THE DEPARTMENT OF ENERGY’S (DOE), NATIONAL NUCLEAR SECURITY ADMINISTRATION’S (NNSA) OFFICE OF DEFENSE PROGRAMS, DIRECTS RESEARCH AND DEVELOPMENT ACTIVITIES TO MAINTAIN THE SAFETY, SECURITY, AND EFFECTIVENESS OF THE NATION’S NUCLEAR WEAPONS STOCKPILE. THIS NUCLEAR DETERRENT REMAINS A VITAL PART OF OUR NATIONAL SECURITY INFRASTRUCTURE. IT MAINTAINS STRATEGIC STABILITY, DETERS POTENTIAL ADVERSARIES, AND REASSURES OUR ALLIES AND PARTNERS OF OUR SECURITY COMMITMENTS. SINCE 1992, THE UNITED STATES HAS OBSERVED THE MORATORIUM ON UNDERGROUND NUCLEAR TESTING WHILE SIGNIFICANTLY DECREASING THE SIZE OF ITS NUCLEAR ARSENAL. NATIONAL POLICY REQUIRED NNSA AND ITS WEAPONS LABORATORIES TO INSTITUTE THE SCIENCE-BASED STOCKPILE STEWARDSHIP PROGRAM (SSP) TO ENSURE THE SAFETY, SECURITY, AND EFFECTIVENESS OF THE STOCKPILE, WHILE ALLOWING THE COUNTRY TO PURSUE A VARIETY OF NONPROLIFERATION AND DISARMAMENT GOALS. THE SSP COMBINES SOPHISTICATED EXPERIMENTS, HIGHLY ACCURATE PHYSICS MODELING, AND IMPROVED COMPUTATIONAL POWER TO SIMULATE AND PREDICT NUCLEAR WEAPON PERFORMANCE OVER A WIDE RANGE OF CONDITIONS AND SCENARIOS.