Breaking news/No.1 reactor vessel damaged 18 hrs after quake

The operator of the Fukushima Daiichi nuclear power plant says the containment vessel of the No.1 reactor may have been damaged about 18 hours after the March 11th earthquake, allowing highly radioactive water to leak.

The quake knocked out the reactor's cooling system. The situation is believed to have caused the fuel rods to melt, creating holes in the pressure vessel, and damaging the containment vessel.

On Tuesday, Tokyo Electric Power Company, or TEPCO, released the results of its analysis of the temperature and water level of the reactor.

The temperature of the containment vessel began to rise immediately after the earthquake. It shot up 15 hours after the quake, when a meltdown is believed to have occurred.
At 9 AM on March 12th, around 18 hours after the quake, the vessel's temperature had reached 300 degrees Celsius. That's more than double the temperature it was designed to withstand.

http://www3.nhk.or.jp/daily/english/25_03.html

http://www.yomiuri.co.jp/dy/national/T110524005872.htm

Meltdown speed varied by reactor
The Yomiuri Shimbun

Nuclear fuel rods in the No. 2 reactor at the Fukushima No. 1 plant are believed to have mostly melted and dropped to the bottom of the pressure vessel 101 hours after the March 11 earthquake, and those in the No. 3 reactor likely reached the same state in 60 hours, according to Tokyo Electric Power Co.'s worst-case scenario.

The worst-case speculation was based on the assumption the water level in the pressure vessels was lower than originally thought--similar to what happened in the No. 1 reactor.

TEPCO's analysis of the state of the plant's reactors was submitted Monday to the Economy, Trade and Industry Ministry's Nuclear and Industrial Safety Agency. The report was the first admission by the utility that the reactors were in a critical condition soon after the plant automatically shut down when the earthquake hit.

It is highly likely the pressure chambers of the Nos. 2 and 3 reactors were damaged when the melted fuel dropped down, which caused the hydrogen explosions, TEPCO's report said.

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Fuel in No. 1 melted in 15 hours

At 15:36 JST on 12 March, there was an explosion in the reactor building at unit 1. The side walls of the upper level were blown away, leaving in place only the vertical steel framed gridworks. The roof collapsed covering the floor and some machinery on the south side. The walls were relatively intact compared to later explosions at units 3 and 4.[93][94] A video of the explosion shows that it was primarily directed sideways.
Wikipedia