According to hidden data, the Paks NPP has repeatedly heated the Danube above environmental limits

The Paks Nuclear Power Plant has persistently strived to conceal the data measured by the line of buoys we found in the Danube a year and a half ago near the power plant. The results we have now found out confirm our previous experience: the water temperature has several times exceeded the legal limit of 30 degrees Celsius set to protect the Danube’s wildlife. The regulation was relaxed by Parliament this year. The importance of the issue has been also indicated by the authorities, in relation to the lifetime-extension of the nuclear power plant.

On 19 July last year, we spotted a line of buoys in Paks, at the spot where the regulation requires to measure whether the Danube is warming above 30 degrees Celsius. On the shore, young men were monitoring the equipments from their laptops. We tried to get them to talk, but they were just staring in front of them in silence. After our repeated attempts, they finally told us that they could not say anything.

We then asked everyone who potentially had any information about the buoys, but received no substantive information. After two freedom of information requests, a parliamentary interpellation and two visits in the power plant, we finally found out that the measurements were carried out on behalf of the Paks NPP.

The assignment was awarded to Inno-Water Zrt. through a public procurement procedure. Their task is to inspect the cold water and hot water channels of the Paks Nuclear Power Plant, the associated water systems and the Danube, to do measurements, to carry out maintenance and calibration tasks, to evaluate data and to prepare reports. The work will assess the consequences of additional hot water emissions of the planned new nuclear units (Paks II) and prepare for future critical periods. Total contract value: HUF 250 million (around EUR 610,000).

Although we have not received the requested data and reports, finally we were allowed to inspect some of them – on paper – at the plant.

In the documents provided, we found the data recorded by the measuring buoys between 17 and 19 July 2023. According to the diagrams there were several periods when the water was warmer than the permitted 30 degrees Celsius. (We were allowed to take a few photos on site, but the quality of the pictures is rather poor due to the conditions. We will publish the data if we receive them in electronic form.)

The graphs show how many degrees warmer the water was below the nuclear power plant, after the warm water was discharged, compared to the Danube’s base temperature.

On 17 July, in the evening hours, between about 6 pm and 9 pm, several buoys measured a temperature rise of more than 4 degrees Celsius. As the base temperature of the Danube was 26 degrees Celsius during this time, it means that, according to the charts, the water at the buoys was warmer than the permitted 30 degrees Celsius. The situation was similar on 18 July in the morning hours: between about 7 and 11 am, some buoys also recorded a warming of around 4 degrees Celsius, compared to the Danube temperature of 26.2 degrees Celsius. It was mainly buoys closer to the shore that recorded higher values.

The warm current stays relatively close to the right bank of the Danube, and only drifts slightly towards the middle of the river. This is partly the reason why the water is warmer near the shore, and partly because it is shallower and therefore warmer. The buoy line extended up to 177 metres towards the centre of the midden, and the warmest values were typically measured by the buoys at 16, 24, 32 and 41 metres.

At 4 pm on 18 July, the plant’s output was reduced by 320 megawatts, which helped the situation, however the charts show that even in the early afternoon of the next day, 19 July, some buoys still recorded a warming up to around 4 degrees Celsius, compared to the background temperature of 26.1 degrees Celsius. At 3 pm on 19 July, further capacity reduction was made at the plant.

We were also in Paks on 19 July and measured the temperature of the Danube at around noon and 5 pm, using a simple handheld water thermometer. At both times we observed water temperatures above 30 degrees Celsius, again mainly at points closer to the shore.

This happened last summer, and this year the parliament passed an amendment to the law that allows the Paks nuclear power plant to exceed the water temperature limit for “security of supply reasons”, with the permission of the Minister of Energy.

The 30 degrees Celsius limit is set to protect the Danube’s wildlife

The preliminary consultation document related to the environmental impact assessment of the Paks NPP’s lifetime extension claimed that the impact of hot water discharges on the fish communities is already detectable. There has been a noticeable change in the species at the affected stretch: the number and abundance of invasive species increases, especially in hot years with low water flows. The affected stretch is typically 2 kilometres long, but can double in extremely warm years.

Besides the fish, changes can also be detected in macroscopic aquatic invertebrates e.g. mussels and snails. One of the most important indirect effects of hot water emissions is that a significant proportion of the known macroinvertebrate communities are now invasive, vigorously and aggressively expanding alien species. However, the number of protected species is also high, meaning that these lower stretches of the Danube are outstandingly important to preserve. At the same time, it is noted by the study that the natural value of the area is steadily deteriorating, irrespective of the hot water discharges from the Paks NPP, e.g. due to climate change, human interventions and pollution.

Examining the thermal load of the Danube important for the licensing of the lifetime extension too

The preparatory document was also commented on by the relevant authorities in October 2024.

According to the Lower Danube Valley Water Management Directorate, the environmental impact of the parallel operation of the Paks NPP and the planned Paks II needs to be presented in detail and with up-to-date data during the environmental licensing procedure, with particular reference to the Danube temperature increase and the forecasts. The lifetime extension will significantly increase the duration of the parallel operation of the two plants compared to what was previously planned, thus the impacts will occur over a much longer period, the Directorate claims in its opinion.

The environmental impact assessment documentation to be submitted shall include, in particular, an assessment of the effects of the thermal load on the Danube’s and the directly affected floodplain’s biota, based on updated climatological and hydrological forecasts, according to the Tolna County Government Office. This should include a detailed assessment of the environmental impacts of elements not included in the previous EIA documents of the Paks NPP and Paks II (e.g. the “peak cooling system”). Since a part of the affected area is a protected Natura 2000 site, the impact assessment should also focus on the environmental impacts of the thermal load on the Danube on Natura 2000 species and habitats.

According to the Danube-Drava National Park Directorate, the environmental impact assessment must examine the effects of the cooling water of the Paks NPP and its quantitative, qualitative and temperature changes.

The expert opinions have been requested by the competent environmental authority, the Baranya County Government Office which must ensure their compliance during the environmental impact assessment procedure for the lifetime extension.

Written and translated by Orsolya Fülöp. Cover photo: Átlátszó / Bence Bodoky. The Hungarian version of this story can be read here.