Yuanzineng kexue jishu (Jan 2023)
Study on Dynamic Simulation Model of Continuous Dissolution Process of Spent Fuel
Abstract
Spent fuel reprocessing is one of the most critical links in the process of closed nuclear fuel cycle process. Carrying out computer simulation research on this process and establishing its dynamic simulation model can carry out process analysis and optimization with less human and material resources and in a more general scope. In this paper, by analyzing the mass transfer process of the dissolution reaction between spent fuel pellets and nitric acid and the mass transfer process of solute in the solution, a dynamic dissolution model of spent fuel pellets dissolution process was obtained based on mass balance calculation. The model includes three parts: chemical reaction module, solute transfer module and solution flow field analysis module, which are respectively used to calculate the mass transfer caused by chemical reaction, the mass transfer caused by the convection and diffusion of liquid in the liquid phase and the analysis of the flow state of fluid in the solution system. The turbulent flow state of the dissolved liquid in the dissolver was simulated by Comsol software, and the flow field cloud diagram of the dissolved liquid flow was obtained, which provided the analysis data of the liquid phase flow state for the established dynamic dissolution model of the spent fuel pellet dissolution process. The numerical simulation program for solving the real-time simulation model of spent fuel pellet dissolution process was established by using Matlab software, and the feeding dynamic simulation of spent fuel dissolution process in continuous dissolver was carried out under the process conditions of 90 ℃, nitric acid feed concentration of 6 mol/L, feed flow rate of 11 L/min and return flow of 35 L/min. The change trend of the simulation results is basically consistent with the actual process, and the dissolution process needs about 2 000 minutes to reach dynamic equilibrium. After equilibrium, the concentration of nitric acid in the solution discharge is 2.78 mol/L and the concentration of uranium is 253.23 g/L. The relative error of material balance calculation of uranium in the whole dissolution process is generally in an acceptable range. When it reaches equilibrium, the relative error of overall mass balance calculation is only 2.57%. The simulation results show that the dynamic dissolution simulation model of the rotary continuous dissolver established in this study can better describe the actual dissolution behavior of the spent fuel in the dissolver, and provide simulation data support for the spent fuel dissolution process in the actual production process.
