Study finds Nazi Germany needed far more material for nuclear reactor

A model of Nazi Germany’s B8 reactor shows it would have needed several times more uranium and heavy water to sustain a chain reaction, ERR reported. The findings challenge physicist Werner Heisenberg’s postwar claims about how close the programme came to building a working reactor.

Heisenberg joined the German nuclear programme, known as the Uranium Club, in 1939. He led eight major experimental series at the University of Leipzig and the Kaiser Wilhelm Institute for Physics in Berlin, aiming to demonstrate that uranium could produce energy.

After the war, Heisenberg argued that the B8 reactor built at Haigerloch had fallen short of criticality by only a relatively small amount of uranium. In a 1948 review, he said roughly twice as much nuclear fuel would have been needed. His claims divided historians and scientists: some accepted that the programme was held back by a shortage of materials, while others argued Germany had chosen the wrong approach by using heavy water instead of graphite.

Researchers led by Patrick Park of Columbia University and other institutions examined components of the B8 reactor, completed in April 1945. Using archival documents and uranium cubes, they built a computer model and used forensic methods to assess the uranium’s density and the heavy water’s purity.

The model found that the reactor could not have worked with the materials available to Heisenberg at Haigerloch: 664 uranium cubes and 1,400 litres of heavy water. Depending on the configuration, the team estimated that the project would have needed 1.9 to 2.7 times more uranium and 2.1 to 2.4 times more heavy water. Even gathering all the supplies available to the programme in Germany and Norway would not have been enough.

The researchers also concluded that the reactor would have required several times more fuel even if the heavy water had been 100 per cent pure.