Not long after the end of World War II, Manhattan Project Director and U.S. General Leslie Groves speculated that the Soviet Union wouldn’t have the know-how to develop an atomic weapon until the late 1960s. Instead, the Soviet Union detonated its first atomic device in August 1949, just four years after Manhattan Project scientists successfully tested their atomic “Gadget” at the Trinity site in southern New Mexico. By August 1953, the United States had tested dozens of nuclear (including two thermonuclear) devices, and the Soviet Union was not far behind.
Faced with a burgeoning arms race and the knowledge that—as Great Britain had demonstrated in 1952— it was only a matter of time before other countries also developed nuclear weapons, U.S. President Dwight Eisenhower chose to discourage states from pursuing nuclear weapons while also promoting peaceful uses of nuclear technology.
In December 1953, Eisenhower delivered a speech titled “Atoms for Peace” to the United Nations General Assembly. In closing, he said, “The United States pledges before you, and therefore before the world, its determination to help solve the fearful atomic dilemma—to devote its entire heart and mind to finding the way by which the miraculous inventiveness of man shall not be dedicated to his death, but consecrated to his life.”
The ideas expressed in Eisenhower’s speech led, four years later, to the creation of the International Atomic Energy Agency (IAEA). According to its statute, which was signed by 81 nations in 1956, the IAEA seeks to “accelerate and enlarge the contribution of atomic energy to peace, health, and prosperity throughout the world.”
Safeguards come to Los Alamos
Since its inception, the IAEA enacted safeguards— measures to verify that nuclear material around the world is not diverted from peaceful purposes. These safeguards ensure that countries can develop nuclear technology for peaceful purposes, while the IAEA provides credible assurance to the world that nuclear weapons are not being developed and proliferated in those countries.
The safeguards of the late 1950s and early 1960s were hard to verify. Inspectors had no concrete way of knowing if a facility’s operating log was accurate or if containers of material were labeled correctly.
To address these shortcomings, IAEA inspectors would send chemical samples to laboratories for destructive analysis, meaning that the samples would be destroyed during the process of finding out what they were.
Not only did the process destroy valuable material, but it also was time consuming and often disrupted facility operations. In addition, some materials weren’t easily accessible. And, perhaps most importantly, once a sample had been destroyed, it couldn’t be analyzed again, which was problematic if a facility’s operator disputed an inspector’s findings.
George Robert (Bob) Keepin Jr., a nuclear physicist at Los Alamos National Laboratory, knew there had to be a better way—or at least another way that would supplement destructive analysis. In 1966, Keepin had just returned to Los Alamos after a two-year stint at the IAEA headquarters in Vienna, Austria. He thought it possible to develop tools that would allow inspectors to assay, or measure, a nuclear facility’s materials quickly, accurately, and safely, without destroying anything. And he thought that Los Alamos was the right place for this work.
Laboratory Director Norris Bradbury was quick to agree. “Los Alamos’ interest in safeguards should not really surprise you,” Bradbury said in 1969. “Our pioneering work in nuclear weapons has left us with the profound concern that these devices never get used in anger, never get used surreptitiously, never get made by surprise, by theft, or by diversion.”
Howard Menlove, who joined Keepin’s team in 1967 and still works at Los Alamos today, recalls that “when Keepin sold the program, one of his sales points was that Los Alamos had technical staff who were among the best in the nation. We’ve got the staff, we’ve got nuclear material, and we’ve got instrumentation and technology to keep track of nuclear material. That’s why the program’s birth belonged at Los Alamos.”
In December 1966, with support from the Atomic Energy Commission and others, the Los Alamos Safeguards R&D (research and development) program officially launched.
The Safeguards R&D program’s origins were humble; some 15 scientists worked in offices frequented by chipmunks and rattlesnakes. But what the program lacked in accommodations, it made up for with a sense of mission. “The challenge was to develop new nondestructive assay [NDA] technology to quantify nuclear material in all of its different forms,” Menlove says.
And although the challenge was real, it seemed hardly insurmountable. In fact, the Lab’s first safeguards scientists were so confident in their abilities that, according to Menlove, “We thought we’d have exhausted the field within five years.”
The group’s optimism lay in the fact that the principles of nondestructive assay are fairly straightforward. The nuclear materials used in power plants, along with the “daughter” and fission byproducts produced by using those materials in reactors, are radioactive. This radiation varies in type and intensity depending on the material. By measuring the radiation emitted from a sample, scientists can determine the type and quantity of nuclear material present at a given point in the fuel cycle.
