Once the monitor is in the works, it could promote higher standards of safety and security, said researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL).
Commercial nuclear fuel cycle facilities end up licensed and regulated to control nuclear materials, preventing their diversion and ensuring worker, public, and environmental safety. An d robust monitoring systems are essential to prevent the accumulation of radiological materials in areas such as air ducts.
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 they screen airflow 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.
Low-cost Monitoring
In contrast, the detector Witherspoon designed provides continuous, low-cost monitoring. The device is a cylinder about 12 inches tall that can easily attach 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, it is possible to save more data and then transmit it every second.
Researchers successfully demonstrated the detector in battery mode inside an ORNL nuclear material processing facility. The data collected will be used to train an AI-enhanced algorithm developed by Callie Goetz, who leads the overall project.
Landon Crawford adjusts the circuit board of the radiation sensor the ORNL team developed preventing unsafe accumulation or illicit removal of radioactive particles from air ducts in nuclear facilities.
Source: Carlos Jones/ORNL
The software will incorporate 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 ended up programmed to count the number of pulses that represent unsafe radiation levels for the relevant nuclear material.
Combining Old with New
“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.”
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.