Improvement of the condensation heat transfer model of the MARS-KS1.3 code using a modified diffusion layer model

The thermal-hydraulic system code, MARS-KS1.3, tends to underestimate the condensation heat transfer under the presence of non-condensable gases. To improve its condensation heat transfer model, we adopted the Herranz's diffusion layer model and further developed it, mainly focusing on thermal-hydraulic conditions in a nuclear containment during a hypothetical accident. Two key modifications include (i) the correlations to calculate heat and mass transfer on a vertical external surface for various flow conditions are adopted and (ii) a turbulent diffusion coefficient is applied to consider the effect of turbulence on mass diffusion. The modified diffusion layer model was implemented into MARS-KS1.3 and it has been validated using 157 condensation experiments from six different facilities. By using the turbulent diffusion coefficient in the modified diffusion layer model, the effect of turbulence on mass diffusion and then condensation was captured very well. For most cases, the results of the modified model are in a better agreement with the experimental data, resulting in a root-mean-square error of 21.3%. It is also shown that the modified diffusion layer model can predict local condensation heat transfer change along the condensation surface well. •MARS-KS1.3 under-predicts condensation in the presence of noncondensable gases.•The Herranz's diffusion layer model was adopted for the MARS code improvement.•We considered the effect of turbulence on mass diffusion through diffusion layer.•The results of the modified model show a better agreement with experimental data.