MOISTURE PROBE BASED UPON NEUTRON MODERATION FOR IN-SITU USE IN A CONE PENETROMETER SYSTEM

A moisture probe based upon neutron moderation has been designed, test ed and built for measuring the moisture concentration of hazardous was te stored in the underground waste tanks at the DOE Hanford site. The probe is 1 inch in diameter, 24 inches long, and is deployed using a c omputer controlled winch into a cone penetrometer for in situ moisture measurements. Two thermal neutron detectors in a near-far geometry an d a low-intensity Cf-252 source are used in the probe to count thermal ized neutrons for determining the moisture content. Several testbeds w ere constructed and a variety of experiments were performed to determi ne the optimal detector-source geometry and to test that the sensor is capable of operating in the expected high temperature and very high g amma-ray fields within the tanks. Several calibration curves of the ne ar-far count rate ratio were determined for tanks contaminated with va rious levels of neutron absorbing materials. A field-ready probe and a winch deployment system have been delivered for application of this t echnology to the Hanford Site tank farms.