Note: Descriptions are shown in the official language in which they were submitted.
~ 9
LEAD-IRON PHOSPHATE GLASS AS A CONTAINMENT MEDIUM
FOR THE DISPOSAL OF ~IGH-LEVEL NUCLEAR WASTES
~ACKGROUND OF THE INVENTION
Field 0~ The Inventlon
_
The invention relates to primary containment med~a ~or
the di~posal of high-level rad~oactive nuclear w~e.
Dlscussion or Background And Prlor Art
In the pa8t, nuclear wa~te has been temporarily
stored, rrequentl~ a3 a liquld or as a qludge in
conJunctlon wltb a liquld. Th~ art has recognlzed that
means mu~t be provlded ror p~rmanent di~possl o~ the wa~te,
prererably aJ hlghly ~table solld~. Such 3011ds mu8t havo
- certain chsracterlstlc~ ~hlch make such solldo ~afe and
economical ~or the lon~-ter~ (103 to 105 years) retention
o~ radloactlve ~a3te i80topes.
2 ~23383~
Because of the long half-llve~ oP some radionuclides
(e.g., certa1n actlnide i~otopes~, it is nece~sary that the
~elected ~torage med~um exhib~t certain properties in order
to achieve the desired long-term stabllity~ Some o~ the
factors which must be considered ln the selectlon o~ a
storage medium lnclude: high chemical stability, l.e., low
corrosion rate ; ~tructural stability; simple to
manufacture; acceptable preparation temperature; ability to
store a high propor~ion of wa~te to insure minimum storage
volume; and availabllity to components making up the
8 torage medlum~
Various glass compositions have been ~uggested and
tested for suitability as a storage medium. The
borosilicate gla3se~ have been con~idered among the more
prom~ing composition~. However, the borosillcate glasses
have demon~trated significant instability under
hydrothermal condi~lons, l.e., exposure to water at
temperatures greater than 100C. Such hydrothermal
condit~ons can be encountered in deep geological
reposi~ories.
Two highly deslrable properties Or any potential
nuclear waste glass are a low preparation temperature and a
low melt viscosity at the ~lass processing temperature.
Pure lead phosphate glasses exhibit both o~ these
propertie~ [see: Ar~yle, J. F.,_and F. A. Hummel, J. Amer.
3 J ;~3~
Ceram. Soc. 43 (1960) 452; Osterheld,_R X. and R._P.
_ang~uth, J. Amer. Chem. Soc. 59 ~1955) 76; Ray, N. H.,
Glass Tech. 16 (1~75) 107; Klonkowski, A., Phys. and Chem.
Glasses 22 (1981) 163; and Furdanowicz, H. and L. C. Klein,
Glass Tech. 24 (1983) 198]. Unfortunately, it is well known
that these substances are susceptible to aqueous corrosion
and that they tend to devitrify at temperatures as iow as
300C. [see: Furdanowicz, H., et al., ibid.; Ray, N. H.,
C. J. ~ , Glass
Tech. 14 (1973~ 50; and Longman, G. W., and G. D. Wignall,
J. Mat. Sci. 8 (1973) 212].
Scientific Bases for Nuclear Waste Management, Vol. 1,
Edited by G. J. McCarthy, Plenum Press (1979), pp. 43-50,
69 to 81 and 195 to 200 describes phosphate glasses
including sodium aluminum phosphate glasses, or very
complicated combinations of metal oxides and P2O5. Of those
phosphate glasses in the reference, only p. 74, Table 2,
shows a composition containing lead oxide along with
phosphorus pentoxide and nuclear waste oxides. The ratio
of the phosphorus to lead content is very high and the
phosphate glasses discussed therein are a multicomponent
mixture of up to eight oxides.
In addition, the composition ranges given for each
oxide in the reference on page 74 covers such a broad
spectrum of possible phosphate glasses that the table has
123;~3~
no ~lgnlflcance due to th~ lack Or spec~rici~y re3ultlng
rrom an efrect~vely lnrlnite array o~ permutation~ and
comblnatlons of gla99 constltuents and conc~tratlon~.
See also: Sc~entlrlc Basls for Nuclear Waste
~ , Vol. 2, Edited by C. J. M. Northrup, Jr.,
Plenum Pres tl980), p. 109 to 116; Report ~NL-50130,
Development of the Phosphate Gla~ Proceqs ror Ultlmate
D~qposal o~ Hlgh-LeYel Radioactive Wa~te, R. ~. Drager, et
al. r Jan. 1968; and Symposiu~ on_Management o~ Radloactlve
WaYtes rrom Fuel Reproceqs~n~, November 27 to December 1,
1972, pp. 593-612.
