Medical Isotopes, Gordon Edwards
Medical isotopes: the Chalk River crisis
Notes by Gordon Edwards
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.
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 “hard” 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 (short half-life) isotope called
technetium-99m (the “m” 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 “softer” than those from cobalt-60 so
they give a good “picture” without giving too high a dose
to the patient. Because of its 6-hour half-life, Tc-99m does
not pose a long-term radioactive waste problem. The Mo-99
is used as a “cow” which can be “milked” to give Tc-99m
over a period of many days. Just a few micrograms of Mo-99
is enough to produce enough Tc-99m to be used to diagnose
10,000 patients. However, the supply of Mo-99 has to be
uninterrupted or they will run out of Tc-99m in a short time.
The downside to this is that Mo-99 (called “moly” for short)
is only produced, now, in a very high-intensity neutron field,
which means a nuclear reactor that uses weapons-grade
uranium (over 95% enriched!!). AECL’s Maple-1 and Maple-2
reactors were designed specifically to produce Mo-99 using
weapons-grade uranium as fuel. 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
use HEU; but MDS-Nordion (a private company that markets
the Mo-99 that is produced by AECL) shows little sign of
taking this seriously. “Mr. Malkoske said Nordion never agreed to convert to low-enriched uranium at any cost.
“‘It is not written in stone,’ he says. ‘Technically, it seems
feasible to me, but what’s it going to cost to do this?
Everytime you add costs you pass that on to the health-care
community, you increase the cost of nuclear medicine.
“‘What 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.'”
Another problem: in the past, HEU irradiated fuel has been returned
to the USA (Savannah River) from Chalk River where it has
been recycled into the bomb program (which uses HEU as
“driver rods” 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
reactors do not operate as the AECL designers said they should,
and the difference is a matter of safety — instead of being “self-
braking” 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
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 Gov’t of Canada was reluctant to spend the money to build
the NRU reactor, but AECL argued that it could help defray its
own cost by producing plutonium in the reactor and selling it to the
USA. And that’s what they did — sold plutonium 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 “loops” that would allow you 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 “target” 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 backup electricity
supply at the NRU reactor, in order to prevent a core meltdown in case
of 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 orders have not been carried out, AECL is scrambling
to find the necessary parts from around the world to finally bring
the NRU reactor into compliance, and the medical community is
aghast that they were never informed of the problems with the
much-ballyhooed Maple reactors and the fact that the supply of
Molybdenum-99 was so fragile, depending as it does on the
operation of an aging and improperly equipped NRY reactor.
Which raises another question: who makes the profits from all this?
In 1988, the Gov’t of Canada privatized the only really proftable
part of AECL’s 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, and
it was reported that AECL received $150.5 million from CDIC, and
that this “together with interest earned thereon between the dates
of receipt and disbursement, has been distributed to the shareholder
(i.e. gov’t of Canada) by way of dividends”.
So AECL is responsible for designing and building and operating the
reactors 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 medical people are currently
addicted to. I’m not saying this would be easy nor that the replacement
is obvious, but I do believe that necessity if the mother of invention.
Hope all this info helps to sort out the situation somewhat in your mind.