Nuclear Energy

Meet the RELAP5-3D Team

Meet the researchers and engineers who develop, maintain and advance RELAP5-3D while supporting nuclear reactor analysis, software development and user applications.

IRUG Team Photo containing 5 individuals
Portrait: Konor Frick

Konor Frick

Manager

Portrait: Aaron Epiney

Aaron Epiney

Program Manager

Portrait: George Mesina

Dr. George Mesina

Senior Technical Advisor

Portrait: Connie Stevens

Connie Stevens

Project Operations Lead

Portrait: Jan Vermaak

Dr. Jan Vermaak

Senior Nuclear Multiphysics Engineer

Mauricio Eduardo Tano Retamales

Dr. Mauricio Tano Retamales

Lead Analyst

RELAP5 team portraits: Brandon Cox

Brandon Cox

Engineer & Software Developer

Portrait: Robert Kile

Dr. Robert Kile

Senior Analyst

Portrait: Ethan Lang

Ethan Lang

Developer

Connect with our Team

Questions about our research, capabilities or collaboration opportunities?
Our team is ready to connect you with the right experts and resources at INL.

Contact Us

Program Manager: R53DProgram.Manager@inl.gov

Project Coordinator: R53DProject.Coordinator@inl.gov​

Custodian: R53DCode.Custodian@inl.gov

Developers: R53DCode.Developers@inl.gov

RELAP5-3D Code Architect: R53DCode.Architect@inl.gov

Portrait: Aaron Epiney

Aaron Epiney

Program Manager

Dr. Aaron Epiney is the RELAP5-3D program manager. In this role, he is responsible for identifying and executing strategic RELAP5-3D goals and enabling collaboration with partners around the world.

Prior to this role, he helped develop the reactor analysis code package PHISICS and its coupling to RELAP5-3D, making PHISICS a comprehensive reactor physics package for reactor design and safety analysis.  He also helped develop the modeling and simulation framework FORCE to assess the technical and economic viability and real-time controls of nuclear integrated energy systems that include renewable energy sources like wind or solar. 

Dr. Epiney’s research interests include thermal-hydraulic safety analysis, in-core and system design and modelling, multi-physics simulations using coupled neutronics and thermal-hydraulics, economic performance analysis of power plants in integrated combined heat and power systems, code development as well as uncertainty quantification and propagation.

Portrait: George Mesina

Dr. George Mesina

Senior Technical Advisor

Dr. George Mesina earned his PhD in Applied Mathematics in 1988 from the University of Pittsburgh. He is the Senior Technical Advisor for the RELAP5-3D team and was the RELAP5-3D Code Architect for 25 years. As Code Architect, he rewrote most of the 350,000 lines of code in RELAP5-3D in Fortran90, Fortran 2003, and GNU Fortran 2008. He replaced the time advancement algorithm for accurate code coupling, augmented its ability to couple with other computer programs, significantly reduced its runtime through vector, parallel, and other optimizations, adapted it for nuclear power plant operator training simulators, added other capabilities and features, and improved code robustness and testing.

Portrait: Connie Stevens

Connie Stevens

Project Operations Lead

Connie Stevens serves as the Project Operations Lead where she is responsible for building and strengthening relationships with domestic and international RELAP5-3D license holders and providing program management support to the department manager and RELAP5 team.

Portrait: Jan Vermaak

Dr. Jan Vermaak

Code Architect 

Jan Vermaak joined INL in 2022 as a Senior Nuclear Multiphysics Engineer. He has 17 years of diverse experience in reactor engineering ranging from nuclear safety analysis to managing reactor engineering at the Texas A&M University TRIGA reactor. He holds a bachelor’s degree in mechanical engineering and a master’s and PhD in nuclear engineering. Jan’s current work is focused on code development and analysis in the fields of neutronics, computational fluid dynamics (CFD), thermal-hydraulics, mechanical stress, and nuclear fuel performance. He is currently the RELAP5-3D Code Architect.

Mauricio Eduardo Tano Retamales

Mauricio Tano Retamales

Lead Analyst 

Dr. Mauricio Tano-Retamales is a Staff Scientist in the Thermal Fluids Systems and Methods Analysis group at Idaho National Laboratory (INL). He currently leads efforts for high- and intermediate-fidelity modeling and simulation of multiphysics phenomena in advanced nuclear reactors, which include the development of models coupling between neutronics, thermal-hydraulics, thermomechanics, salt chemistry, and corrosion. Additionally, Dr. Tano-Retamales is an active developer of INL’s coarse-mesh computational fluid dynamics (CFD) code Pronghorn and INL’s MOOSE-based subchannel code for advanced nuclear reactors. Dr. Tano-Retamales leads the coupling between RELAP5-3D and CFD codes and performs nuclear reactor analyses using RELAP5-3D. 

RELAP5 team portraits: Brandon Cox

Brandon Cox

Code Custodian

Brandon Cox is an engineer and software developer in the Thermal Fluid System Methods & Analysis Department at Idaho National Laboratory. In 2019 he graduated from Brigham Young University with a B.S. in Chemical Engineering. He has experience developing engineering software and computational fluid dynamics (CFD). He is currently a RELAP5-3D Developer and Analyst. In this capacity, he participates in various RELAP5-3D updates and development activities and corrects user errors. He also performs engineering calculations and analyses using RELAP5-3D and CFD. He has experience using Python, Fortran, Linux, and OpenFOAM. Outside of work he enjoys spending time with family and many outdoor activities including hiking, hunting, fishing, and photography.

 

Portrait: Robert Kile

Dr. Robert Kile

Senior Analyst

Dr. Robert Kile is a nuclear engineer at Idaho National Laboratory and the thermal hydraulics lead for the MARVEL microreactor project. His work focuses on thermal hydraulics, multiphysics and safety analysis for advanced reactors.

Portrait: Ethan Lang

Ethan Lang

Developer

Ethan Lang joined Idaho National Laboratory in 2025 as a nuclear engineer and RELAP5-3D code developer. He holds a bachelor’s degree in nuclear engineering from Idaho State University. He leads verification and validation (V&V) and continuous integration (CI) activities for RELAP5-3D, maintaining the associated testing and development infrastructure. He also supports thermal-hydraulics, computational fluid dynamics and neutronics analyses.