Development of an Equilibrium Modeling Method for Modeling Micro-Modular Pebble-Bed High-Temperature Gas-Cooled Reactors

As a new generation of pebble-bed reactors (PBRs) are developed in fulfillment of the push by private industry and government to license and operate advanced generation IV reactors, it is also important to continue the development of the computational modeling methods used for PBRs.A variety of high-fidelity modeling methods for PBRs exist, but these are typically very computationally expensive and not well-suited for efficient calculations.In previous work at Oak Ridge National Laboratory, an equilibrium modeling method was developed around tools within the SCALE code system.This iterative method is capable of effectively generating PBR zone-wise fuel inventories at equilibrium core operation within a reasonable computational time.This method was recently extended to the Axial Zone Equilibrium Modeling (A-ZEM) method for use in generating equilibrium models of micro-modular pebble-bed high-temperature gas-cooled reactors.In contrast to the original method which uses surrogate models for depletion, the A-ZEM method incorporates full core depletion calculations to accurately consider leakage effects in small PBRs.The A-ZEM method was applied to a model of the HTR-10 built with publicly available design specifications.E quilibrium was reached within five i terations, t aking o nly 1,920 C PU-hours.T he e quilibrium e igenvalue k_effective and discharge burnup of the A-ZEM method was compared to other published results.The obtained good agreement indicates that the A-ZEM method is generating a representative equilibrium core.However, a comparison of the discharge inventory to other published equilibrium results, if they become available in the future, would be required to fully understand the performance of the model.