Abstract: The purpose of this study is to establish a detailed 3D model of containment safety verification via integral test (CERT) using containment code GOTHIC. A full-process of main steamline break (MSLB) accident case was selected as a benchmark. The 3D model simulates such key heat removal process as energy absorption by gas volume and heat sinks inside vessel, steam condensation on the inside shell surface, heat conduction through the steel shell, and evaporation of water film covered on the outer vessel shell surface. The model prediction results were compared and evaluated based on test data. The results show that the 3D model can predict vessel temperature and pressure response trend well. Model predictions agree well with test results during post-blowdown period. It also shows that the break jet types affect temperature stratification phenomenon inside vessel dramatically, which has an effect on steam condensation on vessel inside wall. The analysis is of significance on application of GOTHIC code to containment response simulation in passive nuclear power plant.