NE Seminar: “Demonstration of Utilization of High to Low (Hi2Lo) Fidelity Information Schemes within Advanced Multi-Physics Modeling and Simulation Frameworks”

Date(s) - 04/13/2023
1:55 pm - 2:55 pm

Rhines 125


Kostadin Ivanov, Ph.D.

Professor and Department Head, Department of Nuclear Engineering
North Carolina State University

Dr. Kostadin Ivanov earned his Ph.D. degree in reactor physics from the Bulgarian Academy of Sciences in 1990. Prior to joining the North Carolina State University (NCSU) in 2015, he held research and academic positions at the Pennsylvania State University (PSU), Karlsruhe Institute of Technology (KIT) and Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany; Institute of Nuclear Research and Nuclear Energy (INRNE) in Sofia; Technical University (TU) of Sofia; and Kozloduy Nuclear Power Plants (KNPP) in Bulgaria.

At PSU Dr. Ivanov established Reactor Dynamics and Fuel Modeling Group (RDFMG) in order to address the current demands for more accurate and efficient analyses, which directly relate to the safety and economic performance of current and next generations of nuclear systems; in 2015 he reestablished RDFMG at NCSU.

The research performed by RDFMG is in the area of developing methods and computer codes for multi-dimensional reactor core analysis. These developments include computational methods, numerical algorithms and iterative techniques, nuclear fuel management and reloading optimization techniques, reactor kinetics and core dynamics methods, cross-section generation and modeling algorithms for multi-dimensional steady-state and transient reactor calculations and coupling three-dimensional (3-D) kinetics models with thermal-hydraulic codes.

He has also led the development of multi-dimensional neutronics, in-core fuel management and coupled 3-D kinetics/thermal-hydraulic computer code benchmarks, multi-dimensional reactor transient and safety analysis methodologies as well as integrated analysis of safety-related parameters, system transient modeling of power plants, and in-core fuel management analyses. The effort has led to establishing his group, initially at PSU and currently at NCSU, as an international center for qualification of coupled 3-D kinetics/thermal-hydraulics codes.


The modeling and simulation (M&S) of nuclear reactors is continuously improving beyond the traditional multi-physics coupling tools. Novel multi-physics tools have recently been developed in US and abroad. These tools, although have impressive capabilities, are very computationally expensive, which limits their applicability to providing reference solutions.

This is even more prominent in routine design and safety analyses and uncertainty quantification studies, and this is the reason why traditional multi-physics tools are mainly used. There is thus a need for High to Low (Hi2lo) model fidelity information approaches that will expand the usage of novel tools to a larger spectrum of applications and at the same time improve the predictive capabilities of traditional multi-physics tools at a reasonable computational cost.

In this project, consistent Hi2Lo approaches between the different modeling fidelities and for three physics domains are developed: reactor physics, thermal-hydraulics and fuel performance. These different Hi2Lo approaches are integrated into a multi-physics framework. The developed framework utilizes high-fidelity tools to inform the conventional tools and is demonstrated on established benchmarks. Uncertainty quantification capabilities are included in the multi-physics framework that propagates consistently the uncertainties through the Hi2Lo approaches and allow the computations of sensitivities between multi-physics outputs of interest and the High Fidelity (HiFi) inputs.

The reactor physics Hi2Lo approach involves an iterative scheme between the high-fidelity neutron transport heterogeneous and traditional nodal solutions. The numerical results show that Hi2Lo scheme outperforms the conventional two-step approach result in terms of accuracy.

The thermal-hydraulics Hi2Lo approach uses high-fidelity detailed models of the various spacer grids to calculate the friction velocity and the transverse and axial heat flux. The obtained high-fidelity results are used to calibrate the friction factors and the temperature mixing coefficient within a subchannel code.

The fuel performance Hi2Lo approach identifies as the gap conductance as the quantity of interest to be informed between the high and low-fidelity codes.

The UTAB (Uncertain TABular) method is developed that extends the traditional two- dimensional (2D) gap conductance tabulated methods to include high-fidelity uncertainties and to allow for an additional parameter that accounts for historical effects. The UTAB results indicate a significant improvement in gap conductance prediction and a moderate improvement in the fuel temperature prediction.

Finally, all single-physics Hi2Lo developments are integrated into a flexible multi-physics framework. The framework is successfully demonstrated on a benchmark core by performing an uncertainty quantification study. The obtained results involve the uncertainty propagation to pin-by-pin fields and the computation of correlation coefficients between these fields and the high-fidelity uncertain inputs.