An integral 3D full-scale steady-state thermohydraulic calculation of the high temperature pebble bed gas-cooled reactor HTR-10

Abstract

The Very High Temperature Reactor (VHTR) is one of the next generation candidates for nuclear reactors, according to the IAEA. Predicting the thermohydraulic performance of high temperature reactors is an important contribution to technology development. The evaluation of the thermohydraulic behavior of the steady-state of the HTR-10 gas-cooled pebble bed high temperature test reactor was a challenge proposed to the international scientific community by the IAEA. This paper proposes a methodology for the thermohydraulic study of steady-states of high temperature gas-cooled pebble bed nuclear reactors, using real scale three-dimensional computational thermohydraulic modeling. The focus of this paper is to discuss the methodology that was improved. Analyses were carried out from comparative studies with experimental data and data obtained by other computational codes. A CFD method was developed to analyzes the main thermohydraulic parameters. The ANSYS CFX's full porous media approach was used to model the pebble bed reactor core. A variable porosity model was implemented in the pebble bed simulation to consider the closeness of the walls. The effect of the Reactor Core Cooling System was modeled from variable boundary conditions in the reactor pressure vessel surfaces. The temperature values obtained in the pebbles, the coolant, and the structural elements were confirmed to be under the normal operating limits. Also were obtained the threedimensional coolant velocities and pressures drop profiles which are important information to understand the thermohydraulic behavior of the reactor. Additionally, was evidenced the presence of thermohydraulic three-dimensional effects showing the important role of the 3D thermohydraulic modeling. With this paper was bear out that use of CFD applied to nuclear thermohydraulic modeling of HTR-10 increase the understanding of the phenomena occurring in high temperature gas-cooled pebble bed nuclear reactors.