Japanese workers entered the No. 1 reactor building at the crippled Fukushima Dai-ichi nuclear power plant yesterday for the first time since a hydrogen explosion ripped off its roof a day after a devastating March 11 earthquake and tsunami.
High radiation levels inside the building had prevented staff from entering to start installing a new cooling system to finally bring the plant under control, a process plant operator Tokyo Electric Power (TEPCO) has said may take all year.
The magnitude 9.0 quake and massive tsunami that followed killed about 14,800 people, left about 11,000 missing and destroyed tens of thousands of homes.
It also knocked out all the cooling systems at the Fukushima plant, 240km north of Tokyo, leading to the greatest leak of radiation since the 1986 Chernobyl disaster.
Two TEPCO staff and 10 contractors with protective suits, masks and air tanks worked for an hour-and-a-half, moving in and out in small groups to connect duct pipes to ventilators that will filter out 95 percent of the radioactive material in the air, a company spokesman said.
“We will operate the [ventilators] for about two or three days. After that, we plan to start work on actually installing the cooling system,” spokesman Naoyuki Matsumoto said.
The nuclear safety agency later said the ventilator system and filters were running.
TEPCO said the workers who did the work were expected to have been exposed to about 3 millisievert of radiation each in the operation.
Under Japanese law, nuclear plant workers cannot be exposed to more than 100 millisievert over five years, but to cope with the Fukushima crisis, the Japanese health ministry raised the legal limit on March 15 to 250 millisievert in an emergency.
Radiation of up to 49 millisievert per hour was detected inside the building on April 17.
TEPCO also said in a report issued to the nuclear safety agency yesterday that there was no possibility of another hydrogen explosion at the No.1 reactor because of progress in filling the containment vessel, an outer shell of steel and concrete that houses the reactor vessel, with water.