Geoff FordenA Primer on Iran’s Medical Reactor Plans

A swimming pool-type reactor similar to the TRR in Iran whose fuel is apparently the subject of a deal between Iran and the P5+1. The eerie blue light is Cherenkov radiation given off as subatomic particles streak through the surrounding water.

( Techno-Wonk Alert: There are a lot of numbers in this post so if you are not into that, skip to the Summary and Discussion section.)

Friday’s apparent agreement to send Iranian LEU out of the country for further enrichment, so that it can be used to produce medical isotopes in the Tehran Research Reactor (TRR), will undoubtedly cause a lot of people to want to know more about the production of medical isotopes. It certainly made me want to know more. Fortunately, a great deal of information about Iran’s plans for isotope production can be gleaned from a paper in Annals of Nuclear Energy (vol. 30, pp. 883-895, 2003) but Sayareh, Ghannadi Maragheh, and Shamsaie; three researchers at Amir Kabir Technical University and the Atomic Energy Organization of Iran.

Most importantly, they are planning on producing 20 Curies (Ci) of Molybdenum 99 (99Mo) every other week. This is about half their diagnostic requirements for 99Mo, which they currently import. Currently, 95% of the world’s 99Mo supply is produced in six reactors around the world. As of 2006, the reactors in Canada (which produces 40% of the world’s needs), the Netherlands, Brussels, France, Germany, and South Africa used weapons grade uranium as the target . That means that sheets of 90+% Uranium 235 are inserted into the high neutron densities found inside these reactors for very brief periods of time. The US supplies about 25 kg of weapons grade uranium each year to Canada’s NRU reactor alone. This HEU is inserted into the reactor for a short time, just long enough to “burn up” about 5% of the uranium 235. The irradiated fuel is removed and the molybdenum is extracted from the fission products; molybdenum is produced in about six percent of the fissions. Thus, in a year, Canada’s NRU reactor burns about 1.25 kg of HEU and produces about 32 grams of 99Mo each year. (The remaining 23.75 kg of HEU exported to Canada each year is considered “waste” and is not recycled. That’s a lot of nuclear bombs waiting around in the trash can north of the border.) The entire world’s 99Mo production is 80 grams per year. Iran currently imports about 0.2 grams of 99Mo each year. That is about 0.25% of the diagnostic molybdenum produced in the world while Iran has 1% of the world’s population. By way of contrast, the United States with 4.5% of the world’s population, uses about 40% of the world’s diagnostic molybdenum.

Technetium Generators

Molybdenum 99 is not the isotope used for medical diagnostics. Instead, 99Mo is the “long half-life” warehouse for storing and transporting Technetium-99m. Technetium-99m is written as 99mTc where the “m” means “metastable;” just a fancy way of saying that it has a 6 hour half life and decays by emitting a gamma ray, just a very powerful X-ray. As soon as a quantity of 99Mo is made, it starts to decay into 99mTc, however, since the Tc’s half-life is a tenth of the molybdenum, the amount of 99mTc at essentially any time is a constant fraction of the amount of molybdenum. The solution that arrives in the mail is a solution of 99Mo (with a proportionate amount of 99mTc) dissolved in sodium hydroxide. When a dose is required, the same volume of Technetium removed in a column separator (technically a chromatograph) to get a similar amount of 99mTc isotope. This device is known as a Technetium generator or even, apparently, a “moly cow” because it is being “milked” for isotopes, though I would have thought “techni-cow” would be more appropriate. Iran’s weekly requirement of 20 Ci of 99Mo corresponds to, I think, about 4,000 diagnostic doses of 99mTc when the decay of the molybdenum is taken into account.

TRR Specific Information

As is well known by now, the TRR (or Tehran Research Reactor) uses 19.75% enriched uranium as its fuel. This is just shy of the 20% threshold for the fuel not being considered Low Enriched Uranium. When the TRR was supplied to Iran by the United States in 1967 (the date of first criticality), the reactor used weapons grade uranium but in 1992 Argentina sold Iran the present LEU supply. According to Khalafi and Gharib (Ann. Nuc. Ener., vol. 26, pp. 1601-1610), an initial load of the reactor consists of 32 kg of 19.75% uranium in the form of U3O8. The IAEA reports that a reload occurs when a maximum of 42% burn up has occurred. The reactor itself is run, when it is run at full operating power, essentially every other week and burns up 2% of its fuel each week. (I believe that refers to 2% of its initial load since they use the control rods to maintain a constant neutron density over time but I could be wrong about that. Wonk-readers?) If I am correct then this burn up rate means they replace the fuel load every year and a five year supply would amount to 5 × 32 kg = 160 kg (of uranium “metal”). Higher amounts of fuel required for five years have been reported in the press, but I believe that this is the correct amount and will be used in the rest of this post.

