An experimental study of external reactor vessel cooling strategy on the critical heat flux using the graphene oxide nanofluid

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&D efforts to use the reactor vessel with micro-porous coating and nanofluids boiling-induced coating. 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. Results showed that graphene-oxide nanofluids were very stable under ERVC environment. The critical heat flux (CHF) on the reactor vessel external wall was measured using the small scale two-dimensional slide test section. The radius of the curvature is 0.1m. The dimension of each part in the facility simulated the APR-1400. The heater was designed to produce the different heat flux. The magnitude of heat flux follows the one of the APR-1400 when the severe accident occurred. All tests were conducted under inlet subcooling 10K. Graphene-oxide nanofluids (concentration : 10 -4 V%) enhanced CHF limits up to about 20% at mass flux 50kg/m2s and 100kg/m2s in comparison with the results of the distilled water at same test condition.