Surprisingly, the scientific level of these media coverages is pretty intense, lots of jargon. I thought I'd do my part and briefly explain some key elements to nuclear reactors.
What is a nuclear plant?
Power plants using nuclear fuel are just a reinvention of the mousetrap. All power plants do one thing, make steam to drive a turbine. That spinning turbine makes electricity and the means to do that though varies. In reality, all power plants carry the risk of explosion because they all handle high-pressure steam.
Firstly, nuclear reactor plants do not explode on account of their nuclear fuel. There just isn't enough percentage of radioactive substance to trigger the massive explosions we're familiar with.
How do they work?
Nuclear reactors work by using a small yet critical amount of radioactive material that creates a chain reaction. When all of the variable line up the reaction produces heat, which can be used to boil water.
Fuel Rods: These are the main source of energy and contain the primary radioactive materials used to create the heat. They are triggered by neutrons. When neutrons are flying around the fuel rods, a lot of energy is being released.
-More info about the entire fission process as a result of neutrons HERE Someone has already said it better than I could.
Control Rods: These are neutron absorbing rods that can be inserted into the chamber where the fuel rods are producing heat. The control rods help stop the bombardment of neutrons and can stop the reaction in the fuel rods all together.
|A simple diagram showing the basics of nuclear plant designs|
The bottom line: Japan's reactors are in danger due to power failures. The plant's main power supply was damaged as a result of the earthquake and tsunami. The facility did have backup battery power but those eventually ran out. Without the electricity they were not able to keep the water pumps running.
These water pumps are essential in keeping a continuous supply of cool water to absorb the heat and keep things at a manageable temperature. If they cannot be cooled, steam builds and so does the pressure inside the reactor core and housing. The engineers are able to release some of the steam but that is risky because it's a direct release of radioactive materials into the atmosphere.
Some tech'ier stuff:
The Fukushima Daiichi plant reported that once they detected seismic activity they began the fission shutdown process. Inserting the control rods successfully stopped the primary fission process in all 6 reactors. Within the fuel rods though are highly-radioactive elements that continue decaying and radiating large amounts of heat.
There is also the issue of hydrogen gas buildup as a result of water oxidizing with the metals in the reactor. Hydrogen gas is very flammable and can be cause for more troubles.
Something unclear? Science need a little tweaking? Let me know in the comments.