No abstract

Lead bismuth eutectic (LBE) is one of the most potential materials for coolant and spallation target for Accelerator Driven Systems (ADS). Thermal-hydraulic behavior of LBE in fuel assembly is a key issue for development of the systems. To get a deeper understanding on the complex thermal-hydraulic features of wire-wrapped rod bundle cooled by upward LBE, an electrically bundle with 7 rods wrapped with helical wire was developed in KYLIN-II thermal-hydraulic forced circulation loop. The flow resistance, thermal entrance characteristic and heat transfer coefficient were investigated. As for the entrance characteristics, during the full heating length (exceeding 140 times the hydraulic diameter), the thermal field did not reach a fully developed and stable condition which is contrary to the ducted flows. The experimental heat transfer coefficient showed that the hexagonal shell has a great influence on the heat transfer coefficient in rod bundle geometry. For this reason the application of empirical correlation should be kept cautious in rod bundle analysis.

In this paper, the computational fluid dynamic (CFD) method was used to simulate the three-dimension, unsteady turbulent flow in a primary pump. Moving mesh method was used to simulate the rotation of the impeller. Sufficient monitoring points in the impeller channel, diffuser channel and interaction zone are set to get the instantaneous pressure. Fast Fourier Transformation (FFT) method was used to get the fluctuation frequency and amplitude. Steady and unsteady calculations were carried out in small and nominal flow rates. Unsteady flow in the flow channel at off design condition was revealed. The vibration frequency variation of the pump in different flow rates was analysed. The pressure fluctuation amplitude in different positions of the pump was shown. The results showed that in the clearance between impeller and diffuser, it has the largest fluctuation and higher frequencies. The fluctuation transports downstream. In off design flow rate, the pressure fluctuation is larger than in nominal flow conditions. The dominant frequency is 1 BPF in small flow rate and 3 BPF in large flow rate. The pressure fluctuation happened in the pump is caused by the stator-rotor interaction. This is clearly shown in the internal flow field.

A hydraulic-force coupling method was used to simulate the transient process of power failure condition. Computational fluid dynamics (CFD) was used to study the three-dimensional (3D), unsteady, incompressible viscous flows in a mixed flow pump in power failure accident. The dynamic mesh (DM) method with nonconformal grid boundaries was applied to simulate the variation of rotational speed of the field around the impeller. User-defined function (UDF) was used to obtain the rotational speed by solving the momentum conservation equation. External characteristics, such as rotational speed, head, flow rate, and hydraulic torque, were obtained during the transient process. Numerical speed and flow rate were compared with results calculated by semiempirical equation and they were in good agreement. The differences between transient and quasisteady results were also studied. Transient head and quasisteady head did not differ too much. The reason that caused this deviation was theoretically analyzed. The difference was explained to be caused by the inertia effect of the fluid contained in the pump and the pipeline. Internal flow field was also shown. Relative velocity vectors showed that the stall form and existence time in transient simulation were different from those in the quasisteady simulation. It is suspected to be one reason for head deviation.