Nuclear Science and Engineering

Griffin

A MOOSE-based Reactor Physics Analysis Tool for Advanced Nuclear Reactors

Griffin is a reactor physics code for multiphysics simulation of advanced nuclear reactors, built on the Multiphysics Object-Oriented Simulation Environment (MOOSE) and jointly developed by Argonne National Laboratory and Idaho National Laboratory under the DOE-NE NEAMS program. It is designed for steady-state and transient coupled neutronics calculations, solving the Boltzmann transport equation in fully heterogeneous and homogeneous geometries using finite element spatial discretization with diffusion, PN, and SN methods. Griffin provides a broad set of reactor analysis capabilities, including traditional two-step and on-the-fly multigroup cross-section generation, isotopic depletion with few hundreds to thousands of tracked nuclides, decay-heat, fuel management schemes, and perturbation-based sensitivity and uncertainty analysis. 

Griffin’s modular architecture includes functionality for multigroup cross-section preparation and management, neutron transport, and user-oriented reactor analysis. It has been applied to a broad range of advanced reactor concepts, including pebble-bed and prismatic high-temperature reactors (HTRs), molten-salt reactors (MSRs), fast reactors (FRs), microreactors, nuclear thermal propulsion (NTP) systems, and experimental facilities. Developed under the MOOSE software quality assurance process with requirements consistent with NQA-1, Griffin has been adopted into the reactor analysis system (BlueCrab) for the U.S. Nuclear Regulatory Commission and is used by industry, universities, and national laboratories.

Fast Reactor with cross sections generated with the built-in MC2-3 workflow

Cross section generation in Griffin is streamlined using MC2-3 for fully homogeneous, duct-heterogeneous, and ring-heterogeneous core configurations, with pin power reconstruction enabling pin-resolved solutions. 

ABTR core configuration, power distribution (left), and reconstructed pin powers (right)
Pebble-bed HTR with online cross section generation

A fuel self-shielding method applicable to both TRISO and annular compact or spherical shell fuel zone enables modeling of PBR and FHR pebbles, with full support for running-in calculations including depletion and online self-shielding. 

PBR configuration (left), Gas-cooled PBR (power and %error from Serpent) (right)
Prismatic HTR (microreactor) with online cross section generation

Prismatic-type microreactor cores consisting of TRISO compacts with 19.95 at% UCO fuel at a 40% TRISO packing fraction are simulated using online cross section generation, demonstrating good agreement with Serpent Monte Carlo solutions, within 0.7% RMS pin power, 190 pcm reactivity, and 1.4% control drum worth. 

PBR configuration, gas-cooled HTR (power and %error from Serpent) (left), heat-pipe-cooled HTR (power and %error from Serpent) (right)
Molten Salt Reactor

Delayed neutron drift due to fuel flow is accounted for in simulations of MCRE, MSFR, LOTUS-MSR, etc. through coupling with other MOOSE-based physics tools.

Power distributions of MSFR (left) and Lotus-MSR (right)

For code questions or licensing, please contact Argonne Codes at necodes@​anl.​gov or NCRC at https://​inl​.gov/ncrc.

References

  1. Griffin Theory and User Manual
  2. C. H. Lee, J. Ortensi, et al., ​“Griffin Software Development Plan,” ANL/NSE-21/23, INL/EXT-21-63185, June 2021.
  3. Y. Wang, Z. Prince, H. Park, et al., ​“Griffin: A MOOSE-based reactor physics application for multiphysics simulation of advanced nuclear reactors,” Ann. Nucl. Eng., 211, 2025.
  4. S. Jeon, C. H. Lee, Y. Wang, and H. Park, ​“Implementation of Perturbation Theory and Sensitivity Capabilities in Griffin,” ANS/NSE-25/73, INL/RPT-25-88017, September 2025.
  5. C. H. Lee, S. M. Park, S. Kumar, N. Stauff, ​“Simulation of the Sodium-cooled Fast Reactor Benchmark Cores Using MC2-3/Griffin,” ANS Annual meeting, Indianapolis, IN, June 11-14, 2023.
  6. S. Kumar, C. H. Lee, V. Laboure, Y. Jung, S. Terlizzi, Y. Wang, J. Ortensi, ​“Transient Mulitphysics Simulations with Pin Power Reconstruction in Griffin,” Ann. Nucl. Eng., 2026.
  7. H. Park and C. H. Lee, ​“Improvement and Verification of Online Cross Section Generation Capability of Griffin for TRISO-fueled Reactors,” ANL/NSE-25/82, September 2025.