Nuclear Power 101

How it works, how safe it is, and, ultimately, how its costs outweigh its benefits.

Two large nuclear cooling towers stand in the distance with a cornfield in the foreground

Byron Nuclear Generating Station in Ogle County, Illinois



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What Is Nuclear Energy?

Nuclear energy comes from the core of an atom. Atoms make up all matter: the device you’re reading this on, the surface it’s resting on, and the air you’re breathing. And within each atom is a nucleus, a tightly packed core that holds protons and neutrons bound together by what’s known as the strong nuclear force. But when a neutron strikes the nucleus of certain atoms—uranium, for example—this atomic center can break into pieces in a process called nuclear fission, releasing enormous energy in the form of heat and radiation.

Nuclear power

Nuclear power comes from the energy that is released in the process of nuclear fission. Most nuclear power plants use enriched uranium as their fuel to produce electricity. This fuel contains greater amounts of a certain kind (or isotope) of uranium known as U-235. Its atoms are more easily split apart in nuclear reactors.

In fission, the nuclear fuel is placed in a nuclear reactor core and the atoms making up the fuel are broken into pieces, releasing energy. The neutrons that are released by one atomic fission go on to fission other nuclei, triggering a chain reaction that produces heat, radiation, and radioactive waste products. If uncontrolled, that chain reaction could produce so much heat that the nuclear reactor core itself could actually melt and release dangerous radiation. That’s why power plants use “control rods” that absorb some of the released neutrons, preventing them from causing further fissions.

The energy released from the fission of uranium atoms heats water, which produces steam. That’s how we get electricity. The steam goes on to spin turbines, which then drive generators. It’s the same basic principle used in coal or gas plants.

What Is Nuclear Power Used For?

We use nuclear power mainly for electricity generation. The United States is the world’s largest producer of nuclear energy, accounting for more than 30 percent of global nuclear electricity generation. One-fifth of the country’s electricity comes from nuclear power. While the energy produced in a nuclear reactor could also be used in other industrial and chemical processes, these other uses have not been adopted (except in some isolated cases), due to concerns over safety, security, and cost.

Nuclear Power Plants in the United States

A map entitled "Commercial Nuclear Power Reactors Active in the United States"


According to the U.S. Energy Information Administration, in the United States, as of January 1, 2022, there are 55 commercially operating nuclear power plants running 93 nuclear reactors in 28 states. (Most plants have more than one reactor.) Over the next few years, a few reactors are scheduled to be shut down, including California’s last nuclear reactor in 2025. Some reactors are being shut down before their operating licenses expire because of a combination of safety concerns and economic competition.

At the same time, however, some nuclear power plants are being allowed to remain operating longer than ever intended. The U.S. Nuclear Regulatory Commission (NRC) licenses plants for 40 years, and then the plant’s owners can apply to renew the license for an additional 20 years. (The regulations do not limit the number of times a license can be renewed.)

The NRC has approved a license renewal for more than 75 percent of U.S. nuclear reactors, the average age of which is currently 40 years old. This means plants are being allowed to operate for up to 60 years. Some are even starting to obtain renewals for a total of 80 years, including the Turkey Point nuclear power plant in Florida, which is being allowed to operate through at least 2053. (NRDC is in litigation challenging this decision.) And while keeping a nuclear reactor operating for 80 years is itself unprecedented, the NRC is already discussing a third round of license extensions to allow reactors to operate for 100 years.

“These aging nuclear reactors cannot compete economically with other low-carbon energy sources, like solar and wind, or with investments in energy efficiency. And new nuclear power plant designs are not proven to be safe, reliable, or economically viable,” explains Caroline Reiser, a staff attorney with NRDC’s nuclear team. “So while industry advocates argue that nuclear power is important to decarbonizing the economy, it simply isn’t a solution to the climate crisis, especially in the time frame that we need to act.”

Why Is Nuclear Power a Problem?

Nuclear reactor safety

Although U.S. nuclear power plant regulators monitor operational safety, natural hazards (such as hurricanes, floods, and earthquakes), human error, mechanical failure, and design flaws can still trigger the release of radioactive contamination.

