A total loss of coolant led to a power excursion and explosion of an experimental nuclear reactor in a large rock cavern at Lucens. The underground location of this reactor acted like a containment building and prevented any outside contamination. The cavern was contaminated and was sealed. No injuries or fatalities resulted.

Defueling and partial dismantling occurred from 1969 to 1973. In 1988, the lowest caverns were filled with concrete, and a regulatory permit was issued in December 1990. Currently, the archives of the Canton of Vaud are located in the caverns.