No non-patent rererence wa~ round that indlcated that
lead-lron phosphate glas~es have çver been serlou~ly
considered as a viable potential ~torage medlum ~or the
lmmobillzatlon Or nuclear wa~tes.
The glass and ceramlc ~leld~ lnclude the rollowlng
domestic patents.
U. S. Patent No. 3,365,578 (Grover et al.) dlsclo~e~
placlng radloactlve wa~te ln a Na-Pb-Fe-phosphate/sll~cate
gla~, wlth~n a ~teel vessel. (Other Na-Pb-pho~phate
systems are dl~clo~ed in the exampleJ o~ arover et al;) To
recap, Grover et al. teaches the use o~ a glas~ containlng
both Pb and phosphate ~or nuclear wa~te contalnment.
U. ~. Patent No. 4~314,909 (aeall et al.) teachc~
glas~-ceramlc whlch i~ u~ed ror ~aste ~torage and whlch
123~l33~
con~i~t~ o~ monazlte, polluclte and ZrO2 and/or mullit~.
Thc gla~a-ceramlc can contain up to 20 percent Or P205.
8eail et al. does not mention the presence Or Pb.
U. S. Patent No. 4,351,749 (Ropp I) te~ches nucle~r
waste s~orage block3 whlch include a polymeric pho~phate
gla~s from a trivalent metal ~elected ~rom Al, In or Ga.
U. S. Patent No. 4,382,974 (Yannopoulos) dlsclose~ a
glass conta~nlng nuclear waqte whlch ls stabilized by the
application Or synthetic monazite by mean3 o~ chemlcal
vepor depo~ltlon or detonatlon gun. The monaxite contains
27 to 35 ~e~ght percent Or P2O5. No Pb i~ mentioned ln
Yannopoulo~.
U. S. Patent No. 3,161,600 (Bar~on I) and U. S. Patent
No. 3,161,601 ~Barton II), reepectively, show Sr and C3
lS sequestrated ln phosphate glasses.
U. S. Patent No. 3,120,493 (Clark et al.) teaches a
proces~ whereln ruthenium volatlllzat1On 1~ ~uppres3ed
durlng the evaporatlon and calclnat1On Or nuclear wa~te
solutions by tho addltion of phosphlte or hypophoqphite. A
20 gla~s~llke sol~d iJ obt~lned.
U . ~ . Patent No . 4, 049, 779 (Ropp II ) te~ches ~tsble
phosphate ~la~se3 of rormula M(H2P04)n, ~hereln M may bc Pb
and n 1~ 2 or 3 (~or divalent or trlvalent M), ~h~ch hrc
prepare~ vla H3P04 and a n~etal compound bj ~ddlng 8
25 preclpltant, cry~talllzing ~ro~ solutlon and 'ch~n meltlng
.~
6 ~ ~3;~139
thc material. While Ropp II disclo es lead phosphat~
~la~se~, lt 1~ not dlrected to nuclear waste dlsposal,
although 1~ ~oe~ no~ ment~on stabllity to leachlng.
U. S. Patent No. 3,994,823 (A~nger et al.~ di closes
lead zlrconate ceramic, which may also contaln Bi. U may
be added to reduce electr~cal reslstivity. The ceramlc of
Alnger et al. i~ not aimed at nuclear waste storage.
SUMMARY_OF THE INVENTION
An obJect o~ the invention i~ to provlde an lmproved
glas~ compo~ition and a method Or makinB same for the
primary containment Or h~ gh-level radloactive nuclear
waste. Another obJect of the in~entlsn i8 to provide a
wa~terorm les~ subJect to corroslon or ionlc release than
the prior art waste rorms. A ~urther obJect of the
~nvention ~s to prov~de a stable wasteform whlch can be
processed (~.e., that will di3solve the waste constituents)
at a temperature lower than borosilicate glasse~. A stlll
rurther obJect Or the invent~on iq to provide a stable
wasteror~ that e%hibits a lower vlscoslty than borosillcate
gla~ in the temperature r~nge between 825 and 1050C. A
yet rurther obJect Or the inventlon is to provlde a sta~le
wasterorm ror hlgh-level radioactlve nuclear wastes whlch
i~ adaptable ror usc ~lth e~istlng glas~ rabrlcatlon
technology. Other ob~ects and adYantages Or the lnventlon
are 3et out hereln or are obvious here~ro~ to one
ordlnarlly skilled in the art.
