During a discussion or
symposium on
Nuclear power, a group of scientists from around the world were discussing the theoretical consequences of a
meltdown.
If the reactor undergoes a catastrophic loss of coolant, the reactor and its rods will overheat. With nothing to cool them down, the heat will increase until it begins to melt the reactor. Once it gets that hot, if it comes in contact with the water/coolant, it will flash it to steam and cause an explosion such as what happened at Chernobyl. The fuel, either Uranium or Plutonium, will reach such an extreme temperature that it wil melt together into a lava-like clump, called slag.
Once it becomes slag, there is no stopping it. It gets so hot that it melts through the container, no matter how much coolant you dump on it. The lump has reached critical mass, and begins to melt through the ground, because of gravity. The radiation is very intense, and the temperature is well above 10,000 degrees (Farenheit or Celsius, take your pick). At this point everything surrounding it is on fire, including concrete.
The molten core and slag is so hot that it burns a hole right into the ground from gravity, and keeps going. If this happened in America, the scientist reasoned, it would come out the other side in China.
The last assumption is Wrong. First, once you travel past the center of the earth, you have to go against gravity, ie UP to get to China. Second, scientists have concluded that the hole bored into the ground would reach 30 feet in depth, which is bad enough. The scientist was grossly exaggerating, but not everyone knew that.
What would stop it? Water. Once you go deep enough, you'll hit an underground aquifer. Of course, it could create an explosion of radioactive steam, blowing the roof off if it hasn't already, and contaminating the area. Second, it will contaminate the water supply for miles. Even if you built an indestructable dome which didn't break (Three Mile Island's dome held), the radiation there would be disastrous. Cleanup would be extremely bad, and miles around would be evacuated for decades until the radiation decreased.
If you want to read about the steps to a meltdown, go read Tom Clancy's The Hunt for Red October