IB Physics E.4.2 Nuclear Reactors Notes

Components of a Nuclear Reactor and Their Functions

Consider standing in the control room of a nuclear power plant.

1. Giant monitors display the status of various systems, while engineers carefully adjust controls to maintain balance in a process that powers entire cities.
2. At the heart of this system lies the nuclear reactor, a machine that harnesses the energy of nuclear fission.
3. But how does this machine work, and what ensures its safety and efficiency?

Control Rods: Regulating the Chain Reaction

1. In a reactor, the fission chain reaction is self-sustaining.
2. If left unchecked, it accelerates and can cause overheating or even a meltdown.
3. Control rods are the components that prevent this from happening.
   1. Control rods are made of materials like boron or cadmium, which are highly effective at absorbing neutrons.
   2. By inserting these rods deeper into the reactor core, more neutrons are absorbed, slowing the chain reaction.
   3. Pulling the rods out allows more neutrons to sustain the reaction, increasing its rate.

How It Works:

1. If the reaction is too fast: Insert the control rods deeper to absorb more neutrons and slow the reaction.
2. If the reaction is too slow: Withdraw the control rods slightly to allow more neutrons to sustain the chain reaction.

Moderators: Slowing Down Neutrons for Effective Fission

1. The neutrons released during fission are fast-moving, but uranium-235 nuclei are more likely to capture slow-moving neutrons.
2. This is where the moderator plays a critical role.
3. The moderator slows down fast neutrons, increasing the likelihood of further fission reactions.

Common Moderator Materials:

1. Water: Used in pressurized water reactors (PWRs) and boiling water reactors (BWRs).
2. Graphite: Found in certain reactor designs, such as RBMK reactors.

How It Works: