Study thwarts 79-year-old belief about the 'Nazi bomb' reactor project ‪

A new study has dismissed a long-standing claim about the Nazis and their nuclear ambition. German physicist Werner Heisenberg, who led the project to create a reactor for the "Nazi bomb" project, wrote in 1947 that it was almost ready by the time the Second World War ended. He claimed that the reactor was "just insufficient" to create a self-sustaining fission reaction, adding that it needed only a "relatively small amount of uranium".

However, his claims have been refuted by scientists in a new study published in the journal PNAS Nexus. They used historical documents and forensic investigations of two surviving uranium cubes to state that Heisenberg had wrongly made this claim.

If the German B8 reactor had worked, Germany would have taken a major step towards the development of the atomic bomb. It could have also created the platform for specialised fission reactors which can be used to create weapons-grade plutonium from uranium.

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According to the new study, Germany’s B8 reactor contained less than half the heavy water and roughly half the uranium required to sustain a continuous chain reaction.

Why Heisenberg got it wrong

Lead author Patrick Park, a doctoral student at Princeton University, said, "My results argue that Heisenberg was off by roughly a factor of two." He also admitted that Heisenberg should be given grace for believing that the reactor was almost ready, since his calculations were only approximate. Besides, the project was relocated to a rock cellar in Haigerloch, Germany, after Berlin was bombed.

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Because of the bombing, the reactor calculation took a backseat as taking care of the affected people became the priority. Park further told Live Science that many details of neutron physics were also not known at this time.

The B8 reactor used five concentric circles of uranium cubes suspended on chains within the heavy water tank. The study utilised archival records of hundreds of these cubes to determine how far the Nazis actually reached in their quest to complete the reactor. Kickstarting the chain reaction required a whole lot of neutrons that would split the uranium nuclei and release more neutrons. For this, German scientists were going to place a radium-beryllium neutron source into the reactor's core.

Heavy water can be used to "moderate" or slow down fast neutrons. They also used graphite in their reactor for coating to reflect neutrons into the chamber. The researchers combined cubes, heavy water and graphite records with the measurements of the two cubes to make a mathematical model of the reactor. This helped them conclude that the heavy water reactor was nowhere near achieving a stable reaction.