A new study challenges Werner Heisenberg's postwar claim that Nazi Germany's final experimental reactor was close to working. By examining surviving natural uranium cubes and wartime documents, researchers reconstructed the B8 pile's likely performance and found it fell far short of a sustained chain reaction.
The B8 reactor, built in 1945 under Heisenberg, used uranium cubes suspended in heavy water. According to the team's calculations, it would have required approximately twice as much uranium and more than twice as much heavy water as it actually contained. German forces controlled the only European heavy-water facility, but Allied sabotage and bombing at Vemork, Norway, had disrupted that supply.
Graphite could have replaced heavy water as a neutron moderator, as it did in the American reactor of 1942. But the graphite available under German control contained boron impurities that absorb neutrons, making it unusable. The findings suggest the Nazi program was much further from a functioning reactor than its leading physicist suggested.