“Leading science holds to the linear no-threshold (LNT) model for radiation protection, which assumes that even very small doses of radiation can still increase the risk for cancer,” says Bemnet Alemayehu, a staff scientist with NRDC’s Climate & Clean Energy Program. In a nuclear power plant, a specific type of radiation known as ionizing radiation, which is a form of energy that’s capable of removing electrons from atoms, is emitted both naturally from uranium and as part of the nuclear fission process. “This radiation can negatively impact workers and public health more broadly,” says Alemayehu.

After a severe accident such as a core meltdown (a kind of accident U.S. nuclear regulators call “beyond design basis”), a reactor may emit radiation into the environment, impacting all life and land around it. Immediately after such an accident, plant workers and emergency teams are most at risk of high radiation exposure, which can lead to acute radiation syndrome (ARS), also known as radiation sickness or radiation poisoning. Symptoms of ARS include skin burns, vomiting, diarrhea, and possibly even coma. The cause of death in most cases of ARS is damage to the bone marrow, which leads to infection and internal bleeding. High exposure to ionizing radiation also damages the DNA, causing cancers and genetic mutations that can be transmitted to future generations. Lower exposures to ionizing radiation also may increase the risk of developing cancers such as leukemia and thyroid cancer.

In a black and white image, a worker with protective gear reads a handheld meter, with a partially-collapsed structure in the background

A Chernobyl nuclear power plant worker holding a dosimeter to measure radiation level is seen against the background of the under-construction sarcophagus meant to confine the remains of the number 4 reactor unit, Ukraine, 1986.


Volodymyr Repik/AP

Nuclear reactor accidents

Since nuclear power began operations in the 1950s, there have been three major commercial nuclear reactor accidents. The 1986 accident at the Chernobyl plant in Ukraine (then part of the Soviet Union) is considered the worst nuclear disaster in history. An uncontrolled power surge led to explosions and fire that destroyed Unit 4 of the plant and released radioactive material—after which government secrecy and misinformation put victims at much greater risk. Radiation contamination reached all the way to Sweden. Rather than attempt to clean up the local contamination by collecting radioactively contaminated material and moving it to a permanent disposal site, the Soviet government created an “exclusion zone” within a radius of about 19 miles around the plant where access remains restricted. Approximately 350,000 people had to be permanently resettled away from the site. The accident killed 31 people directly and caused thousands of additional cancer deaths.

The second-largest nuclear accident occurred after an earthquake struck off Japan’s northeastern coast in 2011. A tsunami with 30-foot waves disabled the power supply and cooling capacity of three reactors and four spent nuclear fuel storage pools at the Japanese’s Fukushima Daiichi Nuclear Power Station, causing a nuclear accident that released radioactive material into the surrounding air and water. Radioactive substances were eventually found in all of Japan’s prefectures, and while there were no immediate deaths or cases of radiation sickness, more than 100,000 people were evacuated from their homes due to radiation risk. A decade after the accident, several towns in the area remain off-limits and, even in the areas that the government has deemed safe, many residents have chosen not to return. Indirectly, the Fukushima accident caused extreme losses in industries across Japan, including energy, tourism, agriculture, and fishing. The direct economic cost of the Fukushima accident is staggering, likely to far exceed $200 billion for cleanup and recovery, a process which is expected to take decades and comes with its own complications. Most recently, Japan has struggled with addressing radioactively contaminated wastewater, which is currently building up in on-site storage. Japan has proposed treating the wastewater and releasing it into the Pacific, an action opposed by many neighboring countries, fishing organizations, and environmental groups. Unfortunately, there’s no good choice here: Accumulation of water will overwhelm the area if stored indefinitely but any decision to release radioactive material without proper monitoring into the environment is irresponsible.

