“We have commenced war-reserve pit production”

Before diving into this article, make sure to read “Pit production explained” in the winter 2021 issue of National Security Science (or at least the CliffsNotes below!). That article describes the history of plutonium pit production, why new pits are being made, and why much of that manufacturing work is taking place at Los Alamos.

John Benner, an engineer, has made a career in the nuclear security enterprise. Working for more than 30 years at Los Alamos National Laboratory, he’s led efforts to maintain or modernize every Los Alamos–designed weapon in the current nuclear stockpile (the B61, W76, W78, and W88).

Since 2022, Benner has served as the associate Laboratory director for Weapons Production. In this role, he oversees the Lab’s effort to manufacture plutonium pits—the cores of nuclear weapons. When compressed by explosives inside a warhead or bomb, a pit generates incredible amounts of energy. Los Alamos is establishing the capacity to manufacture at least 30 pits per year, starting with pits for the forthcoming W87-1 warhead. The first war-reserve (stockpile-bound) pit was built this summer. Also called the first production unit (FPU), this pit underwent extensive inspection to ensure it met all design and military requirements. On October 1, the pit was diamond stamped—essentially given the stamp of approval to be placed into a weapon.

“Los Alamos is the only place in the nation that has the people and facilities to accomplish this mission,” Benner explains. “And now we have commenced war-reserve pit production.”

Benner sat down with NSS to discuss the path to pit FPU.

You became the associate Laboratory director for Weapons Production in January 2022. How has the pit mission evolved since then?

We’ve addressed a lot of significant, technical challenges. We engaged the full science and engineering base of the Laboratory to solve metallurgical challenges, material science challenges, and engineering challenges. Innovative solutions were identified for problems that were encountered in production. Solutions were needed to address production challenges; we changed aspects of the pit design to make it more producible. We now have a producible design and an initial production process. We will be refining that as we scale up production toward 30 pits per year.

We’ve also improved operational discipline in the Plutonium Facility as equipment has been removed or installed, as we’ve refined our processes, and as we’ve trained our workforce. In 2021, we had 19 operational weeks in the pit production areas, and we’ve improved that to about 33 weeks. To fully support the 30-pits-per-year plan, we must improve the operational availability to 40 weeks. Operational availability is when an area is online and available for producing pits. It can’t be down for any reason. And keep in mind that in addition to actual production work, we are running security, a cafeteria, nuclear materials control and accountability, and a lot of other support work. There is a large ecosystem of people that has really come together.

Lawrence Livermore National Laboratory, a design agency, developed the design for the W87-1 warhead and pit. Los Alamos, also a design agency, has put on its production agency hat as the organization doing the pit manufacturing work. How does design inform production?

My experience as part of the Los Alamos design agency involved developing components here at Los Alamos and then producing them at production sites such as the Kansas City National Security Campus and the Y-12 National Security Complex. When you are designing, you may think that a certain production process will be sufficient. But as you get into production, you learn by doing as you move from early production into full rate production. Now that you’re having to do it every day, even multiple times a day, suddenly it dawns on you: Wouldn’t it be better if we had different tooling? How might we tweak the process? Could we cut down on the variance and do something twice as fast?

Typically, you can develop a more efficient process because people bring improvements that they thought of as they’re building parts. Production staff and product engineers find efficiencies and learn from early issues to help refine production, reduce scrap rates, and improve yield rates as production continues. Necessity is the mother of invention, as they say.

What are some of the manufacturing processes necessary to make a pit?

I can say a few of them. We purify plutonium, which involves electrorefining. We cast plutonium shapes. We weld. We rough-machine and then final-machine some components. We assemble the components into pits.

Over the past couple years, we’ve developed an improved engineering understanding of how and why pit production works—not just that it works. I’m happy about that. That understanding will allow us to continue to solve problems and eventually build different pit types—there are only a small number of operations that are unique to specific pit types.

Los Alamos is currently manufacturing pits to go inside the still-in-development W87-1 warheads, which will sit atop the still-in-development Sentinel missiles. What happens to these pits from now until these missiles are finally on alert, some time in the 2030s?

The plan of record was always to build ahead and create a stockpile of W87-1 pits in advance of the W87-1 system FPU. That is because the production rate at Los Alamos is less than the production rate of W87 systems at the Pantex Plant, where weapons are assembled. In the interim, the pits will be temporarily staged in a safe and secure location.

After a war-reserve pit is manufactured, it is diamond stamped. What does that signify?

The diamond stamp indicates that a nuclear weapon component meets the design, production, and quality requirements for insertion into the nuclear stockpile.

On different types of components, the diamond stamp shows up differently. Many components are physically stamped with a diamond shape. Some components—like wires—are not physically stamped, but they have a diamond-stamped label or tag. 

What is the significance of the FPU—to you personally and to the nation?

My background is in weapons engineering, and I’ve worked in support of all the Los Alamos–designed weapons in the enduring stockpile at one time or another. In my previous roles, I helped put into production most weapons components with a few exceptions, including pits, which were always reused in my experience. So, here at the end of my career, it’s interesting that I am putting pits into production.

But that’s not why FPU is significant. It’s significant because the United States now has the ability to produce war-reserve pits and has the ability to fully refresh warheads and build new warheads to support the nuclear stockpile. ★

John Benner will retire from the Laboratory in January 2025.

Haven’t read “Pit production explained”? Here are the CliffsNotes.

• Los Alamos produced the first plutonium pits in 1945, during the Manhattan Project. These pits were used in the atomic bombs detonated in the Trinity test and above Nagasaki, Japan.
• From 1952 to 1989, the majority of plutonium pits for U.S. nuclear weapons were manufactured at the Rocky Flats Plant near Denver, Colorado. Most of the pits in the current stockpile were made at Rocky Flats. 
• Plutonium is unstable and radioactively decays over time. Plutonium can also absorb neutrons. Eventually, the loss or gain of particles causes the plutonium to transform into daughter products, such as uranium, neptunium, and americium. In plutonium pits, these daughters start to build up as impurities. They don’t perform or behave the way plutonium does, and they can even react with the original plutonium.
• To ensure that aging pits pose no risk to the nuclear stockpile, the National Nuclear Security Administration tasked Los Alamos with developing a pit production process and delivering a minimum of 30 new pits per year.
• Los Alamos will salvage usable plutonium from old pits to make new pits. Plutonium from multiple old pits is necessary to make one new pit. 
• Plutonium, which is radioactive, is handled inside gloveboxes—sealed compartments that are accessed through two holes to which gloves are attached. Technicians insert their hands into the gloves and are able to handle the plutonium with no exposure to the element. 
• The Savannah River Site in South Carolina is also tasked with producing pits. Using the Los Alamos process, Savannah River plans to deliver at least 50 pits per year, starting in the 2030s. ★