A new article revisiting Heisenberg’s B8 reactor

[Svilen]

A new article revisits an old topic: “Nuclear archaeology reassesses Heisenberg’s last reactor experiment.” It shows that the B8 reactor was roughly a factor of two short of criticality in both its heavy-water and uranium requirements, while also demonstrating that a graphite-moderated reactor was not a viable alternative.

Those fascinated by nuclear history may find it of interest.

Abstract:
The B8 pile, built in April 1945, was a natural uranium, heavy water reactor experiment and the culmination of Nazi
Germany’s nuclear program. Its designer, Werner Heisenberg, claimed in a 1947 Nature article that the B8 was “just
insufficient” in achieving self-sustaining fission, lacking only a “relatively small amount of uranium.” In the following
decades, historians have then suggested that the Germans should have pursued graphite reactors like the Americans.
Here, we present forensics and document-based archaeology of the B8’s uranium, heavy water, and graphites. We create
a neutronics model that is validated by in situ 1945 measurements. Our calculations show that the B8, as built, had
keff = 0.94. To achieve self-sustaining fission at keff = 1.0, the Germans would have needed about 2.0 times the uranium
and about 2.2 times the heavy water than they used, far exceeding Heisenberg’s predictions; these inventories were
about 1.2 and 1.8 times, respectively, Germany’s estimated available wartime inventories. Furthermore, we determine
that their graphite, with 3.4 wppm boron impurities and re-used from the prior B7 experiment, would not allow
criticality in a hypothetical graphite-natural uranium pile. German graphites were made of metallurgical coke, which
naturally carry more boron than petroleum coke-based graphites, which were available in America and uniquely enabled
Chicago Pile 1’s criticality. Our findings indicate that Germany could not have built either a heavy water nor a graphite
reactor in World War II.

[Sesselmann]

Thanks for posting - interesting history..