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Research Papers

Investigation of Natural Convection in Heat Generating Molten Nuclear Fuel and Assessment of Core Damage Propagation

[+] Author and Article Information
L. Ravi

Thermal Hydraulics Section,
Indira Gandhi Centre for Atomic Research,
Kalpakkam 603102, India
e-mail: raviths@igcar.gov.in

K. Velusamy

Thermal Hydraulics Section,
Indira Gandhi Centre for Atomic Research,
Kalpakkam 603102, India
e-mail: kvelu@igcar.gov.in

P. Chellapandi

Thermal Hydraulics Section,
Indira Gandhi Centre for Atomic Research,
Kalpakkam 603102, India
e-mail: pcp@igcar.gov.in

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received June 9, 2014; final manuscript received January 15, 2015; published online April 21, 2015. Assoc. Editor: P. K. Das.

J. Thermal Sci. Eng. Appl 7(3), 031009 (Sep 01, 2015) (10 pages) Paper No: TSEA-14-1147; doi: 10.1115/1.4030248 History: Received June 09, 2014; Revised January 15, 2015; Online April 21, 2015

Total instantaneous blockage (TIB) is a severe subassembly accident in a sodium cooled fast reactor. During such an accident, a heat generating fuel pool is formed which is bounded by six neighboring subassemblies which are force-cooled by sodium. The molten fuel pool attacks the walls of the neighboring hexcan, melting them layer by layer. The rate of propagation of such damage and the temperature rise in sodium due to heat transfer from fuel pool through hexcan wall are investigated by a two-step mathematical approach. In the first step, natural convection in the fuel pool is studied by a 2D axisymmetric computational fluid dynamic model and correlations for effective conductivity as a function of internal Rayleigh number and aspect ratio have been developed. In the second step, rate of damage propagation to the hexcan wall and sodium temperature rise are predicted by a 1D transient enthalpy model. It is found that rate of damage propagation is accelerated by natural convection inside the pool. Further, the rate of heat transfer to neighboring subassembly sodium also increases due to natural convection in the pool. Eventually, the residual thickness of hexcan at the time of reactor trip is found to be insensitive to the presence/absence of natural convection in the pool.

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References

Figures

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Fig. 1

Sketch showing TIB event progression: (a) normal condition, (b) molten fuel attacking neighboring subassembly, and (c) fuel pool details

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Fig. 2

Physical model with boundary conditions

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Fig. 3

Physical model of neighboring subassembly hexcan melting

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Fig. 4

Comparison of stream function and isotherms for a square cavity at RaE = 105 and Ra = 107 against the results of Acharya and Goldstein [3]

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Fig. 5

Evolution of temperature contour in the cavity for RaI = 107 and A = 5 for: (a) pure conduction, (b) convection, (c) velocity vector plot, and (d) stream function considering convection

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Fig. 6

Dimensionless temperature variation along the centerline of the pool

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Fig. 7

Dimensionless temperature variation along the centerline of the pool for different values of aspect ratio

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Fig. 8(a)

Dimensionless local heat flux variation along the hexcan wall with different values of aspect ratios of the pool for A = 1 and (b) dimensionless local heat flux variation along the hexcan wall with different values of aspect ratios of the pool for A = 2

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Fig. 9

Variation of dimensionless bulk temperature of pool with RaI for different values of aspect ratio

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Fig. 10

Equivalent conductivity factor for various values of aspect ratio

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Fig. 11

(a) Evolution of fuel and hexcan temperature during initial stage of molten fuel attack and (b) evolution of fuel and hexcan temperature during molten fuel attack for long duration

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Fig. 12

Progression of neighboring subassembly hexcan melting as a function of conductivity factor

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Fig. 13

Time dependent temperature rise of neighboring subassembly sodium during molten fuel attack as a function of conductivity factor

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