22.08.2015   Comprehensive nuclear materials

Predicting the Thermal Conductivity of Irradiated Graphite for Reactor Core Assessments

A method derived by Kelly71 is often used in the prediction ofirradiated graphite thermal conductivity
in the assessment of UK reactor cores. The thermal resistivity, 1/K(T), induced because of irradiation as a function of temperature, T can be given by the differ­ence between the thermal resistivity due to fast neu­tron damage, and the unirradiated thermal resistivity:

1 _ 1 1

K(T)_ Kjt) ~ K0(T)

However,

and as Ka ^ Ka Ka is assumed to dominate in polycrys­talline graphite, Kai(T) = Ki(T) and Kai(30) = K*(30) = Kirr(30), and hence,

 

The addition in these two factors in this way appears to be arbitrary as the author does not know of any validation of this method. Other methods do exist, but they depend on many more measurements

of thermal conductivity at various irradiation and

72 73

measurement temperatures.

 
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The irradiation-induced fractional changes in ther­mal resistivity measured at 30 °C are available for graphite irradiated at various temperatures, Tirr. Therefore, for graphite irradiated and measured at 30 °C, we can write