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GapConductance_web

# GapConductance_web - ENU 4134 – Gap Conductance D...

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Unformatted text preview: ENU 4134 – Gap Conductance D. Schubring October 27, 2010 Learning Objectives I 3-d Evaluate models for gap conductance (“evaluate” meaning both getting a result and considering if the model is physical) I 5-a Develop familiarity with terminology and mathematical symbols common to nuclear TH, including those symbols which do not map one-to-one to terminology I 5-b Use correlations and/or models to analyze problems in nuclear thermal hydraulics Gap Conductance (1) In a typical LWR, the second biggest Δ T is across the gas gap. At BOL, this is a narrow (order of 100 μ m) space between the UO 2 fuel and Zircalloy cladding. It is filled with an inert gas, usually helium. The gap gets smaller as the reactor first comes to temperature; both the width and composition of the gap vary with burnup. Width: fuel swelling and cracking leads to shrinking gap and fuel-clad contact. Composition: fission gases displace some of the helium and reduce conductance through the gap. Gap Conductance (2) The term gap conductance can be confusing. It is possible to formulate this Δ T using a parameter with dimensions of W K- 1 , W m- 1 K- 1 , or W m- 2 K- 1 . Strictly, thermal conductance should have a dimension of W K- 1 , but modeling with dimensions of W m- 2 K- 1 is conventional (consider as a heat transfer coefficient) q 00 g = htc g ( T fo- T ci ) (1) Since the thickness of the gap δ g << D , the gap is usually modeled without regard to curvature effects.modeled without regard to curvature effects....
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GapConductance_web - ENU 4134 – Gap Conductance D...

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