Question

Graphite is used in nuclcar reactors (1) as a lubricant (2) as a fucl (3) for lining inside walls of the reactors as an insulator (4) for decreasing the velocity of ncutrons

Short answer

Option 4 is correct: Graphite is used for decreasing the velocity of neutrons.

Step-by-step solution

Identify the function of graphite in nuclear reactors

Analyze the given options to determine the correct function of graphite in a nuclear reactor setup.

Evaluate each option

Assess each of the four provided options to see which one accurately describes the role of graphite in nuclear reactors:

Examine Option 1

Graphite is not typically used as a lubricant in nuclear reactors, making option 1 unlikely.

Examine Option 2

Graphite is not used as a fuel in nuclear reactors; instead, materials like uranium are used as fuel. Hence, option 2 is incorrect.

Examine Option 3

Graphite is also not used for lining inside walls as an insulator. This eliminates option 3.

Examine Option 4

Graphite is actually used as a moderator to decrease the velocity of neutrons in nuclear reactors. This makes option 4 the correct answer.

Key concepts

Graphite as a Moderator

In nuclear reactors, graphite serves an essential function as a moderator. Moderators are crucial in nuclear reactors because they help sustain the nuclear chain reaction. One of graphite's primary roles is to slow down fast-moving neutrons. Fast neutrons are produced during nuclear fission, and if these neutrons remain too fast, they are less likely to cause subsequent fissions.
Graphite achieves this by scattering the neutrons through numerous collisions. With each collision, the neutron loses energy and slows down. This process increases the likelihood of the neutron causing additional fission events when it collides with fuel atoms like uranium-235. So, by using graphite as a moderator, reactors can maintain a controlled and steady chain reaction.
Other materials, such as heavy water, can also serve as moderators. However, graphite remains one of the most common choices due to its effective neutron slowing properties and relatively low cost.

Nuclear Reactor Components

Nuclear reactors are complex systems made up of several critical components, all of which work together to harness nuclear energy safely and efficiently. Here's an overview of the main components:

• Fuel: Typically enriched uranium or plutonium, the fuel undergoes fission to produce energy.
• Moderator: Materials like graphite or heavy water slow down fast neutrons, making them more likely to cause fission.
• Control Rods: Made of neutron-absorbing materials like cadmium or boron, these rods are inserted or removed to control the rate of the fission reaction.
• Coolant: Substances like water, carbon dioxide, or liquid metals that transfer heat away from the reactor core, preventing overheating.
• Pressure Vessel: Contains the reactor core and the moderator, designed to withstand high pressures.
• Containment Structure: A robust barrier to prevent the release of radioactive materials in case of an accident.

Each component plays a specialized role, ensuring the reactor operates safely and efficiently.

Neutron Velocity Reduction

In nuclear reactors, reducing the velocity of neutrons is crucial for sustaining a nuclear chain reaction. Neutron velocity reduction, also known as thermalization, involves slowing down fast-moving neutrons produced during fission. Here’s how this process benefits the reactor:

• Increased Likelihood of Fission: Slower, 'thermal' neutrons are more likely to be captured by fuel nuclei like uranium-235, inducing further fission reactions.
• Chain Reaction Control: By moderating neutron speed, reactors can maintain a steady rate of fission, avoiding runaway reactions or shutdowns.
• Efficiency: Thermal neutrons are highly efficient at causing fission, meaning more energy can be extracted from the fuel.

Materials like graphite are excellent for this purpose due to their ability to effectively slow down neutrons without capturing them. This delicate balance ensures that enough neutrons are available to sustain the chain reaction but not so many that the reaction becomes uncontrollable.
By reducing neutron velocity, moderators like graphite enable reactors to operate smoothly and safely, maximizing energy output from the nuclear fuel.