March 17, 2011 - how nuclear power works in 250 words

As we watch the situation in Japan, where a number of reactors at the Fukushima Daiichi power plant have been damaged by the earthquake and tsunami, I've been looking for a simple explanation of how nuclear power plants -- in Japan and here in the U.S. -- work.  Perhaps because it's a complex technology, or because there are a variety of ways humans use nuclear fission to generate electricity, I haven't found a very simple explanation -- so I decided to write one up myself.

Most nuclear power plants use the energy released by fission -- splitting atoms (usually uranium or plutonium) to heat water into steam.  The steam spins a turbine, which spins a generator to create electricity.   These turbines work much like other steam turbines found in other thermal electricity plants (such as those powered by biomass, natural gas, or coal).

The reactor is the heart of a nuclear power plant.  This key component differentiates nuclear plants from other thermal generators.  While most thermal generators create or release thermal energy (heat) through combustion, nuclear fission creates thermal energy by splitting atoms.  When one uranium atom splits, it releases heat and several neutrons -- subatomic particles that fly off the split atom.  If one of those neutrons smacks into another uranium atom at the right speed, that atom will then split, releasing more heat -- and importantly, more neutrons.  By controlling the speed at which these splits occur, operators create a sustained but controlled fission chain reaction.

When the heat produced by this chain reaction is absorbed by cooling water (like in your home’s boiler or car's radiator system), the water heats up to between 500 °F and 600 °F.  Depending on the reactor design, this heat either transforms the water into steam (in an open-loop boiling water reactor), or goes through a heat exchanger to create steam in a secondary loop (in a closed-loop pressurized water reactor).  Either way, the steam produced flows through a turbine, which spins a generator to create electricity.

That's an overview of the basics of nuclear power generation.  I've simplified it greatly to make it easier to understand.  If you dig deeper, the details are fascinating, and point to both the challenges and opportunities of harnessing fission to create electricity.