The isotope question is a complicated one.It is important to realize that isotopes were being used for diagnosis and therapy long before the discovery of nuclear fission -- and that even after the discovery of fission, cyclotrons and other types of particle accelerators were widely used to produce isotopes for medical and scientific research purposes.
See Nuclear Medicine, Radioisotopes and Nuclear Reactors But AECL has deliberately worked over the years to create a market for specialized isotopes that are produced in nuclear reactors, chiefly cobalt-60 and molybdenum-99.Cobalt-60 is a ÒhardÓ gamma emitter and is used outside the body to irradiate tumours and to sterilize medical instruments, for example. It has a half-life of 5.3 years and so loses about 13% of its inventory in one year through radioactive decay.
Molybdenum-99 has a half-life of 66 hours, and it decays into a metastable isotope -- a pure gamma emitter -- called technetium-99m (the ÒmÓ has to be included) which has a half-life of only 6 hours.
The technetium-99m is used internally for many many diagnostic purposes. Tc-99m can easily be attached to various molecules which can then be injected into patients.
The gamma rays given off by Tc-99m are a lot ÒsofterÓ than those from cobalt-60 so they give a good clear picture (caught on film or on a screen) without giving too high a dose to the patient. It's like having little x-ray machines inside the patient rather than having one big x-ray machine outside the patient. This allows doctors to see details of the soft organs which can be helpful in diagnosing cancer and other ailments.
The Mo-99 isotope is used as a ÒcowÓ which can be ÒmilkedÓ to give Tc-99m over a period of many days. Just a few micrograms of Mo-99 is sufficient to produce enough Tc-99m to be used to diagnose 10,000 patients. However, the supply of Mo-99 has to be uninterrupted or hospitals will run out of Tc-99m in a short time.
The downside to this is that Mo-99 (called ÒmolyÓ for short) is only produced, now, in a very high-intensity neutron field, which means a nuclear reactor. And at Chalk River they use targets made of weapons-grade uranium (over 90% enriched!!) in order to get the Mo-99.
The 50-year old NRU reactor is used to produce Mo-99. That very old reactor was supposed to have been permanently retired in 2000 and replaced by the two new Maple reactors. But AECLÕs Maple reactors were designed to produce Mo-99 using weapons-grade uranium targets also.
In the USA, the Nuclear Control Institute (NCI) went to court to stop the shipment of HEU (highly enriched uranium) to Chalk River because there is a US law (the Schumer amendment) which is meant to halt all shipments of weapons-grade materials to other countries.
AECL has been told by US authorities that they must develop technologies to produce Mo-99 that do not require HEU; but MDS-Nordion (a private company that markets the Mo-99 that is produced by AECL) shows little sign of taking this seriously.
Vice-President Malkoske said Nordion never agreed to convert to low-enriched uranium at any cost. ÒIt is not written in stone," he says. ÔTechnically, it seems feasible to me, but whatÕs it going to cost to do this? Every time you add costs you pass that on to the health-care community, you increase the cost of nuclear medicine."
ÒWhat we said we would do . . . is do a technical and economic feasibility (study) and if it was economically feasible then we would convert. We didn't say we were going to convert at any cost. That could kill our business.Ó
Another problem: in the past, HEU irradiated fuel has been returned to the USA (Savannah River Site in South Carolina) from Chalk River where it has been recycled into the bomb program (which uses HEU Òdriver rodsÓ in plutonium-production reactors to produce the plutonium needed for warheads).
So in this sense, Mo-99 is like a piece of candy that is produced as a byproduct of the nuclear weapons business. Without nuclear weapons it would be too expensive to produce the HEU in the first place, and without the cash credit obtained by returning the HEU to the USA the costs become prohibitive also. I am not sure whether this practice of returning the irradiated HEU is still going on.
Yet another problem is that the Maple reactors cannot be operated safely and so they are at least 6 years behind schedule. The Maple reactors do not operate as the AECL designers said they should, and the difference is a matter of safety; instead of being Òself-brakingÓ when the power of the reactor is increased, the Maple reactors accelerate in power when any attempt is made to just increase the power a little bit. This makes the reactors too unsafe to operate.
The NRU (National Research Universal) reactor started up in 1957. It was about 10 times more powerful than the earlier NRX (National Research eXperimental) reactor that started up in 1946. The GovÕt of Canada was reluctant to spend the money to build the NRU reactor, but AECL argued that the new reactor could help defray its own cost by producing plutonium in the reactor and selling it to the US military. And thatÕs what they did; sold plutonium produced at NRU that was of course used in the American bomb program.
But the main purpose of the NRU was to produce isotopes of various kinds by using ingenious ÒloopsÓ that allowed one to insert non-radioactive materials into those loops without shutting down the reactor or opening up the core of the reactor, so as to irradiate those ÒtargetÓ materials and make them radioactive.
