Multiphysics Analysis of Load Following and Safety Transients for MicroReactors

Abstract

The tools developed within the U.S. Department of Energy (DOE) Office of Nuclear Energy's Nuclear Energy Advanced Modeling and Simulation (NEAMS) program aim at providing highfidelity multiphysics modeling capabilities to support design and licensing of various types of advanced nuclear reactors, including the technologies being developed by U.S. microreactor vendors relying on heat pipe and gas-cooled technologies. In FY-2022, the NEAMS Multiphysics Applications team made significant progress both in demonstrating capabilities applied to microreactor problems, and in supporting NEAMS developers.Three microreactor models were developed through this project to support a demonstration of NEAMS tools capabilities for solving challenging microreactor modeling problems:1-The Heat Pipe MicroReactor (HP-MR) unit-cell and full core models developed in FY-2021 were updated with increased fidelity. This work demonstrates the capability to perform high-fidelity multiphysics load-following and heat pipe cascading failures using coupled Griffin-BISON-Sockeye simulations. Such analysis confirmed the HP-MR concept ability to operate in a flexible way and for the reactor to follow the load, and its ability to avoid heat pipe cascading failure unless designed with high power close to operating failure limits of its heat pipes.2-A Gas-Cooled MicroReactor (GC-MR) assembly model was developed incorporating various modeling challenges expected for horizontal gas-cooled microreactors. A wide range of high-fidelity multiphysics transient analyses were simulated by coupling Griffin/BISON/SAM. These simulations showcased various types of load-following transients (large daily or short frequent power variations) and accidental transients that are specific to GC-MRs (flow blockage, depressurization, etc.). This initial analysis confirms the ability of the GC-MR to withstand such accidental transients without leading to severe accidents. Leveraging this experience, a full core GC-MR was also modelled based on industry design and initial steady-state multiphysics simulations (Griffin/SAM) were completed.3-An initial model of the Kilopower Reactor Using Stirling Technology (KRUSTY) experiment was developed leveraging initial work performed at LANL. This model was significantly updated and improved, and initial steady-state multiphysics simulations (with coupled Griffin/BISON/Sockeye) were completed.

Overview of Virtual Test Bed FY23 Activities

“…The most recent coupling showcases a complete multiphysics simulation including neutronics (Griffin), heat pipe hydraulics (Sockeye), and thermomechanics (Bison). [11] Both steady-state and transient models were uploaded in the VTB. The transient scenario considers a cascading heat pipe failure accident as seen in Figure 17.…”

“…The goal of this pebble bed reactor tutorial is to provide new users of Pronghorn with step-bystep instructions on how to construct gas-cooled pebble reactor thermal-hydraulics models. The tutorial starts out with a channel flow through a porous bed and gradually develops a realistic pebble bed model -a simplified version of the generic PBR (GPBR200) [11] -in about 12 steps. The final exercise is envisioned to tie together the thermal-hydraulics model with the stochastic tools module to perform a sensitivity analysis of maximum fuel temperatures to thermal properties of graphite.…”

NEAMS Advanced Reactor Model Contributions to the NRIC Virtual Test Bed

“…A loss of flow transient model based on this steady state model is also under preparation and will be contributed to the VTB in the near future. Description: The gas-cooled microreactor assembly model (GC-MR) is based on the microreactor design under analysis by the NEAMS Multiphysics Applications microreactor analysis team [24]. The horizontal GC-MR concept was designed at Argonne National Laboratory as a modeling exercise.…”

“…[23,24]. As a modeling exercise, a HP-MR concept was designed at Argonne National Laboratory to gather some of the most pressing modeling challenges faced by the microreactor industry: a) the use of heat pipe technologies to remove the thermal energy; b) the use of TRi-structural ISOtropic (…”

High-fidelity multiphysics load following and accidental transient modeling of microreactors using NEAMS tools: Application of NEAMS codes to perform multiphysics modeling analyses of micro-reactor concepts

“…Finally, the assembly GC-MR model developed in FY-2022 coupling Griffin, BISON and SAM through flow blockage and rod ejection transients was This project builds on years of expertise acquired by different teams and programs [2] [3] [4]. In previous work completed in FY-2022 [4], detailed multiphysics modeling of a heat pipe microreactor (HP-MR) full-core and gas-cooled microreactor (GC-MR) assembly were completed, demonstrating the ability of NEAMS codes to perform multiphysics simulations on two example microreactor concepts. In addition, an initial model for the Kilopower Reactor Using Stirling Technology (KRUSTY) experiment was developed.…”