RICHLAND, Wash.-Researchers at the Department of Energy's Pacific Northwest National Laboratory (PNNL) have begun a series of experiments that could result in more energy for the grid by increasing nuclear fuel efficiency. The tests are made possible by the special delivery of 11 "high burnup" rods that were irradiated for research purposes.
The rods will be punctured, cut, mechanically stressed and closely examined-all part of testing to learn how the metal alloys fared inside the extreme environment of a nuclear reactor for six years, where temperatures can soar to hundreds of degrees Celsius. The larger aim: to understand how advanced fuels developed by Global Nuclear Fuel react to "higher burnup" conditions. Those conditions partly entail keeping the fuels inside a reactor for longer than is typical, with the goal of extracting more energy out of the fuel than is done today.
"To draw more energy from these materials and increase plant power is like putting new generating capacity on the grid without having to build any new infrastructure," said Mark Nutt, director of PNNL's nuclear energy market sector. "That's a useful thing for both fuel vendors and a nation that seeks to realize a fuller nuclear potential."
The series of experiments underway at PNNL will reveal important information about how the research rods reacted to the conditions, and may even inform how future fuels are designed. High burnup fuels stand to boost the performance of the country's nuclear power fleet by making more efficient use of existing fuel materials, making reactors more resistant to nuclear incidents and perhaps even lowering the cost of electricity. The work is funded by the Department of Energy Office of Nuclear Energy's Accident Tolerant Fuel program.
"This is a significant milestone for our Accident Tolerant Fuel program," said Frank Goldner, the Accident Tolerant Fuel federal program manager in the Office of Nuclear Energy. "The development of this fuel could further support the Trump Administration's executive order to facilitate five gigawatts of power uprates at existing power plants by 2030 and high burnup fuels could be a big part of that."
(Video by Eddie Pablo | Pacific Northwest National Laboratory)
Delivered safe and sound
When the rods first arrived at the PNNL-Richland campus, many of the scientists watching the delivery wore expressions of anticipation. The shipping process was well-regulated, requiring complex logistical coordination between agencies over a span of 14 months. As an unloading crew meticulously transferred the 60,000-pound stainless steel rod-carrying cask into the Radiochemical Processing Laboratory (RPL), a team of technicians, radiation chemists, material scientists and nuclear engineers was at the ready. Testing was to begin right away.
Almost like forensic analysis, signatures of past exposure imbued throughout the materials will answer important questions for curious scientists. Did the outer casing, called "cladding," perform as expected under high burnup conditions? Researchers will search for changes in the material through "tensile testing" techniques. They'll also use a digital image correlation method to paint the cladding with thousands of dots, then trace the movement of those dots as the cladding is pulled apart with great mechanical force to gather significantly more data.
In one test, researchers used remotely operated manipulators inside a heavily shielded hot cell to puncture the cladding, releasing the rods' internal pressure. They then capture the radioactive gasses that released, which reveal how much pressure built up inside the cladding as the rods' internal contents underwent fission reactions. All of these data will help Global Nuclear Fuel to further validate the models that estimate how their fuel may perform under various conditions.
"The examination of these rods is the next step in our continuous drive to develop higher efficiency fuels that are safer and more reliable," said Craig Ranson, Installed Base CEO, GE Vernova Hitachi Nuclear Energy. "We are proud to be part of this collaboration with the U.S. Department of Energy, PNNL and our utility partners to benefit the entire industry."
It's exactly the kind of post-irradiation examination that PNNL is poised to do, thanks in part to the uniqueness of the RPL, a hazard category II non-reactor nuclear research facility. Equipped with precision instruments and staffed by researchers and technicians with diverse expertise, it's rare that a single facility can perform such wide-ranging and specialized analyses for multiple sponsors.
"The RPL provides a unique opportunity where we can actually accept full-length high burnup rods, perform the research in the hot cells and take the material to different labs within the same space-without having to transfer buildings-for testing. It's very efficient," said PNNL chemist and project co-lead Susan Asmussen. "We have the ability to do work on materials-from post-irradiation examination to liquid-liquid separation chemistry-that few other facilities have."
Co-lead Brady Hanson, a nuclear engineer at PNNL, concurs, also citing the research team's breadth of experience as a key advantage.
"We can perform all the kinds of chemistry you could dream of under this roof, but we can also do mechanical and material testing here and we can quite literally get all the way down to the atomic level. There are few questions we can't answer," Hanson said. "That's a feature of both our facility and our diverse research team. We've got nuclear, mechanical and chemical engineers, materials scientists and a chemist. It takes all of us to look at the scope of the work from different angles and provide different viewpoints, and I think that's what really makes us a strong team."
PNNL also benefits from its extensive research scope and varied mission partners, as scientists from several disciplines work onsite and can collaborate on experiments to maximize the use of valuable nuclear materials for mission needs across the U.S. government. For instance, debris generated from the decladding process will be used to train the next generation of scientists tasked with developing technologies to detect and monitor nuclear activities-a key part of the U.S. National Nuclear Security Administration's nonproliferation mission. Through the Nonproliferation Stewardship Program, RPL staff will leverage the debris to understand how to characterize and monitor the movements of special nuclear materials, like uranium and plutonium, through a chemical separations process.
"This delivery represents a rare and valuable opportunity," said Nutt. "We look forward to realizing the full scientific potential of this material-that's an area where PNNL is especially capable, given our multidisciplinary strengths. The resulting research could help achieve several important goals in service to the nation and go a long way toward providing abundant and reliable energy to the grid allowing for U.S. energy dominance."
