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Risks of geologic disposal of weapons plutonium

The Bulletin, By Cameron Tracy | January 13, 2025

The United States has a plutonium problem. This heavy metal, rarely found in nature but produced by nuclear reactors, is a primary ingredient of nuclear weaponry. A modern thermonuclear weapon, containing just a few kilograms of this material, could level much of a metropolitan area. During the Cold War, the United States and the Soviet Union produced enough plutonium to make tens of thousands of nuclear weapons (IPFM 2015). Both the United States and Russia, which inherited the Soviet nuclear weapons enterprise, have since declared large portions of their stockpiles to be excess: unnecessary for purposes of national defense. But after decades of effort and billions of dollars spent trying to dispose of this material, their weapons plutonium stockpiles remain undiminished (von Hippel and Takubo 2020).

The United States currently plans to bury about one third of this stockpile in the Waste Isolation Pilot Plant (WIPP), a geologic repository mined 650 meters below the surface of southeastern New Mexico’s Delaware Basin (NASEM 2020). Preparation to dispose of this material is well underway, but key questions about this approach remain unresolved. Will the repository safely contain this radiotoxic material over the thousands of years for which it presents a threat to the environment? Can the repository be effectively secured against attempts to illicitly recover weaponizable material? Can all of this be accomplished on a realistic schedule and budget?

……  Given sufficient effort, funding, and good fortune, the United States may arrive at a workable solution to its plutonium problem. But until questions of safety, security, and cost are addressed, and the associated risks are weighed, agreement on just what it means for a geological plutonium repository to “work” is likely to remain out of reach.

…………………………………. Recognizing these risks, the US National Academy of Science and its Russian counterpart met in 1992 to discuss the issue (NASEM 1994). This agenda eventually rose to the highest levels of government, serving as a centerpiece of discussion between Presidents Bill Clinton and Boris Yeltsin over the next few years. By 2000, the United States and Russia had negotiated and signed the Plutonium Management and Disposition Agreement (PMDA), pledging to reciprocally dispose of 34 metric tons of excess weapons plutonium..

……………………………………………………… both sides agreed to a primary disposal method that was complex and difficult, but jointly seen as effective: conversion of weapons plutonium to nuclear fuel and irradiation in nuclear power plants.

Despite this diplomatic achievement, progress on bilateral plutonium stockpile reduction was short-lived. Construction began on the US facility that would convert this material to nuclear fuel in 2007, but in less than a decade, cost estimates grew from initial projections of a few billion dollars to over one-hundred billion (Hart et al. 2015). In 2016, the Obama administration unilaterally pivoted from the irradiation approach mandated by the plutonium disposal agreement with Russia to a new plan: burial in WIPP. 

Russia balked at this shift. In an April 2016 speech in St. Petersburg, Russia’s president, Vladimir Putin, accused the United States of seeking to “preserve what is known as the breakout potential,” disposing of plutonium in name only while ensuring that it could be “retrieved, reprocessed, and converted into weapons-grade plutonium again.” Citing this, alongside a broad array of other grievances related to steadily worsening US-Russian relations amid the Russo-Ukrainian War, Russia suspended its commitment to the bilateral plutonium disposal agreement later that year.

A new mission for WIPP (Waste Isolation Pilot Project)

WIPP is mined into the underground salt formations………………. Congress established the facility as a pilot project, a “research and development facility to demonstrate the safe disposal of radioactive wastes resulting from the defense activities and programs” (US Congress 1979). WIPP was originally designed to store wastes made up of clothing, gloves, lab equipment, and other detritus contaminated with heavy, radioactive elements like plutonium, which was sitting at nuclear weapons production sites scattered across the United States. Following decades of site characterization, repository design, and construction—alongside $2.5 billion in funding—WIPP accepted its first shipment of this material in 1999 (Feder 1999).

WIPP’s mission now extends far beyond its original role as a demonstration project. As the sole US site for the disposal of actinide wastes (referring to the class of heavy, radioactive elements including uranium and plutonium), it is now slated as the permanent disposal site for the 34 metric tons of excess weapons plutonium covered by the now defunct US-Russia plutonium disposal agreement. 

