Can corrosion and CRUD actually improve safety margins in LWRs?

Abstract

It is well known that boiling and quenching heat transfer depends strongly on the morphology and composition of the solid surface through which the heat transfer occurs. The relevant surface features are roughness, wettability (hydrophilicity), porosity, presence of cavities, size and shape of cavities, and thermo-physical properties of the surface material. Recent work at MIT has explored the separate effects of surface roughness, wettability and porosity on both Critical Heat Flux (CHF) and quenching heat transfer (Leidenfrost point temperature). Briefly, interconnected porosity within a hydrophilic matrix greatly enhances the CHF (by as much as ∼60%) and the Leidenfrost temperature (by as much as ∼150 °C). Surprisingly, surface roughness has a comparably minor effect on both CHF and quenching. There are opportunities to exploit in Light Water Reactor (LWR) nuclear plants, where CHF and quenching determine the thermal margins in during loss-of-flow and loss-of-coolant accidents, respectively, and the surface of the fuel naturally develops porous hydrophilic layers because of CRUD deposition and corrosion. This paper reviews the MIT experimental database generated using engineered surfaces with carefully-controlled characteristics, and discuss its applications to LWR safety, both design-basis and beyond-design-basis accidents.