Year 1998

"Controlled" Sodium Fire at Cadarache

WISE-Paris, MP, MS 1 October 1998

[Posted 01/10/1998]

A large sodium fire occurred on Friday 25 September 1998 in a non nuclear installation of the Nuclear Research Center of the Commissariat à l'Energie Atomique (CEA) at Cadarache, in the South of France.

The facility in question, operated by CEA's Institut de Protection et de Sûreté Nucléaire (IPSN), is a test facility where sodium is normally voluntarily ignited in order to study burning characteristics and fire fighting options. Sodium is a solid metal which ignites in air and reacts violently with water. Molten sodium is used as a coolant in fast-breeder reactors. The 250 MWe demonstration Phénix reactor is the only fast-breeder reactor currently operated in France. The 1,200 MWe Superphénix reactor has been shut down for good. However, the core is still in the reactor tank and the primary coolant pumps are operated to remove residual heat and to keep the primary sodium liquid.

It is during the transfer of sodium through a test facility that the fire started. Instead of trying to turn the fire out, IPSN staff instead decided to let the fire burn out alone, since the fire happened in a facility which is designed to withhold such fires. Or is it that they realized that they would not have any chance of putting the fire out ? The building is said to be designed to withstand fires involving 70 tons of sodium ("sheet" or "layer" types of fires of sodium, which are less violent than the "spray" types of fires).

According to IPSN, the fire is believed to be due to a non-totally inert atmosphere in a container.

The sodium which reacted was destined to be destroyed, since the fast-breeder technology is not to be developed anymore in France, and IPSN has now put an end to its safety programs on the burning of sodium. IPSN still has more than 30 tons of sodium from the testing programs to be converted into stable soda, a slow controlled reaction between water and sodium.

According to IPSN's Gonzalez at Cadarache, only 10 to 15 kg out of the 2 tons of sodium involved actually burnt, according to the quantity of aerosols which were generated during the burning of the sodium. On 1 October 1998, IPSN transferred the sodium which had not burnt and the ashes into inert storage containers.

Cadarache already had a deadly accident, on 31 March 1994, when during the decommissioning of the demonstration fast-breeder Rapsodie, a chemical reaction with 100 kg of sodium remaining from the cooling circuit of the reactor led to a violent explosion. The explosion destroyed a building and killed one operator. Four other workers were injured.

With these two accidents in mind, NERSA, owner-"operator" of the shut-down Superphénix reactor, will have to demonstrate particular caution during the destruction of some 6,000 tons of sodium from the reactor, which is in this case radioactive.

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