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Chapter 38: Problem 9

Explain and distinguish the roles of the control rods and moderator in a nuclear reactor.

Short Answer

Expert verified
In a nuclear reactor, control rods and moderators perform different roles. Control rods absorb neutrons, effectively controlling the rate of the nuclear fission reaction and the power output of the reactor. The moderator, on the other hand, slows down fast neutrons without absorbing them to make the fission process more efficient.

Step by step solution

01

Understanding the Role of Control rods

When explaining the role of control rods in a nuclear reactor, it is important to say that control rods are devices that are capable of absorbing neutrons. This capacity makes control rods useful in controlling the rate of fission in a nuclear reactor. They are inserted into or withdrawn from the reactor's core to increase or decrease the number of neutrons that can cause fission. If more neutrons are absorbed by the control rods, fewer are available to cause fission, and so the reactor's power output decreases. If fewer neutrons are absorbed, more neutrons are available to cause fission, and the power output increases.
02

Understanding the Role of Moderator

In contrast to control rods, the role of a moderator in a nuclear reactor is to slow down the speed of the neutron produced by nuclear fission. Fast neutrons are not efficient at causing further fission, so they need to be slowed down. Moderators are capable of slowing down these neutrons without absorbing them. Common moderators include light water, heavy water, and graphite.
03

Differentiating the Roles of Control Rods and Moderator

While both control rods and moderators have roles that contribute to the nuclear fission process, they perform different tasks. Control rods control the rate of the nuclear fission reaction, essentially controlling the power output of the reactor by absorbing excess neutrons. On the other hand, the moderator slows down fast neutrons to make this reaction more efficient, without absorbing the neutrons.

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Most popular questions from this chapter

Nitrogen-13 is a 9.97-min-half-life isotope used to "tag" ammonia for PET scans, including quantification of myocardial infarction. Consider an intravenous injection incorporating \(20.0 \mathrm{mCi}\) of N-13. Plot a graph of \(\mathrm{N}-13\) activity versus time, with your vertical axis logarithmic and your horizontal axis linear. Why is the graph a straight line? What's the significance of its slope?

Find the nuclear mass of plutonium-239, given its atomic mass of \(239.052157 \mathrm{u}\).

The power output from fission at Oklo was \(10 \mathrm{kW}\) to \(100 \mathrm{kW}\). If at some point that power had been sufficient to boil away the water at the reaction site, the chain reaction would have a. ceased. b. continued, but more slowly. c. becn unaffected. d. sped up.

On an energy-release-per-unit-mass basis, by approximately what factor do nuclear reactions exceed chemical reactions?

Why are fission fragments necessarily radioactive?
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