JULY 2020 - Nuclear Power: Today’s Climate Change Solution or Tomorrow’s Predicament?

Nuclear power offers a low-carbon energy source, but radioactive waste management still presents significant challenges for the industry.

Credit: Nuclear Regulatory Commission

With substantially lower greenhouse gas (GHG) emissions than fossil fuel-generated electricity, nuclear power has received new attention as one measure to lower global GHG emissions and help mitigate climate change. While there is mounting urgency to develop and deploy carbon-free energy technologies, it is important to consider related environmental, health, and safety risks regardless of those technologies. Is the U.S., and indeed the world, prepared to deal with the unique risks and challenges that nuclear energy presents in return for its carbon benefits?

What’s in a Nuclear Power Plant?

Nuclear power plants use controlled nuclear fission to release energy that is used to drive a steam turbine, which in turn runs a generator. The nuclear fuel that powers all these processes, commonly uranium, is packaged into fuel pellets that are placed into a fuel rod, and a group of rods is then arranged into a fuel bundle. A commercial nuclear power plant can contain hundreds of fuel bundles. Nuclear fuel is placed inside a reactor pressure vessel, a sealed chamber designed to operate under conditions of high temperature and pressure, where the fission reaction takes place. Coolant (typically water) enters the reactor vessel, absorbs thermal energy released by the fission reactions, and transfers it to a steam turbine. 

The reactor pressure vessel is housed inside a containment structure typically constructed of steel and concrete. This containment structure and the components within it are collectively known as a nuclear reactor. Nuclear power plants also include many ancillary systems in addition to the reactor, including monitoring and control equipment, steam turbines and electric generators, transformers, cooling towers, and spent nuclear fuel storage. 

In the U.S., approximately two-thirds of all commercial nuclear power plants use a type of reactor known as a pressurized water reactor, while the remaining one-third use boiling water reactors. In boiling water reactors, the coolant (water) is allowed to boil inside the reactor, and the steam is then pumped directly to a steam turbine. In pressurized water reactors, water does not boil but exits the reactor vessel as a highly pressurized, superheated liquid. A steam generator inside the reactor transfers this energy to a secondary coolant circuit, which drives the turbine, while the primary coolant returns to the reactor vessel. 

There are various other types of commercial reactors in use globally, although these are not common in the U.S. Some of these reactor designs include gas-cooled reactors, liquid sodium reactors, and heavy-water reactors. Research is ongoing in the U.S. and elsewhere to develop new designs that increase efficiency and minimize the generation of spent fuel.

Schematic diagram of a boiling water reactor (BWR). Credit: Nuclear Regulatory Commission

The GHG emissions from nuclear power generation are actually comparable to wind energy, slightly less than solar photovoltaic, and significantly lower than fossil fuels. While carbon capture and sequestration (CCS) does provide a potential means to lower emissions from fossil fuel-based electricity generation, CCS technologies have not yet been deployed on a commercial scale, partly due to their high initial costs. Viewed from this perspective, nuclear power, which has been commercially deployed worldwide for several decades, would appear to offer a significant benefit over coal and natural gas, the other common fuels used for electricity generation. Nuclear power already accounts for 20 percent of total electricity generation in the U.S., while solar and wind account for approximately 2 percent and 7 percent, respectively. Coal and natural gas have by far the largest share, together accounting for approximately 60 percent of all electricity generated in 2019. However, as we explain below, nuclear power has its own unique set of challenges that stem from the use of radioactive materials as fuel.

Source: Intergovernmental Panel on Climate Change

When uranium undergoes fission, it creates byproducts that are even more radioactive than the original fuel. Most of these highly radioactive materials are contained within the spent nuclear fuel, but significant amounts of radioactivity can also be present in certain reactor components. Safe, long-term disposal of spent nuclear fuel and other highly radioactive reactor components is likely the greatest unsolved challenge facing the nuclear industry, not only in the U.S. but globally.

While a nuclear power plant is in operation, it releases small, permitted amounts of radioactivity on an ongoing basis through wastewater discharges and air emissions. Like any other type of infrastructure, however, pipes and other components in a nuclear power plant are subject to corrosion and decay over time. As these components age, the potential for leaks into the environment increases. The average age of operating nuclear reactors in the U.S. is 38 years, and only 4 reactors are less than 30 years old. The safe operation of these aging plants is another challenge.

