DOME: Legacy built, future ready
In 2019, a familiar landmark at Idaho National Laboratory was scheduled for demolition. Though striking for both its physical presence and its significance to nuclear history, the containment dome that once housed Experimental Breeder Reactor-II sat unused—that is, until INL realized its potential as a reactor testing facility.
The EBR-II connection
(Photos: Making a Contribution: The Story of EBR-II [video], Mike Hart/DOE)
DOME is housed in the containment dome of Experimental Breeder Reactor-II. EBR-II was built at what was then called the National Reactor Testing Station in eastern Idaho and designed by Argonne National Laboratory–West. Construction began in 1958, and the reactor first reached criticality in 1964. EBR-II was a landmark in American nuclear history: a sodium-cooled fast breeder reactor that demonstrated the possibility of a closed fuel cycle by reprocessing its own spent fuel on-site.
EBR-II’s distinctive dome was spared, and that same year, the National Reactor Innovation Center was formed with the mission of partnering with industry to develop and deploy advanced reactor technologies.
Plans for the DOME—Demonstration of Microreactor Experiments—test bed began to coalesce, and refurbishment and construction kicked off in October 2023.
In May 2025, INL received priority rating authorization from the federal government to expedite construction under the Defense Production Act, and with the help of industry leaders like construction contractor Estech and crane and rigging contractor Barnhart, NRIC’s DOME officially celebrated its grand opening on April 8, 2026.
At the opening, INL Director John Wagner said, “DOME represents the kind of bold and creative infrastructure investment that America’s nuclear resurgence demands.”
NRIC Director Brad Tomer agreed, saying, “With the information gathered from their testing at DOME, reactor developers will turn pioneering ideas into validated technologies to advance nuclear energy. We are extremely proud to offer this capability and cannot wait to see the impact it has on the nuclear industry.”
Whether it’s the three layers of aluminum paint gleaming in the Idaho sun, its astonishing modification from containment structure to high-tech test bed, or the industry-changing advances that will be made in this facility, it will be hard for the world to turn its eyes away from DOME.
Nearly three decades after EBR-II was decommissioned, the reactor’s containment dome—80 feet in diameter, 100 feet tall, and made of concrete and steel—was slated to be demolished. But INL and the Department of Energy saw potential in preserving the structure and decided to retrofit it for the DOME test bed.
The DOE’s Office of Nuclear Energy and INL officially began construction of NRIC’s DOME test bed with a ground-breaking ceremony in October 2023. DOME addresses a critical gap in the advanced reactor development pipeline—providing a place where developers can test a microreactor in a safe, controlled environment.
A multidisciplinary team of engineers, designers, and project managers across INL and NRIC collaborated to take DOME from initial concept to operational facility. The test bed is engineered to support experimental reactors up to 20 MWt, employing fuels enriched to less than 20 percent uranium-235.
Renovating the iconic EBR-II containment dome required extensive engineering to accommodate advanced reactor testing while maintaining the building’s structural integrity. To facilitate timely construction, NRIC obtained priority rating authorization from the federal government for procurements and subcontracts through the Defense Priorities and Allocations System, elevating the test bed priority status within the U.S. supply chain.
In the fall of 2025, crews installed a large equipment hatch to provide easy access for installing and removing reactor experiments—essential for the facility’s objective of accommodating multiple developers in succession.
At 17 feet tall and 15 feet wide, the hatch weighed 59,000 pounds. It took several months to install and required hundreds of hours of welding to fit it in place.
The DOME facility extends well beyond the dome itself to include a control room and a surrounding yard housing the power systems, radiological ventilation, and instrumentation infrastructure that experimental reactor developers will need.
One dedicated set of penetrations through the containment wall was reserved specifically for developer use, because each test campaign will have specialized instrumentation and monitoring requirements.
DOME’s open, adaptable layout will accommodate a range of reactor technologies and configurations, from heat pipe microreactors to molten salt and gas-cooled concepts.
Careful scheduling will enable rapid turnover between developers, maximizing the facility’s utility across the nuclear industry.
As the nerve center for experimental reactor campaigns, the DOME control room is where developers and INL staff members will monitor reactor performance, manage safety systems, and collect the data that design teams need to support licensing applications with the Nuclear Regulatory Commission.
The legacy crane was decommissioned and removed from DOME in April 2025.
That same month, new equipment was installed. The new system features two trolleys, each fitted with a 40-ton-capacity hoist.
On April 8, leaders, contractors, and support staff involved in the project convened at INL’s Materials and Fuels Complex to commemorate DOME’s grand opening. To align with federal nuclear executive orders, the test bed’s construction was expedited by nearly one year, enabling industry stakeholders to address the urgent need for advanced nuclear energy in the United States.
Six decades after EBR-II first demonstrated what an advanced reactor could do, its containment dome stands ready to do it again—and again and again, for every developer who earns a place in the queue.
