GENERAL KNOWLEDGE

FUNCTION OF BORON RODS, URANIUM-235 AND GRAPHITE MODERATORS IN AN OPERATING NUCLEAR REACTOR

1) Function of Boron Rods in an Operating Nuclear Reactor

Boron rods are commonly used in nuclear reactors as a control mechanism to regulate the rate of fission reactions and maintain the desired power level. The primary function of boron rods is to absorb excess neutrons, which helps control the nuclear chain reaction within the reactor.

During normal reactor operation, the boron rods are partially inserted into the reactor core. The boron atoms present in the rods have a high propensity to absorb thermal neutrons. By adjusting the position of the boron rods, operators can control the number of neutrons available for causing fission in the fuel.

In case of emergencies or when shutting down the reactor, the boron rods are fully inserted into the core. This action significantly increases neutron absorption and effectively stops or reduces the fission reactions occurring in the fuel. Boron’s ability to absorb neutrons makes it an effective tool for controlling and maintaining a safe and stable nuclear reaction.

2) Function of U235 in an Operating Nuclear Reactor

Uranium-235 (U235) is a fissile isotope of uranium that plays a critical role in sustaining a controlled nuclear chain reaction within a reactor. Its primary function is to act as fuel for the nuclear fission process.

When U235 absorbs a neutron, it becomes unstable and undergoes fission, splitting into two smaller nuclei and releasing additional neutrons and a significant amount of energy. These released neutrons can then be absorbed by other U235 nuclei, leading to a self-sustaining chain reaction.

To ensure sustained fission reactions, a sufficient concentration of U235 is required within the fuel assembly or reactor core. Typically, natural uranium contains only about 0.7% U235, which is not enough to sustain a chain reaction on its own. Therefore, enrichment processes are employed to increase the concentration of U235 to around 3-5% for use in most commercial reactors.

U235 provides the fuel source for nuclear reactors, releasing a substantial amount of energy through fission reactions. Its ability to sustain a chain reaction makes it an essential component in the operation of nuclear power plants.

3) Function of Graphite Moderators in an Operating Nuclear Reactor

Graphite moderators are utilized in certain types of nuclear reactors, such as graphite-moderated reactors or gas-cooled reactors, to slow down fast neutrons and increase their chances of causing fission. The primary function of graphite moderators is to moderate or reduce the energy of fast neutrons produced during the fission process.

In a nuclear reactor, fast neutrons are generated when atoms undergo fission. However, these fast neutrons have high kinetic energy and are less likely to be absorbed by fissile nuclei, hindering the efficiency of the chain reaction. By passing through a graphite moderator, fast neutrons collide with carbon atoms, transferring some of their energy and slowing down in the process.

The moderation process allows the slowed-down or thermal neutrons to have a higher probability of being captured by fissile isotopes like U235 or plutonium-239. This increases the likelihood of sustaining a chain reaction and enables efficient utilization of the available fuel.

Graphite moderators also possess good thermal properties, allowing them to handle high temperatures without significant structural damage. Their ability to slow down fast neutrons and withstand high temperatures makes graphite an important material for maintaining a controlled and sustained nuclear reaction within certain types of reactors.

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