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[en] The International Organization for Standardization (ISO) Guide to the expression of Uncertainty in Measurement (GUM) was developed to meet the demand for a standardized way of evaluating and expressing uncertainties. The Davies and Gray (D and G) titrimetry method is routinely used in nuclear safeguards for uranium accountability measurement and a statement of the uncertainty that can reasonably be attributed to the measured assay value is therefore of importance. A mathematical model for an uncertainty evaluation of D and G measurements in compliance with ISO GUM is presented. This is illustrated by a numerical example and the utilization of the uncertainty budget is explored. (author)
[en] In a recent paper, Mathew et al. detailed, for a specific titration-based assay of uranium, a 'step-by-step approach to calculate the GUM uncertainty of the measurand', in which their uncertainty assessment was based solely on prior knowledge, ignoring the manifest variability in their replication data. A simple analysis of the variance from their data reveals that the uncertainty in the average of the replicated quantity (TEF) was at least 3.5 times their estimate. Since the observables that contribute most to the final uncertainty in their method were not replicated, it is unknown whether the estimates for the uncertainties of those quantities, and thus of the output quantity, were also underestimated. This comment demonstrates how a better uncertainty evaluation is possible by extracting as much knowledge as possible from the extant data. (author)
[en] The design and test of a small volume calorimeter of high precision and simple design is described. The calorimeter operates with solution sample volumes in the range of 3 to 5 ml. The results of experiments on the entropy changes for two standard reactions: (1) reaction of tris(hydroxymethyl)aminomethane with hydrochloric acid and (2) reaction between mercury(II) and bromide ions are reported to confirm the accuracy and overall performance of the calorimeter
[en] Geometric optimization techniques useful for studying chemical equilibrium traditionally rely upon principles of euclidean geometry, but such algorithms may also be based upon principles of a non-euclidean geometry. The sequential simplex method is adapted to the hyperbolic plane, and application of optimization to problems such as the potentiometric titration of plutonium is suggested
[en] A non-aqueous titration method has been used for quantifying the suppressor concentration in the MCU solvent hold tank (SHT) monthly samples since the Next Generation Solvent (NGS) was implemented in 2013. The titration method measures the concentration of the NGS suppressor (TiDG) as well as the residual tri-n-octylamine (TOA) that is a carryover from the previous solvent. As the TOA concentration has decreased over time, it has become difficult to resolve the TiDG equivalence point as the TOA equivalence point has moved closer. In recent samples, the TiDG equivalence point could not be resolved, and therefore, the TiDG concentration was determined by subtracting the TOA concentration as measured by semi-volatile organic analysis (SVOA) from the total base concentration as measured by titration. In order to improve the titration method so that the TiDG concentration can be measured directly, without the need for the SVOA data, a new method has been developed that involves spiking of the sample with additional TOA to further separate the two equivalence points in the titration. This method has been demonstrated on four recent SHT samples and comparison to results obtained using the SVOA TOA subtraction method shows good agreement. Therefore, it is recommended that the titration procedure be revised to include the TOA spike addition, and this to become the primary method for quantifying the TiDG.
[en] The original Macdonald and Savage amperometric method scaled down to milligram-sized plutonium samples was further modified. The electro-chemical process of each redox step and the end-point of the final titration were monitored potentiometrically. The method is designed to determine 4 mg of plutonium dissolved in nitric acid solution. It is suitable for the direct determination of plutonium in non-irradiated fuel with a uranium-to-plutonium ratio of up to 30. The precision and accuracy are ca. 0.05-0.1% (relative standard deviation). Although the procedure is very selective, the following species interfere: vanadyl(IV) and vanadate (almost quantitatively), neptunium (one electron exchange per mole), nitrites, fluorosilicates (milligram amounts yield a slight bias) and iodates. (author). 15 refs.; 8 figs.; 7 tabs
[en] In this paper a technique for the determination of free carbon in boron carbide was studied. This technique consists in the treatment of the carbide samples with hot sulfocromic mixture, to the free carbon oxidation. The released gases are then circulated in barium hydroxide solutions, whose concentrations are previously determined and by titration the remain quantity of hydroxide in solution is determined. From convenient calculations the amount of free carbon present initially in the samples is then obtained, and these results are here evaluated. (author)
[en] Highlights: • Comprehensive description of an experimental apparatus for coulometric titrations. • In-detail discussion of difficulties and challenges. • Validation of the system by measurements conducted in the Li-Sn system. - Abstract: The thermodynamic description of Li containing systems is readily accessible by coulometric titrations in combination with EMF measurements. Although this method is often encountered in literature, the experimental apparatus needed is in general only poorly described. As Li and its alloys are very reactive substances, many parameters like the materials used for the electrochemical cell, cell geometry, establishment of O2- and H2O-free atmosphere, etc. are all important factors for a successful measuring device. Therefore, an instrumental setup for coulometric titrations combined with EMF measurements is presented in detail, covering the general and the electronic setup used, as well as the structure of the electrochemical cell. The apparatus is validated with two measurements conducted in the Li-Sn system, which are further compared with literature data.