Ukrainian Prime Minister Arseny Yatseniuk said there was an accident at the Zaporizhye nuclear power plant in the Ukraine.
The accident happened at a 1000-megawatt reactor which plays a role in supplying electricity to the country.
According to media reports, officials say there is no threat from the accident, and the accident only affected power output from a reaction. Ukraine is suffering from, among other things, a power crisis, and this may exasperate that situation.
It is expected to go back online in a few days.
In 1986, the Chernobyl reactor, in then Southern Ukraine, melted down.
