Plenum-To-Plenum Natural Circulation Heat Transfer in a Prismatic Very High-Temperature Reactor for Different Coolants


Multiphase Reactors Engineering and Applications Laboratory (mReal) at Missouri University of Science and Technology (S&T) has developed a natural convection heat transfer test facility with one riser and one downcomer between two plena to investigate loss of flow accident scenario (LOFA) for a prismatic very high temperature reactor (VHTR). Using advanced heat transfer coefficient probe and T-thermocouples (1.6 mm), this paper reports the effect of the outer surface temperatures of the upper plenum and downcomer channel (278.15, 288.15, 298.15, and 308.15 K) on the intensity of natural circulation during LOFA with helium at 413.685 kPa. The results showed that there is a reduction in the centerline temperature of ∼10.14% and inner wall surface temperatures of ∼7.4% along the riser channel with decreasing upper plenum and downcomer temperatures from 308.15 K to 278.15 K. A reversal in the direction of heat transfer is observed close to the exit of the riser channel (Z/L = 0.773) for outer surface temperature 288.15, 298.15, and 308.15 K due to the end effect. It is worth mention that, the negative signals of heat fluxes are observed along the downcomer channel for all operating conditions, which confirms heat removal from helium and a downward flow along the downcomer channel, hence establishment of natural circulation. The results also showed a gain in the values of heat transfer coefficients along the riser channel with decreasing the outer surface temperature which is consistent with the literature. In comparison to the literature with air as coolant, the current results showed the role of helium on the thermal performance of natural circulation loop in terms of co-circulation of plumes and end effects.

Meeting Name

International Topical Meeting on Advances in Thermal Hydraulics, ATH 2018 (2018: Nov. 11-15, Orlando, FL)


Chemical and Biochemical Engineering

Second Department

Nuclear Engineering and Radiation Science

Research Center/Lab(s)

Center for High Performance Computing Research


The authors would like to express their gratitude for the financial support provided by the U.S. Department of Energy-Nuclear Energy Research Initiative (DOE-NERI) under project (NEUP 13-4953 [DENE0000744]), which made this work possible. The first author would also to acknowledge King Abdulaziz City for Science and Technology in Riyadh (KACST), Saudi Arabia and Saudi Arabian Cultural Mission (SACM) in Washington, D.C. USA for their support.

Keywords and Phrases

Argon; Atmospheric temperature; Carbon dioxide; Coolants; Fluids; Heat transfer coefficients; Helium; Hydraulics; Natural convection; Nitrogen; Surface properties; Conduction cooldown; High operating pressure; Local heat transfer coefficient; Modular reactors; Natural circulation; Nonuniform heating; Oregon State University; Transfer technique; High temperature reactors; Heat transfer technique; Prismatic modular reactor

International Standard Book Number (ISBN)


Document Type

Article - Conference proceedings

Document Version


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© 2018 American Nuclear Society (ANS), All rights reserved.

Publication Date

01 Nov 2018

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