into final waste form

rangebeaverMécanique

22 févr. 2014 (il y a 3 années et 6 mois)

61 vue(s)










Cementitious composite

for immobilization of radioactive waste
into final waste form




Andrey P. Varlakov

(
Moscow Scientific
-
Industrial Association RADON

2/14, 7 Rostovskij lane, Moscow, 119121, Russia)






Second RCM Meeting
-

Romania, Nov.24
-
28, 2008










SIA“Radon” carries out a whole range of radioactive waste (RW) operations:




collection, transportation, reprocessing and storage and radiological
monitoring.


collect and reprocessing of RW from 11 regions of central Russia.


deal with various radioactive waste from industry, science, medicine and
other branches.



Each type of the wastes requires application of a special cementation method
and kind of binding materials and additives.


Application of different binding materials, increase of quantity of various
additives and their application in diverse aggregative state causes
considerable increase of radioactive waste conditioning costs and
complication of the technology.


It is important that a special composite should be developed for the
cementation both solid radioactive wastes and liquid ones having different
and problem chemical composition. Problem wastes are defined as those
wastes which are solidified with difficulty, have poor volumetric efficiencies
or produce an unsatisfactory product.










Moscow SIA “Radon” has been created a special cementitious composite (SCC).


Contents of special c
ementitious

composition for RAW cementation

Component

Contents

in additive,


%wt.

Purpose of use, modified properties of cement
compound

Special cement of 3
-
10

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-
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-
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-
㌰3

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с
o
-
processing of toxic and radioactive wastes,
reduction of binding material price.


Bentonitic clay powder

5
-
15

Leaching rate, crack resistance.

Hydraulic micro silica

0,
5
-
10

Bonding ash, stability of consistence,
penetrating ability.


Polymeric strengthening additive

0
,
05
-
1

Strength, stability of consistence, vitality,
penetrating ability, biological resistance.


Defoamer


0
,
1
-
1

Defoaming (suppression of air
-
entraining),
decrease of porosity and leaching rate.


Properties of materials


Material

Specific surface, cm
2
/g

Normal thickness

Special cement

6 000
-
12 000

0
,
60

0
,
70

Hydraulic micro silica

1
2

000
-
15

000

0
,
60

0
,
70

Ash after domestic waste incineration

7 000
-
10 000

1
,
00

1
,
10

Portland cement

2 900


3 500

0
,
18
-
0
,
23

The cementitious composite consists of 5
-
6 macro
-

and micro components.


Each

component improves simultaneously several properties of cement compound.

(SCC).










At SIA “Radon”, the following different types of solid radioactive waste (SRW)
are cemented with the use of SCC:


lump SRW;


fine
-
dispersed or close
-
packed SRW including ash residue after incineration
of solid radioactive waste with average particle sizes 0,5
-
2 mm.


Lump SRW are cemented by means of top filling of containers.


Fine
-
dispersed and close packed SRW are cemented by means of bottom
impregnation


Cement grout on the
basis

SCC

Fide pipe


Cement grout on the
basis

SCC


Cementation

SRW

with use

SCC









Equipment for SRW impregnation with high penetrating grout
.


Container (100 liter)
with ash residue after
impregnation

Equipment for ash
residue impregnation
with highpenetrating
cement grout


Equipment for SRW impregnation in
2,7 m
3

container with high penetrating
cement grout


Equipment for SRW impregnation in 100
and 200 liters container with high
-
penetrating cement grout










Properties of cement compound with ash residue prepared by
impregnation method. Content of ash residue in the final product
makes 65
-
75 % wt.

.

Compressive

strength
(top of 200

l drum),
MPa



Water/

Cement
ratio

28
days

After of

free
z
ing
-

tha
w
ing
a

After
water

storage
b

Leaching rate

137
Cs
,
g/(sm
2
*
day)

0,5

17,5

17,6

30,2

(1
-
2)
*
10

4

0,6

12,7

11,7

16,6

(3
-
7)
*
10

4

0,8

11,0

10,5

14,8

(5
-
8)
*
1
0

4

0,9

8,1

7,2

9,9

6
*
10

4



1
*
10

3

1,1

6,1

5,5

6,5

8
*
10

4



1
*
10

3

a
A
fter 30 cycles of freezing
-
thawing
(
-
20
о
С
…+2
о
С
),
b
After water storage for 90 days
.










