Skip to main content
Ch.21 - Nuclear Chemistry
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.21 - Nuclear ChemistryProblem 6
Chapter 21, Problem 6

(a) What is the function of the moderator in a nuclear reactor? (b) What substance acts as the moderator in a pressurized water generator?

Verified step by step guidance
1
Step 1: Understand the role of a moderator in a nuclear reactor. A moderator is used to slow down the neutrons produced during fission. Fast neutrons are less likely to cause further fission reactions, so slowing them down increases the probability of sustaining a chain reaction.
Step 2: Learn about the process of neutron moderation. Moderators work by reducing the kinetic energy of neutrons through collisions. This process is crucial for maintaining a controlled and sustained nuclear reaction.
Step 3: Identify common substances used as moderators. In nuclear reactors, materials with light nuclei are typically used as moderators because they are effective at slowing down neutrons without absorbing them.
Step 4: Recognize the specific moderator used in a pressurized water reactor (PWR). In PWRs, the moderator is usually ordinary water (H₂O). Water serves both as a coolant and a moderator, making it a dual-purpose component in the reactor design.
Step 5: Consider the properties of water that make it suitable as a moderator. Water is abundant, has a high specific heat capacity, and its hydrogen atoms are effective at slowing down neutrons through elastic scattering.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nuclear Reactor Functionality

A nuclear reactor generates energy through nuclear fission, where heavy atomic nuclei split into smaller parts, releasing energy. The reactor's design includes various components that control the fission process, including moderators, which slow down neutrons to sustain a controlled chain reaction.
Recommended video:
Guided course
02:06
Nuclear Binding Energy

Role of the Moderator

The moderator in a nuclear reactor is a substance that slows down fast neutrons produced during fission, increasing the likelihood of these neutrons being captured by fissile material, such as uranium-235. This process is crucial for maintaining a sustained and controlled nuclear reaction.
Recommended video:
Guided course
00:46
Writing Formulas

Common Moderators in Reactors

In pressurized water reactors (PWRs), water serves as both a coolant and a moderator. The high density of water effectively slows down neutrons while also removing heat from the reactor core, ensuring efficient energy production and maintaining safe operating conditions.
Recommended video:
Guided course
02:53
Common Ion Effect
Related Practice
Textbook Question

The accompanying graph illustrates the decay of 8842Mo, which decays via positron emission. (a) What is the halflife of the decay? [Section 21.4]

580
views
Textbook Question

In the sketch below, the red spheres represent protons and the gray spheres represent neutrons. (c) Based on its atomic number and mass number, do you think the product nucleus is stable or radioactive? [Section 21.3]

500
views
1
rank
Textbook Question

The steps below show three of the steps in the radioactive decay chain for 23290Th. The half-life of each isotope is shown below the symbol of the isotope. (a) Identify the type of radioactive decay for each of the steps (i), (ii), and (iii). [Sections 21.2 and 21.4]


747
views
Textbook Question

The accompanying graph illustrates the decay of 8842Mo, which decays via positron emission. (c) What fraction of the original sample of 8842Mo remains after 12 min? [Section 21.4]

496
views