In May 1943, Davidenko and many other scientists joined Igor Kurchatov's Laboratory No.2 of the Academy of Sciences of the USSR. He was admired for his knowledge, meticulousness and modesty. From 1943-45, three types of nuclear reactor designs were developed there: heavy water reactors, graphite-water reactors, and uranium-fueled water reactors. Davidenko worked with Georgy Flyorov in studying reactor technology. In May 1948, Kurchatov's group, together with a number of other scientists, was directed to the All-Russian Scientific Research Institute of Experimental Physics or KB-11 in the closed city of Sarov, Nizhny Novgorod Oblast, as part of the Soviet nuclear weapons program. While there, he witnessed a deception during an unexpected visit by Lavrentiy Beria, the feared head of Soviet security and the politician in charge of the nuclear program under Stalin. Kurchatov was in the middle of querying the beveled edge on a plutonium hemisphere, when – reacting quickly before Beria and his entourage – he directed Yakov Zel'dovich to double-check the calculations, which Zel'dovich 'confirmed' to Kurchatov's satisfaction shortly afterwards. Kurchatov put Davidenko in charge of one of three teams working simultaneously on neutron primers for nuclear bombs. The laboratory of the chemist Vitaly Aleksandrovich was selected to continue but Davidenko's laboratory provided equipment. He became director of Department 4 of the 'Installation' – the experimental nuclear research department – in 1952. Starting that year, he had repeatedly and strongly encouraged the theoretical physicistsAndrei Sakharov and Zel'dovich to pursue the route of atomic implosion to compress thermonuclear fuel for a hydrogen bomb in a two-stage device. In November, he and Sakharov went to a laboratory in Leningrad where preparations were being made to monitor radiation from an upcoming nuclear test. While there, they collected newly-fallen snow to concentrate and analyse for radionuclides from the U.S.'s Operation Ivy test earlier that month at Enewetak Atoll. The concentrate was mistakenly thrown away by another chemist. Davidenko was already amongst several employees of the Installation who were considered too important to risk flying; for example, in 1953 he returned from preparations at the Semipalatinsk Test Site in Kazakhstan for the RDS-6 device – the first Soviet hydrogen bomb – in chief nuclear weapons designer Yuli Khariton's train carriage with other scientists. After detonation of that device, he was awarded the title Hero of Socialist Labour and in October was awarded the degree of candidate of the physical and mathematical sciences. In January 1955, his suggestions about an atomic implosion as the first stage in a two-stage thermonuclear device were finally accepted by the theorists. On 14 January, Zel'dovich wrote a note to Khariton outlining the preliminary design scheme, with the following line: "The A.I. idea is due to Viktor Aleksandrovich Davidenko." The introduction to the final report by Sakharov and Zel'dovich on 25 June stated, "The participation of V. A. Davidenko was extremely profitable in the discussion of the problem during its early stage." He became a doctor and professor of physico-mathematical sciences and deputy supervisor of the Institute in 1957. In 1959, he stated a deep admiration for his long-time boss Kurchatov, but insisted that Kurchatov was "first and foremost an 'operator', and what's more, an operator under Stalin." He remained at KB-11 until 1963, when he was seconded to the Kurchatov Institute. Later, he worked at the Joint Institute for Nuclear Research. He is buried in Kuntsevo Cemetery.