The ob~ect~ and advantages o~ the inventlon ar~
achleved by the compo31tion and process o~ the lnventlon.
To achleve the ~oregolng and other obJects and ln
s accordance wlth the purpose Or the inventlon, as embodied
and broadly described hereln, the inventlon lnvolves a
gla~ compo~t~on ror the Immobil~zat~on and dlspo3al of
high-level radioaetlve nuclear waste. Lead-iron phosphate
glasses with ~everal difrerent compo~ltion3 can be u3ed zs
hosts ror high level radioactive waste. The lead-lron
phosphate glass frit that ~8 comblned with the nuclear
waste and melted to rorm radloactive wa~te monollths can be
prepared using either Or two slmple proce~3e~. In one
proces~, the approprlate amounts of PbO and Fe203 are
combined with (NH4)H2~04 and the glaas 19 formed by heating
the mixture to about 850C~ A ~econd procedure for formlng
the lead-lron phosphate gla3~ frlt lnvolves s~mpl~ mi~in8
PbO and Fe203 with the approprlate amount o~ Y205. The
rormatlon o~ the lead-lron pho~phate glas~ rrit can be
accomplished ln standard chemlcal processlng racilltle~,
slnce radloactive materlal i~ not involved at this stage Or
the productlon Or a nuclear glas~ waste form. The most
economlcal proces~ would be u~ed, bu~ rO~ tho purpose~ Or
dlscus~lne~ the rormation Or the rrlt and lt~
25 character~st~cs~ the dlscus~lon lo temporarlly limited to
8 1;~3;~83~
the second process lnvolving onl~ th~ almple ox~de~. In
thl~ ca~e, the practical concentration limita for the three
oxlde C~.13t~UC/lt9 0~ the hoat glass (l.e., P~O~ Fe2O3, and
P2O5) are listed ~n Table I.
Pure lead pho~phate glass (i.e., a glass that does not
contain either ~ron or nuclear waste) can be prepared by
fu~ing PbO (lead oxlde) wlth P2O5 (phosphorous pentoxlde)
between 800 and 900C. The compasition o~ the resultlng
glass frlt can be contlnuou~ly varled by adju~tlng the
ratio o~ le~d oxide to phosphorus oxlde. I~ the welght
percentage o~ lead ox~de exceeds about 66 percent, however,
a cr~stalllne torm of lead phosphate and not a gla3~ i9
rormed. Hence, the compo~ltion (66 wt. percent Or PbO)
repre~ents a crltical limit in the sense that compo ltions
whlch contain larger amount~ Or lead oxide whlch can be
melted together wi~h P2O5 to ~orm a uitable hoat 61a3s ~or
nuclear wa~e is not as well de~ined. The compo~ltlon
con~i~ting Or about 45 wt. percent Or PbO and 55 wt.
percent Or P2O5 wa~ taken to represent the practlcal lower
llmit ~or the amount Or lead oxlde, Jlnc~ the viqcoslt~ o~
the molten gla~s increa~ed rapidly aJ th~ PbO content was
reduced below 45 wt. percent. The hlgher the melt
vlscoaityJ the harder the gla~s i8 to pour and the higher
the proces~ing temperature becomea. Hlgh proceaslng
temperatures rOr nuclear wa~te are unde~lrable ~ince
g ~ 3;~3~
volatlle radioactlve species may be lost through
vaporlzatlon, and the operatlon ~nd maln~enance Or hlgh
~ m~rature equipment ~n a remote proces~lng ~aclllty are
not economlcal. The amount Or iron oxlde whlch must be
added to rorm the lead-lron phosphate waste glas~ depends
on the iron concentratlon already present In the nuclear
waste. High-level de~ense waste typlcally contains about
50 wt. percent o~ Fe203 tsee Table II, ~lrst slmulated
nuclear wa3te compo~ltion), and~ ror thi~ type of nuclear
waste, no add~tlonal ~ron is added to the pure lead
pho~phate rrlt for the rormation Or a very stable nuclear
waste glas~. For most hlgh level commerclal waste Or the
type generated by llght water nuclear power reactor~ (3ee
Table II, ~econd 31mulated nuclear waste compo~tlon),
however, addltlonal iron oxlde must be added to the pure
lead phosphate glas~ ln order to form a u~rlclently
stable, corroslon resl~tant nuclear wa~t~ glas~.
