Research Areas and Descriptors

General experience and professional interests include development of advanced numerical methods and algorithms for fuel depletion and thermal hydraulic coupled Monte Carlo codes. In addition, a special interest is to implement the developed methodologies in analysis of advanced reactor systems. Since, advanced systems usually aim to maximize a certain performance (e.g. fuel utilization), design optimization techniques are needed and are part of my research as well.


  • B.Sc., Nuclear Engineering, Ben-Gurion University of the Negev, 2008
  • M.Sc., Nuclear Engineering, Ben-Gurion University of the Negev, 2010
  • Ph.D., Nuclear Engineering, Ben-Gurion University of the Negev, 2013


Dr. Dan Kotlyar is an Assistant Professor in the Nuclear and Radiological Engineering, G.W.W. School of Mechanical Engineering. He received his B.Sc. in Engineering in 2008, MSc in Nuclear Engineering in 2010, and PhD in Nuclear Engineering in 2013 from Ben-Gurion University, Israel. In 2014, he joined the University of Cambridge as a Research Associate in the Engineering Design Center. In 2014, he was elected as a Research Fellow at Jesus College. He is the recipient of the NRC Faculty Development Fellowship. Dr. Kotlyar’s research interests include development of numerical methods and algorithms for coupled Monte Carlo, fuel depletion and thermal hydraulic codes. In particular, he specializes in applying these methods to the analysis of advanced reactor systems. Dr. Kotlyar’s research also focuses on optimizing the performance of various fuel cycles in terms of fuel utilization, proliferation, and cost. Dr. Kotlyar profoundly believes in education through research and thus integrates practical reactor system design into his lectures.  


Dr. Kotlyar has established a sustainable research program in the field of advanced nuclear reactor design and multi-physics analysis. His Computational Reactor Engineering Laboratory (CoRE) focuses on developing the next generation production tools as well as designing advanced and low cost nuclear energy systems. Dr. Kotlyar’s research aims to bridge the theoretical reactor physics with the practical aspects of nuclear engineering and design. His research relies on the following thrust areas:

  • Thrust 1: Advanced Reactor Physics Modeling Tools, which are necessary to understand the operational limits and assess fuel performance, in terms of burnup and thermal hydraulic reliability, and the associated safety margins.
  • Thrust 2: Design of Advanced Nuclear Systemsfor both terrestrial and special purpose applications. Dr. Kotlyar’s research in this area includes the design of various reactor types and fuel cycle options to address the issues of the current fuel cycles most efficiently. This part of his research also focuses on concerns about nuclear proliferation, resource utilization, and waste repository sizing. 

Thrust 1: Advanced Reactor Physics Modeling Tools

The unique characteristics of different advanced reactor systems have led to the conclusion that conventional techniques commonly used to model Light Water Reactors (LWRs) are no longer valid. These innovative nuclear systems require new tools that will be capable of accurate and efficient modeling. Dr. Kotlyar’s group focuses on developing tools to model universal reactors.

Monte Carlo (MC) methods are particularly well suited for modeling complicated 3D problems, especially those that cannot be reliably modelled with existing deterministic methods. MC codes have been available for decades; however, their applicability was limited due to prohibitively high computational power requirements. Recent advances in computer technology and parallel processing methods are gradually changing the reactor analysis environment and MC codes are increasingly used as a standard calculation tool in reactor calculations.  It is even becoming practical to consider MC methods with multi-physics coupling (i.e., depletion and thermal-hydraulics) to expand the range of applications even further. During the past years, Dr. Kotlyar has been developing novel and efficient methods to be implemented in reactor simulation physics packages. 

Thrust 2: Design of Advanced Nuclear Systems

Recent research endeavors include the development of a nuclear thermal propulsion engine and a directly-coupled thermophotovoltaic microreactor.

