At a recent training course at the Department of Energy’s 91, one question echoed throughout the class: What’s the holdup?
Holdup — the gradual buildup of fissile material in pipes and equipment — poses both a safety and an accountability challenge for nuclear facilities. To tackle this, professionals from government and industry gathered at ORNL from January 21 to 24 for the Nondestructive Assay Holdup Measurements Training Course for Nuclear Criticality Safety, a hands-on training in nondestructive assay, or NDA, a technique for detecting and quantifying holdup without disturbing operations. By refining these measurement skills, participants help ensure nuclear materials remain safely managed and fully accounted for.
“Non-destructive assay is a simple and cost-effective tool for determining the location and amount of holdup, if you understand what you are looking at," said Robert Bean, the course’s facilitator and a senior R&D staff scientist in ORNL’s Nondestructive Measurement Science and Technology group. “This course is designed to enhance the technical knowledge of NDA practitioners, as well as modelers who use this data to inform criticality safety models. Better models are informed by better understanding the measurement process.”
During the four-day training, participants learned the fundamentals of NDA testing using gamma-ray spectrometry, a method for identifying and quantifying radiation emitted by gamma rays, as well as key measurement concepts. This knowledge was supplemented by hands-on exercises to emphasize the challenges of NDA testing. Working in small groups at ORNL’s safeguards lab, students used the Generalized Geometry Holdup Methodology to locate and quantify sample fissile materials in simulated conditions.
“In a real-world setting, NDA testers would analyze gamma rays from uranium-235’s natural decay emitted from holdup in ducts and piping around nuclear facilities,” Bean said. “By simulating this environment, modelers and technical professionals are gaining a deeper perspective on how holdup measurements are determined, and the layers of complexity that can contribute to our confidence in that number.”
With world-class expertise in nuclear criticality safety, detection methods and NDA measurement, ORNL is uniquely positioned to host this training. In 2018, the Nuclear Criticality Safety Program tasked ORNL with enhancing an existing NDA training program to improve holdup measurements in nuclear facilities to enhance both safety and material accountability across DOE’s programs and facilities. Since then, ORNL has conducted the course annually, equipping operations staff and nuclear criticality safety researchers with the skills needed to detect and quantify holdup.
By leveraging its expertise and resources, ORNL continues to play a key role in advancing best practices for nuclear material measurement and nuclear criticality safety.
This training was conducted with funding from the National Nuclear Security Administration’s Nuclear Criticality Safety Program. Future NDA Holdup courses and other courses related to nuclear criticality safety can be found by visiting ncsp.llnl.gov/.
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