For example, “most nuclear material emits gamma radiation,” explains Alexis Trahan, a nuclear engineer with Los Alamos’ Safeguards Science and Technology group. “When you’re measuring gamma rays, you’re essentially counting how many you get at specific energies, and that’s what you use to determine what the material is.”
However, gamma ray readings may become difficult if a material emits too many gamma rays, if a material is so large that only gamma rays from its surface are detectable, or if a material is heavily shielded (by lead or stainless steel, perhaps) inside equipment or storage containers.
In such cases, an inspector might turn to neutron counting for confirming the presence or mass of nuclear material. Neutrons are more penetrating than gamma rays, so they can be measured even through shielding materials. Neutron counting is especially well-suited to plutonium assay because certain plutonium isotopes spontaneously fission at a high rate, causing them to emit more neutrons.
Some materials call for a more active assay approach. To get the best mass measurements for uranium-235, plutonium-239, and plutonium-241—all isotopes of uranium or plutonium that don’t spontaneously fission at a high rate—scientists fire neutrons at them to induce fission and allow for assay.
Calorimetry is another NDA technique that measures heat energy and can be used for the accurate assay of plutonium or tritium. Since 1996, calorimetry technologies developed at the Laboratory have helped the United States keep track of plutonium in its domestic facilities, including the Plutonium Facility at Los Alamos.
Safeguards under the NPT
In 1970, the international Treaty on the Non-Proliferation of Nuclear Weapons (NPT, see p. 6) entered into force. The treaty’s tripartite aim—to prevent the spread of nuclear weapons, promote the peaceful use of nuclear energy, and achieve widespread disarmament—remains central to nuclear nonproliferation.
As the IAEA saw its role in the global safeguards regime codified by the NPT, its inspectors’ workload increased. Between 1970 and the end of 1980, the number of power reactors under IAEA safeguards rose from 10 to 126. Enrichment, reprocessing, and fuel fabrication plants likewise grew in number over the course of the decade.
The quick assessments afforded by NDA technologies accordingly became more important than ever. Tools developed and deployed internally at Los Alamos in the 1970s became critical for IAEA safeguards inspections globally.
In 1971, Los Alamos presented the first portable NDA tool to the IAEA. The stabilized assay meter (SAM-II) was a battery-powered gamma ray–detection instrument. Although especially useful for detecting uranium enrichment and assessing uranium fuel rods, the tool could be supplemented with a neutron counter to assay plutonium, making it a versatile device. One IAEA bulletin called it “as important to the safeguards inspector as his briefcase.” The device was about the same size as a briefcase, too, and resembled a stereo amplifier with a thermos-sized cylinder attached via a cable.
Another tool, the hex counter—so named for its hexagonal shape—quickly became a standby for plutonium assay. Likewise, the active well coincidence counter, which uses neutron counting to assess bulk uranium, soon attained widespread use.
NDA technologies developed at Los Alamos also began to be incorporated into the design of reactors and nuclear facilities. By the mid-’90s, using special cameras and other tools, inspectors could monitor a facility without setting foot inside.
Today, the IAEA employs more than 100 NDA systems, the majority of which were developed at Los Alamos.
The spent-fuel challenge
In 2008, the U.S. Department of Energy’s National Nuclear Security Administration launched the Next‑Generation Safeguards Initiative. Then-Secretary of Energy Samuel Bodman described the initiative as an effort to “plan and stay ahead” as climate change and other developments made nuclear power more attractive to nations around the world.
The Spent-Fuel Nondestructive Assay project was inaugurated at Los Alamos in response to this initiative. The multi-year project developed ways to more quickly and accurately assay the highly radioactive fuel that has been irradiated for months or years inside reactors. Or, as Trahan says, “the most complicated nuclear material on the planet.”
Initially, the project considered 14 possible spent-fuel NDA methods, before settling on five that it developed, fabricated, and tested at facilities around the world.
Two such methods, which were developed at Los Alamos and tested in Sweden as a proof‑of‑concept technology, are called differential die-away self‑interrogation (DDSI) and differential die-away (DDA). Because these techniques assay large and heavy spent-fuel assemblies, the instruments are the size of a commercial refrigerator. They contain tubes of helium that ionize in response to the neutrons emitted by spent-fuel, allowing for assay of the material.
The DDSI device was the first to use “list mode” data acquisition in measuring the neutrons emitted by a power reactor spent-fuel assembly passively. List mode allowed DDSI a far greater degree of accuracy than that afforded by traditional technologies, often yielding terabytes of data in a single assay. The DDA device then used a neutron generator to perform active interrogation and list mode analysis to obtain results even more effectively. “The results of this project significantly improved our ability to both measure and model burnup, cooling time, and fissile content of an assembly, far exceeding what was state-ofthe-art even a few short years ago,” says Los Alamos’ Holly Trellue, who led the multi-laboratory Spent-Fuel Nondestructive Assay project. Although not currently used in safeguards evaluations, both instruments offer potential future uses.
