Sub-channel analysis code development and core thermal calculation for fast reactor refueling cycle

Abstract

Sub-channel analysis is an indispensable method for core safety evaluation. As a part of the fast reactor program series, development of SAC-SUB (System analysis code – SUB channel) program has been completed. Experiments performed with a 19-rod test assembly in the fuel failure mockup (FFM) sodium loop in Oak Ridge National Laboratory (ORNL) was selected as the benchmark to verify the SAC-SUB program capability. The maximum outlet temperature deviation is within 5%, which preliminarily verifies the availability of the program for fast reactor. Then the code was used to analyze CEFR thermal response during refueling cycle and MOX equilibrium state. During each refueling cycle, highest sodium temperature occurs in the fourth flow zone, and highest fuel temperature rise occurs in the first flow zone. The highest sodium temperature is 606.8 °C appearing in 3rd cycle, and the highest fuel temperature rise is 880.93 °C appearing in 4th cycle. Maximum temperature rise across the cladding and film do not change much. After reaching MOX core equilibrium state, all the key temperature will reach a lower level compared with refueling transition process, which indicating that the power distribution and flow distribution of the core are more matched in the equilibrium state.