UPDATE 1-Czech CEZ says Temelin 1 reactor shuts down again

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PRAGUE, April 26 (Reuters) - Temelin, the Czech Republic's biggest power station, shut down its 1,000 megawatt Unit 1 due to a pump failure early on Thursday, several hours after re-connecting it to the grid, the plant's owner CEZ said.

The reactor was linked to the power grid as originally planned on Wednesday afternoon after a pump repair, but a new pump failure following a false power protection signal triggered another outage, a Temelin spokesman said in a statement.

"Technicians are currently changing the power protection systems on the pump and will afterwards run tests and start preparations for a renewed start-up of the first bloc," said spokesman Vaclav Brom.

He added the reactor was tentatively expected to come back online on Friday but a restart schedule had yet to be confirmed.

Temelin has suffered several outages on the Unit 1 following a re-launch in early April after a fuel exchange.

CEZ operates two 1,000-megawatt reactors at Temelin, which is near the Austrian border in south of the country.

The Unit 2 was running at full capacity on Thursday morning.

Temelin is the biggest asset of state-owned CEZ , Europe's second largest power exporter after France's EDF . The station accounts for 16 percent of CEZ's installed domestic capacity.