Andreas PersboThe Blue and Yellow Bomb (part 2)

Many things remain unknown about Sweden’s nuclear programme, especially why it was suddenly discontinued. It is interesting to note, of course, that the US intelligence community estimated that Sweden was on its way to the weapon up until 1964. Later intelligence assessments are considerably more cautious. That’s probably because our American cousins knew that Sweden wasn’t seeking it any more. I say cousins as about 1 in 20 of the US population is said to have Scandinavian heritage. My favourites of those are probably Uma Thurman, Charles Lindbergh, Kim Basinger and Buzz Aldrin: beautiful women and daredevil pilots.

Cultural similarities aside, little is known about the deal that was made between the Swedish and U.S. governments at that time. Details seem to be heavily classified on both sides of the Atlantic. Swedish historian Wilhelm Agrell, however, points to the mysterious enlargement of Swedish Air Force bases in the latter half of the 1960s, where several runways were extended to be able to receive strategic bombers. Of course, the Swedish Air Force had none of those. This week, I spoke with Ove Bring, a mentor of mine and author of a 2008 book on Swedish Neutrality. He also told me of the Air Force’s decision to equip Swedish tankers with NATO specification nozzles. It would seem like the Air Force started to work closely with its NATO counterparts in the mid 1960s, but few primary sources exist to confirm this.

While it will take some time to get confirmation on why Sweden abandoned its weapons plans, it is possible to piece together the programme itself. Sweden’s fuel cycle activities in the 1950s and 1960s are fairly well documented. When reading about many of these assets, their relationship with the military programme is implied, but never stated and sometimes denied. Most fuel cycle assets except a reprocessing facility were in place in 1969. However, by that time Sweden had joined the 1968 Nuclear Non-Proliferation Treaty, and its weapons experts had become disarmament experts. In the 25 years that followed, most assets were shut down or decommissioned.

This post is based on a number of sources, including some primary documentation, papers written by FOA researchers, as well as, surprisingly, local community history websites. There are a number of good reports written on the programme, but some of them seem speculative or vague in parts. Of course, the writings of Wilhelm Agrell and Thomas Jonter is highly recommended.

Uranium extraction

The designers of Sweden’s nuclear programme realized, as so many other states seeking nuclear weapons, that the key to the bomb is easy access to uranium ore. If you do not have access to domestic ore, its little point engaging on a full-scale weapons programme. In this respect, Sweden found itself in a favourable position. The country 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. According to a relatively recent survey, Sweden has something between 4 and 32 million tonnes of extractable ore – which was enough for the surveyor to call the country “the Saudi Arabia of uranium” (Continental Precious Minerals Inc., 2005: Results of NI 43-101 Geological Report 7/29/05).

Be that as it may, the ore grade in Sweden varies between 200 and 300 parts per million, which makes it mostly uneconomic to extract. The uranium is hidden in Cambrian period seabed, formed some 400 to 600 million years ago. The Swedish weapons programme focussed on two areas.

Kvarntorp (59° 7’32.11“N 15°16’23.32“E). Uranium extraction started in 1953 by a Swedish government public venture (Svenska Skifferoljebolaget), which had been conducting oil exploration in the region since 1941. The ore in the area is extremely low grade (only 200 parts per million). By 1956, the company had only managed to extract about five metric tonnes of uranium. When mining stopped in 1963, the company had managed to extract about 50 metric tonnes of uranium.

Ranstad (58°16’19.09“N13°42’44.36“E). The government instead decided to go for the mine in Ranstad. AB Atomenergi got permission to excavate the area in 1959. Ranstadsverket was inaugurated in 1965, but was only running for about four years. In 1969 the mine was shut. It had extracted about 200 metric tonnes of uranium. This production is still accounted for in the OECD Red Book.

Norwegian heavy water
(59°52’43.59“N 8°33’27.03“E)

Another asset that the Swedes needed was heavy water to moderate their reactors. US supplied heavy water came with a troublesome string attached – namely the right to inspect the facilities where the water was used. However, neighbouring Norway had no qualms exporting the precious commodity without strings. Under secrecy, Sweden purchased five tonnes of heavy water from its neighbour.