Of course, irradiating natural uranium for short amounts of time is a flag for potential weapons grade plutonium production. However, Iran will only be irradiating about 100 g of natural uranium every two weeks. This corresponds to a plutonium production of about 26 milligrams of plutonium each year.

Cost/Benefit Analysis

It costs Iran about a $1 million per annum to import its current needs for diagnostic 99Mo. About half of that is “wasted” in transit as the molybdenum decays, an amount that could be saved if the isotope was produced locally. If, as has been discussed in the media, Iran transfers enough LEU (currently at an average enrichment of 3.5% U235) for five years worth of fuel for the TRR (about 160 kg of 19.75% U235 metal according to my calculations) then it will need to ship about 2200 1500 kg of LEU to Russia. However, according to the IAEA, Iran only has about 1508 kg of UF6 LEU, as of 31 July 2009. So Iran will either have to get less TRR fuel or process more 3.5% LEU. The required amount nicely matches the amount of LEU Iran had as of the beginning of August.

How much does this cost? Assuming $90 per SWU for enrichment services, this further enrichment will cost $170,000, plus shipping. Not counting operating expenses, this is a considerable savings over the $5 million continuing to import diagnostic Molybdenum would cost over the five years the TRR fuel is expected to last. However, this does not count the sunk costs associated with the Iran’s original LEU enrichment. If that is included, again at the artificial rate of $90/SWU, the total opportunity cost to Iran for this fuel would be $380,000. Again, a remarkable percentage savings when compared to the $5 million it would cost to import the same amount of 99Mo.

The real benefit to Iran for completing this deal, however, will not be the savings of a few million dollars or even the savings of nearly half the imported diagnostic radioisotopes from unavoidable wastage due to decays during shipment. The real savings will be the foot up Iran gets in its health care from starting to develop its own nuclear medicine industry. The discrepancy between the use of diagnostic isotopes in Iran and the developed world can, and should, be dramatically reduced; as it should for the entire world.

Summary and Discussion

It seems ironic, considering the problems for enrichment that naturally occurring molybdenum in Iran’s uranium feed stock has already caused, that Iran is going to these lengths to produce it. However, Iran has developed plans to use naturally occurring uranium as a “target” for producing an important medical diagnostic isotope of molybdenum, an isotope whose decay product can be used to scan for cancers in bone, heart, lung, and kidney. Iran already imports a sizable quantity of this pharmacological radionuclide but producing it indigenously would not only save Iran a considerable amount of money each year, much more than it would pay for the fuel for the reactor it would use to produce it, but also allow a more efficient use of this short lived isotope by preventing the decay of nearly half of the amount bought before it even reached the patients. Perhaps the biggest incentive indigenous production of 99Mo in Iran would be the encouragement of its entire nuclear medicine infrastructure; an infrastructure that might right the imbalance of medical isotopes into this developing country relative to other nations.

Sending essentially all of its current LEU stock that it has produced over the past two and half years out of the country is a big deal for Iran. Iran has experienced a history of being denied access to the nuclear infrastructure it bought into in the West. (I’m primarily thinking of the $1 Billon it investing in Eurodiff but Iran can, and does, list other examples.) It is a tremendous leap of faith for Iran to send this material out of country and the world should appreciate it. It is also, or at least should be, a big deal for the West. Even though this uranium has been under safeguards and most analysts feel it would be unlikely for Iran to use it to build a bomb, if they decided to do so, it should still be very reassuring. After all, it was only in early September that high US officials were publicly worrying about just such a diversion of materials.

If Iran goes ahead and sends its LEU out of country, the West needs to respond with a bold diplomatic option of its own. The best such proposal would be a multinational enrichment center in Iran.

Note on units: The customary unit for medical doses is curies (or Becquerels, I suppose, for us SI enthusiasts) which is related to the number of radioactive decays per second at the time of administration. This makes a lot of sense for practitioners since they care very much about the amount of radioactivity they are exposed to and to how much they use on their patients. Thus, the “standard” diagnostic dose of 99mTc is 25 mCi and Iran imports 20 Ci of 99Mo per week. Note that since 99mTc has one tenth the lifetime, a gram of 99mTc is ten times as radioactive as a gram of 99Mo, which has a “typical” radioactivity of 1,850 Ci. I find this unit convention not very informative for my purposes so I have tried to consistently use grams produced.

