B. A. R. C.-1028
iu
GOVERNMENT OF INDIA
ATOMIC ENERGY COMMISSION
DEVELOPMENT OF SUITABLE VITRIFIED RADIOACTIVE WASTE
PRODUCTS WITH LOW FORMATION TEMPERATURES AND IMPROVED
LEACH RESISTANCE-A PRACTICAL APPROACH
by
G. A. Vaswani, P. B. Jahagirdar, R. C. Rastogi and
N. S. Sunder Rajan
Hi-Level Waste Management Section
BHABHA ATOMIC RESEARCH CENTRE
BOMBAY, INDIA1979
B . A . R . C - 1 0 2 8
GOVERNMENT OF 171 ilkATOMIC ENERGY COHaSSIOH
3
DEVELOPMENT OF SUITABLE VITRIFIED RADIOACTIVE WASTEPRODUCTS WITH LOW FORMATION TBMPERATURBS AND IMPROVED
LEACH RESISTANCE - A PRACTICAL APPROACH
by
G.A. Vaawani, P .B. J a h a g i r d a r , R.C. Rastog i andN . S . Sunder Rajan
H i - l e v e l Vas te Management S e c t i o n
BHABHA ATOMIC RESEARCH CENTREBOMBAY, INDIA
1979
IHI3 Subject Category : E 5'
Desc r ip to r s :
liADJOACriVE WASTE PROCESSING
viminc/moN
1.KACHIHG
fiLAiiS
(ircilf-liEVt'l- RAD!OACTrVR iVASTKS
HOKON OX1DKS
VtSY HTCH
CUB/1] CAL COMPOSITION
t.'.!-.JiTING i'OlN'1'8
D H R A F I L 1 T Y
In contrast to normal practive ©tf employing theoretloal
considerations, a achene based on practical approach has
been evolved for the development of suitable glass compo-
sitions to produce vitrified radioactive wastes with low
forming temperatures of around 1OOO°C and low leach rates
of the order of 10"5 to 10~6 gm cm"2 d"1
After fixing the percentage of the waste content at a
moderate value, a number of formulations in the sodium
borosilicate system are studied for their melting and leachl"
characteristics by simple and quick laboratory techniques.
Based on the resultB, a composition with scope for further
lowering of melting temperature and improvement in product
durability is subjected to the introduction of different
durability enhancing and/or melting temperature lowering
oxides as well as the waste oxides so as to obtain an optimum
composition.
This coapoaition is further subjected to variations in its
Ha20, BgOj and 3i02 content to get a region of compositions
with optimum leaching and melting characteristics. A compo-
sition selected from the central portion of this region will
retain its properties even if the proportion of waste
oxides and glass forming additives vary during the commercial
production of vitrified radioactive wastes.
•DBVBMPMRNT OF SUITABLE VITRIFT3D BADIOACTIVB WASTBPRO0UCT8 WITH LOW FORMATION TE. 11/BRATURBS AND IMPROVED
LKACH RBSISTAWCB - A PRACTICAL A » f ItfAOH'.
b y
O.A. Vaswani, P.B. Jahagirdar, R.C. Rastogi andN.3. Sunder Rajan
1. INTRODUCTION
The high level radioactive waste generated during the
reprocessing of Irradiated fuels from nuolear reactors
needs to be immobilised by converting them into non-
volatile, insoluble, stable solid forms for their assured
iaolaticn from man's environment until radioactivity
decays down to innocuous levels. Amongst various solidi-
fioation processes, vitrification of the waste in bo-o-
silicate glass forming system has been more widely adoptvi
throughout the world'-1-'.
Apart from various desirable characteristics of vitrified
waste product(VWP) such as relatively higher theraal
conductivity, nechanical, thenna},and radiation stabili-
ties etc, the two most important characteristics are the
low formation temperatures o£ around 1000°C and low leach
rates of the order ot 10 gn/cm /day in water.
