Accelerator-Driven Subcritical Reactor

An accelerator-driven subcritical reactor, or ADSR, is a nuclear reactor design that couples a substantially subcritical reactor core with a high-energy proton or electron accelerator, allowing it to sustain fission without ever reaching criticality on its own. A particle accelerator fires high-energy protons at a heavy metal target, typically lead, producing neutrons through spallation; those neutrons can convert thorium into fissile uranium-233, which then undergoes fission to generate power. The concept is credited to the Italian physicist and Nobel laureate Carlo Rubbia, a former director of CERN, who published a proposal known as the Rubbiatron based on a proton cyclotron design.