Retrieval and conditioning of graphite legacy waste in La Hague plant - 000105

The UP2-400 reprocessing plant at La Hague, France, was commissioned in 1967, and operated until 1998. Over the period, it has processed over 9500 tons of fuel, 5000 tons of which were gas cooled natural uranium fuel (UNGG). During that period, graphite sleeves and magnesium cladding separated from the fuel elements were stored together in two large silos, with some eventual other solid waste. The accumulated total amounted to 1100 tons at the end of the period. The aim of the RCD UNGG 130 Project is to remove all the wastes from Silo 130. Retrieval will be performed in 4 main stages, aiming at optimizing schedule and hazard reduction. In the first stage the bulk of the waste is retrieved. A cable-driven harrow is used to move the waste within the silo towards the retrieval gripper. In the second stage the incoming waste is emptied on a rinsing and size separation table, where the waste pieces are separated according to their size though a vibrating screen with a 15 mm mesh. The finer pieces are evacuated directly into the canister. The bulkiest fragments are transferred and piled into a receiving tank. At this stage, each remaining piece needs to be staged individually. This is done using a picking robot. Once the object has been selected by the robot, it passes through a laser line and is scanned simultaneously by two cameras located above the conveyor. A 3D image is built and submitted to a pattern recognition software which is then able to compare the image to a databank and classify the object. When the software recognizes aluminum pieces, the conveyor automatically stops and the object is removed by the operator with the help of a remote manipulator. When the software recognizes a piece of magnesium (cap or slider), a conventional (upper bound) surface area is recorded and the object is introduced into the storage container. The last step involves the final operations. All kind of waste is introduced into the container (mostly crushed graphite and magnesium) with the exception of aluminium and bulky operational waste. Once the canister is filled with waste and demineralized water, sodium hydroxide and lime are added and the solution is recirculated to homogenize the mixture. The canister is then capped with a vented cover prior to control and dispatching to the interim storage facility. (authors)