After World War II, Sweden considered building nuclear weapons to defend themselves against an offensive assault from the Soviet Union. From 1945 to 1972 the government ran a clandestine nuclear weapons program under the guise of civilian defence research at the Swedish National Defence Research Institute (FOA).
By the late 1950s the work had reached the point where underground testing was feasible. However, at this time the Riksdag prohibited research and development of nuclear weapons, pledging that research should be done only for the purpose of defence against nuclear attack. They reserved the right to continue development of offensive weapons in the future.
In recent years declassified documents have shown that Sweden was much closer to possessing the nuclear bomb than previously thought. By 1965 most of the bomb was already built and another 6 months would have been needed to arm it, had the project been given the green light. Another two bombs would have been built shortly thereafter.
The option to continue development of weapons was abandoned in 1966, and Sweden's subsequent signing of the Non-Proliferation Treaty (NPT) in 1968 began the wind-down of the program, which finally concluded in 1972. Sweden was strongly influenced to abandon its nuclear weapons program by the United States.
Background
During the final phase of World War II, the Swedish Government saw value in the future of nuclear energy, especially the Allied interest in Sweden's uranium-bearing black shale deposits. This led to suggestions that Sweden should establish state control over its natural resources, including uranium. Specifically, such controls would include export controls on uranium in collaboration with the American and British governments, exclusive Swedish controls over uranium ore, and a ban on commercial mining of uranium.
Through its advisors, including Manne Siegbahn among others, the government realized the link between its ore and nuclear weapons. After American Ambassador Herschel Johnson brought up that question in a conversation with State Secretary for Foreign Affairs Stig Sahlin on 27 July 1945, the issue was raised at the government meeting on 2 August. On 11 September, Sweden committed itself to establish state control over mining and export of uranium. Sweden rejected the American suggestion of a right to purchase Swedish uranium as well as a right to veto proposed Swedish uranium exports.
The opening of the Cold War and fears of an attack by the Soviet Union led to increasing interest in Sweden possessing its own nuclear arsenal. They were only interested in tactical nuclear weapons that would be used in a defensive role on Swedish territory or nearby seas. For reasons not directly related to security, Sweden never considered strategic nuclear weapons that could reach the Soviet Union. British and U.S. ideas heavily influenced the Swedish Armed Forces’ doctrinal thinking at that time.
Early studies Physics-oriented defence research started in Sweden during World War II, and drew many outstanding Swedish physicists to the Military Institute of Physics (MFI) founded in 1941. Here the focus was on conventional weapons. In 1945, MFI merged with two other organizations to form the Swedish National Defence Research Institute (FOA) in compliance with a 1944 proposal to reorganize the Swedish defence research. Research at the FOA was focused on such things as jet engines, rocket technology, shaped charge systems, and radars.
In August 1945, just a few days after the Hiroshima bombing, Sweden's Supreme Commander of the Armed Forces, Helge Jung, made a request via newly appointed research officer Torsten Schmidt that the recently founded FOA should find out what was known about those new weapons. FOA's first report to the Supreme Commander in late 1945 was largely based on the Smyth Report, the official US report on Manhattan Project and physics behind it, which was published on 12 August.
Connection between nuclear weapons program and civilian use of nuclear energy As soon as nuclear bombs became known, both nuclear weapons and nuclear energy drew significant attention in many countries. Immediately after the Smyth Report came out, discussions around peaceful use of nuclear energy in the US began.
Studies of military and civilian use of nuclear energy started in Sweden even before the end of 1945. In November 1945, the Atomic Committee (Atomkommittén, AC) was founded. AC was an advisory committee of experts with the mission to work out a defence plan and outline the alternative pathways for the development of civilian nuclear program (nuclear energy). In 1947, the government established the atomic energy company AB Atomenergi, 57 percent owned by the Government and the remaining 43 percent owned by a number of private companies active in the mining, steel and manufacturing industries. The company's task was to develop civilian nuclear power.
Even though much of the military research was kept in secret, it seems that the connection between the military and civilian projects initially was not controversial, and necessary because of the lack of available resources and expertise. AB Atomenergi had a close relationship with FOA from the start, and signed a co-operation agreement in 1948. The FOA had already established a research area south of Stockholm (FOA Grindsjön) that became the epicentre for military research and development (R&D). Thus, the Swedish nuclear program emerged as a joint government-business venture quite distinct from other nuclear weapon programs - traditionally solely state-run. When the anti-nuclear weapons movement began to gain influence during the late 1950s and became stronger during the 1960s, the connection between military and civilian nuclear research became viewed with suspicion.
