Abstract: A system for monitoring the radioactivity of a liquid waste stream includes a pair of tanks into which the liquid waste stream is directed during alternating fill cycles. At the conclusion of each fill cycle, the liquid waste is recirculated through the chamber of a radioactivity monitor. A pair of opposed radiation detectors, external to the chamber, generate activity measurements to a controller indicative of the radionuclide concentration levels in the liquid waste. The tanks are then emptied either to the environment or back to a decontamination facility for further processing depending on the indicated radionuclide concentration level. System operation, including periodic servicing of the monitor, is automatically coordinated by the controller to avoid interruption of the liquid waste stream filling the tanks.