Proposal of Healthiness Confirmation Procedure in Electro Manometer System in terms of Nuclear Material Accountancy

In general, high precision electro manometer system (ELTM) for density, level and volume measurements of high concentrated plutonium and uranium solution is used for nuclear material accountancy (NMA) in the bulk handling facilities. The ELTM is based on the differential pressure measurement between the dip-tubes which corresponds to solution level and density, and measured level is converted to volume using calibration equation determined at the initial tank calibration. The measurement uncertainty of volume should be kept within 0.36% in accordance with the international target value (ITV). In order to achieve the expected uncertainty continuously, not only high precision manometer transducers are calibrated by standard pressure periodically, but also operator should maintain the integrity of entire volume measurement system. If clogging at a tip of dip-tube is occurred by drying or precipitation, it directly causes measurement bias, and then operator has to remove it as soon as possible. Therefore, we elaborately studied confirmation procedure of healthiness in the system during solution storage. We propose that following points are effective to know the cause of measurement bias: (1) To confirm the consistency between the Kumar’s density formula and the actual analysis results of plutonium and uranium concentration, density and acidity determined by periodical sampling and high accuracy destructive analysis (DA). (2) To confirm that the plutonium and uranium mass are maintained within the uncertainty of the previous sampling/DA result at the material balance viewpoint. (3) To compare the densities between measured by ELTM and analyzed by vibration tube density meter (VTDM) in standard temperature in order to confirm the integrity of the dip-tube measurement of ELTM. In many cases, since the temperatures between them are different, it has to be adjusted to same temperature for comparison. Concerning the adjustment, we could establish a new correction method derived from the partial differentiation of Kumar’s density formula and acquired analysis results. This knowledge will help to maintain the expected measurement uncertainty of density, level and volume in the entire volume measurement system using ELTM continuously and contributed to appropriate NMA.