Nuclear thermal propulsion(NTP) is a potential technology for future crewed missions to Mars due to its high thrust, and high specific impulse. This technology is expected to enable reduced interplanetary travel times, which could increase the crew's safety by reducing exposure to cosmic radiation and other hazards of deep space travel. BWX Technologies, Inc. (BWXT) is working with NASA to develop critical reactor fuel technologies and mature the design of a low-enriched uranium engine. Dr. Dan Kotlyar’s research group is funded by BWXT to support further research in NTP technology by developing a computational multi-physics framework that will allow a better understanding of the operational limits, reliability, and associated safety margins of the engine.

A Directly-Coupled Reactor TPVProject focuses on developing a nuclear core that incorporates advanced, high efficiency thermophotovoltaics as a directly coupled heat engine and to demonstrate that said design can meet safety and regulatory requirements while being economically competitive.


Selected Honors and Awards

  • 2019 AIAA Aerospace Power Systems Best Student Paper Competition Award “Hydrogen Loss Effects on Mircoreactors for Space and Planetary Nuclear Power Production” (AIAA 2019-4452).

  • 2019 Spring Capstone Expo, Best senior design project in Nuclear and Radiological Engineering- NTP: Fueling the Future

  • Vedant Mehta, a Ph.D. student in Nuclear Engineering at the Georgia Institute of Technology, has been awarded a First Place prize in the Innovations in Nuclear Technology R&D Awards sponsored by the U.S. Department of Energy, Office of Nuclear Technology R&D (2019).

  • M&C2017 Best Student Paper Competition (3rd place) presented to Andrew Johnson in recognition of the technical quality of the paper titles: SERPENT-TOOLS: A Python Package for Expediting Analysis with Serpent Data.

  • ANS Best Student Poster Award (3rd place). J.T. Gates, A. Denig, R. Ahmed, V. Mehta, D. Kotlyar. “Design of a Nuclear Thermal Rocket with Low-enriched Cermet fuel”.  ANS meeting, Washington, DC, USA, October 29- November 2, 2017.

Representative Publications

  • V.K. Mehta, S.C. Vogel, A.P. Shivprasad, E.P. Luther, D.A. Andersson, D.V. Rao, D. Kotlyar, B. Clausen, M.W.D. Cooper, 2021. “A Density Functional Theory and Neutron Diffraction Study of the Ambient Condition Properties of Sub-Stoichiometric Yttrium Hydride,” Journal of Nuclear Materials, Journal of Nuclear Material, 547, 152837.

  • A. Johnson, D. Kotlyar, 2021. “Hybrid Depletion Framework Using Mixed-Fidelity Transport Solutions and Substeps,” Annals of Nuclear Energy, 155, 108120.

  • J. Wang, D. Kotlyar, 2021. “High-Resolution Thermal Analysis of Nuclear Thermal Propulsion Fuel Element Using OpenFOAM,” Nuclear Design and Engineering, 372, 110957.

  • V.K. Mehta, M.W.D. Cooper, R.B. Wilkerson, D. Kotlyar, D.V. Rao, S.C. Vogel, 2021. “Evaluation of Yttrium Hydride (δ-YH2-x) Thermal Neutron Scattering Laws and Thermophysical Properties,” Nuclear Science and Engineering,

  • M. Krecicki, D. Kotlyar, 2020. “Low Enriched Nuclear Thermal Propulsion Neutronic, Thermal Hydraulic, and System Design Space Analysis,” Nuclear Design and Engineering, 363, 110605.

  • A. Johnson, D. Kotlyar, 2020. “serpentTools: A Python Package for Expediting Analysis with Serpent,” Nuclear Science and Engineering, 194(11), 1016-1024.

  • N. Kaffezakis, S. Terlizzi, C. Smith, A. S. Erickson, S. K. Yee, D. Kotlyar, 2020. “High Temperature Ultra-Small Modular Reactor: Pre-conceptual Design,” Annals of Nuclear Energy, 141, 1-13.

