacement supply arrangements.
The low Danube conditions have also affected nuclear operations elsewhere in the region. Hungary’s Paks plant encountered water-level restrictions during the summer and subsequently returned to full operation following engineering measures, while Bulgaria has examined measures to protect plants against future low-water conditions. Cooling-water intake arrangements, river hydraulics and operating limits differ between sites, resulting in different restrictions and engineering responses along the river.
Nuclearelectrica continues to monitor hydrological forecasts and the intake basin with the relevant authorities. The operator has committed to seeking reconnection as soon as the required conditions are sustained, and it will disclose changes to the station’s status under its stock-market reporting obligations. Both units remained safely shut down at the 29 October update, with the timing of any restart dependent on the Danube’s subsequent behaviour and the plant’s operating procedures.
