Simulation of Pressurized Conduction Cooldown in a Scaled High Temperature Gas Reactor Experiment using GOTHIC

Abstract

Among the candidates for the next generation of nuclear power plant is the high temperature gas reactor (HTGR). Since the HTGR does not have the same operational history as water cooled reactors do in the United States, investigation into the response of different accident phenomena is still an active area of research. The current work investigates the pressurized conduction cooldown (PCC) accident in an integrally scaled high temperature gas reactor experimental facility.

A PCC accident occurs when the primary circulator loses the ability to provide forced convection to the core. During a PCC accident, coolant that is normally forced downward through the core during normal operation loses momentum after the circulator functionality is lost leading to flow stagnation and eventually results in an intracore natural circulation flow path which brings hot coolant into the upper plenum. Critical instrumentation such as the control rod drive shafts are located in the upper plenum. As such, it is important to understand the upper plenum mixing and temperature profile to better support the safety of HTGRs during these accidents.

The upper plenum environment was analyzed by simulating a PCC experiment in the Oregon State University High Temperature Test Facility (HTTF) using the GOTHIC multi-physics software package. GOTHIC integrates coarse-grid multi-phase CFD and traditional system level thermal hydraulics modeling capabilities using a multi-volume, domain decomposition approach that provides an efficient 3D analysis tool. This paper summarizes GOTHIC’s capabilities for HTGR analysis and compares the upper plenum temperature comparisons for the PCC at HTTF.