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February 13, 2023

FNST Project takes to the skies with a “drone” mounted detector

During the week of October 10, a team from CNL conducted a major unmanned aerial vehicle (UAV, also referred to as a drone) testing campaign at the BR-1 reactor in Belgium as part of a collaboration with SCK-CEN, Belgium’s nuclear research organization. More than simply airborne plume tracking and measurement, this project explored using UAVs to identify and measure the radiation being emitted from the plume source. While CNL does have some experience building customized detectors for onboard UAVs, this particular exercise was unique for CNL, and allowed CNL to showcase the value of an integrated S&T team.

This campaign was specifically about testing how a shielded, upward-facing gamma spectrometer can be used to monitor the quantity of radioactivity being emitted during an incident, including individual isotopes, by flying transects (predetermined routes) which cross the plume from underneath.  The BR-1 reactor in Belgium was used because it emits an argon-41 plume from its stack during normal operation. These plumes can be picked up by radiation detectors, providing information which could be invaluable to emergency response teams during an accident, and to the recovery team after the initial emergency.

The sensor package, including a Kromek Sigma50 gamma spectrometer and CNL-designed tungsten collimator, were flown by the Belgian civil protection agency on their UAV’s platform.  While CNL has done similar flights here at the CRL site, with the NRU in safe shutdown, the Belgian reactor provided a great alternative.

CNL’s contribution to this collaboration really lies in the customized detection equipment, flight plan development, and interpretation of the results.  Measurement of plumes has been done with UAVs many times in the past, but this was an opportunity to enhance the practices, technologies and results being gathered.

“To do this we need to precisely pinpoint the data (dose) that is being received by the gamma spectrometer and identify where it is coming from.  This is where the collimator comes in.  I could send you a photo of my white board with all the math on it, but that’ll be way more boring than a picture of the CAD model of the collimator itself.” (See picture)

A collimator is a device which filters a stream of rays so that only those traveling parallel to a specified direction are allowed through. In optics, collimators often use lenses to collect and focus a beam of light.  However, in the nuclear field – and in this particular case – we are using a specially designed collimator which allows only those gamma rays travelling in a particular direction (parallel to the collimator axis) to pass through.  All other rays would be absorbed by the tungsten collimator.  This collimator, when paired with a precise flight path, enables the team to build a very accurate understanding of the source of the plume.

James Carr, a Research Scientist with Mechanical Equipment Development (MED) explains further: “Collimating the shielded sensor essentially means we control what and how the sensor’s crystal “sees” by limiting its exposure. (Imagine looking through a paper towel roll.) In this case, we’ve designed the setup to fit around our existing UAV mounted gamma spectrometer. The unit also has a swappable collimator plug to let us experiment with the viewing angle parameters. We went through extensive iterative prototyping and took full advantage of Mechanical Equipment Design (MED)’s 3D printing and machining services.

“Beyond the shielded/collimated sensor, MED also designed and implemented the electronics and software to support interfacing with the system. Computational Techniques assisted with the software algorithm to generate the preprogrammed flight paths and CNL’s B750 manufacturing services assisted in machining the tungsten components.”

The reason for an upward facing sensor?  While technically, we could collect collimated data from any direction outside the plume, an upward facing sensor, flown below the plume, allows the team to simplify variables used to calculate the source term of the release.

The execution of these field trials by staff in the MED branch was a major achievement in the Safety & Security theme area of the Federal Nuclear Science and Technology Work Plan and the start of a very positive new relationship of Belgian-Canadian scientific exchange.

The federal stakeholders for this project are Health Canada, Environment and Climate Change Canada and Natural Resources Canada.

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