Underground reactors: a good idea put aside too readily?

The first nuclear accident with partial core meltdown happened in 1969 in Switzerland and involved the Lucens reactor. The Lucens power plant (6 MWe) was a heavy water moderated and CO₂ cooled reactor with the specificity to be installed in a cave. There were no radioactive releases in the atmosphere. At that time the main advantage of underground reactors was their discretion and some were built secretly in Siberia, and others more openly in Scandinavia and in France (Chooz A). Today the main advantage of underground facilities is their quasi invulnerability in terms of humane attacks (terrorism, airplane crash...) or natural disasters (storms, hurricane...). The reduced size of Small Modular Reactors (SMR) makes them well suited for underground facilities. (A.C.)