The efrects Or ~ron oxide on the properties Or pure
lead phosphate glasses are crltical. The addltlon Or lron
oxlde to these gla~se~ improves the corro~lon reslstance by
a ractor Or more than 1OJOOO (see ~lg. 3) and result3 ln
the rormatlon o~ glasse~ that do not e~hlblt any evldenc~
Or devltrlrlcation arter belng heate~ ln air at 575C
lOOho
Perhap~ most slgniricantly, extremely ~tabl~ lead-iron
~23;~ 9
phosphate glasqes can be prepared and poured easily at
temperatures between 800 and 900C. The results
illustrated in ~lg. 3 can b~ used ln tallo~lng the
composltlon Or the lead-iron phosphate glass rrlt depending
upon the iron concentra~ion o~ a glven type of nuclear
waste. The highly stable waste rorm ~8 reallzed when the
iron concentration ls adJus~ed to correspond to a content
3~8~g
Or ~bout 9.0 ~t.percent Or ~e203 re1at1v~ to the total
we~ght of the glass compost10n.
PreI`ersbly the f~nal nuolear wa~te gla~ compo31kion
oon~a~na about 9 ~ei~h~ percent Or Pe203. ~l~o preterabl~
S thn Pe203 o~n be ndded to th~ gla~8 oo~po~ on ~n the ~or~
o~ o~o Or th~ ~etal o~1de8 pre3ent ~n th~ rad10act~ve
nucleAr ~ast~ matori~l. Th~ Pe203 can al40 b6 added ~o th~
~la~ co~po~tlon a~ a separate oo~ponent~
Prererabl~ the radloact~vs nuclear a~to ~ater~al ~5
pre~en~ in an amoun~ o~ abou~ 15 ~e~ht pe~cent, ba~ed on
the total ~eight of the ~la86 co~pos~t~on, ~ th~ gla~
compo~t~on.
The lnvention can also qenerally be described as a
stable primary contai~ment medium for dispo~al of high-
level radioactive nuclear wastes compri~ing lead-iron
phosphate glass having a composition in the range~ indicated
in Table I plu~ preferably a~out lS weight percent of a
metal oxide nuclear waste material. Such nuclear waste
mater$al can be, for example, of the type in interim storage
at nuclear facilitie~ or ~ combination of ~uch ~nterim
storage ~ype and the type of high level wa~te generated by
commercial power reactors.
~ ha 2dvanta~0 o~ lead-~ron ~ho~h~1;e u¢lear wa~te
~las~e~ ~16 oo~pare~ to ~o~o~lioate nuclear lt~st~ glas~
2S ~r~:
12 123~3~
1. Corroqlon re~istance at elevated temperature
bet~een 90 and 135C. i~ at leas~ 100 to 1000 t~me~
better;
2. Lower proces3in~ temperature ror the waste~orm
(260 to 110C. lower);
3. Lower melt vi9c09ity ~n the 800 to 1050C.
temperature range;
4, Waste loading per unit volume whlch 1~ at lea~t as
good as the practlcal waQte loadln~s per unlt volume
achlevable b~ uslng borosilicate gla3se~;
5. The abll~ty to use a relatlvely inexpenqlve
alumlnum, aluminum alloy or ~talnles~ steel canni~ter for
the glass ca~tlng step in procç3~1ng; and
6. The lead-lron pho~phate nuclear waste gla~3 can be
prepared u31ng ba~ically the ~ame technology that has been
developed to produce large monollth3 o~ boro~illcate
nuclear wa~t~ gla~s.
The lead-lron phosphate gla~ wa~teform o~ the
lnventlon prov~des an excellent contalnment medium ~or
wa~te~ such a~ those ln lnterlm stora6e at government
nuclear rac~lltle~ an~ hlgh-level waste~ 8enerated by
- commerclal nuclear power reactorJ.
