Perfecting the use of hybrid models in scaling analysis

Highlights: • Use of hybrid models in scaling analysis for the qualification of NPP nodalizations. • The UPC SCUP methodology in scaling analysis: description and applications. • Hybrid calculations to support forthcoming thermal hydraulics experimentation. - Abstract: Different methodologies devoted to qualify Nuclear Power Plant (NPP) system-code nodalizations rely on Kv-scaled calculations as an essential tool for their purpose. In the framework of Power-To-Volume strategy, a Kv-scaled calculation is a simulation in which, defined Integral Test Facility (ITF) test conditions are scaled-up to a NPP nodalization to reproduce the same scenario. In the recent years, the "Universitat Politècnica de Catalunya" (UPC) has developed SCUP, a scaling methodology to qualify NPP models. Following the steps established in UPC's SCUP methodology, Kv-scaled calculations become really useful when two different kinds of them, the so-called "pure scaled" and "hybrid" are properly combined. This paper starts summarizing the most relevant features of UPC's SCUP methodology and its validation process. It also includes important aspects of the usefulness of hybrid calculations in their role of explaining distortions that may appear when a plant simulation is compared with a scaled-up version of test results. Some ideas on the forthcoming uses of hybrid nodalizations are also presented. Among such uses the most significant is the support to test design. Hybrid calculations are used to justify facility modifications. This particular, despite being more specific for future modular ITFs, is illustrated in the paper for minor changes in existing facilities.