Nuclearelectrica had shut down Cernavoda unit 1 and disconnected it from the National Energy System on 28 July “due to the unprecedentedly low level of the Danube, caused by severe drought”.
To redirect water flows, last week the energy ministry used explosives to remove a rock obstruction, dredged the river bed and sank four rock-filled barges, reporting that this raised water levels around unit 2 of the plant by 4 centimetres. “Based on forecasts available at the moment this development allows for the necessary conditions for the reactor to function for at least the next nine days,” the ministry said on 9 August after sinking the rock-filled barges.
However, on the morning of 12 August, the water level in the Danube had reportedly reached 182 centimetres – below the 185-centimetre mark required for the normal operation of the Cernavoda plant. Nuclearelectrica announced it would begin the controlled shutdown of unit 2 at 7.00am on 13 August.
“The controlled shutdown of unit 2 is being carried out in accordance with procedures for such situations, based on strict monitoring of safety margins, equipment, and the INHGA [the National Institute of Hydrology and Water Management] forecast for the coming days,” Nuclearelectrica CEO Cosmin Ghita said in a letter to the Bucharest Stock Exchange. “Depending on how the forecasts for the Danube’s water level evolve, CNE Cernavoda specialists will decide when to restart the nuclear units, prioritising all nuclear safety margins. Keeping both units in a safe shutdown state has no impact on nuclear safety parameters, and therefore on personnel, the environment, or the population.”
The Ministry of Energy noted that the shutdown and disconnection of Cernavoda 2 was completed at 10.53am.
Cernavoda is the only nuclear power plant in Romania and consists of two 650 MWe Candu reactors, generating about one-fifth of its electricity. Unit 1 went into commercial operation in 1996 and unit 2 in 2007.
The Ministry of Energy said that following the shutdown of unit 2, the National Energy System “is stable and activity is proceeding normally. All estimates available at this time show that there are no risks to the constant supply of electricity at the national level.” It added: “By combining available domestic production, imports, hydro and wind resources and reserve capacities, the National Energy System currently has the necessary tools to cover the production deficit caused by the temporary unavailability of the two units at the Cernavoda NPP.”
Hungary acts to ensure water supplies to Paks
In neighbouring Hungary, units 1, 3 and 4 of the Paks plant had to be shut down due to the low water level of the Danube, while unit 2 has continued operating at reduced power.
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Paks (Image: MVM)
On 10 August, operator Magyar Villamos Művek (MVM) said that the slow rise in the water level of the river in recent days had allowed the output of unit 2 – which had operated at 50% capacity for the previous 11 days – to be increased. It gradually started increasing the unit’s output at 6.00pm on Monday and it reached its nominal power at just before 10.30pm that evening.
“Our most important goal is for the unit to operate stably and safely after the load is applied, thus supporting the satisfaction of domestic electricity demand – however, the drought and its negative impact on the low water level of the Danube are not over,” MVM said. “If the water level starts to decrease again, the nuclear power plant will take the necessary steps in a similar way as before, constantly keeping in mind the control principle of ‘safety above all’.”
The Hungarian government announced on 12 August that it was taking action to ensure the supply of cooling water to the reactors from the Danube.
“Following the site visit on Wednesday, the government made two decisions based on the unanimous recommendation of water, energy and defence experts to ensure the cooling water supply of the Paks nuclear power plant even when the water level of the Danube is low,” it said. “The longer-term measure is to build a bottom sill in the riverbed, but if rapid intervention is required, the water level will be temporarily raised with two barges sunk in appropriate places. Given the conditions known, these two measures, complementing each other, are the most effective and safest option for quickly eliminating the problem, and they enjoy the support of all authorities and experts.”
The construction of a weir between the Paks plant and the village of Dunaszentbenedek will begin immediately, it said. “By using 35,000 and then 110,000 cubic metres of stone in the first round, it can be ensured within a few weeks that the water level in the Danube at the cooling channel of the nuclear power plant will not drop below -90 cm, meaning that Hungary’s most important power plant can operate at full capacity,” the government said.
“The design of the bottom sill was undertaken by Hungary’s best engineers, with the involvement of the Budapest University of Technology,” it added. “The Prime Minister entrusted General Pál Kádár, head of the Defence Administration Office, with the coordination and management of the construction. The Minister of Defence assigned about a hundred national guardsmen from Budapest and Szentes to support the works. The bottom sill could raise the water level of the Danube by up to one metre, but at the same time it would not pose any danger during a possible later flood.”
Due to the expected rapid decline in water levels, the government has also decided to place two 80-metre-long barges on standby at Paks as a temporary solution, in parallel with the construction of the weir. If necessary, the controlled sinking of the two barges could raise the water level of the Danube by up to 20 cm in the short term, it said. This will avoid the complete shutdown of the Paks plant until the final weir is completed. The first barge was due to arrive from Mohács on Wednesday, the second on Thursday near Paks. The government said it will decide on Friday whether the data and forecasts available at that time make it necessary to apply the temporary solution.
The cost of the measures is put at about HUF6 billion (USD10 million).
“The necessary works have been planned in such a way that nuclear safety is not compromised,” the government stressed. “Every step of the operation will be carried out based on the plans of water and nuclear experts, with the tightest possible schedule. The necessary licensing procedure will run in parallel with the investment, because according to the water forecast, without external interventions, the water level of the Danube could drop to close to -140 centimetres next week, which threatens to completely shut down the production of the Paks nuclear power plant.”
The Paks plant, 100 kilometres south of Budapest, currently comprises four Russian-supplied VVER-440 pressurised water reactors, which started up between 1982 and 1987 and generate about half the country’s electricity. Construction work has also begun on the first of two new VVER-1200 reactors planned at the neighbouring Paks II site.
