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In this paper, the application of small channels to the extraction separations in spent nuclear fuel reprocessing has been investigated via a modelling approach. The results are compared with conventional liquid-liquid extraction technologies such as mixer-settlers and pulsed columns, using models from the literature. In the model mass transfer, redox reactions, pressure drop and nuclear criticality are taken into account, as well as manifold and two-phase separator designs for the small-scale technology. The resulting model, posed as an optimisation problem, is a mixed integer nonlinear problem, implemented in the General Algebraic Modeling System (GAMS). An alternative flowsheet for the codecontamination section of the PUREX process, as a case study, has been investigated. The results show that the small-scale technology could be beneficial, in particular in terms of volumetric mass transfer coefficients, nuclear criticality safety and short residence time, which improves neptunium separation and reduces solvent degradation.

In this work, a dynamic model of a twin screw feeder, for continuous tablet manufacturing, has been developed. In particular, a First Order Plus Dead Time (FOPDT) model has been suggested. The delayed dynamics depends on operating conditions, equipment design and physical properties of the bulk solid. Model parameters are estimated by fitting the model to experimental data. Due to the nonlinear input-output relationships and the time delays involved, a Nonlinear Model Predictive Control (NMPC) is investigated to maintain an accurate mass flow rate, with the ultimate goal to improve product homogeneity in an inherently complex process. The performance of the designed control system is found to be satisfactory in a wide operating range and its potential use in a continuous manufacturing process is worth being investigated in the future.

Nowadays, pyrohydrolysis techniques are widely applied for regeneration of spent pickling liquors providing an excellent environmental and economical strategy to the problem of waste disposal/recovery, also thanks to the high acid recovery efficiencies (>99%) achieved. In fact, in these processes, iron chlorides are converted into iron oxides and hydrogen chloride at high temperature in spray roasting or fluidized bed reactors. Though the state-of-the-art technologies have been successfully applied only to large-scale plants, the development of small-scale units, able to perform a delocalized regeneration of spent solutions where these latter are actually produced, would be strongly needed in order to minimize the transportation of hazardous spent pickling and fresh HCl solutions to/from pickling factories from/to large centralized regeneration plants. In the present work, a steady-state simulation model for regeneration of spent pickling liquor via spray roasting has been developed, aiming at the analysis of performance of a small-scale unit. The simulation and optimization of the process has been carried out using Aspen Plus simulator. A simplified model of the spray roaster, based on the data collected from studies reported in the literature, has been implemented and exported from Aspen Custom Modeler. Solid recovery from roaster off-gases has been obtained by a cyclone and a Venturi scrubber, where the spent pickling liquor is concentrated prior to be sprayed into the reactor. Hydrogen chloride is absorbed in an adiabatic absorber, where a sub-azeotropic (18–20 wt%) hydrochloric solution is obtained. Prior to the stack, a scrubber is required to wash off the exhaust gases. Several parametric studies have been performed. Different designs of solid separators have been compared in order to investigate the particulate separation efficiency of the process, while absorption column’s packing types and rinse water flow rates have been varied in order to investigate their effects on HCl recovery and acid gas emissions.

The use of small channels for liquid-liquid extraction seems to be promising, since hydrodynamics are more easily controlled and mass transfer is enhanced. The use of small scale contactors may be particularly beneficial for spent nuclear fuel (SNF) reprocessing, due to the small size and consequent safety improvements. In this paper, a mathematical model for the intensified liquid-liquid extraction in small channels has been developed. A multi-component system is considered, including most of the components in the SNF. The resulting model is a large scale mixed integer nonlinear optimisation problem. A novel design of the COEX (co-extraction of uranium and plutonium) process, employing small channels, is presented. Results show that several improvements are obtained, compared to traditional technologies, in terms of safety and solvent degradation.

The preliminary design of a process consisting of extraction, back extraction and solvent recycling using small extractors has been investigated. In this paper a mathematical model of multicomponent Liquid-Liquid Extraction (LLE) during segmented flow in small channels is presented. The resulting model, suitable for applications to Spent Nuclear Fuel (SNF) reprocessing, can be used to explore alternative flowsheets for the nuclear fuel cycle employing the novel two-phase contactors. Case studies have shown that, using small scale contactors, significant improvements may be achieved.