The history of the uranium project of the Third Reich, as it is usually presented, personally reminds me very much of a book with torn pages. All of it appears as a history of continuous failures and failures, a program with unclear goals and a waste of valuable resources. In fact, a certain narrative about the German atomic program has been built, which is illogical, in which there are significant inconsistencies, but which is being strenuously imposed.
However, some information that we managed to find in publications, including comparatively recent studies on the history of German military-technical developments, allows us to look at the German uranium project in a completely different way. The Nazis were primarily interested in a compact power reactor and thermonuclear weapons.
Power reactor
Günther Nagel's extensive and German-quality work "Wissenschaft für den Krieg", more than a thousand pages based on rich archival material, provides very interesting information about how physicists of the Third Reich envisioned the use of atomic energy. The book deals mainly with the secret work of the research department of the Department of Land Armaments, in which work was also carried out on nuclear physics.
Since 1937, in this department, Kurt Diebner conducted research in the field of initiation of the detonation of explosives by means of radiation. Even before the first artificial fission of uranium was carried out in January 1939, the Germans tried to apply nuclear physics to military affairs. The Department of Land Armaments immediately became interested in the uranium fission reaction, which launched the German uranium project and, first of all, set the task for scientists to determine the areas of application of atomic energy. The order was given by Karl Becker, head of the Department of Land Armaments, President of the Imperial Research Council and General of Artillery. The instruction was fulfilled by theoretical physicist Siegfried Flyugge, who in July 1939 made a report on the use of atomic energy, drew attention to the enormous energy potential of the fissionable atomic nucleus and even drew up a sketch of a "uranium machine", that is, a reactor.
The construction of the "uranium machine" formed the basis of the uranium project of the Third Reich. The Uranium Machine was a prototype of a power reactor, not a production reactor. Usually this circumstance is either ignored in the framework of the narrative about the German nuclear program, created mainly by the Americans, or it is grossly underestimated. Meanwhile, the issue of energy for Germany was the most important issue due to the acute shortage of oil, the need to produce motor fuel from coal, and significant difficulties in the extraction, transportation and use of coal. Therefore, the very first glimpse of the idea of a new energy source inspired them very much. Gunther Nagel writes that it was supposed to use the "uranium machine" as a stationary source of energy in industry and in the army, to install it on large warships and submarines. The latter, as can be seen from the epic of the Battle of the Atlantic, was of great importance. The submarine reactor turned the boat from a diving into a truly underwater one, and made it much less vulnerable to anti-submarine forces of opponents. The nuclear boat did not need to surface to charge the batteries, and its range of operations was not limited by the supply of fuel. Even a single nuclear reactor boat would be very valuable.
But the interest of German designers in the nuclear reactor was not limited to this. The list of machines on which they thought to install the reactor included, for example, tanks. In June 1942, Hitler and Reich Armaments Minister Albert Speer discussed a project for a "large combat vehicle" weighing about 1,000 tons. Apparently, the reactor was intended specifically for this kind of tank.
Also, the rocket scientists became interested in the nuclear reactor. In August 1941, the Peenemünde Research Center requested the possibility of using the "uranium machine" as a rocket engine. Dr. Karl Friedrich von Weizsacker replied that it is possible, but faces technical difficulties. Reactive thrust can be created using the decay products of an atomic nucleus or using some substance heated by the heat of a reactor.
So the demand for a power nuclear reactor was significant enough for research institutes, groups and organizations to launch work in this direction. Already at the beginning of 1940, three projects began to build a nuclear reactor: Werner Heisenberg at the Kaiser Wilhelm Institute in Leipzig, Kurt Diebner in the Department of Land Armaments near Berlin and Paul Harteck at the University of Hamburg. These projects had to split the available supplies of uranium dioxide and heavy water among themselves.
Judging by the available data, Heisenberg was able to assemble and launch the first demonstration reactor at the end of May 1942. 750 kg of uranium metal powder together with 140 kg of heavy water were placed inside two firmly screwed aluminum hemispheres, that is, inside an aluminum ball, which was placed in a container with water. The experiment went well at first, an excess of neutrons was noted. But on June 23, 1942, the ball began to overheat, the water in the container began to boil. The attempt to open the balloon was unsuccessful, and in the end the balloon exploded, scattering uranium powder in the room, which immediately caught fire. The fire was extinguished with great difficulty. At the end of 1944, Heisenberg built an even larger reactor in Berlin (1.25 tons of uranium and 1.5 tons of heavy water), and in January-February 1945 he built a similar reactor in the basement at Haigerloch. Heisenberg managed to obtain a decent neutron yield, but he did not achieve a controlled chain reaction.
Diebner experimented with both uranium dioxide and uranium metal, building four reactors in succession from 1942 to the end of 1944 at Gottow (west of the Kummersdorf test site, south of Berlin). The first reactor, Gottow-I, contained 25 tons of uranium oxide in 6800 cubic meters and 4 tons of paraffin as a moderator. G-II in 1943 was already on metallic uranium (232 kg of uranium and 189 liters of heavy water; uranium formed two spheres, inside which was placed heavy water, and the whole device was placed in a container with light water).
The G-III, built later, was distinguished by a compact core size (250 x 230 cm) and a high neutron yield; its modification at the beginning of 1944 contained 564 uranium and 600 liters of heavy water. Diebner consistently worked out the design of the reactor, gradually approaching a chain reaction. Finally, he succeeded, albeit with an overabundance. Reactor G-IV in November 1944 suffered a disaster: the boiler burst, the uranium partially melted, and the employees were highly irradiated.
