Diameter deviation calculation for UO2 kernel by sol-gel process

Highlights: → UO2 kernels are produced by a sol-gel method. → The formula about jet velocity, solution level and gas pressure on solution was established. → The decline of solution level leads to the decreasing of jet velocity and the solution mass flow rate, as a result, the diameter deviation increased. → After compensating the pressure on the liquid gradually during the casting process, the standard deviation of kernel diameter was less than 12 μm. - Abstract: UO2 kernels for HTR (High Temperature Gas-cooled Reactor) fuel element are produced using a sol-gel method. The size of UO2 kernels was controlled strictly by minimizing the dispersion of the UO2 kernel diameter during the casting process. A relationship between the filling gas tank pressure and solution level in the tank was developed to keep a constant solution mass flow rate in the nozzles. Based on equation of flow energy conservation, a formula about jet velocity, solution level and gas tank pressure on solution was established. Using the formula, the minimum pressure and maximum pressure were calculated. During the casting process, the decline of solution level will lead to the decreasing of jet velocity and the solution mass flow rate that can cause the increasing of diameter deviation. By compensating the pressure on the liquid gradually during the casting process, the flow fluency was kept in an acceptable range stably, the standard deviation of kernel diameter was less than 12 μm.