Properties of cement compound with close packed SRW prepared
by means of bottom impregnation method
.


a
A
fter 30 cycle
s of freezing
-
thawing
(
-
20
0
С
…+2
С
),
b
After water storage for 90 days


Compressive

strength

(top of 200l drum),
MPa

Cement
type

Water/

Cement
ratio

Additive,
%wt.

Density
grout,
g/cm
3
,
initial/

top of
drum

28
days

After of

free
z
ing
-

tha
w
ing
a

After water

storage
b

Leaching
rate

137
Cs
,
g/(sm
2
*
day)

1,78

28,8

18,9

27,0

2*
10
-
2

-

1,46

10,8

8,5

10,9

3*
10
-
2

1,79

23,8

17,7

24,0

4*
10
-
4

0,6

Bentonitic
clay, 5

1,40

8,3

6,1

10,1

6*
10
-
4

1,62

17,3

10,6

18,8

7*
10
-
4

Bentonitic
clay, 5

1,29

4,9

3,7

7,9

9*
10
-
4

1,62

20,3

12,6

18,6

7*
1
0
-
4

0,7


SCC
,
30

1,55

14,8

9,7

17,7

9*
10
-
4

1,57

17,6

10,5

18,8

7*
10
-
4

Portland
cement

0,8

SCC
,
30

1,48

10,3

7,7

9,9

7*
10
-
4

1,52

25,3

19,7

24,6

8*
10
-
5

0,9

-

1,52

23,2

15,9

25,4

2*
10
-
4

1,46

19,1

16,3

20,4

8*
10
-
5

SCC

1,0

-

1,36

12,6

8,3

16,8

4*
10
-
4









LRW type


Specific

β
-
activity,

Bq/l


рН

Density,

g/cm
3


Salt,

g/l


SAS,

g/l


Fixed
residue,

g/l


LRW


3,65
*
10
3


7,0


1,10


75


5


3


Concentrated
LRW

5
,
70
*
10
4


7
,
9

1
,
1
5


35
0


<1

120


LRW
containing
SAS

3
,
64
*
10
4


-
)
5
,
1
×
10
4


11
,0


1
,
3
0


130


70

0
,
2

Properties

of

LRW

At SIA “Radon”, the following different compositions of liquid radioactive waste
(LRW) are cemented:


LRW high containing NaNO
3
;


LRW additionally containing surface
-
active substances coming with detergents
in decontaminating solutions in quantities up to 30
-
40 % wt.


LRW containing
oil.









Properties of cement compounds prepared of SCC and

traditional Portland cement
.

Compressive strength, MPa

Cement
(specific
surface,
cm
2
/g)

Water/Cement
ratio

Flowability,
mm

Se
t
tling,
%

7
days

28
days

56
days

After of
free
z
ing
-

tha
w
ing

After
water
storage

LRW

0
,
7

230

5

7
,
9

15
,
6

17
,
9

19
,
9

17
,
7

0
,
8

>240

9

5
,
1

7
,
1

11
,
5

10
,
5

11
,
2

Portland
cement

0
,
9

>240

13

4
,
0

5
,
9

8
,
5

5
,
5

9
,
6

0
,
7

207

2

14
,
3

18
,
7

27
,
5

13
,
6

36
,
3

0
,
8

238

2

10
,
9

11
,
6

22
,
2

11
,
9

25
,
9

0
,
9

>240

3

7
,
5

9
,
3

15
,
8

8
,
7

17
,
0

SCC


1
,
0

>240

5

3
,
8

8
,
6

12
,
7

7
,
9

15
,
5

Concentrated LRW

0
,
7

180

2

4
,
2

5
,
3

7
,
4

5
,
1

7
,
6

0
,
8

210

7

5
,
1

4
,
1

6
,
5

6
,
5

7
,
2

Portland
cement

0
,
9

>240

15

2
,
4

3
,
3

5
,
8

-

-

0
,
9

>240

3

6
,
3

7
,
2

14
,
9

6
,
7

12
,
7

SCC

1
,
0

>240

4

3
,
9

5
,
6

9
,
5

7
,
7

10
,
1


At LRW cementation with the use of ordinary Portland cement without additives, the water cement ratio
should not exceed 0,7
-
0,75. Increase of W/C ratio will cause demixing of cement grout (separation of
water).


Application of SCC allows increasing
:


W/C ratio up to 1


1,1 due to its stabilizing influence;


contents of radioactive waste in the final product.


At that all the regulated properties of cement compound do not worsen in comparison with the
properties of cement compound prepared on the base of traditional Portland cement.









Properties of cement compounds
containing SAS

prepared of
special cementitious composite and traditional Portland cement
.

