Nuclear Power

Radioactive wastes, must for the protection of
mankind be stored or disposed in such a manner
that isolation from the biosphere is assured until
they have decayed to innocuous levels. If this is
not done, the world could face severe physical
problems to living species living on this planet.
Some atoms can disintegrate spontaneously. As
they do, they emit ionizing radiation. Atoms having
this property are called radioactive. By far the
greatest number of uses for radioactivity in
Canada relate not to the fission, but to the decay
of radioactive materials - radioisotopes. These are
unstable atoms that emit energy for a period of
time that varies with the isotope. During this active
period, while the atoms are \'decaying\' to a stable
state their energies can be used according to the
kind of energy they emit. Since the mid 1900\'s
radioactive wastes have been stored in different
manners, but since several years new ways of
disposing and storing these wastes have been
developed so they may no longer be harmful. A
very advantageous way of storing radioactive
wastes is by a process called \'vitrification\'.
Vitrification is a semi-continuous process that
enables the following operations to be carried out
with the same equipment: evaporation of the waste
solution mixed with the
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borosilicate: any of several salts derived from both
boric acid and silicic acid and found in certain
minerals such as tourmaline. additives necesary for
the production of borosilicate glass, calcination
and elaboration of the glass. These operations are
carried out in a metallic pot that is heated in an
induction furnace. The vitrification of one load of
wastes comprises of the following stages. The first
step is \'Feeding\'. In this step the vitrification
receives a constant flow of mixture of wastes and
of additives until it is 80% full of calcine. The
feeding rate and heating power are adjusted so
that an aqueous phase of several litres is
permanently maintained at the surface of the pot.
The second step is the \'Calcination and glass
evaporation\'. In this step when the pot is
practically full of calcine, the temperature is
progressively increased up to 1100 to 1500 C and
then is maintained for several hours so to allow the
glass to elaborate. The third step is \'Glass casting\'.
The glass is cast in a special container. The heating
of the output of the vitrification pot causes the
glass plug to melt, thus allowing the glass to flow
into containers which are then transferred into the
storage. Although part of the waste is transformed
into a solid product there is still treatment of
gaseous and liquid wastes. The gases that escape
from the pot during feeding and calcination are
collected and sent to ruthenium filters, condensers
and scrubbing columns. The ruthenium filters
consist of a bed of
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2) condensacate: product of condensation. glass
pellets coated with ferrous oxide and maintained at
a temperature of 500 C. In the treatment of liquid
wastes, the condensates collected contain about
15% ruthenium. This is then concentrated in an
evaporator where nitric acid is destroyed by
formaldehyde so as to maintain low acidity. The
concentration is then neutralized and enters the
vitrification pot. Once the vitrification process is
finished, the containers are stored in a storage pit.
This pit has been designed so that the number of
containers that may be stored is equivalent to nine
years of production. Powerful ventilators provide
air circulation to cool down glass. The glass
produced has the advantage of being stored as
solid rather than liquid. The advantages of the
solids are that they have almost complete
insolubility, chemical inertias, absence of volatile
products and good radiation resistance. The
ruthenium that escapes is absorbed by a filter. The
amount of ruthenium likely to be released into the
environment is minimal. Another method that is
being used today to get rid of radioactive waste is
the \'placement and self processing radioactive
wastes in deep underground cavities\'. This is the
disposing of toxic wastes by incorporating them
into molten silicate rock, with low permeability. By
this method, liquid wastes are injected into a deep
underground cavity with mineral treatment and
allowed to self-boil. The resulting steam is
processed at ground level and recycled in a closed
system. When waste addition is terminated, the
chimney is allowed to boil dry. The heat generated
by the radioactive wastes then melts the
surrounding rock, thus dissolving the wastes.
When waste and water addition stop, the cavity
temperature would rise to the melting point of the
rock. As the molten rock mass increases in size,
so does the surface area. This results in a higher
rate of conductive heat loss to the surrounding
rock. Concurrently the heat production rate of
radioactivity diminishes because of decay. When
the heat loss rate exceeds that of input, the molten
rock will begin to cool and solidify. Finally the
rock refreezes, trapping