Cerenkov Glow Viewing Technique for Spent Fuel Verification Current Status and Future Prospectus

The Cerenkov Glow viewing technique is a simple, non—intrusive method of spent fuel verification, widely used by IAEA inspectors. In the course of 1986, Cerenkov Viewing Devices (CVDs) were used in about 179 inspections in 98 NBAs (Material Balance Areas). The two main limitations of the technique are: 1. The Cerenkov glow may be too weak to be visible in the presence of facility light (low signal to noise ratio); 2. There may be interfering radiation from neighbouring fuel elements which makes conclusions difficult. To overcome the first limitation, selectively sensitive devices were developed under Support Programmes of Canada, Japan and the US. Results obtained with them are summarized in the paper. Regarding the second limitation, systematic work has been done with CANDU fuel bundles in a specially prepared tray; similar systematic study is planned with LWR (Light Water Reactor) fuel. The paper examines the merits and limitations of the techniques in the light of the latest results obtained with the new CVDs. The need for calibration of CVDs before use by inspectors and the need for laying down standardized procedures of use are also be discussed. Latest results in these directions are summarized.