Kyushu Electric Power has shut down operations at its 600MW No 4 unit at its gas-fired Shin-Kokura power plant in Japan.
The unit experienced an automatic shut down of a steam turbine, while generating 400MW of power.
Operations are expected to resume in a week if the damage is minor, reports Reuters.
Kyushu Electric said the breakdown of the unit would not have any effect on its ability to meet electricity demand this year.
One of the three other active reactors at the plant will undergo maintenance by early September, while the other two will be shut by the end of this year.