Restarting Hungary’s Paks Nuclear Power Plant could take up to a week if all four reactor units are shut down simultaneously, according to the plant’s Deputy CEO for Technical Affairs. The unprecedented situation is expected due to the record-low water level of the Danube, which has reduced the availability of cooling water.
Speaking to the Hungarian News Agency (MTI), László Nagy said that while shutting down an individual reactor is a relatively straightforward procedure, restarting the plant becomes significantly more complex if all four units have been out of operation for weeks.
A situation never seen before at Paks
Nagy explained that reactor shutdowns and restarts are routine at Paks, as each of the plant’s four units is taken offline roughly once a year for scheduled maintenance and refuelling.
However, this has never happened to all four reactors at the same time.
Under normal circumstances, the remaining operating reactors provide the steam needed to reheat equipment in the reactor being restarted. This process usually takes one to two days before the reactor can begin its physical start-up, followed by another one to two days before the unit reaches full generating capacity.
If every reactor has cooled down, however, there is no neighbouring unit available to provide auxiliary steam, making the restart of the first reactor much more complicated and considerably slower.
External electricity needed to heat the first reactor
Nagy recalled that when the plant first entered service, dedicated boilers were used to start the initial reactor. This time, following the anticipated shutdown, the plant will instead use its own existing equipment together with externally supplied electricity to heat the first reactor to the required operating temperature.
Once the reactor reaches the necessary temperature, the standard start-up procedure can begin. According to Nagy, the entire process of bringing the first unit back online and restoring operations could take up to one week.
Restart depends on Danube water levels
Even if heavy rainfall occurs across the Danube catchment area, the restart process cannot begin immediately. Nagy stressed that the plant can only begin reheating equipment once there is sufficient cooling water available at the Paks site itself. Until the Danube reaches an adequate water level, the restart procedure cannot even start.
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Gradual shutdown expected next week
Based on current water level forecasts, one of the two reactors still operating is expected to begin a gradual shutdown on Sunday evening. From Monday, only one reactor is expected to remain in operation, and even that unit will likely run below its nominal capacity, as only one of the eight pumps supplying cooling water from the Danube will remain operational.
According to the current forecast, the output of the final operating reactor will then be progressively reduced before it is shut down entirely around the middle of next week.
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