On the application of field codes to the analysis of gas mixing in large volumes: case studies using CFX and GOTHIC

Abstract The analytical investigation of containment system response and associated key phenomena in design-basis-accidents (DBA) and beyond-design-base accident (BDBA) is an important component of the ALPHA (Advanced LWR Passive Heat Removal and Aerosol Retention) programme. Simulation of the distribution of non-condensable gases within distinct gas spaces, such as separate containment compartments, is a key issue, and one which requires computer codes with three-dimensional capabilities. It is shown in the present article that such advanced codes (often referred to as field codes) have the potential to produce more accurate predictions than were possible with more established methods, i.e. lumped-parameter codes. A few problems, however, have also been identified, which must be resolved in current and future code validation and development exercises if such methods are to gain universal acceptance.