Lastly, a partial meltdown of one of the reactors at the Three Mile Island Generating Station (TMI) in Pennsylvania in 1979 released radioactive materials into the environment. Hundreds of thousands of people who lived nearby voluntarily evacuated. While there were no immediate deaths, some epidemiological studies have found inconclusive evidence that the radiation influenced cancer risk. The cleanup of the accident took more than a decade and cost approximately $1 billion (in 1993 dollars).

“Roughly speaking, the Fukushima accident was 10 times worse than the Three Mile Island accident, and the Chernobyl accident was 10 times as bad as Fukushima,” says Reiser. “The accidents have led to calls for improved safety and regulatory processes, though the extent to which reforms followed each accident is minimal in the United States.” The Chernobyl accident proved the importance of effective regulations, a safety culture, and an off-site emergency plan, as well as the value of timely and accurate government information to communities at risk from the radiation release. Yet U.S. regulators largely dismissed the lessons learned from Chernobyl as inapplicable because of the differences in culture and design between the Soviet Union and United States. While the Fukushima Daiichi accident illustrated the impact of natural disasters on nuclear power plants, the NRC declined to adopt several important and protective recommendations by its own task force. Instead, it mostly opted to allow the nuclear industry to make updates voluntary. After the Three Mile Island partial meltdown revealed the importance of human factors, U.S. regulators did require enhanced trainings, changes in emergency response procedures, and preparation of evacuation plans. However, the NRC declined a broader risk review of the accident.

Radiation exposure and protection

Current radiation protection standards are based on the premise that any exposure to radiation carries some risk, and that that risk increases directly with dose of exposure. This method of estimating risk is called the “linear no-threshold” dose-response model (LNT). “This long-standing and well-supported model states that the risk of cancer due to a low-dose exposure is proportional to dose, with no threshold,” explains Alemayehu. “In other words, a large dose exposure to radiation causes a large chance of cancer and a very small dose exposure to radiation creates a very small chance of cancer.” There is strong scientific consistency, including from groups like the U.S. National Academy of Sciences and the National Council on Radiation Protection and Measurements, that supports the use of the LNT model to develop practical guidance that protects workers and the public from the potentially harmful effects of radiation—in balance with important and commercially justified uses of radiation. To limit harmful impacts of radiation to workers from external radiation sources, LNT is a protective standard that we need to keep in place.

Nuclear power cost

Existing nuclear plants have relatively low operation, maintenance, and fuel costs compared to many fossil fuel plants; however, these routine costs still make nuclear power economically uncompetitive in comparison with wind, solar, and gas. The World Nuclear Industry Status Report estimates that the cost of generating nuclear energy in 2021 ranges between $112 and $189 per megawatt-hour (MWh), while solar power costs between $36 and $44 and onshore wind power comes in at $29 to $56. That’s why some nuclear power plants are closing before their licenses expire.

In some states, existing nuclear reactors are subsidized out of concerns about job losses, maintaining local tax bases, and climate impacts, should the nuclear plants be replaced by fossil fuels like gas power plants. “If state leaders decide to provide subsidies, it is imperative that they also enact policies to accelerate a clean energy future—one based on efficiency and renewable energy,” says Jackson Morris, director of NRDC’s work on climate and clean energy in the eastern states. “These policies should include limiting the amount of aid, instituting best practices for waste management and plant retirement, retraining or offering compensation for workers, and supporting economic development in affected communities. Companies should also have to show their books to prove the plants are actually in financial distress.”

The high construction costs of new nuclear power plants makes them uneconomical. Reactors also require a long period of planning, licensing, and building. The only new construction still being pursued in the United States are two nuclear reactors at Plant Vogtle in Georgia. These reactors are now years behind schedule and projected to cost more than twice their original budget of $14 billion. The cost of “advanced” nuclear power plants, such as small modular reactors or non-light water reactors, remain uncertain. “Advanced nuclear power is a misnomer, as the designs are descendants from those proposed decades ago,” explains Matthew McKinzie, a nuclear physicist and a senior director for NRDC’s Climate & Clean Energy Program. “None of these nuclear reactor designs have been demonstrated, let alone licensed and deployed. All costs and development timelines are merely projections, and historically, nuclear development has always cost more and taken longer than projected.”

