Problem 38 - A Complete Resource Book in Chemistry for JEE Main

Question

The common moderator of a nuclear reactor (a) \(\mathrm{D}_{2} \mathrm{O}\) (b) graphite (c) beryllium (d) all are correct

Step-by-Step Solution

Answer

(d) all are correct.

Step 1: Understanding the Question

The question asks us to identify the common moderator used in a nuclear reactor from the given options (a) ackslash( ext{D}_2 ext{O}), (b) graphite, (c) beryllium, and (d) all are correct.

Step 1: Check Option (a) ackslash( ext{D}_2 ext{O})

Option (a) is ackslash( ext{D}_2 ext{O}), which is heavy water. This is indeed a common moderator used in certain types of nuclear reactors, like CANDU reactors.

Step 2: Check Option (b) Graphite

Option (b) is graphite, which is also a common moderator used in nuclear reactors, particularly in gas-cooled reactors and some Soviet-designed reactors as it efficiently slows down neutrons.

Step 3: Check Option (c) Beryllium

Option (c) is beryllium, which is used as a neutron reflector or moderator in some reactor designs, though it is less common compared to heavy water and graphite.

Step 4: Evaluate Option (d) All Are Correct

Option (d) suggests that all the previous options (heavy water, graphite, and beryllium) are correct moderators. Since each has been validated as a moderator, option (d) must be the correct choice.

Key Concepts

Heavy Water (D2O)

Heavy water, known chemically as \( \text{D}_2\text{O} \), is similar to regular water, but with one fundamental difference. Instead of ordinary hydrogen atoms, it contains deuterium, an isotope of hydrogen with an additional neutron.
This gives heavy water a higher molecular weight compared to regular water, leading to its unique properties. In the context of nuclear reactors, heavy water is a valuable moderator. It is specifically employed to slow down fast neutrons effectively without absorbing them significantly.
This slowing down process increases the likelihood of neutrons inducing fission reactions in fuel materials such as uranium-235, making the nuclear chain reactions more efficient. Heavy water is notably used in CANDU reactors, a Canadian reactor type that can use natural (unenriched) uranium as fuel.

• Contains deuterium, a heavier isotope of hydrogen.
• Slows down neutrons effectively, increasing fission efficiency.
• Used extensively in CANDU reactors.

Graphite

Graphite is another essential moderator used in the nuclear power industry. It is a form of carbon where atoms are arranged in a hexagonal lattice, providing it with excellent stability and physical properties.
Graphite's ability to moderate neutrons stems from its interaction with neutrons, where it slows them down with minimal absorption. This property is crucial for sustaining a chain reaction in reactors that use solid or gaseous fuels.
Graphite was famously used in the first artificial nuclear reactor, the Chicago Pile-1, and remains a choice material for several reactor designs, including the British Advanced Gas-cooled Reactor (AGR) and some Russian designs.

• Composed of layered carbon atoms.
• Slows neutrons efficiently without absorbing them.
• Utilized in various reactor designs worldwide.

Beryllium

Beryllium, a steel-grey metal, possesses unique attributes that make it suitable as a neutron moderator, though it is less commonly used than heavy water or graphite. This lightweight element is highly effective at reflecting and slowing down neutrons due to its atomic structure and relatively low absorption cross-section for neutrons.
In reactors, beryllium can act in dual roles, both as a moderator and as a reflector, returning stray neutrons back into the reactor core to enhance the reaction rate.
Despite its benefits, beryllium is less frequently used because it is more challenging to handle, and it's expensive. Moreover, its toxicity adds to the considerations during its application in nuclear reactors.

• Effective neutron reflector and moderator.
• Lighter and stronger than many other metals.
• Its use is limited due to cost and handling challenges.