April Novak

• PhD
• Assistant Professor at University of Illinois Urbana-Champaign

Pebble bed High Temperature Reactors (HTRs) are characterized by many advantageous design features, such as excellent passive heat removal in accidents, large margins to fuel failure, and online refueling potential. However, a significant challenge in the core modeling of pebble bed reactors is the complex fuel-coolant structure. This paper present...

The complex core geometry of Pebble Bed Reactors (PBRs) necessitates multiscale techniques for accurate prediction of temperature and flow distributions. This paper presents the multiscale Thermal-Hydraulic (T/H) models used in the Pronghorn PBR simulation tool with application to the Mark-1 Pebble Bed Fluoride-Salt Cooled High-Temperature Reactor...

Cardinal is a MOOSE application that couples OpenMC Monte Carlo transport and NekRS computational fluid dynamics to the MOOSE framework, closing the neutronics and thermal-fluid gaps in conducting tightly-coupled, high-resolution multiscale and multiphysics analyses. By leveraging MOOSE's interfaces for wrapping external codes, Cardinal overcomes m...

Worldwide, there is significant interest in the development of high-fidelity multiphysics tools for nuclear energy systems. Due to its convenient multi-application execution and mesh transfers, the Multiphysics Object-Oriented Simulation Environment (MOOSE) is becoming widely-adopted as a platform for coupling different physics codes. In 2022, Argo...

TRistructural ISOtropic (TRISO) fuel particles are candidate fuels for High-Temperature Gas cooled Reactors (HTGRs) and many other advanced fission concepts due to their inherent safety features and high-temperature operation. Multiphysics modelling of a fuel compact with hundreds of thousands of TRISO particles (or more) is computationally challen...

Multiphysics interactions between radiation transport and thermal-fluids play an important role in fission reactor design. Progress and challenges in Monte Carlo-based multiphysics modeling are reviewed, with emphasis on software design, data transfers, and iterative solution. This paper then introduces Cardinal, an innovative approach to high-fide...

Fluid-Structure Interaction (FSI) is a significant phenomenon in most nuclear reactors, causing effects such as Flow-Induced Vibration (FIV) and thermally-driven Core-Radial Expansion (CRE). We demonstrate that Cardinal, an open-source coupling of NekRS and OpenMC to MOOSE, can be used for modelling FSI by coupling the Tensor Mechanics Module from...

Interassembly flow in Sodium Fast Reactors (SFRs) represents a bypass flow path exterior to the fuel assembly ducts. Heat transferred across this thin laminar-transitional gap is an important component of core radial expansion, where the coupling between thermal-fluids, neutronics, and solid mechanics results in time-dependent duct bowing. These ge...

The development of multiphysics, high fidelity modeling and simulations tools is important for nuclear reactor design and safety analyses. However, one challenge is the verification of numerical schemes developed to solve nonlinear, coupled problems, such as coupled neutronics and thermal-hydraulics physics. A lack of high-quality experimental data...

Cardinal is a multiphysics software tool that couples OpenMC Monte Carlo transport and NekRS Computational Fluid Dynamics (CFD) to the Multiphysics Object-Oriented Simulation Environment (MOOSE). This work verifies Cardinal for coupled neutron transport and heat conduction using a 1-D analytical solution from previous work by the Naval Nuclear Labo...

The Griffin reactor physics code, MOOSE heat conduction module, and NekRS (Cardinal) computational fluid dynamics codes are coupled using the MOOSE framework to develop a high-fidelity multi-physics modeling capability for hot channel factor calculation. The coupled simulation is driven by Griffin, using the new multiphysics coupling capability of...

Cardinal is an open-source application that couples OpenMC Monte Carlo transport and NekRS computational fluid dynamics (CFD) to the Multiphysics Object-Oriented Simulation Environment (MOOSE), closing neutronics and thermal-fluid gaps in conducting high-resolution multiscale and multi-physics analyses of nuclear systems. We first provide a brief i...

With the next generation of nuclear reactors under development, modeling and simulation tools are being developed by the U.S. Department of Energy to support their design, licensing, and future operation. Mirroring the physical test beds currently under construction (i.e., Demonstration and Operation of Microreactor Experiments, known as DOME, and...

The last 2 years have been a period of unprecedented growth for the MOOSE community and the software itself. The number of monthly visitors to the website has grown from just over 3,000 to now averaging 5,000. In addition, over 1,800 pull requests have been merged since the beginning of 2020, and the new discussions forum has averaged 600 unique vi...

Cardinal is an open-source application that couples OpenMC Monte Carlo transport and NekRS computational fluid dynamics to the Multiphysics Object-Oriented Simulation Environment (MOOSE), closing neutronics and thermal-fluid gaps in conducting high-resolution multiscale and multiphysics analyses of nuclear systems. We provide an introduction to Car...

