Challenges regarding the Experimental Validation of Thermal-Hydraulic Modeling Tools for a European SMR

Abstract

Interest in SMRs has been growing steadily in recent years, promising market competitiveness through technological optimizations such as simplified passive safety features compared to conventional NPPs. Innovation in passive safety involves deeper studies on underpinning physical phenomena, requiring thermal-hydraulic system codes to support reactor design, safety assessment, and licensing. On the other hand, the predictive capabilities of the safety systems codes need to be proved through the verification and validation process. The present study aims to highlight some of the SMR-relevant phenomena for which existing thermal-hydraulic codes require dedicated validation. This study encompasses a literature review and the analysis of accidental transients with a RELAP5 model of a potential European SMR, characterized by an integral layout and the adoption of plate-type compact heat exchangers for both steam generators and safety heat exchangers. In particular, the investigated phenomena are different phenomena affecting the natural circulation based DHRS for long-term cooling, thermal stratification at the pool’s containment and the influence of the increased amount of internal structures that feature the integral SMR designs. In the case of the DHRS behavior and containment pool cooling, an extensive literature review has revealed the need for a deep experimental approach for validating their analytical models. In addition, the RELAP5 model analysis has shown that inner structures may have certain impact on the accident dynamics.