Researchers at Oak Ridge National Laboratory (ORNL) have added real-time visual tracking to their nuclear accident simulation equipment. By installing a camera window into a specialized furnace wall, scientists use digital image correlation to measure fuel cladding deformation as it happens. 

This is the first time researchers have captured these physical changes visually during a simulated loss-of-coolant accident (LOCA).

The severe accident testing station (SATS) at ORNL is the only domestic facility that can run these simulated failures on commercial, radioactive fuel rods. The protective outer layer, known as cladding, holds the nuclear fuel. Gathering precise data on this setup helps the nuclear industry reduce regulatory uncertainty.

This testing supports a broader national effort to approve accident-tolerant and high-burnup fuels, which allow commercial reactors to run longer and generate more power without raising costs.

Grid demand and regulatory approvals

Data centers and artificial intelligence systems are increasing the demand for steady electricity. Rather than building new facilities, power companies want to optimize current light-water reactors. This process, called a power uprate, increases electricity output by running fuel at higher temperatures and adjusting operational margins.

“A power uprate means increasing a plant’s electrical output by optimizing its operational margins — and removing overly conservative guidelines where appropriate — so that the fuel can operate at higher power levels,” said Nathan Capps, senior R&D staff in the Fuel Cladding and Core Internals group.

When utilities combine power uprates with extended fuel lifespans, they generate more energy from the same resources. To date, the Nuclear Regulatory Commission (NRC) has approved 171 power uprates. 

This has added power equivalent to eight new reactors to the U.S. grid without new construction. However, utilities must submit experimental data proving safety before the NRC approves these operational changes.

The simulation process

To replicate an accident where cooling water drops out of a reactor core, ORNL scientists follow a specific sequence. A fuel rod segment between 1 and 12 inches long is placed inside a quartz tube and centered with spacer disks. Next, researchers pressurize the inside of the segment to replicate the internal stress of a full-length active rod. 

An infrared furnace then heats the sample to a target temperature at a controlled rate. Finally, water floods the chamber to cool the segment back to room temperature. The entire process takes two to three minutes.

SATS uses two stations to complete this research. The first operates in a standard lab to map out experiments and test non-radioactive materials. The second station sits inside a heavily shielded hot cell to run identical parameters on radioactive commercial fuel. 

Beyond structural changes, the system tracks how trapped gases escape during temperature spikes and how fuel moves during a failure.

Industry applications

Fuel manufacturers use ORNL’s data to create safety reports for regulatory review. Over the past four years, ORNL has completed 16 LOCA tests alongside companies like Southern Nuclear, Constellation, Westinghouse, Framatome, and Global Nuclear Fuel. 

The laboratory plans to double its testing volume to help utilities meet rising grid demands.

The US Department of Energy (DOE) has officially cleared the preconceptual design and technology development roadmap for Xcimer Energy’s fusion power plant architecture, named Athena.

This regulatory clearance follows an intense evaluation of a 724-page proposal that covered system engineering, safety protocols, economic projections, and environmental impacts.

The government’s sign-off concludes Xcimer’s initial 18-month budget cycle within the federal Milestone-Based Fusion Development Program, an initiative intended to advance commercial fusion through public-private partnerships.

This administrative milestone closely follows the activation of Xcimer’s prototype laser system, Phoenix, last week. Located inside a 74,000-square-foot facility in Denver, Phoenix is currently the largest operational private laser system globally.

“Phoenix is a proof of concept for an unconventional fusion architecture: a krypton fluoride (KrF) excimer laser using Stimulated Brillouin Scattering (SBS) to compress a microsecond-long pulse into the nanosecond timescales fusion requires,” said the company in a press release.

Viability of long-term power generation

While historical laboratory efforts, such as those at the National Ignition Facility, proved that laser fusion physics could surpass the scientific breakeven point, Xcimer’s program focuses on the financial and mechanical viability of long-term power generation.

The Athena platform serves as the blueprint for a projected fleet of commercial plants designed to operate continuously for multiple decades.

A central challenge in fusion engineering is protecting reactor structures from degrading under constant radiation. Xcimer intends to address this by using a moving curtain of molten salt inside the reactor chamber instead of a static solid wall.

According to Susana Reyes, Vice President for Chamber and Plant Design, this liquid barrier absorbs neutron flux, generates tritium fuel, and transfers heat while constantly renewing itself.

“We are designing Athena to run continuously at a repetition rate of up to 1 Hz, and the use of a liquid wall chamber maximizes availability by protecting the solid structures from the fusion reaction emissions over the entire plant lifetime,” said Reyes.

Establishing scalable industrial manufacturing

Company officials state that the primary obstacle to fusion energy is no longer validating the underlying science, but establishing scalable industrial manufacturing.

Conner Galloway, CEO and Chief Science Officer, noted that the DOE’s review confirms the mechanical viability of the Athena framework and establishes a structured pathway toward commercial deployment.

“The question facing laser fusion is no longer whether the physics works,” said Galloway. “The question is how fast we can industrialize it.

Xcimer’s engineering targets include limiting laser manufacturing expenses to less than $100 per joule to ensure competitive energy pricing. Following the federal approval of the Athena roadmap, the Denver-based firm plans to transition into its next operational phase.

The upcoming schedule requires Xcimer to begin full-scale subsystem testing, complete engineering validations, and finalize the technical preparations necessary for a comprehensive, integrated pilot plant demonstration.

“We designed Athena around that property from day one, and it shapes everything: the materials choices, the thermal management, the maintenance philosophy, the economics. And Xcimer’s laser architecture uniquely enables this design,” concluded Reyes.