Session: Validation Methods

Paper Number: 158434

158434 - Experimental Characterization of Upper Plenum Natural Circulation Phenomena Under Pressurized Transient Accident Conditions 

Abstract: 

              The flow characteristics in the upper plenum of molten salt (MSRs) and high-temperature gas-cooled reactors (HTGRs), during the pressurized conduction cooldown accident (PCC) scenario, are dominated by natural convection jets emitted from the top of the reactor core. These reactor types have garnered attention as promising candidates for next-generation designs, yet their accident behavior remains less understood compared to traditional light water reactors (LWRs). To address this disparity, benchmark experiments are necessary to validate the Computational Fluid Dynamics (CFD) codes currently being used to further characterize the PCC scenario.

 

            This study focuses on providing benchmark data for the upper plenum PCC natural circulation phenomena. The experimental facility is a scaled-down generic model of the upper plenum of MSRs and HTGRs. The working fluid used in the facility is a heat-transfer fluid named Dowtherm-A which possesses a Prandtl number (Pr) similar to that of proposed molten salt coolants at reactor operating temperatures. Optical fiber-distributed temperature sensors and thermocouples are utilized to determine geometry surface and bulk fluid temperatures in the experiment. This information, along with volumetric flow rate data, is used to calculate the conjugate heat transfer characteristics of the plenum and provide boundary conditions for the CFD models. These boundary conditions include heat flux, three-dimensional surface temperature profiles, and mass flow rates.

 

            This study also produces velocity field measurement data, via Particle Image Velocimetry (PIV). The velocity field data is the primary experimental result used for CFD model validation. Error propagation is accounted for throughout the entire analysis methodology and large sample sizes of raw data are used to reduce the experimental uncertainty. Various methods of data post-processing are applied to compensate for minor experimental errors. These methods include dynamic image masking to negate the visual effect of unintended solid objects in the flow visualization field. Only two such objects were present in the experiments and both had volumes approximately that of a cubic millimeter.

 

            Three test cases are performed as part of this study. The primary test case is a non-isothermal natural circulation scenario where fluid flow is induced by buoyancy forces. Isothermal test cases are also studied, where flow is driven by a pump-induced pressure gradient. This presentation provides a detailed description of the experimental methods, analysis techniques, and uncertainty reduction methods utilized in this study. The results of this work will subsequently be used for the validation of current and future CFD models of upper plenum natural circulation phenomena.

Presenting Author: Tristen Rogers Texas A and M University

Presenting Author Biography: Tristen Rogers is currently a PhD student at Texas A and M University pursuing a doctorate degree in Nuclear Engineering. He received two bachelors of science degrees from Idaho state University in Nuclear and Mechanical Engineering.

Authors:

Tristen Rogers Texas A and M University
Yassin Hassan Texas A and M University