Note: Descriptions are shown in the official language in which they were submitted.
10'~90SS
This application is a division of co-pending Canadian
Patent Application No. 207,793 filed August 26, 1974.
BACKGROUND OF THE INVENTION
Nuclear-fueled generating plants comprise the fastest
growing segment of the electrical power-generating industry.
But, because of the environmental impact of additional nuclear
power plant facilities, plant design is progressing in the
direction of closed release plants, i.e., plants which contain
and internally process substantially all radioactive wastes to
thereby prevent atmospheric or water-borne releases. The
impact of closed release plants will result in large quantities
of liquid wastes of low-level radioactivity being generated by
each power plant and the wastes will require processing,
transporting and burial at commercial burial sites. The con-
sequence of large processing requirements increases capital
investments and operating costs as well as higher annual waste
disposal costs. Also, such larger quantities of wastes
required to be shipped annually will increase the probability
of accidents, risks of public exposure, risks of environmental
releases, consumption of burial space at a faster rate, and
increased capital investment in equipment required to transport,
handle and bury the waste materials. All of these costs will
in all likelihood be reflected in higher overall cost of
electrical power to the consumer.
Low-level radioactive liquid wastes, exclusive of wastes
due to spent fuel elements, are generated in the primary
reactor water coolant loop of light water reactors. These
wastes result from fission products released from the fuel
elements and/or corrosion products which become radioactive
after passing through the coolant passages of the reactor core.
~ ~ -2-
` 10'79()5S
Acceptable levels of radioactive contamination in the primary
coolant are achieved by processing the coolant water through
ion exchange media and filtration systems. These units
initially concentrate radioactive material and, upon either
regeneration or back-washing, result in liquid radioactive
wastes which require further processing before disposal.
In disposal techniques now usually practiced by the
nuclear power industry, dilute radioactive wastes are further
concentrated by means of an evaporator. The liquid concentrates
from the evaporator, which are made richer in chemical and
radio-isotopes, are conventionally diluted when mixed with
solidifying material~ such as cement and vermiculite, and
packaged in a container as a solid. However, the portion of
the concentrated wastes in each such container has a relatively
small volume when compared with the solidifying material added ~ -
thereto. Thus, it is desirable to increase the volume of the
wasteC added to each container yet still be able to comply
with safety requirements in storing, transporting and burying
the packaged wastes.
By 1969, application of the present state of the art of
radioactive liquid waste handling produced in the order of
4,000 fifty-five gallon barrels for burial. Without improvements
in process methods, this volume can be expected to increase to
more than 200,000 fifty-five gallon barrels per year by 1980.
Burial site limitations, perpetual surveillance and costs
clearly emphasize the desirability of improved processes ~or
radioactive waste volume reduction.
~ 3-
. ~ .
.
~790SS
SUMMARY OF THE INVENTION
The improved process and apparatus of this invention
operates to effect approximately a ten-fold reduction in volume
of radioactive wastes generated during power plant operation.
The resultant minimum volume waste product is solid and may be
stored on site indefinitely in a recoverable form, thereby
maximizing radioactive decay prior to shipment. Alternatively,
it can be removed to an off-site burial facility by conventional
means. The unit cost for transport and burial of the waste
product in accordance with the present invention may be higher
than the corresponding unit costs incurred with the use of
conventional disposal techniques. Nonetheless, a volume
reduction to at least one-tenth of the original volume, as
achieved with the present invention, results in a significant
overall cost reduction for disposal of such wastes.
The apparatus of the invention includes a processing unit
in the form of a calciner-dryer which drives off the liquid
portion of the wastes, leaving the wastes in the form of
anhydrous, particulate solids containing substantially all the
chemicals and radioactivity of the incoming wastes. The solids,
which have a volume of approximately five times less than that
of the input wastes to the processing unit, are directed to a
packaging station at which a number of containers or packages
are filled with the solids. In each package, a solidifying agent
is placed to fill the spaces between the particles and, upon
curing, solidification occurs, resulting in a monolithic block
suitable for storage or transit to a burial site. The volume
of solids placed
~ 4-
1079~55
in each package is 2 to 2.5 times the volume of liquid wastes
placed in such a package using conventional packaging techniques
since, conventionally, the package is filled only to 40% or 50%
of its capacity, following which cement or vermiculite is added
to fill the package. Thus, the overall volume reduction that
can be realized by carrying out the teachings of the process of
this invention is at least of the order of ten to one depending
upon the feed composition of the input radioactive wastes to
the processor. The off-gas drawn off from the processor can
be further processed, such as by filtering, scrubbing and
cooling, to form reusable water and innocuous gases which can
be passed to the atmosphere.
