No.3 meltdown happened earlier than previously thought

 August 6, 2014

Meltdown at Fukushima reactor 3 worse than thought

http://www3.nhk.or.jp/nhkworld/english/news/20140806_21.html

The operator of the crippled Fukushima Daiichi nuclear plant says the damage to nuclear fuel in one of its reactors may be worse than previously thought.

Tokyo Electric Power Company engineers have been working to size up damage at the plant from the March 2011 accident and start the process of decommission.

Officials with the utility now say most of the nuclear fuel in the No. 3 reactor melted through the reactor core and is now resting at the bottom of the containment vessel.

They had previously said some of the fuel was still inside the reactor. Their latest assessment suggests decommissioning the No. 3 reactor could be more challenging than previously thought.

A government panel investigating the meltdown had said an improper shutdown of an emergency cooling system called "HPCI" had contributed to the accident.

But the utility's latest analysis states the cooling system was already dysfunctional before workers shut it down. It says a meltdown in the No. 3 reactor started at 5.30 AM on March 13th. That's about 5 hours earlier than previously estimated.

It says most of the fuel melted through the reactor core and had dropped into the containment vessel by the following morning.