Enleashed

Learning objectives

By the end of this lesson you should be able to:

Understand how nuclear power stations generate electricity.
Explain the strengths and limitations of nuclear generation.
Recognise the role nuclear power can play in a low-carbon electricity system.
Understand why nuclear plants are often described as providing dependable baseload generation.
Appreciate why nuclear technologies should be evaluated according to the system services they provide, not simply their cost per megawatt-hour.

Introduction

Few electricity technologies generate as much debate as nuclear power.

Supporters point to its ability to produce enormous quantities of low-carbon electricity reliably for many decades.

Critics highlight the high construction costs, long development times, radioactive waste and the consequences of rare but severe accidents.

Regardless of these debates, nuclear power remains one of the largest sources of low-carbon electricity in many countries.

From an engineering perspective, nuclear power stations are simply another way of producing heat.

Instead of burning coal or natural gas, they obtain heat from controlled nuclear fission.

That heat is then used to generate electricity in much the same way as a conventional thermal power station.

How does nuclear power work?

A nuclear power station converts nuclear energy into electrical energy through several stages.

Nuclear fuel undergoes controlled fission inside the reactor.
The fission process releases heat.
The heat converts water into high-pressure steam.
The steam drives a turbine.
The turbine rotates a synchronous generator.
Electricity is produced.

Although the source of heat differs, the turbine-generator arrangement is remarkably similar to that used in coal-fired power stations.

Nuclear fission

The fuel used in most nuclear reactors contains uranium.

When a uranium nucleus absorbs a neutron, it becomes unstable and splits into two smaller nuclei.

This process is called nuclear fission.

Fission releases:

Heat.
Additional neutrons.
Radiation.

The newly released neutrons can trigger further fission reactions.

This creates a chain reaction.

Inside a reactor, this chain reaction is carefully controlled so that it proceeds steadily rather than explosively.

Controlling the reactor

The power output of a nuclear reactor is controlled by regulating the chain reaction.

This is achieved using control rods, which absorb neutrons.

When the control rods are inserted further into the reactor:

More neutrons are absorbed.
Fewer fission reactions occur.
Heat production decreases.

When they are withdrawn:

More neutrons remain available.
The chain reaction increases.
Heat production rises.

This allows operators to regulate reactor output safely.

Why nuclear fuel is so energy dense

One of the most remarkable characteristics of nuclear fuel is its energy density.

A very small quantity of uranium contains an enormous amount of usable energy compared with fossil fuels.

This means nuclear stations require relatively small amounts of fuel to produce very large quantities of electricity over many years.

Fuel transport and storage therefore represent a much smaller part of operating costs than they do for conventional thermal power stations.

Nuclear as a thermal generator

Although nuclear energy is fundamentally different from burning fossil fuels, nuclear stations behave operationally much like other thermal generators.

They:

Produce electricity continuously.
Use steam turbines.
Operate synchronous generators.
Contribute inertia.
Provide voltage support.
Supply fault current.

From the perspective of the electricity network, they behave much more like coal or gas stations than wind or solar farms.

Baseload generation

Nuclear power stations are often described as baseload generators.

Historically, this meant they operated continuously at high output to meet the relatively constant portion of electricity demand.

There are several reasons for this.

Nuclear plants have:

Very high construction costs.
Relatively low fuel costs.
Long start-up and shutdown times.

Once operating, it is generally most economical to run them continuously rather than frequently changing their output.

Although many modern reactors can adjust their output, they are generally less flexible than gas-fired generators.

Strengths of nuclear power

Nuclear generation offers several significant advantages.

Very low operational carbon emissions

Unlike fossil fuel generators, nuclear reactors produce electricity without emitting carbon dioxide during normal operation.

This makes nuclear one of the lowest-carbon large-scale electricity technologies.

High availability

Nuclear stations typically operate for long periods between refuelling outages.

Many reactors achieve capacity factors exceeding 90%, meaning they generate electricity for most of the year.

Dependable generation

Unlike wind and solar generation, nuclear output does not depend on weather conditions.

Provided maintenance and refuelling are properly managed, output remains highly predictable.

