Title page 1

Contents 3

Highlights 2

Letter 7

Background 10

Acquisition Process for NNSA Major Projects 10

NNSA Cost and Schedule Commitments 13

Design and Technology Maturity 15

Nuclear Security Enterprise Sites 16

NNSA Major Projects Reviewed in GAO's Assessment 17

NNSA Major Projects Excluded from GAO's Assessment 19

Recent GAO Work on Selected NNSA Projects 20

NNSA's Portfolio of Major Projects in the Execution Phase Continues to Face Cost Overruns and Schedule Delays 22

Most Projects in Definition Phase Are Implementing Significant Design Changes, and Those with Critical Technologies Have Reached Maturity Milestones 27

Projects Are at Different Stages of Design Maturity, and Most Are Implementing Design Changes or Experiencing Design Challenges 27

Projects in the Definition Phase with Critical Technologies Have Reached Maturity Milestones 32

Agency Comments 32

Appendix I: Individual Project Summaries 34

Appendix II: Objectives, Scope, and Methodology 80

Appendix III: Estimated Costs and Schedules for the National Nuclear Security Administration's Projects Assessed by GAO 83

Appendix IV: Estimated Costs and Schedules for Major Projects in the Initiation Phase 86

Appendix V: Estimated Costs and Schedules for the Major Projects Managed by the Office of Naval Reactors 87

Appendix VI: Design Costs and Schedules for the National Nuclear Security Administration's Projects Assessed by GAO 88

Appendix VII: Technology Readiness Levels 91

Appendix VIII: GAO Contact and Staff Acknowledgments 93

Appendix IX: Additional Source Information for Images and Figures 94

Related GAO Products 95

Tables 4

Table 1. NNSA's 28 Major Projects Assessed by GAO, by Phase and Site, as of June 2025 18

Table 2. Cost and Schedule Performance of 16 NNSA Major Projects in the Execution Phase, as of June 2025 23

Table 3. Design Review Status for NNSA's 12 Major Projects in the Definition Phase, as of June 2025 28

Table 4. NNSA Major Projects in the Definition Phase Implementing Design Changes or Facing Design Challenges, as of June 2025 29

Table 5. Four NNSA Major Projects in the Definition Phase Have Identified Critical Technologies, as of June 2025 32

Table 6. Preliminary Cost and Schedule Estimates for NNSA's 12 Major Projects in the Definition Phase, as of June 2025 83

Table 7. Cost and Schedule Estimates for NNSA's 16 Major Projects in the Execution Phase, as of June 2025 84

Table 8. Initial Cost and Schedule Estimates for NNSA's Nine Major Projects in the Initiation Phase, as of June 2025 86

Table 9. Preliminary Cost and Schedule Estimates for the National Nuclear Security Administration Office of Naval Reactor's Major Projects... 87

Table 10. Cost and Schedule Estimates for the National Nuclear Security Administration Office of Naval Reactor's Major Projects... 87

Table 11. Estimates of Time to Complete Design Activities and Associated Costs for NNSA's 12 Major Projects in the Definition Phase,... 88

Table 12. Time to Complete Design Activities and Associated Costs for NNSA's 16 Major Projects in the Execution Phase, as of June 2025 89

Table 13. Department of Energy Technology Readiness Levels (TRL) 91

Figures 5

Figure 1. GAO Presentation of Acquisition Phases for NNSA Major Projects 12

Figure 2. Sites in the Nuclear Security Enterprise 17

Figure 3. Cumulative Cost and Schedule Overruns for NNSA's Portfolio of Major Projects in Execution Phase, 2023 to 2025 23

Figure 4. Illustration of a Sample Project Summary 35