The Wallenberg family might have facilitated the deal. Marcus Wallenberg, a Swedish lawyer and banker, sat on the Norsk Hydro board for 37 years. Norsk Hydro owned and operated the Norwegian heavy water plant in Rjukan. Wallenberg was also a founder of ASEA (which were later in charge of developing Sweden’s nuclear power plants) and the family controlled SAAB, the makers of most fighter-bombers of the Swedish Air Force.

The Swedes also had a good ally in Jens Christian Hauge, the Norwegian defence minister, an eccentric former resistance fighter. The Social Democratic leadership in Sweden despised him. Prime Minister Erlander, for instance, once described him as reckless. But Hauge had a good relationship with the Swedish military, and that relationship is sometimes described as one contributing factor to Sweden’s closeness to NATO. The Swedes had noted that Mr. Hauge had already helped orchestrate an export of safeguards-free heavy water to Israel. If Norway could export to Israel, why would it not export to its good neighbour?

FOA Grindsjoen
(59° 5’8.08“N 17°52’16.51“E)

The Swedish weaponization effort was located in a research area south of Stockholm, called Grindsjoen. The research facility was established in 1941 through a personal donation of Olof Arrhenius, son of the Nobel-prize winner Svante Arrhenius (a Swedish chemist and physicist). It was established to promote ‘natural sciences for defence needs’. It was initially never a formal authority of the state, but rather a collaboration of the physics faculties of all Swedish universities. The military found the location perfect. Since it was so remote, it was easy to keep it secret. The remote location was also appealing to the young scientists employed there. The nature was beautiful, and the local waterways were perfect for fishing and other activities.

At the end of the 1950s, it employed about a hundred scientists and engineers, all tasked to figure out how to build a nuclear weapon. According to some who worked there, they never actually received any instruction to build the weapon. They were conducting basic theoretical studies: such as implosion technology, material studies (especially on UK supplied plutonium), and other basic calculations. The design team early opted for a plutonium-fuelled implosion device. Calculations on the optimum configuration were made on a state-of-the-art IBM 7090 computer installed by FOA in 1961 (the IBM 7090 was also used by NASA in the Mercury Programme). They validated the calculations by conducting cold tests with suitable surrogate materials. The conclusion was that it was not a simple feat to achieve ideal geometry. However, within a couple of years, the team felt that they had good knowledge of what needed to be done.

The Grindsjoen team also needed to know how plutonium behaved under intense pressure. They knew that if they could increase the metal’s density (under pressure), the critical mass would decrease. For that reason alone, high explosive research got priority. The FOA team therefore conducted compression tests where small samples of plutonium were compressed by high explosives within a steel container (which in turn was placed in a facility glove box). The team studied, albeit not very extensively, casting, shearing, and stabilization of plutonium metal. And they also developed a prototype neutron initiator.

The R1 reactor
(59°21’0.33” N18° 4’0.91“E)

The R1 was Sweden’s first reactor. It was fuelled by three metric tonnes of uranium metal provided by France, and moderated by five tonnes of heavy water supplied by Norway. The reactor is located 27 meters under the buildings of the prestigious Royal Institute of Technology. It was not a reactor designed to produce significant quantities of weapons grade plutonium (its effect was only 1 MWth). Rather it was built to give the Swedes reactor operation experience and to supply knowledge for how to build bigger, more powerful, reactors down the line. The CEO of AB Atomenergi, none other that Sigvard Eklund, inaugurated the reactor in 1954. One of the scientists who worked there was Professor Rolf Maximilian Sievert. AB Atomenergi made no secret of the reactor. Indeed, the Swedish King was present at the inauguration, and there were even postcards produced with the reactor as a motif.

