TOKYO — Japan's nuclear safety agency says workers have entered the reactor building of Unit 1 at the damaged Fukushima Daiichi nuclear power plant for the first time since right after the March 11 earthquake.
The plant's operator Tokyo Electric Power Co. said workers were installing six ventilation machines Thursday in an attempt to absorb radiation from the air inside the building. The work is expected to take about four or five days.
TEPCO said 12 staff members equipped with protective suits, masks and air tanks would go through a special tent set up at the entrance to prevent radiation leaks.
They will then spend about 10 minutes each inside connecting eight duct-pipes to ventilators that will filter out the radioactive material in the air.
"Groups of four will go in one by one to install the ducts. They'll be working in a narrow space," TEPCO spokesman Junichi Matsumoto told reporters at a news conference.
The decision to send the workers in was made after robots last Friday collected fresh data that showed radiation levels had fallen in some areas of the reactor, said Taisuke Tomikawa, a spokesman for TEPCO.
Two workers entered the reactor building around 11:30 a.m. local time.
"This is an effort to improve the environment inside the reactor building," Tomikawa said.
The high radiation levels inside the building had prevented workers from entering to repair its cooling systems, and TEPCO has said it may take the rest of the year to bring the nuclear plant back under control.
The workers are expected to be exposed to about 3 millisieverts of radioactivity in the 10 minutes they will spend in the building, Matsumoto said.
Under Japanese law, nuclear plant workers cannot be exposed to more than 100 millisieverts over five years, but to cope with the Fukushima crisis, the health ministry raised the legal limit on March 15 to 250 millisieverts in an emergency situation.
Radiation of up to 49 millisieverts per hour was detected inside the building on April 17 when the company sent in a robot.
The magnitude 9.0 quake and massive tsunami that followed on March 11 killed about 14,800 people, left some 11,000 missing and destroyed tens of thousands of homes.
It also knocked out all the cooling systems at the Fukushima plant, 150 miles north of Tokyo, leading to the greatest leak of radiation since the 1986 Chernobyl disaster.
Workers have not gone inside the reactor building since it was damaged by a hydrogen explosion on March 12.
Tepco plans to cool the reactor by filling the containment vessel with water, the Japan Times reported Thursday.
However, workers must first verify that the water gauge in the pressure vessel and the pressure gauge in the containment vessel are working properly.
Tepco is unsure if readings are accurate, the Japan Times said.Tsunami debris: Mountain of a challenge for Japan
The ventilation should be completed by Saturday, when Tepco plans to set up air coolers outside the reactor building to cool the water filling the containment vessel of the reactor.
If the new cooling system works as planned, Tepco said the temperature in the reactor will drop to under 100 degrees, achieving cold shutdown, within several days.
People living within a 12-mile radius of the plant were evacuated and banned from returning home on April 21 due to concerns about radiation levels.
The Japanese government and TEPCO have come under fire both at home and abroad for their handling of the crisis.
Angry families at an evacuation center shouted at TEPCO President Masataka Shimizu when he visited on Wednesday, telling him to kneel down and apologize.
"I could live with this if it was all caused by the natural disaster, but this is a man-made disaster and we have to pay for it," one man said.
"You told us for years that nuclear energy was safe. We believed you. Now look where we are," said another.
Reuters and The Associated Press contributed to this report.