Researchers reveal how close the Nazis came to building a nuclear reactor

1 May 2019

One of the 664 uranium cubes used by the Nazis as part of their nuclear reactor. Image: John T Consoli/University of Maryland

How close were the Nazis to building a working nuclear reactor? Researchers find they could have been closer, except for one big problem.

One of the greatest – and chilling – ‘what if?’ scenarios of the past century has been the question of what would have happened if Nazi Germany had become a nuclear power before the US. While it never came to be, historians have shown that the regime’s top scientists had attempted to develop their own nuclear reactor.

So in 2013, it came as a surprise to Timothy Koeth of the University of Maryland on his birthday when he received a little cloth lunch pouch containing a small object wrapped in brown paper towels. Within it, to his astonishment, was a heavy metal cube with a message that read: “Taken from Germany, from the nuclear reactor Hitler tried to build. Gift from Ninninger.”

Despite measuring just 5cm on each side, the cube weighed more than 2kg and was discovered to have been one of the 664 uranium metal components strung together as part of the reactor design. Writing in Physics Today, Koeth and his colleague Miriam Hiebert described their attempts to uncover the truth behind the Nazi nuclear reactor.

The string of uranium cubes would have been reminiscent of a chandelier, comprising the core of the Nazi reactor experiment attempted towards the end of the war. Including a team of brilliant theoretical physicists such as Werner Heisenberg, the chandelier structure would have been submerged in heavy water to regulate the rate of fission.

Looking into the experiment more, the researchers were surprised to discover that while the 664 uranium cubes located deep underground in the town of Haigerloch weren’t enough to build a reactor, there were still 400 cubes available within Germany at the time.

“If the Germans had pooled their resources, rather than keeping them divided among separate, rival experiments, they may have been able to build a working nuclear reactor,” said Hiebert.

“This highlights perhaps the biggest difference between the German and American nuclear research programmes. The German programmes was divided and competitive whereas, under the leadership of General Leslie Groves, the American Manhattan Project was centralised and collaborative.”

Working against one another

So, how close did the Nazis get? While difficult to answer, the researchers believe that the reactor would have needed 50pc more uranium to run. Even if they had pooled the 400 additional cubes elsewhere in the country, they would have needed more heavy water to make the reactor work.

Koeth said: “Despite being the birthplace of nuclear physics and having nearly a two-year head start on American efforts, there was no imminent threat of a nuclear Germany by the end of the war.”

The big question for Koeth and Hiebert now is to determine how many of these cubes are still out there, including 400 that ended up on the black market in Europe after the end of World War II.

“We hope to speak to as many people as possible who’ve had contact with these cubes,” said Hiebert. “As much as we’ve learned about our cube and others like it, we still don’t have an answer about how exactly it ended up in Maryland 70 years after being captured by Allied forces in southern Germany.”

Colm Gorey was a senior journalist with Silicon Republic