How the United States Plans to Dispose of its Surplus Weapons-Grade Plutonium

Based on a National Academies April 2020 Report

The federal government is developing plans to dilute and dispose of the majority of its weapons-grade surplus plutonium inventory in the United States’ only nuclear waste repository, changing the characteristics of the waste the facility was built for. Congress asked the National Academies to evaluate these conceptual plans, as they are in the early stages of development. Explore how we got here, what the new plan entails, and our expert recommendations below.


I want to ensure that high level or weapons material wastes can never be simply diluted in order to comply with criteria for WIPP disposal.

Senator Pete Domenici’s 2002 letter to DOE Secretary Abraham

Currently, the United States has more than 60 metric tons (MT) of weapons-grade surplus plutonium. Rather than use the surplus for weapons, the United States is developing long-term plans for its safe and secure disposition.

For the past two decades, the Department of Energy’s National Nuclear Security Administration (DOE-NNSA) has moved forward with a plan to use the surplus plutonium to make MOX (mixed oxide) fuel, which would be used to generate electricity by nuclear power plants. Once used to generate electricity, the MOX fuel becomes highly radioactive and the plutonium can no longer be easily recovered and reused to make nuclear weapons. In a historic move toward nuclear non-proliferation, Russia and the United States signed an agreement to use at least 34 MT of their respective declared surplus plutonium inventories to make MOX fuel for use in power reactors. But after the U.S. program to develop MOX fuel ran far over-budget and over-schedule, the DOE-NNSA decided to explore an alternative “dilute and dispose” plan.

The DOE-NNSA plans to dilute more than half of the U.S. surplus plutonium and place it in an underground nuclear waste repository in New Mexico called the Waste Isolation Pilot Plant (WIPP). Construction of the WIPP began more than three decades ago to serve as a place for disposing of contaminated clothing and equipment from the nuclear weapons making process and early exploration of nuclear energy – known as defense transuranic waste. Putting this much concentrated plutonium waste in the WIPP is not what the citizens of New Mexico or their governor agreed to when the facility was built. Also, diluted surplus plutonium emplaced underground can be recovered and used to make nuclear weapons. While less expensive than operating the MOX Plant, the dilute and dispose plan will take 30 years and cost at least $18 billion.

TIMELINE 1993-2020 view detailed timeline here
  1. President Bill Clinton announces the U.S. will seek to eliminate its weapons-grade plutonium stockpile.
  2. Officials announce they will turn surplus plutonium into mixed oxide (MOX) fuel, which can be used to generate electricity.
  3. The U.S. and Russia sign The Plutonium Management and Disposition Agreement (PMDA), both agreeing to disposition no less than 34 metric tons.
  4. Construction of the MOX plant begins in South Carolina.
  5. The U.S. and Russia amend the PMDA, both agreeing to use MOX fuel in commerical reactors to generate electricity.
  6. The MOX plant construction faces cost overruns and scheduling delays.
  7. Russian officials announce that they suspend the PMDA.
    The DOE issues a record of decision to dilute and dispose 6 metric tons of surplus plutonium (an amount separate from the 34 metric tons)
  8. The MOX plant construction is canceled. The National Academies releases an interim report evaluating an alternative plan—to dilute and dispose the 34 metric tons.
  9. The National Academies completes a congressionally mandated evaluation of the alternative plan.

The Plan

How Surplus Plutonium Travels 3,300 miles Through the United States

  • STEP 1
    Surplus plutonium is stored in multiple U.S. locations. The majority is in the Pantex Facility near Amarillo, Texas.

  • STEP2
    The plutonium is transported to Los Alamos National Laboratory in New Mexico where it is oxidized.

  • STEP3
    The oxidized plutonium is transported to the Savannah River Site in South Carolina where it is diluted to meet WIPP’s acceptance criteria.

  • STEP4
    The diluted plutonium oxide is transported in specialized packages via trucks to the WIPP near Carlsbad, New Mexico. View Image. It is then unloaded and emplaced underground.

The U.S. Surplus Plutonium Inventory Breakdown

While the DOE-NNSA’s plan is focused on diluting and disposing of 34 MT, up to 48.2MT – 78 percent of the U.S. surplus plutonium inventory – could end up in the WIPP.

The Three Main Challenges

Physical Space and Statutory Capacity Limits

bar graph

[click to enlarge]

accent img175,564 m3

The amount of waste that can be emplaced in WIPP is limited both by the physical space currently available in the facility and by the Land Withdrawal Act, which caps the total amount of waste that can be in the WIPP at 175,564 cubic meters.

The addition of the diluted surplus plutonium in question would require building additional underground storage wings. A recent decision to change how waste volume is measured may help DOE to stay within the limits of the Land Withdrawal Act.

