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New lab to help establish databases to improve nuclear reactor safety, design

September 8, 2016

Two-phase flow
The two-phase flow facility allows engineers to record the transition of flow from bubbly (the small bubbles) to slug (the large area in the center of the image). Differences in flow are important in the safe storage and operation of fuel rod bundles.

A new lab, to be built in Randolph Hall on Virginia Tech’s Blacksburg campus, will help nuclear engineers develop and test a database for computational fluid dynamics (CFD) codes. The codes are used to model and simulate two-phase flow, which will help engineers design safer and more efficient nuclear reactors.

Yang Liu, assistant professor of nuclear engineering in the College of Engineering's Department of Mechanical Engineering, recently received an $800,000 grant from the Nuclear Energy University Programs, overseen by the Department of Energy.

Two-phase flow modeling is one of the most challenging issues in simulating nuclear reactors. The grant will help establish three high-quality, high-resolution databases to develop advanced models and validate the NEK-2P code, a multiphase CFD code developed at Argonne National Laboratory.

“There are reactor thermal-hydraulics codes that exist from the 1960s and 1970s,” said Liu, principle investigator on the project, “but the uncertainties of these codes are generally very large. This project will help us create a database for the advancement of more accurate CFD codes, such as NEK-2P.”

The codes and models created as part of the project will be used for safety analysis, power uprate and life extension of existing reactors, and potential new reactor designs.

The new lab will include a test rig of a 3x3 heated rod bundle section to generate vapor bubbles – in line with the type produced in nuclear rod bundles. The instrumentation system will include particle image velocimetry, planar laser-induced fluorescence, high-speed imaging, X-ray densitometry, and multisensor conductivity probes. In the Virginia Tech and Ohio State University labs, researchers will conduct high-fidelity optical measurements using existing air-water flow loops, followed by tests in the new rod bundle facility.

Dewei Wang
Dewei Wang, a mechanical engineering Ph.D. student working with Assistant Professor Yang Liu, installs a visualization window on a two-phase flow test facility.

“Our bundle will consist of nine rods contained in pressurized water and heated to produce vapor bubbles,” Liu said. “By measuring both the gas and the liquid, we will be able to characterize the process and create accurate, advanced models of the flow, and we’ll look at the void distribution in the bundle’s geometry, which is important for the fission reaction rate in nuclear reactors.”

Liu uses automobiles as an example of the importance of modeling data. “Thirty years ago, if you punched your car, you’d stand a chance of breaking your hand,” he said. “Today, if you punch your car, you stand a better chance of breaking your car. But despite that, today’s cars are much safer than the thicker, heavier models of the past. The same holds true for how buildings and aircraft are designed. By improving the predictive accuracy of our models through code validation and verification, our simulations become more robust and useful. We can build facilities that are safer, more reliable, and more efficient.”

Liu will collaborate on the project with Ohio State University, Argonne National Laboratory, and Westinghouse Electric Company to develop a comprehensive two-phase flow database for the validation of NEK-2P.

The new lab is expected to be completed in the spring of 2018.

Written by Rosaire Bushey

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