Data released for the first time this week show three of the damaged Fukushima Daiichi nuclear reactors probably began spewing radiation within a few hours of Japan’s devastating earthquake and at least one may have gone into a full meltdown within about 15 hours of the tsunami striking the plant and shutting off its cooling systems.
Yet for the first days of the disaster, the plant’s operators and Japan’s nuclear safety regulators studiously avoided using the word “meltdown.” They repeatedly said they believed the reactors’ fuel rods were still intact and safely contained inside their zirconium sheaths.
In reality, the rods in the core of the No. 1 reactor had fully melted by the morning of March 12 and had fallen to the bottom of the reactor’s pressure vessel.
The documents show the plant’s managers dithered over whether or not to vent the reactor to reduce a build-up of dangerous pressure inside.
When they did decide to act, seven hours after being ordered to do so by the government, they discovered the vent system was inoperable, probably having been damaged in the earthquake, and had to be activated by hand.
By that time, radiation levels in the reactor were so high, volunteers could only spend a few minutes taking turns to crank the vents open.
In the end, the build-up of pressure from steam and explosive hydrogen gas was so great, the reactor exploded, damaging its outer containment walls and spewing radiation into the atmosphere.
A similar pattern of disaster befell the No. 2 and No. 3 reactors. Japanese officials now believe all three reactors may be leaking highly radioactive water outside the containment buildings as a result of damage caused to their pressure vessels by suspected meltdowns.
Most of the 190 tonnes of water being injected every day into the reactors is leaking from the pressure vessels because they are more seriously damaged than previously thought.
“It is a very serious accident and it still continues,” Yukiya Amano, director general of the International Atomic Energy Agency said Thursday.
“The situation continues to be very serious.”