Using genetic algorithms to calibrate the user-defined parameters of IIST model for SBLOCA analysis

The thermal-hydraulic system codes, i.e., TRACE, have been designed to predict, investigate, and simulate nuclear reactor transients and accidents. Implementing relevant correlations, these codes are able to represent important phenomena such as two-phase flow, critical flow, and countercurrent flow. Furthermore, the thermal-hydraulic system codes permit users to modify the coefficients corresponding to the correlations, providing a certain degree of freedom to calibrate the numerical results, i.e., peak cladding temperature. These coefficients are known as user-defined parameters (UDPs). Practically, defining a series of UDPs is complex, highly relied on expert opinions and engineering experiences. This study proposes another approach - the genetic algorithms (GAs), providing rigorous procedures and mitigating human judgments and mistakes, to calibrate the UDPs of important correlations for a 2% small break loss of coolant accident (SBLOCA). The TRACE IIST model was employed as a case study to demonstrate the capability of GAs. The UDPs were evolved by GAs to reduce the deviations between TRACE results and IIST experimental data.