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 (short half-life) isotope 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 ÒpictureÓ 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 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 hospitals
will
run out of Tc-99m in a short time.
See Molybdenum and Technetium
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"
which are made of weapons-grade uranium (over
95% enriched!!)
in order to get the Mo-99. The 50-year old
NRU
reactor is used to produce the M0-99. That very old
reactor
was supposed to have been permanently retired in
2000
and replaced by the two Maple reactors. But AECLÕs
Maple-1
and Maple-2 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) from Chalk River where
it
has been recycled into the bomb program (which uses HEU
as 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
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 NRU 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 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 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 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
licensing
requirements have not been met, 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
NRU reactor.
Which
raises another question: who makes the 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, and
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 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 "nuclear medicine" practitioners
are
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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