Nuclear Fission

Background
Nuclear power is electricity derived from the energy at the core of an atom. Energy is released when the nucleus of an atom splits (fission) or merges with the nucleus of another atom (fusion).

Conventional nuclear power relies on fission; it accounts for nearly 20% of electricity production in the United States and 10% worldwide. But we’re still learning how to utilize fusion reactions.

Nuclear plants take years and cost tens of billions of dollars to build, but they don’t produce greenhouse gases and have large generating capacities. See a map of active US nuclear plants here.


History
Nuclear fission was discovered in 1938 in a Berlin laboratory. It was quickly co-opted by the Axis and Allied powers racing to create destructive weapons during World War II. The top-secret American effort, known as the Manhattan Project, produced the atomic bombs that were dropped on Hiroshima and Nagasaki, Japan, in August 1945.

Six years later, in a rural Idaho desert, the US built the world’s first nuclear power plant. At first, it could power only four 200-watt light bulbs. Today, nuclear power accounts for roughly half of carbon-free electricity in the US.

Most US nuclear reactors were built between 1967 and 1990. Further construction became hindered, however, for a variety of reasons, including construction time, cost, safety concerns, and the introduction of cheap natural gas.


How It Works
All commercially operating nuclear plants generate power via fission, and most use uranium as fuel. The silvery-white metal is mined, milled, and then enriched (see overview).

When a neutron hits these uranium atoms, it sets off a chain reaction (visualize here). As the atoms split into smaller atoms and neutrons, they release energy in the form of heat and radiation. The heat is used to boil water. The resulting steam is funneled through a large turbine, causing it to spin and produce electricity that’s fed to the power grid.

Spent uranium fuel must be carefully cooled and buried underground because it’s highly radioactive and capable of damaging or killing cells in living things. Read about the long-standing debate over waste storage here.

Meltdowns are rare but dangerous accidents that occur when the core of a reactor overheats and melts. Radioactive materials can escape into the surrounding area, poisoning nearby communities and ecosystems. The worst meltdowns occurred at Ukraine’s Chernobyl plant in 1986 and Japan’s Fukushima Daiichi plant in 2011. The most serious domestic accident was a partial meltdown at Pennsylvania's Three Mile Island plant in 1979.

While it's difficult to trace diseases back to radiation exposure, studies have linked the Chernobyl meltdown to increased cancer prevalence, and these accidents have severely damaged public perception of nuclear power.


Future
The advent of power-hungry data centers and the race to reach net-zero emissions by midcentury have renewed interest in nuclear power. The Biden administration unveiled a roadmap to triple the nation’s nuclear capacity by 2050, and tech giants at the forefront of AI have also announced multibillion-dollar investments in nuclear power.

Since building traditional reactors is so expensive and time-intensive, significant attention is being given to restarting mothballed reactors and developing small modular reactors, which produce less power but are safer and cheaper.

Scientists have also spent decades trying to generate power from fusion, which could bring more low-carbon electricity to the grid without producing long-lasting nuclear waste. They achieved a breakthrough in California Dec. 5, 2022, sparking a fusion reaction that created more energy than it used. The feat, known as ignition, has since been replicated with steadily increasing energy yields.