Beginning of the nuclear program
In October 1945, FOA made a request for additional funding for studies of nuclear weapons. The funding was eventually granted. Beginning in 1946, Sweden quickly established a well-organized and well-funded nuclear weapons research program (under guise of "civilian defence research") divided into five distinct areas: research, plutonium production, construction funding for reactors and enrichment facilities, acquisition of delivery systems, and testing and assembly of nuclear weapons. The Department of Nuclear Physics was founded in early 1946 within FOA's department of Physics (FOA 2), and by mid-1946 there were about 20 FOA-researchers and similar number of external researchers engaged in research on nuclear weapons or nuclear energy. Sweden found itself in a favorable position as it was, and still is, very rich in natural uranium. However, the ore grade is quite low (mostly shale), and therefore requires extensive mining and milling. The natural uranium was subsequently supposed to be reprocessed and used as a fuel in the reactors (plutonium recycling).
In 1947, AB Atomenergi (AE) was founded under initiative of the Atom Committee with the goal of building experimental reactors and developing methods to extract uranium from low-grade Swedish deposits for both civilian and military needs. Since 1948, a division of functions occurred between FOA and AB Atomenergi. AE focused on developing methods to separate plutonium from uranium and fission products (reprocessing) in order to allow the plutonium to be used as fuel in the reactors (plutonium recycling). This procedure would enable a more efficient use of the natural uranium. While FOA's uranium activities were carried out, a collaboration agreement was drawn up (with final approval by the Government in 1950) to make sure that military research could benefit from the recently launched civilian nuclear activities.
The actual start of the nuclear weapons program occurred in 1948. In February, the FOA's board decided to turn defence research toward work on nuclear weapons, perhaps because of the divisions that occurred between FOA and AB Atomenergi. Only a few days after the decision, the Supreme Commander, Nils Swedlund, assigned the FOA to explore possibilities for Sweden to acquire nuclear weapons. The exploration was carried out quickly, and on 4 May 1948, the report was finalized with Gustaf Ljunggren (Chief of FOA 1, Department of Chemistry) and Torsten Magnusson (Chief of FOA 2) as signatories. Central in the investigation was that they advocated for investing in nuclear weapons based on plutonium rather than on highly enriched uranium (U-235) since the uranium option turned out to be technically more difficult. The investigation also included a summarized plan for a Swedish nuclear weapons project with primary estimates of time and expenses. According to the report, the time framework was determined by the installation of reactors, mining of the raw material for them and production of plutonium in the reactors rather than the construction of the nuclear weapon itself. The contributing factor for this estimate was the misestimated critical mass of a plutonium pit, believing it to be 20–50 kg instead of the actual 6 kg.
Basic materials
In order to create the plutonium needed for nuclear weapons, the plan was to run heavy water reactors where uranium would be turned into plutonium-239 (Pu-239). The basic materials needed in large amounts included, uranium, heavy water, and graphite, materials hard to obtain because of American export controls established to prevent other countries from acquiring nuclear weapons. Significant amounts of uranium existed as admixture in the Swedish black shale deposits that had already been used during WWII by Swedish shale oil companies to produce fuel, whose strategic value was first realized following Allied propositions. Ranstad was projected to be a major source of uranium.
Under secrecy, Sweden purchased five tons of heavy water from Norway. Later, they planned to produce heavy water at a plant in Ljungaverk. Acquisition of graphite was thought to be straightforward. Access to the required amount of plutonium remained the key technological question throughout the entire Swedish nuclear weapons program.
Already in Autumn 1948, criticism came out in a joint statement by AB Atomenergi and Atom Commission. The FOA reports predicted a military monopoly over Swedish uranium resources to the detriment of civilian research, and that much larger resources were being assigned to plutonium production. The feasibility of the plutonium project was under question. That was the first sign of antagonism of interests between military and civilian nuclear proponents. The plans had been predicated on the idea that each nuclear device required 50 kg rather than 6 kg of plutonium. None of those involved in the project realized that this was, in fact, an overestimation. Although the program was scaled to produce 5-10 weapons per year, given the estimated production of 1 kg of Pu-239 per day, it was actually scaled to produce sixty.
1950s: The Government favors nuclear program
In the early 1950s, the rivalry between the United States and the USSR accelerated markedly. Nuclear arms production proliferation increased as significantly as the Soviet Union exploded its first nuclear bomb in 1949, and in 1953, their first hydrogen bomb. The Korean War broke out and the US adopted the strategy of massive retaliation following any use of nuclear weapons. This policy boosted the strategic value of Scandinavia as a potential location for strategic bombers within striking distance of the USSR.