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Nuclear Weapons: Program Management Improvements Would Benefit U.S. Efforts to Build New Experimental Capabilities

GAO-23-105714 Published: Aug 30, 2023. Publicly Released: Aug 30, 2023.
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Fast Facts

The National Nuclear Security Administration must regularly assess the nation's nuclear weapon stockpile—without nuclear explosive testing.

However, the data that NNSA uses to model the stockpile's safety and more needs to be updated. To do so, the agency performs plutonium experiments in a facility about 1,000 feet underground. It plans to upgrade infrastructure and build 2 new tools to get more data from these experiments. NNSA's risk management was less rigorous for one of the projects, resulting in cost increases and schedule delays.

We recommended that NNSA address the management issues that led to the increases and delays.

Illustration of a nuclear atom

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What GAO Found

The National Nuclear Security Administration's (NNSA) objective for the Enhanced Capabilities for Subcritical Experiments (ECSE) program is to improve NNSA's ability to assess the performance, safety, and reliability of nuclear weapons without nuclear explosive testing. To do so, NNSA plans to make new measurements of plutonium during subcritical experiments by building

  • an instrument named Scorpius to produce a series of x-ray images of the plutonium and
  • an instrument named Zeus to measure the rate of the nuclear chain reaction.

As of March 2023, NNSA estimated that constructing both instruments and related infrastructure upgrades in the U1a facility will cost about $2.5 billion to $2.6 billion. NNSA requires both instruments by 2030 to inform plans for modernizing the nuclear weapons stockpile.

Images of a Subcritical Experiment Vessel and the U1a Underground Experimental Facility

Images of a Subcritical Experiment Vessel and the U1a Underground Experimental Facility

NNSA has identified risks to the ECSE program and has appropriately managed risks to build Scorpius. Specifically, NNSA identified risks to the ECSE program in four categories: integration of efforts, safety, economic conditions, and technology development. GAO found that NNSA applied appropriate processes to manage these risks for Scorpius and associated infrastructure, such as using a technical change control board to integrate the efforts to design and build Scorpius and the associated infrastructure upgrades.

NNSA used less rigorous processes to manage risks for Zeus and its associated infrastructure, resulting in a 2-year delay and increased cost. Specifically, the lack of processes to integrate the instrument and infrastructure, such as a technical change control review board, resulted in the need for additional mining at U1a to accommodate instrument design changes. While NNSA used less rigorous management processes typical of research and development programs, such as Zeus, NNSA's program management requirements provide flexibility to use additional processes to appropriately address risks. As of May 2023, NNSA began implementing more rigorous processes to manage Zeus' infrastructure, but NNSA has not yet adopted more rigorous processes to manage risks for the Zeus instrument, in particular related to technology development and integration. By implementing additional risk management processes, NNSA may prevent further delays to Zeus and the associated infrastructure and ensure that it obtains necessary data for stockpile modernization.

Why GAO Did This Study

NNSA is responsible for ensuring the performance, safety, and reliability of the nation's nuclear stockpile without nuclear explosive testing. Subcritical experiments are used to support NNSA's assessments. NNSA conducts these experiments at the U1a underground facility at the Nevada National Security Site. This allows NNSA to obtain experimental data on plutonium and high explosives together without a nuclear explosion—hence, the experiments remain subcritical.

In 2014, NNSA identified the need for new data from these experiments and established the ECSE program to provide such data.

House Report 117-118, accompanying a bill for the National Defense Authorization Act for Fiscal Year 2022, included a provision for GAO to review the ECSE program. GAO's report (1) describes the objective of the program and (2) examines the risks that NNSA has identified to completing the program and the extent to which NNSA has used appropriate program management processes to manage these risks.

To address both objectives, GAO reviewed program documentation, interviewed NNSA and contractor officials, and conducted site visits.


GAO is recommending that NNSA ensure adoption of additional management processes to improve risk management of the Zeus ECSE program elements. NNSA concurred with GAO's recommendation and plans to implement it by September 2025.

Recommendations for Executive Action

Agency Affected Recommendation Status
National Nuclear Security Administration The Assistant Deputy Administrator of the Office of Research, Development, Test, and Evaluation should ensure that program management processes are adopted to appropriately address risks to designing and building the Zeus instrument and constructing the associated U1a infrastructure upgrades. In particular, these processes should include documented risk management plans that define the process for identifying, handling, and monitoring risks, as well as the roles and responsibilities for managing risks; processes to manage risks related to the integration of efforts across the instrument and infrastructure program elements, such as a technical change control board to manage design changes to the Zeus instrument; and processes to independently assess the maturity of new technologies needed for the instrument to meet program goals and timelines. (Recommendation 1)
As of November 2023, we are following up with the agency and will update the response to this recommendation in the future.

Full Report

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Acquisition managementCapital assetsConstructionCost estimatesEconomic conditionsNational securityNew technologiesNuclear securityNuclear weaponsPlutoniumProgram managementRisk assessmentTechnology development