The fire at reactor number one occurred late Sunday. It was rapidly put out and the reactor was shut down immediately, the newspaper said.

Officials at Rivne were not available to comment on the report as Tuesday was a bank holiday in Ukraine.

The Interfax-Ukraine news agency on Monday reported the shutdown but said it was caused by a breakdown in a transformer.

A commission has been set up to investigate the causes of the fire, Segodnya said.

The reactor will be reactivated in the next few days after the transformer has been repaired, Interfax reported.

The plant has three VVER-440 heavy water reactors. A fourth block is currently under construction and is expected to come onstream later this year.

Ukraine's four nuclear power plants provide roughly half of its power requirement.

In April 1986 a reactor at the Chernobyl nuclear power plant in northern Ukraine caught fire, causing the world's worst nuclear disaster.

The plant was closed down in December 2000 after the international community offered substantial financial aid.

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