Fukushima Meltdown Took Place on March 11th-12th
After confirming that a meltdown has taken place in reactor 1 of the Fukushima Daiichi nuclear power plant, Tokyo Electric Power Company (TEPCO) has released analysis on when and how the meltdown took place. They believe that the fuel began to melt only a few hours after the March 11th earthquake, and that it had almost completely melted down by the morning of the 12th:
Preliminary analysis shows that No. 1 had already entered a critical state by 6:50 a.m. on March 12, with most of its fuel having melted and fallen to the bottom of the pressure vessel, the plant operator said. Tepco released data Thursday showing some of the fuel rods had melted.
The reactor automatically halted operations immediately after the 2:46 p.m. quake, but the water level in the reactor dropped and the temperature began rising at around 6 p.m. The damage to the fuel rods had begun by 7:30 p.m., with most of them having melted by 6:50 a.m. the following day, the utility said.
Since March, TEPCO had made statements acknowledging the possibility that fuel had melted in reactor 1, initially estimating that 70% of the fuel had suffered damage. They based those estimates on data from a water level monitoring gauge. A few days ago, they discovered that the gauge was faulty, so they have re-assessed the situation, estimating that nearly all of the fuel has melted.
They have also said that it is very possible that similar meltdowns have occurred in reactors 2 and 3.