TRIPWIRE: Pioneering radiation detection

IDAHO FALLS – As nations look for ways to reduce carbon emissions, nuclear energy is increasingly being recognized as a safe and reliable option to address rising electricity consumption.

Additionally, tomorrow’s advanced nuclear reactors will be smaller and more flexible than today’s reactor fleet, allowing them to integrate more renewable energy into the grid, provide heat for industry, and power remote applications such as mines and data centers.

Just as the world needs the next generation of nuclear reactors to meet climate goals, it also needs new options for safely storing radioactive materials. In 2022, approximately 400,000 tons of spent fuel were stored worldwide, including approximately 90,000 tons in the United States alone.

Nuclear experts say deep geological repositories are a necessary long-term solution for the safe storage of nuclear waste. Although there are currently no commercial nuclear repositories, Finland plans to open the world’s first deep geological repository by the middle of this decade. Switzerland, Canada and France license their own disposal facilities.

In the US, consolidated spent fuel storage facilities will bridge the gap between on-site storage and a national repository.

Likewise, states must secure nuclear material for arms control purposes to meet treaty obligations and prevent the proliferation of nuclear material in an increasingly volatile world.

These nuclear stockpile scenarios require reliable detection equipment to ensure public trust and non-proliferation of nuclear material.

At Idaho National Laboratory, researchers developed TRIPWIRE to enable detection of radiation in large and inaccessible areas such as nuclear material storage facilities. Winner of the 2024 R&D 100 Award, TRIPWIRE provides governments and industry with a cost-effective, durable and unique option for monitoring radioactive materials.

The work was originally funded by INL’s laboratory-led research and development program. TRIPWIRE has also received funding from the National Nuclear Security Administration.

Sparkling fibers

TRIPWIRE uses thin scintillation fibers for radiation detection. Large blocks of sparkling material are made of plastic and are sometimes used to detect radiation in above-ground locations such as border crossings.

“The radiation excites the molecules in the scintillation fibers,” said David Chichester, nuclear engineer and director at INL. “When they are no longer excited, they emit visible photons. There is a sensor that detects this light.”

With TRIPWIRE, the sparkling plastic is pulled out into approx. 1 mm thin fibers. At this thickness, the fibers exhibit a property similar to fiber optics called total internal reflection. Total internal reflection means that the light is reflected along the entire length of the fiber until it reaches the end.

“With these plastic scintillators, the maximum length that effectively transmits light is a little less than 50 meters,” Chichester said. “But we can couple the scintillation fiber with fiber optics, then the sensor can be miles away.”

This 50 meters – the length of an Olympic swimming pool – allows detection over a much greater length and orders of magnitude longer than current gamma radiation detectors, which are typically limited to just a few inches.

The result of TRIPWIRE is that the technology eliminates the need to bury electronic devices in repository. Instead, the electronic equipment remains on the surface, where it can be easily repaired or replaced if necessary.

“Originally our sponsor was interested in uncovering undeclared activity,” Chichester said. “Imagine a repository that is sealed and a host country is trying to get back in. A real-time sensor underground with the spent fuel provides a strong deterrent to theft or diversion.”

Spreading like a spider web

In underground systems and tunnels, TRIPWIRE can spread like a spider web and cover a three-dimensional area.

TRIPWIRE’s optical fibers are inexpensive and readily available, making the technology a good option to significantly reduce personnel exposure to potentially dangerous radiation and maintenance costs in long-term nuclear storage facilities.

The sparkling fibers are coated with protective materials that resist abrasion, chemical degradation, and fluctuations in temperature and humidity. The fibers can withstand kicks or falling rocks, which is essential for long-term use in a closed repository where the fibers may need to function unattended for decades or even centuries.

TRIPWIRE also has applications beyond repositories, including natural background radiation monitoring along oil and gas pipelines, radiation monitoring at ports of entry for national security, and perimeter detection for emergency response.

Researchers have even considered using TRIPWIRE in the gloves used to move and examine radioactive materials as radiation safety monitoring.

“TRIPWIRE is a versatile, cost-effective radiation monitoring technology, it has the potential for huge impact across multiple areas and we look forward to its potential use in the coming years,” said Chichester.