. Th~ lnvent~on al~o lnclude~ a proce~ ror preparlng
the gl J0 compo~ltlon Or the inventlon. Th~ proce~s
lncludes admlxln6 about 34 to about 55 welght percent,
based on the total weight of the glass composition. of
phosphorus oxide. about 45 to about 66 weight percent,
based on the total weight of the glass composition, of lead
oxide, and about 0 to 9 weight percent of Fe2O3,
based on the total of the glass composition and the amount
of iron content in the nuclear waste to be processed. The
asmixture, to which about 15 weight percent of nuclear
waste oxides have been added, is then melted to provide a
liquid melt of a lead-iron phosphate glass. Usually the
melt is heated to and kept at 800° to 1050°C. About 10 to
about 220 weight percent, based on the total weight of the
glass composition, of radioactive nuclear waste material
containing at least one metal oxide is added to the liquid
melt of lead phosphate glass. Preferably the radioactive
nuclear waste material contains sufficient Fe2O3 to provide
preferably about 9 weight percent, based on the total
weight of the glass composition, of Fe2O3 in the glass
composition. The liquid melt is then solidified to provide
the glass composition for the immoblization and disposal
of the radioactive nuclear waste material.
Preferably the phosphorus oxide is used in the form of
ammonium orthophosphate monohydrogen, i.e., (NH4)2HPO4.
The addition steps for the nuclear waste and the Fe2O3 can
be conductedf simultaneously or in any desired sequence.
In an alternative to the preferred embodiment of the
14
~23~839
lnvention, all or part Or the ~e203 used ln the gla99
composltlon can be added a~ a ~eparate component. In such
case the Fe203 can be added dlrectly to a liquld melt Or
lead pho~phate gla99 and/or added to the radloactlve
nuclear waste materlal berore such ls added to the llquid
melt o~ the lead pho~phate gla ~.
The lead-lron pho~pha~e nuclear wa~te glas~ Or the
lnvention i5 a very stable, ea311y prepared storage medium
for some important clas3es o~ nuclear waste. Relative to
borosilicate nuclear wa3te glas~, the lead-iron phosphate
nuclear waste glass has ~everal di~tinct advantages. The~e
advantage. Or the invention glas~ compo~ltlons lnclude:
(1) a corrosion resl~tance at 90C. that i~ about 1000
t~me~ h~Bher than a comparable boro~ilicate gla~ ~n the pH
range between 5 and 9~ which i~ mostly due to the pre3ence
o~ lron ln the phosphate glas~ compo~itlon, (2) a
processing temperature that i~ lOQ ~o 250C. lower than
that currently requlred to proces~ borostllcate glass, and
(3) a lower melt vl~c091ty ln the 800 to 1050C. range.
The pre~ence Or iron i8 pr~marlly responslble ror the very
hlgh corroslon reslstance Or the lead-lron phosphato -
nuclear wa~te glass Or the lnvention relative to that Or
tho pure lead pho phate glass. The lead-iron pho~phat~
glass Or th~ lnventlon la an e~cellent 3torage mediu~ for
high-level radloactlv~ nuclear wa~te.
339
Rererence will now be made in deta~l to the preaent
preferred embod~ment of the inven~ion~ ~ome o~ the
advantages of wh~ch are lllustra~ed in the accompanyln~
draw~n~s.
BRIEF DESCRIPTION OP THE DRAWINGS
The accompany~ng drawings, which are ~ncorporated ln
and rorm a part Or the speciftcatlon, illustrate some Or
the advantage~ of the ~nventlon and, together with the
de~crlptlon, serve to explaln the principlea o~ the
lnventlon.
In the drewlng3:
Flgure 1 i9 a bar graph comparlng the corro~on
character~tlc~ Or a slmulated-waste-loaded convent~onal
boro~licate gla~ wlth those o~ the ~nYentlon;
Figure 2 19 a plot Or the corro~lon rate at 90C. o~
both the lead-~ron pho3phate wa~terorm and the borosllicate
gla3~ waste~orm versus th~ pH Or ~he corroding aolution;.
and
Flgure 3 i8 a plot Or the errect Or the Iron content
at 90C. on the corro~ion Or lead phosphste glas~.
DETAILED DESCRIPTION OP THE INVENTION
All parts, percentages~ ratlo~ and proportion~ ar~ on
a welght ba~ls unlea~ otherwlse 3tsted herein or obvious
hererro~ to one ordlnarlly s~llled in tho art.
Pure lead phosphate glaa~ (l.e., a gla~ that doe~ not
16 ~ 33~3'~
contaln any nuclear wa te or Iron) can be prepared by
meltlng to~ether PbO (lead o~ide) and P205 (phoaphorua
oxtde) at elevated tetnperature~. The compo~ltion Or the
reaulting glaaa can be varled by varying the ratlo o~ the
weight o~ PbO to the wel6ht Or P2O5. However, lr the
we~ght percent Or lead oxide exceed~ abou~ 66 welgh~
percent a crystalllne rorm of lead phoYphate, not a glaYs,
i~ ~ormed. Hence, thls composltlon (66 welght percent o~
PbO, and 34 weight percent o~ P205) representa a crltical
llmlt in the sense that compo~tlon~ which contain larger
amounts Or lead oxide no longer form a glass.
