Leipzig L-IV experiment accident.

The experimental proto-type L-IV nuclear reactor led to the consisting of steam explosion and reactor fire in Leipzig, Nazi Germany on June 23rd, 1942.
 
The L-IV test, indicated that the spherical geometry, with five metric tons of heavy water and 10 metric tons of metallic uranium, could sustain a fission reaction.
 
The fire and subsequent explosion was the world's first nuclear accident in history, 4 died during it and it has a unofficial INES accident rating of 4.
*Sources: https://en.wikipedia.org/wiki/Leipzig_L-IV_experiment_accident, http://www.deutsches-museum.de/archiv/archiv-online/geheimdokumente/forschungszentren/leipzig/ and http://umweltfairaendern.de/wp-content/uploads/2014/05/ArnoldHeinrich-Zu-einem-autobiographischen-Brief-von-Robert-Doepel-an-Fritz-Stratmann-ilm1-2012200288.pdf.
Category:Nuclear accidents and incidents
Category:Nuclear energy in Germany
Category:1942 in Germany
Category:1942 disasters
Category:History of Leipzig
Category:Atomic reactors