An investigation by Tokyo Electric Power Co. has found that efforts to release pressure from a Fukushima No. 1 plant reactor as its fuel melted down likely failed.
Three days after the tsunami on March 11, 2011, engineers tried to vent radioactive steam from the plant's No. 2 reactor to prevent the vessel from rupturing. Radiation levels rose, but the pressure did not fall, the company said Wednesday.
A massive amount of radioactive materials is likely to have leaked from the No. 2 unit after the containment vessel's suppression pool — built to hold cooling water for emergencies and to reduce pressure inside the vessel — was damaged on the fourth day, prompting many workers to evacuate the plant temporarily.
On March 14, Tepco conducted an operation to open the valves of a pipe connected to the container of the No. 2 unit, but the pressure inside did not fall even though radiation levels on the premises of the plant rose.
The probe found no major radioactive contamination inside the pipe, which suggests that the venting failed, the company said.
However, venting operations at the Nos. 1 and 3 units are believed to have succeeded, according to the utility.
The Nos. 1 to 3 reactors at the Fukushima complex all suffered meltdowns following the March 2011 earthquake and tsunami, while the No. 4 was damaged by a hydrogen explosion.