A Continuous Photometer for Low Concentrations of Uranium in Aluminum Nitrate-Nitric Acid Solutions

In the recovery of uranium from spent nuclear fuel elements, a waste stream from one solvent extraction cycle may be recycled as scrub solution to the prior cycle of the process. The waste solution may, as a result of this recycle, enter large columns where a critical accumulation of U-235 is prevented by concentration rather than size limitations. A continuous monitor was required to detect changes in uranium content of these recycled streams. Evaluation of the time lags and dilution effects in the sampling system showed that the sample monitored would increase by 2 grams uranium/liter before the situation could become dangerous. An in-line photometer was developed that could detect changes in uranium concentration of about 0.02 grams/liter in the 0-2 gram/liter range; it was set to alarm at a maximum uranium content of 1 gram/liter. The photometer is basically a simple instrument, depending primarily on the use of a photo-voltaic cell to compensate for the logarithmic characteristics of light absorption. The sample stream is analyzed in the wave length region of 425 millimicrons, where uranium absorbs light, and the instrument is standardized in the 525 millimicron region, where uranium does not absorb. A Brown amplifier is utilized to adjust the instrument output to the recorder for the reference cycle to zero, so that the recorded output for the measuring cycle is a linear function of uranium concentration. Fail-safe techniques incorporated account for the bulk of the instrument hardware.