Because of the multicomponent nature of the waste, it is
not easy to formulate the desired compositions on theoretic
considerations alone. However, after making a few simpli-
fying assumptions such as to consider 31, B and Al to be
tetrahedral -net- work formers and all the rest of cations
as network modifiers, a number of attempts have been i»de
- 2 -
to formulate the suitable glass compositions for vitri-
fication of High Level Radioactive(H1R) wastes in boro-
sil icate Byetern. In these attempts, some of the theore-
tical considerations'-2'*''*•' taken into account are listed
below:
i) Oxygen ratio "Si~+~ff »
S ii i ) ratio of number of silicon to boronatosns -g— i
i i i ) ratio of number of silicon. ) Si+B
iv) the ratio of number of net )work modifiers to the number / 5®.*_?2-^_52di?iers
of oxygen atoms exceeding ) « 7 rthese linked to B or 3i atoms ) u ~in three dimensional net work )
But, even after taking the help of these criteria, i t
becomes necessary to try scores of compositions on
laboratory scale for selecting the compositions with
optimum characteristics. Experience hae shown that
while trying to limit one's trial formulations in the
optimum region of above parameters, one may miss a far
more rewarding region of malt compositions. It was,
therefore, fe l t that a practical approach towards the
development of low-melting and more leach-resistant
glass compositions for any particular type of waste
might be more appropriate. An attempt has been made
to establish one such approach in the present study.
- 3 -
2. THE PRACTICE APWiOACH
The following steps are uaed In the development of
suitable low melting g lass compositions for the production
of v i t r i f i e d wastes with improved loach res is tance .
. i ) The percentage of waste oxide content i s f ixed
at a moderate value of say around 22.25 weight
percent or around 16 jnol percent. Then, s tart ing
from the s i l i c a rich region of compositional trjangular
diagram for SiO2- B2°5~ Sa2°~^ m o 1 Percent waste
oxides Byatern, t r i a l compositions are formulated
towards B-0» a n d N a 2° rich regions in the iteps
of variation of 5 mol percent at a time for each
of the three variable constituents v i z . , 310 . ,
BgO^ and ifogO.
l i ) The melting and leaching character is t ics of about
30 compositions formulated i n above manner are
Studied by using t o t a l l y Inactive simulated waste
and by employing r e l a t i v e l y quicker and simpler
laboratory techniques. Although, these techniques
may not be very reproducible and r e l i a b l e , they
should a t l eas t serve the purpose of inter-comparison
of the sot of t r i a l composition.
H i ) The pouring temperatures and leach rates for the
dif ferent compositions are plotted as triangular
diagram. This w i l l help to ident i fy the compositional
regions with s p e c i f i c melting and leaching chara-
c t e r i s t i c s . From these, a composition with the
acope lor .1 improvement in netting and leaching
characteristics in chosen for further melt deve-
lopment i*o :ck,
iv) Various Eicclif lcstions of this composition are
formulafcal by incorporating established melting
temperatv. n.'-lowei'i n& uiul/ox durability-enhancing
oxldea (iacJ.udin^ the waste oxides ) as minor additives
in the raage of 2.5 to 10 mol percent.
v) The leaohLng character.latics of these modifications
are then studied and compared with those of parent
composition as well as with each other so ae to
select a :few modifications which produce optimum
effect on melting and leaching characteristics.
vi) Thereafter, a few compositions around the selected
modified compositions are formulated by varying tha
percentage of Na20, BgO,, and SiOg while keeping
the percentage of minor additives and waste oxides
at constant level, and are studied for their
melting and leaching characteristics. In this way,
regions of the best compositions are found. A
composition from the central portion of Ifrese regions
will retain i t s characteristics inspite of the minor
variations in the actual composition under plant
conditions of metering the waste and chemical feea.
However, before adopting any of these selected
compositions on plant scale, their acceptabilities
with respect to other desired characteristics such as
thermal conductivity and mechanical, thermal andradiation stabilities should be checked.
-5-
3, RESULTS AND D.ISCU3SI0N3
To cite an example of the above melt development
approach, the results of studies on a particular
simulated purex waste are presented here. The compo-
sition of this waste is given in Table-I. The melting
and leaching studies for the compositions foimulated
in NagO-B^Oj-SiC^-lS mol percent waste oxide were carried
out as per the methods given in Appendix-I and the results
are presented in Tables II and III respectively. The
pouring temperatures and cumulative fractions of weight
loss in five daya in conventional boiling water leaching
setup for these compositions are brought out in the
triangular diagrams presented in Figure-1.
The values of loach rate during first four hours were
not taken into account while calculating the average
leach rates during the week. The ratios of leach rate
during first four hours to average leach rate during
the rest of week were between one and three for a
majority of the cases. But in case of compositions with
low silica content, this ratio was Very high i.e. between
five and thirty and therefore such compositions are
to have very poor leach resistance in the triangular
diagram.
