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Crisis in the U.S. Nuclear Weapons Complex: Part 3—The Problem Starts with the Pits

The views expressed are those of the author and do not necessarily reflect the views of ASPA as an organization.

By Erik Devereux
July 15, 2022

This is the third column in a series regarding the unfolding, unprecedented crisis in the U.S. Nuclear Weapons Complex (NWC) (the first column on how U.S. budget politics since 1969 have damaged the NWC is here; the second on how nuclear weapons ended exponentially deadly warfare among the great powers is here). This column turns to discuss specific problems afflicting the NWC amidst new plans by the United States to replace its existing nuclear arsenal. The focus of this column is on Los Alamos National Laboratory (LANL) and Savanah River Site (SRS), the two facilities within the NWC charged with building one of the crucial components of all future bombs: the plutonium 239 (Pu239) triggers or “pits” responsible for igniting the nuclear reactions that yield the immense explosive force of these weapons.

LANL and SRS are at opposite ends of the spectrum in the crisis facing the NWC.

One of the oldest NWC sites still operating, LANL’s Pu239 handling facilities need serious re-investment amidst decades of retirement of the personnel directly involved with building the prior generation of pits. After having pioneered the science, engineering and craft of working with Pu239 (a difficult, tricky substance as discussed further below), LANL is on the verge of losing its capacities and has not manufactured any quantity of pits since the early 1990s. I should mention that there is organized opposition in New Mexico to re-starting pit manufacturing at LANL.

SRS is attempting to repurpose the failed MOX (“mixed oxides”) facility, originally intended to transform 35 metric tons of excess Pu239 left over from the Cold War into civilian reactor fuel, into a new facility also for manufacturing pits. SRS previously never built any pits. Under current NWC plans, LANL is to manufacture 30 pits per year and SRS 50 pits per year for a maximum annual production of 80 pits. In other words, the facility with the least experience is being tasked with the most production if the United States wants to maintain an effective nuclear deterrent.

To get a sense of how difficult this manufacturing is, the budget estimates for this process run into the many billions of dollars. Kilogram per kilogram, Pu239 pits are the most expensive manufactured objects ever built by human beings.

The diagram at the top of this article helps to explain why Pu239 pits are so difficult to make. Contrary to what most Hollywood spy thrillers depict, the pits are not solid spheres. Instead, approximately 4kg to 6kg of Pu239 must be shaped into something akin to a small, hollow ellipsoid (think the shape and size of the classic, small Nerf football). The pit is hollow to allow a quantity of tritium and deuterium gas (“boost gas”) to be injected into that space just prior to detonating the weapon. This boosting greatly increases the efficiency of the fission “burn” of the Pu239. The hollow shape also facilitates the rapid assembly of the supercritical mass of Pu239 when compressed by a traditional explosive “jacket” wrapped around the pit. Finally, the ellipsoid shape of the pit helps the overall weapon to fit within the narrowness of a missile nosecone.

To reference how advanced this design is, consider that the Fat Man bomb dropped on Nagasaki, Japan in August 1945 contained about 6kg of Pu239 and yielded the equivalent force of approximately 25 kilotons of TNT. Today’s pits contain approximately the same amount of Pu239 and yield up to 100 kilotons all on their own.

From the earliest experiments in the Manhattan Project forward, Pu239 has proved to be an incredibly tricky substance to engineer. For those interested in details, Wikipedia offers a useful explanation. Furthermore, Pu239 is highly toxic and emits the most harmful radiation to human health—alpha particles—so it must be handled in clumsy “glove boxes” and with other suitable safeguards to protect workers from harm. Imagine having to manufacture something so precise using a tricky, difficult material while wearing bulky gloves. This is why the maximum production the NWC currently anticipates it can achieve is 80 new Pu239 pits per year. But that is based as much on hope as anything else, and hope is neither a strategy nor a tactic.

Why are new pits needed? It is not just that the next generation of U.S. nuclear weapons might require some updated designs. The existing inventory of pits are approaching 30 to 40 years deployed and are aging out of service. This is not because the Pu239 is undergoing radioactive decay to the point that the material would no longer fission as intended (Pu239 has a half-life of about 24,000 years). Rather, the problem is that the alpha particle radiation from the Pu239 is damaging other components around the pits to the point that the entire apparatus must be replaced.

As it stands at the moment, the NWC cannot manufacture new Pu239 pits at the volume required to maintain the U.S. nuclear deterrent. That alone is a crisis. The next articles in this series will discuss how that is just one crisis among many after years of the NWC experiencing budgetary and administrative neglect.

Author: Erik Devereux is a consultant to nonprofits and higher education and teaches at Georgetown University. He has a B.S. from the Massachusetts Institute of Technology (Political Science, 1985) and a Ph.D. from the University of Texas at Austin (Government, 1993). He is the author of Methods of Policy Analysis: Creating, Deploying, and Assessing Theories of Change (available for free here). Email: [email protected]. Twitter: @eadevereux.

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