Class 12 Exam > Class 12 Questions > In a nuclear reactor:a)moderator is used to s...
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In a nuclear reactor:
- a)moderator is used to slow down the neutrons
- b)moderator is used to control the number of neutrons
- c)control rods are used to slow down the neutrons
- d)coolant is used to slow down the neutrons
Correct answer is option 'A'. Can you explain this answer?
Most Upvoted Answer
In a nuclear reactor:a)moderator is used to slow down the neutronsb)mo...
A moderator in a nuclear reactor is used to slow down the neutrons. The neutrons produced by fission are very fast, around 2 MeV. (Neutron “speed” is generally expressed by it's energy.) At that speed the probability of the neutron causing a fission in another uranium or plutonium atom is fairly low.
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In a nuclear reactor:a)moderator is used to slow down the neutronsb)mo...
Moderator is used to slow down the neutrons in a nuclear reactor.
Explanation:
1. Neutrons in a Nuclear Reactor:
In a nuclear reactor, the fission process occurs where heavy atomic nuclei, such as uranium-235, are bombarded by neutrons. When these atomic nuclei absorb a neutron, they become unstable and split into two smaller nuclei, releasing a large amount of energy in the process. Along with energy, two or three more neutrons are also released.
2. Role of Neutrons in Sustaining a Chain Reaction:
The released neutrons can further collide with other atomic nuclei, causing them to undergo fission and release more neutrons. This creates a chain reaction that can be sustained if each fission event leads to the production of at least one more neutron that can cause another fission event.
3. Slowing Down Neutrons:
However, for the chain reaction to be sustained, the released neutrons need to be slowed down. This is because fast neutrons are less likely to be absorbed by atomic nuclei and are more likely to escape from the reactor without causing further fission events.
4. Role of Moderator:
A moderator is a material used in nuclear reactors to slow down the fast neutrons produced during fission. It accomplishes this by effectively scattering the neutrons, causing them to lose energy and slow down. Slowed down or thermal neutrons have a higher probability of being absorbed by atomic nuclei, thus increasing the chances of initiating further fission events and sustaining the chain reaction.
5. Common Moderators:
Some common materials used as moderators in nuclear reactors include water (in pressurized water reactors), heavy water (in CANDU reactors), and graphite (in graphite-moderated reactors).
Conclusion:
In summary, the role of the moderator in a nuclear reactor is to slow down the fast neutrons produced during fission. By slowing down the neutrons, the moderator increases the chance of their absorption by atomic nuclei and sustains the chain reaction in the reactor.
Explanation:
1. Neutrons in a Nuclear Reactor:
In a nuclear reactor, the fission process occurs where heavy atomic nuclei, such as uranium-235, are bombarded by neutrons. When these atomic nuclei absorb a neutron, they become unstable and split into two smaller nuclei, releasing a large amount of energy in the process. Along with energy, two or three more neutrons are also released.
2. Role of Neutrons in Sustaining a Chain Reaction:
The released neutrons can further collide with other atomic nuclei, causing them to undergo fission and release more neutrons. This creates a chain reaction that can be sustained if each fission event leads to the production of at least one more neutron that can cause another fission event.
3. Slowing Down Neutrons:
However, for the chain reaction to be sustained, the released neutrons need to be slowed down. This is because fast neutrons are less likely to be absorbed by atomic nuclei and are more likely to escape from the reactor without causing further fission events.
4. Role of Moderator:
A moderator is a material used in nuclear reactors to slow down the fast neutrons produced during fission. It accomplishes this by effectively scattering the neutrons, causing them to lose energy and slow down. Slowed down or thermal neutrons have a higher probability of being absorbed by atomic nuclei, thus increasing the chances of initiating further fission events and sustaining the chain reaction.
5. Common Moderators:
Some common materials used as moderators in nuclear reactors include water (in pressurized water reactors), heavy water (in CANDU reactors), and graphite (in graphite-moderated reactors).
Conclusion:
In summary, the role of the moderator in a nuclear reactor is to slow down the fast neutrons produced during fission. By slowing down the neutrons, the moderator increases the chance of their absorption by atomic nuclei and sustains the chain reaction in the reactor.
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