Radioactive discharges have lower environmental impact than thermal discharges, says Finnish study

6 October 2009

A doctoral thesis by Erkki Ilus of the Finnish radiation and nuclear safety authority (STUK) shows that radioactive discharges from nuclear power plants have a minor impact compared to the effects of thermal discharges.

The results are based on hydrobiological and radioecological analyses from monitoring programmes and environmental studies carried out during more than 40 years in the sea areas surrounding the two Finnish nuclear power plants, Loviisa and Olkiluoto.

Loviisa NPP is located on the coast of the Gulf of Finland and Olkiluoto NPP on the coast of the Bothnian Sea. The sea areas surrounding the two plants differ from each other in many ways. For example, the exchange of water, the nutrient concentrations and the salinity of the water are different. In addition to local divergences, also the amounts of discharges and the way the plants discharge their cooling waters deviate from each other.

However what is common for both plants is that thermal discharges have increased the eutrophication process in the water. Eutrophication is the increase in chemical nutrients, mainly compounds containing nitrogen or phosphorus in an ecosystem. The effects of cooling water discharges on the temperatures in the sea were most obvious in the winter when the conditions most differed from those of the natural state.

Radioactive discharges into the sea from the Finnish NPPs have been clearly under the statutory discharge limits. Small amounts of local discharge nuclides were detected in environmental samples taken from the discharge areas. The discharged amounts of tritium were the most abundant at Loviisa but those of activation products, such as cobalt-60, were higher at Olkiluoto. The amounts of local discharge nuclides in the environmental samples decreased significantly during 1990s and 2000s both at Loviisa and at Olkiluoto.

The radiation doses to the public caused by discharges of radioactive substances from the Finnish nuclear power plants were small. During the whole operational history of the power plants the effective dose commitments of the critical groups have been at their highest less than 4%, and during recent years clearly below 1% of the set limit that is 0.1 millisievert per year. The people belonging to the “critical group” of the highest dose are those who spend a lot of time by the sea and eat abundantly of local fish. Similarly, the impact of the radioactive discharges to the environment was negligible, far below the international screening level set for organisms.

Doctoral Thesis by Erkki Ilus Environmental effects of thermal and radioactive discharges from nuclear power plants in the boreal brackish-water conditions of the northern Baltic Sea is published as a STUK-A 238 report.

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