Modeling heat transfer through corrosion product deposits on fuel rods in pressurized water reactors

CRUD is the corrosion product deposit found on a fuel rod surface of pressurized water reactors (PWRs). Problematic phenomena caused by CRUD - CRUD Induced Power Shift (CIPS) and CRUD Induced Localized Corrosion (CILC) - are closely related to the heat transfer mechanism of CRUD. However, heat transfer regimes of CRUD are still not well clarified. Therefore, the heat transfer regimes of CRUD were investigated using existing database from the CRUD heat transfer experiment. As a result, it was found that there are three heat transfer regimes: (i) liquid-saturated regime, (ii) wick-boiling regime, and (iii) film-boiling regime. In addition, the boiling curves from the experiment were categorized according to their heat transfer regimes so that models for CRUD can be validated with appropriate database for the heat transfer regime where they are concerned. After obtaining the categorized databases, the model for the film boiling of CRUD was suggested. Unlike the conventional approaches that use capillary force as a unique source of the liquid supply in pores, the model we present in this paper adopted the disjoining force as an additional liquid supply term. This assumption was validated with the previous heat pipe experiment; the root-mean-square error (RMSE) for the prediction of the vapor film thickness was notably reduced from 790% to 18.7% by including the disjoining force to the supply term. The supply term considering the disjoining force was also applied to a model for the CRUD film boiling. The model estimates the wall superheat by balancing the supply term and the hydraulic resistance terms from fluid flows within CRUD. The model we present in this paper successfully predicted the wall superheat during the film boiling; the RMSE was 19% when the predicted wall superheats were compared with ones from the database categorized as film boiling. Finally, it was found from the sensitivity study using the model we present in this paper that the heat transfer performance of CRUD during the film boiling is highly sensitive to the pore radius.