The use of System Codes for Scaling Analysis and the use of Scaling Tools for the Analysis of Code Predictions

Abstract

Both system codes and experiments are used for simulating nuclear reactor thermal-hydraulic transients in safety analysis. System codes model the whole reactor and must demonstrate their quality by extensive validation against experimental data, which cover the important phenomena. Integral effect test facilities intend to simulate reactor thermal-hydraulic behaviour in reduced scale conditions. Advanced scaling methods exist to define how to respect the dominant phenomena in a scaled experiment and to evaluate distortions. They perform a similarity analysis applied to equations governing the evolution of important parameters at system, component and local levels. They require an evaluation of the order of magnitude of every term of these equations. Today, system codes have reached a good maturity and reliability, and one defines in this work the conditions for a proper use of codes for evaluating terms of the equations used in scaling analyses. It appears that scaling tools at system level can help in the analysis of code predictions, in the establishment of a structured PIRT and for identifying the sources of code predictions differences with experimental data. This paper presents the lessons learnt from a combined use of scaling methods, scaling tools, system codes and integral effect tests data. Some conclusions and recommendations are drawn on the merits of the various scaling methods, on the selection of the equations to be used in the scaling analyses, on the various methods for estimating terms of the selected equations, and on the acceptability limits for the distortions. The applications refer to some PWR LOCA analyses.

Advances in Integral and Separate Effects Experiments for Water-Cooled Small Modular Reactors

“…However, to prove the conceptual design needs supportive computer code analysis and experiments. A new reactor design and development process requires component-level and system-level experiments and analysis [3]. Integral effects test (IET) and separate effects test (SET) facilities are used to perform various reactor system transient and accidental experiments for computer code validation and qualification [4][5].…”

“…Over the past 50 years, several standard IET facilities have been developed worldwide to design and license different reactor designs. These include the SemiScale and Loss of Fluid Test (LOFT) at Idaho National Laboratory (INL), the Advanced Plant Experiment (APEX) at Oregon State University (OSU), the Purdue University Multi-Dimensional Integral Test Assembly (PUMA), and the Full Length Emergency Cooling and Heat Transfer (FLECHT) system in the U.S.; the Rig of Safety Assessment (ROSA)/Large Scale Test Facility (LSTF) and Cylindrical Core Test Facility (CCTF) of a pressurized water reactor (PWR) in Japan; the Simulatore per Esperienze di Sicurezza (SPES) in Italy; the Boucle d'Etudes Thermohydrauliques Système (BETHSY) in France; the Parallel Channel Test Loop (PKL) facility in Germany; the Advanced Thermal-hydraulic Test Loop for Accident Simulation (ATLAS) in Korea; and the Advanced Core-cooling Mechanism Experiment (ACME) in China [3][4][10][11][12]. These programs and facilities were developed for targeted commercial light water reactors (LWRs), like PWRs and boiling water reactors (BWRs), to examine reactor safety issues related to plant response during a loss-of-coolant accident (LOCA) and operational transient.…”