Year
1994
Abstract
As part of the tank calibration process, the instrument heel of the tank must be determined. The instrument heel is that part of the tank that cannot be measured by the liquid level instrumentation. If the tank being calibrated is not a bottom drain tank, some volume of fluid will be present in the bottom of the tank after draining as much as possible. The amount of fluid remaining in the tank at the start of each run can be estimated by measuring a concentration change of an added spiking material. With the great improvement of liquid level measuring instruments, the total error associated with the instrument heel determination can be greatly affected by the laboratory method used to measure the concentration difference. At the Savannah River Site, the laboratory method used has historically been Direct Current Plasma Emission Spectroscopy, which yielded very marginal results at best. In the most recent tank calibrations, the laboratory method was changed to Absorption Spectrophotometry, which reduces the total error on the instrument heel measurement by a factor of 2.5 times. This paper describes the method used to determine tank instrument heels and the improvements made to this process.