APPARATUS AND METHOD FOR DETECTING POWER DISTRIBUTION IN A NUCLEAR REACTOR FUEL ELEMENT

In order to map the power distribution of a nuclear fuel element, a passive detector is laid along the fuel element in situ to record the residual indiation of the fuel element. The detector spatially records the residual radiation as an image in a radioactive reaction product. In the preferred embodiment, the detector comprises a cylindrical casing or wand enshrouding a material which converts incident gamma radiation having an energy level exceeding a preselected threshold to a correspondingly distributed neutron radiation field. The sheath encases a neutron field-sensitive activant, such as gold, in the form of a filament longitudinally disposed in the casing. The image of the low-level radiation field can thereafter be analyzed according to relatively risk-free techniques to map the power distribution of the fuel element.