WEB1 day ago · Proton Power Upgrade reaches turning point, heads for finish line. May 7, 2024. Spallation Neutron Source, Accelerator Tunnel Extension Construction, 2023-2024. Watch on. For the past several months, the most visible component of the Proton Power Upgrade, or PPU, project for the Spallation Neutron Source, or SNS, at Oak Ridge National ...