The R2 and R2-0 reactor at Studsvik

The second reactor to be built was the R2, a pool type reactor with a 50 MW thermal effect. The R2-0 reactor was much smaller, with a 1 MW thermal effect. Both reactors were commissioned in 1960. The idea was to transform the sleepy little town of Studsvik into a nuclear research area. The institute was initially called “Atomic City”. Both reactors were nominally civilian, and was brought on-line for material testing and irradiation. The reactors were shut down in 2005. Remarkably, the US Atomic Energy Commission contributed 350,000 dollars to its construction. The United States also supplied the reactor with its fuel, 93.5 per cent enriched uranium. A typical core started with a load of 12-13 kilograms of highly enriched uranium, but prolonged burn-up often reduced the quantity to about 160 grams.

The R3 reactor at Agesta

One of the most fascinating reactors associated with Sweden’s efforts to seek nuclear weapons is R3/Adam. This was a small nuclear power plant, which was not really part of the weapons programme. It was seen as a test reactor on a very large scale. It had an 80MWth effect (about 12 MWe). The heavy water was supplied by the United States. The reactors burn-up was declared to be 3000 MWd/t. The total fuel load was 18 metric tonnes of natural uranium. If you simulate the reactor with the IAEA’s INFCIS system, you’ll find that the spent fuel if off-loaded within the year, would have contained nearly 27 kilograms of Plutonium-239 and only about a kilogram of Plutonium-240. In other words, near perfect weapons grade plutonium. Some of this plutonium is still stored in Sweden (not enough for a weapon). The vast majority has been shipped off to the United Kingdom.

The idea was not to use Agesta as the plutonium producer. For that purpose, AB Atomenergi was building a huge heavy water moderated reactor near Marviken. However, as the Marviken project was running into difficulties in 1966 and 1967, the military started to turn its attention to Agesta again. However, the heavy water was supplied from the United States, which meant that there was no easy way to bypass safeguards. Some preliminary plans for a crash program were drawn up. This would involve emptying Agesta of all US supplied heavy water and fill it up with Norwegian supplied stocks. However, these plans never materialized.

Agesta is remarkably well preserved today. According to visitors, one gets the feeling that the operators are out on a coffee break and may return any moment. However, the Swedish Nuclear Inspectorate has given assurances that the reactor itself may not be run without significant investment. At present, there is a battle going on between those who want to keep the reactor as a cultural artifact, and those who want to tear it down.

The R4 reactor at Marviken
(58°33’10.65“N 16°49’55.65“E)

R4/Eva was to be the biggest reactor produced. It was finished in 1968, but never got permission to load. Moderated by 185 metric tonnes of heavy water, the reactor effect was about 100MWe. The reactor was designed to be able to be loaded and unloaded while in operation. This is obviously useful when producing plutonium for weapons, since it allows the reactor operator to control the burn-up without having to shut the unit down. However, the link to the military programme was never made explicit. The reactor was planned to produce about 80 kilograms of weapons grade plutonium per year.

In his recollections, Peter Margen, the AB Atomenergi manager responsible for reactor projects wrote “… our design team at Atomenergi had introduced the requirement that it should be possible to refuel at full reactor pressure, and thereafter even at full load for purely economic reasons, initially as part of the studies of future large scale plants, and then in our suggested design for R4/Eve. In our discussion with Atomenergi management, the fact that this could also be of value if a situation would arise in future where the production of military plutonium became desirable was mentioned, but never as a directive for our design work.”

However, the design had a flaw, which necessitated the use of slightly enriched (1.2 per cent) uranium and a higher burn-up. Initially, the designers envisioned a burn-up of 5,000 MWd/t, but this was later increased to about 13,000 MWd/t. This fuel could only be supplied by UKAEA. Large quantities of heavy water had been promised from Savannah River. The changes needed delayed the project by a year and a half, and would have considerably increased cost. The plans to bring the reactor into operation were abandoned.

Lessons learned from Marviken were later applied in the construction of the O1 light water reactor in Oskarshamn. By then, all nuclear weapons plans had been abandoned completely.

