Czech power company ČEZ reported that unit 3 at the Dukovany NPP for the first time had achieved a heat output of 1,475 MWt, which is 2.3% more than before and corresponds to an output of 511 MWe under optimal climatic conditions. The increase, which the power engineers achieved safely without any increase in fuel consumption or emissions, corresponds, for example, to three times the power of the hydroelectric power plant at the foot of the Brno dam. As a result, the annual production of the Dukovany NPP should increase by approximately 300,000 MWh next year after modifications to all four units.

Four VVER-440 units are currently in operation at the Dukovany site, which began operating between 1985 and 1987. Two VVER-1000 units are in operation at Temelín, which began operation in 2000 and 2002. Initially, the output of the Dukovany units corresponded to their original designation – 440 MWe. However, 15 years ago, energy companies managed to increase the installed capacity of each of them to 500 MWe through upgrades and the use of reserves. A similar process took place in Temelín, where the power of both units increased from 981 MWe to the current 1,086 MWe.

“Through the modernisation of our nuclear power plants, we have figuratively managed to build a large coal-fired power plant or a smaller nuclear unit,” said ČEZ Board Chairman & CEO Daniel Beneš. “The current increase in performance in Dukovany is part of this trend. Of course, the absolute priority is safety, we would never have taken such a step without confirming the safety parameters.”

The increase in the power of Dukovany 3 was preceded by several years of preparation consisting of detailed calculations and analyses of safety parameters as well as modernisation of technological and safety systems. The current type of fuel is used for operation at increased power. Increasing power means greater heat output of the reactor. The water temperature at the reactor outlet increased by about 2 °C from 298.4 to 300.4 °C.

“Seemingly small parameter changes will bring us hundreds of thousands of megawatts of electricity a year,” explained Bohdan Zronek Board member and Director of the Nuclear Energy Division at ČEZ. “Preparation for high-performance operations required confirmation of safety analyses, but no large-scale investments were required.

Preparations began in 2020 as part of the programme Utilisation of the Potential of the Dukovany NPP. It also included a project, which since 2023 has ensured the transition from an 11-month fuel cycle to a 16-month fuel cycle and the introduction of a new generation of fuel to improve fuel efficiency.

Dukovany NPP Director Roman Havlín said during 2024 similar work would take place at units 1&2. “If we pass all the tests successfully, we would like to increase production by approximately 300,000 MW from next year. But we still have a number of tasks ahead of us,” he noted. Last year unit 4 began using new generation PK3+ fuel supplied by Russia’s TVEL. The new assemblies are designed to make the use of uranium in the fuel more efficient.

TVEL (part of Rosatom) has long been the fuel supplier for both Temelin and Dukovany but from 2024 US-based Westinghouse and the French Framatome will supply fuel for Temelin. However, as yet, only TVEL can supply fuel for VVER-440 reactors, although Westinghouse is in the process of developing such fuel, which is now being tested at Ukraine’s Rivne NPP. Currently Dukovany has TVEL fuel for several years.

It remains to be seen how fuel from other suppliers will affect plant efficiency. Havlin commented earlier: "If we buy it from another supplier, it does not have such a history. This means that the fuel in our country will be usable, it will be safe, but it may have a higher or lower output, we do not know."

Nuclear power currently supplies 34% of the Czech Republic’s electricity. It plans to build up to four new units and is also considering small modular reactors.

Image: Dukovany nuclear power plant