The Norwegian heavy water sabotage (Bokmål: Tungtvannsaksjonen; Nynorsk: Tungtvassaksjonen) was a series of Allied-led efforts to halt Nazi German heavy water (deuterium) production via hydroelectric plants in German-occupied Norway during World War II, involving both Norwegian commandos and Allied bombing raids. During the war, the Allies sought to inhibit the German development of nuclear weapons with the removal of heavy water and the destruction of heavy-water production plants. The Norwegian heavy water sabotage was aimed at the 60 MW Vemork power station at the Rjukan waterfall in Telemark. The hydroelectric power plant at Vemork was built in 1934. It was the world's first site to mass-produce heavy water (as a byproduct of nitrogen fixing), with a capacity of 1.2 tonnes per year. Before the German invasion of Norway on 9 April 1940, the French Deuxième Bureau removed 185 kilograms (408 lb) of heavy water from the Vemork plant in then-neutral Norway. The plant's managing director agreed to lend France the heavy water for the duration of the war. The French transported it secretly to Oslo, then to Perth, Scotland, and then to France. The plant was still capable of producing heavy water, however, and the Allies were concerned that the Germans would use the facility to produce more. Between 1940 and 1944, a series of sabotage actions by the Norwegian resistance movement and Allied bombing ensured the destruction of the plant and the loss of its heavy water. These operations—code-named Grouse, Freshman, and Gunnerside—knocked the plant out of production in early 1943. In Operation Grouse, the British Special Operations Executive (SOE) successfully placed an advance team of four Norwegians on the Hardanger Plateau above the plant in October 1942. The unsuccessful Operation Freshman was mounted the following month by British paratroopers, who were to rendezvous with the Operation Grouse Norwegians and proceed to Vemork. This attempt failed when the military gliders (and one of their tugs, a Handley Page Halifax) crashed short of their destination. Except for the crew of one Halifax bomber, all the participants were killed in the crashes or captured, interrogated and executed by the Gestapo. In February 1943, a team of Norwegian commandos of SOE's Norwegian Independent Company 1 (Kompani Linge) destroyed the production facility in Operation Gunnerside; this was followed by Allied bombing raids. The Germans ceased operations, and attempted to move the remaining heavy water to Germany. Norwegian resistance forces then sank the ferry carrying the heavy water, the SF Hydro, on Lake Tinn.
Background
Enrico Fermi and his colleagues studied the results of bombarding uranium with neutrons in 1934. That year, Ida Noddack first mentioned the concept of nuclear fission. In December 1938, four years after the Fermi publication, Lise Meitner and Otto Robert Frisch correctly interpreted Otto Hahn and Fritz Strassmann's radiochemical experimental results as evidence of nuclear fission. News of the discovery spread quickly among physicists and it was realized that if chain reactions could be controlled, fission might be a new source of great power. What was needed was a substance which could moderate the energy of the secondary neutrons emitted by fission, so they could be captured by other fissile nuclei. Heavy water and graphite were the prime candidates for moderating neutron energy. When Nazi Germany investigated the production of an atomic bomb, a range of options was identified. Although historical records provide limited detail on the German decision to pursue the heavy water approach, it became clear after the war that they had explored that option. Although ultimately unsuccessful, the approach chosen has been demonstrated as technically viable. Plutonium-239 (239Pu) makes effective weapons material, although it requires an implosion-type mechanism rather than the simpler gun-type trigger used in the Thin Man uranium bomb. Heavy water has been demonstrated as an effective moderator for 239Pu production, and may be separated from ordinary water by electrolysis. The German program had already been handicapped by the Nazi purging of German Jewish physicists and the conscription of others and ended in the autumn of 1942.
Approaches to developing a weapon In nuclear-weapon development, the main problem is securing sufficient weapons-grade material; it is particularly difficult to acquire fissile isotopes of uranium-235 (235U) or 239Pu. Weapons-grade uranium requires mining, extracting and enriching natural ore. Plutonium can be "bred" in reactors fueled by unenriched uranium, which requires chemical separation of the 239Pu produced.
Plutonium production Although the most common isotope of uranium, uranium-238 (238U), can be used as secondary fissionable material in hydrogen (fusion) bombs, it cannot be used as the primary fissile material for an atomic (fission-only) bomb. 238U can be used to produce 239Pu through the fission of 235U, which produces neutrons (some of which will be absorbed by 238U, creating 239U). The 239U will decay after a few days, turning into weapons-usable 239Pu. The Germans found that a chain reaction could not be sustained if graphite was used as a moderator, and abandoned it. Unaware that this was due to impurities, they did not test ultra-pure graphite (which would have been suitable). Instead, they settled on a heavy-water-based reactor design. A heavy-water-moderated nuclear reactor could be used for nuclear-fission research and, ultimately, to breed the plutonium with which a bomb could be made.
Deuterium ("heavy water") production
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