In nuclear power plants, uranium fuel undergoes nuclear fission and generates an enormous amount of heat. The heat makes high-temperature and high-pressure steam that rotates turbines to generate electricity. Japan's electric utilities currently operate 50 light water reactors.
Light Water Reactor (LWR)
LWRs use light water (normal water) as coolant and moderator. Coolant removes heat produced during nuclear fission from a reactor core. Moderator reduces the speed of neutrons produced in nuclear fission to facilitate further fission reaction and sustain a chain reaction.
There are two types of LWRs - a boiling water reactor (BWR) and a pressurized water reactor (PWR). Each type is adopted in almost equal numbers in Japan.
Boiling Water Reactor (BWR)
The same water loop serves as a steam source for turbines.
- A reactor pressure vessel is made of steel and fuel assemblies are installed inside.
- A control rod controls the power of a nuclear reactor. By inserting control rods, excessive fission is prevented.
- A reactor containment vessel, made of steel, accommodates a reactor pressure vessel.
Pressurized Water Reactor (PWR)
The primary water loop transmits heat through the tube walls to the surrounding water of the secondary cooling system to generate steam and rotate turbines.