Twofold application of nanofluids as the primary coolant and reactivity controller in a PWR reactor: Case study VVER-1000 in normal operation

•Application of nanofluid as a complement to the safety systems during normal operation.•Using nanofluid as the means of reactivity control instead of boric acid.•Evaluation of critical nanofluid concentration at the beginning of cycle for a VVER-1000 core.•Coupling detailed fluid dynamic and neutronics calculations to achieve core criticality with the fresh fuel.

The use of nanofluid as a dual heat transfer enhancer and excess reactivity controller in a typical pressurized power reactor (PWR) is the focus of this study. Presently, boric acid is the dominant method for reactivity control in PWRs and Chemical & Volume Control System (CVCS) controls the boric acid concentration during reactor operation. In this study, we have replaced the coolant fluid of the first loop with a nanofluid which act as coolant, neutron moderator and neutron absorber. A full core of VVER-1000 as a typical PWR system is modeled with coupled neutronics and fluid dynamic codes. Among five nanofluids investigated, 2% volume fraction silver oxide is found to satisfy both neutronics and thermohydraulics safety margins of VVER-1000 nuclear reactor.