  • S. Terlizzi, D. Kotlyar, 2020. “A simple FFT-based prediction method of macroscopic cross-sections’ spatial response to TH perturbations: theory and first results”, Nuclear Science and Engineering, In print. DOI: 10.1080/00295639.2019.1698239

  • N. Kaffezakis, D. Kotlyar, 2020. “Fuel Cycle Analysis of Novel Assembly Design for Thorium-Uranium Ceramic Fueled Thermal, High Conversion Reactor,” Nuclear Technology, 206, 48-72. DOI: 10.1080/00295450.2019.1616475

  • A. E. Johnson, D. Kotlyar, 2019. “A Transport-free Method for Predicting the Post-depletion Spatial Neutron Flux Distribution,” Nuclear Science and Engineering, 194(2), 120-137 DOI: 10.1080/00295639.2019.1661171.

  • S. Terlizzi, D. Kotlyar, 2019. “Fission Matrix Domain Decomposition Method for Criticality Calculations: Theory and Proof-of-Concept”, Nuclear Science and Engineering, 193, 948-965.

  • G. Pereira, A. E. Johnson, Y. Bilodid, E. Fridman, D. Kotlyar, 2019. “Applying the Serpent-DYN3D Code Sequence for the Decay Heat Analysis of Metallic Fuel Sodium Fast Reactor,” Annals of Nuclear Energy, 125, 291-306.

  • V. Mehta, D. Kotlyar, 2019. “Core Analysis of spectral shift operated SmAHTR,” Annals of Nuclear Energy, 123, 46-58.

  • Y. Bilodid, E. Fridman, D. Kotlyar, E. Shwageraus, 2018. “Explicit decay heat calculation in the nodal diffusion code DYN3D,” Annals of Nuclear Energy, 121, 374-381.

  • J.T. Gates, A. Denig, R. Ahmed, V. Mehta, D. Kotlyar, 2018. “Low-enriched Cermet-based fuel options for a nuclear thermal propulsion engine,” Design of Nuclear Engineering, 331, 313-330.

  • D. Kotlyar, G.T.P Parks, E. Shwageraus, 2017. “Screening the design space for optimized plutonium incineration performance in the thorium-based I2S-LWR,” Annals of Nuclear Energy, 101, 237-249.

  • B.A. Lindley, D. Kotlyar, G.T. Parks, J.N. Lillington, B. Petrovic, 2016. “Reactor physics modelling of accident tolerant fuel for LWRs using ANSWERS codes,” EPJ Nuclear Sci. Technol. 2, 14.

  • Y. Bilodid, D. Kotlyar, E. Shwageraus , E. Fridman, S. Kliem,  2016. “Hybrid microscopic depletion model in nodal code DYN3D,” Annals of Nuclear Energy, 92, 397-406.

  • D. Kotlyar, E. Shwageraus, 2016. “Sub-step Methodology for Coupled Monte Carlo Depletion and Thermal Hydraulic Codes,” Annals of Nuclear Energy, 96, 61-75.

  • L.W.G. Morgan, D. Kotlyar, 2015. “Weighted-Delta-Tracking for Monte Carlo Particle Transport,” Annals of Nuclear Energy, 85, 1184-1188.

  • Y. Bilodid, D. Kotlyar, M.  Margulis, E. Fridman, E. Shwageraus, 2015. “Spectral History Model in DYN3D: Verification against coupled Monte-Carlo Thermal-Hydraulic Code BGCore,” Annals of Nuclear Energy, 81, 34-40.

  • D. Kotlyar, E. Shwageraus, 2014. “Numerically stable Monte Carlo-Burnup-Thermal Hydraulic Coupling Schemes,” Annals of Nuclear Energy, 63, 371-381.

  • J. Dufek, D. Kotlyar, E. Shwageraus, J. Leppänen, 2013. “Numerical Stability of the Predictor-Corrector Method in Monte Carlo Burnup Calculations of Critical Reactors,” Annals of Nuclear Energy, 56, 34-38.

  • D. Kotlyar, Y. Shaposhnik, E. Fridman, E. Shwageraus, 2011. “Coupled neutronic thermo-hydarulic analysis of full PWR core with Monte-Carlo based BGCore system,” Nuclear Engineering and Design, 241, 3777-3786.