Compressive strength, MPa

Cement
(specific
surface,
cm
2
/g)

Water/Cement
ratio

Flowability,
mm

Se
t
tling,
%

7
days

28
days

56
days

After of
free
z
ing
-

tha
w
ing

After
water
storage

LRW containing SAS

0
,
6

>240

foam

-

5
,
2

7
,
5

-

-

Portland
cement

0
,
7

>240

foam

-

1
,
2

7
,
5

-

-

SCC

0
,
7

>240

not
foam

16
,
3

17
,
6

21
,
6

8
,
2

9
,
5


Liquid radioactive waste containing a considerable quantity of SAS is very difficult for cementation
because of forming a lot of foam.


Cement compound is saturated with air and hardens very slowly forming a porous structure.


Application of SCC allows obtaining the final product of higher quality which is not saturated with air

Acceleration of hydration process is typical for these compounds because of a high dispersity of
cement, ash and hydraulic micro silica.









Cement grout is placed into the containers and compartments of the repository can strongly warm up due to heat of
cement hardening as well as radiation exposure.


Volume of the containers
for cementation waste

can vary from 100 or 200 liters up to 2
-
3 m
3

and is not so great as the
one of compartments of a repository, which can make 200
-
400 m
3
.


Warming up of cement can cause water evaporation from the cement monolith, stop hardening and lead to
crystallization of salts within pores
, that
can lead to destruction of the final product while its long
-
term storage.


For reduction of heating, it is necessary to use cement of mineral additives (fuel ashes, slag and hydraulic silica).


Properties of ashes after domestic waste incineration can be similar to ones of fly fuel ashes.


Utilization of secondary waste (slag and ash) of combustion plants is an important environmental approach to solving
cities’ issues. But ash after domestic waste incineration is toxic industrial waste as it contains toxic elements

Sanitary code

Element

Variation
range

Amount in
ashes of an
experiment
al batch,

mg/kg

MPC, maximum
permissible
concentration in
soil,

mg/kg

MPC, maximum
permissible
concentration in
water, mg/kg

Cadmium,
Cd

50
-
204

93,81

-

0,001

Chromium,
Cr

414
-
500

327,21

90,0 (Cr
+3
)

0,5 (Cr
+3
); 0,05
(Cr
+6
)

Copper, Cu

360
-
570

376,03

3,0

1,0

Mercury, Hg

0,32
-
16,9

-

2,1

0,0005

Manganese,
Mn

520
-
800

311,55

300
-
1500*

0,1

Nickel, Ni

29
-
73

30,55

4,0

0,1

Lead, Pb

1100
-
6900

1466,36

6,0

0,03

Stibium, Sb

80
-
190

-

4,5

0,
05

Zinc, Zn

3180
-
6380

4972,99

23,0

1,0


Contents of most significant microelements in ashes after domestic waste incineration










Results of the research have shown that the special cement composition containing up to 10
-
30 % wt.
of ash after domestic waste incineration allows:



cementing waste by using higher water
-
cement ratio, what in turn allows increasing the amount of
waste included into the final product and reducing the consumption of cement material;



decreasing the amount of hydration heat, which is important for continuous cementation of waste and
hardening of cement compound in compartments of a special repository or big containers.


Co
-
processing of toxic and radioactive waste is
ecological and economic efficiency
.


At SIA “Radon”, experimental batches of cement compositions are used for cementation of waste.

Diagram of chemistry (A) and X
-
ray structure analysis (B) of ash after domestic waste incineration.

1
-

SiO
2
, 2
-
CaO, 3
-
Al
2
O
3
, 4
-
Fe
2
O
3
, 5
-
Na
2
0+K
2
O, 6
-
MgO, 7
-
TiO
2
, 8
-

microelements, 9
-
Cl, 10
-
SO
3
, 11
-
P
2
O
5









Wastes containing technical oils are considerable problem.



Oils can often be in repositories together with salt liquid radioactive waste (LRW), ion exchange
resins, silicon lubricants and other wastes.



Desired methods for treatment of such oil waste are incineration or cleaning.



By many reasons, these methods are a serious technological and economic problem.



Frequently, the only method for the radioactive oils treatment is their temporal storage in metal
tanks.



The simplest solution is them inclusion into a cement compound at cementing liquid salt
radioactive waste.



The experience of radioactive oils cementation at Moscow SIA "Radon" is five years. Radioactive
oils are added into cement grout in quantity of 5
-
7 %wt. at cementing liquid salt radioactive waste.



