Evaluation of the condensation phenomenon in presence of non-condensable gases for PCCS related geometry

This paper presents a summary of results obtained analyzing the condensation phenomenon through the use of some selected models calculating the heat transfer coefficient during condensation in presence of noncondensable gases (air). To achieve this goal, after selecting some widely used and qualified models, these were implemented in the CMTC (Computer Model for Correlations Test) computer code to evaluate their performances in a round tube geometry type. The CMTC code basically provides to the condensation models, (integrating the mass, energy and momentum equations over a control volume) the local values of fluid parameter (as mass flow rates, steam and gas properties, and so on) needed to determine the local heat transfer coefficient and the power exchanged between primary and secondary side of a PCC-like component. After the model was assessed against experimental data, some parametrical studies were performed taking as reference the geometry of PCC component of a SBWR plant, with some expected conditions after a accident transient. Some of the models were also implemented in the RELAP5/Mod3.2 code, to analyze the interactions among code structure and model responses, and the implementation was assessed using the previously mentioned experimental data. The following results were achieved: The CMTC code used to predict the condensation phenomenon in the considered geometry was successfully assessed, and overall acceptable performances were obtained in the prediction of experimental data considered; The parametrical analyses carried on for different postulated conditions of work of PCCs component showed some large spread of results, especially in the region of low non-condensable concentration in the steam bulk flow (less than 10%); The application of some of the selected models in the RELAP5/Mod3.2 showed a general underestimation of the heat transfer coefficient, mainly due to the overestimation of the effect of non-condensable gases in the condensation phenomenon; The comparison of the results obtained with the simple computer program used to test the selected models and the RELAP5 code are in acceptable agreement, making possible to use the program as a standard base to test new models and perform fast parametrical analyses. (author)