Japan's Nuclear Power Emergency

Some recent discussions among my friends have shown the need for more information about Japan's damaged nuclear power plants and the reasons for the escalating crisis. Some very good sources of more detail than what's presented by the mainstream media include the following: 

• Fukushima Nuclear Accident – a simple and accurate explanation
  Has a good explanation of the reactor design and operation, with multiple update links
• Explainer: What Went Wrong in Japan's Nuclear Reactors
  Thursday's update to an ongoing series by IEEE Spectrum
• Japan Earthquake and Reactors in That Region
  Ongoing information from the Nuclear Energy Institute

The operating reactors were, of course, immediately shut down when the earthquake occurred. A Wikipedia article defining reactor SCRAM explains how a reactor core is very rapidly shut down from operating power levels. Based on my experience aboard U.S. Navy nuclear submarines, this shutdown can be executed automatically, according to certain operating parameters, or manually by the human operators. I believe that commercial nuclear power plants are operated in the same manner.  

After such a shutdown there is continued production of decay heat at a much lower level, but this heat must be removed to prevent core damage. For a reactor operated at steady power for an extended period, the decay heat production is initially as high as 6.5% of the reactor's initial operating power. After one hour the decay heat drops to about 1.5% of the initial operating power. Decay heat decreases with time, as described in the article linked above. After one year the decay heat from spent fuel generates about 10 kW of heat per metric ton (of fuel). 

The crisis at the Fukushima Daiichi plant was intensified by the inability to reestablish full electrical power to operate the cooling systems for decay heat removal. A very concise likely timeline of events is presented in this article. 

I suggest consulting the above referenced sources for further updates as the efforts continue to gain the upper hand in controlling the decay heat following unprecedented forces of nature. 

Let us also focus on the much broader human suffering that is the direct result of the earthquake and tsunami.