"We need to change a part of the fuel casings in order to limit geometric alterations," said Jiri Borovec, production director at the Czech electricity company (CEZ), which runs the plant in the southwest.

Temelin's two reactors are now both facing technical problems with their fuel mechanisms, with some of the casings for fuel rods deforming in the first reactor and a failure of waterproofing in the second.

The unscheduled shutdown of Temelin's first reactor will last 55 days, Borovec said, adding that it will not reduce the nuclear site's safety.

The news will be "markedly negative for stakeholders" of CEZ, Global Brokers analyst Tomas Kanka said in Prague on Wednesday. He added that the shutdown could cost 12 million koruna (427,250 euros or 316,592 dollars) per day.

The Temelin plant has encountered a series of problems that have caused it to shut down its reactors since it came into service in October 2000, notably in its secondary non-nuclear circuit.

Environmentalists from Austria, where all nuclear plants were closed in 1978, have strongly objected to the Temelin reactors which are situated 60 kilometres (40 miles) from its border. Protests have centred on environment and safety fears.

Construction at Temelin started in 1987. The initial plan included four thousand-watt Soviet reactors, but was cut back to two after the end of the Communist regime in 1999.

CEZ (Ceske Energeticke Zavody) announced the same day in Prague that in the first nine months of 2006 it made net earnings of 22.02 billion koruna (785 million euros or 1.005 billion dollars) against 14.58 billion koruna (520 million euros or 665 million dollars) for the same period in 2005.

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