Fractional Scaling Analysis - Methodology application to LSTF facility and a PWR for a small break LOCA transient

Scaling methodologies quantitatively assess the behavioral differences between small-scale experimental systems and full-size commercial plants during specific accidental scenarios. These methods guide the design and operation of experimental facilities to reliably replicate larger systems, ensuring safety systems are developed and accident sequences predicted accurately. Early integration of scaling calculations into the experimental design phase allows for reliable extrapolation of results to commercial plants. This study applied Fractional Scaling Analysis (FSA) to compare a scaled LSTF experimental facility and a full-size Siemens-KWU reactor during a Small Break LOCA in the hot leg (ROSA 1.2 test). The transient was divided into five phases, each analyzed for thermal-hydraulic similarity. Despite minor scaling distortions, the results showed strong consistency in pressure and level evolution, confirming good scalability between the facilities for this scenario. FSA demonstrated its versatility, allowing data from one type of facility (e.g., Westinghouse-type) to inform analyses for plants of a different type (e.g., Siemens-KWU). A new method provided a "normalized scalability" metric for the entire transient, with figures of merit for pressure and level reaching ∼0.3 (far below 1), indicating good scalability. Non-conservative distortions were minimal (<0.16), enabling quantitative comparisons across plants and transients for enhanced safety and design validation.