Why didn't the control rods in Fukushima shut down the reactor?

Per this article on the subject: http://theenergycollective.com/nathantemple/53384/how-shutdown-and-core-cooling-japanese-reactors-likely-functions

Even with rods inserted, the reactor continues to produce heat equivalent to about 3% of its full power level. This is not the same as taking a pot off the stove and letting it cool. There are still some atoms splitting and fission products decaying that produce heat. This drops off slowly and is why there needs to be layers of redundant cooling with backup power. During such an earthquake, power from outside the plant would not be expected to be available.

Using the Unit 1 electric power rating of 460MW and the 3% figure above give us ~14MW at scram, that is still a lot of power! So every second 14 million Joules is released(1 Watt = 1 J/S). Now it takes ~4200 joules to heat 1 kilogram of water by 1 degree C. So 14 million joules would heat 1 kg of water to ~3300 degrees C in 1s. You can see why we have a problem!

Can someone check my math, it has been a few years since physics class