High radiation levels inside the Fukushima Daiichi plant had kept workers out until Thursday's re-entry [Reuters]

Workers have entered the Unit 1 reactor building of Japan's damaged Fukushima Daiichi nuclear plant for the first time since a hydrogen explosion hit the facility a day after the devastating March earthquake and tsunami.

Twelve staff members stepped in to install duct pipes to six ventillation machines that will filter out the radioactive material in the air, Tokyo Electric Power Company (TEPCO), the plant operator, said on Thursday.

"Groups of four will go in one by one to install the ducts. They'll be working in a narrow space," Junichi Matsumoto, TEPCO's spokesman, said.

High radiation levels inside the plant have kept workers from entering the facility to repair the plant's cooling systems. No one has entered the reactor building since the March 12 explosion.

TEPCO has said it may take a year to bring the nuclear plant back up to speed.

The workers, equipped with protective suits, masks and air tanks, went through a special tent set up at the entrance to prevent radiation leaks.

They will work for 10 minutes inside the building. The operation is expected to take about four or five days.

The Fukushima Daiichi nuclear power plant has been releasing radioactive materials since the magnitude 9.0 earthquake and tsunami hit northeast Japan on March 11.

More than 14,000 people have so far been confirmed dead, while another 12,000 remain missing and are presumed dead.

Source: Agencies