Researchers in the Oregon State University College of Engineering have developed new technology for uranium enrichment measurement and trace element detection, vital for nuclear non-proliferation and supporting the development and operation of next-generation nuclear reactors.
Findings were published by the Royal Society of Chemistry.
"The technology that we are developing can support nuclear safeguards as well as nuclear energy development," said Haori Yang, associate professor of nuclear science and engineering. "It can enable on-site enrichment measurements with minimal or no sample preparation, which means a quick turnaround time. It can also be used to monitor fuel in Gen-IV nuclear reactors, such as liquid metal cooled reactors."
In its naturally occurring state, uranium contains less than 1% U-235, the isotope that can sustain a nuclear chain reaction; the rest is U-238, which is much less able to do so.
Uranium enrichment is a process through which the proportion of U-235 is increased to varying levels depending on whether the intended use is power generation, weaponry or propulsion for aircraft carriers and submarines.
Detection technologies are crucial for the International Atomic Energy Agency, which acts as the United Nations' nuclear watchdog, and the Treaty on the Non-Proliferation of Nuclear Weapons, which prevents the transfer of weapons from nuclear weapons states to non-nuclear weapons states while allowing access, under safeguards, to nuclear technology for peaceful purposes.
The collaboration between Oregon State and the Pacific Northwest National Laboratory combines three detection techniques in a single system: laser-induced breakdown spectroscopy, laser absorption spectroscopy and laser-induced fluorescence spectroscopy. Spectroscopy is a type of analysis made possible by the unique ways that different substances emit, absorb or reflect light.
Laser-induced breakdown spectroscopy uses a high-energy laser pulse to generate plasma - hot gas made up of free electrons and positive ions. The light emitted by the plasma, measured with a spectrograph, shows a sample's composition.
"LIBS enables remote, rapid, onsite analysis with minimal sample preparation," Yang said. "However, its spectral resolution is limited compared with absorption-based techniques."
In laser absorption spectroscopy, a tunable laser is passed through the laser-induced plasma and the amount of light absorption is measured. The narrow bandwidth of the probing laser enables higher spectral resolution and sensitivity, making it ideal for isotope-specific measurements. A drawback, though, is that it requires the laser excitation to happen at a 90-degree angle, and the careful alignment of the laser and detector can add complexity to experimental setups.
Laser-induced fluorescent spectroscopy combines absorption and emission. Atoms in the plasma are excited with a probing laser and their fluorescence is measured with a spectrograph, enabling precise isotope identification at a distance. That makes it particularly useful for applications requiring remote, high-sensitivity measurements.
"Our system is fully capable of implementing fiber-optic laser induced breakdown spectroscopy," Yang said. "Unlike conventional LIBS, which requires direct line-of-sight access to the target, fiber-optic LIBS delivers the pulsed laser and collects emitted light through optical fibers. This decouples the front-end measurement head from the main system, enabling safe and effective measurements in hazardous or hard-to-reach environments."
The research, which included doctoral student Yichen Zhao, was funded by the U.S. Department of Energy, the Nuclear Regulatory Commission and the Defense Threat Reduction Agency.
In addition to his spectroscopy work, Yang is developing a muon tomography imaging system for monitoring spent nuclear fuel assemblies. Muons, high-energy particles similar to electrons but much heavier, are produced in the upper atmosphere when cosmic rays collide with atoms. Their ability to penetrate deep into materials including concrete and steel allow nuclear inspectors to see inside dry storage casks.
Yang is also working on a photon-induced fission technique to detect concealed nuclear material and is investigating low-cost, high-performance radiation detection based on nanostructured sensors and spintronics devices as alternatives to traditional detectors. Spintronics involves using electrons' spin, a quantum property that underpins magnetism, to store and process information.
"The revolutionary improvements that we're studying will have significant impact in areas beyond nuclear material detection, including medical imaging, high-energy physics and nondestructive testing," he said.
