It is remarkable that so much attention has been given to the radioactive release from Fukushima, considering that the direct death and destruction from the tsunami was enormously greater.
"It's hard to make a comparison between Three Mile Island, Chernobyl and Fukushima because the radioactive release is different and so is the population, " said John Large, a UK-based independent nuclear engineer.
Solid nuclear fuel like that used at Fukushima-Daiichi can melt and release radioactive materials if not cooled consistently during shutdown.
FORBES: Explainer: What Caused The Incident At Fukushima-Daiichi
Even during the process we should never release any radioactive material into the surrounding environment.
And the longer a major release of radioactive material is avoided, the chances increase that the reactors cool on their own.
FORBES: Japan Radiation Fears May Outstrip The Real Health Dangers
They have a primary and a secondary containment structure, both made from thick reinforced concrete, to protect against the release of radioactive materials.
FORBES: Explainer: What Caused The Incident At Fukushima-Daiichi
There was a small release of radioactive steam at Three Mile Island in 1979, and there have also been a few releases at Fukushima Daiichi.
None of the Daiichi accidents were considered major safety hazards, and none caused any injuries or led to the release of any radioactive material outside the plant, until this month's accident.
The human and economic damage from the earthquake and tsunami are terrible, and the apparent release of some radioactive materials into the atmosphere compounds the significant sense of unease in global markets.
But because of power outages cooling systems failed, leading to fears of a meltdown and possible release of large amounts of radioactive material.
FORBES: Japan Radiation Fears May Outstrip The Real Health Dangers
In a full meltdown, such as the 1986 Chernobyl disaster in the Soviet Union, the rods melt completely and the release of energy causes an explosion that contaminates the surrounding area with radioactive material.
The company initially said there was no release of radiation, but admitted later that the quake released radiation and spilled radioactive water into the Sea of Japan.
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