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Firing Tank Operator Drew Carlson (foreground) safeguards the mouth of the 10kg spherical firing tank at LLNL’s High Explosives Applications Facility as Electronic Technician Raya Yy (background, left) and Ramrod Shawn Strickland wire a high explosive charge for an experiment. The experiment will provide data important to certifying that a refurbished nuclear warhead will work without conducting a full-scale explosive nuclear test. (Photo: Julie Russell/LLNL)

The program to extend the life of the W80 nuclear warhead recently achieved a significant milestone when the National Nuclear Security Administration (NNSA) gave passing grades to the plans to refurbish certain components and the proposed approach to developing component cost estimates. Passing the milestone confirms that the life extension program (LEP), dubbed the W80-4 LEP, remains on track. The refurbished warhead will be paired with a new cruise missile that is being developed in parallel by the U.S. Air Force, making this the first life extended warhead to be implemented in a new delivery system since the start of the Stockpile Stewardship Program more than 25 years ago.

Lawrence Livermore National Laboratory (LLNL) is the lead nuclear design agency, partnered with Sandia National Laboratories, which is the lead non-nuclear design agency. The work being carried out is driven by military requirements to pair the warhead with the new delivery system and improve weapon safety, security and operational logistics and maintain effectiveness without the need for additional explosive nuclear tests. First production of the W80-4 is planned for 2025.

The W80-4 design concepts have been matured, and the organizations involved are focused on developing the details involved in producing the W80-4 and certifying that it meets requirements. With the work scope and component cost approach now accepted, the next milestone in this effort will be a detailed weapon development cost report.

LLNL has implemented the project management team needed to meet the scheduling, coordination and integration associated with such a complex project. Significant attention is also being given to assure the design will meet military requirements. The choice of materials to be used in the LEP is just one of the key areas. Some aged materials and components that need replacement cannot be produced exactly as they were originally manufactured. For instance, the main explosive charge needs replacement, but the original high-explosive constituents are not available and therefore must be reconstituted. In addition to refurbishing the warhead itself, considerable attention must be paid to ensuring that it integrates with a brand-new delivery system and can be certified to be safe (won’t go off by accident), secure (can’t be set off without formal permissions) and effective (will work as designed) without ever conducting a full-scale explosive nuclear test of the system.

In the absence of nuclear testing, researchers use non-nuclear experiments and supercomputers as their virtual test ground. Anyone who has ever made a mistake punching numbers into a calculator knows that the answer is only as good as the numbers that go into the calculation. To verify that the supercomputer simulations reflect reality, and to understand the limitations of these calculations, researchers are validating the computer codes with data from legacy nuclear tests and smaller-scale, modern experiments. Together, these experiments and simulations help make sure the judgments made by the W80-4 team are sound.

The next-generation supercomputer, Sierra, with a peak speed of 125-petaFLOPs (floating point operations per second), is sited at Livermore and will play a central role in certifying the replacement warhead. In addition to the new hardware, code advances have enabled a shift from 2D to 3D modeling, with a special focus on uncertainty quantification. These advances alleviate the need to rely on approximations that were required during the nuclear test era.

Hundreds of tests and experiments are underway at LLNL and Site 300, its experimental test site, to verify that the design options will perform as expected. These experiments helped down-select these design options developed during the earlier “paper study” phase of the LEP (phase 6.1) and will continue to play a role to provide confidence that the final design and associated components and materials will function as required.

“This LEP is driving significant innovation at LLNL,” said Des Pilkington, Weapon Physics and Design program director. “I’m seeing some really creative work in the options, focused on meeting established performance requirements and to minimize costs, always with an eye to what we can ultimately certify will work. That’s where the experimental and code innovations we’ve made under the Stockpile Stewardship Program come into play. They will be critical to the success of our certification plan.”

One area of design innovation is the use of additive manufacturing – commonly referred to as 3D printing – to improve the quality of replacement parts and reduce the cost of production. Researchers are engineering specific material properties into these 3D-printed replacement parts by controlling the microstructure of the printed material. To verify the 3D-printed parts would perform as expected, researchers executed a pair of innovative hydrodynamic (full-scale non-nuclear) experiments in 2016. The data those experiments returned are used to ensure supercomputer simulations accurately represent reality. In addition, extensive material-aging and compatibility experiments are underway to ensure the additively manufactured material will meet performance requirements for the system lifetime.

To date, five of the 25 major milestones in the LEP are complete. A mature set of requirements are being refined by the DoD and NNSA, design concepts have been developed, business systems are being put in place to track schedule and budget, and NNSA has made significant investments in the infrastructure at LLNL that will be needed to certify the warhead. LLNL also is leading the effort to reconstitute the capability to manufacture the required insensitive high explosives. Manufacturing of production-scale quantities of the new explosives is underway and on schedule.

The W80-4 program anticipates entering into the development engineering phase (phase 6.3) in 2019, when researchers will test individual components to ensure they will meet military requirements. The next phases in the effort are production engineering (phase 6.4), first production (phase 6.5) and full-scale production (phase 6.6).

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