Nazi nuclear team was far from building an atomic bomb, new study shows

UPDATE - follow-up to Nazis and the bomb: nuclear archaeology finds Werner Heisenberg mistook how close he was: New scientific analysis reveals that physicist Werner Heisenberg and his Nazi German research team were far further away from building a working nuclear reactor or atomic bomb than they claimed after World War II. Researchers examining surviving material from the wartime project found that Heisenberg grossly overestimated how close his team was to success.

The Findings

Only about 14 of the roughly 1,100 uranium cubes made for the wartime Nazi project still survive today. U.S. researchers used a pycnometer to test one surviving cube and found its density was 18.535 grams per cubic centimetre, which is lower than solid uranium and shows the cube was porous. Another tested cube contained 0.724 percent of uranium-235 by mass, proving it was natural uranium rather than enriched fuel. German physicist Karl Wirtz reported in March 1944 that the nation's heavy water stocks were accidentally diluted to 98.85 percent purity, while a 1947 post-war sample from the test site in Haigerloch found purity had dropped to 96.8 percent.

The Reactor Shortfalls

Heisenberg's team built their final test setup, called the B8 pile, in a cellar beneath a church in Haigerloch before Allied forces captured the area in April 1945. The setup used 664 uranium cubes suspended on chains in about 1,400 litres of heavy water, surrounded by a graphite shell and layers of aluminium and ordinary water. When researchers simulated the design, they found its neutron multiplication factor was 0.942, far short of the value of 1.0 required for a nuclear chain reaction. The simulation showed the B8 pile needed at least 2,994 kg of uranium and 3,411 litres of heavy water to work, but it actually contained only 1,538 kg of uranium and 1,549 kg of heavy water when dismantled.

Industrial Limits

Furthermore, the graphite used in the German reactors was heavily contaminated with boron, which absorbs neutrons and makes a chain reaction impossible. The American Manhattan Project, by contrast, had massive industrial capacity, creating 1.3 lakh jobs and investing $2.2 billion at its peak, while Nazi Germany lacked any comparable scale or resources.

Context

This follows an earlier report, covered earlier on 06 Oct 2026: 'Nazis and the bomb: nuclear archaeology finds Werner Heisenberg mistook how close he was'.