Experimental Study of Natural Circulation Phenomena in a Micro Prismatic Modular Reactor Core Channel

Abstract

Motivated by the need to experimentally investigate natural circulation thermal–hydraulic behavior in horizontal prismatic gas-cooled microreactors, this study examines the effect of varying cooling water temperatures (5–20 °C) on flow characteristics within a dual-channel plenum-to-plenum facility (P2PF). An integrated experimental setup was developed, incorporating micro-foil heat flux sensors, T-type thermocouples, and advanced thermal gas flow sensors to simultaneously measure surface temperature, gas temperature, heat flux, and flow direction at multiple axial and radial locations. Results indicate that stable natural circulation of air is established when the temperature gradient is sufficiently high. However, at lower temperature differences, the flow becomes unstable and non-unidirectional. Radial temperature asymmetries and buoyancy-induced flow reversal were observed, leading to enhanced heat transfer at the channel outlet. The local convection heat transfer coefficient exhibited a non-monotonic trend, decreasing initially along the channel and increasing near the outlet. These measurements offer valuable data for validating computational fluid dynamics (CFD) models and contribute to a deeper understanding of natural circulation and passive cooling mechanisms in advanced microreactor designs.

Department(s)

Chemical and Biochemical Engineering

Comments

U.S. Department of Energy, Grant NEUP 21-24104

Keywords and Phrases

Natural circulation; Nuclear microreactor; Passive safety; Prismatic modular reactor; Thermal hydraulics

International Standard Serial Number (ISSN)

0029-5493

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 Elsevier, All rights reserved.

Publication Date

01 Dec 2025

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