Nuclear regulators and agencies are perennially concerned that the materials they are responsible for might be misused, lost or tampered with. Security is therefore a key issue but one that has seen little advancement over many decades. One of the main tools that International Atomic Energy Agency (IAEA) inspectors and others use to detect unauthorised access to nuclear materials and technology comes in the form of a coin-sized tamper indicating device.

The IAEA and other treaty verification regimes use E-CAP metal seal (CAPS) or metal cup seals. This is a general purpose, non-reusable copper and brass device used as a passive loop seal. To close the seal, a double copper cap is snapped onto the base. The metal base and its cap serve as the point of closure with a multistranded wire threaded between which encircles the item to be sealed. This device was developed in the 1960s and its still in use today. While they will reveal any evidence of potential criminal activity or tampering, they also present a number of challenges.

Heidi Smartt explains the problem: “It’s a very simple two-part metal cup seal to ensure that the item hasn’t been accessed without detection. To do a unique identifier on these seals they do a scratch and solder where they’ll solder inside the seal before they deploy it. They take an image of it at IAEA headquarters and then when they remove the seal, whether that’s a few months or a few years later, they cut the wire, take it back to the IAEA, open it up and make sure it’s the same seal.”

Smartt continues: “The metal cup seal is theoretically cheap, it’s maybe a dollar for the material, but it can’t be verified in the field. That’s been the big issue as it actually costs the IAEA about two staff to examine these seals when they come back. They might look for things like some kind of sign of tamper, but it’s relatively subjective. So, they have to touch the seal, feel it, study it, see if there’s anything that worries them about the appearance.”

According to the IAEA, in 2021, the Agency verified over 17,000 seals that had been applied to nuclear material, facility critical equipment or IAEA monitoring and other equipment at nuclear facilities. This clearly represents a substantial cost and, in response, the Agency has been looking for an alternative for some time. The goal is that the replacement has better tamper indication, better unique identifiers and can also be verified in the field. To that end the IAEA published a list of requirements for passive loop seals which the Sandia researchers used as the basis of their R&D programme.

Exploring alternative tamper detection

The IAEA has been considering advancements in materials, technologies and machining techniques to develop a new type of seal. Now, following prototyping and testing, the Agency has adopted the Field Verifiable Passive Seal (FVPS). Made from aluminium and polycarbonate, each FVPS has a unique pattern of designs etched onto their surface to ensure that they cannot be replicated or replaced, as well as other tamper-indicating features.

A device is used to verify the seal that employs customised software and a specialised lens and light attachment to take three reference photos. When an inspector attaches a new seal, they use the dedicated software to input information about the seal location and application and this information together with the photos is relayed back to the IAEA. Inspecting the seal at a later date, the verification device is used to take photos for comparison with the reference photos to confirm the integrity of the seal. Unlike the CAPS seals, tamper verification can be done in the field. As with the CAPS seal, the FVPS also requires no tools to apply, no maintenance while deployed, and no batteries or electronics to power.

Above: The newly adopted Field Verifiable Passive Seal (FVPS) (Source: IAEA)

“Having an in-field verification technique for the seal means we have faster verification results, and we can reduce the administrative burden,” said Nicolette Seyffert, the new seal implementation project team member and Information Security Officer at the IAEA. “By having an in-field customised reader, it is immediately obvious if a seal was tampered with and removes the need to bring the seal back to the IAEA’s Headquarters in Vienna.”

The new FVPS has been deployed for pilot use, with a planned expansion over the coming months before they eventually come to replace all of the traditional CAPS
seals. Nonetheless, while emphasising that the IAEA is not a customer, Sandia’s scientists continued to pursue the research that had been underway for several years using the IAEA guidelines for these types of applications. Smartt explains: “We thought of the idea of visually obvious tamper indication six or seven years ago. It was a concept and we started studying different chemical formulations but having the idea that an inspector sees something that’s visually obvious is more immediately conclusive. We hope that it’s a safer approach because they can do their job more quickly.”

Above: A conventional CAPS seal (Source: IAEA)

From visual concept to reality

From this visual concept, the Sandia National Laboratories engineers developed a system based on “bruising” materials. The core of the colour-changing solution is a chemical called L-DOPA. Found in the human body, this chemical can react with oxygen to make melanin which in humans is responsible for turning hair, skin and eyes their brown colour.

The research team had explored several other colour-changing chemicals before determining that the melanin-producing reaction was the most practical. Using a few commercially available products, the team made puck-shaped security devices that quickly reveal a dark brown stain at the site of any damage, including when the wire loop that is threaded through them is removed.

