European SMR station blackout thermal–hydraulic analysis with the Apros system code

• A 1D thermal-hydraulic model of the European SMR was developed using the Apros code for design basis accident analyses. • Hydroaccumulators could temporarily disrupt the natural circulation in the reactor. • Buoyancy forces restored the natural circulation in an hour, enabling the reactor to drive the passive loop. • The passive heat removal system played a critical role in the stratification of the upper layer of the water wall. • The thermocline analysis showed that the containment atmosphere had negligible impact on water wall behaviour. Recent years have seen the global development of small modular reactors (SMRs), introducing many innovative design concepts, particularly in safety systems focusing at the optimization of economic feasibility and passive reliability. Vendors, regulatory bodies and technical support organizations have been preparing for the deployment of various first-of-a-kind projects, along with international organizations who aim to streamline such efforts. The Euratom-funded ELSMOR project contributed to this work by developing the European SMR (E-SMR) dataset, which integrates publicly available information from different SMR designs. This dataset has been used to simulate various station blackout (SBO) and loss-of-coolant accident (LOCA) transients to better understand the safety aspects of design basis accidents in light-water SMRs, with a highlight on the performance of passive safety systems. This paper presents the analysis of an SBO scenario using the Apros code, showcasing the operation of a passive heat removal system, supported by the water wall and hydroaccumulators. The study also examines the interactions of these safety systems. Additionally, the paper discusses stratification processes in the water wall and other factors related to sensitivity analysis and performance optimization.