CFD Modeling of Natural Convection Heat Transfer and Fluid Flow in Yucca Mountain Project (YMP) Enclosures

Francis, Nicholas; Itamura, Michael T.; Webb, Stephen W.; James, Darryl

doi:10.2172/809609

Cited by 6 publications

(9 citation statements)

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“…Reference to Francis et al, (2003), indicates that both tests probably exhibit turbulent flow behavior. In order to determine if the natural convection test operating conditions are turbulent, hand calculations are performed for an idealized geometry (concentric cylinders) that is similar to the test geometries.…”

Section: Appendix a Hand Calculation For Horizontal Concentric Cylindersmentioning

confidence: 98%

Two-Dimensional CFD Calculations for YMP Natural Convection Tests

Francis¹,

Itamura²,

Webb³

et al. 2003

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Processes important to the performance of a nuclear waste repository include cooling of spent nuclear fuel casks emplaced in tunnels bored into volcanic tuff. The geometry consists of an emplacement drift (tunnel), waste package, and a layer of gravel invert providing a flow barrier at the bottom of the drift. During the postclosure period, a drip shield, which is a thin metal sheet that covers the waste package, is also included. The geometry is in essence an enclosed annulus where the heated inner cylinder represents the waste package and the outer cylinder represents the emplacement drift. The waste package is below the centerline of the drift, so the geometry is eccentric. The invert floor impedes the flow in the lower portion of the annulus. Yucca Mountain Project (YMP) has developed two natural convection tests (25% and 44%-scale) in order to understand the heat transfer and fluid flow processes associated with this geometry. Measurements of temperature and fluid velocity are the primary results of the tests. Computational fluid dynamics (CFD) is used to determine the heating characteristics associated with the natural convection tests. The CFD analysis described in this report is two-dimensional. Steady-state annulus temperature distributions and flow fields are presented for different experimental heating conditions. Maximum heat source temperatures from the CFD models range from 37 o C to 50 o C for cases without a drip shield and from 40 o C to 56 o C for cases with a drip shield. Hand calculations for a simplified geometry without a drip shield resulted in a temperature of 42.8 o C for the 25%-scale configuration and 43.4 o C for the 44%-scale configuration.

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Section: Appendix a Hand Calculation For Horizontal Concentric Cylindersmentioning

confidence: 98%

Two-Dimensional CFD Calculations for YMP Natural Convection Tests

Francis¹,

Itamura²,

Webb³

et al. 2003

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“…Goldstein (1976, 1978) provided correlating equations for the equivalent thermal conductivity as a function of Rayleigh (Nusselt) number. As detailed in Section 2 of this paper Francis et al (2003) generated the equivalent thermal conductivity for two-dimensional natural convection in the YMP drifts using FLUENT runs with and without convection.…”

Section: Equivalent Thermal Conductivitymentioning

confidence: 99%

“…The waste package is represented by the average waste package diameter. The geometries of the other drift components are as given in Francis et al (2003). The domain for the drift CFD models is a half-cylinder 15.5 m in diameter including the rock.…”

Section: Model Geometrymentioning

confidence: 99%

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Comparison of CFD Natural Convection and Conduction-only Models for Heat Transfer in the Yucca Mountain Project Drifts

Hadgu¹,

Webb²,

Itamura³

2004

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Yucca Mountain, Nevada has been designated as the nation's high-level radioactive waste repository and the U.S. Department of Energy has been approved to apply to the U.S. Nuclear Regulatory Commission for a license to construct a repository. Heat transfer in the Yucca Mountain Project (YMP) drift enclosures is an important aspect of repository waste emplacement. Canisters containing radioactive waste are to be emplaced in tunnels drilled 500 m below the ground surface. After repository closure, decaying heat is transferred from waste packages to the host rock by a combination of thermal radiation, natural convection and conduction heat transfer mechanism?. Current YMP mountain-scale and drift-scale numerical models often use a simplified porous medium code to model fluid and heat flow in the drift openings. To account for natural convection heat transfer, the thermal conductivity of the air was increased in the porous medium model. The equivalent thermal conductivity, defined as the ratio of total heat flow to conductive heat flow, used in the porous media models was based on horizontal concentric cylinders. In order to mechanistically model natural convection conditions in YMP drifts, the computational fluid dynamics (CFD) code FLUENT (Fluent, Incorporated, 2001) has been used to model natural convection heat transfer in the YMP emplacement drifts. A two-dimensional (2D) model representative of YMP geometry (e.g., includes waste package, drip shield, invert and drift wall) has been developed and numerical simulations made . Using CFD simulation results for both natural convection and conduction-only heat transfer in a single phase, single component fluid, equivalent thermal conductivities have been calculated for different Rayleigh numbers. Correlation equations for equivalent thermal conductivity as a function of Rayleigh number were developed for the Yucca Mountain geometry and comparisons were made to experimental data and correlations found in the literature on natural convection in horizontal concentric cylinders, a geometry similar to YMP.The objective of this work is to compare the results of CFD natural convection simulations and conduction-only calculations that used the equivalent thermal conductivity to represent heat transfer by turbulent natural convection. The FLUENT code was used for both simulations with heat generation boundary condition at the waste package and constant temperature boundary condition 5 meters into the host rock formation. Comparisons are made of temperature contours in the drift air and temperature profiles at surfaces of the different engineered components using the two 'approaches. The results show that for the two-dimensional YMP geometry considered, 1 the average surface temperatures of the CFD natural convection and conduction-only using the equivalent thermal conductivity are similar and the maximum local temperature differences for the different surfaces were within two 2°C. The differences in temperature profiles reflect the use of a constant equivalent therm...

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“…This report focuses on heat transfer and fluid flow within the annulus between horizontal concentric cylinders at the scale appropriate to YMP. Francis et al, 2002, develops an analysis of heat transfer and fluid flow within the annulus of non-concentric cylinders.…”

Section: Introductionmentioning

confidence: 99%

CFD Calculation of Internal Natural Convection in the Annulus between Horizontal Concentric Cylinders

Francis¹,

Itamura²,

Webb³

et al. 2002

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--The objective of this heat transfer and fluid flow study is to assess the ability of a computational fluid dynamics (CFD) code to reproduce the experimental results, numerical simulation results, and heat transfer correlation equations developed in the literature for natural convection heat transfer within the annulus of horizontal concentric cylinders. In the literature, a variety of heat transfer expressions have been developed to compute average equivalent thermal conductivities. However, the expressions have been primarily developed for very small inner and outer cylinder radii and gap-widths. In this comparative study, interest is primarily focused on large gap widths (on the order of half meter or greater) and large radius ratios. From the steady-state CFD analysis it is found that the concentric cylinder models for the larger geometries compare favorably to the results of the Kuehn and Goldstein correlations in the Rayleigh number range of about 1 O5 to 10' (a range that encompasses the laminar to turbulent transition). For Rayleigh numbers greater than 1 Os, both numerical simulations and experimental data (from the literature) are consistent and result in slightly lower equivalent thermal conductivities than those obtained from the Kuehn and Goldstein correlations.

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CFD Modeling of Natural Convection Heat Transfer and Fluid Flow in Yucca Mountain Project (YMP) Enclosures

Cited by 6 publications

References 0 publications

Two-Dimensional CFD Calculations for YMP Natural Convection Tests

Two-Dimensional CFD Calculations for YMP Natural Convection Tests

Comparison of CFD Natural Convection and Conduction-only Models for Heat Transfer in the Yucca Mountain Project Drifts

CFD Calculation of Internal Natural Convection in the Annulus between Horizontal Concentric Cylinders

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