The primary object of this invention is to provide an
improved process and apparatus for disposing of low-level liquid
radioactive wastes wherein the volume of the wastes can be
reduced by a factor of at least ten to thereby minimize costs
of storage and ultimate disposal of the wastes yet the wastes
will be in a form more suitable for storage, transit and burial
while still conforming to safety codes with respect thereto.
Another object of this invention is to provide a process
of disposing of low-level liquid radioactive wastes wherein the
wastes are reduced in volume to a mass of free-flowing,
solid particles by calcining and the particles are packaged
in the presence of a solidifying agent or the particles are
compressed, sintered or fused to cause the wastes to be con-
verted to a monolithic product capable of being readily and
more safely stored or moved to a burial site.
~ -5-
- . : . ~ . - . , - :
1079055
In one particular aspect the present application, which
_s a division of aforementioned Canadian Application No.
207,793, is concerned with the provision of a process for
handling radioactive wastes in theform of a dilute salt solution
comprising: directing the solution into a first region having
a fluidized bed; applying heat to the bed particles from a
location externally of the fluidized bed to evaporate the
liquid fraction of said solution to form an effluent and to
cause the solid fraction to adhere to the bed particles, moving
at least a portion of the bed particles and solid fraction
adhering thereto out of said first region-and to a second region
for containerization; directing the effluent through a third
region to remove the fines therefrom and to decontaminate the -
effluent; and returning the effluent after it has been decon-
taminated from said third region to said first region as
fluidizing medium for fluidizing said fluidized bed, whereby
said first, second and third regions form parts of a closed
fluid path.
Other ob~ects of this invention will become apparent
as the following specification progresses, reference being had
to the accompanying drawings for an illustration of the apparatus
for carrying out the process of the invention.
In the drawings:
Fig. 1 is a schematic view of the apparatus;
Fig. 2 is a representative plot of waste volume versus
liquid waste feed composition showing direct volume reductions
achieved with the invention; and
Fig. 3 is a representative plot similar to Fig. 2 showing
- relative volume reductions for various liquid waste compositions
and a number of relative packaging efficiencies.
jl/ 6
~0790S5
.
A preerred embodiment of the apparatus for carrying
out the process of this invention is denoted by the numeral 10
and includes a liquid waste processor 12 comprised of a
calciner-drier unit which operates at but is not limited to
temperatures between 400F and 1200F depending upon the
composition of the waste feed solutions directed to it for
processing. Processor 12 has a lower portion 13 for containing
a fluidized bed, portion 13 having a source of incoming
fluidizing gas. Portion 13 also has a waste feed inlet 18
for in-bed atomization through single or multiple injection
nozzles (not shown). Processor 12 can also have another
waste inlet 20 coupled to nozzles (not shown) for overhead
spraying of wastes onto the fluidized bed.
An effluent outlet 21 is coupled by a tube 22 to the
input of a particulate separator 24. The separator 24 may
be of any of the types commonly known to those skilled in the
art, e.g., cyclone, filter, settling chamber, etc. Portion 13
has an outlet 26 from which solids in the form of anhydrous
partlcles can be discharged therefrom to a waste product
storage container 28. The particles can be batchwise or
continuously withdrawn either by mechanical, pneumatic or
gravity transfer. Separator 24 also communicates with container
28 to teliver particles separated from the processor effluent.
The energy required for calcining the wastes can be
supplied in any suitable manner, such as by any or all of the
following sources: external or immersion resistance heating;
induction heating; infrared heating; microwave heating; internal
immersion heat exchangers; in-bed combustion of fuel; and over-
bed combustion of fuels. For purposes of illustration, an
external resistance heater 30 is shown surrounding portion 13.
:-:
- .-: .
lV79~)S5
The rate of energy required by processor 12 is precisely
controlled from a remote console (not shown) as are the volume
- of fluidizing gas entering portion 13 through gas inlet 14 and
the volume of the input liquors.
The liquid, low-level radioactive wastes are directed from
a storage tank 31 to processor 12 in any suitable manner. If
the incomlng feed liquor is dilute in dissolved solids, the
liquor can be further concentrated by directing the same through
an evaporator 32 which can be fired in any suitable manner, such
as by fuel combustion, waste heat, steam or electrical resistance
heating. The evaporator operates to pre-concentrate the feed
liquor to a form having a desired percentage of waste solids
therein for greater operating efficiencies. The effluent from
evaporator 32 is passed by a tube 33 to a condensor 34 from
which the condensate is collected, evaluated for chemical and
radioactive contamination and recycled back for reuse in the
power plant by a pump 36. The liquid feed stream from evaporator
32 is directed by a pump 38 to a waste storage tank 40 from
which the liquid wastes are directed by a pump 42 to either or
both of inlets 18 and 20 of processor 12.
