Scale analysis using FSA methodology for single-phase natural circulation in a simplified RCCS

Abstract

Improving the safety and reliability of innovative Generation IV nuclear reactors can be achieved by adopting passive safety systems for accident prevention. These systems rely only on physical phenomena such as natural circulation and eliminate the need for an external response in the event of an accident. While passive natural circulation systems are widely used in modern nuclear reactors, their complexity and high thermal power output make them difficult to simulate at full scale. One solution is to study reduced-scale systems that are more feasible for experimental investigation. The correct scale procedure is essential to ensure that the results of these systems represent those expected in a real facility. This article describes a small-scale, single-phase water natural circulation circuit representing a simplified reactor cavity cooling system. The standard scale method is combined with an innovative fractional scaling analysis to determine the conditions and similarity parameters for a test facility. This analysis outlines the necessary simplifications required to achieve a certain similarity between natural circulation systems in the transient regime. The methodology is applied to two studies from the literature, demonstrating the feasibility of comparing different passive heat removal systems.