Disadvantages of the cementing way of technical oils and LRW:



low contents of oils (about 5
-
7 wt.%) in cement grout depending on LRW salinity;



low (not more than 0,5) water
-
cement ratio;



worsening of cement compound properties;



uneven distribution of oils in cement compound, which causes local decrease of its properties
lower than determined values and degradation;



settling of oils during cement compound tempering;



mixing of cement grout requires a special mixer because of cement grout disintegration;



depending on type and state of waste it is possible air
-
inclusion at mixing cement grout,
worsening all regulated properties of the final product;


biological degradation of oils and consequently cement matrix.









Influence of the SCC on Properties Cement Compounds with Radioactive Oil.

Properties of Grout

Compressive Strength, MPa

Water/

Cement
ratio

Oil,

wt.%

Bind
er
+Bind
er
in
suspension,

wt%


Floatability,
mm

Settling,

%

7

days

28

days

56

days

TM
a

>240

0

3
,
4

5
,
8

7
,
3

PC+30%
PC

>240

0

3
,
6

6
,
1

7
,
9

PC
b
+30%SCC
b

215

0

3
,
7

8
,
6

10
,
8

5

70%SCC
+
30%SCC

120

0

5
,
0

10
,
6

11
,
0

TM

>240

2
,
5

1
,
2

2
,
5

2
,
9

PC+30%
SCC


190

0

2
,
0

5
,
1

5
,
4

10

70%
SCC
+30%
SCC


115

0

6
,
7

7
,
6

9
,
8

TM

>240

7

1
,
1

1
,
4

1
,
6

PC+
30% SCC

187

0

1
,
0

3
,
8

3
,
1

15

70% SCC
+
30% SCC

110

0

1
,
7

4
,
9

5
,
1

TM

240

16

-

0
,
6

0
,
3

PC+30% SCC

120

0
,
2

0
,
6

1
,
1

1
,
6

0,7

20

70%
SCC
+30%
SCC


<100

0

1
,
9

3
,
6

3
,
8

TM

185

1
,
2

1
,
4

1
,
3

2
,
0

PC+10%
SCC


179

0

1
,
5

3
,
7

5
,
3

0,5

15

70%
SCC
+30%
SCC


<10
0

0

4
,
3

5
,
4

6
,
5

a
Traditional mixing without preliminary suspension.

b
PC

Portland
Cement


SIA”Radon” has been developed the new method for increasing contents of oils in cement compound up to 15 %.


The new method offered for cementation of radioactive oil consists in the following.

Stable to stratification a suspension is prepared on the base of oils and saline LRW.

This suspension is introduced into the main cement grout, which allows evenly distributing oils in hardened cement
compound.


To increase the degree of oils inclusion into the final product SCC should be introduced in suspension. This suspension is
introduced into the main cement grout, which allows evenly distributing oils in hardened cement compound.

Ultra fine high mark quickly hardening cement improves all properties of the final cement compound.











Influence of the SCC on process of hydration cement compound with radioactive oil
.

SEM of cement compounds
containing 20 %wt. of oil
received by traditional mixing
with portland cement.
Hardening time


1 day.

The oil film complicates
reaction with water of initial
cement minerals.

SEM of cement compounds
containing 20 %wt. of oil
received by preliminary
suspension with SCC.

Hardening time


1 day. The oil
phase is submitted by the fine
drops surrounded with "shell"
bentonite. Products of
hydration are observed.

Components of SCC are able adsorbing oils and increasing the cement compound quality. SCC contains bentonite and
ash, which are able to adsorb oils and decreases its contents in liquid phase.



Influence of the SCC on process of hydration cement compound with radioactive oil is shown on of Scanning electron
microscopy (SEM) picture. Where we can see that the oil film complicate reaction with water of initial cement minerals (a).

The oil phase is submitted by the fine drops surrounded with "shell" SCC (b). Products of hydration are observed (b).









Nitrate
-
containing cement blocks.


Appearance

of nitrate
-
containing cement blocks without
biocide

after
20 months of field tests in open container (samples №№ 2,4,10,12,14).
The thin
-
porous “sponge
-
like” surface, wearing on sides, color
changes can be seen.

Nitrate
-
containing cement blocks.


Appearance

of cement blocks with
biocide

additions after 20 months of
field tests (open container) samples
№№5 and 6


cement blocks
without nitrates; samples №№7 and
8


cement blocks with nitrates. The
structures are not changed.

Oil in structure of cement is nutrient for development of bacteria.



