Session: Flow Visualization and Regular Poster Session

Paper Number: 158431

158431 - High-Fidelity Simulations of Helium-Air Mixing in Htgr Cavities 

Abstract: 

The accident scenario in which a pipe break occurs in the pressure or steam generator vessel of a High Temperature Gas Reactor (HTGR) is investigated computationally. Following the pipe break, high temperature helium is discharged from the high pressure primary loop into the surrounding reactor cavities, which contains cold air, leading to helium-air mixing in the HTGR cavities. The simulated HTGR cavity system is set up such that a heated cylindrical injection pipe is connected to the lower left side of a rectangular prism cavity and another cylindrical pipe, which may act as a vent, is connected to the lower right side of the cavity. The vent in this case is controlled by a valve which opens when a certain pressure is reached. The present study examines the injection of high temperature helium through the injection pipe into air in the simulated reactor cavities.

The current work is broken up into a series of test cases to ensure accurate simulation of the HTGR cavity system. A single-species baseline simulation is conducted where air is injected into air in the cavity. The temperature is held constant everywhere in this case. Another simulation is conducted to introduce the heat transfer aspect of the system where heated air (500°C) is injected into room temperature air (25°C) in the cavity. Lastly, the simulation of the injection of heated helium (500°C) into the air (25°C) filled cavity is performed. This study is split into two main sections in terms of simulation setup, one analyzing turbulent pipe flow and another analyzing jet flow into a cavity. The turbulent pipe flow simulations correspond to the long injection pipe which leads into the cavity. A periodic pipe is simulated until turbulence as well as the desired temperature is reached. The pipe simulation is run with an injection velocity of 50m/s using a cylindrical domain with a diameter of 1 and a length of 8.05. Splitting the simulated setup into a pipe and a cavity when conducting the simulations allows for a smaller computational domain overall since the pipe length can be cut down to reach the same desired turbulent conditions. The pipe flow output data is then used as the inlet condition for the jet flow into the cavity. The turbulent statistics such as mean velocities, turbulence intensities, Reynolds shear stress, budgets of the Reynolds stresses, and turbulent kinetic energy budgets are analyzed. For the jet into the cavity case, H-convergence is also examined.

The present simulations are carried out using the computational fluid dynamics (CFD) codes Nek5000 and NekRS. They are highly scalable open source spectral element method (SEM) based Navier-Stokes solvers. Nek5000 is a well established code, which only supports CPU-based platforms, whereas NekRS is newer code, which is optimized for GPU acceleration but also supports CPU-based platforms. The current study takes advantage of the GPU-accelerated NekRS code. The cases are run on the supercomputer, Polaris, at the Argonne Leadership Computing Facility.

Presenting Author: Hai Lu Lin The City College of New York

Presenting Author Biography: