|
 |
Combustible
solid waste is reduced to ashes in an industrial incinerator
at a temperature of 900°C. The combustion gases are filtered and
checked prior to being discharged into the atmosphere. The ashes are
poured into a 200-litre steel drum, which is compacted under a 2,000-tonne
press. The product obtained is a pellet with a maximum thickness of
40 cm.
Non-combustible
solid waste that is compressible, is collected in the same
type of steel drum, then compacted under the 2,000-tonne press.
Non-compressible waste is cut up into pieces.
|
|
The
pellets.
|
|
The volume of liquid radioactive waste can be reduced in two
ways: chemical treatment, heat treatment or incineration.
| • |
Chemical
treatment is a flocculation process, by which flakes are formed on
which the radioactive substances are fixed. After settling, these
flakes produce residual sludge which is filtered and dried, while
the purified water is checked prior to being discharged. |
| • |
Heat
treatment consists in bringing the liquid waste to the boil, which
leads to a residue in the form of radioactive sludge and steam, which
is condensed then discharged after checking. |
| • |
Certain
organic or aqueous low-active liquid waste are treated in the same
incinerator as the combustible solid waste. However, liquid and solid
waste are never mixed during the combustion. |
|
Stabilizing
and containing
| After
the waste volume has been reduced, a compact, chemically stable and
non-dispersible material must be obtained in order to facilitate subsequent
handling.
Solid
radioactive waste (pellets of compressed waste and non-compressible
cut-up waste) is contained in cylindrical steel 400-litre drums
resistant to corrosion (height: 1.07 m; diameter: 0.77 m). It is
then stabilized by means of a matrix of cement, mortar or concrete,
which is poured into the drums. When full, a drum weighs most often
around 1 ton.
The
radioactive sludge coming from the volume reduction of the liquid
waste is dried, mixed in a homogeneous way with bitumen
(stabilization) and poured into steel drums of 200 or 400 litres
(containment).
Starting
from raw and heterogeneous radioactive waste, a standard product
is thus obtained: a 400-litre drum which can be easily handled.
After being closed, every drum receives its own identification sheet
indicating the origin, the radioactive inventory and the physical
and chemical characteristics of its contents.
|
 |
|
Section
of a 400-litre drum, showing the various pellets and the immobilization
matrix.
|
Where is radioactive waste processed ?
The great
majority of radioactive waste produced and to be produced in Belgium,
whether it is solid or liquid, of low, medium or high activity, is processed
in the facilities of Belgoprocess in Dessel, at the same site where it
will be stored
provisionally until a decision is taken as to its long-term
management (final disposal).
A part of the waste of the nuclear power plants is processed on the site
of these power plants.
Spent nuclear fuel
Spent nuclear
fuel from Belgian nuclear power stations is not processed at Belgoprocess.
There are two technical options for its management :
•
reprocessing
;
•
storing it provisionally on the site of the nuclear power plants, if it
cannot be reprocessed.
 |
Reprocessing
of spent nuclear fuel takes place in the factory of COGEMA
in La Hague in France. The fuel rods are first cut into pieces. In
order to reduce the volume of the materials considered to be radioactive
waste, the nuclear fuel is then poured into nitric acid. The result
of this dissolving is a radioactive liquid which contains 97% of reusable
fuel - in the form of uranium and plutonium - and 3% of high-level
waste, the fission products. The 97% of reusable fuel is used to manufacture
new nuclear fuel (for example MOX).
The 3% of high-level waste is vitrified, in other words mixed with
a special molten glass (borosilicate glass) and poured into cylindrical
stainless-steel containers where it solidifies to a homogeneous product
in whose structure the radioactive substances are immobilized.
|
|
Molten
glass leaving the furnace.
|
|
|
|
The
containers which hold the waste from reprocessing Belgian
spent nuclear fuel by COGEMA have a capacity of 150 litres
and measure 1.34 m in height with a diameter of 0.43 m. When
full, a container weighs on average 450 kg and releases a
maximum amount of heat of 2,000 Watt, which is comparable
to the heat emitted by an electric radiator. The contents
of each container correspond to the reprocessing of 1,5 metric
tons of spent fuel, or the quantity of fuel necessary to assure
the electric consumption of about 116.000 Belgian households
for one year.
(Illustration
: mock-up of a stainless-steel container holding 400 kg of
vitrified waste. The wall of the mock-up is open, showing
the structure of the glass in black).
|
|
The
stainless-steel containers temporarily at COGEMA must be transported
to Belgium by rail (see our Transport
section on this subject). There is indeed a storage
building specially designed to accommodate them at
the Belgoprocess site.
If
you don't understand a term, please refer to our glossary.
|
|
.gif){kind=small}
