High explosives research and development booms at Los Alamos National Laboratory.
December 9, 2024
Some days when Los Alamos National Laboratory chemist Virginia Manner goes to work, she—literally—has a blast. That’s because Manner works with high explosives, materials that, when triggered, produce a rapid and powerful release of energy.
High explosives differ from regular explosives, such as fireworks or gunpowder, primarily in the speed and intensity of their chemical reactions. A high-explosive reaction occurs almost instantaneously after it’s triggered, creating a powerful blast and high-pressure shock waves. But before new high-explosives formulas are considered for national security uses, including for use in nuclear weapons, Manner and her colleagues put them to the test.
“Our initial tests involve hitting pea-sized amounts of explosive powder with a hammer and lighting them on fire,” Manner says. The goal is to see how the explosives react to heat, impact, friction, and electrical discharge (such as static).
“Much of our research is based on finding ways to make explosives safer—safer to handle, safer to transport, and safer in the event of an accident,” Manner says. “Our goal is to make sure the high explosives cannot detonate accidentally but will perform as needed if detonated intentionally.” (See “Science plus safety” for more on Manner’s thoughts regarding safety and risk.)
Decades of detonation
For decades, Los Alamos scientists have detonated explosives and studied the results. This research began nearly 80 years ago as Manhattan Project scientists developed a way to use high explosives to set off the Gadget, the world’s first nuclear device, at the Trinity site in July 1945.
“During World War II, Los Alamos scientists really worked hard to understand explosive materials and how they perform,” says scientist Alex Cleveland of the Lab’s High Explosives Science and Technology group.
Inside the Gadget (and in fact inside all nuclear weapons), high explosives serve two roles. First, they are found inside detonators, tiny electrical devices. When explosives in detonators go off, they trigger the detonation of a larger quantity of high explosives located around a weapon’s plutonium core, called the pit. When the explosives surrounding the pit detonate, the pit implodes, which creates nuclear yield, or power.
In other words, Cleveland says, “the detonator creates a smaller bang to then get the larger bang.”
In 1952, the Lab created the first plastic-bonded explosives, in which explosive powder is mixed with a plastic binder. This process makes explosive material easier to handle and shape and less sensitive to accidental detonation. Plastic-bonded explosives are used in all modern nuclear weapons and in conventional munitions, rocket propellants, and other civilian and military applications.
Today high-explosives research, development, and manufacturing continues to boom at Los Alamos. Scientists are constantly creating new explosives because different characteristics and properties are necessary to meet various needs.
“We are working to develop formulations that are safer, more powerful, easier to make, or less expensive to produce,” says explosives scientist Bryce Tappan. “Plus, the physicists researching new weapons designs are asking us to develop new and different explosives that have unique characteristics, such as enhanced detonation pressure or higher velocity. We interact closely with these scientists to develop energetic materials that meet their needs.”
Cleveland explains that the group is “always reevaluating the materials we have in the stockpile and working on ways to make them safer and more stable and better performing.”
This work also contributes to advancing counterterrorism efforts and detecting and defeating explosive devices. Additionally, high explosives play an essential role in many experiments conducted at the Lab. When scientists want to analyze a material’s properties, discover how components react to shockwaves and pressure, or generate an extreme amount of energy for physics experiments, they often start by blowing things up.
Synthesis and formulation
Chemist Bi Nguyen creates new explosive molecules (groups of two or more atoms chemically bonded together) by combining different atoms or smaller molecules to form a larger, more complex molecule. This process is called synthesis and is similar to combining ingredients when cooking to create a new dish. “We are always trying to synthesize new molecules so we can stay competitive and keep our technical edge,” Nguyen says.
Creating a new explosive starts with research. “When I make a new molecule, I review the literature and think about what properties I want it to have,” Nguyen says. “New synthesis is hard and takes a long time.” Nguyen says she can tweak different characteristics such as melting point, power, detonation velocity, and other factors depending on the molecules she chooses to combine.
Tappan notes that “the ease of manufacturing and the scalability of production are key considerations when developing something new. Every molecule carries a compromise,” he says. “To make a safer formulation, one that is less susceptible to accidental initiation, we might have to give up some of its power or make it heavier, which could impact a weapon’s performance.”
Coming up with new explosives is challenging. “It takes a lot of creative work,” says Manner, who leads the Energetic Materials Synthesis team. “Plus, we want to create a broad array of explosives with different properties for different applications.” Other concerns involve production costs, environmental impacts, and speed of manufacturing. “Synthesizing new molecules requires trying many different things before you succeed.”
When scientists make a new formulation, they must develop a process to mix the explosive with selected binder components. They often use the wet slurry method, which suspends particles of explosive material in water while the binder is added. After filtering and drying, this process produces prills, tiny explosive pellets that look like Nerds candy. The prills can then be pressed and machined into specific shapes. The type of explosive dictates whether the process will be conducted in person or remotely to ensure safety.
