The illustration below shows the typical steam cycle of a boiling water reactor - the type of reactor used at Limerick Generating Station.
The Nuclear Fuel
- The reactor vessels at Limerick contain the uranium fuel.
- The fuel is in the form of pellets and is stacked in fuel rods.
- The fuel rods are bundled into fuel assemblies.
- The fuel assemblies make up the reactor core that sits inside the reactor vessel.
The Reactor Vessel
- The fission process occurs in the reactor vessel.
- Neutrons collide with the uranium atoms and split the atoms, releasing an enormous amount of energy in the form of heat.
- The heat boils the water inside of the reactor vessel and creates steam.
- Plant operators can control the nuclear reaction by inserting or withdrawing control rods between the fuel assemblies in the reactor.
The Turbine and Generator
The steam travels from the reactor vessel and passes over the turbine blades, causing them to spin.
The spinning turbine spins the electromagnetic generator, producing electricity.
- After the steam spins the turbine, it passes into the condenser and is cooled into water.
- Cooling water from the plant’s cooling tower flows through pipes into the condenser – never mixing with the reactor water – and cools the reactor water before the reactor water returns to the reactor vessel to continue its cycle.
The Cooling Tower
After passing through the condenser tubing, the cooling water is pumped back to the cooling tower where it trickles down over a series of baffle plates.
As the water falls, it is cooled by evaporation.
The heat that is taken from the water rises from the cooling towers as water vapor.
The cooled water is pumped back to the condenser to continue the cooling cycle.
Safely Storing Used Fuel
Limerick’s used fuel is safely stored on site in a used fuel pool and in dry cask storage. Every two years, on alternating years, each unit shuts down for a refueling outage. At this time, used fuel is removed from the reactor and placed in the used fuel pool for storage.
Also each year, the oldest used fuel assemblies are carefully selected from the used fuel pool to be stored using dry cask storage.