The Lucens reactor at Lucens, Vaud, Switzerland, was a small pilot nuclear reactor destroyed by an accident in 1969.In 1962 the construction of a Swiss-designed pilot nuclear power plant began. The heavy-water moderated, carbon dioxide gas-cooled, reactor was built in an underground cavern and produced 30 megawatts of heat (which was used to generate 8.3 megawatts of electricity). It became critical in 1966 and the plant was decommissioned in 1988. It was fueled by 0.96% enriched uranium alloyed with chromium cased in magnesium alloy (magnesium with 0.6% zirconium) inserted into a graphite matrix. Carbon dioxide gas was pumped into the top of the channels at 6.28 MPa and 223 °C and exited the channels at a pressure of 5.79 MPa and at a temperature of 378 °C.It was intended to operate until the end of 1969, but during a startup on January 21, 1969, it suffered a loss-of-coolant accident, leading to a partial core meltdown and massive radioactive contamination of the cavern, which was then sealed.