Key Point: The Stockpile Stewardship Program successfully sustains the nation’s nuclear weapons stockpile in the absence of nuclear explosive testing.

The Stockpile Stewardship Program (SSP) began in the mid-1990s in order to maintain the continued safety, security and reliability of the nation’s nuclear weapons in the absence of nuclear explosive testing. A key goal of the SSP is to increase scientific understanding of nuclear device performance, as well as the aging behavior of weapon materials and components. Today, the Directors of the National Laboratories assess that we understand more now about how nuclear weapons work than during the period of nuclear explosive testing.

The SSP is supported by a wide range of National Nuclear Security Administration (NNSA) activities, including weapon system-specific assessments, Science and Engineering Campaigns, Stockpile Services, and Readiness in Technical Base and Facilities. The NNSA conducts a robust and extensive surveillance program, collecting data from flight tests, laboratory tests, and component evaluations in order to assess stockpile reliability, safety and performance. NNSA also conducts experiments to understand more fully the behavior of materials at extreme conditions relative to nuclear performance; update computer models; and validate predictions against experimental results. The results are used to produce the Annual Assessment Reports and Laboratory Director letters to the President. These programs and activities have enabled the Secretaries of Defense and Energy to report to the President that the stockpile is safe and reliable for more than 15 years.

Examples of recent Stockpile Stewardship accomplishments:

• Produced five W88 war reserve pits.
   
• Executed two tests at the Dual Axis Radiographic Hydrodynamic Test (DARHT) facility exploring surety mechanisms and options for retrofitting the current stockpile.
   
• Compiled a complete catalog of observed failures in historical underground nuclear explosive tests, and the associated first generation explanations of mechanisms, metrics, and thresholds to facilitate resolution of similar issues in the future without nuclear explosive testing.
   
• Based on an analysis of a series of three related underground nuclear explosive tests, proposed a new Quantification of Margins and Uncertainties (QMU) metric for the failure mechanism and proposed a threshold for that metric. Supported the use of this new metric through the analysis of a suite of simulations of a class of devices.
   
• Executed the first National Ignition Facility (NIF) experiments for the Stockpile Stewardship mission.
   
• Lawrence Livermore National Laboratory (LLNL) and Los Alamos National Laboratory (LANL) experts resolved a long-standing discrepancy in simulations of the performance of a weapon’s secondary component, which will provide the basis for future Life Extension Program (LEP) options and improves confidence in stockpile assessments.
   
• Demonstrated high precision techniques to assess the potential impact of aging on radiation hardness during overall system lifetime. A spin-off of the research and development was then established as a surveillance protocol now being conducted on select W76-1 Submarine-Launched Ballistic Missile (SLBM) warhead parts.
   
• Demonstrated the methodology for the estimation of an integrated lifetime of a Nuclear Explosive Package (NEP) component; in this case a lifetime was established for a W88 SLBM warhead primary that advanced the pit lifetime estimates produced in 2006.
   
• Developed or used improved component aging models for canned subassemblies, polymers, high explosives, and initiation systems to support lifetime assessments, and developed the initial framework to incorporate these improved aging signatures into quantitative predictive models for assessing uncertainties to support stockpile maintenance more effectively.
   
• Resolved a major long-standing uncertainty in weapons physics simulation known as the “energy balance” problem at LANL. A broad range of experimental data, from both modern experimental facilities and the legacy underground test database, was used to validate the simulation capabilities of the numerical simulation codes to represent the applicable physics with sufficient fidelity.
   
• Used high resolution 3-D simulations of the B83 strategic bomb at LLNL to conclude that conditions that could be encountered in the stockpile to target sequence resulted in a minimal impact on yield.
   
• Deployed Neutron Generator Testers, which assure neutron generator test capability by modernizing testers as required supporting neutron generator production and shelf-life programs.
   
• Resumed plutonium experiments at the Joint Actinide Shock Physics Experimental Research (JASPER) facility and Z facility.
   
• Completed operational qualification for the first set of NIF ignition diagnostics and installed capabilities to support high yield cryogenic target implosions.
   
• Completed first set of NIF experiments to tune and control the shape, implosion velocity, compressed fuel density, and mix of cryogenic target design.

Many additional, similar examples of accomplishments of the SSP could be listed for past years. In the roughly 15 years since it was established, the SSP has evolved into a robust tool for maintaining high confidence in the safety, security and effectiveness of the U.S. nuclear weapons stockpile without underground nuclear explosive testing.