Study: B8 reactor lacked uranium and heavy water — Live Science

Researchers have established that the German B8 nuclear reactor in Haigerloch, Germany, was far from a self-sustaining chain reaction at the end of World War II. A mathematical model created on the basis of archival documents and an analysis of two surviving uranium cubes showed a shortage of both uranium and heavy water, Live Science reports.

Uranium and heavy water were insufficient

The B8 reactor consisted of five concentric circles of uranium cubes suspended on chains in a tank of heavy water. A radium-beryllium neutron source was planned to be placed at the center of the installation to initiate a nuclear fission chain reaction.

The reactor contained 664 natural uranium cubes weighing approximately 2.32 kilograms each, or about 1,540 kilograms in total. According to the study's authors, at least 1,200 cubes were needed for a self-sustaining reaction. The total stock of uranium cubes distributed among experimental groups in wartime Germany amounted to about 1,100 units.

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B8 also contained approximately 1,400 liters of heavy water, although more than 3,000 liters were required for a continuous chain reaction. Heavy water contains the hydrogen isotope deuterium and can slow neutrons, facilitating uranium nuclear fission.

Testing Heisenberg's claim

German physicist Werner Heisenberg, who led the reactor's development, wrote in 1947 that the installation was nearly ready and required only a relatively small additional amount of uranium. The study's first author, Patrick Park, a doctoral student at Princeton University, concluded that this estimate differed from actual requirements by roughly a factor of two.

The authors of the paper, published in the journal PNAS Nexus, also assessed the possibility of building a reactor in Germany with a graphite moderator, similar to the installation in Chicago during the American atomic program. They concluded that this was impossible because of the high boron content in the coal available for graphite production: boron absorbs neutrons. Heavy water for B8 was produced by the only plant in German-occupied Norway, but its capacity would not have been sufficient to supply the reactor with the required volume.