This is a major shift from WIPP’s original design basis, and has introduced new sociotechnical challenges to the safe, secure, and effective operation of the repository—and, therefore, to the plutonium stockpile reduction mission to which it is now intimately tied. What started as a pilot program to aid in the clean-up of contaminated Cold War weapons production facilities is now both a potential solution to the long-standing problem of excess weapons plutonium disposal, and a potential threat to both the environment and to global nuclear security. Whether this one-of-a-kind experiment on the long-term safety, security, and risk of the geologic disposal of nuclear materials is ultimately judged a success or failure will depend on its ability to meet several complex challenges.

Challenge 1: Isolating radioactive material from the biosphere

WIPP’s central role is to isolate potentially dangerous materials deep underground, preventing the leakage of radioactive material to the surface or to groundwater flows. Designed to store about 12 metric tons of plutonium, it is now slated to contain nearly four times that inventory (Tracy, Dustin, and Ewing 2016). Of course, more radioactive material means greater potential for its release.

To forecast the risk of release, every five years the US Department of Energy, which operates WIPP, performs a repository performance assessment and submits the results to the US Environmental Protection Agency (EPA 2022)……………………. However, predicting the future is challenging, even when legally mandated.

Consider, for instance, one of the key repository failure modes: borehole intrusion………………………..  Drilling in the region was virtually nonexistent prior to 1960 and rose exponentially following a boom in the early 1990s………………………………………………………………… When considering the behavior of magnesium oxide in the complex geochemical environment of a repository pierced by a borehole and infiltrated by groundwater, this should be taken as a cautionary tale.

None of this is to say that WIPP cannot operate safely. However, its ability to do so with the current plutonium inventory is uncertain, as uncertainties in long-term local drilling rates and repository chemistry demonstrate. A fourfold increase in WIPP’s plutonium inventory will only add to this safety challenge.

Challenge 2: Ensuring that buried plutonium remains buried

…………………………………………………………The use of two alternative techniques that were overlooked in the prior literature, salt solution mining and in situ leaching, would allow rapid access to buried plutonium with minimal excavation (Tracy and Ewing 2022). 

……………………Applied to WIPP, these techniques could provide access to large quantities of weapons plutonium via only a single borehole just tens of centimeters in diameter (Tracy and Ewing 2022). Plutonium might then be extracted in a matter of days. Afterwards, plastic flow of salt would seal the borehole, removing evidence of the clandestine extraction.

……. the risks of recovery have been insufficiently studied, and WIPP’s design does little to mitigate these risks. Thus, confidence in the security of weapons plutonium disposed of in WIPP is unwarranted. Most worryingly, much of the work on this issue has sought merely to dismiss the risk of plutonium recovery, rather than to establish a design basis for mitigating that risk.

Challenge 3: Managing a complex and costly disposal program

Even if solutions were found for the safety and security challenges detailed above, there would still remain the monumental challenge of implementing those solutions alongside the unprecedented task of burying 34 metric tons of weapons plutonium over half-a-kilometer below ground.  Two of the most serious obstacles to successful disposal are the cost and time required………

………………These challenges are uniquely substantive for the Department of Energy. Analysis of past projects of similar scope overseen by the part of this agency that manages the weapons plutonium stockpile shows that many were cancelled before completion and that “of the few major projects that were successfully completed, all experienced substantial cost growth and schedule slippage” (IDA 2019). The Government Accountability Office, a congressional organization that audits and evaluates US government agency performance, regularly cites management and budgetary failings in the Department of Energy’s plutonium stockpile programs (GAO 2017).

Working towards a repository that “works”

…………………… For technologies like geologic plutonium repositories, problems of risk come to the forefront: What level of risk is expected, what level is acceptable, and even how risk should be measured. Plutonium disposal presents a means of reducing global nuclear risk by shrinking stockpiles of weapons material—a yet unrealized dream of the post-Cold War world. At the same time, burial of this material at WIPP presents new risks of radioactive contamination of the environment, lower barriers to the production of nuclear weapons, and unsustainable cost overruns.

……………the risk to WIPP posed by ongoing mission creep. ……The imposition of a dramatically expanded plutonium inventory and a fundamentally different mission, however, introduces new threats to WIPP’s continuing success [as a pilot research project]   https://thebulletin.org/premium/2025-01/risks-of-geologic-disposal-of-weapons-plutonium/?utm_source=ActiveCampaign&utm_medium=email&utm_content=US%20Nuclear%20Notebook%20Update&utm_campaign=20250116%20Thursday%20Newsletter
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January 19, 2025 - Posted by Christina Macpherson | Uncategorized