It means 'handed over' here. So whoever controls it now will no longer control it. It will belong to (or at least be controlled by) the state.

Hi there Sasha. It essentially means that Onkalo will be closed and handed over to the government/state.

'turn' is a very flexible and confusing term that changes radically depending on the preposition turn over - transfer control - "I'll turn it over to you" turn up - to arrive - "they didn't turn up until after dinner" turn down - to refuse - "I had to turn down the job" turn down (service) - to make a bed - "The hotel provides turn down service" turn in - to go to bed "I'm tired, I'm going to turn in" turn in - to hand over "I turned in my homework early" turn out - to get results - "That cake turned out great" turn out - crowd size - "There was a huge turn out for the opening" turn off - to have a negative reaction - "The book was a turn off" turn off - exit ramp - "Exit the second turn off and make left" turn on - to be excited - "Flying is a turn on" turn into - become - "This turned into a good party" turn around - the time it takes to finish a job - "the turn around for the remodel should be a week"