From this diagram in Fig.l, it is seen that the
composition, corresponding to code Ho.1-60, a pouring
temperature of 1050°C and a leach rate of the order of
- 6 -
TABLB-ICOHtOJITION_OP 3IMULATEU PUKEX Wa3TE USED ?OA MELT DBVELOPMEaT WORK
^ r 7 J Constituent ' Molarity of the °*No. . ions J lona
2 . Br2*"
3 . •So7+(Ho6*)
4 . Mo6*
5.
6.
7.
8 .
9.
10.
11.
12.
13. Hi2*
1 4 .
1 5 .
0
0
0
0
0
0
0
0,
0.
0,
0,
0.
o.
0.
2.
.005
.0086
.0067
.057
.045
.0105
.016
,02
.0134
.051
,072
018
009
2
0
The s u b s t i t u t e ion used.
HOMOOSHBITT CHA,RACTEMSTIC3 0? THE SIA33 COHPO-: r l 6 MOLE fSHCSiVj! WABIij OXIB'ja sYS'g^
_ cm* ,*«reent solar c o m p o s i t i o n , ,«-* ,£^i . of Bav Mi*, .on ,ng • Apparent product homogeniety,
S Wa0t«*3iO'B,d { B a , 0 , temp., temp, ',£^i . of Bav Mi*, .on ,ngtSo Wa0t«*3iO,'B,d, { B a , 0 , temp., temp, '
.'dee. •• / ! J
g gpores.
900 XIOO(DP) Orsen glaso, shining, slightly porous,homogeneous.Grey glass, quite ahiaing, homogeneous,smooth wire drawn, a slight amount ofSTP° present on Burface as a tain layer.
Dark grey glass, shining, homogeneous,f«w small pores, aaall amount of 3Y?(about0,1 percent) in the form of flakes.Dark green glass , extremly shining, f«wdots of 3TP on surface.
Dark green glass , quite shining, fev smallpores, a thin layer of SXF on the surface.
Dark graon glass, shining, few small pores,a thin layer and few spots of SIP on thesurface,Dark green glass, ahlning, few dots of STParri a thin layer of SYP Qri aur?_cof
« 3T? •• Solatia yeJiow phaoe consistL»g of isaialy Dolybd=.taa, ohroaates and sulphates ofl U ions;.
1.
2.
3.
4.
5.
6.
7.
1:
1-174
I-X73
X-172
X-140
1-110
i-iu
1-112
16
16
16
16
16
16
16
X6
60
60
60
60
57.
57.
57.
57,
5
5
5
5
6-5
9
11.
14
6.
9
11.
14
50
5
5
17.5
15
12.5
10
20
17.5
15
12.5
900
900
900
950
900
950
950
900
1100(D]
1100(DI
1050
1050
1050
1100
1100
1050
TABES-Hcaatd.)
1
9.
1 0 ,
1 1 .
1 2 .
1 3 .
1 4 .
15.
16 .
17.
1 8 ,
19 .
2 0 ,
—» r• 2 '
1-32
1-132
1-130
1-105
1-176
1-107
1-108
1-109
1-133
1-128
1-102
1-178
_
16
1 6
1 6
16
16
16
16
16
16
16
1 6
16
4
57,5
57.5
55
55
55
55
55
55
55
52.5
52.5
52,5
5
1 6 .
19
6,
9
1 1 .
14
16,
19
21
9
U
u
5
5
,5
.5
.5
.5
6
10
7,
2 2 .
20
17.
15
1 2 ,
10
7.
22.
20
17
t
5
5
5
.5
.5
.5
.5
7
950
950
900
900
850
900
900
300
1000
900
900
900
a ;
1050 Light brown glass, quite shining, fesspota of STP on aurfac*.
1100 Brownish green glaos, shining, homogen-eous, few small pores.
UQQ Dark brown glass,, good ahiuo, homogeneous,few spots of SIP oa surface.
1050 Dark green glass , 3hi.rii.ng, few pores, fawdots of STE on fe
1000 0r«en colored glaar,, ercall porea, shining,alight amount of S".? present on surfaceas flakes.
1050 Dark green glass , homogeneous STP in the 00form of a thick patch. 1
1050 Dark gre<sn glass , homogeneous but SIP lain the fona of a thin layer.
1050 Dirty grsen g las j , quite shining, homogene-ous, liquid phase separation present.
1100 Brown glass , ahining, homogeneous, no SIP.
1050 Dark green glass, shining, smooth wiredrawn, no SIP present.
1000 Dsrk green glass, shining, a thin layer andfew spots of 3Y? on surface.
17.5 900 1100 Ds.rk: green, quite shining, very homogeneousSPYP in the form o£ a lump.
tASLMZ(oontd)
1 LA 3 , 4 , 5 ' 6 1 7
21. 1-104 16 52.5 16.5 15 900
22. 1-143 16 52.5 19
24.
