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Plutonium Pits Are a Critical Obstacle in U.S. Nuclear Plans

Modernization programs need to be realistic—and may be unnecessary.

By , a writer on scientific and political commentary.
Los Alamos National Laboratory
Los Alamos National Laboratory
The entrance to Technical Area 18 of the Los Alamos National Laboratory, which houses several tons of highly enriched uranium and plutonium, is shown in Los Alamos, New Mexico, on Aug. 12, 2002. Neil Jacobs/Getty Images

The United States cannot make its projected numbers of plutonium pits for nuclear weapons. Not now nor the immediate future. Maybe never.

The United States cannot make its projected numbers of plutonium pits for nuclear weapons. Not now nor the immediate future. Maybe never.

That’s important because plutonium pits are part of the fission-fusion chain that is a nuclear explosion. The fission part of a nuclear weapon is a sphere of explosive and metal shells. The pit is the central shell. In early weapon designs, it was solid like the pit in a peach. Its explosion sets off the secondary fusion reaction in another part of the weapon. As part of the United States’ modernization program, the National Nuclear Safety Administration (NNSA) committed to a surge production capacity of at least 80 plutonium pits a year by 2030. It is not clear why rebuilding pits is necessary; a study by Jason, a key group of U.S. scientific advisors, indicated pits should be stable for a century or more.

All declared nuclear nations are upgrading or “modernizing” their nuclear forces. That can mean many things. North Korea is increasing its number of nuclear weapons. The United Kingdom has decided to increase its numbers to as many as 240 weapons. China has built a field of missile silos that may or may not all contain missiles and warheads. Modernization is becoming a fresh arms race.

Modernization programs in the United States and Russia are the largest, including everything from control bunkers to warheads to delivery vehicles. The United States is estimated to have 3,800 warheads stockpiled. The New Strategic Arms Reduction Treaty (New START), signed in 2010 and extended for five more years beginning in 2021, limits deployed warheads to 1,550 weapons each. An additional 1,750 Russian warheads await decommissioning. The others are in storage.

At around 80 new pits a year, it would take about 20 years to replace the pits in the United States’ 1,550 deployed warheads. This makes some sense. Baseline planning is for 30 pits a year (51 years for replacement).

The difficulty lies in where and how the pits are to be fabricated. This isn’t something that existing facilities can be casually repurposed for—it’s a technically challenging and potentially dangerous process that needs dedicated facilities.

In 1989, the plutonium pit factory at Rocky Flats near Denver, Colorado, was shut down for environmental violations. Since then, the buildings were removed, and the area where the plant stood is now a nature reserve. That left the Los Alamos and Lawrence Livermore National Laboratories as the only places in the country that can do plutonium fabrication, and Livermore, with suburban growth creeping up to its boundaries, soon was out of the running because of potential danger to its neighbors.

The Los Alamos plutonium handling building, known as PF-4 in Technical Area 55 (TA-55), began operations in 1978, primarily as a research facility with the capability to do small amounts of processing and fabrication. It has been upgraded since. I spent part of my own career working there.

For the past decade and more, Los Alamos has been working to reach a rate of 30 pits a year. Los Alamos produced 31 pits between 2007 and 2013—but none since. Reasons for the lack of success are probably many, including inadequate facilities and the need to relearn what had once been institutional knowledge. Safety problems shut down portions of PF-4 for nearly four years.

Fabricating a pit requires a number of operations: melting down an old pit, casting the metal, machining, and finishing the formed piece. There may be other operations as well, particularly if impurities are to be removed from the metal—let’s make a rough estimate of 10 operations.

Each operation requires at least one glovebox with equipment. A glovebox has a window and gloves to reach into a working space that is separate from the room atmosphere. The toxicity of plutonium requires it be contained. Gloveboxes may be ganged together in a production line or a part may be sent to another room for the next step. PF-4 is set up to transfer parts without breaking containment. Because of the danger of a critical incident, when too much plutonium in one place interacts to produce a burst of radiation, both engineering and procedures must be designed to limit amounts of plutonium in one place at one time.

With 10 operations, 10 pits could be in process at once. The time required by the slowest operation will determine how quickly pits can move through the system. A rate of 30 pits a year implies about a week and a half to produce a pit. Eighty pits a year implies less than a week per pit. Multiple production lines may be necessary for the surge goal.

Enter the Savannah River NNSA complex.

