Difference Between Controlled and Uncontrolled Chain Reaction

Key Difference – Controlled vs Uncontrolled Chain Reaction
 

The key difference between controlled and uncontrolled chain reactions is that controlled chain reactions do not lead to any explosive effects whereas uncontrolled chain reactions lead to explosive energy release.

The terms controlled chain reactions, and uncontrolled chain reactions are discussed under nuclear chemistry. A nuclear chain reaction occurs when one nuclear reaction causes the progression of some other nuclear reactions subsequently. These chain reactions release a very high amount of energy.

CONTENTS

1. Overview and Key Difference
2. What is Controlled Chain Reaction
3. What is Uncontrolled Chain Reaction
4. Side by Side Comparison – Controlled vs Uncontrolled Chain Reaction in Tabular Form
5. Summary

What is Controlled Chain Reaction?

A controlled chain reaction is a chain of nuclear reactions that take place subsequently under controlled conditions. Let us understand this concept using nuclear fission reactions as an example. A fission chain reaction takes place when a neutron and a fissile isotope interact with each other. This interaction causes the release of some neutrons from the fissile nucleus. These released neutrons can interact with other fissile isotopes and cause the initiation of subsequent fission reactions. When these reactions are controlled and regulated properly, it is called a controlled chain reaction. Controlled fission reactions can be carried out in the presence of moderators.

Nuclear power plants use controlled chain reactions. There, the chain reactions are controlled by controlling the rate of nuclear reactions. Controlled chain reactions can easily be converted into uncontrolled form. The reactions can be controlled by regulating the amount of starting material used (the fissile isotope). For example, if the amount of Uranium used is high, then the reaction speed will also be high because then the probability of a neutron interacting with a fissile isotope is high. Then the reaction becomes uncontrollable. And also, by regulating the time of the reaction, a nuclear chain reaction can be made into a controlled reaction. When the time of reaction is reduced, the probability of a neutron interacting with a fissile isotope is low. Then the reaction can easily be controlled.

What is Uncontrolled Chain Reaction?

An uncontrolled chain reaction is a chain of nuclear reactions that take place subsequently, but not under controlled conditions. Therefore, an uncontrolled chain reaction can become highly explosive. That is because these reactions can release a very high amount of energy at a time.

For example, the radioactive isotope Uranium-235 can undergo nuclear fission be releasing neutron slowly. One isotope releases three neutrons at a time. These three neutrons can react with three other Uranium-235 isotopes releasing 9 neutrons (3 neutrons per each isotope). Likewise, the chain reaction will progress and release a very high amount of energy. These uncontrolled nuclear chain reactions are used in nuclear bombs.

What is the Difference Between Controlled and Uncontrolled Chain Reaction?

Summary – Controlled vs Uncontrolled Chain Reaction

Nuclear chain reactions can be found mainly regarding nuclear fission reactions. nuclear fission is the breakdown of an unstable atomic nucleus. The difference between controlled and uncontrolled chain reactions is that controlled chain reactions do not lead to any explosive effects whereas uncontrolled chain reactions lead to explosive energy release.

Reference:

1. Ramakrishnan, Dinesh. “Infofavour.” Nuclear Fission – Controlled and Uncontrolled Fission Reactions. Available here
2. “Controlled Fission vs Uncontrolled Fission.” JISIBHLPhysics – Controlled Fission vs Uncontrolled Fission. Available here 
3. “Nuclear Chain Reaction.” Wikipedia, Wikimedia Foundation, 31 Mar. 2018. Available here

Image Courtesy:

1.’Nuclear fission chain reaction’ By MikeRun – Own work, (CC BY-SA 4.0) via Commons Wikimedia