Numerical Simulation of Transient Thermal-Hydraulic Characteristics of Intermediate Heat Exchanger for Sodium Cooled Fast Reactor Under Accident Conditions

Abstract

In Generation IV nuclear systems, Sodium Cooled Fast Reactor has attracted extensive attention for its particular advantages. Intermediate Heat Exchanger (IHX) is a significant equipment connecting the primary circuit system and secondary circuit system in Sodium Cooled Fast Reactor. Under normal and accident conditions, the temperature fluctuation of the IHX component may cause the alternating change of the local stress, such as sealing weld zones mixing chamber, and the area between inner and outer sleeves. This fluctuation may result in the thermal fatigue of IHX and consequently affect the safety and economy of the reactor operation. Therefore, it is essential to carry out mechanical analysis by experiments or simulations to ensure the structural stability under complex conditions. However, the mechanical analysis must take transient thermal-hydraulic characteristics as boundary and input conditions. Thus, a thorough thermal-hydraulic assessment of IHX is required to guarantee its security under accident conditions. In this paper, a thermal-hydraulic simulation of IHX was carried out using system code under steady and transient state conditions. Thermal parameters of steady-state calculation agreed well with the design requirements. Transient-state accident conditions, such as emergency shutdown, Station Blackout (SBO), and Steam Generator Tube Rupture (SGTR), were conducted in this paper. In the emergency shutdown, the wall temperature increased from 703.15 K to 798.41 K in three seconds, and then decreased slowly and stabilized at 626.15K. In the SBO accident, the temperature of the primary and secondary circuit fluids fluctuated violently from 0 to 100 seconds. When the secondary side flow drops to 0, the wall temperature of typical positions changes with the inlet temperature of the primary side, showing a trend of rapid decline and stable. In the SGTR accident, the temperature of the heat transfer tube wall increased rapidly during the early stage of the accident. After that, the primary side flow reduced gradually to 0 with the decrease of the secondary side flow. Because of the trend of flow, the temperature of the tube wall decreased rapidly and then increased slowly. Therefore, the results of various accident conditions in this investigation can contribute to the thermal fatigue analysis of IHX in the near future.