Nanofluid application in post SB-LOCA transient in VVER-1000 NPP

This paper is the third in a series of four papers that the application of nanofluid as a coolant to improve heat transfer in a VVER-1000 nuclear reactor is investigated. In the first and second papers, neutronics and thermo-hydraulic behavior of nano-particles in normal operation mode of the reactor were reported. In this study, the effects of nanofluids in Small Break Loss of Coolant Accident (SB-LOCA) to complement the existing safety systems is investigated. During SB-LOCA transient, due to reduced mass flow rate and Reynolds number, flow boiling along with vapor formation around the fuel rods occur. The fuel assembly coolant channel of a VVER-1000 core is modeled using a CFD code and heat transfer coefficients, pressure drop and volume fraction distribution of phases are computed for water/Al2O3 nanofluid. We observe that with the escalation of heat transfer enhancement, due to reduction in void fraction, pressure drop along the channel is reduced. This new phenomenon of lower pressure drop along with heat transfer enhancement, would be a significant factor for the use of nanofluids during reactor SB-LOCA transients.