Device detects traces of nuclear material, enhances safety at fuel cycle facilities

Researchers at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) developed a new type of monitor that can check every minute or even every second for the buildup of nuclear material in the air ducts of nuclear fuel cycle facilities, promoting the highest standards of safety and security.

Commercial nuclear fuel cycle facilities are licensed and regulated to control nuclear materials, preventing their diversion and ensuring worker, public, and environmental safety.

Robust monitoring systems are essential to prevent the accumulation of radiological materials in areas such as air ducts. Elevated levels of unshielded radiation can pose worker health risks. Further, unmonitored nuclear material could also be gathered for illicit uses, posing a national security risk.

To support industry objectives of continually enhancing efficiency and safety, ORNL developed a new device that offers unprecedented monitoring frequency and accuracy to protect safety, nuclear facilities, the environment and national security - at a more affordable price than other detection systems.

Facilities that fabricate nuclear fuel or process nuclear waste keep the material in sealed areas, where airflow is screened through high-efficiency particulate air filters. But even these cannot prevent the tiniest particles from escaping into the building's air ducts. Today, sporadic monitoring relies on a person extending a radiation counter at the end of a long pole through overhead ventilation ducts, said Brett Witherspoon, the technical lead of the ORNL project.

In contrast, the detector Witherspoon designed provides continuous, low-cost monitoring. The device is a cylinder about 12 inches tall that can be easily attached to the side of a duct, operating either with a battery or through power over ethernet. In battery mode it can run for about a month at a time, sampling about once a minute and recording the data, Witherspoon said. Powering the device over an ethernet connection, more data can be saved and transmitted every second.

Old and new technologies combine for affordable radiation monitoring

The detector has been demonstrated successfully in battery mode inside an ORNL nuclear material processing facility. The data collected will be used to train an AI-enhanced algorithm being developed by Callie Goetz, who leads the overall project. The software will be incorporated into the detector to alert operators automatically when nuclear material builds up to a level of concern.

The monitor works using a low-cost plastic scintillating crystal: When hit with radiation, it emits light in the form of photon particles. A silicon photomultiplier translates these photons into electrical pulses. Uranium and other nuclear materials have specific energy signatures, and the detector is programmed to count the number of pulses that represent unsafe radiation levels for the relevant nuclear material.

"We're really combining the old and the new - the best of historical analog processing, which needs less power, combined with the latest digital microcontrollers incorporating advanced security features," Witherspoon said. The design replaced old vacuum tube technology with arrays of silicon photomultipliers to convert light into an electrical signal. This technology is smaller, cheaper and better equipped to handle temperature swings. And facilities will be able to monitor more widely because the plastic crystal costs a dollar or two, compared to traditional alternatives such as an inorganic scintillator crystal or semiconductor radiation detector, which run from $1,000 to $10,000.

"This is a thousand times more affordable than current technology, while the purpose-built design offers a more accurate, user-friendly and financially beneficial alternative for nuclear facilities," Goetz said. "These devices will make nuclear facilities safer and more efficient as it reduces their regulatory burden."

Partners and further applications

The research team is testing to make sure the device electronics can handle high heat before incorporating the algorithm. They plan to demonstrate the full detection system using power-over-ethernet soon inside an ORNL building containing a nuclear molten salt reactor test loop. Researchers are also working with Oak Ridge fuel enrichment and nuclear fabrication companies to validate the monitors in their facilities and provide the resulting data.

The radiation detectors could be valuable in other nuclear safety and security facilities and contexts, as well as molten salt reactor loops and small modular nuclear reactors. Improving heat tolerance and fine-tuning the data acquisition system could enable them to be used as portal monitors outside nuclear facilities - even those located in extreme environments - to prevent theft of nuclear material, Goetz said.

Other ORNL members of the detection monitor team include Nick Prins, Chuck Britton, Landon Crawford, Jesse Davis, Irakli Garishvili and former ORNL researcher Philip Gibbs. Thomas Ruland of the Air Force Institute of Technology also contributed to the research. The project was funded by the Material Protection, Accounting and Control Technologies (MPACT) campaign of the DOE Office of Nuclear Energy.

ORNL is committed to supporting U.S. energy needs by pursuing strategic research that advances a wide variety of affordable, abundant and competitive nuclear technologies, and strengthens national security. The lab's scientific expertise and world-class facilities are often the first step in advancing nuclear energy innovations.

UT-Battelle manages ORNL for the Department of Energy'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. For more information, please visit energy.gov/science. - S. Heather Duncan