Los Alamos and international nonproliferation
Over the years, the initial 15-person Safeguards R&D program at Los Alamos has grown to four groups in the Lab’s Nuclear Engineering and Nonproliferation division. These 300-or-so employees work with others across the Lab, across the government, and beyond to support the IAEA’s work.
Los Alamos has been providing safeguards technical support to the IAEA for the past half-century. “The fact that Los Alamos has such unique and extensive technical expertise in safeguards, verification, and security technologies greatly contributes to our engagement with the international community,” says Olga Martin, program manager of Los Alamos’ Global Engagement and Material Security programs.
Beyond developing the tools that allow IAEA inspectors to conduct safeguards inspections, the Laboratory plays a key role in instructing inspectors on the use of these tools. IAEA inspectors have visited Los Alamos for training in nondestructive assay since 1980.
“A lot of the NDA equipment, especially neutron-based equipment, was developed at Los Alamos,” says Bill Geist, who conducts the Laboratory’s safeguards training programs. “So we’re certainly qualified to train inspectors on the use of that equipment.”
Today, new IAEA inspectors undergo a four- to six-month training program at the Agency’s headquarters in Vienna. After that, they travel to the Laboratory for an intensive two-week training course.
Scientists from the United States also work at IAEA’s headquarters in support of the Agency’s safeguards mission. Many of these experts come from Los Alamos. “Our experts spend several years in Vienna on leaves of absence from the Laboratory, and then when they come back, they understand much better what the needs are and how they can support the inspectors in their measurements,” Martin says.
Geist notes that the IAEA trainings and work exchanges also foster relationships within the global safeguards community. “People come to our training, and when a problem arises later, they know that Los Alamos is a resource that can help resolve the issue,” he says.
Menlove agrees that relationships are key. “Most of my innovations, the things that I developed over the years—20 or 30 systems that are being used worldwide—originated by visiting a facility and recognizing what the problem was, and having a good working relationship with the people, and then solving the problem with hardware,” he says.
Just as new nuclear technologies and political realities have called for new NDA tools in the past, novel challenges ensure that future NDA systems will need to be developed.
Today, new nuclear power reactors continue to come online, especially as nations shift from fossil fuels to cleaner sources of energy, as demand for energy grows worldwide, and as countries recognize the importance of energy security.
“As the civilian nuclear energy sector grows, there is more and more demand for these technologies to ensure that nuclear material is protected—and not diverted from peaceful uses,” Martin says.
Geist agrees. “More facilities are coming online, so there’s a lot more to inspect,” he says. “The focus will be on developing tools that allow inspectors to be more efficient, and to conduct inspections unattended.”
Although tools such as DDSI collect abundant and accurate data, the sheer volume of data produced by such technologies poses another challenge. “That’s really where the machine learning, data analytics piece comes in,” Trahan says. “It’s always great to take more data, but that means you’re going to need to have more humans sitting NSS there, interpreting the data. Machine learning can make this process significantly more streamlined and effective.”
“As the civilian nuclear energy sector grows, there is more and more demand for these technologies to ensure that nuclear material is protected—and not diverted from peaceful uses.” —Olga Martin
Computing, therefore, will be an important part of future safeguards design. At Los Alamos, scientists are working to develop machine learning algorithms that enable safeguards inspectors to process such data. They are also developing algorithms to determine if remotely collected data has been manipulated or fabricated. These algorithms may be especially useful as “deep fake” technologies increasingly threaten to undermine confidence in the data collected by NDA tools.
Reactor design continues to evolve, too. Miniature and micro reactors, for example, can be more efficient than traditional reactors. But to attain that efficiency, they rely on uranium that has been enriched to a much higher degree—and is, therefore, more suitable for use in nuclear weapons. In keeping with such developments, future NDA design will continue to seek new ways to incorporate verification technologies into facility design.
“What we don’t want to do is to wait until there are advanced reactor facilities all over the world before we develop the technology to safeguard them,” Trahan explains. “We want to be thinking ahead and saying, ‘Here’s how we can design these facilities to incorporate nondestructive assay into the flow of the facility itself—or maybe even into the reactor itself.’”
Los Alamos’ long involvement with the international community and its long track record in safeguards mean that it is poised to remain central to efforts to meet these new challenges. ★