Sannas Reprocessing Plant
(58°44’29.57“N 11°14’50.93“E)

In the late 1950s, money was allocated to buy land near Sannäsfjorden. It was here, as far away from the Baltic Sea as possible, where the government planned to build a reprocessing facility. AB Atomenergi bought the land in 1963, and later expanded the area to 2.3 square kilometres. Advanced studies were made to build the facility underground, straight into the cliffs by the coast.

The project was discontinued in 1970. Formally, it was due to opposition from the local council. However, it seems more likely that Sannäs was abandoned at the same time as the Marviken project collapsed.

Nuclear testing

The Supreme Commander’s Nuclear Weapons Group (Kärnladdningsgruppen) very briefly touched on nuclear testing in a classified 1962 memorandum. They concluded that Sweden had the capacity to carry out underground nuclear tests in their northern and western mountain ranges. Interestingly, however, they also held that nuclear testing, albeit desired, wasn’t necessary for the production of a nuclear device. This to me, at least, indicates high confidence in the design concepts worked out at FOA Grindsjoen as early as the beginning of the 1960s (Fst/Forskn 21/9 1962 nr KH 0800).

The Ahasverus system

Reportedly, the Swedish Air Force considered deployment and basing of their new weapons. According to some sources, about 100 weapons were ordered. Some of these weapons should have been stored in underground storage facilities, and the operational bombs should have been rotated around on active bases. The Air Force called this the “Ahasverus System”, after the lore of the Jew who taunted Jesus on the way to the Crucifixion and was then cursed to walk the earth until the Second Coming.

So what remained to be done?

According to former FOA researchers, Sweden still had some way to go. Amongst other things, it needed:

√ To accumulate a sufficient stockpile of safeguards-free weapons grade plutonium. This would have involved running the reactors for a while before committing to the weapon.

√ To finish the reprocessing facility.

√ To finish work on the weapons design.

√ To build a metallurgical laboratory capable of treating the plutonium, shaping the pit, and assembling the physics package.

If Sweden had not signed up and ratified the NPT, a blue and yellow bomb could have been reality in the first few years of the 1970s. Without doubt, all preparations for the bomb would have been carried out under the guise of its “peaceful nuclear programme” and under the concept of “expanded defensive research”.


  1. Allen Thomson (History)

    > So what remained to be done?

    A useful checklist to keep in mind when contemplating other nascent weapons programs. Such as, to pick a random example, that implied by the Standard Story concerning the Box on the Euphrates.

  2. Cheryl Rofer (History)

    <lightbulb over head>

    Ranstad! The Swedes took the Sillamäe International Expert Reference Group there to see how they had remediated it in 1998.

    It was a pretty small operation, and the birch trees look nice, but I’m wondering whether they’ll bring up contaminants when the roots grow into the spoils pile.

    Thanks for this series, Andreas. I’ve mentioned the Swedes many times as giving up their nuclear program and gotten incredulous responses. Now I can point to your history.

  3. Rupert (History)

    Don’t be so kind to Sweden.
    We may have given up the Bomb, but we unleashed ABBA on an innocent world…

  4. Andreas Persbo

    Not to mention that we’ve frustrated so many people by flatpacks, impossible schematics, and too many parts in the bag.

  5. Rwendland (History)

    Re on-load refueling for purely economic reasons: The UK similarly only had on-load refueling for the civilian power producing Magnox reactors. The military plutonium Magnox reactors (Calder Hall and Chapelcross) did not have on-load refueling. In the UK on-load refueling was a CEGB requirement to improve the economics of power production; they thought the refueling downtime in a low burnup reactor would be too costly. Though with hindsight the on-load refueling equipment was so troublesome the civilian CEO wrote in a history article that it would have been better not to have bothered with the on-load refueling equipment.

    Re UK supplied plutonium: interesting this is not mentioned in the UK MOD Plutonium and Aldermaston – an historical account though that seems carefully scoped to not include direct exports from BNFL Sellafield. Don’t forget that the U.S. supplied Sweden with 9.3kg of plutonium 1957-1984 as “Fuel elements, sources”. Is it possible you have that UK supply statement wrong?

