Effects of Different Types of Void Volumes on the Radial Temperature Distribution of Fuel Pins

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Abstract
The thermal effects of different types of void volumes within a fuel pin, such as porosity, central void, and the gas gap between fuel and clad are examined. A new general relation for the dependence of thermal conductivity on the closed porosity is deduced. For given gas contents and specific ranges of pore temperatures and sizes, a simple approximate equation is set up, which is in good agreement with experimentally obtained results. A central void is very effective in reducing the maximum temperature; and its use implies a considerable increase in linear pin power. In-pile migration of the porosity in the hotter regions of oxide fuel pins forms or increases the central void and densifies the hotter region. This effect is calculated in a two-zone porosity model. For a uniform gap between fuel and clad, the temperature drop is calculated as a function of gap width, linear pin power, inner temperature of clad, inside radius of clad, emissivities of surfaces, and types of gas within the gap, such a...

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