Update: Unfortunately, I did not incorporate some edits I had planned on making before posting this article. As a consequence, the wrong number for the amount of 3.5% LEU inadvertently ended up on the blog. I’ve correct the numbers after “striking out” the wrong numbers so you can see where the error was.


  1. FSB

    I’m glad this breakthrough seems afoot — and I like your take on it. The hawks must be disappointed though.

    What “bold diplomatic” overtures do you think the West can do in return? How about publicly admitting that Israel has nukes, instead of actively hiding that fact.

    Another nice bold diplomatic option would be to tell Iran that if it forgoes its rights as a signatory of the existing international nonproliferation treaty in a fully verifiable form, the Security Council will ensure that Israel becomes a signatory and surrenders its nuclear weapons.

  2. Allen Thomson (History)

    > I find this unit convention not very informative so I have tried to consistently use grams produced.

    At an extremely nerdish level and not having much to do with the point of the posting, I very much agree.

    Provide the quantity of an isotope/isomer in grams (maybe moles) and let the reader figure how many joules or gamma-quanta per second that produces if the reader cares.

  3. thermopile (History)


    Thanks for a well written, informative article. There were two things I wanted to point out:

    1.) An inconsistency. The usual conversion in nuclear engineering is 1g of U-235 burned up per MW-day of energy. You state that the reactor burns up about 2% of its initial load per week, translating to about 640 g/week. Multiplying 640 g/week * (1 MW-day/gram) * (1 week/7 days) gets me about 90 MW … which is much greater than the pool reactor’s 5 MW rating. I’d be surprised if the burnup rate really was 2% of the initial fuel loading per week. A 5 MW reactor probably burns up about 5 grams of U-235 per day, so I bet the fuel load will last longer than you estimate.

    2.) You state that they use control rods to maintain a constant neutron density. That’s a convenient way to think about it, but it’s not quite right. As the reactor ages, neutron poisons build up and the amount of fuel (U-235) decreases. Hence, your “neutron loss term” increases and your “neutron generation term” decreases … meaning that, over the life of the core, the neutron density will double or triple. The reaction rate stays the same over core life (i.e., the number of U-235 atoms fissioning per second), but the neutron density (particularly the thermal neutron density) increases over life.

    Thanks again. I have been wondering for a loooong time, “What does Iran’s desire for enriched uranium have anything to do with medicinal purposes?” This clears that up.

  4. nukeman

    Detailed references to both the production and purification of a number of different isotopes are available in my most recent Iranian bilbiography. Maybe you can provide a link to the bib on the FAS site.

  5. Norman (History)

    We need to think ahead and have thoughtful proposals to build on Iran’s latest offer wrt LEU, and to move on to the next issue of “intrusive inspections”. The question I keep raising, without any answer from you armscontrolwonks, is:
    If Israel (especially) and the US keep threatening military attacks as an option, how could Iran possibly open up all possible facilities to an Additional Protocol snap inspection? As it stands, there could be many places where they would refuse inspections because they are militarily “sensitive”.

  6. Geoff Forden (History)


    I’m going to let you look at the original Iranian papers and figure out what they really mean. Two percent burn up per week is what they report. So is the amount of uranium loaded in the reactor. Please let me know if you can reconcile what they say.

  7. Bill Bexely

    Ah well, the Iranians are experts at saying something one day and something else the next.

    What deal?

    But a senior Iranian official said the deal was preliminary and contested reports that Iran was ready to send 1.2 tons of its 1.5-tonne low-enriched uranium stockpile abroad for refining to the 20 percent purity needed for the Tehran reactor.

    “Whatever they’ve agreed (in Geneva) on 20 percent enrichment is just based on principles,” the official told Reuters. “We have not agreed on any amount or any numbers.”

  8. kme

    In regard to the bombs in the Canadian trash, isn’t the irradiated U235 target no longer suitable as bomb fuel, due to contamination with a multitude of fission products?

  9. Mike F (History)

    @kme: “In regard to the bombs in the Canadian trash, isn’t the irradiated U235 target no longer suitable as bomb fuel, due to contamination with a multitude of fission products?”

    The short answer is yes. NRU burns the targets for less than a week (usually) and the waste contains not only fission products but chemicals from the dissolution process for the target material. Since it is HEU, there is very little Plutonium in it, but still plenty of U-235 and some fairly screaming hot fission products. If you are going to use it for a weapon, you would need a very significant reprocessing facility.

    As reprocessing is a no-no in North America this material sits around as “waste.”

