Kinetic and Transient Similarity Coefficient Analyses for Coupled Multiphysics Nuclear Transients

Building on the Coupled Adjoint-based Perturbation Theory for dynAmIcs and heat traNsfer (CAPTAIN) multiphysics framework, this work leverages time-dependent, multiphysics sensitivity coefficients to develop a similarity coefficient framework that analyzes shared nuclear and thermal data uncertainties between various systems under transient conditions. To enable this transient simulation similarity assessment, similarity coefficient analyses are extended from the existing correlation coefficients for the effective multiplication factor to kinetic parameters (effective delayed neutron fraction, prompt neutron generation time, and decay constants), which are used to determine the comprehensive similarity between systemwide parameters (time-dependent power, temperature, etc.). With the simplified examples shown in this work, the CAPTAIN similarity coefficient framework shows excellent agreement with direct perturbations and is ready to be verified with higher-fidelity computational codes to enable rapid uncertainty quantification. These computationally efficient, robust uncertainty quantification methods enable the design of steady-state and transient nuclear experiments to capture the impact of relevant uncertainties, thus increasing confidence in the accuracy of modeling and simulation of scenarios that cannot be experimentally validated due to facility limitations, such as rapid reactivity insertions that lead to elevated temperatures. Furthermore, existing nuclear experiment transient data can be leveraged to assess how effectively the uncertainties in smaller-scale experiments can serve to validate uncertainty in conceptual, advanced nuclear reactor systems.