  6. Andreas Persbo

    Import date: 24 August 1964 and 12 October 1966, batch numbers Rfk AETR 48 and Rfk AE/442/AETR 147, shipper UKAEA, total quantity 604 grams. Oddly, I’ve found no reference in Swedish sources on the Pu shipment you refer to.(

  7. Doug (History)

    Do not forget that another nuclear export from Sweden is Hans Blix. A major influence on things nuclear and the whole Iraq WMD situation.

    Interesting article on Sweden nuclear ambitions!

  8. Josh (History)

    Why is it, looking at the control room of the R2 reactor, that another image floats into view?

  9. Rwendland (History)

    Andreas, 899g of the U.S. Pu is covered in Table 4.1 of the SKI Report you refer to. I guess the rest of the 9.3kg Pu was sent after 1972, so not covered in that table.

    The first U.S. 500g Pu was sent (AETR 18, AETR 442) and returned in 1963, preceding the first UK supply. Another 399g (AETR 85) was imported from the U.S. 1965, but this doesn’t seem to have been returned by 1972.

    NB If you are digging thru archives, you might be interested in this UKAEA letter (bottom of page 7 of the pdf) that notes that in 1961 Norway thought Sweeden might possibly be willing to sell heavy water to Israel; in the end Norway/UK sold Israel the heavy water for Dimona.

  10. Rwendland (History)

    … looking at it again, there appears to be a contradiction/discrepancy between these U.S. and Swedish Pu records.

    The U.S. DOE Plutonium: The First 50 Years say the U.S. supplied Sweden with a total of 9.3kg Plutonium in a number of consignments between 1957 and 1984; with the very strong implication that the first consignment was in 1957.

    The SKI Report 2003:18 that you reference states in Table 4.1 that the Swedish State records for the period 1956-1972 show that the Swedish State’s very first import of Plutonium was on 1963-01-17 (500g Pu from USA).

    So any 1957 consignment has gone missing. On the face of it this looks like an interesting contradiction in two state’s Plutonium records. A possible explanation is that the U.S. 1957 Pu supply was not to a state organisation; perhaps a small amount of Pu to a Swedish University, not considered a state organisation, for academic research. Or perhaps the Pu survey SKI is reporting missed a record, or records from 1957 did not survive.

    Anyway an interesting discrepancy. Perhaps one worth some Swedish researcher investigating?

  11. Andreas Persbo

    My initial reaction was that the US shipment was somehow related with the R2 reactor, but that was uranium, and not plutonium. And quantities don’t match. Nevertheless, is it possible that the US records are mislabelled or something? I mean, 9 kilograms of Pu, that’s a very large shipment.

  12. Rwendland (History)

    Andreas, it is frustrating that the U.S. DOE report does not itemise each transfer. Most of the 9.3kg was probably in fuel elements (MOX?); the body of the report merely says “Austria, Canada, Israel, Switzerland, and Sweden received about 24 kg of plutonium under various Agreements for Cooperation. Most of this plutonium was in the form of fuel elements and oxide.”

    The U.S. report also says Sweden returned 8.4kg of plutonium as Spent fuel 1963-1979. That 1963 matches the first return in Table 4.1 SKI Report 2003:18, 500g from AB Atomenergi.

    Speculating, could Sweden be testing the use of MOX-type fuel elements in one of the reactors? U.S. AEC part funded R2 and supplied the HEU fuel – so maybe there was a joint project to test some MOX-type fuel in R2?

    Seems like it might be something someone might be interesting in look into.

  13. Rwendland (History)

    … Here is a PDF version of U.S. DOE Plutonium: The First 50 Years – the Sweden data is identical to the FAS HTML version. This is a seminal post-Cold War report on U.S. Plutonium disposition. I don’t think it can be wrong in the declassified data it discloses.

    The U.S. supplied a lot of Pu to other countries according to the report, mostly as fuel elements: 7.5 tonnes up to 1994. The vast majority (6.3 tonnes) to West Germany and Japan.