French sodium waste storage rules

In the frame of Superphenix Plant decommissioning, CEA and EDF had to determine the rules to apply for safe sodium waste storage. Even if sodium waste storage has been monitored for some decades (but only during Operational Plant phases), some recent events showed that this item had to be secured before beginning large decommissioning operations. Of course, the best way would be an on-line treatment but operational constraints always imply a delay in this operation. Indeed, a number of sodium wastes will be produced during the period before the end of Superphenix sodium treatment (planned in 2013) and will have to wait for further treatment. The events to be avoided, or at least taken into account, are uncontrolled sodium reaction with air moisture (large hydrogen production, important overheating) and sodium reaction with liquid water (pressure waves, large hydrogen production, important overheating). Careful analysis of all abnormal events in sodium waste storage disposal was performed and led to rule evolution. In 2004, experimental studies were undertaken, in order to know how solid sodium at room temperature reacts with air humidity: the conditions of aqueous sodium hydroxide production (which is the main risk source in sodium waste storage) have been observed. Waste classifying: pure sodium and soda to be separated, bulk and residues to be separated; Sodium waste containers: tight, dry, easy to refill with gas, protected against overpressure effect, with specific marking and reference; Dedicated rooms: dry, with specific markings, with specific sodium fire extinguishers; Maximum duration: three months before next refill with inert dry gas, in an over-container if more than one year; Dry gas feeling: inert gas except for sodium film residues (dry air). For Superphenix application, packaging and storage conditions of sodium wastes have been defined, in accordance with container fluxes to sodium waste treatment cell: it was decided to initially fill the containers (packaging phase) with dry air (dew point less than -10 deg. C) whatever are the sodium waste types, because any gas in the container is rapidly ant totally dried by sodium itself. Then, renewal of gas in the containers will be done with dry argon (storage phase), except for sodium film residues (dry air filling). On site feedback experience will confirm the efficiency of these recent rules which have to be adapted to each specific case (sodium waste type, containers) and which can evolve with on site feedback experience. (author)