power plant problem. what are the control rods for? can someone expound on what this paragraph is saying?

Question

Controlling the power level of the submarine requires manual running of control rods. So instead, the reactor is made so that it will expand when it is hot and therefore decreases the rate of reaction and contracts when it cools which increases the rate of production of the power plant.

Answer 1

The expansion is discussing the density of water. In water moderated reactors the density of water is related to the ability of the water to slow down neutrons, allowing them to initiate fission. As water expands the density goes down, thus reducing the amount of slow neutrons available for fission.

Answer 2

Control Rods in a Reactor are usually made from Graphite or Boron.

They simply absorb any excess Free Neutrons which may cause the chain reaction to happen too quickly and thus generate too much heat energy for the reactor to safetly handle.

In a Nuclear Submarine, the reactor expands, so that there is now less chance of the Free Neutrons splitting more atoms, as more space is available, thus reducing the possibility of Fission Occurring, as it cools the reactor contracts, meaning the available space is reduced and the chances of Fission increased once again and thus more energy is produced.

Hope this helps...;o).