Study on a re-verification detection system for IAEA safeguard to a consolidated spent fuel storage system

A modular type storage system that has an enhanced storage density has been developed. It has storage density more than twice larger than silo type which stands alone. The storage module can accommodates 40 cylinders in 4 rows of 10, with 24 located close to periphery of the module and 16 located internally at some distance from the peripheral walls. As for IAEA Safeguards, the module is equipped with a comprehensive set of receptacles into which the IAEA can install seals and verification equipment. The Safeguards equipment, coupled with related measures for physical protection, will facilitate the timely detection of any diversion of significant quantities of nuclear material from the spent fuels stored in the modules. Nevertheless, due to its generic design feature it makes very difficult to provide re-verification of the loaded or under loaded cylinders inside module, along with an unattended monitoring system re-verification is an IAEA safeguard requirement to measure the gamma dose rate and spectrum of each irradiated fuel basket once the storage cylinders are loaded with spent fuel. The gamma profile is read by lowering a detector inside the tube so that it can be registered at the level of each basket. For the 24 peripheral storage cylinders this method of measurement is retained on the side wall of the module. However, an alternate method is required for the 16 internal dry fuel storage cylinders since they are located some distance from the module walls and thus surrounded by storage cylinders. (author)