Japanese workers entered the Fukushima No. 1 power plant Thursday for the first time since the complex was damaged by the March 11 twin disasters of earthquake and tsunami, Tokyo Electric Power Co. (TEPCO) officials said.

As part of efforts to install a cooling system at the No. 1 reactor, workers entered the reactor building to remove air contaminated with radioactive substances from inside the reactor building by connecting it to a ventilating device installed at the adjacent turbine building.

Twelve workers with protective suits, masks and air packs will operate for about 40 minutes within the reactor building to connect it to the ventilator with eight pipes, according to Kyodo News.

High radiation levels inside the building have so far prevented workers from entering it. Radiation up to 49 milisieverts per hour was detected inside the reactor building on April 17 during a survey using a robot.