RELAP5-3D Simulation of Oregon State University High Temperature Test Facility Lower Plenum Mixing Test

Abstract

Canadian Nuclear Laboratories (CNL) is developing modelling capabilities for small High-Temperature Gas-cooled Reactors (HTGRs). Within one study, the applicability of the system thermalhydraulics code RELAP5-3D to HTGR analysis was assessed through simulation of the lower plenum mixing test PG-28, undertaken at the Oregon State University (OSU) High Temperature Test Facility (HTTF). The OSU HTTF is a scaled integral effect facility modeled after the modular high-temperature gas-cooled reactor (MHTGR), and was designed to generate data for transient events representative of prismatic gas-cooled reactors.

CNL developed a RELAP5-3D model of test PG-28 that simulates the HTTF primary helium coolant loop, the secondary water-cooled loop, and the air-cooling loop. A unique aspect of the model is the grouping of the HTTF core blocks and reflectors into six azimuthal sectors with each sector divided into seven radial rings, to represent the asymmetric core heating of test PG-28. The HTTF core hydraulics are represented by 32 coolant channel groups. Heat transfer in the core is modeled using 32 cylindrical heat structures. Heat conduction between the solid structures is modeled using 70 conduction/radiation enclosures.

The simulation results are in reasonable agreement with measurements of the solid core and helium coolant temperatures within the heated sectors; however, the model under predicted temperatures in unheated sectors.