Nuclear weapons are developed, produced, and maintained in the stockpile, and then retired and dismantled. This sequence of events is known as the nuclear weapons life cycle. The Department of Energy (DOE) through the National Nuclear Security Administration (NNSA) and in partnership with Department of Defense (DoD) conducts activities in a joint nuclear weapons life cycle process. The major steps, or phases, of the life cycle are described below. Currently, the United States only utilizes phases 6 and 7 of this process, as no new nuclear weapons designs have been introduced since 1991.
Phase 1 – Concept Study - DOE/NNSA and/or DoD make preliminary assessments of the effectiveness and survivability of a weapon concept and identify delivery system/nuclear warhead trade-offs.
Phase 2 – Program Feasibility Study - The technical feasibility of weapon concepts developed in Phase 1 is determined. Alternatives within the concepts are also developed.
Phase 2A – Design Definition and Cost Study - Once the feasibility study is completed, the Phase 2A study is conducted to refine warhead design definition, program schedule, and cost estimates.
Phase 3 – Full-Scale Engineering Development - The program baseline is established in Phase 3, and additional efforts to test and evaluate the warhead to engineering standards are completed.
Phase 4 – Production Engineering - DOE/NNSA transitions the developmental warhead design into manufacturing processes. The required production line equipment and tools are designed to ensure that all required components can be produced.
Phase 5 – First Production - DOE/NNSA procures raw materials, establishes the production line, starts producing components, evaluates the production processes and products, and makes modifications if necessary. DOE/NNSA conducts tests and evaluations of the warhead components from the production line.
Phase 6  – Quantity Production and Stockpile Maintenance and Evaluation - DOE/NNSA increases the production rate of warheads and components and delivers the completed warheads to DoD for the stockpile. NNSA continues to test and evaluate components as required. Stockpile maintenance is performed. Safety; security; personnel reliability; use control; transportation; supply publications; accountability; inspections; emergency response preparation and exercises; and technical operations training are performed.
Phase 7 - Retirement/Storage - Retirement is the reduction quantity of that warhead-type in the stockpile. This phase initiates a process that continues until all warheads of that type are retired and dismantled. This phase is also organized into three sub-phases: Phase 7A - Weapon Retirement, Phase 7B - Weapon Dismantlement, and Phase 7C - Component and Material Disposal.