This started up in 1985, but two years later suffered a serious accident when some of the liquid sodium coolant leaked out.

All large-scale fast reactors have used molten sodium coolant.

There are no rapid violent reactions with water and air that sodium coolant has.

The high volume of liquid sodium primary coolant in the pool configuration is designed to absorb decay heat without reaching fuel melting temperature.

Metal sodium (Na) coolant in many ways has the most attractive combination of properties for this purpose.

Secondly, safety issues are cited as a concern with fast reactors that use a sodium coolant - a leak could lead to a sodium fire.

In May 2005 the core support basket was drilled to drain the remaining sodium coolant, which effectively made the reactor unusable.

The sodium coolant is already running through the coolant loop and has to be kept hot using electric heating elements so it does not solidify.

Thousands of pounds of sodium coolant from the time of the meltdown are not yet accounted for.

The $6 billion reactor has been shut since a huge leak of sodium coolant in December 1995, but the government has intended to resume operations.