  10. lizz (History)

    The following interview with Salehi (Iran’s current nuclear program head) in the Financial Times in Sept 2004 should be read more widely, specifically on why they’re enriching uranium:

    FT: You were at the apparently successful meeting that reached agreement with the Europeans last October – an agreement that the Europeans interpreted to mean that Iran would give up control of the nuclear enrichment cycle. The Iranian side says it will not give up control of the cycle. How can this divergence have happened?

    Salehi: Mr [Hassan] Rowhani [head of Iran’s Supreme Council of National Security] in the meeting, in front of the three ministers [the foreign ministers of Britain, Germany and France], stressed over and over again that the voluntary suspension, and not cessation, [of uranium enrichment] could last from a day to a year. This was very clear to the three ministers.

    We have told the Europeans – and we are telling them now – that we are wise enough not to expect you to think like us. We are ready to give any kind of meaningful guarantees and assurances that Iran will never divert its fuel-cycle technology to non-peaceful use.

    We have even once indicated – not officially – that we are ready to enter into a joint venture in the enrichment of uranium. [We have said to the Europeans] ‘Bring your expertise to Natanz, join us, and sell to us, and to others.’

    Iran has 10 per cent of Eurodif [the European consortium], which has a European enrichment plant [in France] … It sells enrichment services to the world, and Iran has a 10 per cent share dating from the time of the past regime.

    Why not repeat this same thing here, and we will assure you we will buy all the production. Natanz has been designed to produce 30 tons of enriched uranium up to 5 per cent maximum [ – below the level required for a nuclear bomb], and that is only enough for one year’s refuelling. Nantaz, with all its vastness, can supply only one reactor for a year. We are to construct seven reactors, we are starting the bid for the twin reactor in Bushehr in a year’s time, so for that one we need to buy our uranium from outside.

    But this is a bargaining chip for us….We have made an economic calculation that with the facilities we have developed, the fuel we are going to fabricate in Iran would be a lot cheaper that what we can buy internationally. The manpower here is much cheaper and the capital investment we’ve made is in rials not in dollars.

    FT: When you say bargaining chip, do you mean Iran might compromise over this?

    Salehi: We say that for other plants we are going to buy our fuel from outside, but we are not going to become hostage to their wishes. Once they know we can develop our own enrichment, then they will enter into bargaining with us – like any other country.

    FT: Is the control over the fuel cycle a matter of national sovereignty?

    Salehi:Nuclear technology, of you are able to master it, opens the way to other technologies, because you are dealing with the highest limits of engineering – the highest pressures, highest temperatures, the highest material properties. This know-how can be used in other industries.

    With technology you cannot have big jumps. You can’t suddenly expect an underdeveloped country to send a rocket to the moon.

    Nuclear technology would give us the base for future technology in fusion, which is the ultimate answer to unlimited supply of energy for human beings. If you do not master fission now, when fusion comes in 20 to 30 years you will be totally ignorant.

    FT: So when the Europeans say they want an international supply of enriched uranium….

    Salehi: The Europeans have said they would assure us of the supply of nuclear fuel for the lifetime of the power plants, which run for 60 years, which is almost three generations. Who can believe such a guarantee? The world may change, we don’t know what will happen, even the European Union may break up in three generations …

    FT: You said that to them?

    Salehi: Yes.

    FT: How did they react?

    Salehi: Nothing. No answer.

  11. Tom F (History)

    Just as a point of note the Canadian reactors at Chalk River are at the utter end of their lifespan and we seem to be experiencing epic difficulties sourcing a replacement for them.

    It’s definitely impacted isotope supply worldwide.

  12. Cristina Hansell (History)

    In answer to Mike F: the level of radioactivity in irradiated target waste is a problem, but still far less than the radioactivity of spent reactor fuel. You can find studies by Vandegrift et al indicating that after 3 months the target waste is contact handlable (and incidentally, in the past the US classed this as low level waste).

    All wonk readers, I have my own question: the NRU and other major isotope producers employ HEU targets for Mo-99 production (even where the fuel is LEU). Do we know that Iran will use LEU targets? Where will they get those? Also, the target waste will include large amounts of remaining enriched uranium that is not all that hot — thus raising concerns. If anyone has any thoughts on the targets, I would love to see your comments here.

  13. Geoff Forden (History)


    As I say in the post, Iran is planning on using natural uranium as its target material.

