ASSESSMENT OF THE MELCOR AND RELAP5-3D CODE FOR CONDENSATION IN THE PRESENCE OF NONCONDENSABLE GAS

摘要

Condensation of steam plays an important part in removing heat from the reactor containment. The process is complicated by the presence of noncondensable gases in the containment. The condensation models considering the presence of noncondensable gases of RELAP5-3D code, MELCOR code and the generalized diffusion layer model were examined via simulation of the scaled AP600 atmospheric containment tests at UW-Madison. Examining the basic models and assumptions each code uses for the condensation mechanism, it was found that MELCOR and RELAP-3D use different models for calculating condensation mass flux. After examination of the models for each system code, we found that the condensation model in RELAP-3D needs to be corrected to properly account for the presence of noncondensable gases. The MELCOR simulation results showed good agreement with the experimental data. Also the effect of nodalizations on condensation heat transfer predictions was studied.