Smarter Approach to Nuclear Expenditures Act This bill prohibits the obligation or expenditure of Department of Defense (DOD) funds: (1) for procuring more than eight Columbia-class submarines; (2) to maintain more than 150 deployed intercontinental ballistic missiles; or (3) through FY2024, for the research, development, test, and evaluation (RDT&E) or the procurement of the B-21 long-range penetrating bomber aircraft. The bill prohibits the obligation or expenditure of DOD or Department of Energy (DOE) funds: to maintain more than 1,000 deployed strategic warheads, as counted under the New START Treaty; to make the F-35 Joint Strike Fighter aircraft capable of carrying nuclear weapons; for extending the life of tactical versions of the B61 gravity bomb; for the RDT&E or procurement of a new air-launched cruise missile or for the W80 warhead life extension program; for the RDT&E or procurement of the ground-based strategic deterrent or any new intercontinental ballistic missile; for the IW-1 life extension program; for the Mixed Oxide Fuel Fabrication Facility project at the Savannah River Site, Aiken, South Carolina; or for the Uranium Processing Facility located at the Y-12 National Security Complex, Oak Ridge, Tennessee. DOD and DOE must report to Congress on the plans for, and the estimated cost savings from, carrying out this bill.