The Departments of Energy and Defense should better explain their 10-year nuclear deterrent modernization budget estimates and address future affordability concerns, the Government Accountability Office (GAO) said in a newly released report.

The GAO examined the DoD and DoE’s fiscal year 2017 joint report, which places the total cost of the two Cabinet agencies’ nuclear modernization plans at nearly $342 billion through fiscal year 2026. The Pentagon represents roughly $234 billion of that total, while the DOE’s portion accounts for $107.8 billion.

The Energy Department estimated in the joint report that modernization would cost $49.4 billion between fiscal years 2017 and 2021, and $58.4 billion between fiscal years 2022 and 2026; the majority of this would go toward stockpile and infrastructure activities, the GAO noted.

Congressional auditors said DoE’s nuclear modernization cost estimates might exceed its projections in internal funding plans for some major weapons modernization programs, raising affordability concerns – a problem the GAO has identified in other recent reports.

Specifically, low-range cost estimates for the W76-1, B61-12, W80-4, and Interoperable Warhead-1 life-extension programs, as well as the W88 Alteration 370 program, exceeded DoE’s budget estimates for some fiscal years. Potential cost increases in the future could exacerbate that problem, the GAO said.Aerial view of the Pentagon, Arlington, VA

The GAO also said it could not verify that the Defense Department’s nuclear command, control, and communications (NC3) budget estimates were consistent with the department’s internal funding plans, because the DoD “does not describe how it selects program elements, determines its weighted analysis ratios, or differentiates methodologies for some funding streams” for those systems, which will cost $40.5 billion over 10 years.

The report recommended the Defense Department explain its methodology in preparing NC3 system cost estimates to increase transparency in its future budget reporting, which Pentagon agreed to do in future joint reports. The GAO did not make recommendations to the Energy Department, because it has already asked DoE to address these concerns through an affordability assessment for future iterations of the Stockpile Stewardship and Management Plan.