Nuclear Energy: Fission

Learning Objectives

Describe the structure of an atom's nucleus.

Define nuclear fission as the splitting of a heavy nucleus.

Explain the concept of a nuclear chain reaction.

Understand that fission releases a large amount of energy from a small amount of mass (E=mc²).

Identify the main advantages and disadvantages of nuclear power.

Energy from the Atom's Core

Most of the energy we use, from burning wood to burning fossil fuels, comes from chemical reactions. These reactions involve rearranging the electrons on the outside of atoms. But there is another, much more powerful source of energy that is stored inside the atom: nuclear energy.

Nuclear energy is the energy stored in the nucleus, the tiny, dense core of an atom. The nucleus is made of protons and neutrons. There is a tremendous amount of force (the strong nuclear force) holding these particles together.

Fission: Splitting the Atom

There are two ways to release nuclear energy. The one we use in nuclear power plants is called nuclear fission.

Fission is the process of splitting a large, unstable atomic nucleus (like Uranium-235) into two or more smaller nuclei.

How it works: A neutron is fired at a large nucleus. The nucleus absorbs the neutron, becomes extremely unstable, and splits apart.

What is produced:

1.Two smaller nuclei (called fission products).

2.A few extra free neutrons.

3.A massive amount of energy.

E=mc²: Mass into Energy

Where does this energy come from? It comes from converting mass directly into energy. If you were to measure the total mass of all the pieces after the fission reaction, it would be slightly less than the mass of the original atom and neutron. This tiny amount of 'missing' mass has been converted into a huge amount of energy, according to Albert Einstein's famous equation, E = mc².

Chain Reaction

The key to making fission useful is the chain reaction.

When the first uranium nucleus splits, it releases 2 or 3 new neutrons.

These new neutrons can then fly off and strike other uranium nuclei, causing them to split.

Those fissions then release even more neutrons, which cause even more fissions.

This creates a rapidly growing chain reaction.

In a nuclear weapon, this chain reaction is uncontrolled, releasing a massive amount of energy all at once.

In a nuclear power plant, control rods are used to absorb some of the neutrons, keeping the chain reaction at a steady, controlled rate to produce a constant amount of heat.

Pros and Cons of Nuclear Power

Nuclear power is a complex issue with significant advantages and disadvantages.

Advantages:

No Greenhouse Gases: Nuclear power plants do not burn anything, so they produce no carbon dioxide. This makes them a major source of carbon-free electricity.

Huge Power Output: A very small amount of uranium fuel can produce a massive amount of electricity.

Disadvantages:

Radioactive Waste: The spent nuclear fuel is highly radioactive and remains dangerous for thousands of years. Storing this waste safely is a major challenge.

Safety Concerns: Although rare, accidents at nuclear power plants (like Chernobyl or Fukushima) can be catastrophic and release dangerous radiation into the environment.

Key Terms

**Nucleus: The central and most important part of an object, movement, or group, forming the basis for its activity and growth. In an atom, it is the positively charged central core containing protons and neutrons.
**Nuclear Fission: The splitting of a heavy, unstable nucleus into two lighter nuclei.
**Chain Reaction: A process in which neutrons released in fission produce an additional fission in at least one further nucleus. This nucleus in turn produces neutrons, and the process repeats.
**Uranium-235: A specific isotope of uranium that is the primary fuel used in nuclear fission reactors because it can easily sustain a chain reaction.
**Radioactive Waste: Hazardous waste that contains radioactive material. It is a byproduct of nuclear power generation.