It was intended to operate until the end of 1969, but during a startup on 21 January 1969, it suffered a
loss-of-coolant accident, leading to a partial core meltdown and the
radioactive contamination of the cavern, which was then sealed. Using the criteria of the
International Nuclear Event Scale, introduced in 1990 by the
International Atomic Energy Agency, the event has been assessed as a Level 4 "Accident with local consequences". The accident was caused by water condensation forming on some magnesium alloy
fuel element components during shutdown and corroding them. These
corrosion products accumulated in some fuel channels. One of the vertical fuel channels was sufficiently blocked by it to impede the flow of carbon dioxide coolant, causing the magnesium alloy cladding to melt and further block the channel. The increase in temperature and exposure of the uranium metal fuel to the
coolant eventually caused the fuel to catch fire in the carbon dioxide coolant atmosphere. The pressure tube surrounding the fuel channel split because of overheating and bowing of the burning fuel assembly, and the carbon dioxide coolant leaked out of the reactor. No
irradiation of workers or the population occurred, though the reactor's cavern was seriously contaminated. The cavern was decontaminated, and the reactor was dismantled over the next few years. The plant was decommissioned in 1988, and the last radioactive waste was removed in 2003. The remaining waste lies buried in the concrete filled reactor. A removal is not planned. == See also ==