A man in a hardhat walks in a large industrial building

The turbine deck at Three Mile Island nuclear power plant in Middletown, Pennsylvania, May 22, 2017. (Decommissioned as of 2019)


Matt Rourke/AP

Decommissioning nuclear plants

The United States’ fleet of nuclear power plants is aging. In the last decade, several nuclear reactors have permanently retired. America’s oldest operating nuclear power plant, the Oyster Creek Generating Station in New Jersey, shut down in 2018. Projections on additional retirements of nuclear power plants fluctuate based on economics.

Decommissioning nuclear power plants involves removing and safely storing spent nuclear fuel, decontaminating the plant to reduce residual radioactivity, dismantling plant structures, transferring contaminated materials to disposal facilities, and then releasing the property for other uses once the NRC has determined the site is safe. Typically, a nuclear power plant takes decades to decommission, and lax regulations allow this to stretch to as much as 60 years. The process is extremely expensive, labor-intensive, and time-consuming, with continued health and safety risks, which add to the overall cost of nuclear energy generation. Decommissioning costs are commonly estimated at $500 million per unit but the costs can run much higher. The Connecticut Yankee nuclear power plant, for example, initially had a decommissioning cost estimate of $719 million; this eventually bloated to $1.2 billion due to waste contamination in municipal landfills. And unfortunately, as of 2021, the NRC is proposing to codify the weakest of rules for decommissioning reactors, setting the stage for inadequate cleanups, a lack of support for workers and communities, and no method of meaningful public involvement.

Nuclear proliferation

A major concern about peaceful nuclear power programs is the risk of nuclear proliferation—the spread of nuclear weapons and weapons-usable material, technology, and expertise. The same technology used to make nuclear fuel for power plants can also be used to produce explosive material for nuclear weapons. In other words, if countries have the capability to enrich uranium and reprocess plutonium, then they can also manufacture nuclear warheads. In a number of countries, peaceful nuclear materials and equipment have been diverted to secret nuclear weapons programs.

The United Nations Treaty on the Non-Proliferation of Nuclear Weapons (NPT), which entered into force in March 1970, aims to prevent the spread of nuclear weapons and weapons technology, to promote cooperation in the peaceful uses of nuclear energy, and eventually to achieve nuclear disarmament. The NPT has nearly universal participation, with 191 parties, though there are four countries (India, Israel, North Korea, and Pakistan) that have nuclear arms but aren’t part of the NPT. A requirement of the NPT is that countries with nuclear arsenals—China, France, Russia, the United Kingdom, and United States—must negotiate and reduce their nuclear weapons stockpiles, ultimately eliminating these weapons of mass destruction. Distressingly, nuclear weapons are instead increasing in number, and so is the danger that they could be used in war again.

Nuclear Power and the Environment

Uranium mining

Two tall rigs and other heavy equipment sit on a large expanse of land with mountains in the background

In-situ recovery mining in Crow Butte, Nebraska


Courtesy of Cameco Corp.

Uranium, the fuel for nuclear power plants, is generally extracted in one of three ways: underground mining, surface or open-pit mining, or a chemical process called in situ leaching (ISL). Each technique has broad impacts on the human and natural environment.

Underground mining exposes workers to high levels of radon gas. Studies have found strong evidence for an increased risk of lung cancer in uranium miners due to exposure to this odorless, colorless radioactive gas formed during the natural breakdown of uranium in soil, rocks, and water. Miners are also exposed to the risk of cave-ins and pneumoconiosis, a lung disease caused by inhaling dust.

Surface or open-pit mining is safer for miners than underground mines, but the process involves blasting 30 times more earth, and the material left over after processing is radioactive and toxic. The surrounding land is also left with increased erosion, landslides, and polluted soil and water.

