The leak, caused by a water-level measuring problem in a reservoir, was contained within a limited area and did not pose a risk to the environment or to workers' health, according to the spokesman Milan Nebesar.

The problem occurred inside the plant's second block, which had been reconnected to the national grid early Monday after a four-day interruption to allow work to be carried out on a cooling system, Nebesar said.

The European Union had dispatched a team of experts to the Temelin site after 3,000 litres radioactive water leaked from the same block in June this year.

Located just 60 kilometres (40 miles) from the Austrian border, the Temelin plant has been a source of controversy ever since its launch in 2000, with nuclear-free Austria campaigning for its closure.

Its opponents say the plant, which was launched in the mid-1980s under the communist regime, is not safe because it combines Soviet design with Western fuel and safety technology.

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