632 MANAGEMENT OF RADIOACTIVE WASTES
Sealed sources are, however, a very difficult matter. While
they remain sealed they are usually within heavy shielding
in teletherapy machines, which are only operated by compe-
tent people, or they are in the form of needles and plaques
for implantation, or instrumental standard sources used by
specialists. However, the time comes when such sources
have decayed to the point where they are no longer useful.
Sufficient activity remains for them to be highly dangerous
to the unwary, so they are dealt with in special ways, usually
after return to the supplier.Isotope Production PlantsThese facilities are often associated with large reactors,
and wastes are similar to those generated in Research and
Development plants. Processing of very large sources of
volatile elements such as iodine and tellurium necessitates
an elaborate ventilation cleaning system. Manufacture of
large sources of^90 Sr,^137 Cs or the trans-uranic elements as
power sources may call for sophisticated remote handling
equipment in heavily shielded cells. But the waste prob-
lems are difficult only in scale from those encountered in
an R and D plant.
Some people have considered the separation of^90 Sr and(^137) Cs from fuel processing wastes as a helpful step in their
management. Removal of these nuclides leaves a mixture
which, during 20 years’ storage, would decrease in activity
by a factor of about 30,000. However, an industry handling
the fission products from 50 tons of^235 U burned in one year
would have to deal with 500,000,000 Curies of separated
(^90) Sr and about the same amount of (^137) Cs. It might be difficult
to find a market for sources of this scale unless they were
cheap, and it must be remembered that they would eventu-
ally come back as “waste.”
Industrial Applications
Use of radioisotopes in industry is not a significant source
of wastes. Most industrial sources are sealed, and nearly all
unsealed sources are short-lived.
Transportation
Ships are the only form of transportation using nuclear
reactors as a source of power. They include naval ships, ice
breakers and merchant vessels. They contain large amounts
of fission products within the reactors, but as a source of
waste they are not important, except possibly in some har-
bours and inshore waters.
During start-up of the reactor the secondary coolant
expands and the limited space in submarines necessitates the
dumping of this expansion water. In common with landbased
reactor coolant it contains radioactive corrosion products and
tritium. The coolant is maintained at a low level of activity
by means of ion exchangers, which become waste eventually.
Normally this material is disposed of on land, although it has
been shown by the Brynielsson Panel of the International
Atomic Energy Agency that resin from a fleet of as many as
300 nuclear ships could be dumped safely if this were done
only on the high seas.
Apart from these sources wastes from nuclear shipping
consist of clean-up solutions, laboratory wastes, laundry
effluent and other minor sources common to all reactor
operations. Except in submarines, practically all wastes can
if necessary be retained on board for disposal ashore.
DISPOSAL PRINCIPLES
There are two main procedures available for disposal—
Concentration and Confinement: or Dilution and Dispersion.
a) If wastes are truly confined, in the sense that in
no credible circumstances could they be liberated
into the environment, then the only additional
requirement is “perpetual custody” to ensure that
the confinement is never broken. This is easier
said than done. In the field of high level wastes
when we say “perpetual” we are speaking in
terms of thousands of years. Few private firms go
back for 100 years, political regimes have seldom
lasted for as long as 500 years, and there are few
civilizations that have survived for 2000 years.
In our own day forecasters tend to regard dates
beyond 2000 AD as being in the distant future.
What, then, can we do about “perpetual custody”
of wastes containing, for example, plutonium with
a half-life of 24,000 years?
This is not a fanciful dilemma. A story from
Chalk River will illustrate the point. When the
Canadians decided to concentrate on natural ura-
nium heavy water reactors for power production
it became apparent that processing of spent fuel
would be uneconomic until the price of uranium or
plutonium rose considerably. Processing was there-
fore stopped, but the wastes accumulated during
the pilot plant operation had to be disposed of.
A considerable volume of medium level waste was
mixed with cement in steel drums and enclosed
within solid concrete monoliths below ground in
the waste management area (Figure 3).The ques-
tion then arose “What if some archeologist digs
this structure up 1000 years from now and thinks
it is an ancient temple or tomb?” Eventually some-
one suggested that its true nature should be inlaid
in non-corrodible metal on the top of the monolith.
Dr. A. J. Cipriani, who had listened to the debate in
silence, then asked “In what language?”
The implications of this question are profound.
Some of the wastes for which we are responsible
will still be radioactive after our present civilization
has disappeared and perhaps been forgotten. So
far as we know there is no practicable solution to
the problem. The best we can do is ensure that the
nature, amount and location of all major disposals
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