31.
32.
12.5 850
23. 1-129 16 52.5 21.5 10 850
1-142 16 52.5 24
25. 1-126 16 50
1-127 16 50
7.5 850
25 800
26. 1-133 16 50 11.5 22.5 800
27. 1-134 16 50
28. 1-135 16 50
29. Z-121 16 50
30. 1-136 16 50
14
16.
19
21.
24
11.
5
5
5
20
17.
15
12.
10
25
5
5
800
SCO
900
850
350
350
1000
1000
1000
1000
• 1000
950
1050 Dark green glass, bomogeneoua, few pci^s,slight amount of dYP in the fora of looseflakes.
1000 Tellowish green glass , few pores, a thin,layer of 3TF (about 0.2 percent) and liquidphase separation present.
1000 Dirty green glass , homogeneous, few pores•light amount of 3TP in the form of looseflakes.
1050 Dull brown glass, shining, fey poiaa, no 3TF.
1000 Grey glass , ahlning, homogeneous, a thinlayer of SIP on surface.
950 Dark a oh coloured glass , shining, slightlyporous, few spots of SIP on surface.
Dark ash coloured glass, shining, few pores,few spots of 3TP on surface.
1000 Tellowish groan glaas, shining, sl ightlyporous, small spots of SYi1.
Tellowish green glass, shining, porous,loose flakes of SIP present.
Orey £lass , shining, few small spots of3YP on surface.
Tellowish glass , homogeneous, few pores.
Dirty green glass , homogeneous, few smallpores, a tiiin layer of 3TP present.
1
! I.33.
34.
35.
36.
37.
38.
39.
40 .
4 1 .
4 2 .
• 3 .
1-124
1-125
1-98
1-99
1-100
1-101
1-141
1-140
1-139
1-16
I-ft7
16
16
16
16
16
16
16
16
16
16
16
47.5
47.5
45
45
45
45
42.5
42.5
42.5
40
40
16.5
a.5
9
14
19
24
14
19
24
14
24
20
15
30
25
20
15
n^
22.5
17.5
30
20
850
850
850
850
850
850
800
800
850
850
350
950
950
950
950
950
950
900
950
900
900
900
Dark grey glass, qu:fte shining, homoge-neous, no SYP.
Yellowish graen gln93, homogeneous, looseflakes ot SYP present.
Gray glass, ahiuing, few small pores,SYP in the form of flakes and lumps(about0.4 percent).
Grey gla83, shining, fe* small pores, SYPIn the form of lump (about 0.2 percent).
Yellowish green glass, moderate a bine, fevsmall pores, aaall amount of SYP present.
Yellowish groen glass, shining, homogeaecuEno SYP present.
i
3ray glaas, shining, homogeneous, smooth gwire dravn, no pores. Y
Orey glass, shining, homogeneous, a thinlayer of SYP present.
Light yellowish glaso, shining, homogeneouslot of small pores, a thin layer of 2TPpresent.
Orey glass, shining, few small pores homo-geneous, ao SYi",
Yellowish green glasa, homogeneous, smallamount of SYP in the fora of a layer.
- 1 1 -
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- 1 2 -
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-15 -
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8
£ 3 3 £ £ .-T *r i t i TM M M W M M
03 01 O r4 (M K>
2)
Sr.Io.,MeltCod*
Leaca rate £ \(r on Ws, leached basis An gm/cm^/day during:.Percentage ..Of glass Of £l
first ,4 bra.,
Haxt 20 ,2nd daydays.
,3rd day , 4th day 5th day ,attacbed 'attacked on,on Na lea- .weight loss,'ched basis 'basis during;.during: '
,4 hrs>'days i4 hrs..days.
10 11 12 14 15 16 18 19 20
1 .
2 .
3 .
4 .
5-6 .7 .8 .9 .1 0 .1 1 .1 2 .1 3 .1 4 .1 5 .1 5 .