Separator 24 can be of various types commonly known to
those skilled in the art and is designed such that the largest
diameter dust particles entrained therein are removed and
transferred either by, but not limited to, gravity or by
pneumatic conveyance to storage container 28. Alternatively,
such dust particles can be returned to the fluid bed in portion
13 of processor 12 to form nuclei for bed growth. Dust returned
to the
:.
~07~S5
fluid bed can be accomplished in any manner, such as by
fluidiæed weir pots with dipleg seals, a screw conveyor or by
pneumatic injection.
The exhaust from separator 24 is passed by a tube 44 to
a scrubber sys~em 46 or directly to condensor 68 if the scrubber
system 46 is not required to effect the desired degree of
gaseous effluent decontamination. The scrubber system 46 may
include various components commonly known to those skilled in
the art of gas scrubbing such as a pre-cooler 48, a high-energy
venturi scrubber 50, a deentrainment section 52 and a low-energy
scrubber 54. In the sample scrubber system 46 shown, all of
the liquor from the scrubbers are cooled and collected, evaluated
for solid concentration and adjusted for pH, and recycled for
further scrubbing duty. A portion of the scrub liquor is bled ~-
via a line 57 to tank 31 or tank 40 to control scrub liquor
composition. A scrub solution sump 56 receives the scrubbed
liquor from pre-cooler 48 and deentrainment section 52 and a
pump 58 returns such liquor through a heat exchanger 60 back to
pre-cooler 48 over path 62, back to scrubber 50 over path 64
and to section 52 and scrubber 54 over path 66. During the
scrubbing operations, the effluent gases are cooled to their
dew point and a small amount of condensation occurs to assure
essentially complete particle elimination from the effluent.
In excess of 50% of the water in the effluent issuing
from final scrubber 54 or separator 24, if scrubber system 46
is not required, is condensed by a condensor 68 coupled by a
tube 70 to the outlet of scrubber 54 or by tube 44 to the outlet
of
1079055
separator 24. Condensor 68 may be a surface-type condensor
or a barometric condensor. The quantity of water extracted
therefrom is limited only by the condensing temperature. The
condensate is collected in a tank 72 and returned by means of
a pump 74 back to the nuclear power plant for reuse therein.
As a safety measure, the condensate is evaluated continuously
for quality and if the quality reaches a predetermined lower
limit, the condensate will automatically be diverted to tank
31 for return to processor 12. The condensate may also be used
as make-up water for the scrub solution and/or as wash-down
water for the scrub system components.
Exhaust gases from condensor 68 pass through a heater 76
to raise the dry-bulb temperature of the gases and to prevent
further condensation before entering the high efficiency filter
and adsorbers denoted by the numeral 78. Radiation monitors
(not shown) audit the gas quality during this time and, after
being monitored, the gases are exhausted to the atmosphere
through a stack 80.
The foregoing explanation relates to an open loop cycle
of processing the effluent Lrom processor 12. If the gas
discharge quality becomes more restrictive due to Federal or
State regulatory changes, such open loop cycle can be changed
to a closed loop cycle by directing the exhaust gases from
condensor 68 to the input of blower 16. In this way, the
exhaust gases can be directed into the fluid bed for fluidizing
purposes. Moreover, waste heat from the effluent from
processor 12 may be used to pre-heat the fluidizing air from
blower 16 or for providing part
10'79055
of heat energy for evaporator 32. Moreover, such waste heat
may be used in other energy-recovery systems or in providing
temperature control of storage container 28 of tank 31.
The solid particulate matter received in storage container
28 is packaged in the containers or packages approved by the
U.S. Department of Transportation. The packaging of the solid
wastes from container 28 is done at a packaging station denoted
by the numeral 82 and the waste solids are directed thereto
in any suitable manner, such as by gravity or by mechanical
or pneumatic means. At the packaging station, the solids are
directed into each package so as to fill the same to its
maximum capacity. Then, a solidifying agent is directed into
each package, specifically into the spaces between the particles
to fill such spaces. After a predetermined curing time,
solidification occurs to cause the particles to form a monolithic
block, thereby maintaining maximum loading of the package while
assuring a minimal environmental contamination in the event that ~-
the package ruptures during transit and burial.
The solid particulate matter from container 28 is directed
along a line 29 into a container at station 82 through a dust-
type hood 81. Generally, the container will be elevated into
tight engagement with the hood and after being filled, will
be lowered away from the hood. The container at station 82 is
maintained at a constant temperature by a heater 87.