Large generating capacity

Individual nuclear stations often produce more than one gigawatt of electricity.

This allows relatively few sites to supply significant proportions of national demand.

Grid support

Because nuclear stations use large synchronous generators, they naturally provide:

Inertia.
Voltage support.
Fault current.
Frequency response.

These services contribute to overall system reliability.

Limitations of nuclear power

Despite these advantages, nuclear power also faces important challenges.

High construction costs

Building nuclear stations requires enormous upfront investment.

Projects often cost many billions of pounds.

Long construction times

Planning, licensing and construction may take more than a decade.

This makes nuclear a long-term investment rather than a rapid solution to increasing electricity demand.

Operational flexibility

Although modern reactors can vary their output, many are designed primarily for continuous operation rather than frequent cycling.

Radioactive waste

Spent nuclear fuel remains radioactive for long periods.

Managing and storing this waste safely is an important engineering and policy challenge.

Public acceptance

Accidents such as:

Three Mile Island.
Chernobyl.
Fukushima.

have significantly influenced public attitudes towards nuclear power, despite major improvements in reactor safety over recent decades.

Safety

Modern nuclear power stations are designed with multiple layers of protection.

These include:

Physical containment structures.
Redundant cooling systems.
Automatic shutdown systems.
Extensive monitoring and regulation.

The objective is to ensure that no single equipment failure can lead directly to a serious accident.

Nuclear engineering therefore places exceptional emphasis on defence-in-depth and conservative safety design.

Small Modular Reactors (SMRs)

One proposed development is the Small Modular Reactor (SMR).

Rather than constructing very large bespoke reactors on site, SMRs aim to manufacture much of the plant in factories before transporting modules for assembly.

Potential advantages include:

Lower upfront investment.
Shorter construction times.
Standardised designs.
Easier financing.

Whether SMRs achieve these objectives remains to be demonstrated at commercial scale.

Nuclear in a low-carbon electricity system

Many countries view nuclear power as one possible component of achieving net-zero emissions.

Nuclear complements renewable generation because it provides:

Low-carbon electricity.
High availability.
Predictable output.
Large-scale generation.

However, electricity systems with high shares of renewable generation also require flexibility.

Nuclear contributes relatively little operational flexibility compared with technologies such as batteries, demand response or gas turbines.

As a result, nuclear is often viewed as one component of a broader portfolio of technologies rather than a complete solution on its own.

Why £/MWh is not enough

Suppose two technologies both produce electricity at £70/MWh.

One generates:

Continuously.
Independently of weather.
With very high availability.
While providing inertia and system strength.

The other generates:

Only when weather conditions permit.
Without inertia.
With highly variable output.

Although both produce electricity at the same energy cost, they contribute different forms of system value.

Comparing them solely using £/MWh ignores these differences.

Instead, technologies should also be evaluated according to:

Availability.
Capacity value.
Flexibility.
Grid support services.
Reliability.
Location.

A key insight

Nuclear power demonstrates an important principle that applies throughout electricity system design.

A technology's contribution is determined not only by how much energy it produces, but also by the reliability and engineering services it provides.

Nuclear generation combines:

Very high energy production.
High availability.
Low operational emissions.
Strong contributions to system stability.

Its principal challenges lie in construction cost, development time and long-term waste management rather than day-to-day system operation.

Key takeaways

Nuclear power generates electricity using heat produced by controlled nuclear fission.
Nuclear stations behave operationally much like other large thermal power stations.
Nuclear generation provides low-carbon electricity with very high availability.
Nuclear plants contribute important system services including inertia, voltage support and system strength.
High capital costs and long construction times are among nuclear power's principal challenges.
Radioactive waste management and public acceptance remain important policy considerations.
Small Modular Reactors aim to reduce construction cost and complexity, but their long-term commercial performance remains uncertain.
Nuclear technologies should be evaluated according to the full range of system services they provide, not simply their cost per megawatt-hour.

Looking ahead

Nuclear power provides dependable, low-carbon generation that is largely independent of weather.

The next lesson examines two very different technologies—wind and solar power—whose output depends directly on natural resources and which are transforming electricity systems around the world.