Tritium detector for continuous underground monitoring

Thomas Jefferson National Accelerator Facility announced yesterday that it has entered a cooperative research and development agreement (CRADA) with Canary Instruments to commercialize a tritium detector it developed for monitoring groundwater near nuclear facilities.

"We have an excited and eager partner who wants to dig in and do the hard work of identifying markets and building a business around our intellectual property," said Marla Schuchman, Jefferson Lab's chief innovation officer and leader of the Research and Technology Partnerships Office. "Ultimately, the goal of our innovation efforts is to make sure impactful technologies find their way out of the lab so they can improve society and provide economic benefit to the United States."

Water monitoring: Nuclear power plants and nuclear fuel facilities generally monitor nearby groundwater for tritium contamination. As fusion pilot plants start to come on line, those facilities likely also will require groundwater monitoring.

Jefferson Lab has developed the Subsurface Continuous Radioisotope Environmental Monitor (SCREM), and while its patent describes the use case as it relates to fission power plants, Canary will be targeting SCREM as a product for fusion facilities, where the regulatory environment may be more open to novel methods.

According to the patent, the primary existing methods for testing water for radioisotopes are "precise and effective but labor intensive or time intensive." They also only provide a snapshot of the water condition at the time of sampling.

At sites that are known to have subsurface tritium contamination, periodic sampling of multiple locations can be required for many years, and the patent states that SCREM was inspired by that use case.

The technology: SCREM is designed to be embedded in a well or borehole in the ground where monitoring is needed. It can continuously detect and record radiation from radioactive species in the sampling area for periods ranging from several months to multiple years, depending on the power source.

The patent states that "continuous monitoring and recording offers [sic] benefits of longitudinal studies in time and greater sensitivity, particularly where episodic flow of contaminants may be occurring and/or the radioisotopes are present at very low levels."

The detector is based on light-emitting fibers, called scintillators, and silicon photomultipliers (SiPMs). When beta particles interact with the fibers, the fibers emit photos that travel to SiPMs. Readouts then collect signals, which can be counted and analyzed. Conceptually, the system is simple, and the team put effort into optimizing the design to ensure packaging and readout for detection are suited to a subsurface environment.

To optimize the low energy of beta particles emitted by tritium, the design puts unclad scintillating fibers directly in contact with ground water. The fibers are positioned in a grid structure that allows water to flow between them, maximizing the wetted surface. The photon signal is collected from both ends of the fibers, and coincidence detection is applied, which "almost completely eliminates the thermal background noise," according to the patent.

"The SiPM makes a good detector for this application," said Jack McKisson, an electronics engineer at Jefferson Lab. "It's got a good match of the spectral sensitivity to the emission from the fiber. It only takes a low voltage and provides a much bigger signal in a tiny package. These are all characteristics that fit the requirements for a subsurface monitoring system that conventional photomultiplier tubes could not provide."

The design also could be adapted to detect gamma rays, alpha particles, or neutrons by altering the dimensions of the scintillating fibers, which changes the detection efficiency for different types of radiation.

Move to commercialization: Canary Instruments is a start-up that grew out of the Department of Energy's Boost Platform program for the purpose of licensing this subsurface monitor. Boost's goal is to bring promising, lab-created technologies to commercial markets, offering business and mentoring resources.

"The CRADA mechanism is great because we get to partner with many types of institutions, hospitals, universities, and businesses. Some of those have turned into valuable projects, so this one is very exciting," said John McKisson, a computer engineer at Jefferson Lab.

Canary Instruments will work closely with researchers at Jefferson Lab as they refine the device's electronics and readout systems, perform baseline testing, and develop prototypes.

"Taking a technology, building a strong team, and successfully launching a company in 16 weeks is an impressive accomplishment," said Kelli Howie, business development manager at Sandia National Laboratories and the Boost Platform's project manager. "This CRADA reflects Boost's broader goal of helping move DOE lab-developed technologies into the marketplace, where they can address critical energy and infrastructure needs."

Canary is led by Walter Xu and Adil Ahmed.

"This CRADA allows us to continue working with Jefferson Lab and tap into that relationship to codevelop the best product possible," Xu said. "Having access to Jefferson Lab's expertise, facilities, radiation control team and available materials is really massive as far our first steps as a young company."