Biologisk recipientkontroll för Ringhals kärnkraftverk: årsrapport för 2024

Ringhals nuclear power plant is one of Sweden’s main producers of electricity. Due to intake and discharge of seawater that cools the reactors in the power plant, there is an impact on the surrounding coastal environment. This impact is monitored and analysed in a biological recipient control program. This annual report presents the result of the surveys within the control program for 2024. It focuses on the communities of fish and crustaceans, losses of eggs, larvae and fry in the cooling waterways as well as the presence of alien species. During spring 2024, two types of annual sampling were carried out in the cooling water intake channel to monitor the losses of different life stages of fish in the power plant. A Bongo net was used to monitor eggs and larvae, where large flatfish eggs (plaice) and cod were the most common eggs, and sand lance and European flounder were the most common larvae. Sampling in the cooling water intake after juvenile fish and fry is largely focused on the catches of glass eel and is carried out using a modified Isaacs-Kidd-trawl. Herring fry dominated the catches, followed by transparent goby, sand lance fry and glass eel. The effect of the release of cooling water into the sea is monitored by yearly fyke net surveys in three locations: The recipient area of Ringhals, which is directly affected by the cooling water, Vendelsö, used as a reference area unaffected by cooling water, and Norra Horta, which is affected to some extent. To include seasonal variations in water temperature, two surveys are conducted, one in April and one in August. In 2024, the most common fish species was corkwing wrasse, except for April in the partly affected area where cod was most common and in the reference area in April where shorthorn sculpin was the most common. The highest number of corkwing wrasse was found in the partly affected area in August. In general, the occurrence of warm-water species was higher in the recipient area and the occurrence of cold-water species was higher in the reference area. The total catch of shore crab was relatively high in all areas and fishing periods, with a peak in the recipient area in August. The area around the outlet of the water sieving stations exhaust pipe was examined with a ROV (Remotely Operated Vehicle) to visually inspect impact on the sea floor. Discharge and sedimentation of shell parts of mussels and crabs was low, similar to last year. To investigate the presence of marine invasive alien species, a scuba diving survey was conducted in five locations outside of Ringhals: The recipient area of Ringhals, Norra Horta, Vendelsö and two locations in Båtafjorden. Two species of algae alien to the west coast were found during the survey: Gracilaria vermiculophylla and Sargassum muticum, as well as one alien animal species, Magellana gigas. All species have previously been observed along the Swedish west coast. Additionally, brush-clawed shore crab (Hemigrapsus takanoi) was found in April in the fyke net survey at the recipient area, the first observation in the survey but not the first observation in Sweden. Presence of alien species were also surveyed in the Ringhals cooling waterways via one survey in the surge basin T2, and one in the cooling water tunnel R4. These surveys of the cooling waterways resulted in generally fewer species and lower biomass compared to previous years due to the chlorination of the surge basin from April to October since 2023.