Topic 6.6 Notes – Nuclear Power

What Nuclear Power Is

Nuclear power plants make electricity from nuclear fission, not from burning fuel. That matters because there is no combustion in the reactor, so the plant does not directly release the usual air pollutants from fossil fuels during operation.

The fuel you need to know is U-235. In fission, a neutron hits a U-235 nucleus, and the nucleus splits into smaller nuclei. That split releases:

• heat that can be used to boil water
• radiation from unstable particles and nuclei
• more neutrons that can hit other U-235 atoms

Those extra neutrons create a chain reaction. In a reactor, that chain reaction is controlled so energy comes out steadily. In an uncontrolled release, energy is released dangerously fast.

A quick reminder on vocabulary:

• Radioactivity means an unstable nucleus gives off radiation and loses energy on its own.
• Fission splits large nuclei and is used in power plants.
• Fusion joins small nuclei and powers the Sun. It is not what current commercial nuclear plants use.

Even though uranium is very energy-dense, nuclear power is still nonrenewable because uranium is finite.

How a Nuclear Power Plant Generates Electricity

Here’s the basic flow from fuel to electricity. The diagram traces the reactor, steam system, turbine, generator, condenser, and cooling tower in one continuous process.

Nuclear power plant diagram

1. Uranium is mined, processed, enriched, and sealed into fuel rods.
2. In the reactor core, U-235 atoms undergo fission and release nuclear energy.
3. That energy becomes thermal energy in the reactor and coolant.
4. Water is heated into steam.
5. Steam spins a turbine.
6. The turbine turns a generator, which makes electricity.
7. A condenser and cooling system cool the water so it can be reused.

Main parts to know:

• Fuel rods contain U-235 fuel.
• Control rods absorb neutrons and slow or regulate the chain reaction.
• Moderator is usually water and slows neutrons so fission is more likely.
• Coolant carries heat away from the core.
• Containment building helps limit radiation release.

One common test trap: cooling towers release water vapor, not smoke. The diagram labels this clearly at the top of the tower. Also, nuclear plants do not directly produce combustion air pollutants like coal plants do.

Radioactivity, Half-Life, and Nuclear Waste

Radioactive isotopes have unstable nuclei that emit ionizing radiation, which can damage cells and DNA. That is why nuclear waste has to be isolated from organisms and the environment.

Half-life is the time required for half of a radioactive sample to decay. Decay is exponential, not linear.

$$N = N_0\left(\frac{1}{2}\right)^{t/T_{1/2}}$$

You may also see activity instead of amount:

$$A = A_0\left(\frac{1}{2}\right)^{t/T_{1/2}}$$

Where:

• $N_0$ or $A_0$ = initial amount or activity
• $t$ = elapsed time
• $T_{1/2}$ = half-life

The graph here is the pattern to remember. Each half-life cuts the parent isotope remaining in half, so the curve drops quickly at first and then more slowly.

Radioactive decay over successive half-lives

A very common mistake is mixing up amount remaining and amount decayed. After 3 half-lives, $\left(\frac{1}{2}\right)^3 = \frac{1}{8}$ remains, so 7/8 has decayed.

Why this matters here:

• U-235 has a very long half-life
• spent fuel stays hazardous for a long time
• no treatment makes radioactive waste immediately harmless

Storage methods:

• Spent-fuel pools cool and shield fuel right after removal
• Dry casks are safer interim storage
• Deep geologic disposal is the proposed permanent solution

Environmental Benefits and Costs

Nuclear power has a clear trade-off.

Benefits

• low direct air pollution during operation
• low operational greenhouse-gas emissions
• no direct emissions of sulfur dioxide, nitrogen oxides, particulate matter, or mercury
• reliable, high-output electricity
• very high energy density

Costs

• uranium mining and processing disturb land and can pollute water
• radioactive solid waste is hazardous
• plants need a lot of cooling water
• thermal pollution can harm aquatic ecosystems because warmer water holds less dissolved oxygen and can cause thermal shock
• accidents are low-probability but high-impact

So nuclear is cleaner than fossil fuels for routine air pollution, but it is not renewable, waste-free, or risk-free.

Major Nuclear Accidents and Their Environmental Effects

Three Mile Island

Equipment malfunction plus human error led to a partial core meltdown. Containment mostly worked, so radiation release was limited. There was major public fear and stricter regulation, but little clear population-wide health effect.

Three Mile Island nuclear power plant

Chernobyl

An unsafe test plus reactor design flaws caused explosions and fire. The reactor had no robust containment structure, so there was a massive atmospheric radiation release. Effects included worker and responder deaths, increased thyroid cancer, contaminated soil, water, and crops, and a long-term exclusion zone.

Fukushima Daiichi

An earthquake and tsunami knocked out backup power and cooling. That led to multiple meltdowns and hydrogen explosions. Radiation was released to air and water, including the ocean. Effects included evacuations, food and water restrictions, and long-term cleanup and decommissioning.

Shared effects show up a lot on tests:

• Short-term includes evacuation, contaminated food and water, and acute exposure at high doses.
• Long-term includes cancer risk, contaminated land and water, monitoring, decontamination, land-use limits, and displacement.