The solidifying agent is contained in a solidification
mix tank 83 and heated by an external heater 86. The agent is
pumped out of tank 83 by a metering pump 84 and directed
through line 85 into hood 81 and then into the container
engaging the hood.
1079~S~
The solidifying agent can be of any suitable composition.
For instance, the agent can be a mixture of polyethylene and
paraffin or can be a styrene copolymer with a polyester resin
added thereto. Generally, the agent will be in solid form and
can be packaged and stored ready for use. When the agent is
to be used, it is heated to a flowable condition and poured or
injected into the package either before or after the waste
solids are directed into the package. In order to obtain the
maximum volume reduction of the waste product,-the solid
particulate matter recieved in storage container 28 may be -
compressed, sintered or fused into a monolithic structure such
that the theoretical density of the compounds are nearly obtained.
Apparatus 10 incorporates other structure (not shown) for
usual maintenance problems. For instance, the apparatus
includes decontamination process piping, valving and controls
to periodically wash internally all process equipment. In this
way, the major portion of radioactive contamination is removed,
thereby permitting manned access to the various components of
the apparatus. Moreover, the apparatus can be constructed so
that it forms a self-contained unit which is of minimum size
and can be moved to an operating site with a minimum of
difficulty.
1~'79~55
OPERATION
Waste feed liquor from a nuclear power plant is directed
into tank 31 for storage until ready for use. If an evaporator
is used, the waste liquor in tank 31 is pumped to evaporator 32
by a pump 35 and the output of the evaporator is directed to
tank 40 from which the liquor is pumped to either or both inlets
18 and 20 of processor 12. The input liquor to processor 12
will vary generally from 2% to 50% of solids concentration.
In the processor, the heat energy therein immediately
vaporizes all of the incoming water in the liquid wastes. Thus,
processor 12 functions as a drier. It also operates to oxidize
all carbonaceous materials, if present, and the resultant solid
residue is deposited in the fluidized bed in portion 13. The
bed particles, which are spheroidal in shape and free-flowing,
are withdrawn from outlet 26 to storage container 28. The
solids from container 28 are then directed to packaging station
82 where various packages are filled with the solids, following
which or before which the solidifying agent is directed into
each package. The result is that the soIids in each package
- become a monolithic block which can be stored or moved easily
and safely to a burial site.
The effluent from processor 12 is directed through
separator 24 to remove the dust particles therefrom. The
exhaust gases from separator 24 are effectively cleaned by
scrubbing and/or filtering to purify the same so that the ~-
exhaust gases can ultimately be vented to the atmosphere if
the gas quality meets regulatory standards.
jl/b~ 13 ; ~
SS
Processor 12 utilizes differential pressures to measure
fluidizing efficiency and fluid bed height. The processor also
operates to regulate the rate at which solids are discharged
from the fluid bed. Fluidizing gas entering inlet 14 of
processor 12 is controlled at, but not limited to, superficial
bed velocities in the range of .5 to 4 feet per second. Various
instruments (not shown) are used to maintain and monitor feed
solution quality, scrubber solution concentration, condensate
quality and flow rate, and to maintain pipeline temperatures
of incoming feed liquor well above normal crystallization
temperatures.
The results of utilizing the process of the present
invention can be shown graphically in Figs. 2 and 3. For
instance, in Fig. 2, curve A represents the approximate
reduction in waste volume for liquid waste feeds of various
dissolved solid concentrations as compared with curve B
representing the raw liquid waste. Curve A shows that a
significant reduction in volume occurs when the waste is
calcined and also indicates that such volume reduction varies
as a function of the solids in the input liquor. The
achievable direct-volume reductions are impressive and the
improved physical characteristics of the solid wastes, when
compared with those of the liquid wastes, allow more efficient
packaging thereof, thereby permitting an even greater volume
reduction.
In Fig. 3, the packaged volumes of calcined-dried
liquid wastes compared with those of unprocessed liquid wastes
for various liquid waste compositions and relative packaging
jl/\`~i"-~ 14
~079055
efficiencies are shown. Relative packaging efficiency is the
ratio of the volume of the packaged product obtained from the
process of the present invention placed in a given package
configuration compared with the volume of raw liquid waste
placed in the same package according to conventional techniques
of radioactive liquid waste disposal. Because raw liquid wastes
are conventionally packed with large quantities of additives,
such as cement and vermiculite which act as a diluent, the
relative packaging efficiency will typically be near 2 to 1.
If, in addition, the solid particulate matter is compressed,
sintered or fused, the value of the relative packaging efficiency
will typically be near 4 to 1.
Essentially all of the radioactive material present in i~
the liquid radioactive waste feed stream are ultimately removed
in the form of solid products.
