Study On Comparation Of Different Arrangement Schemes For The Residual Heat Removal System In Sodium-cooled Fast Reactors Based On The FRTAC System Code

The residual heat removal system is an extremely important safety system that ensures the removal of core heat in the event of a reactor accident.Most fourth-generation sodium-cooled fast reactors use advanced residual heat removal systems,but their system layout varies greatly and can be classified into different arrangements such as direct residual heat removal,intermediate loop residual heat removal,and main loop residual heat removal.The different layout schemes of residual heat removal systems have different effects on critical parameters such as the establishment of natural circulation under accident conditions,residual heat removal capacity,and core outlet temperature.Therefore,it is of great engineering value to compare different schemes.Currently,there are studies on the above schemes internationally,but no comparative study of residual heat removal characteristics and capabilities of different design schemes under the same reactor type has been carried out.Therefore,conducting a comparative study of different layouts of residual heat removal systems for sodium-cooled fast reactors has important academic significance.In.this paper,based on the fast reactor system safety analysis program FRTAC,modeling calculations were carried out for the LOFWOS Test#13 of the FFTF fast reactor provided by the Argonne National Laboratory to preliminarily verify the accuracy of the FRTAC program.For large sodium-cooled fast reactors,primary system,secondary system,and tertiary system were established.The built-in neutron calculation module and thermal-hydraulic calculation module were used to divide the core of the large sodium-cooled fast reactor into multiple channels and to model the sodium pool in layers.This paper established four schemes for direct heat exchanger layout and secondary loop residual heat removal,namely two direct heat exchangers arranged in the hot sodium pool,two direct heat exchangers arranged in the cold sodium pool,four direct heat exchangers arranged in the hot sodium pool,four direct heat exchangers arranged in the cold sodium pool,and intermediate loop residual heat removal system.Transient analysis of the residual heat removal system characteristics under different conditions was conducted,and the following conclusions were obtained:Regarding the thermal stratification phenomenon in the sodium pool,the more direct heat exchangers(DHXs)are arranged in the cold sodium pool,the lower the maximum temperature of the cold sodium pool and the more uniform the thermal stratification in the cold sodium pool.The more direct heat exchangers(DHXs)are arranged in the hot sodium pool,the lower the maximum temperature of the hot sodium pool.Regarding heat exchange capacity,under the condition of steam generator loss of feedwater,the heat exchange capacity of Scheme 4 is better than that of Schemes 1,2,and 3.Under the condition of a complete power outage,the heat exchange capacity of Scheme 4 is lower than that of Scheme 1 but higher than that of Schemes 2 and 3.Regarding the time to reach long-term cooling stage of natural convection,under the condition of steam generator loss of feedwater,Scheme 4 reaches it earliest,Scheme 1 is second,and Scheme 3 is the latest.The time to reach long-term cooling stage of natural convection for Schemes 1-4 is 747s,781s,947s,and 658s,respectively.Under the condition of station blackout,Scheme 4 reaches it earliest,Scheme 1 is second,and Scheme 2 is the latest.The time to reach long-term cooling stage of natural convection for Schemes 1-4 is 527s,952s,924s,and 502s,respectively.Based on the above characteristics,this paper proposes a new layout scheme that combines the intermediate loop residual heat removal system with the direct heat exchanger lay out of Scheme 1.