Before this change, the DOE measured the outer volume of all waste containers. After a permit modification was approved by New Mexico officials, the DOE now reports volume by inner containers – in instances where one is present. For instance, rather than counting the volume of the 55-gallon drum waste container (0.21 cubic meters), the DOE now reports only the volume of the pipe within the drum that contains the diluted plutonium (0.013 cubic meters) – a reduction of a factor of ~15. This is why there is a large size reduction in the red striped boxes in the figure. Our experts recommend that DOE reserve space in WIPP for the diluted surplus plutonium waste, since these graphs show that WIPP is likely to reach its maximum capacity even with the recalculation of volumes.

Extended Timeframe and Aging Infrastructure

accent img

The WIPP became operations in 1999 and was originally planned to close in 2034. The final shipment for the new dilute and dispose plan is scheduled for 2049; but according to an independent evaluation from the Army Corps of Engineers, the end date is more likely to be 2056 at the earliest.

accent img
160,660 Containers

In total, the diluted surplus plutonium will take up approximately 160,660 waste containers (55 gallon drums) – more than has been emplaced in WIPP since 1999. Each shipment to WIPP carries up to 42 of these containers. For this new plan to work, 3,825 shipments from SRS – about four per week – would need to be made to the WIPP, more than double the current shipment rate.

accent img
65 years

The extended timeframe also affects the South Carolina facility in which the dilution and packaging takes place. The facility is currently 65 years old and in “poor condition,” according to the DOE. Assuming an on-time completion in 2049, the facility will be close to a century old.

Diluted Surplus Plutonium’s Chemical and Radiological Impact

By virtually any measure, the dilute and dispose plan substantially changes the physical, radiological, and chemical composition of emplaced wastes at the WIPP as well as the “social contract” for WIPP and the State of New Mexico. No previous waste stream headed to the WIPP has affected the facility’s technical measures at this high of a level. While the initial analyses indicate that the WIPP repository will maintain regulatory compliance with the increased amount of plutonium in its inventory, such a substantive change raises technical, social, and political questions that, if unaddressed, could translate to system vulnerabilities.


What will help this new plan succeed?

DOE-NNSA’s early-stage dilute and dispose plans are technically viable and cheaper than the mixed oxide (MOX) fuel plan, provided that current implementation challenges and system vulnerabilities are resolved. Our committee made several recommendations that can be implemented by the DOE and policymakers and demanded by citizens from their government.

  1. The DOE should treat the statutory capacity of the WIPP as a valuable and limited resource. Also, if the U.S. government decides to pursue the dilute and dispose approach for the majority of its surplus plutonium inventory, it should reserve future capacity in WIPP.
  2. The DOE should reinstate the Environmental Evaluation Group to represent the concerns of New Mexico citizens.
  3. The State of New Mexico, the EPA, and the DOE should develop an agreed-upon strategy to vet the impacts of the full amount of proposed surplus plutonium to be diluted and disposed of in WIPP, rather than an incremental or piecemeal approach of reviewing smaller amounts.
  1. The DOE Office of Security’s Materials Risk Review Committee should periodically reevaluate the WIPP’s security assessment .
  2. The DOE should work collaboratively with all states on the transport route to ensure the safety of the shipments. For instance, states must enforce their respective highway laws on transport vehicles while the DOE will be responsible for maintaining permits, monitoring shipments on route, and giving states advanced notice about shipments.

*Security details are still under development and not available for review.

  1. Independent technical experts should conduct periodic reviews for Congress and the DOE. This project has a long timeframe and should be consistently re-evaluated as it matures.
  2. The DOE should expand on the Risk and Opportunity Analysis Report – which currently focuses on cost and schedule-related risks – to include an examination of ecological health, human exposure, and nuclear safety risks.
  3. The DOE should conduct a comprehensive Programmatic Environmental Impact Assessment to better understand the potential environmental effects of scaling up the inventory and timeframe across the full DOE laboratory complex.
  1. The DOE should maintain a sustained hiring effort and plan for the associated workforce costs. A project of this scale requires a large, trained workforce familiar with complex plutonium dilution processes and the many safety standards that apply to handling radioactive and hazardous materials.
  2. The DOE should seek out and utilize automated labor-saving technology wherever possible, in order to avoid human radiation exposure.
  1. While not required for the dilute and dispose plan to move forward, the Plutonium Management and Disposition Agreement (PMDA) signals a commitment to achieving success by the agreed upon methods for disposition. A renegotiated PMDA could improve the chances of successful completion of DOE’s dilute and dispose program.
  2. The DOE should affirm its intent to adhere to material inspections from the International Atomic Energy Agency (IAEA) at the WIPP prior to the start of disposal of surplus plutonium. The IAEA has yet to develop monitoring protocols for emplaced materials, but working with the IAEA is important in demonstrating a commitment to non-proliferation.