No, it wasn't TEPCO. According to Wikipedia it was an experimental fast breeder sodium cooled plant called Monju run by a governmental agency called Power Reactor and Nuclear Fuel Development Corporation: Click here for report!

"Monju Sodium Leak and Fire

On December 8, 1995, the reactor suffered a serious accident. Intense vibration caused a thermowell inside a pipe carrying sodium coolant to break, possibly at a defective weld point, allowing several hundred kilograms of sodium to leak out onto the floor below the pipe. Upon coming into contact with the air, the liquid sodium reacted with oxygen and moisture in the air, filling the room with caustic fumes and producing temperatures of several hundred degrees Celsius. The heat was so intense that it melted several steel structures in the room. An alarm sounded around 7:30 p.m., switching the system over to manual operations, but a full operational shutdown was not ordered until around 9:00 p.m., after the fumes were spotted. When investigators located the source of the spill they found as much as three tons of solidified sodium.

Fortunately, the leak occurred in the plant's secondary cooling system, so the sodium was not radioactive. However, there was massive public outrage in Japan when it was revealed that Power Reactor and Nuclear Fuel Development Corporation (PNC), the semigovernmental agency then in charge of Monju, had tried to cover up the extent of the accident and resulting damage. This coverup included falsifying reports and the editing of a videotape taken immediately after the accident, as well as the issuing of a gag order to employees regarding the existence of the real tapes."

Not a pretty incident and fortunately not a disaster. But certainly a major cover-up.

Charley Noble