This paper describes the evolution of an ultrasonic sensor to non-invasively measure slurry density and solids concentration. Three generations of probe are discussed: 1) density sensor, 2) densimeter, and 3) fluid and solids monitor. The initial application was to measure slurry density during radioactive waste transport. The probe uses ultrasonic signal reflection at the fluid-pipe wall interface to quantify density in situ in real time and signal attenuation to evaluate solid concentration. In the latest configuration, the transducers are mounted on the wall of the pipe spool piece. This instrument was selected for monitoring radioactive waste transport based on several characteristic features: the sensing surface is non-intrusive and does not disrupt the slurry flow, instrument performance is not affected by slight amounts of entrained air that could be present during waste retrieval and transfer; nor is it affected by electromagnetic noise from nearby pumps and other equipment; and the instrument is compact. The densimeter has been deployed at Hanford tank SY-101 in the prefabricated pump pit process manifold to monitor slurry properties during radioactive waste transfers. To qualify densimeter performance prior to manifold installation in the radioactive pipeline, the probe was installed in the process manifold and performance was evaluated during tests using non-radioactive waste simulants over the density range from 1000 to 1500 kg/m3. The probe predicted density within ± 2%. The sensor is installed in a nominal 5-cm-diameter (2-in.) pipe spool piece; the design pressure is 2.8 MPa (400 psi). To ensure operability during prolonged contact with radioactive waste, the probe wedge in contact with the slurry was selected to operate up to pH 14, and the probe components were radiation tested at exposures of 1×106 R.

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