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 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 semicontinuous process that enables
the following operations to be carried out with the same
equipment: evaporation of the waste solution mixed with the 
1) borosilicate: any of several salts derived from both boric
acid and silicic acid and found in certain minerals such as
tourmaline.   h)        0*0*0*  Ԍadditives 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 

2) condensacate: product of condensation. 

(    (         0*0*0*  Ԍglass 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 selfboil. The resulting 
   (         0*0*0*  Ԍsteam 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 the
radioactivity in an insoluble rock matrix deep underground.
The heat surrounding the radioactivity would prevent the
intrusion of ground water. After all, the steam and vapour are
no longer released. The outlet hole would be sealed. To go a
little deeper into this concept, the treatment of the wastes
before injection is very important. To avoid breakdown of the
rock that constitutes the formation, the acidity of he wastes
has to be reduced. It has been established experimentally that
pH values of 6.5 to 9.5 are the best for all receiving
formations. With such a pH range, breakdown of the formation 
rock and dissociation of the formation water are avoided. The
stability of waste containing metal cations which become
hydrolysed in acid can be guaranteed only by complexing agents
which form 'watersoluble complexes' with cations in the 
   (         0*0*0*  Ԍrelevant pH range. The importance of complexing in the
preparation of wastes increases because raising of the waste
solution pH to neutrality, or slight alkalinity results in
increased sorption by the formation rock of radioisotopes
present in the form of free cations. The incorporation of such
cations causes a pronounced change in their distribution
between the liquid and solid phases and weakens the bonds
between isotopes and formation rock. Now preparation of the 
formation is as equally important. To reduce the possibility
of chemical interaction between the waste and the formation,
the waste is first flushed with acid solutions. This operation
removes the principal minerals likely to become involved in
exchange reactions and the soluble rock particles, thereby
creating a porous zone capable of accommodating the waste. In
this case the required acidity of the flushing solution is
established experimentally, while the required amount of
radial dispersion is determined using the formula:
 R = Qt
        2 mn       
    R is the waste dispersion radius (metres)
Q is the flow rate (m/day)
t is the solution pumping time (days)
m is the effective thickness of the formation (metres)
n is the effective porosity of the formation (%)
     
 `	`	 In this concept, the storage and processing are
minimized. There is no surface storage of wastes required. The
permanent binding of radioactive wastes in rock matrix gives
assurance of its permanent elimination in the environment. 
   h)         0*0*0*  ԌThis is a method of disposal safe from the effects of
earthquakes, floods or sabotages. 
 With the development of new ion exchangers and the
advances made in ion technology, the field of application of
these materials in waste treatment continues to grow.
Decontamination factors achieved in ion exchange treatment of
waste solutions vary with the type and composition of the
waste stream, the radionuclides in the solution and the type
of exchanger. 
 Waste solution to be processed by ion exchange should
have a low suspended solids concentration, less than 4ppm,
since this material will interfere with the process by coating
the exchanger surface. Generally the waste solutions should
contain less than 2500mg/l total solids. Most of the dissolved
solids would be ionized and would compete with the
radionuclides for the exchange sites. In the event where the
waste can meet these specifications, two principal techniques
are used: batch operation and column operation.
 The batch operation consists of placing a given quantity 
of waste solution and a predetermined amount of exchanger in
a vessel, mixing them well and permitting them to stay in
contact until equilibrium is reached. The solution is then
filtered. The extent of the exchange is limited by the
selectivity of the resin. Therefore, unless the selectivity
for the radioactive ion is very favourable, the efficiency of 
removal will be low. 
    (         0*0*0*  Ԍ Column application is essentially a large number of batch
operations in series. Column operations become more practical.
In many waste solutions, the radioactive ions are cations and
a single column or series of columns of cation exchanger will
provide decontamination. High capacity organic resins are
often used because of their good flow rate and rapid rate of
exchange.
 Monobed or mixed bed columns contain cation and anion
exchangers in the same vessel. Synthetic organic resins, of
the strong acid and strong base type are usually used. During
operation of mixed bed columns, cation and anion exchangers
are mixed to ensure that the acis formed after contact with
the Hform cation resins immediately neutralized by the OHform anion resin. The monobed or mixed bed systems are
normally more economical to process waste solutions. 
 Against background of growing concern over the exposure
of the population or any portion of it to any level of 
radiation, however small, the methods which have been
successfully used in the past to dispose of radioactive wastes
must be reexamined. There are two commonly used methods, the
storage of highly active liquid wastes and the disposal of low
activity liquid wastes to a natural environment: sea, river or
ground. In the case of the storage of highly active wastes, no
absolute guarantee can ever be given. This is because of a
possible vessel deterioration or catastrophe which would cause
a release of radioactivity. The only alternative to dilution 
   (         0*0*0*  Ԍand dispersion is that of concentration and storage. This is
implied for the low activity wastes disposed into the
environment. The alternative may be to evaporate off the bulk
of the waste to obtain a small concentrated volume. The aim is
to develop more efficient types of evaporators. At the same
time the decontamination factors obtained in evaporation must
be high to ensure that the activity of the condensate is
negligible, though there remains the problem of accidental
dispersion. Much effort is current in many countries on the
establishment of the ultimate disposal methods. These are
defined to those who fix the fission product activity in a
nonleakable solid state, so that the general dispersion can
never occur. The most promising outlines in the near future
are; 'the absorbtion of montmorillonite clay' which is
comprised of natural clays that have a good capacity for
chemical exchange of cations and can store radioactive wastes,
'fused salt calcination' which will neutralize the wastes and
'high  temperature processing'. Even though man has made many
breakthroughs in the processing, storage and disintegration of
radioactive wastes, there is still much work ahead to render
the wastes absolutely harmless.      
