An assessment of COMGAS and STARGAP code for the hydrogen control analysis under design basis accidents

During and following a design basis loss of coolant accident where relatively small amounts of hydrogen and oxygen can be released to the containment, combustible gas control system is required to prevent volume average concentrations from reaching combustible levels. The design process for this system includes analytical verification through sophisticated prediction by a numerical tool. Whereas the COMGAS computer code had been used for this work since Yonggwang 3 and 4 Units, STARGAP computer code had been developed to consider a new, simpler device called a passive autocatalytic recombiner (PAR) developed for cost-effective control of combustible gases. It is, therefore, necessary that a comparative analysis of detailed models of both codes should be provided to elicit the adaptability of STARGAP code on practical design process. The analysis includes hydrogen generation mechanisms such as fuel-clad metal-water reaction, radiolysis of water, and corrosion of containment materials, and control system performance models. As a result, it was concluded that except for the numerical methods and the modeling of the radiolytic energy absorbed by the coolant, there was little difference on the prediction of hydrogen concentration between two codes. This paper is expected to contribute to understanding of characteristics of two codes and provide some practical guidance on design applications of two codes. (author)