Nondestructive Determination of Fresh and Spent Nuclear Fuel Rod Density Distributions through Computerised Gamma-Ray Transmission Tomography

Abstract

The morphology of single PWR UO 2 fuel rods has been investigated by employing computerised gamma-ray transmission tomography. Four highly burnt fuel rods of different burnups (from 52 GWd/t to 126 GWd/t) and a fresh rod have been investigated. This paper describes the tomographic station built to acquire the projections together with the related experimental procedure, followed by the description of the image reconstruction techniques implemented. The principal results obtained are presented and analysed at three levels. First, the derived linear attenuation coefficient matrix, which is very useful for the implementation of emission tomography, is discussed. Second, the variation of density as a function of rod radius is presented, showing an interesting morphological change of the fuel with burnup. Particularly for the highest burnup sample, the periphery is characterised by a lower density (a steep decrease of almost 10% from the adjacent region) characteristic of an ultrahigh-burnup high-porosity structure. Finally, the nondestructive derivation of the volume-averaged fuel density was performed, compared with other experimental data, and plotted as a function of burnup, so that an interesting linear relationship between density and burnup was established, providing a potential indicator for the noninvasive determination of nuclear fuel rod burnup.

Performance Evaluation of a Novel Gamma Transmission Micro-Densitometer for Pie of Nuclear Fuel

“…In this application, a collimator is used to limit the field of view of the detector and allow for local measurement of the density. The GTD technique has also been used to investigate the density profile in high burnup fuel, as well as used to obtain a tomographic reconstruction of the linear attenuation coefficient (Caruso et al, 2008;Caruso, 2007). This latter application also had practical implementation in gamma emission tomography (Caruso et al, 2009).…”