Advances in simulation and computing capabilities, aided by investments in the science-based Stockpile Stewardship Program (SSP), provide confidence in the ability to model and evaluate the performance and safety of nuclear weapons without nuclear explosive testing.

Since the end of U.S. nuclear explosive testing in 1992, investments in science-based Stockpile Stewardship have led to dramatic improvements in simulation capabilities. Computers have become at least a hundred-thousand times more powerful, and modern integrated design codes now more realistically capture the behavior of real nuclear devices. As of December 2012, the National Nuclear Security Administration (NNSA) has the world’s fastest supercomputer used for nuclear weapons simulations and modeling. The supercomputer, named Sequoia, is also the second fastest supercomputer in the world overall. As a result of these advancements, our modern, integrated nuclear weapon design codes have reduced a number of adjustment parameters, which previously required a nuclear explosive test to be calibrated. Weapons designers can now conduct hundreds of calculations to determine where the results are most sensitive to model uncertainties or fundamental data. This is a critical element to inform expert judgment and guide SSP experiments.

Today, weapons designers benefit from better simulation tools and computers capable of running highly detailed calculations. Successes to date indicate that a cadre of world-class scientists and engineers can employ physics-based simulations, modern experiments, validations against collections of re-analyzed data from previous underground nuclear explosive tests, and peer reviews to support stockpile decisions well into the future without the need to return to nuclear explosive testing. These computer simulation advances provide the United States with the ability to monitor and maintain the nuclear weapons stockpile without nuclear explosive testing.