Accidental hydrogen formation and explosion at a nuclear reactor

The event occurred during the decommissioning of a nuclear power plant.
It involved a tank containing 100 kg of residual sodium from the decommissioned experimental nuclear reactor which was using liquid sodium as coolant. The reactor had been shut for many years.

A heavy alcohol compound was used to create a stable salt (sodium is very reactive in presence of oxygen or water). This method had previously proved successful. This time however, the alcohol compound probably decomposed, releasing hydrogen and other gasses and eventually rupturing the tank.
The pressure wave caused by the explosion caused one fatality, some injuries and the destruction of a gallery nearby.

According to one of the source (Nucleonics Week, see References), the alcohol used was ethyl carbitol, and research had already shown the possibility that the chemical decomposition (cracking, creating gaseous hydrogen) of this heavy alcohol could occur at temperatures much lower than previously assumed.

experimental nuclear reactor, waste treatment, storage tank with sodium

Theincident occurred during de-commissioning of a nuclear reactor was an experimental fast breeder using sodium as coolant.

According to the New Scientist article (see References), most of the radioactive elements contained in the coolant had been filtered out of 37 t of sodium, by using an ad-hoc process. In this process, the sodium is mixed with a solution of sodium hydroxide. The reaction takes place in an oxygen-free environment to prevent explosions, and hydrogen is pumped out. The sodium left in the tank was thus radiation-free.

Local damage. No radioactive contamination of personnel,

A legal procedure was started, but in 2009 was not yet completed.

The sources do not mention corrective actions or recommendations issued to avoid the repetition of the accident, but the ARIA report (see References) reports that the inspection experts identified a series of operative inadequacies and shortcoming in installation safety. These are unfortunately not spelled out in the report.