The zirconium oxide thickness can be measured by the eddy current (EC) technique. However, before measuring the fuel rod oxide thickness it is important to remove as much crud from the rods as possible. This may be done by brushing the rod before the oxide is measured by the EC probe. If crud is not removed, the oxide thickness value normally obtained is too large. In many cases the crud deposited onto the fuel rods may be ferro­magnetic and therefore the EC technique may fail to give reliable results unless the EC equipment has been designed to compensate for ferromag­netic crud. Eddy Current technique can also be used to detect fuel claddings defects, for example non-penetrating cracks.