1-1741-173
1-69
1-172
1-1461-1101-1111-1121-321-1321-1301-1041-1761-1071-103X-iO9
0.130.16
8.03
1.30
0.260.994.9*2.172.827.360.626.891.283.987.579.15
0.270.13
2.41
0.43
0.150.270.780.942*263.340.303.540.9i1.862«3S
0.040.08
4.4
0.29
0.150.451.01.480.342.310.254.521.09i.463.90v.35
0.040.18
4.-T
0.29
0.150.330.851.240.671.980.274.10.981-552.414. OS
0.04
0.13
2.36
0.25
0.170.350.80
1.120.672.170.293.711.281.602.903.72
0.07
0.24
3.20
0.29
0.170.350.911.180.671.840.333.371.401.853.063,12
0.078
0.07
0.55
0.62
0.280.460.621.080.673.40.282.750.801.373 .05 .0
0.7
2 .2
7.0
4.8
13.95.4
13.318.4
6.734-8
4.047.3421.6319.2236.065.23
0.14
0.15
0.38
0.36
0.180.280.630.77C.371.140.361.950.601.12.43 .3
6.4
1.93
4.1
2.9
11.13.7
10.114.2
4.820.23 . 8
33.012.322.013.2332.3
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-16 -
-17 - POURING TEMPERATURES
900* c a 9so'c • moo cI050C # POURABLE WITH o
HOCIC DIFFICULTY ATIIOOC
AVERAGE LEACH RATES DURING THEWEEK- (gm/CmZ /Oayl
50 f>5 60 65 70 75 80 R4
FIG.1 REGIONS OF APPRENTLY HOMOGENEOUS VITREOUS MASS FORMATIONS
WITH SPECIFIC MELTING AND LEACHING CHARACHTERISTICS FOR THE
SYSTEM N020-B 2 03-S i02- I6 MOL % WASTEOXIDES-
-18-
10" gm/cm2/day Is near the bowler line of compositions
with pouring temperatures of 1000°0 and 1O5O°C as well as
the border line of composition regions with leach rates
of the order of 10""'' and 10 gm/cm /day. This composition
was, therefore, chosen for studying ths affect of different
minor additives for lowering of melting temperature and/or
improvement in its leach resistance. Eleven modifications
nf this compoeition were formulated and studied for their
melting and leaching characteristics.
J'o check hoinogeniety, optical photomicrographs were
taken for a set of twelve vitreous products at a magni-
fication of 500 in reflection mode. A lot of surface
scratches seen in these micrographs (shown in Figures
2A, 2B and 20) were due to incomplete fine polishing of
the specimens. It can be clearly seen that apart from a
few open and closed pores, a definite but small amount
of crystalline phase separation has taken place in cae»
of compositions cntaining MnO or PbO. The phase separation
in these cases is in the form of micron size fine crysta-
llites. However, the formation of this crystalline
phase did not deterioriate the product as can be seen
from the melting and leaohing characteristics of these
composition; presented la Tables IV and T respectively.
Jrom these Tables it is seen that except for calcium and
barium oxide* all other additive oxides had produced
improvement in the leach resistance of parent compositionI - 60.
* i
....I
1-60 1-70
1-71 1-72
Fig. 2. (A) : PHOTO MICROGRAPH OF FEW OF THE VITRIFIED WASTEPRODUCTS AT 320 X
1-74 1-75
1-76 1-77
2. (B) : PHOTO MICROGRAPH OF FEW OF THE VITRIFIED WASTEPRODUCTS AT 320 X
4f< *
1-78 1-79
1-80 1-81
Fig. 2. (C) : PHOTO MICROGRAPH OF FEW OF THE VITRIFIED WASTEPRODUCTS AT 320 X
1ABI&- 17
Cod*He.
-
Compositionof oxldee.Wast* ' QOxides ; S i 0
..2 3
of
2
Raw Mix
'fl 0- ,H
4
i n
a 2 C
5
terns of
) ,RnO
Hoi*
iTiOr
7
percent.
, ,Otha-f
- ,TB. ;
SOMX-iRsteap.i n ©C
_3
•
'Apparent,
TI
product
10
Somogeaiiy.
1-60
1-70
1-71
1-75
16
55 14
51.1 13
15
13.9
48.5 12.3 13.2
I-Y2
1-74
16
18
44
53
.5
.7
U
13
.3
.7
12
14
.2
.6
10
52.5 13.3
- 1050 Quite homogeneous dark glass,quite BhiAing, smooth wire drawn,about 1.5 percent of STP* on thesurface.
- 1000 Quite homogeneous and shiningglasB, slight amount of liquid -liquid phase separation in theforx of layers.