An aerial view of a vast open mine pit, with green land and a body of water surrounding it

An open pit uranium mine in McLean Lake, Canada


David Boily/AFP via Getty

ISL mining now accounts for most uranium production in the United States. Rather than dig uranium straight out of the earth, ISL sends liquid underground to dissolve uranium directly from the underground ore. This solution is then pumped to the surface where the mineral can be recovered. ISL operations, currently located mainly in Nebraska, Texas, and Wyoming release considerable amounts of radon and produce waste slurries and wastewater during recovery of the uranium from the liquid solution. The most pressing environmental risk associated with ISL, however, is the contamination of groundwater. Restoring natural groundwater conditions after completion of leaching operations is virtually impossible and has never been achieved.

A tunnel is formed out of rock, with a brick doorway and facade at the far end. The rock surfaces are covered in a yellow-brown subtance.

An abandoned underground uranium mine


Alexey Dozmorov/iStock

Uranium mining in the United States has dropped sharply since its 1980 peak. (Today, Kazakhstan is the biggest uranium miner, followed by Australia and Canada.) But the southwestern United States is littered with thousands of abandoned uranium mines—presenting serious issues of environmental injustice. Just east of Grand Canyon National Park, in the Navajo Nation, hundreds of abandoned uranium mines remain a threat to the health of communities and the Colorado River ecosystem. Many communities still suffer from environmental contamination, toxic spills, and under-addressed cancer and disease clusters.

Three long rows of gray tanks are lined up inside an enclosed building

Nuclear waste storage at a decommissioned plant


Enrico Salvadori/Alamy

Nuclear waste

The most infamous among nuclear power’s environmental impacts is nuclear waste. Nuclear waste is generated at every step in the processing and use of nuclear power, from so-called low-level waste (LLW) to spent nuclear fuel and uranium mill tailings (radioactive sandy waste containing heavy metals and radium). The United States also has high-level waste (HLW) from the production of nuclear weapons.

LLW includes items that have been contaminated with radioactive material or become radioactive through exposure to neutron radiation in the nuclear power plant, like containers used for shipment, workers’ clothes and shoes, paper, rags, and anything else that might have been used for handling or cleanup of nuclear waste. The radioactivity from LLW can vary from natural background levels to much greater amounts, such as parts from inside a reactor vessel.

Spent nuclear fuel is used fuel from a nuclear reactor that is no longer efficient in creating electricity because its fission process has slowed. “It is both deadly and long-lasting,” says Geoffrey Fettus, a senior attorney at NRDC and director of NRDC’s nuclear team. “It remains dangerous to people’s health and the environment for millennia.” Even a U.S. federal court described the time frame as “seemingly beyond human comprehension. For example, iodine-129…has a half-life of 17 million years.”

The United States currently has more than 90,000 metric tons of nuclear waste to dispose of. That number is projected to rise to 140,000 metric tons over the next several decades. Most of this waste is stored where it was generated with no permanent disposal solution. In 1987, for political rather than technical reasons, Yucca Mountain, Nevada, was chosen as a final repository for the country’s nuclear waste. “But the plan was abandoned and has remained in limbo due to a number of concerns: potential leaks at the site, the lack of a waste transportation plan, a failure to ensure protective health and oversight standards—which apply to all other forms of environmental law—and the lack of consent from Nevada itself,” explains Fettus. Since the Obama administration’s U.S. Department of Energy terminated the license application in 2010, there has been no consensus between the executive branch and Congress on what to do with all of the nuclear waste.

“There is a path forward. One based on sound science that could earn public acceptance,” says Fettus. “The regulation of nuclear waste needs to be harmonized with core environmental laws that follow the basic premise of federalism—a real partnership between states and the federal government. This change will create an accountable consent-based siting process that provides host states and communities an equal role in managing any nuclear waste site. Fortunately, Congress has taken some first steps toward breaking the logjam.”

An aerial view of a power plant situated on a coastline with mountains behind it

Diablo Canyon Power Plant


Marya via Wikimedia Commons

Climate change

In 2020, nuclear power made up half of the low-carbon energy generated in the country. But it remains unclear how great a role nuclear will continue to play in a zero-carbon future and in our fight against climate change.

