Question

The moderator used in nuclear reactors is (a) TEL (b) \(\mathrm{D}_{2} \mathrm{O}\) (c) \(\mathrm{H}_{2} \mathrm{O}_{2}\) (d) \(\mathrm{R}-\mathrm{O}-\mathrm{R}\)

Short answer

Option (b) \( \mathrm{D}_{2} \mathrm{O} \) (heavy water) is the moderator used in nuclear reactors.

Step-by-step solution

Understand the Role of a Moderator

A moderator in a nuclear reactor is a substance that slows down fast neutrons, making them more likely to cause further nuclear fission. Slowing down neutrons increases the reactor's efficiency.

Analyze the Options

Review the given options to identify the candidates that might serve as a neutron moderator: (a) TEL - Tetraethyl lead, a chemical compound used in gasoline, is not suitable for slowing neutrons.(b) \( \mathrm{D}_{2} \mathrm{O} \) - Heavy water, known for its neutron moderating properties.(c) \( \mathrm{H}_{2} \mathrm{O}_{2} \) - Hydrogen peroxide, used as an oxidizer, not a neutron moderator.(d) \( \mathrm{R}-\mathrm{O}-\mathrm{R} \) - Represents ethers, organic compounds that are not used as moderators.

Identify the Correct Moderator

Among the given options, \( \mathrm{D}_{2} \mathrm{O} \) (heavy water) is commonly used as a neutron moderator in certain types of nuclear reactors due to its effectiveness in slowing down neutrons.

Key concepts

Neutron Moderator

In the heart of a nuclear reactor, one vital component is the neutron moderator. A neutron moderator functions to slow down fast-moving neutrons produced during nuclear fission. By slowing these neutrons, they are more likely to initiate further fission reactions. This is crucial because fast neutrons are not as effective at sustaining a controlled chain reaction needed for energy production.
The ability to slow down neutrons helps increase the likelihood of them interacting with nuclear fuel, thus improving the reactor's efficiency. Materials used as neutron moderators must have certain characteristics, such as low atomic mass and the ability to not absorb neutrons significantly. These qualities make them ideal for reducing the kinetic energy of the neutrons without capturing them.

Heavy Water

Heavy water, commonly denoted as \( \mathrm{D}_2 \mathrm{O} \), is a form of water where the typical hydrogen atoms are replaced with deuterium, a heavier isotope. This adds a bit of mass, making heavy water significantly effective as a neutron moderator.
Deuterium’s additional mass compared to ordinary hydrogen results in more efficient slowing of neutrons without capturing them, which improves fission likelihood. Heavy water is thus pivotal in certain nuclear reactors, like the CANDU reactor, where it also allows the use of natural uranium as fuel. In return, the system remains efficient, and heavy water plays a duel role of serving as both the coolant and the moderator. This unique property makes it a preferred choice in various reactor designs.

Nuclear Fission Efficiency

The efficiency of a nuclear reactor is greatly influenced by how well nuclear fission is maintained and controlled. Efficient nuclear fission ensures that a reactor can produce a significant amount of energy from a given amount of fuel. This minimizes waste and optimizes fuel usage.

• Neutron moderators like heavy water are essential for enhancing efficiency, as they increase the probability of fission by slowing down neutrons.
• This process ensures that slow neutrons can cause new fission reactions, leading to a sustainable chain reaction in the reactor core.

By reducing waste and optimizing reactions, reactors can harness more power without needing excessive amounts of fuel. This is crucial for maintaining economic viability and safety in nuclear power generation.

Types of Nuclear Reactors

There are various types of nuclear reactors, each tailored to specific needs, fuel types, and methods of moderation. Here are a few common types:

• Pressurized Water Reactors (PWR): These reactors use normal water as both coolant and neutron moderator. They are among the most widely used reactors globally.
• Boiling Water Reactors (BWR): In BWRs, the coolant water is allowed to boil in the reactor core, producing steam directly in the reactor vessel.
• Heavy Water Reactors: As the name implies, these use heavy water as a moderator, allowing them to use natural uranium as fuel. CANDU reactors are a prominent example.
• Fast Neutron Reactors: These don’t use a neutron moderator, unlike other reactors, and instead rely on fast neutrons, which require different technologies and safety measures.

Each reactor type serves a different purpose and uses a variety of technologies and materials depending on energy needs, safety requirements, and resource availability.