TVA continues to evaluate emerging nuclear technologies, including small modular reactors, as part of technology innovation efforts aimed at developing the energy system of the future. While TVA actively works to extend the life of our existing reactors, we are also taking steps to be able to add next-generation nuclear power, such as advanced light water small modular reactors (SMRs) and advanced non-light water reactors, to the TVA portfolio. TVA's goal is to identify an economically viable advanced nuclear technology to generate carbon-free electricity in the 2030s and beyond.
An advanced nuclear reactor is defined as a nuclear fission reactor with significant improvements over the most recent generation of nuclear fission reactors. Such reactors include Light Water Reactor (LWR) designs, both pressurized and boiling water reactors, and non-LWR designs using various moderators, coolants, and types of fuel. Many of the LWR designs are considered to be small modular reactors (SMRs), which are defined as reactors with electric generating capacity of 300 megawatts or less, in contrast to an average of about 1,000 megawatts for existing commercial reactors.
Advanced or unconventional reactor designs seek to use combinations of new and existing technologies and materials to improve upon earlier generations of nuclear reactors. Advanced reactor designs may be grouped into three primary categories:
Advanced nuclear reactors may be characterized by a range of technological maturity. Advanced light water-cooled SMRs are considered to be among the most mature of the advanced reactor technologies. Advanced Non-LWR reactors are considered to be further from commercialization.
TVA is evaluating advanced nuclear technologies, including small modular and micro reactors, as part of TVA’s technology innovation mission. Advanced Nuclear reactors offer clean energy technology that would play a key role in TVA’s continued mission of environmental stewardship while increasing capability for future energy demands.
Small modular reactors are advanced light water reactors with an electric generating capacity of up to 300 MW. SMR designs are based on existing commercial LWR technology but are generally small enough to allow major reactor components to be placed in a single pressure vessel, thereby eliminating the need for primary circuit pipework with the intention of enhancing safety and reliability. The reactor vessel and its components are designed to be assembled in a factory and transported to the plant site for installation, potentially reducing construction time and costs from those of large LWRs.
Potential SMR Advantages:
High temperature gas reactors (HTGRs), including very high temperature gas reactors (VHTRs), refer to graphite-moderated, typically helium-cooled systems that use tri-structural isotropic fuel micro particles. The particles are packed into a graphite matrix to form either spherical or cylindrical fuel elements. The pebble bed version of the HTGR uses spherical billiard ball-sized fuel elements that flow continuously through the reactor. The prismatic version of the HTGR uses the cylindrical fuel compacts in hexagonal blocks in a fixed geometry. HTGRs may be used for electricity production and/or process heat applications.
MSRs come in several varieties. Some designs use molten fluoride salt, while others use chloride salts as the coolant. Some designs have stationary fuel rods or plates, while others have moving fuel pebbles or fissile material dissolved within the flowing coolant. In addition, some MSRs use a fast neutron spectrum, while others use a thermal spectrum.
MSRs vary in their design; there are fast and thermal variants, and different moderator materials have been proposed for the thermal variants. Different molten salts may also be used, depending on the other design features.
FHRs are a hybrid design that uses pebble fuel elements (like pebble bed HTGRs) and a fluoride salt coolant (like salt-cooled molten salt reactors). Some fixed-fuel FHR designs (like prismatic HTGRs) have been proposed, but none are currently under commercial consideration.
LMRs are an advanced type of nuclear reactor in which the primary coolant is a liquid metal. LMRs are classified based on the liquid metal coolant used, such as sodium, lead-bismuth eutectic alloy, and lead-bismuth.
Heat pipe reactors typically consist of a solid block core with the fuel in holes inside the solid block. Heat pipes are built into the block in a lattice configuration and remove the heat from the block as the liquid in the heat pipe is vaporized.
Microreactor designs vary, but most would be able to produce 1-20 megawatts of thermal energy that could be used directly as heat or converted to electric power. Microreactors are not defined by their fuel form or coolant.
TVA's Site Selection process evaluated multiple sites in an effort to identify the most suitable site to deploy an Advanced Nuclear Reactor and found the CRN Site to be the preferred site. The CRN Site was originally the site of the Clinch River Breeder Reactor Project in the early 1980s. Extensive grading and excavation disturbed approximately 240 acres on the project site before the project was terminated. Upon termination of the project, the site was redressed and returned to an environmentally acceptable condition.
The CRN property is approximately 1200 acres of land located on the northern bank of the Clinch River arm of the Watts Bar Reservoir in Oak Ridge, Roane County, Tennessee. This property includes the CRN Site, which is approximately 935 acres, and the Grassy Creek Habitat Protection Area, which is approximately 265 acres and located north of the CRN Site. The property itself is owned by the Federal government and is managed by TVA in accordance with the Watts Bar Land Management Plan.
The Site has a number of significant advantages including two existing power lines that cross the site, easy access off of Highway 58, a brownfield site previously disturbed and characterized as a part of the Clinch River Breeder Reactor project. It is immediately adjacent to DOE’s Oak Ridge Reservation, has a skilled local work force, and easy access to the reservoir and major transportation routes.
In 2010, TVA began exploring advanced nuclear technologies and started its characterization of the site. In 2016, TVA submitted an application to the NRC for an Early Site Permit for one or more small modular reactors with a total combined generating capacity not to exceed 800 megawatts electric for the Site.
In December 2019, TVA became the first utility in the nation to successfully obtain approval for an early site permit from the NRC to potentially construct and operate small modular reactors at its CRN Site. In 2021, TVA initiated the development of a Programmatic Environmental Impact Statement to evaluate the effects of a proposed advanced nuclear technology park at the CRN Site. The decision to potentially build small modular reactors is an ongoing discussion as part of the asset strategy for TVA’s future generation portfolio, and TVA will make the decision that’s best for the 10 million people we serve.
University of Tennessee at Knoxville
This partnership provides a unique opportunity to engage with students and prepare the nuclear workforce of the future.
“Established in 1957, our department is the oldest and one of the most prestigious in the country,” said UT Engineering Department Head Wes Hines. “This strategic partnership with TVA to build highly efficient advanced reactors will help us pave the way for a clean, reliable energy future.”
The University of Tennessee, Knoxville, is the flagship campus of the UT System and the state’s land-grant institution. UT’s unique partnership with the US Department of Energy and nearby Oak Ridge National Laboratory addresses critical issues in energy, transportation, climate and the environment.
Oak Ridge National Laboratory
The research performed at ORNL through DOE’s national programs has enabled multiple utilities to innovate and improve power generation through the development and use of new materials, processes and state-of-the-art technologies.
“We are combining our world-leading research capabilities and TVA’s operating expertise to accelerate the next generation of cost effective nuclear power,” ORNL Director Thomas Zacharia said. “Nuclear has long been a key component of the U.S. energy portfolio, and growing demand for emission-free electricity requires that we innovate to ensure safe, affordable and efficient nuclear power for generations to come.”
The partnership will take advantage of ORNL’s scientific expertise and its unique facilities including the High Flux Isotope Reactor, Oak Ridge Leadership Computing Facility and Manufacturing Demonstration Facility. This new effort builds on decades of collaboration between TVA and ORNL, leveraging nuclear capabilities and assets from both organizations, including a 2016 effort using modeling tools developed at ORNL to predict the first six months of operations of TVA’s Watts Bar Unit 2 nuclear power plant.
UT-Battelle LLC manages ORNL for DOE’s Office of Science, the single largest supporter of basic research in the physical sciences in the United States. The Office of Science is working to address some of the most pressing challenges of our time