One major issue is that existing nuclear plants are extremely vulnerable to the impacts of climate change. Changes to air and water temperatures, wind speeds and patterns, precipitation extremes, and sea level rise—all consequences of climate change—can decrease the efficiency of nuclear reactors, require operators to cut back or shut off reactors, increase the cost of nuclear power, and increase safety and environmental risks.

For instance, rising temperatures can warm the power plant’s source of cooling water, which operators rely on to ensure safety within the core and in spent fuel storage areas. Inland reactors that use rivers as a source for cooling water are particularly at risk during heat waves—which are very likely to occur more often and last longer in the coming decades. Warming waters have already caused several nuclear power plants to scale back generation or shut down temporarily. Operators of a number of plants, such as the Millstone plant in Connecticut and Turkey Point in Florida, have obtained permission from the NRC to increase the maximum temperature limit for the cooling water they release back into the environment. This allows the nuclear plants to continue producing electricity but can negatively impact water quality and ecosystem health.

Increasingly severe hurricanes and flooding can also damage nuclear power plants and cut off access to cooling water, similar to the events of the Fukushima Daiichi nuclear accident. The NRC has concluded that 55 of the 61 evaluated U.S. nuclear sites face flooding hazards beyond what they were designed to withstand (yet it has failed to require updates based on that information).

With sea level rise and increasing frequency and severity of extreme weather events, the risks to both operational and decommissioned nuclear plants that store nuclear waste on-site continue to grow. While all power-generating technologies are vulnerable to climate change, impacts to nuclear power plants can lead to catastrophic accidents with irreversible and widespread health and environmental effects.

Some adaptations can be made but, with the average age of nuclear plants in the United States hitting 40 years, “the possibility and value of continuing to update these aging plants rather than replacing them with more efficient and resilient alternatives comes ever more into question,” says McKinzie. “And replacing old, existing nuclear reactors with new so-called ‘advanced’ reactors is questionable as well. Advanced reactors may suffer the same challenges as existing reactors—including ever-increasing costs and design and construction timelines. The evidence suggests that advanced reactors will not be economical or developed in time to create a zero-carbon electricity grid.”

A worker sits on a large flat room among an array of solar panels, with wind turbines in the background

Franco Lucato/Shutterstock

Alternatives to Nuclear Power

Nuclear power has beneficial low-carbon attributes, but the significant safety, global security, environmental, and economic risks make the future of nuclear energy in the United States uncertain. “Thankfully, there are pathways to a low-carbon future with minimal nuclear support,” says Reiser. “The energy sector is undergoing a major shift toward renewable energy and energy efficiency. Wind farms have become a familiar part of the landscape and solar panels have spread across rooftops from coast to coast.”

A 2019 report from the International Energy Agency (IEA) predicts global renewable power capacity will expand by 50 percent between 2019 and 2024, led largely by solar. That is an increase of 1,200 gigawatts, the equivalent of the total installed power capacity of the United States. Another 2019 IEA report projects that global capacity for offshore wind—which has the potential to generate more than 18 times the current electricity demand of the entire world—will grow to 15 times its current size by 2040. Renewable energy costs have also dropped dramatically. Since 2015, costs for solar energy have fallen by 33 percent, onshore wind by 22 percent, offshore wind by 40 percent, and battery storage by 49 percent.

Energy efficiency is the art of getting the same or better performance using less energy, and it’s one of the most powerful weapons for combating global climate change, boosting the economy, and ensuring that the air is safe to breathe. “Energy efficiency is America’s largest energy resource, says Morris. “It contributes more to the nation’s energy needs over the last 40 years than oil, coal, natural gas, or nuclear power.” Thanks to energy efficiency, annual U.S. consumption of energy is about the same now as it was 15 years ago. And huge opportunities for efficiency remain untapped in every sector of the economy.

These renewable energy and efficiency technologies are growing, but support for research and development is critical for continued innovation. “We have to ensure a more economical and equitable transition away from nuclear power and fossil fuels,” says McKinzie, “so that we can move toward a cleaner power sector and safer climate future.”

This story was originally published on May 14, 2020, and has been updated with new information and links.

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