- 10C0 Quite homogeneous brown and ehinin.glass. A thin layer of 3IP onsurface.
- 1000 Quite homogeneous! few pores
present.1050 Dark green glass , quite shining,
Tery homogeneous, transparent, tswspots of 3YP In surface and lumpof SYP also pres»nt(about 0.5percent).
- 1050 Greenish grey glasa, shining, fewpores, no JYP.
3TP - Soluble yellow phaaa consisting of au.inl/ moi;?-bda.tes, Chromatis and sulphates ofalkali .tons.
T
USLK-M7
| 4 , 5 ; 6 { 7 ; 8 ; 9 ; 10
1-76
1-77
1-78
1-79
1-30
1-81
16
16
16
16
16
16
51.7
51.7
53.5
53.5
53.5
53.5
13.2
13.2
13.5
13.5
13.5
13.5
14.1 -
14.1 -
14.5 -
14.5 -
14.5 -
14.5 -
ZnO5
PbO5
2rO22-5
- A12O
2.5
2.5BaO
2.5CaO
1050 Light greenish gray glass, shining,homogeneous, tew pores, about 0.2percent of 3TJ? on surface.
1050 Dark green glass , extremely good•bine, transparent and smooth wiredram, lump of STP at few places.
1100 3a»e as 1-74.
1100 Dark green glass , shining, transpa-rent, fev luatps aod few spot* of 3TPon surface.
U00 Dark grey glass , shining, homogeneousfew pores, a thin layer and fev spotsOf 37?. (Percentage of STP about0.6 percent approximately).
1050 -do-
1ABLS-7 (Part l )
LBACHIBP CHARACTERISTICS OF TUB VITRIFICATION WASTB
PH0DPCT3 FOR MODIFIED MELT COMPOSITIONS OF I - 6 0
USIN8 CONTOTTIOKAL BOIL I JIB VfATEB CACHING- TOUT
.MBit
••••••"51!Leach rate x 10^ on weight loss bast 3 in sm/cm /day during:.on. l o s
First 4 hrs. ,Hezt 20 hrs. ,2nd day , 3rd day 4th day 5th day
1 .
2 .
3 .
4 .
5 .
6 .
7 .
8 .
9.
1 0 .
1 1 .
1 2 .
1-601-70
1-71
1-72
1-74
1-75
1-76
1-77
1-78
1-79Z-80
1-81
3.251.37
1.28
0.96
1.97
2.04
0.09
0.35
0.54
1.273.80
1.98
2.690.64
0.33
0.17
1.82
1.56
0.19
0.23
0.43
1.19
0.291.78
3.170.63
0*33
0.11
1.92
1.57
0.91
0.04
0.18
1.18
0.13
2.05
3.430.73
0.35
0.16
2.16
1.96
0.08
0 . 4
0.391.86
0.17
2.33
1.660.72
0.11
0.06
1.44
1.36
0.08
0.062
0.18
2.05
0.12
1.59
2.74
0.63
0.1 A
0.06
1.55
1.83
0.17
0.36
0.37
1.96
0.20
2.32
+
4!
a
' : . • o
- as:•' +>ii vt M •o vi !•;•U r3 -r< u\O J r l S 3
m
51?
4» 03
•d i
t) ai o
«) r> ni ro
ft Mojo
•»•( o i
g «
3 t»
1?
Ssl
r-!
-22-
ir\ irv ir> if\ t-
t - UN <M CM VOH W J i t C N i r i t - ^ V O K N t - r - t ^ J
OJ O* O O 4 O O O H O H O
O K N O O O C l A O H O W )• • • ( < % • • • • • • • •
! ^ H t H N H «<N K\
t - v o t - O ^ - I r t S S S i r v l ^ H
^ O O H <M H O O* O H r! H
r * t r » H O H H O O O « M o o
u i < n c M r i t - « < - r ^ H C o r ~ t f » « n
r H c r i i T i m H ( r i f M 1 > * - ^ H H O
! M i r , O O M H O O O N O 0 4
H H 3 - * K o N i n K c » H " i
O N V O K N H C M C J O O O W f J o
M l T i C M O C V N O O O H O H
Ch N « N N H UN H O OJO K \ O * « * H r - N e 0 « O * M K \
O I I N C M f M f U I O ' i r O O < M O <M
H - ^ n H O C 0 i n e u \ K > H ( Q
? ? ? ? • ? ? ? ? ? ?• • •
-n-improvement in leach resistance was produced
iu case of atleast five modifications viz, those with
10 mole percent MnO plus 6 mol percent TiOgj 5 <&ol
percent ZnO; 5 mol percent PbO; 2.5 mol percent Zr02f
and 2.5 mol percent AljO,. Out of these five modifi-
fications, the first one is also accompanied with lowering
of pouring temperature while next two do not produce
any change in pouring temperature and the last two are
accompanied by an increase in pouring temperature.
