Explosion of radioactive waste due to metals-water reactions

The accident occurred in a disposal storage for contaminated waste, consisting in a 65-metre shaft flooded with seawater. At the origin of the explosion was the reaction with water of at least two kilograms of sodium and potassium. They reacted violently with the water, producing hydrogen.
The explosion opened the ceiling of the storage. A plume of white smoke blowing out to sea was reported by witness. Probably also an emission of radioactive particles occurred.

According to some report, the accident was possible due to lack of waste disposal control (inadequate safety design, inventory, monitoring).

radioactive waste storage (odium and potassium)

DESCRIPTION of the FACILITY
The power plant was an experimental fast-breeder reactor of 15MW, liquid sodium-cooled, which started operations in 1959. The waste shaft was containing intermediate level waste.

According to one of the sources, the explosion blew off the shaft’s concrete lid, threw its steel top plate 12 metres to one side, badly damaged the 5-tonne concrete blocks at the mouth of the shaft, and blasted scaffold poles up to 40 metres away. A plume of white smoke blowing out to sea was reported by witness. Probably also an emission of radioactive particles occurred.

The role of hydrogen in this event is only secondary. It was produced by the reaction of sodium and potassium containing waste with water: 2Na + 2H2O → 2NaOH + H2.
The reaction is explosive, and the ignition of hydrogen can contribute to the overall energy release.

Because of this hazard, in this fast-breeder reactor hydrogen sensors were installed at the sodium side of the heat exchanger between the primary coolant circuit (sodium) and the secondary circuit (steam, water).
The possibility of a reaction was not considered in the waste storage.