Assessment of MOOSE-Based Tools for Calculating Radial Core Expansion

Abstract

Radial core expansion in liquid-metal cooled fast reactor systems is a well-known phenomenon that produces strong reactivity feedback effects. An inherently safe reactor design takes advantage of negative reactivity feedback in accident scenarios by utilizing a core restraint system which produces a bowed shape that allows for radial expansion of the fuel regions. Detailed modeling and simulation of radial core expansion itself as well as subsequent reactivity feedback is a challenging task involving contact of many fuel assembly elements and physics feedback from neutronics, thermal hydraulics, and thermal mechanical response. A variety of physics codes have been developed to model aspects of radial core expansion but in general invoke geometrical or physics approximations [1]. No code system currently exists which tightly and robustly couples these physics with enough detail to fully resolve the complex radial core expansion reactivity feedback effects. The future availability of such a code system is of vital importance to fully understanding the reactivity feedback effects that occur due to radial expansion, and consequently to optimizing the design of the core restraint system. A high-fidelity code will also be used to benchmark existing lower fidelity, faster running models to understand their benefits, limitations, and range of applications. A code development path using MOOSE-based [2] tools is proposed in order to leverage the detailed geometry capabilities and natural tight coupling and robustness of MOOSE-based applications for modeling this complex phenomena.While simulation of the full phenomenon involves several physics, an assessment has been initiated on the capabilities and readiness of the currently available Tensor Mechanics module within MOOSE for calculation of the structural mechanical responses which occur within the reactor core. This report focuses on modeling the force-deformation response which mimics the physics of a duct contact deformation, as well as differential thermal expansion which produces a thermal bowed shaped for the fuel assemblies in a core. Simple examples were initially performed such as simple supported beam bending under load. The complexity of examples was progressively increased to better mimic the duct behavior by including a differential thermal example and inclusion of hexagonal cross-sections in the geometry. Further assessment of the structural mechanical response simulation capability is still required for modeling duct contact interactions and irradiation creep and swelling.Companion thermal hydraulic and neutronics assessments will also be required; these activities are planned for future years. Finally, integration of the multiple physics components through MOOSE is required to predict the radial core expansion and subsequent feedback effects.

Continued Verification of MOOSE Structural Mechanics Tools for Modeling Core Bowing Phenomena in Fast Reactors

“…ParsedMaterial is a dynamic method to change material properties without writing code. [2] by adding duct-to-duct contact and irradiation swelling material properties, showing good agreement between IAEA, NUBOW-3D, and analytical results. These examples indicate that the MOOSE Tensor Mechanics and Contact modules will be able to accurately model clusters of ducts and small core problems with and without symmetry behavior and estimate the bowing deflection taking into account contact interactions.…”

“…This report expands on the single duct, thermal bowing behavior examples in [2] and includes clusters of ducts with contact at the load pads and irradiation material swelling behavior. Assessment is still needed on larger core configurations and full limited-free bow behavior including restraint rings.…”

“…In this configuration, the center duct thermally bows into the top 1/6 sector and has a free boundary around the sector as shown in red dashed lines in Figure 2-1. The center duct has a thermal gradient identical to VP1 [2] while all the other ducts remain at 400 °C. The gradient is shown schematically here for reference in Figure 2-2.…”

“…The first stage of the work, which commenced in FY21 [2] and continues through FY22, assesses thermo-mechanical modeling tools for producing core bowing predictions consistent with conventional tools. The Multiphysics Object Oriented Simulation Environment (MOOSE) [3] Tensor Mechanics [4] and Contact Modules [5] are employed.…”

Grizzly Development for Light Water Reactor and Advanced Reactor Applications in Fiscal Year 2021

“…An ANL-led effort was carried out this year to assess the ability of Grizzly (or other MOOSE-based tools) to model the deformation of core ducts as part of the larger effort to develop a multiphysics tool for these reactors. INL supported this effort, which is documented in detail in [38 ].…”