Powerful proton linacs are being studied at Los Alamos as drivers for high-flux neutron sources that can transmute long-lived fission products and actinides in defense nuclear waste, and also as drivers of advanced fission-energy systems that could generate electric power with no long-term waste legacy. A transmuter fed by an 800-McV, 140-mA cw conventional copper linac could destroy the accumulated 99Tc and 129I at the DOE's Hanford site within 30 years. A high-efficiency 1200-McV, 140-mA niobium superconducting linac could drive an energy-producing system generating 1-GWc electric power. Preliminary design concepts for these different high-power linacs are discussed, along with the principal technical issues and the status of the technology base.