Evaluation of Nanofluid Coolant Effects on Safety margins and Fuel cycle Period of VVER-1000 Reactor

In this study, coupled neutronic-thermal hydraulic analysis is utilized to investigate the effects of using water/silver nanofluid both as the coolant and reactivity controller during the first operating cycle of VVER1000/446 nuclear reactor. A detailed neutronic model of the reactor core is created using MCNP and the porous media approach is used for thermal hydraulic model. Results show that the value of silver nanoparticle decreases as the cycle goes on and the maximum value (1.3 Vol. %) is at the beginning of cycle and its value becomes zero at the end of cycle (EOC). Due to replacement of water/boric acid with water/Ag nanofluid, reactor operates more 63.5 days at maximum power. The coolant temperature coefficient of reactivity becomes higher negative in the presence of nanofluid and it indicates that the reactor is inherently safer. Also, minimum departure from nucleate boiling ratio (MDNBR) , as another important safety margin, is calculated to be 2.16 (recommendation is 1.75).