Installation of ESPIGA Device in fuel assemblies with accessibility difficulties in vertical direction

To the date, Enusa has accomplished the conditioning of around 470 spent fuel assemblies in Spanish nuclear plants using ESPIGA device. This type of process makes possible the handling of those fuel assemblies affected by intergranular stress corrosion cracking on union sleeve between top nozzle and guide tubes.

This specific project has the goal to develop and manufacture the necessary tools to condition 168 fuel assemblies placed on non-vertical accessible positions on three spent fuel pools. A new process and tool adaptation is necessary for these special positions, as the fuel assemblies have handling limitation using normal methods and the ESPIGA device requires to be installed in those positions.

Several tools are required for ESPIGA device installation process on non-vertical accessible fuel positions. The process starts with an electrical discharge machine making a hole on fuel assembly top nozzle that allow vertical access to instrumentation tube. Subsequently hole dimensions and non-debris on instrumentation tube is verified. Afterwards, ESPIGA device is moved and introduced throw the hole made by the electrical discharge process. The ESPIGA installation continues using a specific tool which allows to hold the ESPIGA device from its top and make the necessary rotations that cause a geometric change on device bottom part, leading to the blockage that permits structural connexion between fuel assembly top and bottom nozzles.

In addition to ESPIGA installation it could be necessary a previous movement of burnable poison assembly, neutronic source or thimble plugging device. For this reason, new handling tools have been also designed and manufactured. They will allow to capture all these components and move there from not vertical accessible locations to other pool positions before ESPIGA device reparations started.

First Installation of ESPIGA devices in non-vertical accessible positions was successfully performed on nuclear plant on 2022. The installation of ESPIGA device in pending assemblies will allow their movement with the tools already available at the nuclear power plants in order to continue with the spent fuel management process.

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