Theoretical Investigations of Tomographic Methods used for Determination of the Integrity of Spent BWR Nuclear Fuel

Abstract: Tomographic reconstructions of the activity distribution within nuclear fuel assemblies have been accomplished from simulated gamma-ray intensity patterns. The possibilities of detecting a missing fuel rod in the inner parts of an assembly have been examined. Three algebraic reconstruction algorithms have been tested. The algorithms rely on contribution coefficients, depending on attenuation and geometric conditions, describing to what extent emitted gamma-rays from each picture element reaches the detector in various positions. Methods of determining the contribution coefficients have been described. Various measurement strategies have been examined. The removal of a fuel rod might imply replacement by some other material. It has been shown that the detection of a missing rod is complicated due to the fact that attenuation of fuel will be assumed in that position, since the removal is to be considered unknown. The reconstructions indicate that the detection of a missing rod in the inner parts of an assembly should be possible.