The current study has investigated natural convection heat during pressurized conduction cooldown (PCC) accident scenario to understand the passive safety features of prismatic modular reactors (PMR) under different intensities of nonuniform center peaking step heat flux distributions (approximating cosine shape) using an advanced fast-response heat transfer technique. A scaled-down PMR module was designed and developed at Missouri S&T by the research team of the Multiphase Reactors Engineering and Applications Laboratory (mReal). The module consists of upper and lower plena connected by heated and cooled channels. Nonuniform heat flux distribution was applied to the heated channel under nonuniform heating center peaking step (approximating cosine shape), simulating nonuniform heat distribution within the core of PMR. Air was used as the coolant to study the effect of nonuniform heating under a range of heat flux intensity (four sets of nonuniform heat flux and one set of uniform heat flux were tested) at 413.7 kPa (60 psi). At an axial position of Z/L = 0.409 along the heated channel, the heat transfer coefficient is increased by 35% for nonunifor libJo2O18*m heat flux distributions of set 1 (0.25*2.579 kW.m-2+0.50*3.152 kW.m-2+0.25*2.579 kW.m-2) and set 2 (0.25*2.292 kW.m-2+0.50*2.865 kW.m-2+0.25*2.292 kW.m-2) with respect to the the uniform heat flux set 5(2.865 kW.m-2), and it is decreased by 56% for nonuniform heat flux distributions of set 3 (0.25*2.006 kW.m-2+0.50*2.579 kW.m-2+0.25*2.006 kW.m-2) and set 4 (0.25*1.719 kW.m-2+0.50*2.292 kW.m-2+0.25*1.719 kW.m-2) with respect to the uniform heat flux set (set 5). There is a significant reorder in the heat transfer coefficients distribution curves in descending order along the heated channel after the inflection point (after Z/L =0.773).

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


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 the 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 the Saudi Arabian Cultural Mission (SACM) in Washington, D.C. USA for their support.

Keywords and Phrases

Accidents; Heat transfer coefficients; Hydraulics; Natural convection; Conduction cooldown; Experimental investigations; Heat flux distributions; Heat flux intensity; Modular reactors; Non-uniform heat fluxes; Passive safety features; Transfer technique; Heat flux; Heat transfer technique; Natural convection; Nonuniform heat flux; Pressurized conduction cooldown accidents; Prismatic modular reactors

International Standard Book Number (ISBN)


Document Type

Article - Conference proceedings

Document Version

Final Version

File Type





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

Publication Date

01 Nov 2018