Above: The bead bits turn brown when exposed to oxygen, making any tampering extremely obvious (Source: Sandia National Labs by Craig Fritz)

“In this system, water beads of different colours are blended to give a colour swirl as a unique visual indicator. The point of the unique identification is to mitigate the potential for counterfeiting. Those aren’t barcodes or QR codes, those are features with randomness that would be extremely difficult to counterfeit,” says Smartt. The water beads are commonly available throughout the world and while they are used to absorb water in this case they become saturated with L-DOPA. The particles also produce a mix of easily identifiable colours that can give a quick visual indication if the seal has been swapped or changed by taking a series of photographs for comparison. However, the Sandia approach doesn’t just rely on a visual comparison. As Corbin explains: “That [photo comparison] is the ideal scenario but that may not be possible in all applications, for instance it may not be possible to take a camera into certain facilities.”

Once the seal has been damaged the chemical reaction starts immediately and the colour change continues to spread as long as the damage allows oxygen to penetrate the seal.

Cody says: “You can start seeing things within the hour, if not faster but you can really see stuff within 24 hours when it’s very, very easily seen. It’s visibly obvious, that’s the key thing, and with the seal it’s just small, but with the enclosure, not only is tampering visibly obvious, but depending on the timing you could identify the attack location, which could be very useful to provide information potentially.”

The time taken for assessment is also an important characteristic. “There is that conclusive nature of the seal but also the rapid part. Inspectors have limited time in a facility and there are a lot of other activities they could do rather than spending time touching a seal and examining it,” Corbin says. It’s also important to note that even at 24 hours post breach for an obvious indication of tampering, that is still far quicker than the CAPS system which involves sending it back to the IAEA to be examined.

However, Cody identifies one potential benefit of the colour change system: “Because the inspectors will come in every few months to a few years depending on the material and the agreement with the country, the timing is not critical. It just has to happen before the inspectors get there. It’s not real time. That said, if there were surveillance cameras in the room with a view of containers and these seals, you could probably see on that camera that one of those seals had been compromised and turned black, and then maybe send an inspector much sooner. That’s very different. You can’t do that with any of the other seals unless they’re the electronic versions.”

Commercialising security

Cost focus has also been key for the research team since the earliest conceptual stages, as Smartt says: “Because we’re in a research and development cycle we are not at a place where we are commercialising. That said, the materials themselves are inexpensive and one of the reasons we chose the water beads was for ease of processing. It made it a lot easier, but there will be labour costs and if someone were to pick this up commercially, we would hope that there would be some sort of efficient process to manufacture these.”

Corbin picks up on this theme, saying: “A lot of stuff in materials R&D these days is synthesised. It takes effort to make something like that to change one molecule to another. For example, that takes solvents and lots of other chemistry and time. In this case, every single component is something that is commercial. The sealing materials are thermosets or epoxies, the water beads are cheap, the materials are 3D printed, the little seals are 3D printed. The enclosures are made of acrylic tubes with different diameters. It’s all commercial and they don’t take long to build once we have everything.” Because the L-DOPA reacts with oxygen, the final assembly must take place in an anaerobic environment and here Corbin suggests a commercial approach will address potential costs too. “The key component and where the cost may go up again, theoretically, is the requirement of an inert atmosphere to build it but I believe there are automated systems that can operate in an atmosphere where this could be processed. It could be streamlined, but this is not something we have investigated because we’re not anywhere near that point,” he says.

Nonetheless, while low cost, commercially available components was an important consideration, the sealing technology also placed further demands on the system chemistry. Corbin explains: “This process came from cheaper materials that have inherently unique features. Water beads can absorb a lot of material, and then it was a case of finding something that can change colour visibly and using the beads as a ‘holder’ of the sensor. There were additional requirements around that application. Once that colour change has happened, you have to be positive that it can’t be reversed. It’s a one-way street so if you put it in an anaerobic environment, for example, it doesn’t change back. The chemistry is irreversible.”

Moving beyond nuclear

Having developed a prototype the next steps are to conduct further testing and finalise the reporting. “After that, we will continue to talk to interested parties that could be in other treaty verification regimes, for regional inspectorates, or for other industry types. I think there could be value in many different industry fields. The IAEA requirements were pretty stringent and so when we come up with something that meets most of those requirements, other industries could benefit from that work,” says Corbin.

Indeed, the nuclear sector is relatively niche, as Smartt observes: “The IAEA uses about 18,000 seals per year, that’s still a small number. If someone were to pick this up commercially, I don’t think we are looking at rolling out really high volumes for this particular market. We do think there’s a space for asset monitoring, to protect something high value. We think there could be other application spaces for these enclosures and they are probably close to ready to be commercialised if that came up.”

It is clear that the colour changing security device does have a number of advantages over other approaches that may suit markets beyond nuclear. These advantages centre on cost and functionality, as Corbin concludes: “Even though the metal cup seal is the lowest cost in terms of materials and pretty high cost in terms of verification, some of the other seals the IAEA uses, like the Cobra Seal, are about a hundred dollars per seal and that goes all the way up to electronic seals, which can be a few thousand dollars. These things really vary in price,” he says.

“How functional it is for that cost is a big deal as well, the security aspect, the tamper indication and the unique identifying colours mean the overall design has a layered security protection. There’s a lot of thought going into what materials were used and how they were done to deliver value with function, which is the best-case scenario for lifecycle cost.”