IAEA informed in March that No. 1 reactor core started melting about 50 minutes after cooling stopped — Melted pile of fuel in 3.5 hours

A meltdown occurred at one of the reactors at the Fukushima No. 1 Nuclear Power Plant three and a half hours after its cooling system started malfunctioning, according to the result of a simulation using “severe accident” analyzing software developed by the Idaho National Laboratory.

Chris Allison, who had actually developed the analysis and simulation software, reported the result to the International Atomic Energy Agency (IAEA) in late March. It was only May 15 when Tokyo Electric Power Co. (TEPCO) admitted for the first time that a meltdown had occurred at the No. 1 reactor at the Fukushima nuclear plant. [...]

According to the simulation, the reactor core started melting about 50 minutes after the emergency core cooling system of the No. 1 reactor stopped functioning and the injection of water into the reactor pressure vessel came to a halt. About an hour and 20 minutes later, the control rod and pipes used to gauge neutrons started melting and falling onto the bottom of the pressure vessel. After about three hours and 20 minutes, most of the melted fuel had piled up on the bottom of the pressure vessel. At the four hour and 20 minute mark, the temperature of the bottom of the pressure vessel had risen to 1,642 degrees Celsius, close to the melting point for the stainless steel lining, probably damaging the pressure vessel. [...]

[link to enenews.com]