The Savannah River Site in South Carolina was built in the early 1950s to supplement plutonium production at the Hanford Site in the state of Washington. Five reactors operated at Savannah River, and the first full-scale PUREX (or plutonium uranium reduction extraction) reprocessing facility extracted plutonium from irradiated fuel rods. In the 1980s, the reactors were shut down, and environmental cleanup started.

Savannah River has produced small amounts of plutonium-238 metal to provide electrical power for spaceflight missions. But it has no facility equivalent to Los Alamos’s TA-55. It has tried to change that over the years by attracting work related to using plutonium as a fuel in civilian reactors. The market for plutonium fuel, however, has never taken off in the United States. Most recently, the MOX Fuel Fabrication Facility, intended to produce mixed-oxide (MOX) uranium-plutonium reactor fuel, went wildly over budget. The project was shut down in 2018, and a large building stands partially completed.

South Carolina has a love-hate relationship with plutonium. State and local authorities have complained that surplus weapons plutonium has been left there with no plans for the future. In response to a court order, Savannah River shipped some of that plutonium to the Nevada National Security Site (formerly the Nevada Test Site), apparently without proper notice. An NNSA fact sheet from March 2019 lays out its view. Nevada doesn’t want it either, but as recently as May, the plutonium remained there.

On the other hand, there is that partially built MOX building and the job loss from its shutdown. The design can be modified to pit production; plutonium handling requires the same sorts of ventilation, floor space, and other construction no matter what the product is. It will take years to repurpose the MOX plant to pit production—2030 is the date mentioned—and cost estimates are already ballooning.

So, of course, the South Carolina congressional delegation pressed the NNSA and Congress for the pit project to include them as well.

That’s where the hate part of that love-hate relationship comes in. Surrounding communities in New Mexico and South Carolina harbor significant opposition to pit production plans on both anti-nuclear grounds and broader environmental concerns. A lawsuit has already been brought in South Carolina to prevent the project from going forward. There will be more.

On June 10, testifying to Congress, an administration official admitted that the 80-pit surge capacity is not going to happen. “Based on our latest information, we assess that meeting the 2030 [deadline] … is not going to be achievable,” Charles Verdon, acting NNSA administrator, testified. This is the first time an NNSA administrator has admitted this. Earlier testimony by Jill Hruby, now confirmed by Congress to replace Verdon, and the budget are consistent.

The admission was limited; Verdon suggested 2035 might be a target date: 14 years away. The history of the U.S. Energy Department’s inability to control the cost and schedule of the MOX building and other large projects suggests 2035 is optimistic. Safety problems at Los Alamos were partly inflicted by a management that did not understand its job and has been replaced. A new generation of workers at PF-4 are finding it difficult to learn the necessary skills. A Savannah River operation would start from even further back. The lawsuits may take years to resolve.

Not being able to build new plutonium pits and admitting it publicly has implications for strategic security talks with Russia and U.S. nuclear weapons policy. The Biden administration has admitted only to a delay, but the possibility of no new pits hangs over that admission.

The implications are broad. New warheads would have to be designed around current and available pit designs. If there are issues with warhead reliability, targeting may have to be rethought. These issues are highly classified, so details will not be discussed publicly.

China and Russia have probably figured out what I’ve written here, which comes from public sources and a bit of knowledge about the facilities. It puts the United States at a disadvantage if the negotiations are to be about warhead numbers.

With the destruction of basic arms control treaties except for New START and multiple disagreements between the United States and Russia, negotiations have backed off to what is called strategic stability, a more general approach than the more quantitative arms control. It may be the Biden administration, with this admission, is preparing to negotiate nuclear stability on broader terms—including concerns Russia and China have repeated about the danger missile defense poses to stability.

Economist Thomas Schelling, one of the originators of deterrence theory, saw mutual vulnerability as part of nuclear stability. Former U.S. President Ronald Reagan’s fantasy of an invulnerable missile shield was intended to remove U.S. vulnerability from the equation. So Russia has announced the development of new weapons, and China has built new missile silos to make the United States vulnerable again.

Admitting the United States will not be able to produce more pits for nuclear weapons soon could be a first move toward damping down an incipient arms race. Realistically accepting limits—even unintentional ones—may be the best step the United States can take.

Cheryl Rofer writes scientific and political commentary. She was a chemist at the Los Alamos National Laboratory for 35 years.

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