Gaseous products of activity of bacteria and also organic acids and
aldehydes

promote increasing of
porosity cement compound and can lead to destruction it at long storage.



On the research data biocide additive of a
polyhexametylenguanidine

class included in SCC can give
protection from
biodistruction

preventing biogenic gas formation, which is important for long term
storage.










А
.

С
.

В
.

D
.

Е
xperimental
-
industrial cementation of radioactive oil.

А

-

general view of plant of cementation of LRW.

В

-

module for preparation of radioactive oil for cementation.

С

-

Measuring tank.
D
-

cement compound of radioactive oil in quantity of 10%wt.

Hardening time


1 day.

In SIA"Radon" the module for preparation of radioactive oil for cementation is created.




The module includes unit for preparation of suspension using liquid waste, oil and powder
additives.



The main device of unit for preparation of suspension is disperser, which creates a turbulent
stream and a pulsation of suspension with the help of special flanges.



The prepared waste feed to the mixer of cementation installation.


Tests

have

shown,

that

due

to

preparation

of

preliminary

suspension

and

uniform

distribution

of

oil

in

a

cement

grout,

inclusion

of

radioactive

oil

in

cement

compound

in

quantity

of

10
-
15

%

wt
.

is

possible
.



Properties

of

cement

compounds

obtained

in

experimental
-
industrial

scale

satisfied

the

meet

requirements
.









CONCLUSION


As it can be seen from above data, SCC can be universal cementitious material at nuclear
site like “Radon”. Were there are a lot of various waste, which requires different cements and
additives.



In having varied the quantity of SCC in mixture with traditional Portland cement, it can be
used for different methods of cementation both various liquid radioactive waste and solid
ones. SCC can be used for cementation difficult LRW like oil containing waste.


At that SCC will allow improving the quality of final product and increasing its loading with
radioactive waste and decreasing the final product volume.


It is important that the cementitious composite can have been applied as an independent
cement material or as an additive to the ordinary Portland cement changing properties of the
cement compound in a required range depending on a technological process and wastes.


SCC is used in dry form at cementation and introduced directly into the mixture as cement.


Presence of components in macro quantities does not practically influence on cost of
additive and makes free of necessity to complicate the RW cementation equipment by means
of applying expensive and fragile dosing equipment in the installation.


Besides, evenly distributed macro components in the additive make cementation simpler,
increasing the productivity due to decreasing time for thorough mixing of cement compound
components.









New technology for cementation of problem liquid radioactive wastes


A new technology for cementation of problem liquid radioactive wastes has been developed
at SIA”Radon”.



These wastes are



organic liquid (oil, solvents, extractants, scintillation cocktail and others);



high containing surface
-
active substances LRW;



subacid aqueous saline LRW and high containing alpha nuclides LRW.


The technology can be used for conditioning of problem liquid radioactive wastes directly at
nuclear sites without use stationary cementation plant.


The technology consists in as follows
:



porous concrete is prepared by a special mixer and placed into a standard container 100 or
200 l.



problem LRW is pumped into pore space of porous concrete matrix through previously
positioned special feed tube at the age
-
hardening of concrete not less than 28 days.



the wastes are effectively fixed in pores of the cement matrix.



The final product has all the regulated properties.



Compressive strength of porous concrete matrix at the age
-
hardening 28 days is 6
-
10 MPa.

The average size pores makes 0,1
-
0,05 mm, density of concrete
-

0,7
-
0,9 g/sm
3
.

Feed pressure of LRW makes 0,15
-
0,3 MPa.

Capacity of impregnation depends on kind of LRW and makes 20
-
40 l/h.

Impregnation of several containers can simultaneously be carried out.









Container and
device for
impregnation of
porous

concrete
by LRW

Structure of
porous

concrete
at 28 days of
hardening

At SIA “Radon”, an experimental
-
industrial tests of problem liquid radioactive wastes
cementation in such way carry on.


For impregnation various waste products have been used (oil, blend of tributylphosphate
and sintin, subacid aqueous saline high containing alpha nuclides LRW).


Properties of the final product have been corresponded to all the regulated requirements.

Depending on kind of LRW contents of waste in final product has made 50
-
65 % vol.


The new method of conditioning has the following advantages:



the degree of inclusion of problem LRW into the final product can be up to 50
-
65 % vol.;



the technology excludes negative influence of wastes on of cement hydration;



there are no difficulties in mixing the cement grout and wastes;



small amounts of radioactive wastes are processing directly at nuclear sites;



equipment for conditioning radioactive wastes directly at nuclear sites can be mobile.