Modeling of Purex Process and Its Simulation

The objective of this thesis is to contribute for design and operation of Purex process, which is adopted as commercial spent nuclear fuel reprocessing plant, by modeling of the Purex process and its simulation. The following studies were carried out in this thesis especially for the dissolution process in the head end process and the extraction process as the main process.(i) Modeling of the dissolution dynamics and its simulation: Rate equations developed here involve both penetration of nitric acid solution into the uranium dioxide pellet and chemical reaction kinetics. Rate constants in the equations were determined from several experimental results of the U02 pellet dissolution. Simulated results based on the rate equations gave good agreement with the experimental ones.(ii) Modeling of the extraction process in the pulsed column and its simulation:A progression model, which was able to describe axial change of back-mixing in the pulsed column and had simple expression, was adopted as the simulation model of the extraction process in the pulsed column. Both the steady-state and dynamic simulation of extraction behavior in the pulsed column gave good agreement with simulated experimental results.(iii) Estimation of distribution coefficients of neptunium, uranium and plutonium in TBP/n-dodecane-nitric acid system: The estimation equations of the distribution coefficients of neptunium, uranium and plutonium in TBP/n-dodecane-nitric acid system were developed. Respective equilibrium constants in the equations were correlated with the total ionic strength in the aqueous phase. Distribution coefficients estimated by these quations gave good agreement with the experimental data presented.(iv) Analysis of oxidation-reduction reaction between Np(V) and Np(VI) by nitrous acid and simulation of neptunium behavior in the extractor:Rate and equilibrium constants of the oxidation-reduction reaction were determined from extraction experiments with mixer-settler based on a new extraction model, which had an assumption that all oxidation-reduction reactions occurred only in aqueous phase. By using determined rate equation, simulated neptunium concentration profiles in the mixer-settler gave good agreement with the experimental profiles.(v) Development of Purex process flowsheet calculation system: A COMPAS (COMputer aided Process flowsheet design and analysis system for nuclear fuel reprocessing) system was summarized. An example of the application was shown for the determination of operational conditions for flow control of neptunium in the Purex process. This system is available for R&D study on the safety operation and waste minimization of the Purex process.指導教授 : 松本史