Nuclear power

Nuclear power refers to the use of nuclear reactions to generate electricity, primarily through the harnessing of energy released from nuclear fission. Additional, smaller-scale applications employ nuclear decay, while nuclear fusion—although experimentally demonstrated since the 1950s—has not yet achieved commercial viability. The global nuclear power sector has evolved through rapid early expansion, subsequent regulatory and economic challenges, and renewed interest driven by the need for low-carbon energy systems.

Overview and Principles

In modern electricity generation, most nuclear power comes from the fission of uranium and plutonium in nuclear reactors. These reactors use controlled chain reactions to produce large amounts of heat, which is converted into electrical energy. The fission of heavy nuclei releases energy several million times greater per unit mass than chemical fuels, making it one of the most concentrated energy sources available.
Other nuclear processes contribute in specialised contexts. Radioisotope thermoelectric generators (RTGs), powered by nuclear decay, are widely used in deep-space missions such as Voyager 2, where long-term electrical power is required without sunlight. Fusion reactors, which aim to merge light nuclei to release energy, have been operated experimentally since 1958. However, they have yet to generate net power and remain a long-term technological goal.
Globally, nuclear power plants supplied over 2,600 TWh of electricity in 2023, providing around 9% of total electricity generation. This output makes nuclear energy the second-largest low-carbon electricity source, after hydropower. The world nuclear fleet consists of hundreds of reactors with a combined capacity of more than 370 GW, alongside dozens under construction or planned.

Historical Development

The foundations of nuclear power were laid through early twentieth-century studies of radioactivity and the eventual discovery of nuclear fission in 1938. By 1939, scientists had demonstrated that the neutrons released during fission could sustain a nuclear chain reaction, prompting major wartime research initiatives.
The world’s first human-made nuclear reactor, Chicago Pile-1, achieved criticality in 1942 under the University of Chicago stadium as part of the Manhattan Project. This wartime research also produced large reactors designed to manufacture weapons-grade plutonium. The first nuclear weapon test, Trinity, occurred in 1945, followed soon after by the atomic bombings in Japan, demonstrating the profound power of nuclear reactions.
Despite these military origins, optimism grew in the post-war years about the peaceful potential of atomic energy. Electricity from nuclear fission was first generated on 20 December 1951 at the Experimental Breeder Reactor I in Idaho. In 1953, President Dwight Eisenhower’s Atoms for Peace address encouraged international collaboration on civilian nuclear power, followed by legislative changes that enabled private-sector reactor development.
The Soviet Union’s Obninsk Nuclear Power Plant became the first station to supply electricity to an electrical grid in 1954. The United Kingdom then opened Calder Hall in 1956, the world’s first commercial-scale plant, which served both power generation and plutonium production.

Expansion and Early Opposition

Nuclear power expanded rapidly from the 1960s to the 1980s. Global installed capacity rose from under 1 GW to around 300 GW by 1990. This period included dramatic national programmes, notably in France, which constructed dozens of reactors in response to the 1973 oil crisis, ultimately meeting over two-thirds of its electricity demand with nuclear power.
However, public scrutiny began to intensify from the late 1960s onward. Concerns about reactor safety, nuclear waste management, proliferation risks, and the possibility of nuclear terrorism helped fuel opposition movements. Protests in countries such as West Germany, the United States, and others influenced political perceptions of nuclear power.
Two major accidents significantly affected global attitudes:

• Three Mile Island (1979) in the United States, which involved a partial reactor core melt but no fatalities.
• Chernobyl (1986) in the Soviet Union, which released significant radioactive material, led to widespread contamination, and resulted in long-term health and environmental consequences.

These events prompted stricter regulatory regimes, extended construction timelines, higher costs, and reduced investor confidence. In several countries, planned reactors were cancelled, and new construction slowed markedly through the 1990s.

Modern Era and Reactor Technologies

By the late 1980s, one new nuclear reactor began operation roughly every few weeks. After this period, growth slowed, but nuclear power remained a stable contributor to global electricity. In the twenty-first century, most new reactors under construction are Generation III designs, offering improved safety systems, passive cooling features, and longer operational lifetimes.
The United States maintains the world’s largest reactor fleet, generating nearly 800 TWh annually with a high average capacity factor of around 92%, indicating the reliable performance of existing plants. Asia, particularly China, has become the leading region for new reactor construction.
Nuclear power plants are recognised as low-carbon energy sources, emitting virtually no greenhouse gases during operation and demonstrating low lifetime emissions even when construction and decommissioning are included. By several independent assessments, nuclear energy has among the lowest fatality rates per unit of energy produced, largely due to minimal air pollution impacts. Economists estimate that the deployment of a single nuclear plant can save hundreds of thousands of life-years relative to fossil fuel-based generation.
Nonetheless, the technology remains contentious. Critics emphasise issues such as nuclear accidents, long-term waste disposal, high capital costs, and competition from cheaper renewable energy technologies. The Fukushima Daiichi accident in Japan in 2011 reignited global debate, although many countries retained or adjusted their nuclear programmes rather than abandoning them.

Uses, Benefits, and Challenges

Nuclear power offers several significant advantages:

• Baseload reliability, with high capacity factors
• Very low greenhouse gas emissions
• Energy density, enabling significant output from compact facilities
• Reduced dependence on fossil fuels, improving energy security

However, the sector faces enduring challenges:

• High upfront construction costs and long project timelines
• Management of high-level radioactive waste requiring long-term isolation
• Public perception and political opposition
• Risk of accidents, although rare, with potentially severe consequences

Balancing these factors remains at the core of global energy policy debates.

Outlook and Future Prospects

Current projections indicate that nuclear power will continue to play an important role in the global low-carbon energy mix. Nations pursuing ambitious climate targets increasingly evaluate nuclear energy as complementary to renewables, particularly for stable baseload supply.
Advanced reactor concepts—such as small modular reactors (SMRs), Generation IV systems, and eventually fusion—form part of long-term plans to enhance safety, flexibility, and sustainability. While fusion remains experimental, its potential for abundant clean energy sustains significant international research investment.