The lower limit on the minimum amount Or PbO which can
be melted together wlth P2O5 ~ rorm a suitable host gla~s
ror nuclear waste is important9 although not as clear cut.
The composltion con~lating Or about 45 weight percent PbO
nd 55 welght percent Or P2O5 was taken to be a practlcal
lower limlt on the amount Or lead oxide needed, since the
visco~ity o~ the molten glasa became much lar~er aQ the PbO
content waa reduced rurtherO The hl~her the vi~co~lty, the
harder the gla~s 18 to pour snd the hlgher the required
processlng temperature become~.
The additlon Or simulated nuclear waste to the pure
lead phosphate host glaa~ doe~ not substantlally modiry the
lead o~de and phoaphorus o~lde limlt~ dl~cusaed above. It
was round, however, thnt th~ addition Or simulated
17 ~;~;33~9
rad~oactlve nuclear ~aste contalning Pe203 to the lead
pho3phate host glasa produced a drams~ic decrease in the
corrosion rate. That i8, pure lead phosphate ~laaaea
(l.e., wlth no Fe2O3 containing nuclear waste added1 are
quite au3ceptible to aqueou~ corroalon. When the sl~ulated
rad~oac~lve nuclear wa~te contalning Fe2O3 wa~ added to the
lead phosphate hoat 61ass, however, a hlghly corros~on
re lstant and atable nuclear waste glaqs wa3 rormed.
The lead phospha~e glasa appeara to be inaen31tive to
the detall~ o~ the preparatlon procedure and can be made
with a very large variation ln ~he ~olar ratlo Or PbO to
P2O5 as lndlcated. For example, specimen~ Or homogeneou~
lead-lron phosphate nuclear waste glasae~ loaded wlth lS
we~ght percent Or sl~ulated radloactlve nuclear waste
materlal have been prepared w~th the amount Or PbO in the
lead-~ron phosphate host glaas varled rro~ 45 to 66 weight
percent, the amount Or P205 ~aried rrom 34 to 55 wei6ht
percent, and the amount Or ~e203 varied rro~ O to 10 ~eight
percent dependlng on the iron content Or the ~imulated
nuclear waate.
Most Or the decreaae in the corro~ion rate Or thc
lead-lron phosphate nuclear wa~te gla~ i3 due to the l~rgc
amount~ Or iron oxlde present in th~ radloactiYe nuclear
wa~t~ ~aterial (ror example, at one nuclear racllit~ about
50 weight percent Or the radloact~ve nuclear ~a~te ~a~erial
, .
18
1~3~3~3
i~ iron oxide Fe203). The erIect Or varloue amount~
iron oxide on the corros~on rate of lead pho~phate are
~hown in Figure 3~ As can be ea~lly ~een rrom ~lgure 3,
the additlon Or 9 weigh~ percent Fe203 to a pure lead
phosphate gla s improves the corro~ion reslstance by a
fac~or Or about lO,000. Hence, by purposely adding abou~ 9
weight percent lron oxide to pure lead phosphate glass, one
can produce a very stsble and ea~ily prepared glass, which
can then be used to immoblllze other type~ of radloactive
nuclear waste material which do not contain large amount~
Or lron oxide. These was~e~ lnclude reproce sed commercial
nuclear power reactor wastes. Figure 3 3hows that ~he
sorro~lon rate is sub~'cantially reduced by lncludlng at
lea~t about 9 welght percent o~ lron oxlde (Fe~03) in the
lead phosphate gla3~ oomposition. This appllcatl~n has
been ~ucce3s~ully demonstrated in experiments where both
slmulated hlgh-level derense nuclear waste and slmulated
radloactive nuclear-power reactor wastes were ~dded ts the
lead-iron pho~phate host glas~. The resultlng nuclear
waste gla3s was a highly corros~on reslstant and stable
wa~te~orm.
