Boiling heat transfer characteristics and thermal resistance modeling of corrosion-related unidentified deposit (CRUD) under PWR conditions

Abstract

The fouling deposit in PWR called CRUD (Chalk River Unidentified Deposits) is one of the critical operational challenges for Pressurized Water Reactors (PWRs). It introduces additional thermal resistance on boiling surfaces and accelerates localized corrosion and fuel failure. Despite its importance, the phenomenological understanding of CRUD-induced thermal resistance and the availability of relevant experimental data remain limited. This study presents a comprehensive experimental investigation of subcooled flow boiling heat transfer on CRUD-deposited surfaces under simulated PWR conditions. A series of controlled experiments was conducted to simulate CRUD and to quantify its thermal resistance characteristics. Based on the experimental results, key physical insights were derived. In this study, the formation of localized vapor films within the porous structure was pointed out as a root cause of the thermal resistance characteristics of CRUD. A semi-empirical correlation to predict the thermal resistance characteristics of CRUD was developed as a function of wall superheat. The proposed model effectively captures the boiling heat transfer deterioration induced by the CRUD and shows agreement with the selected database within an error range (+/- 50 %). This work provides essential experimental evidence and a physically grounded modeling framework for incorporating CRUD into PWR safety analyses.