Resonance Integral and Its Temperature Coefficient for Finite ²³⁸UO₂ Rod

Abstract

The resonance absorption integral and its temperature coefficient for finite ²³⁸UO₂ rods with a density of 10g/cm³, radii of 0.2, 0.3, 0.5, 1.0 and 2.0cm, and heights of 10, 20 and 50cm are calculated by using the RICM code and collision probabilities derived by improving Carlvik's equation.
It is found that assumption of infinite rod height underestimates the resonance integral and the coefficient by about 4.5 and 2.5%, respectively, in the case where the height is 10cm and the radius 2cm, if the finite cylinder is substituted by an infinite one of the same radius. By adopting an infinite cylinder with the same mean chord length as the finite one, however, substitution of the finite by infinite cylinder is not unduly affect accuracy.
Next, the validity of the flat flux approximation in the axial direction of a finite cylinder is examined by using collision probabilities for a cylinder system divided along its axis into meshes of equal height. It is concluded that no correction is necessary for this approximation.