Neutron poison

Neutron poison is a term used in nuclear physics and nuclear engineering to describe substances that absorb neutrons in a nuclear reactor. These substances are used to decrease the excess neutrons, control the rate of the nuclear chain reaction, and to shut down the reactor in case of emergency.

Overview

Neutron poisons, also known as neutron absorbers, play a crucial role in the control of nuclear reactors. They are used to adjust the power output of a reactor, prevent a reactor from going critical, and to shut down a reactor in an emergency situation.

Types of Neutron Poisons

There are two types of neutron poisons: fixed and burnable.

Fixed Poisons

Fixed poisons are materials that have a high neutron absorption cross section and are placed in a reactor to balance the excess reactivity. They are not intended to be replaced or moved during the reactor operation. Examples of fixed poisons include boron, cadmium, and hafnium.

Burnable Poisons

Burnable poisons are materials that absorb neutrons and are converted into isotopes that are not neutron absorbers. They are used to compensate for the excess reactivity of fresh fuel. Examples of burnable poisons include gadolinium, samarium, and boron.

Role in Nuclear Reactors

In a nuclear reactor, neutron poisons are used to control the rate of the nuclear chain reaction. They absorb excess neutrons, preventing them from causing further fissions. This helps to maintain the reactor at a steady power level and prevents it from going critical.

In addition, neutron poisons are used in emergency shutdown systems (also known as SCRAM systems) in nuclear reactors. In these systems, a large amount of neutron poison is rapidly introduced into the reactor to absorb a large number of neutrons and quickly stop the chain reaction.

See Also

• Nuclear fission
• Nuclear reactor
• Nuclear chain reaction
• SCRAM