Does Kozloduy NPP need a new steam generator and what are the options?

The accident at the 6th unit of the Kozloduy NPP has already raised the question of whether the Bulgarian nuclear plant needs a new steam generator after the problem has occurred several times in recent years. There’s also the question of where another one can be found as a replacement.

The country’s Acting Minister of Energy, Vladimir Malinov, spoke to the Bulgarian Parliament on the subject on Thursday, explaining that due to the frequent accidents, it may be necessary to replace the steam generator at the plant. It became clear that one of the options was to use one of the generators delivered for the abandoned Belene NPP project as a replacement.

Belene NPP equipment

However, there is no clear answer as to whether the steam generators from the equipment purchased for Belene NPP can be used for our 6th unit,” Valentin Nikolov, the executive director of Kozloduy NPP, told Economic.bg.

In 2023, the task force for the sale of the equipment for the Belene NPP twice requested an opinion from the Kozloduy NPP on the possibility of steam generators being used in the operating nuclear power plant, but the two answers received were contradictory, Malinov explained in the National Assembly.

In every report, we say that we need this equipment as a reserve, because we expect this equipment to work for another 30 years, and it has already been working for that long, Nikolov explained.

We must have at least one steam generator as a backup," he emphasized.

A sound engineering analysis needs to be done regarding this possibility, but Nikolov said that the plant does not yet have the necessary documentation because the country’s National Electricity Company (NEK) is worried about providing it without permission from the manufacturer.

However, changing the steam generators would be very complicated, and the reason is that the ones in Kozloduy NPP are horizontal. For comparison, the American-made ones are vertical, and their replacement is easier.

In addition, at Kozloduy NPP, the steam generators are surrounded by other equipment. They got installed vertically, but they are brought out horizontally, which requires a good justification of the dimensions in the eventual installation of a new steam generator, explained Nikolov.

First of all, we need to answer the question of whether a third steam generator can be changed specifically because there is a small difference in size between those meant for Belene NPP and those in Kozloduy NPP.

In the end, the minister was also adamant that a thorough analysis and external expertise would be required regarding the applicability and possibility of using the steam generators from Belene NPP in Kozloduy NPP.

What’s more, the steam generators are part of the equipment which Bulgaria is negotiating with Ukraine for sale. On Friday, the Bulgarian Socialist Party (BSP) submitted a decision to the National Assembly to suspend negotiations and actions on the sale of the equipment intended for the Belene NPP.

The Russian options

The manufacture and delivery of a new steam generator from the Russian Federation will take about four to five years, and it will be necessary to conclude a contract with a Russian organization for the preparation of a working project for the replacement, Malinov explained during the hearing. At the moment, the Bulgarian nuclear power plant does not have confirmation from another manufacturer for the design, manufacture and supply of a steam generator.

Nikolov confirmed that the only alternative option for producing one remains in Russia, as the other option, which was for the Czech Republic to make it, is no longer possible.

For now, the problem is manageable

The leaks from the 6th unit of the Kozloduy NPP, which was stopped for early repairs, have not yet been plugged, there are still several problem pipes, where the plugging process is now beginning, Valentin Nikolov told Economic.bg.

At the moment, the 3rd steam generator does not need to be replaced", he assured.

On June 15, the unit was stopped for planned preventive maintenance due to malfunctions of the oil system of the 24/400kV unit transformer (the non-nuclear part of the unit) found during operation, as well as indications of a coolant leak in a steam generator.

"At the time when they first installed it, there was an area that wasn't made well, there was a problem with the heating, but it nevertheless managed to function for 30 years somehow," explains the director of the plant.

The only way to deal with this problem is to block the pipes, but before this is done, they must be identified, added Nikolov.

At the moment, there is a blockage of less than 1%, and in fact the project documentation says that everything will still be fine with up to 5% of that issue, that is, we still have a lot of opportunity to plug," says the director of the plant.

However, it is not clear when the 6th unit will be back in order, and both Malinov and Nikolov did not commit to a time frame for its re-launch.

Translated by Tzvetozar Vincent Iolov