Gas-Cooled High-Temperature Pebble-Bed Reactor Reference Plant Model

Abstract

This report details a fully coupled neutronics thermal hydraulics reference plant model for a gas-cooled high-temperature pebble-bed reactor. The multiphysics model is developed on the Nuclear Regulatory Commission's Comprehensive Reactor Analysis Bundle available on the Idaho National Laboratory high-performance computer, which natively and seamlessly couples Griffin, Pronghorn, and the BISON Multiphysics Object-Oriented Simulation Environment-based applications. Griffin provides the reactor physics capabilities, including depletion to the equilibrium core, k-eigenvalue, adjoint, and transient solutions. Pronghorn solves the porous medium equations for the fluid regions and conduction in the solid regions. BISON solves thermal conduction problems for the average and tristructural isotropic pebbles in the pebble-bed core thus providing the fuel and moderator spatial fields for each pebble burnup group. The neutronics feedback relies primarily on fuel and moderator temperatures. This report presents our results for the coupled steady state equilibrium core and a protected loss of flow event. Although this model is prototypical regarding capabilities in the Comprehensive Reactor Analysis Bundle, its results are consistent with published work by the Institute of Nuclear and New Energy Technology in China and other research entities. iii • Javier Ortensi-conceptual development, cross sections, neutronics model development, multiphysics analysis • Sebastian Schunert-conceptual development, code development (Nuclear Energy Advanced Modeling and Simulation), thermal fluids model development This work would not have been possible without the contributions from the Idaho National Laboratory Griffin development team:

Coupled SAM/Griffin Model of a Reference Pebble Bed High-Temperature Gas Cooled Reactor for Multi-Physics Simulations

“…To improve the overall fidelity of the PB-HTGR transient modeling, another effort has been made to couple SAM with the Griffin code to capture the spatial kinetics effects in the reactor [9]. For this study, using publicly available information of the HTR-PM reactor and the Pronghorn model developed by Idaho National Laboratory (INL), a coupled model with a 2-D porous medium core and 0-D/1-D components, along with a 0-D/1-D RCCS loop is presented in this report [10].…”

“…Currently, there are two operational HTR-PM reactors at the Shidao Bay nuclear power plant in China. As stated by Jaradat et al [10], the availability of open literature data coupled with it being the only operational pebble-bed reactor make the HTR-PM an ideal reactor design for code verification and validation studies.…”

“…Each pebble contains approximately 12,000 Tristructural-isotropic (TRISO) fuel particles of 0.91 mm in diameter scattered in the inner graphite matrix. Each TRISO particle consists of a UO2 kernel of roughly 0.5 mm in diameter followed by a buffer pyrocarbon layer, an inner high-density pyrocarbon layer, a silicon carbon (SiC) layer, and an outer high-density pyrocarbon layer [10,13,14]. The specifications of the pebbles and TRISO fuel are summarized in Tables 2-2 and 2-3. correlation by Hanh and Achenbach [17].…”

“…The effective thermal conductivity of the pebble bed is calculated with the ZBS correlation which calculates the effective thermal conductivity of the pebble bed core with the consideration of pebble-pebble conduction, pebble-coolant convection/conduction, pebble-pebble radiation [18,19]. Outside of the pebble bed, the gas gaps between the graphite block and core barrel and between the core barrel and RPV are modeled as solid structures where the thermal conductivity and heat capacity of the gap are adjusted to replicate the thermal radiation across the gaps, as done by Jaradat et al [10]. The heat transfer across the gaps of the bypass channel, riser, and the hot plenum is modeled with GapHeatTransferConstraint with an arbitrarily large gap heat transfer coefficient, hgap, of 100,000 W/m 2 K to replicate the heat transfer in these regions in the actual reactor.…”

“…The flow area of the bypass channel is adjusted such that it has a flow rate of about 1 kg/s during steady-state normal operation, as in the work by Jaradat et al [10]. Velocity and temperature boundary conditions are set at the inlet of the riser while a pressure boundary condition is set at the outlet of the hot plenum.…”