a measuring head is used in measuring an assembly part of a nuclear facility , such as a fuel rod , a fuel assembly box , or a spacer of the fuel assembly . the measuring head is capable of augmenting a comparatively large data base representing the overall aging state of the fuel elements in a simple manner and within a short measuring time . the measuring head has a probe tip on the sensor housing and a layer thickness measuring probe is integrated into said probe housing , said measuring probe working according to the eddy current principle . the contour or the diameter of the fuel rod can be determined by the measured deflection of the probe .