Research Papers

Investigation of Natural Convection Heat-Transfer Phenomena in Packed Beds: Lead-Way Toward New Nuclear Fuel Design

[+] Author and Article Information
Olugbenga O. Noah

Department of Mechanical and Aeronautical Engineering,
University of Pretoria,
Private Bag X20, Hatfield, 0028 Pretoria, South Africa
e-mail: Noah.Olugbenga@tuks.co.za

Johan F. Slabber

Department of Mechanical and Aeronautical Engineering,
University of Pretoria,
Private Bag X20, Hatfield, 0028 Pretoria, South Africa
e-mail: johan.slabber@up.ac.za

Josua P. Meyer

Department of Mechanical and Aeronautical Engineering,
University of Pretoria,
Private Bag X20, Hatfield, 0028 Pretoria, South Africa
e-mail: josua.meyer@up.ac.za

Manuscript received January 20, 2015; final manuscript received June 28, 2015; published online September 3, 2015. Assoc. Editor: Mark Anderson.

ASME J of Nuclear Rad Sci 1(4), 041014 (Sep 03, 2015) (12 pages) Paper No: NERS-15-1007; doi: 10.1115/1.4030983 History: Received January 20, 2015; Accepted July 02, 2015; Online September 16, 2015

The ability of coated particles of enriched uranium dioxide fuel encased in graphite to discontinue nuclear fission reaction without human action in the case of complete loss of cooling is a vital safety measure over traditional nuclear fuel. As a possible solution toward enhancing the safety of light water reactors (LWRs), it is envisaged that the fuel, in the form of loose, coated particles in a helium atmosphere, can be used inside the cladding tubes of the fuel elements. This study is therefore a first step toward understanding the heat-transfer characteristics under natural convective conditions within the fuel cladding tubes of such a revolutionary new fuel design. The coated particle fuels are treated as a bed, from which the heat is transferred to the cladding tube and the gas movement occurs due to natural convection. A basic unit cell model was used where a single unit of the packed bed was analyzed and taken as representative of the entire bed. The model is a combination of both analytical and numerical methods accounting for the thermophysical properties of sphere particles, the interstitial gas effect, gas temperature, contact interface between particles, particle size, and particle temperature distribution used in this study to investigate the heat-transfer effect. The experimental setup was a packed bed heated from below with gas circulation due to natural convection. This allows for the development of an appropriate, conservative thermal energy balance that can be used in determining the heat-transfer characteristics in homogeneous porous media. Success in this method, when validated with suitable correlation, such as Gunn, suggests that the heat-transfer phenomenon/characteristics in the fuel cladding tube of the new design can be evaluated using this approach for design purpose.

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Fig. 1

Section through part of the test facility with a particle test sample highlighted. (i) Heat transfer by particle-to-fluid mode, (ii) heat transfer by fluid-to-particle mode, (iii) heat transfer from the bed wall to the particles, (iv) heat transfer by particle-to-particle mode, (v) radiant heat transfer between particles, and (vi) radiant heat transfer between side wall and particles.

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Fig. 2

(a) Schematic diagram of experimental setup (for illustration purpose), (b) sectional view of instrumented test particle/particle test sample, and (c) experimental setup

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Fig. 3

(a) Schematic representation of contacting adjacent particles, (b) control volumes with grid points, (c) finite contact spot of smooth contacting spherical surfaces, and (d) temperature distribution with increasing length along particle diameter

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Fig. 4

Heat conduction between two smooth-elastic particles in perfect contact

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Fig. 5

Thermal resistance network for spherical Hertzian contact

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Fig. 6

Schematics of the regular LWR cladding tube with fuel pellets

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Fig. 7

Schematics of proposed coated particle fuel design in a cladding SiC tube

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Fig. 8

Effect of gas thermal conductivity on convective fluid-to-particle heat-transfer coefficient in the packed bed

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Fig. 9

Nusselt number in the packed bed as a function of convective fluid-to-particle heat-transfer coefficient

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Fig. 10

Variation of Nusselt number on the Rayleigh number for fluid-to-particle heat transfer




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