Enriching Uranium-235 is not the only way to produce a nuclear bomb Image: Jewish Federation of Sarasota-Manatee

The UN’s IAEA has reported that Iran has 55.6 kilograms (122.6 pounds) of 60% enriched uranium. The body says this means Iran is able to produce up to 25 kg (55 lbs) of 90% enriched uranium, enough for a nuclear bomb.

The real story could be even more concerning. Consider the hoary phrase, “There’s more than one way to skin a cat.” Similarly, there’s more than one way to make a nuclear bomb.

The Union of Concerned Scientists has said that it might be possible to produce a fission-type nuclear weapon with as little as 15kg (33 lbs) of highly enriched uranium. The Hiroshima bomb, which was uranium-fueled, required 64kg (141 lbs) of enriched uranium.

But if enriched Uranium-235 is one way to produce a nuclear bomb, a plutonium bomb is also possible – and Iran has pursued both. It is worth considering that Iran could have a hidden plutonium program – or, alternatively, is acquiring plutonium from outside. 

North Korea produces plutonium at its Yongbyon reactor complex situated 60 miles north of Pyongyang. It appears to have surplus plutonium and is aiming to produce even more. North Korea, Iran and Syria cooperated in building a clone of this reactor in eastern Syria at Al Kibar. That reactor was destroyed in a complex Israeli operation on September 5-6, 2007.

For the record, the 2015 Joint Comprehensive Plan of Action (JCPOA) nuclear agreement declared all plutonium production off limits for Iran. Iran was required to halt the construction of a plutonium reactor at Arak and was said to have filled the reactor’s core with cement. 

But in 2020 Iran’s atomic energy chief, Ali Akbar Salehi, announced that the JCPOA-required optic was only for show. “When they told us to pour cement into the tubes,” he recalled, “we said: ‘Fine. We will pour.’ But we did not tell them that we had other tubes. Otherwise, they would have told us to pour cement into those tubes, as well.”

Fereydoun Abbasi, a member of the Iranian parliament’s energy committee, said this week that Iran should build a plutonium reactor in addition to enriching uranium. While Abbasi claimed plutonium was needed for peaceful purposes, his declaration could nonetheless be decoded to signify that Iran already has an active plutonium program.  

An Iranian nuclear power plant. Photo: thebulletin.org / Creative Commons

What seems to be true is that, for Iran to be able to assemble a significant nuclear weapons arsenal, it will need plutonium in addition to uranium – on the simple basis that Iran, like the United States, would never be able to enrich enough uranium for bombs.

The story of the Hiroshima bomb may tell us something about Iran’s program and may illustrate that it is not depending on uranium to make nuclear weapons.   

In 1945, the US was developing both uranium- and plutonium-fueled atomic weapons. The US bomb that struck Hiroshima was a uranium bomb while the one that was dropped on Nagasaki was a plutonium bomb.  

The US Manhattan Project during World War II was primarily enriching uranium at Oak Ridge, Tennessee. Three programs operated there: two uranium enrichment plants (K-25 and Y-12) and a liquid thermal diffusion plant (S-50). The Y-12 plant used electromagnetic separation to extract the weapon’s grade enriched uranium using calutrons. 

It is worth noting that Iraq also used calutrons to extract uranium – and a nuclear reactor for plutonium production – although it never got to the point of producing a nuclear weapon.

The Oak Ridge K-25 plant was a massive complex using gaseous diffusion to extract uranium, which was then sent to the Y-12 plant to raise the level of enrichment.

At Oak Ridge, there also was an early graphite reactor, based on the work of Enrico Fermi and his team at the University of Chicago – work that finally resulted in a huge installation at Hanford, Washington state, for producing plutonium.  

Even today there is some controversy about the Manhattan Project’s weapons-grade uranium manufacturing program. The controversy is over whether there was ever enough enriched uranium even for the Hiroshima bomb.

What is indisputable is that at the end of the day there was so little production that only one bomb was built. Additionally, prototypes of that bomb were never tested because of the lack of fissile material.    

Perhaps related: In May 1945 after Germany’s surrender, German submarine U-234, an XB-4U type, surrendered at sea to the US Navy and the submarine and its crew were taken to the US Navy base at Portsmouth, New Hampshire. The submarine was carrying uranium and was originally ordered to take its cargo to Japan.

Surrender of the German U-boat U-234. Photo: Wikipedia

The type of uranium on board remains unclear. There are claims from some crew members that the submarine was carrying lead-encased containers marked U-235 (enriched uranium). For other types of uranium, lead containers would not have been needed because the uranium would not have been radioactive.

In any case, one theory is that the uranium was quickly moved to Oak Ridge and used as part of the material put into the Hiroshima bomb.

Even with the sub’s uranium cargo available, the US turned to plutonium, which was being produced at Hanford.  In late 1945, the US had enough plutonium for about five bombs and from there the production of atomic weapons ramped up.

The IAEA thinks Iran, probably in one or two years, will be able to produce a small number of nuclear weapons. If these mirror the explosive power of North Korea’s nuclear weapons, their size will be roughly equal to the bombs used on Hiroshima and Nagasaki. They may even be significantly smaller in yield. 

But what if Iran also has a plutonium program? That would require a reactor and plutonium extraction capabilities, but all are within reach. Given that major parts of Iran’s weaponry program are underground and inaccessible to inspection, it is impossible to rule out the possibility. 

Iran also could be getting plutonium from outside, possibly from North Korea.   

Iran is getting closer and closer to having nuclear weapons, but plutonium will be needed to give the Islamic Republic a credible arsenal – perhaps 20 to 25 weapons (similar to North Korea’s arsenal) in the next few years.

Instead of focusing solely on uranium enrichment, monitoring authorities need to obtain more intelligence on what Iran might be doing to produce plutonium or smuggle it into the country.

Follow Stephen Bryen on Twitter at @stevebryen