Validation methods in modelling the PANDA IPSS experiment: A MELCOR 2.2 assessment of a passive isolation condenser

Nuclear power plants (NPPs) are becoming increasingly interesting for future energy supply. Nowadays, most of the modern NPPs, such as Generation III+ and Small Modular Reactors (SMRs), offer an even higher safety standard than their predecessors, often relying on passive systems. Due to the continuous improvement of design and safety solutions in the nuclear field, it is essential to simultaneously increase modelling capabilities. This can be achieved by the advancement of modelling tools and by increasing the experience of the analyst. This work focuses on code validation to potentially allow users to gain modelling experience and to provide insights for further code development. Due to the complexity of severe accidents, it may prove to be challenging to model passive systems under such conditions, thus the validation is especially important for numerical codes, such as MELCOR. Codes used for the simulation of severe accidents are simplified in order to be capable of capturing all occurring phenomena in a realistic computational time frame. Thus, it is not trivial if these codes are capable of modelling the combination of passive safety systems within the new integrated features present in many NPP designs. For this reason, this work aims to investigate how such assessments should be performed as well as to consider the severe accidents code MELCOR with respect to the simulation of a passive isolation condenser at the large-scale experimental facility PANDA with and without the presence of non-condensable gases. Our work summarises the present ideas with regards to validation and verification of nuclear codes and highlights the fact that the severe accident code MELCOR is capable of simulating passive safety systems, such as the passive isolation condenser. Improvements can be made when modelling condensation in the presence of non-condensable gases and thus suggestions were made for the improved modelling.