Is a Nuclear Reactor Headed to the Heart of Your City?

It's not uncommon for nuclear power plants to be sited relatively close to large metropolitan areas (within 50 miles, for example), after all, that is where the biggest loads are, but reactors are rarely placed near the center of large cities. This is mainly due to the risks associated with a meltdown, or even a minor release of radioactive contamination, which could force evacuations of people within a certain distance of the facilities. It's something planners had to consider when reactors were originally sited.

However, a new initiative known as Nuclear in District Energy Applications (NuIDEA), developed by EPRI and a group of more than 20 other organizations, could result in nuclear reactors coming closer to downtown. While this may raise concern among some people wary of nuclear power, the plan's creators see a great opportunity to decarbonize urban energy systems by utilizing this carbon-free energy resource.

There is great interest in highly reliable and resilient decarbonized energy sources. EPRI sees nuclear energy as one of many options to help meet that need," Jeremy Shook, principal project manager, Nuclear Innovation, at EPRI, told POWER. In our discussions with district energy system operators, they are keenly interested in understanding the unique challenges with this technology and how to overcome them. EPRI is helping to support this with the NuIDEA Initiative."

Understanding District Energy Systems

In the NuIDEA Action Plan," which was recently released by EPRI, the authors explain that district energy systems connect multiple heating and cooling energy users to central energy sources. These plants utilize equipment such as boilers and chillers to produce steam, hot water, and chilled water. In addition to thermal energy, district energy facilities can cogenerate electricity utilizing equipment such as combustion turbines paired with heat recovery steam generators," it says.

Traditionally, district energy systems have used either fossil fuel or electricity from the grid as an energy source. Fossil fuel use started with coal as a primary fuel, which has been largely replaced by natural gas. Fuel oil is often used as a backup fuel in critical applications.

The NuIDEA action plan outlines how nuclear energy could be a viable option to power highly efficient district energy heating and cooling systems. Using nuclear power could help building owners reduce their carbon footprint and assist countries in meeting economy-wide clean energy targets.

Microreactors Provide a New Option

There are current applications of using waste heat from large nuclear plants to provide district heating for cities in Europe and Asia. However, due to the large land requirements for traditional plants, EPRI sees limited application for these technologies for district energy. Microreactors offer greater flexibility in siting, and therefore can serve a greater portion of the market. Microreactors are a class of reactors that produce less than 50 MW of energy (often less than 10 MW) and which can be tailored to occupy less than an acre of land.

Having microreactors as an option for a power source gives district energy users the ability to meet their needs with a stable, carbon-free source of energy," Neil Wilmshurst, EPRI senior vice president of Energy System Resources and chief nuclear officer, said in a statement issued to POWER. Working with our collaborators in energy, academia, and engineering, we hope to provide buildings with yet another tool in the decarbonization toolbox."

A Team of Experts

Among the other participants in the initiative are specialists from Burns & McDonnell; CenTrio; Constellation Energy; Duke Energy; International District Energy Association; Massachusetts Institute of Technology; Nebraska Public Power District; North Carolina State University; Nuclear Energy Agency; Nuclear Energy Institute; Nuclear Electric Insurance Limited; Sargent & Lundy; Southern Company; University of Illinois, Urbana-Champaign; and University of Wisconsin, Madison. The groups worked together for the past year to develop the action plan, which defines the work necessary to fulfill the NuIDEA mission, that is, to Enable nuclear energy as an option for the district energy market by 2026."

District energy has been used for nearly 150 years, and its use continues to grow around the world. The number of customer buildings served by a district energy system range from as few as three in the initial stages of new system development to more than 1,000 for mature systems. The Con Edison Steam Business Unit in Manhattan, New York, for example, serves more than 1,800 customer buildings, making it the largest district steam system in the world.

Smaller and Safer Reactor Designs

Microreactors are uniquely suited to supplying thermal and electric energy to district energy systems. Many of the microreactor designs provide high-temperature steam (up to 1,200F), which enables the efficient production of chilled water and electricity using steam-driven chillers and steam turbine generators. By producing multiple energy products, the utilization of the plant can be optimized," the plan says.

EPRI outlined a few prominent microreactor technologies that are currently available on the market. The most common is the high-temperature gas reactor (HTGR). These designs use tristructural isotropic (TRISO) fuel, small kernels of uranium enclosed by graphitic materials for protection. This fuel form can withstand temperatures high enough that it is essentially impossible to melt the fuel," the plan says. Helium is typically used as the coolant to transfer the heat to a steam generator.

Another common microreactor type is the liquid-metal-cooled reactor. This reactor commonly uses liquid metal heat pipes for passive heat removal. An example is the Microreactor Applications Research Validation and EvaLuation (MARVEL) project being built by the U.S. Department of Energy (DOE) at the Idaho National Laboratory. The MARVEL design is a liquid-metal-cooled microreactor with Stirling engines that will produce 100 kW of energy. The MARVEL test platform is a collaborative effort between the DOE Microreactor Program and the National Reactor Innovation Center to bring innovative advanced reactor technologies to market.

Idaho National Laboratory (INL) recently built a full-scale, electrically heated prototype to support the U.S. Department of Energy's new MARVEL microreactor project. The prototype is one of the largest components ever machined at the lab and will be used to help validate the project's final microreactor design that could be operational within the next two years. This image shows the MARVEL microreactor prototype at INL's Materials and Fuels Complex's machine shop. Courtesy: INL

Microreactor designs often utilize passive safety concepts, which allow the reactors to cool themselves, even when power is lost. In such cases, natural convection is able to return the core to a safe state, which makes these designs safer and less likely to melt down.

Next Steps

Through the NuIDEA Initiative, EPRI is bringing together district energy system owner-operators, architect engineering firms, and non-profit organizations to build a community of organizations interested in making nuclear energy an option for the market, so that they can have discussions, ask questions, and share lessons learned through this journey," Shook said.

Initiative participants developed the action plan to address the market need. The action plan was initially focused on the North American market, but the goal is to also engage with international parties in the future.

The plan lays out work to be done in 11 distinct areas, which are: policy, public awareness, ownership models, finance, insurance, project development and execution, technical, regulatory, permitting, operations and maintenance, and security. The NuIDEA Initiative will work over the next three years to address the actions identified for completion by 2026.

-Aaron Larson is POWER's executive editor (@AaronL_Power, @POWERmagazine).

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