1 Mars 2012
March 1, 2012
It has been nearly a year since the Great East Japan Earthquake and tsunami triggered the triple meltdown at the Fukushima No. 1 nuclear plant. How did this man-made disaster happen?
The government Investigation Committee on the Accident at the Fukushima Nuclear Power Stations stated in a midterm report released in December last year that, first and foremost, the actions taken to protect the reactors from danger were not appropriate.
For instance, in the opening hours of the crisis, the report claims that Fukushima No. 1 plant manager Masao Yoshida and his staff failed to properly grasp the condition of one emergency cooling system called an isolation condenser (IC). The report furthermore pointed to the clumsy handling of water injections into the No. 3 reactor. The cores in both these reactors melted down, and both reactor buildings were blown apart by hydrogen explosions -- No. 1 on March 12, 2011, and No. 3 on March 14.
"March 11, 4:42 p.m.: Water level in No.1 reactor dropping," reads the plant event log on the day the disaster began. "Same day, 5:50 p.m.: Radiation rising around No. 1 reactor building."
After the No. 1 reactor lost power, it is possible an IC system valve was stuck closed, and there were plenty of signs that it was not working properly. Both staff on site and the headquarters of plant operator Tokyo Electric Power Co. (TEPCO), however, believed the valve was functioning until 11:50 p.m. This misinterpretation was at least partially responsible for the dispatch of firefighters to pump water into the reactors from outside, and the late venting of gas building up inside the reactor structures.
But why didn't the TEPCO workers understand that the IC valve in the No. 1 reactor was shut?
First of all, the reactor operators had never been trained how to open and close IC valves, and didn't have the necessary skills. TEPCO headquarters in Tokyo, too, could not contribute any helpful direction.
"If the situation had been evaluated correctly, then there should have been no misapprehensions regarding the state of the IC valve," the investigative committee report stated. TEPCO's workers, however, did not have enough training to deal with the realities of the growing disaster.
At the No. 3 reactor, at 2:42 a.m. on March 13, one of the reactor operators stopped the reactor's high pressure coolant injection system (HPCI), which had been pumping water into the core, to switch over to another injection method. That second method, however, failed.
The midterm report stated that partly due to poor communication, Yoshida and other senior managers at the plant didn't find out that the HPCI system had even been stopped for about an hour. Staff took countermeasures, but they were already behind the curve and the crisis grew that much worse.
"It cannot be said for certain that the hydrogen explosions could have been averted had the alternate water injection methods gone well," the report says of the No. 1 and 3 reactors, "but it is possible that damage to the reactors could have been retarded, the amount of radioactive material emitted constrained, and later operations made easier."