The nuclear plant disaster in Japan is now worse than the 3-Mile Island incident in the US in 1979. The 3 Mile Island plant was returned to operation, the Japanese plants will now never be restored as sea water is being used in 'an act of desperation' to cool the fuel before it can melt the 6 inches of stainless steel that lie between it and the concrete floor, which it might also eat through and which also could lead to a more deadly explosion than the one that occurred yesterday.
The problem is 'critical heat flux' which is a huge safety concern for the cooling of nuclear fuel bundles. This occurs when water cooling the reactor flashes to steam at a point or surface in the fuel rod assembly, and thereby at that region it loses the heat transfer properties of liquid water. This is called burnout, and can damage the rod surface. Steam, or water vapor, doesn't cool very well!
Normally the hot fuel rods are cooled by superheated water which is maintained in a liquid state by high pressures of up to 2000 lbs/sq inch, and which then is used to generate steam in heat exchangers to spin turbines. If the coolant pressure is diminished as it may be with the sea water now used, the chance that the water will flash to steam increases, greatly decreasing the heat transfer properties at that point in the fuel rod bundle. With the reactor in shut down mode the cooling of the nuclear reactions will hopefully reduce the need for cooling.
If any super hot nuclear fuel does get released from its zirconium rod in the reactor it may be difficult to cool it. It may pool on the floor of the reactor vessel where it may flash any water that hits it to steam at the interface, reducing the transfer of heat.
Robert Alvarez, senior scholar at the Institute for Policy Studies and former senior policy adviser to the U.S. secretary of energy, said in a briefing for reporters that the seawater was a desperate measure.
"It's a Hail Mary pass," he said.
He said that the success of using seawater and boron to cool the reactor will depend on the volume and rate of their distribution. He said the dousing would need to continue nonstop for days....
According to experts interviewed by The Associated Press, any melted fuel would eat through the bottom of the reactor vessel. Next, it would eat through the floor of the already-damaged containment building. At that point, the uranium and dangerous byproducts would start escaping into the environment.
At some point in the process, the walls of the reactor vessel — 6 inches (15 centimeters) of stainless steel — would melt into a lava-like pile, slump into any remaining water on the floor, and potentially cause an explosion much bigger than the one caused by the hydrogen. Such an explosion would enhance the spread of radioactive contaminants.
If the reactor core became exposed to the external environment, officials would likely began pouring cement and sand over the entire facility, as was done at the 1986 Chernobyl nuclear accident in the Ukraine, Peter Bradford, a former commissioner of the U.S. Nuclear Regulatory Commission, said in a briefing for reporters.
At that point, Bradford added, "many first responders would die."
