Measurement of void fraction distributions in full scale fuel element bundles using gamma ray tomography

We introduce first results of a void fraction distribution measurement in boiling water reactor fuel element bundles. We employed a recently developed high resolution gamma ray tomography system with a collimated Cs137 isotopic source and a 320 element detector arc. The average spatial resolution of the system is 3 mm in plane and 8 mm axial. We performed transversal scans in six axial planes, with approximately 25 minutes recording time for each scan. To determine void fraction calibration measurements have been recorded at zero and one hundred percent void fraction respectively. Image reconstruction was performed with standard filtered back projection algorithms.