Time for a Nuclear Comeback?

Advanced Reactor Technologies Offer Diverse Options for the Electric Power Industry

By Scott Sowers

It’s an uncertain juncture for nuclear power generation. On one hand, the World Nuclear Association reports that China is ramping up investment in nuclear, with 20 plants under construction and plans for up to 150 gigawatts of nuclear capacity by 2030. Globally, 58 nuclear reactors are under construction in countries such as France, Finland, South Korea, United Arab Emirates, India, and Russia.

Outside of Asia, deployment of new nuclear generation has slowed or stalled. In the United States, most nuclear projects proposed to the U.S. Nuclear Regulatory Commission have been shelved or canceled. After costly delays in constructing its AP1000 plants, Westinghouse filed for bankruptcy in March 2017. In July, South Carolina Electric & Gas halted construction of two reactors at the V.C. Summer Nuclear Station, citing cost overruns. In Georgia, the unfinished Vogtle Units 3 and 4 project faces similar financial challenges, though owner Southern Company signaled its intent to move the project forward, pending approval from the Georgia Public Service Commission.

Falling costs of other generation sources globally—and particularly low natural gas prices in the United States—emerged as a primary challenge to nuclear power’s economic viability. For new nuclear plants, high construction costs and delays are reducing cost-competitiveness.

At the same time, the impetus to address climate change makes zero-carbon nuclear power more attractive. In providing reliable 24/7 baseload power, it potentially remains a key in balancing grids with intermittent renewable energy sources and dynamic loads. With high energy density, nuclear plants need refueling only every two years, providing security against fuel supply disruptions as a result of extreme weather.

These competing factors raise questions regarding nuclear power’s role in meeting the world’s energy needs in the coming decades.

To a great extent, the answer depends on the progress toward commercializing the new safer, more cost-effective nuclear reactors under development. EPRI’s Advanced Nuclear Technology Program conducts collaborative R&D to support and accelerate the near-term deployment of these advanced large light water reactors, small modular light water reactors, and advanced non–light water reactor reactors, often referred to as Generation IV.

Generation III and III+

Most projects under construction today are advanced light water reactors, also known as Generation III and III+ reactors—a technology pioneered in the United States that remains the workhorse of nuclear power generation. Water serves as the coolant and moderator, helping to slow down neutrons to enable sustained nuclear reactions. Compared with the Generation II reactors built between the 1960s and the 1990s, advanced light water reactors offer greater fuel efficiency and longer plant life. They also include enhanced and passive safety features.

Simpler, Cheaper Reactors

Small modular reactors (SMR) are generally rated at 300 megawatts or less and designed so that major components are built in a factory and then shipped by truck or rail to a plant site for assembly. In contrast, most major components for a typical 1,000-megawatt light water reactor are built on-site.

“Nuclear power’s future depends on the cost of electricity generation, and a large percentage of that is cost of construction, followed by the cost of operation. Small modular reactors are designed to be simpler and cheaper to build and operate, and that can help bring down costs,” said EPRI Program Manager Ron King.

Relative to large light water reactors, SMRs can potentially lower construction costs, streamline licensing, and require a smaller footprint. Most SMR designs include passive safety features and a reduced fuel load. Some include below-ground construction. Should an accident occur, there would be a smaller impact on the surrounding area.

SMRs offer a new take on proven light water reactor technology. While nuclear utilities have not yet built SMRs, small reactors have been used for naval propulsion and other military applications since the 1950s. Regulatory approval of SMR designs will take time, but the process is moving forward. In March 2017, the U.S Nuclear Regulatory Commission accepted for review NuScale Power’s SMR Design Certification Application.

In a two-year project with the U.S. Department of Energy (DOE), EPRI is evaluating integrated pressurized water reactors—an SMR design in which the reactor, steam generator, and pressurizer are housed in a smaller containment shell. These reactors have the potential to reduce the deposition of radioactive particles on adjacent land during an accident. This can enable smaller emergency planning zones, reducing regulatory burdens, compliance costs, and a plant’s footprint.

Molten Salt Reactors

Generation IV reactor technologies offer significant potential improvements in economics and safety relative to existing light water reactors. Most use coolants and moderators other than water, enabling operations at higher temperatures and lower pressures.

Higher temperatures can enable higher energy conversion efficiencies, use of water-efficient dry-cooling and hybrid cooling technologies, and access to new markets for high-quality process heat. Lower pressures translate into lower accident risks and thinner walled—and therefore less costly—components.

The Generation IV technology known as a molten salt reactor runs on fuel that is dissolved into the coolant, facilitating heat removal from the reactor core and providing other potentially game-changing safety and operational benefits. Molten salt reactors can be designed as “burner” reactors that consume stockpiles of used fuel and plutonium, or as “breeder” reactors that generate more nuclear fuel than they consume. Because fuel circulates through the coolant system, many have historically believed that the technology poses a greater risk of diversion of nuclear materials for harmful purposes. Developers face the need to address these concerns.

