NRC Multiphysics Analysis Capability Deployment (FY2021 - Part 2)

Abstract

This report details progress and activities of Idaho National Laboratory (INL) on the Nuclear Regulatory Commission (NRC) project "Development and Modeling Support for Advanced Non-Light Water Reactors."The tasks completed for this report are:• Task 2c: Explicit modeling of pebble transient temperature response. In this simulation, the 400 MWth Pebble-Bed Modular Reactor (PBMR) design, PBMR-400, experiences a 20-second power ramp from 100% to 150% power. This is followed by a similar reduction in the power back to 100%. Several multiscale pebble coupling approaches are tested with one pebble per mesh element in the active core region. The results show good conservation behavior and the stability of the coupling.• Extended scope part 1: An assessment of the computational efficiency of the Discontinuous Finite Element Method (DFEM) heat transfer solver shows good scalability. The DFEM solver is a factor of 4 more expensive in solution time than the Finite Element Method (FEM) solver for heat transfer problems due to the increased number of degrees of freedom. Nonetheless, the DFEM approach provides the user with the flexibility to model gap heat transfer problems.• Extended scope part 2: The GapHeatTransferInterfaceMaterial was improved to give the user increased flexibility with the modeling of heat transfer through gaps with the DFEM solver. A number of gap parameters can now be coupled both through functions and variables.• Extended scope part 3: Demonstration of how the gap width between hexagonal fuel cells can be calculated during a heat-up transient and used in the GapHeat-TransferInterface model. A full-domain DFEM model with gap expansion is coupled to a SubApp that models the thermal expansion of the base plate. The results show the expected physical behavior, although have not been fully benchmarked at this point in time. List of FiguresAnnular pebble bed model geometry with linear power distribution (left); Pebble model with example temperature distribution (right). . . . . . . . . 3 Pebble bed total power as function of time, 20s linear power ramp to 150% of the power and back to the 100% after 500s . . . . . . . . . . . . . . . . 4Coupling schemes between the porous medium and the pebble models. The black arrows represent the transferred quantities (the ones used as boundary conditions are followed by as

SCALE Modeling of the Sodium Cooled Fast-Spectrum Advanced Burner Test Reactor

“…Because this is not a defined feature of the benchmark, its dimensions were assumed; the following section provides a brief sensitivity study of the core to different possible dimensions. The INL report notes the radius used for its calculations: 115 cm [13]. This is reasonable since an inner radius of ∼114.1 cm is necessary to fully contain all assemblies at operating temperatures including some spacing for coolant flow.…”

“…SCALE has the capability of modeling the barrel either as a ring of hexagonal barrel assemblies or as a cylindrical encasement of the core. A sensitivity study of different modeling approaches for the barrel was performed, and three states were investigated: the barrel assembly model as given in the benchmark; a cylindrical barrel with an inner and outer radius of 115 and 117.54 cm, respectively, as used in the INL Serpent model [13]; and a cylindrical barrel with an inner and outer radius of 114.413 and 116.973 cm, respectively, derived from the thermal expansion of the barrel at inlet coolant temperature (Figure 5). All three configurations are shown to be statistically equivalent in Table 2.…”

“…Although the benchmark specifications did not provide reference k eff results, a recent INL report using the same benchmark provides results obtained with the Serpent code [13]. This independently produced model using a different code provides a basis for verification of the SCALE input, both codes simulating an identical source benchmark with identical source nuclear data-the ENDF/B-VII.1 cross-section library.…”

“…In addition to k eff , β eff at BOEC was reported in both the initial design report [6] and the INL report [13].…”

“…Great effort was taken to correctly model the system as described, though minor assumptions are noted. Verification of the SCALE model was performed through a comparison with results from a recent Idaho National Laboratory (INL) report [13]. Based on the verified model, SCALE was applied to determine reactivity, neutron flux, and power distributions of the full ABTR core.…”