Thus, it may be inferred that amongst the eleven modi-
fications tried, the one with 10 mol percent MnO plus
6 mol percent TiO represents the optimum composition
with respect to lowering of pouring temperature and
improvement in leach resistance.
This composition was then subjected to variation in
the proportion of basic glass foiming additives vi«v,
Na20, BgO-and 3i02 The plotting of melting and learning
characteristics for these compositions results into the
identification of regions of composition with specific
characteristics as shown in Figure 3. In this diagram,
a region of compositions with deaired optimum product
characteristics was then selected and enclosed by a
bold line.
Final selection of a composition for trial on pilot
plant scale after checldng the accsptibility with
respect to other desired characteristics can then be
made from the central portion of this region BO that
~2*-
POURING
O 850C
D 900*C
A 95OC
TEMPERATURES
• 1000C
• 1050 C
A>l050*C
AVEHAGE LEACH RATES OURING TMF
WEfcK ( IN Gm/Cm2/Doyl- 4 _-
GEE!! i* IOMO Ei-Wi'j 5-10*10
0 3 C3 1 -5 * -0 -
B203 68
38
10 30 40 50SIO,
FI6.3 REGIONS OF HOMOGENEOUS VITREOUS MASS FORMATION
AROUND 9 0 0 - 1 0 0 0 C IN Na g 0-B 2 0 3 -S iO2"W.0-MnO-TIO j
SYSTEM WITH CONSTANT LEVELS OF16MOLV. WO, 10M0L '/.
MnOa 6M0LV. TiO2
-25-
+.Ue product characteristics are not affected by the
possible minor variations in the composition of glass mix
under plant conditions.
4. CONCLUSIONS
On the baels of the results discussed above as well as
studies made on different types of wastes, it is felt
that the above type of general practical approach towards
development of suitable melt compositions for vitrification
of high level wastes is simpler and more reliable than
the theoretical approach. Also, this approach yields
more flexible compositions which would retain the desired
characteristics inspite of minor variation In proportion of
waste feed and additive feed under the plant condition".
However, during studies on certain other wastes, the range
of a few minor additives incorporated in formulations of
modified melt compositions has been increased, 'i'he
incorporation of 10 to 15 mol percent ZnO and PbO was found
to have more beneficial effect on the leach resistance and
pouring temperature. For example, the selected region of
compositions with 10 mol percent of PbO and ZnO in
NagO-BjO^-SiOj-ie mol percent waste oxides system was
found to be superior with respect to melting and leaching
characteristics.
It is thus recommended that depending upon the requirement
for the lowering of pouring temperature and/or improvement
in leach resistance, a few more durability- enhancing and
-26-
n?<-Ui.ng point-lowering oxides may be tried in different
proportions and also in different compositions to get the
necessary effect-
-2 7-
APPENDiX-I
EXPERIMENTAL PROCEDURES FORMELTING AND LEACHING STUDIES
A) Melting Studies,: The routine melting etudieB on glass
compositions formulated for immobilisation of purex
type high level radioactive wastes are carried out on
100 gm scale by using simulated inactive waste a. The
simulated waste is prepared using laboratory grade
chemicals in concentration about four times that of the
actual waste. The constituents like Sr,B,Zr and Mo
which are known to cause the precipitation in the waste
solution are not introduced during the bulk preparation
of stock waste solution.
For preparing the dry mix of different compositions,
the requisite amounts of the glass forming additives
as well as the salts of remaining constituents of waste
viz., Sr, B, Zr and Mo are taken In 200 x 200 mm stainless
steel-316 trays and 160 ml of this waste solution is
added to it with continuous mixing. The resulting slurry
is dried under infra red heat lamp or in oven with inter-
mittent mixing of the slurry so as to get dry cake of
more or less uniform composition. The complete amount
of dried mix is transferred to a pestle and mortar and
powdered to get a uniform dry mix.
