Question

a. What are the products in the fission of uranium-235 that make possible a nuclear chain reaction? b. What is the purpose of placing control rods among uranium samples in a nuclear reactor?

Short answer

a. Krypton, barium, neutrons, and energy. b. To absorb excess neutrons and regulate the fission reaction.

Step-by-step solution

Understanding Fission of Uranium-235

During the fission of uranium-235, the nucleus absorbs a neutron and splits into two smaller nuclei along with the release of several neutrons and a large amount of energy.

Identifying the Products

The primary products of the fission of uranium-235 are two smaller nuclei (known as fission fragments), usually isotopes of elements like krypton, barium, along with 2-3 free neutrons and energy.

Nuclear Chain Reaction

The neutrons released during fission can initiate more fission reactions in other uranium-235 nuclei, leading to a self-sustaining series of reactions called a nuclear chain reaction.

Introduction to Control Rods

Control rods are composed of materials like boron, cadmium, or hafnium that have the ability to absorb neutrons without undergoing fission.

Function of Control Rods

By absorbing excess neutrons, control rods regulate the rate of fission reactions in the reactor. They help prevent the reactor from overheating and maintain a stable chain reaction.

Key concepts

nuclear chain reaction

A nuclear chain reaction occurs when neutrons released from a fission event cause additional fission events, leading to a chain of reactions. In the case of uranium-235, this process begins when a neutron collides with the uranium nucleus, causing it to split into two smaller nuclei (fission fragments) and releasing energy.
During each fission event, 2-3 more neutrons are released, which can strike other uranium-235 nuclei and continue the cycle. This series of reactions can be self-sustaining and is what allows nuclear power plants to generate large amounts of energy from relatively small amounts of fuel.
Key points to remember about nuclear chain reactions:

• A single neutron starts the fission process.
• Each fission event releases additional neutrons.
• A self-sustaining chain reaction releases substantial energy.

control rods

Control rods are essential components of a nuclear reactor and are used to control the rate of the nuclear chain reaction. These rods are made from materials like boron, cadmium, or hafnium, which are capable of absorbing neutrons without undergoing fission themselves.
Here's how control rods function within a nuclear reactor:

• They absorb excess neutrons, slowing down the chain reaction.
• By adjusting the position of the control rods, technicians can regulate the reactor's power output.
• If the reaction rate becomes too high and there is a risk of overheating, control rods can be fully inserted to drastically reduce neutron availability and safely shut down the reactor.

This neutron-absorbing capability is crucial for maintaining a stable and controlled environment within the reactor. Without control rods, the chain reaction could escalate uncontrollably, leading to severe safety hazards.

nuclear reactor

A nuclear reactor is an apparatus designed to harness the energy produced by controlled nuclear chain reactions. The fundamental components of a nuclear reactor include the reactor core, control rods, coolant, and containment structure.
Inside the reactor core, uranium-235 or other fissionable material undergoes controlled fission reactions, releasing energy in the form of heat. The coolant, which could be water, liquid metal, or gas, transfers this heat away from the reactor core, enabling it to be used for generating electricity or other purposes.
Here's an overview of key components and their roles:

• Reactor Core: Contains the fuel (uranium-235) and is the site of the fission reactions.
• Control Rods: Manage the reactor's power output and ensure safety by absorbing excess neutrons.
• Coolant: Transfers heat away from the core to prevent overheating.
• Containment Structure: Protects the environment from radiation and contains any potential leaks.

This careful orchestration of components allows nuclear reactors to safely and efficiently produce energy on a large scale, contributing significantly to the global energy supply.