In collaboration with Southern Company, EPRI in 2015 completed a technology assessment of a liquid-fueled molten salt reactor, which demonstrated the value of examining safety early and often in plant design.

Building on this collaboration and experience, EPRI is participating in a Southern Company–led project to examine a molten salt reactor design known as the chloride fast reactor. TerraPower, a company backed by private investors such as Bill Gates, is developing the technology. DOE is providing $40 million for the project, with a minimum $10 million cost share from industry stakeholders. An EPRI-led team is providing independent technical peer review of the reactor design and testing program. A key task for this large undertaking is to build an “integral effects test machine” for evaluating heat transfer, fuel/coolant chemistry, materials corrosion, and other aspects.

“If successful, at the end of this five-year project the developer and utility will be well-positioned to proceed with licensing and construction of a test reactor to demonstrate that the technology works as intended,” said EPRI Technical Executive Andrew Sowder.

While the technology has never been commercialized, Oak Ridge National Laboratory successfully demonstrated a prototype in the 1960s, and the project team is building on the lab’s expertise. During the Cold War, it was considered for powering long-range strategic bombers.

Other Generation IV Technologies

Researchers globally are working to improve sodium-cooled fast reactors, which have operated at commercial scale in several countries, notably France and Russia. Advantages include sodium’s high thermal conductivity, which provides substantial protection from overheating and enables operation at atmospheric pressures and moderately higher temperatures (about 550°C). Liquid sodium is compatible with proven reactor materials such as stainless steel. As with other fast reactors, the technology can operate as either burners or breeders. A drawback is that sodium is highly reactive with air and water and requires special handling to prevent fires.

A related technology, lead-cooled fast reactors, offers benefits similar to those of sodium-cooled fast reactors. Unlike sodium, lead doesn’t react with air or water but does present significant challenges with materials corrosion.

High-temperature gas-cooled reactors use helium as the heat transfer fluid. Helium is inert, but its low heat capacity requires that it be pressurized for effective heat transfer. In modern designs, microspheres of fuel are dispersed in a large graphite matrix designed and demonstrated to handle the highest temperatures that occur during a severe accident. Like water, graphite is effective at slowing neutrons, making this a thermal reactor technology. The fuel’s lower energy density requires a larger reactor core and plant per unit energy, limiting scalability. High helium pressures and flow rates lead to larger components, increasing material and manufacturing costs.

These are among the most mature advanced reactor designs. In the United States, two high-temperature gas-cooled reactors—Peach Bottom 1 and Fort Saint Vrain—operated between the 1960s and 1980s. Ten larger commercial high-temperature gas-cooled reactor units were canceled in the late 1970s (along with many more light water reactors) primarily because of a sluggish economy and reduced growth in electrical demand. China is expected to start up a commercial prototype in 2018.

Developers of “very-high-temperature gas-cooled reactors” are targeting even higher temperatures (above 850°C) to further enhance economics. Some are pursuing a fast reactor version with new fuel designs that enable operation at very high temperatures.

Options for the Future Power System

Outside of Asia, social, economic, and political headwinds have slowed deployment of nuclear generation capacity. In the United States, factors include low natural gas prices, unfavorable market conditions, a complex licensing process, high construction costs, and long, uncertain lead times. In France, with its traditionally pro-nuclear policy, the nuclear contribution to the electricity mix could drop from 75% to 50% if recent policy shifts hold. Germany reinstated a nuclear phase-out in 2011 and is targeting shutdown of all nuclear plants by 2022.

“Most markets aren’t valuing the zero-carbon emissions of nuclear power and the important benefits it provides to the grid,” said Sowder.

Nevertheless, Sowder sees an opportunity for a new generation of reactor technologies to overcome these hurdles.

“The real promise of the advanced reactor technologies is that they provide new options to maintain safe, reliable power generation in a rapidly transforming power sector,” he said. “They may offer the best hope for nuclear to sustain its substantial role through the 21^st century.”

With uncertainty regarding climate policy, natural gas prices, deployment of intermittent renewable generation, and electricity market structure, the optimal generation mix decades from now is unknown. For utilities, a new generation of nuclear technology broadens their options in navigating these potentially disruptive variables.

For example, Generation IV reactors’ higher operating temperatures can enable more efficient generation while opening to utilities and other owner-operators access to new power markets such as the sale of steam to industrial facilities. The lower operating pressures of many Generation IV designs could result in less costly reactor components and lower construction costs, improving cost-competitiveness with other generation. The ability to “breed” fuel could provide greater energy security. SMR designs could streamline licensing and enable faster deployment.

“One can imagine unique uses of a scalable nuclear energy source that only requires refueling every two, ten, or thirty years,” said Sowder. “For reliability and resiliency, there is no match for a nuclear plant that can operate without the need for functioning pipelines or regular rail and truck transportation of coal or liquid fuels.”

“We don’t know exactly what options or generation attributes will be needed in thirty years,” said Sowder. “Diverse options give the industry the power to adapt to changes.”

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