Nuclear Reactor

The neutrons that are produced in the reaction can then go on and be part of other reactions, creating a chain reaction.

The neutrons that are used are low energy (thermal neutrons) as they can only be captured in this way.

The amount of fissionable material necessary for the chain reaction to sustain itself is called the critical mass.

The moderator slows down or/and absorbs neutrons.

The moderator needs to be able to slow down some neutrons enough to cause further fission and that absorbs more neutrons the higher the temperature will decrease the chance of meltdown.

Water can be used as a moderator.

The control rods control the chain reaction by limiting the number of neutrons in the reactor. These absorb neutrons so that the rate of fission is controlled. Boron can be used as control rods.

Control rods can be inserted by varying amounts to control the reaction rate but in an emergency the reactor will be shut down automatically by the release of the control rods into the reactor.

Boron can be used as control rods.

Coolant is sent around the reactor to remove heat produced in the fission.

Water can also be used as a coolant.

The heat from the reactor can then be used to make steam for powering electricity-generating turbines.

When a neutron is released, one or more of the following events can occur:

• slowed down by the moderator
• taking about 50 collisions to reach thermal speeds
• absorbed by uranium-235 to cause fission event
• one neutron released goes on to cause a further fission is the critical condition
• a neutron may leave the reactor core without further interaction
• be absorbed by uranium-238
• be absorbed by a control rod
• be scattered by uranium-238
• be scattered by uranium-235

The reactor core is thick steel to withstand high temperature and pressure.

The core is within thick concrete walls which absorb neutrons and gamma radiation.

High level waste– spent fuel rods are stored in cooling ponds for at least a year. They are also stored in sealed containers underground.

Intermediate level waste – stored in sealed drums and then encased in concrete, then stored in specially constructed buildings with walls of reinforced concrete.

Low level waste – sealed in metal drums and stored in trenches.

©2011 Grant Dwyer