LANL ASC Science Underpins Stockpile Modernization
Before the end of underground nuclear weapons testing, our nation relied on theory, experiment (testing), and simulation to engineer our nuclear weapons and to understand their performance. In the absence of nuclear weapons testing, we are taking even greater advantage of high-performance computing (HPC) and simulation science to ensure the safety and reliability of the stockpile. An illustrative case study of this is the B61 Life Extension Program (LEP). The National Nuclear Safety Administration (NNSA) recently received approval from the Nuclear Weapons Council to proceed with Phase 6.3 of the B61 LEP.
Los Alamos National Laboratory (LANL) — an NNSA national security laboratory —supports three other weapon systems in the nation's nuclear deterrent — W88, W76, and W78. All work on the weapon systems, including the B61, requires a mix of simulations based on tools provided by the Advanced Simulation & Computing (ASC) Program, experiments carried out by the Science Campaigns, and underground test analysis by Directed Stockpile Work. LANL has begun execution of the B61 LEP.
As the starting point for any work on the B61 LEP, B61 modern system baselines using modern baselining tools will be used for the physics and performance assessments and to certify the B61-12. A system baseline is a collection of models of relevant nuclear tests and aboveground hydrodynamic tests. The system baseline represents our best framework for ensuring confidence in our scientific judgments concerning weapons performance, and ensures consistency and change control as improvements are introduced over time. Using system baselines has shed light on the underlying physics of new insights as well as longstanding mysteries that had persisted since the time of underground tests.
The B61 baselines are being transitioned to ASC simulations. For example, numerous simulations were run in order to develop and understand multipoint safety options. All theoretical work on the B61, as well as the other weapon systems, relies on the capabilities provided by ASC. Capabilities include
- Weapon, diagnostics, and safety computer codes
- Fundamental data for equations of state, opacities, and nuclear cross sections
- Material models and parameters for strength, damage, high explosives, and mix
- Setup tools, including the common model framework
The ASC Program provides the infrastructure for applying the capabilities, such as hardware, software, and visualization tools. It provides verification and validation for all of the capabilities. ASC provides capacity supercomputers to run the smaller simulations and capability supercomputers to run the largest simulations. Software environments and computing facilities are provided for the capacity and capability supercomputers.
Each year the LANL Director performs an annual assessment, which reaffirms the integrity of the weapons' certification to the President. In this way, the nuclear stockpile remains safe, secure, and reliable without the need to carry out underground testing.