In the U.S., the Nuclear Regulatory Commission (NRC) is the agency responsible for regulating nuclear power plants and ensuring that they comply with safety and environmental requirements. Licensing of a new reactor requires, among other steps, preparing an Environmental Impact Statement that analyses the potential impacts of siting, constructing, and operating the plant.

Fukushima Daiichi Nuclear Power Plant, Japan. Credit: International Atomic Energy Agency

Once a nuclear power plant reaches the end of its economic life, it is shut down and decommissioned. During shutdown, the plant’s systems are brought offline and placed into a safe, stable state, which involves removing fuel from the reactor core, draining coolant and steam lines, and de-energizing electrical systems. Decommissioning then moves the shut-down plant through initial planning and characterization, dismantling and removal of onsite structures and components, disposal of wastes, cleanup, and eventual site closure and license termination, so that the site can be released for other uses. Decommissioning projects are extremely complex and expensive undertakings that can last for years, and sometimes decades. Typically, the greatest risk during shutdown and decommissioning is associated with spent fuel handling and storage.

Management of spent nuclear fuel is a significant challenge for both operating and shut-down nuclear power plants. Once a reactor has been shut down, any remaining fuel (known as spent nuclear fuel) must be removed from the reactor. Spent fuel is first cooled in large water-filled pools for a period from 5 to 10 years, until radioactivity has decreased to the point where it can be moved to dry storage. Once the fuel is removed from the spent fuel pool, it is placed in large concrete containers or casks stored onsite, where it continues to undergo radioactive decay. In addition to spent fuel, some reactor components may also be stored onsite in casks if they exhibit high levels of radioactivity.

Currently, spent nuclear fuel and other highly radioactive wastes are being stored onsite at nuclear power plant sites across the country because there is no facility that is licensed to accept this type of waste. At these sites, spent fuel is stored in dry casks at Independent Spent Fuel Storage Installations (ISFSIs), which remain under NRC license even after the rest of the plant is decommissioned.

Spent fuel pool (above); dry cask storage (below). Credit: Nuclear Regulatory Commission

The Long-Term Challenge of Nuclear Power

Under the Nuclear Waste Policy Act of 1982, Congress designated Yucca Mountain in Nevada as the site for permanent geological storage of high-level radioactive waste from across the country. The Department of Energy has spent significant time and effort in studying this site and developing plans for a nuclear waste repository, but opposition from a wide range of stakeholders has effectively blocked this option from moving forward. Spent nuclear fuel and other highly radioactive wastes will likely remain dangerous for many hundreds and even thousands of years. Therefore, any site that will store such waste must be designed to manage it safely for at least as long a period of time. While the current administration has hinted that it intends to move the licensing process for Yucca Mountain forward, the process effectively remains at a standstill.

Unlike the U.S., some other countries have attempted to site a permanent repository using a voluntary, consensus-based approach; however, to date no country in the world has operated a permanent repository for high-level waste. Finland is the closest to achieving this goal, with its permanent repository currently expected to begin operating in 2023. Sweden has successfully used a similar approach to identify its repository site, expected to begin construction in the early 2020s. Canada is also using a consensus approach to site its repository, and is down to two candidate sites, with 2035 as the earliest possible date by which a repository could begin operating.

It is worth noting that the NRC is currently reviewing two license applications seeking to operate consolidated interim storage facilities in Texas and New Mexico. These facilities would receive high-level waste from nuclear power plants and would store it in a consolidated location until it can be moved to a permanent repository. Draft Environmental Impact Statements for both proposed sites are currently available for public review and comment.

Conclusion

Nuclear power has significantly lower GHG emissions than many other commercially available energy sources, especially when compared to other conventional fuels such as coal and natural gas. The need for action to tackle climate change will only become more urgent as time passes, and nuclear power can play a potentially significant role here. However, as we explain above, it has its own unique challenges and risks; in particular, the management of spent nuclear fuel is a complex issue with no ready solution. Resolving these challenges will depend on many factors that are currently difficult to predict; for example, how will technologies evolve, and will public sentiment and political will around the issue of nuclear waste shift significantly? How we deal with these issues over the coming years and decades is likely to shape the future of nuclear power. Can it truly become a global source of clean, low-carbon energy, or will its waste management challenges remain an obstacle to achieving this goal?

PHE has supported a wide range of environmental analyses related to nuclear power, ranging from environmental impact assessments for nuclear waste repositories and new nuclear reactors, to reports summarizing the current state of decommissioning practices. If you have questions about these types of analyses for your project, let us help you! Contact Samir Qadir, Environmental Scientist, at samir.qadir@phe.com.