CFD modeling of the OSU High Temperature Test Facility inlet plenum flow distribution during normal operation

Abstract

This paper investigates the fundamental physical phenomena associated with internal coolant flow distribution in the upper plenum of a prismatic Very High Temperature Reactor (VHTR) during normal operation. Previous studies have revealed the importance of complex flow distribution in the inlet plenum with the potential to generate low velocity or stagnation zones that can subsequently lead to the formation of hot spots in the reactor core and hot streaks in the lower plenum. It is therefore of interest to ensure that coolant is evenly distributed when entering multiple reactor coolant channels. Non-uniformity in the flow distribution is assessed for the reference Oregon State University High Temperature Test Facility (HTTF) case. The HTTF is a reduced scale model (1:4 in height and diameter) of the Modular High Temperature Gas-Cooled Reactor (MHTGR). The developed CFD model reflects complete and detailed geometry of the HTTF upper plenum along with upcomer and metallic core support structure (MCSS). CFD results include parametric studies performed for circulator mass flow rate variation and mesh sensitivity analysis, generated using Siemens Starccm+ software. Outcomes also include variable pressure and temperature boundary conditions impact on the flow distribution.