At Los Alamos, explosive pressing and machining takes place in a building that contains several bays with two-foot-thick concrete walls. “Aside from the obvious fact that the material we are machining is explosive, the biggest difference between machining explosives and other materials is that machining explosives is a lot slower,” says Angelo Echave, deputy group leader for High Explosive Fabrication and Disposition. “We have multiple safety procedures and never take shortcuts.”
Echave walks through the bays pointing out the computer-controlled machining equipment and the remote stations where machinists monitor their work. “The formulations vary in sensitivity—how easily they can detonate—which determines how we machine pieces and implement safety controls. There are different colors for different explosive materials, which can help in identifying the type.”
Pressed explosives are x-rayed before machining and finished explosives are inspected using coordinate measuring machines (CMMs). “Explosives can detonate if you insult the material in some way,” Echave explains, “but everything we do here is considered an insult to the material. We cut it, we press it under thousands of pounds of pressure, and we expose it to heat and handling. That’s why every safety test and process is essential as we produce these parts.”
Performance and safety
Initial safety tests are followed by more advanced safety and performance experiments that involve detonating larger portions of explosives and subjecting the material to more extreme conditions, such as higher heat and stronger impacts. For example, high-speed gas gun experiments and intentional detonations of kilogram quantities of explosives are regularly performed at indoor and outdoor firing sites run by the Lab’s Dynamic Experiments division.
“We do everything from safety testing—looking at how the explosive will behave under accident scenarios—to performance testing, in other words, will it do what it’s supposed to do,” says Philip Rae, High Explosives Physics and Diagnostics team leader. “We’ll measure the velocity of the detonation, how much force is imparted by the whole explosive process, the pressure output, how powerful the explosive blast is. We do a bit of everything and customize each experiment to each specific research need.”
Michelle Hogan runs some of the tests on new explosives. “These tests measure the ignitability and explosiveness of large consolidated charges to ensure worker safety and rank the relative safety of novel explosive formulation,” she says. Hogan primarily performs what’s called the skid test, a safety test that simulates a handling accident in which an explosive charge is dropped onto and dragged across a gritty surface, causing it to reach a temperature high enough to ignite. “Once ignited, we then observe how violently the explosive reacts,” she says.
In another type of experiment, called a cookoff, scientists apply controlled heating to a high-explosive sample until it ignites, often resulting in an explosion. These experiments provide necessary information about the safety of different explosive types.
Advanced diagnostics equipment measures velocities, pressures, and temperatures to study all the characteristics of a high-explosive formula. “It comes down to really understanding how materials behave under all the different conditions to be able to model and predict them,” says High Explosives Science and Technology Group Leader Margo Greenfield. “The science and technology aspects are key. How does the formula age? How does it perform? How safe is it? Answering those questions requires a multidisciplinary effort.”
Scale and supply
As if developing and testing explosives isn’t challenging enough, scientists face an additional obstacle: the supply chain. “After the end of the Cold War, we sometimes depended on materials that could only be sourced from sensitive countries, such as China or Russia,” Tappan says. “Now, we are redesigning our formulations to use chemicals we can obtain without going outside the United States.”
Greenfield stresses the importance of understanding and adapting to these issues. “We must be responsive to supply chain problems and investigate ways to develop different formulations,” she says. “The goal is to use no components that are at risk for supply chain issues.”
To help meet this goal, the National Nuclear Security Administration is investing in a new high-explosives synthesis and formulation facility at the Pantex Plant in Amarillo, Texas. Los Alamos scientists are working with Pantex to develop the facility and help ensure that Pantex can produce larger quantities of the explosives developed at Los Alamos. “Our goal is to make sure that Pantex’s new facility is agile so we can scale up new formulations as needed in the future,” Cleveland says.
Cleveland notes that “scaling up” an explosive means producing kilograms (instead of grams) of the formulation. Currently, Los Alamos works with both Pantex and the Holston Army Ammunition Plant in Kingsport, Tennessee, to scale up formulations. Los Alamos scientists travel to Pantex and Holston to work with the operators, scientists, and engineers producing the explosives. “When they initially run our material, it’s a pilot plant production campaign, and we go out and observe and help guide the work,” Nguyen says. The eventual goal is to move from pilot-scale production to large-scale production of the new explosive.
Future directions
As the Laboratory’s high-explosives scientists look toward the future, they see many opportunities. “Over the next few years, we will be making things that have new benefits, and we will continue developing our understanding of molecular properties and new formulations,” Greenfield says. “Our goal is to be ready when a physicist asks, ‘Do you have this material that will do this thing?’”
At the same time, the group must continue working on research and development so explosives production can become more agile, cost effective, and environmentally friendly. “We try to move where the country needs us while pushing science ahead and predicting future directions,” Manner explains.
Tappan agrees. “Our explosives work is crucial to fulfilling the Lab’s national security mission,” he says. “We will remain competitive with the country’s adversaries.” ★