  14. Miles Pomper (History)

    I would like to add to Tina’s point. It would be beneficial if this deal goes through as a way to buy time, but let’s not get carried away. The deal would still preserve Iran’s break-out and sneak-out capabilities without an additional protocol or enrichment suspension. Indeed, in a break out scenario the new 19.9 metal fuel, could be converted again to HEX and be several steps closer to weapons grade.
    At some point Iran could argue that it should no longer export its fuel but convert it to metal domestically, it could then have an excuse for stores on hand of 19.9 percent fuel.
    It could also take its 19.9 percent HEU “waste” and further enrich since as Tina says it will no longer be self-protecting.
    And according to Bill Potter’s article in the July 2008 nonproliferation review, another research reactor in Iran, the minature source reactor already has 7 kg of HEU onhand (target or core material).

  15. Geoff Forden (History)


    I’m not sure if this is the difficulty or not. But if it is, let me be very clear: Iran burns its 19.75% fuel very, very fully. Any Pu produced in the fuel rods is very definitely reactor grade. It appears, from Iranian publications, that it is going to be using natural uranium for the target. There will not be the same issues about Iran’s targets that there is with Canada’s targets. (I’m beginning to regret even including that very much a side issue in the post.) They are certainly not going to enrich the uranium in their targets . And there is way to little Pu for them to worry about building a bomb with. Of course, I suppose they could separate out the milligram levels of plutonium to obtain laboratory experience with handling plutonium but… By the way, the HEU the US sold Iran for the initial loads to the reactor are still in Tehran; why aren’t you worried about that? Because it is burnt up and it is under safeguards.

    Second, sending the current batch of indigenously enriched LEU out of the country is not the solution to the problem. It is a very important confidence building measure and we in the West should realize that. We need a long term solution but both Iran and the West need to build up confidence in each other first. We cannot do that if we do not fully appreciate the importance of Iran’s CBM.

    Of course, there are decisions that need to be made about the modalities of this CBM. I hope to discuss those in a forthcoming blog post.

    The solution we in the West need is one that increases the barriers to Iran using indigenous centrifuges, perhaps hidden somewhere that the West does not detect to enrich uranium. Multinational enrichment facilities in Iran have higher barriers to just that and provide far more assurance to the West that Iran is not doing that than any agreement to abandon enrichment in Iran could ever have.

  16. TTT.

    Countries developing and using LEU targets are within Iran’s experience. They probably are aiming for the CNEA process.

  17. Rwendland (History)

    > milligram levels of plutonium to obtain laboratory experience with handling plutonium

    Geoff, I’d guess Iran already has this experience from the 0.1 kg of Plutonium the U.S. supplied to Iran in 1967 with the TRR, as “Sources” for calibration, research and development activities. So there seems no point in worrying about milligrams, or indeed grams, of Pu. It doesn’t look like this 0.1 kg had been returned by 1994, so I’d guess Iran still has it (under safeguards).

  18. Anonymous (History)

    Your savings of $2 million per year does not justify the weapons breakout risk of supplying Iran with large quantities of 20% HEU. It would be far cheaper and safer to supply Iran with $2 million of Mo99 per year, or even $10 mm Mo99 per year. 20% HEU is just to dangerous for breakout processing. Thus, the assumption of economic savings in your article is flawed and indeed dangerous cover for an Iranian effort to produce additional nuclear weapons.

  19. loupgarous (History)

    With the impending demise of Chalk River as a source for 99Mo, it is not clear that the worldwide nuclear community will HAVE spare 99Mo with which to supply Iran.

    Perhaps the Russians would be able to supply the needed stocks, but they seem committed to the “refueling TRR” option.

    It’s probably not going to endear me to the hosts of the blog to raise the massive opportunity cost entailed in the US’s having chosen to de-emphasize nuclear power and nuclear engineering projects; by surrendering world leaadership in this area to third countries whose political aims differ from ours, we’ve lost significant leverage in dealing with Iran and other would-be proliferators.

    I do agree with “Anonymous,” however, that Iran’s amassing of significant quantities of 19.75 percent enriched uranium gives them a leg up on accumulating even higher enrichment stocks of uranium; also, that the term “research reactor” is very nearly a cliched euphemism for “plutonium production reactor” in the history of nuclear weapons proliferation in the developing world.

  20. anonymous (History)

    “It is not clear that the world wide nuclear community will have spare 99Mo to supply Iran.”

    This is short sighted. If it is in the interest of (Iranian) non-proliferation, would any person in their right mind believe it is safer to defer the building of what is a low tech and proven 5 MW reactor design in their own country for a similar 5 MW reactor in Iran. World safety must be prioritized, and it is more safe to scrap nuclear taboos and build such a facility in a western country where the U235 can be tracked and disposed as necessary. To do otherwise is to expose the same western countries to extreme proliferation risk all in the name of “medical isotopes” and NIMBY safety. Its absurd.