National Nuclear Security Administration: Information on the Fiscal Year 2021 Budget Request and Affordability of Nuclear Modernization Activities [open pdf - 557KB]
From the Document: "The United States is in the midst of a long-term effort to modernize its nuclear security enterprise. As part of this effort, the Department of Energy's (DOE) National Nuclear Security Administration (NNSA) is currently conducting four weapon modernization programs. NNSA manages its weapon modernization programs in coordination with the Department of Defense (DOD), which undertakes related work to modernize nuclear weapon delivery systems, including heavy bombers, intercontinental ballistic missiles, and submarine-launched ballistic missiles and the submarines that carry them. In addition, NNSA is managing numerous, multi-billion-dollar construction projects and related activities to modernize the infrastructure it uses to produce the components and materials needed for its weapon modernization programs."
Government Accountability Office: http://www.gao.gov/