A 1,000-megawatt reactor at Bulgaria's Kozloduy nuclear plant was temporarily shut down early Saturday due to a turbogenerator problem, but no rise in radioactivity was recorded, a statement said.
"Unit 6 of the Kozloduy plant was shut down by the turbogenerator's protection system," the plant said, adding: "No change in the level of radioactivity has been registered."
The unit was to be restarted by the end of the day.
Kozloduy, Bulgaria's sole nuclear power plant, has two 1,000-megawatt reactors supplying about 30 percent of the country's power.
Four older 440-megawatt reactors at the plant were shut down in 2002 and 2006 as conditions for Bulgaria's entry into the European Union.
Explore further: Solar plane starts next round-the-world leg in China