Pool boiling CHF enhancement by graphene-oxide nanofluid under nuclear coolant chemical environments

Highlights: ► We investigate CHF limits of graphene-oxide nanofluids for IVR-ERVC. ► Graphene-oxide nanofluids were stable under ERVC coolant chemical environments. ► GO nanofluids enhanced CHF up to about 40–200% with heater orientation. - Abstract: External reactor vessel cooling (ERVC) for in-vessel retention (IVR) of corium as a key severe accident management strategy can be achieved by flooding the reactor cavity during a severe accident. In this accident mitigation strategy, the decay heat removal capability depends on whether the imposed heat flux exceeds critical heat flux (CHF). To provide sufficient cooling for high-power reactors such as APR1400, there have been some R and D efforts to use the reactor vessel with micro-porous coating and nanofluids boiling-induced coating. In present study, an experimental study has been conducted to investigate the viability of using graphene-oxide nanofluid under various coolant chemical environments to enhance CHF during ERVC. Pool boiling CHF experiments were carried out for the thin-wire heater with controlling the heater orientation from horizontal to vertical, or at 0 < θ < 90°. The dispersion stability of graphene-oxide nanofluid in the chemical conditions of flooding water that includes boric acid, lithium hydroxide (LiOH), and tri-sodium phosphate (TSP) was checked in terms of surface charge or zeta potential before the CHF experiments. Finally integral effects of graphene-oxide nanosheets and chemicals on CHF limits were investigated. Results showed that graphene-oxide nanofluids were very stable under ERVC coolant chemical environments and enhanced CHF limits up to about 40% at minimum at 90° of angle (vertical orientation) and about 200% at maximum at 0° of angle (horizontal orientation) in comparison to pure water.