posted on Mar, 14 2011 @ 05:28 PM
"The essential problem is the definition of 'off' in a nuclear reactor. When the nuclear chain reaction is shut and the reactor shuts down, the
fuel is still producing about 6 percent as much heat as it did when it was running, because of continuing heat generation by the radioactivity, the
realease of subatomic particles and of gamma rays.
Usually, when a reactor is first shut down, an electrically driven pump pulls heated water from the vessel to a heat exchanger, and cool water from a
river or ocean is brought in to draw off the heat.
But at the Japanese reactors, after losing electric power, that system could not be used. Instead the operators are dumping sea water into the vessel,
and letting it cool the fuel by boiling. But as it boils, pressure rises too high to pump in more water, so they have to vent the vessel to the
atmosphere, and feed in more water, a procedure known as 'feed and bleed.
When the fuel was intact, the steam they were releasing had only modest amounts of radioactive material, in a nontroublesome form. With damaged fuel,
that steam is getting dirtier.