Preliminary Assessment of Decay Heat Removal Systems in the ESFR-SMART Design: The Role of Natural Air Convection Around Steam Generators Outer Shells in Accidental Conditions

In the frame of the ESFR-SMART European project, aiming at improving the safety level of the European sodium cooled fast reactor (ESFR), this paper presents the preliminary assessment of decay heat removal systems (DHRSs) in the ESFR-SMART design: the role of natural air convection around steam generators (SGs) outer shells in accidental conditions. Both theoretical and CATHARE code (thermal hydraulics reference code) calculations are presented. The impact of an additional chimney at the top of each casing as well as running primary and secondary pumps on the heat removal capacity is equally evaluated. This paper shows that the evacuation of decay heat thanks to completely passive air natural circulation alone, in case of Fukushima like accident, should lead to temperatures of sodium in the reactor vessel temporarily exceeding the safety criterion of 650 °C. The addition of chimneys increases the capacities but is not sufficient to evacuate the decay heat safely. If the primary and secondary side pumps are running, the safety criterion should be met.