The NRU was also used to test various fuels and components of CANDU reactors. But it is 50 years old now and should have been retired years ago. Since the Maple reactors are not running, the geriatric NRU reactor has had to be the workhorse, delivering the Mo-99 to the market.
Two years ago, the Canadian Nuclear Safety Commission (CNSC) required that emergency pumps be connected to a "seismically qualified" backup electricity supply at the NRU reactor, in order to prevent a core meltdown in case of a loss of normal electrical supply as a result of an earthquake or some equivalent event. AECL did not carry out this work however, and now the chickens have come home to roost. The CNSC is furious that their licensing requirements have not been met. AECL is now scrambling to find the necessary parts from around the world to finally bring the NRU reactor into compliance.
Meanwhile, the medical community is aghast that they were never informed of the problems with the much-ballyhooed Maple reactors, nor of the fact that the supply of Molybdenum-99 was so fragile, depending as it does on the operation of an aging and improperly equipped NRU reactor.
Which raises another question: who actually profits from all this? See AECL and MDS Enter Into Long-term Supply Agreement for Medical Isotopes
In 1988, the GovÕt of Canada privatized the only really profitable part of AECLÕs operations, which was the radio-isotope production. AECL sold Nordion International Inc. (formerly the AECL division known as the Radiochemical Company) to the Canada Development Investment Corporation (CDIC) for eventual privatization. In 1991, CDIC sold Nordion to MDS Health Group Ltd. for $165 million. It was reported that AECL received $150.5 million from CDIC, and that this Òtogether with interest earned thereon between the dates of receipt and disbursement, has been distributed to the shareholder (i.e. govÕt of Canada) by way of dividendsÓ.
So AECL is responsible for designing, building and operating the reactors needed to produce the isotopes that MDS-Nordion sells for a profit. This also means that the radwaste and the decommissioning of the reactors is a public responsibility through AECL whereas the profits are a private matter for MDS-Nordion.
As of now, it would be difficult to replace the Mo-99/Tc-99m isotope business with something else, but I believe that if nuclear weapons were phased out the entire isotope business as currently practiced would be unaffordable. In that case I have little doubt that some other more cost-effective isotope production scheme would be found to replace the Mo-99/Tc-99m that the "nuclear medicine" practitionersare currently addicted to.
IÕm not saying this would be easy nor that the replacement is obvious, but I do believe that necessity is the mother of invention.
Gordon Edwards
Notes on the Isotope Shortage
by Gordon Edwards, Ph.D.
(written June 10 2009)
(1) The vast majority of uses of radioisotopes in nuclear medicine
is for diagnosis, not for cancer treatment. Thus a shortage of these
isotopes may cause a lot of difficulties, and a lot of distress, but it is
not in itself a "life-threatening" medical emergency.
(2) The fact that these diagnoses using medical isotopes are not life-
threatening is supported by the fact that the tests are never given after
regular hospital hours or on the weekends, but only during regular
business hours.
(3) McGill University used to produce all of its medical isotopes using a
cyclotron located right on the university campus in downtown Montreal.
A cyclotron is not a nuclear reactor but a "particle Accelerator". It does
not use uranium at all, nor does it produce high-level radioactive waste.
(4) The most frequently used procedure in nuclear medicine is using a
radioactive isotope called technetium-99m to get a picture of the internal
soft organs of a patient. When the radioactive material is taken internally
by the patient, his or her insides light up like a Christmas tree because
of radioactive emissions for a period of a few hours.
(5) Two alternatives to Technetium-99m are (a) using thallium-206, a radioactive
isotope that is produced in a cyclotron (no uranium use) (b) PET-scans, which require
a short-lived radioactive isotope called fluorine-18, which is also produced in a
cyclotron (no uranium use). PET scans often give better pictures than technetium-99m.
(6) PET scan machines are expensive, about 2-3 million dollars each, but remembering
that Ottawa has poured 1.7 billion dollars into Chalk River since 2006, you
could buy 500-600 PET machines with this amount of money. Even the money wasted
on the MAPLE reactors (about 530 million) would buy over 170 PET scan machines.
(7) The main use of radioactive isotopes for treatment is iodine-131, used to treat thyroid
cancer. This isotope is produced in a nuclear reactor, not in a cyclotron. There are very
few other therapeutic uses of isotopes, but there are some. Iodine-131 has a half-life of
8 days, so a given hospital supply can remain useful for some weeks. The availability
of iodine-131 will be reduced because of the isotope shortage. But alternative treatments
are available, and thyroid cancer is not generally life-threatening, though it sometimes is.
(8) The amount of uranium used for medical isotopes is an extremely small fraction of the
uranium used by nuclear power reactors. Even if no new uranium mines were opened up
there would be plenty of uranium to produce medical isotopes for a very long time to come.
Gordon Edwards, Ph.D., President,
Canadian Coalition for Nuclear Responsibility
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