It is the first time the government has ordered a nuclear reactor to be closed because of a safety violation since 1997.

TEPCO admitted last month that staff had manipulated the air pressure of a container holding the reactor at a plant in Fukushima in northern Japan.

The heavy penalty underscored the view that METI sees the breach as even more serious than TEPCO's earlier admission that it had continued to operate nuclear power plants despite suspecting there were cracks in the reactors' shrouds.

The shroud is a stainless steel cylinder that helps regulate the flow of coolant.

The METI official said it was highly unlikely that the length of the suspension would be shortened.

"The order is that the reactor stop operating for one year," he said.

TEPCO suspended operation of the plant on October 26.

Nine of TEPCO's 17 nuclear reactors are currently closed, accounting for about half of the Tokyo-based utility's nuclear generation capacity.

Following the safety scandals, TEPCO plans to bring forward regular maintenance checks at other nuclear reactors. A further four will be shut down early next year, and two more may be added to that list, which would bring the total to 15.

The power utility has had to turn to thermal power plants to cover the shortfall in supplying electricity.

A TEPCO spokesman said last week no timetable had been set for the resumption of its closed nuclear reactors.