- 2 6 •
T.hB dry mixes are then taken into a 80 ml capacity fire
cley crucible and fired in a silicon cax-bide electric
furnace at 800°C for 2 hrB. The melting behaviour of
the dry mixes is observed for the atate of fusion,
homogeniety, porosity and phase separation after
every 50°G riBe in the temperature of the mix and
maintaining the respective temperatures for one and
half hours each.
Xfter the mix is completely fused, pouring of the fueed
mas3 is tried by taking out the crucible and inverting
i t out side the furnace. Normally, the heating is
stopped when the fused mass oan be poured out of i.he
crucible. This temperature is called the 'Pouring
temperature*. The temperature at which the mis K"<(
completely fused if called i t s 'Fusion Tempo-ntm r-'.
Finally to complete the melting study, the apparunc
homogeniety of the poured out vitreous mass as will
as the mass remaining in crucible is checked with
respect to any liquid-liquid or liquid-sAlid phase
separation, porosity, smoothness and any other inhomo••
geniety in the cooled down vitrified product.
B. Leaching Studies; The conventional boiling water leaching
-units/havs been used for the routine leaching test on the
various t r ia l mix compositions. Lumps of vitrified
Fig. 4. Conventional Boiling Water Leaching Unit
- 2 9 -
wastea weighing around 10 gm are crushed in S.S.
pestle and mortar and the crushed mass i s seived
through a set of test selves in a automatic sieve-
shaker for 10 minutes. The grains collected between
B.S. sieve nos.16 and 22 are given a couple of quick
washes with cold water to remove any adhering glass
dust, a few acetone washes to remove the adhering
water and then dried in a hot a i r oven a t 180 C for
one hour. Cooling i s done in open a i r for about 10
minutes and the grains are then stored in a desicator.
Exact 1,0000 gm portions of these grains are encapsu-
lated in tea bags made of SS 316, 200 mesh wire cloth.
These bags are exposed to 80 ml of boiling d i s t i l l ed
water under reflux for 4 hours, next 20 hours and
subsequently every 24 hours during the week in the
conventional leaching set up. After each exposure the
bags containing grains are taken out and weighed accura-
te ly after the acetone washing and drying In the above
manner. The 80 ml leachates and washings of boiling
flask are made up to 100 ml and analysed for the amount
of Na leached during the respective leaching period.
Bruno Lange Model-6A Flame photometer i s used for these
analyses.
The leach ra tes are then calculated on weight loss and
sodium loss basis in terms of gm/cm /day. The formulae
used for the calculation of the two leach rates are as
under.
i> ieaoh rate on weight loae basis « — " —A x T
where W = Weight loss in gm
A = Surface area of 1 gm of glaaa grains
uaed.
T =• lime of leaching in days,
il) Loach rate on Ms loaa basis = No A T
where H = Amount of Sodium in leachate.
No = Amount of aodium present in 1 gm of
glass grains taken for leaching.
The surface area per gm of glass grains is calculated
on geometrical considerations by assmasing the groins
to be spheres of fliam<»ter equivalent to the meen
aperture of the top and bottom teat sieves uaed for
screening.
Surface area 'A' in cm /gm = — - —
where 0 is the density of glass measured with specific
gravity bottle, and D is the assumed average diameter
of glass grains.
- 3 1 -
.••KiiOV/LBDQSMENTS
';>- aathora are thankful to Shri K..T. Thomas,, Director,
Engineering Services Group for hiB keen interest and
encouragement. Sincere thanks are due to Shri V, Ba-vindrani'•:•'"
for hie participation in the ini t ia l stages of this work,.
Thanka are also due to the technical. Bts.tf of the 1 phora+ r-y
for their valuable assistance* in the experimental smrt,
REFERENCES
[ i j INTERNATIONAL ATOMIC! BNBRGlt AGBNCr, Charac ter i s tl c«
of So l id i f i ed High-level Waeto Products , Technical
Report Ser ies No.187, IAEA, Vienna (1979).
[2] N . J . KRBID1, W.A. WEYL, The Development of Low " s i " ' - '
Glasses on tho Baeie of S t r u c t u r a l Consideratin- p,
Glasa Indus t ry , 23„ 355 (1942)
[3 ] J .R. GROVER, B.B. CHIDLEY, Glaeees Su i t ab le for the
Long Term Storage of F i s s ion Products , ABRB-R-5.176(i.9f-n)
[ 4 ] A. DOHA I S , tf. BQCQTJi, ?hs B3TSR Programme High- T«fV(O
Waete S o l i d i f i c a t i o n , Ecergia Nuclear Volume 'i9- "'niuevi 7
Luglis
