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Nuclear Science and Engineering

System Analysis Module

SAM: A Modern System Analysis Tool for Advanced Nuclear Reactors

The System Analysis Module (SAM) is a modern system analysis tool being developed at Argonne National Laboratory for advanced non-LWR safety analysis.  It aims to provide fast-running, whole-plant transient analyses capability with improved-fidelity for various advanced reactor types including liquid-metal-cooled, molten-salt cooled and fueled, gas-cooled, and heat-pipe-cooled reactors. SAM takes advantage of advances in physical modeling, numerical methods, and software engineering, to enhance its user experience and usability. It utilizes an object-oriented application framework (MOOSE), and its underlying meshing and finite-element library (libMesh) and linear and non-linear solvers (PETSc),  to leverage the modern advanced software environments and numerical methods. The major code features include:

  • One-D pipe networks represent general fluid systems such as the reactor coolant loops;
  • Flexible integration of fluid and solid components, able to model complex and generic engineering systems;
  • Multi-channel representation of fuel assembly and inter-assembly heat transfer modeling;
  • Point kinetics model with various reactivity feedback including thermal expansions;
  • A computationally efficient multi-dimensional flow model, for thermal mixing and stratification phenomena in large enclosures for safety analysis;
  • A general mass transport capability to track any number of species carried by the fluid flow for various applications;
  • A general control and trip system models;
  • A general fluid freezing and thawing capability, particularly important for safety assessments of molten-salt-cooled reactors;
  • An infrastructure for coupling with external codes has been developed and demonstrated. The code couplings with Mammoth, Proteus, Nek5000, BISON, STAR-CCM+, SAS4A/SASSYS-1, and TRACE are available.

System Thermal-Fluids Modeling

Temperature Distributions in the Simulation of Advanced Burner Test Reactor (ABTR)

SAM is being developed as a system-level modeling and simulation tool with higher fidelity but yet computationally efficient. As a new code development, the initial effort has been focused on the modeling and simulation capabilities of the heat transfer and single-phase fluid dynamics responses in reactor systems. The transient simulation capabilities of typical reactor accidents have been demonstrated in the transient simulations of various advanced reactor types and validated against the EBR-II, FFTF, MSRE, and many integral effects tests results. The key features include:

  • Robust and high-order FEM model of single-phase fluid flow and heat transfer;
  • Component-based system modeling;
  • Flexible coupling between fluid and solid components enables a wide range of engineering applications;
  • Enhanced built-in closure models and flexible modeling of fluid properties, friction, and convective heat transfer.

Reduced-Order Multi-Dimensional Flow Model

Computationally efficient multi-dimensional flow model is under development for thermal mixing and stratification phenomena in large enclosures for safety analysis. An advanced and efficient thermal mixing and stratification modeling capability embedded in a system analysis code is very desirable to improve the accuracy of reactor safety analyses and to reduce modeling uncertainties.

Simulation results of flow fields and comparisons with experiments for test cases in the SUPERCAVNA facility

Flexible Core Modeling

A pseudo 3-D full-core conjugate heat transfer modeling capability has been developed in SAM for efficient and accurate temperature predictions of SFR structures. A multi-channel rod bundle model is developed to account for the temperature differences between the center region and the edge region of the coolant channel in a fuel assembly. The hexagon lattice core can be modeled with automatically-generated 1-D parallel channels representing the subassembly flow, and 2-D duct walls and inter-assembly gaps.

Comparison of average radial wall temperature distributions between SAM and CFD in a 7-assembly demonstration problem

Multi-Physics Multi-Scale Integration

Flexible coupling interfaces have been developed to allow for convenient integration with other advanced or conventional simulation tools for multi-scale and multi-physics modeling capabilities. SAM simulation results of a heat-pipe-cooled micro reactor are shown in the figures below. This effort utilized several MOOSE-based submodules under NRC’s Comprehensive Reactor Analysis Bundle (CRAB), including SAM, MAMMOTH/Rattlesnake, and MOOSE’s Tensor Mechanics module.

Multi-physics simulation of an unprotected loss of heat sink event of a heat-pipe-cooled micro reactor: horizontal cut view of temperature profile (top left); vertical cut view (top right); transient average solid temperature of different blocks (bottom)

Relevant Publications