To improve the safety of future sodium cooled fast reactor, alternative Decay Heat Removal (DHR) path is envisaged through secondary sodium main circuit. Secondary Sodium Decay Heat Removal System (SSDHRS) transfers heat from secondary sodium to ambient through Air Heat Exchanger (AHX). SSDHRS is planned to operate in forced circulation mode using Class 3 power supply. SSDHRS in addition to Safety Grade Decay Heat Removal System help in demonstrating failure of DHR function is highly unlikely, so as to be regarded as practically eliminated.
Analysis of SSDHR System is carried out using system dynamics code Flownex. Flownex is a general purpose one dimensional code for thermal hydraulic simulation of systems with component level modeling capabilities. Different components of the system, viz., Intermediate heat exchangers, AHX, stack, secondary sodium Pump (SSP), blower are modeled through appropriate component models. Single zone model of core is also developed to represent the decay heat source. Heat transfer capacity of each SSDHR system is found to be 15.17 MW at 544 °C temperature of hot pool sodium. SSP develops 26 % of nominal flow during SSDHRS operation, out of which 4% flows through AHX and the remaining flow is bypassed through a separate bypass path. Flow rates of sodium and air in AHX are estimated as 133 kg/s and 59.5 kg/s respectively. Parametric studies have been carried out by varying hot pool temperature in the range of 200 °C to 650 °C and primary sodium flow rate, and their effect on performance of SSDHRS is studied. Transient analysis of 'off-site power failure' event is carried out and the predicted hot pool and cold pool temperatures are found to be within the design safety limits. Further study is carried out to assess performance of SSDHRS during natural circulation of secondary sodium and air. Heat removal capacity at 544 °C and 650 °C primary sodium temperature is found to be 8.78 MW and 11.07 MW respectively. Study is also carried out to assess the performance of SSDHRS, when all the three circuits are under natural circulation mode. The maximum heat removal capacity is found to be 9.775 MW when the hot pool temperature reaches 650 °C.
|Affiliation/Organization||Indira Gandhi Centre for Atomic Research|
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