Leipzig L-IV experiment accident

The Leipzig L-IV experiment accident was the first nuclear accident in history. It occurred on 23 June 1942 in a laboratory at the Physical Institute of the Leipzig University in Leipzig, Germany. There was a steam explosion and a reactor fire in the "uranium machine", a primitive form of research reactor.

Shortly after the Leipzig L-IV atomic pile—worked on by Werner Heisenberg and Robert Döpel—demonstrated Germany's first signs of neutron propagation, the device was checked for a possible heavy water leak. During the inspection, air leaked in, igniting the uranium powder inside. The burning uranium boiled the water jacket, generating enough steam pressure to blow the reactor apart. Burning uranium powder scattered throughout the lab causing a larger fire at the facility.

This happened after 20 days of operation when Werner Paschen opened the machine at the request of Döpel after blisters formed at the gasket. As glowing uranium powder shot to the 6-meter-high ceiling and the apparatus heated up to 1000 degrees, Heisenberg was asked for help but could not provide it.