This paper introduces a new application, Cardinal, that couples OpenMC Monte Carlo transport and NekRS computational fluid dynamics to the MOOSE framework, closing the neutronics and thermal-fluid gaps in conducting tightly-coupled, high-resolution multiscale and multiphysics analyses of nuclear systems. This coupling specifically aims to address a...

Nek5000/RS is a highly-performant open-source spectral element code for simulation of incompressible and low-Mach fluid flow, heat transfer, and combustion with a particular focus on turbulent flows in complex domains. It is based on high-order discretizations that realize the same (or lower) cost per gridpoint as traditional low-order methods. Sta...

Pronghorn is a coarse-mesh, intermediate-fidelity, and multidimensional thermal-hydraulics code developed by the Idaho National Laboratory (INL). While the friction-dominated equations ("legacy Pronghorn") are expected to work reasonably well in the bed of a pebble bed reactor, its applications to open flow regions, and thus other reactor types, is...

This paper presents an overview of Pronghorn, a multiscale thermal-hydraulic (T/H) application developed by Idaho National Laboratory and the University of California, Berkeley. Pronghorn, built on the open-source finite element Multiphysics Object-Oriented Simulation Environment (MOOSE), leverages state-of-the-art physical models, numerical method...

The complex core geometry of Pebble Bed Reactors (PBRs) necessitates multiscale techniques for fast-turnaround design and analysis. This paper describes the multiscale model implemented in the Pronghorn PBR simulation tool and demonstrates application to steady-state analysis of the Mark-1 Pebble Bed Fluoride-Salt-Cooled High-Temperature Reactor (P...

While the literature has numerous examples of Monte Carlo and computational fluid dynamics (CFD) coupling, most are hard-wired codes intended primarily for research rather than as standalone, general-purpose codes. In this work, we describe an open source application, ENRICO, that allows coupled neutronic and thermal-hydraulic simulations between m...

High temperature gas cooled reactors (HTGR) are a candidate for timely Gen-IV reactor technology deployment because of high technology readiness and walk-away safety. Among HTGRs, pebble bed reactors (PBRs) have attractive features such as low excess reactivity and online refueling. Pebble bed reactors pose unique challenges to analysts and reactor...

While the literature has numerous examples of Monte Carlo (MC) and computational fluid dynamics (CFD) coupling, most are hardwired codes intended primarily for research rather than as stand-alone, general-purpose applications. In this work, we describe an open source application, the Exascale Nuclear Reactor Investigative COde (ENRICO), which enabl...

With the recent development of advanced numerical algorithms, software design, and low-cost high-performance computer hardware, reliance on coupled multiphysics to predict the behavior of complex physical systems is beginning to become standard practice. This is especially true in nuclear energy applications where strong nonlinear interdependencies...

Pebble bed reactors (PBRs) are expected to display excellent heat removal characteristics due to graphite's capability for storing and transferring heat, the high failure temperatures of particle fuel, and the low power densities involved. However, a major challenge associated with the modeling of PBRs is the complex fuel-coolant structure in the c...

While the literature has numerous examples of Monte Carlo and computational fluid dy- namics (CFD) coupling, most are hard-wired codes intended primarily for research rather than as standalone, general-purpose codes. In this work, we describe an open source application, ENRICO, that allows coupled neutronic and thermal-hydraulic simulations betwee...

High temperature gas cooled reactors (HTGR) are a candidate for timely Gen-IV reactor technology deployment because of high technology readiness and walk-away safety. Among HTGRs, pebble bed reactors (PBRs) have attractive features such as low excess reactivity and online refueling. Pebble bed reactors pose unique challenges to analysts and reactor...

A significant challenge in the core modeling of pebble bed reactors (PBRs) is the complex fuel-coolant structure. At the expense of approximating local flow and heat transfer effects, porous media models can provide medium-fidelity predictions of complicated thermal-fluid systems with significantly less computational cost than high-fidelity Computa...

This paper presents a Monte Carlo-computational fluid dynamics coupling of OpenMC and Nek5000 within the MOOSE framework. This coupling specifically aims to address and overcome challenges encountered in earlier coupling works such as file-based communication and overly restrictive one-to-one mesh mappings between the codes. In addition, coupling w...

A high-energy diffraction technique is presented that uses synchrotron X-rays to characterize the in situ deformation response of pressurized creep tubes at elevated temperature. In addition to the X-ray diffraction measurement, the technique allows the macroscopic creep strain to be measured simultaneously during X-ray exposure. We demonstrated th...