"The delay so far totals a dozen days," plant spokesman Milan Nebesar told AFP, adding that he could not give a date when the reactor would resume the production of electricity.

The second reactor was stopped in September for routine maintenance and changing of fuel rods.

Problems have arisen connected with the water tightness of some fuel casings, Nebesar said. "The problem has occured at Temelin for the first time," he added.

Temelin's fuel is supplied to Czech electricity giant CEZ by US-based Westinghouse. In the 1990's the same company installed security systems at Temelin's two reactors.

According to one Czech newspaper, Lidove Noviny, the latest hitch constitutes "apparently the most serious problem in Temelin's history."

But Nebesar said: "That is the opinion of Lidove Noviny. The same problem of watertighness also occurs in other nuclear power plants in the world.

"We have carried out analysis to work out how the fuel will perform from now on. All the documents have been given to the State Office for Nuclear Security (SUJB), which alone will decide when the reactor can restart," he explained.

The Temelin plant, which started service in 2000, has created fierce controversy in neighbouring Austria, which opted to close down its commercial nuclear power plants in 1978.

Austrian protests centre on the safety of the plant, built according to an original Soviet design with Western security systems added on. Temelin is sited 60 kilometres (37 miles) from the Czech-Austrian border.

Original plans for the plant counted on four reactors but this was scaled back to two. CEZ is currently considering the renewal of its existing power plants with one option being for an extra two nuclear reactors at Temelin to be built.

CEZ is 67.7-percent owned by the Czech state.

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