First results with the new high-resolution gamma ray tomograph

For gamma ray tomography measurements of void fraction distributions in fuel rod bundles of boiling water reactors a new high resolution tomography system has been designed and built. Particular objectives of this application are the measurement of sub-channel void distribution and the investigation of dry-out effects in electrically heated fuel rod bundles. The application requires a robust tomography system that works in an industrial environment. In particular it was necessary to develop a high-resolution gamma radiation detector that is unsusceptible to strong magnetic fields, ambient temperature changes, and vibration forces. The developed detector is made of avalanche photodiodes (APD) coupled to small lutetium yttrium orthosilicate scintillation crystals (LYSO). Together with a special data processing unit and either a Cs137 or a Co60 source it can be operated as a tomography device for diverse diagnostic problems in science and engineering.