Analysis of anticipated transient without scram of a Super Fast Reactor with single flow pass core

Abstract

Anticipated transient without scram (ATWS) of the supercritical-pressure light water-cooled fast reactor (Super FR) with single flow pass core is analyzed to clarify its safety characteristics. Abnormal reactivity due to loss of feedwater heating and uncontrolled withdrawal of a control rod is mitigated by density and Doppler reactivity feedback. Increase of the coolant density at the upstream of the fuel channel leads the core flow rate to decrease which in turn decreases the power especially due to the density reactivity feedback. Meanwhile, ATWS accidents which are followed by trip of both RCPs are important. Decreased feedwater flow rate leads directly to a decrease of core flow rate in all fuel assemblies. If the ADS is not used, the MCST increases rapidly due to high power density feature of the Super FR. Coolant expansion effect does not appear in the single flow pass core of Super FR while it appears in the second pass of the two-flow pass core leading to mild increase of MCST of the second pass. However, signal of flow low level 3 (6%) is provided for the ADS actuation and the MCST of each fuel channel is effective to be mitigated due to large core coolant flow rate induced by the ADS operation. The power is also decreased by density and Doppler reactivity feedbacks. MCST and core pressure of all the analyzed events satisfy the criteria.