From the known data, it becomes quite obvious that German physicists tried to create a pressurized water-moderated power reactor in which an active zone of metallic uranium and heavy water would heat the light water surrounding it, and then it could be fed to a steam generator or directly to a turbine.
They immediately tried to create a compact reactor suitable for installation on ships and submarines, which is why they chose metal uranium and heavy water. They apparently did not build a graphite reactor. And not at all because of Walter Bothe's mistake or because Germany could not produce high-purity graphite. Most likely, the graphite reactor, which would have been technically easier to create, turned out to be too large and heavy to be used as a ship's power plant. In my opinion, abandoning the graphite reactor was a deliberate decision.
Uranium enrichment activities were most likely associated with attempts to create a compact power reactor. The first device for the separation of isotopes was created in 1938 by Klaus Klusius, but his "dividing tube" was not suitable as an industrial design. Several methods of isotope separation have been developed in Germany. At least one of them has reached an industrial scale. At the end of 1941, Dr. Hans Martin launched the first prototype of an isotope separation centrifuge, and on this basis, a uranium enrichment plant began to be built in Kiel. Its history, as presented by Nagel, is rather short. It was bombed, then the equipment was moved to Freiburg, where an industrial plant was built in an underground shelter. Nagel writes that there was no success and the plant did not work. Most likely, this is not entirely true, and it is likely that some of the enriched uranium was produced.
Enriched uranium as a nuclear fuel allowed German physicists to solve both the problems of achieving a chain reaction and designing a compact and powerful light water reactor. Heavy water was still too expensive for Germany. In 1943-1944, after the destruction of a plant for the production of heavy water in Norway, a plant was operating at the Leunawerke plant, but obtaining a ton of heavy water required the consumption of 100 thousand tons of coal to generate the necessary electricity. The heavy water reactor could therefore be used on a limited scale. However, the Germans apparently failed to produce enriched uranium for samples in the reactor.
Attempts to create thermonuclear weapons
The question of why the Germans did not create and use nuclear weapons is still hotly debated, but, in my opinion, these debates reinforced the influence of the narrative about the failures of the German uranium project more than answered this question.
Judging by the available data, the Nazis were very little interested in a uranium or plutonium nuclear bomb, and in particular, did not make any attempts to create a production reactor for producing plutonium. But why?
First, German military doctrine left little room for nuclear weapons. The Germans sought not to destroy, but to seize territories, cities, military and industrial facilities. Secondly, in the second half of 1941 and in 1942, when atomic projects entered the stage of active implementation, the Germans believed that they would soon win the war in the USSR and secure dominance on the continent. At this time, even numerous projects were created that were supposed to be implemented after the end of the war. With such sentiments, they did not need a nuclear bomb, or rather, they did not think it was necessary; but a boat or ship reactor was needed for future battles in the ocean. Third, when the war began to lean towards the defeat of Germany, and nuclear weapons became necessary, Germany took a special path.
Erich Schumann, the head of the research department of the Department of Land Armaments, put forward the idea that it is possible to try to use light elements, such as lithium, for a thermonuclear reaction, and ignite it without using a nuclear charge. In October 1943, Schumann launched active research in this direction, and the physicists subordinate to him tried to create conditions for a thermonuclear explosion in a cannon-type device, in which two shaped charges were fired towards each other in the barrel, colliding, creating high temperature and pressure. According to Nagel, the results were impressive, but not enough to start a thermonuclear reaction. An implosion scheme was also discussed to achieve the desired results. Work in this direction was stopped at the beginning of 1945.
It may seem like a rather strange solution, but it had a certain logic. Germany could technically enrich uranium to weapons-grade quality. However, a uranium bomb then required too much uranium - to obtain 60 kg of highly enriched uranium for an atomic bomb, 10.6 to 13.1 tons of natural uranium were required.
Meanwhile, uranium was actively absorbed by experiments with reactors, which were considered priority and more important than nuclear weapons. In addition, apparently, uranium metal in Germany was used as a substitute for tungsten in the cores of armor-piercing shells. In the published minutes of the meetings of Hitler and Reich Minister of Armaments and Ammunition Albert Speer, there is an indication that in early August 1943 Hitler ordered to immediately intensify the processing of uranium for the production of cores. At the same time, studies were carried out on the possibility of replacing tungsten with uranium metal, which ended in March 1944. In the same protocol, there is a mention that in 1942 there were 5600 kg of uranium in Germany, obviously this means uranium metal or in terms of metal. Whether it was true or not remained unclear. But if at least partially armor-piercing shells were produced with uranium cores, then such production also had to consume tons and tons of uranium metal.
This application is also indicated by the curious fact that the production of uranium was launched by Degussa AG at the beginning of the war, before the deployment of experiments with reactors. Uranium oxide was produced at a plant in Oranienbaum (it was bombed at the end of the war, and now it is a radioactive contamination zone), and uranium metal was produced at a plant in Frankfurt am Main. In total, the firm produced 14 tons of uranium metal in powder, plates and cubes. If much more was released than was used in experimental reactors, which allows us to say that uranium metal also had other military applications.
So in the light of these circumstances, Schumann's desire to achieve a non-nuclear ignition of a thermonuclear reaction is quite understandable. First, the available uranium would not be enough for a uranium bomb. Second, the reactors also needed uranium for other military needs.
Why did the Germans fail to have a uranium project? Because, having barely achieved the fission of the atom, they set themselves the extremely ambitious goal of creating a compact power reactor suitable as a mobile power plant. In such a short time and under military conditions, this task was hardly technically solvable for them.
