Neutron tomography of damaged fuel assemblies

Neutron tomography is a three-dimensional imaging technique developed at Argonne National Laboratory's Hot Fuel Examination Facility (HFEF) for use in the nondestructive evaluation of reactor fuel assemblies, including those deliberately damaged to simulate accident conditions. Such damaged fuel assemblies are typically irradiated under abnormally severe conditions, resulting in cladding melting and fuel dispersion. This neutron tomography capability is the result of a cooperative effort between Argonne National Laboratory-West and EG and G Idaho, Inc., which are both located at the Idaho National Engineering Laboratory (INEL). Neutron tomography consists of the following basic steps: (a) neutron radiographs are made of the fuel assembly at many angles, (b) these radiographs are then digitized to convert the film density data to digital data, and (c) the digital data set is then used to produce computer-generated cross-sectional representations of the assembly. These cross-sectional images can be generated at any desired axial location and provide early assessment of fuel assembly damage and failure mechanisms without risking displacement of the internal components by cutting. In fact, neutron tomography reduces or even eliminates the need to conduct costly and time-consuming destructive examination of the assemblies.