France's public nuclear safety institute IRSN said it had not detected any unusual radioactivity in Ukraine after Friday's accident and that it presented no danger to the nearby population or environment.
"We have two sensors installed on the roof of the French Embassy in Kiev, and the embassy has not signalled anything unusual," Michel Chouha, the IRSN's official representative for Central and Eastern Europe, told Reuters.
Interfax news agency said a 1,000-megawatt reactor was housed in the affected plant block.
European stocks trimmed their gains on Wednesday morning after the announcement and the cost of Ukrainian debt insurance traded sharply higher to a five-and-a-half year high.
Data provider Markit said Ukraine's five-year credit default swaps had opened at 1824 basis points but eased to 1775 basis points by 1145 London time as the government confirmed the incident as a minor one. The contract had closed on Tuesday at 1701 basis points.
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In Vienna, the International Atomic Energy Agency, which must be notified if a nuclear accident poses an international threat, said it had no immediate comment on the incident.
Ukraine, Belarus and Russia estimated the death toll from the disaster at Chernobyl at a few thousand while environmental group Greenpeace says the accident will eventually cause up to 93,000 extra cancer deaths worldwide.
Demchyshyn said the stricken block at Zaporizhzhya had been provisionally disconnected from the electro-energy system though its reactor continued to work normally.
"Its power output is not being used. I think that the problem will be resolved by Friday."
The accident has had a slight impact on Ukraine's energy flow but Demchyshyn said he would ask major industrial consumers to impose a "voluntary restriction" on energy consumption.
Ukraine produced more than 60 million tonnes of coal last year, making it self-sufficient in electricity and coal.
—CNBC.com contributed to this report.
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