~ ho comblning Or rsdloaotlve nuclear waste with
lead-lron phosphate gla~8 rorm~ a nuGlear waste gla~s that
i~ highly corros~on rc~i3tant, not ~u~ceptibl~ to
de~itrirication, and that can be prepared at a relatively
19
123~33~
lo~ te~perature~. Th~ pre~cnc~ o~ a high le~rel Or Fe203 ~8
crit~cal. Th~g typ~ o~ syner~Atic er~ect, in wl~ch tho
corro~-~on re~t~lce Or ~ch~ co~bined meterial 19 enhancod,
al~o occurs ~n th~ cas~ Or boros~l~cato glaJ3 ~a~t~ rorm~
in tha~ th~ ~a3t~ loadcd gla~ la slgniricantl~ mor~ stabla
than a glas~ form~d rro~ the pur~ boro311~este glas~ ~rlt.
In rac~, th~ pur~ boro~ilicate ho~t ~las~ typicall~
corrode~ about 10 time~ ras~er than the gl~J in
combination ~it~ ~mulated nucl~ar wa~ts. tSe~:
.C. L.~. Boatner, H. Naramoto and C.W. ~hite, J.
Non-Cr~r~t. Solld~ 53 (1982) 201; aad Clark ~.E., C.A.
Maue~ A._R. Jur~en~on and L. Urwongse ln Sci~ntlric ba~es
ror Nucloar WaJte Mana~ement, Vol. 11, ed. W. ~utze
(~lsevler North Holland, Ne~ ~ork~ 1982) pp. 1 to 1~.] For
15 th~ lead-iron phosphat~ wa~t~ form, ~owe~er, th~
i~provemen~ in corro~o~ resistance ~ollo~ing addit~on Or
the ~imulate~ iron-conta~ning waste i~ much greater.
Lead-~ron pho~phate glao~ i8 quito ~u~tabl~ a~ a
lon6-ter~ ~tora~e mediuQ ~or high-le~el nuclear wa~te. The
propertieJ Or lead-iron phosphate nu¢lear wa~te gla~ are
~uperior ~o a boro~llicat~ nuclear wa~te glaa~, whlch ~a~
reccntl~ Jelected ror the long-tor~ 5torag9 Or ~ome higb
l~v~l nualear derense ~a~te~ Th~ boro~ilicate ~uclear
~a~te gla~8 thorutoro i~ used h~r~in a~ a ~t~nd~rd to ~lch
~5 ne~ ~a~teror~ Or th~ invention i8 compared.
~ 3 ~
The invention pro~lde~ a ~table prlmary conta~nment
medlum ror d~posal Or high-level radloactive nuclear
wa~te. The in~ention wa3terorm typically comprlses a
lead-iron phosphate glaq~ contalnln~ up to 20 weight
percent Or nuclear waste Or th~ type typlcallg con~ist~ng
Or 50 we~ht percent Or Fe203, 9.8 we~ght percent Or A1203,
13.8 welght percen~ Or MnO2, 1~,5 weight percent Or U30B,
3.7 we~ght percent Or CaO, 6.2 weight percent Or N10, 1.2
weight percen'c of SiO2, 7.1 welght percen~ Or Na20, 1
10welght percent Or C~20, 1 weight percen~ Or SrO and 1.3
welght percent of Na2S04 (or other nuclear wa~te m~ure~
with similar compositionA). Such compo3itlon~ with varying
amounts of iron and aluminum represent~ a cla s o~ nuclear
dersn~e wa3te~. In addition, the lead-iron pho~phate
nuclear wa~te gla~s can typically be prepared contalnlng 10
weight percent, Or the above compo~ition plu~ 5 welght
percent o~ a composition that i9 repreqentative 0~ ~he
wa~te generated by nuclear power reactors. In dl~tllled
water at 90C., the net release Or all elements rrom both
type~ Or lead-iron pho~phat~ nuclear waste ~lasseJ are 100
to 1000 tlme~ ~maller (dependlng on the ~pe~iric element)
than the correspondin6 amount~ relea~ed by a compsrably
lo~ded borosillcate glas~ waste~orm.
EXAMPLE
25Several lead-iron pho~phat~ gla~e~ Mere prepared
21 ~ 23383~3
incorporatlng o~ther a~mulat~d rad~oact~v~ derens~ nuclo~r
wa~t~ OF ~mulated reproce~sed commerc~al was~e comblned
wlth ~mulated rad~oactlve defense waat¢ to demonstrat~ the
inventlon. Approprla~e amounts o~ ~bO and ~H4)2HPO~
powder~ were thoroughl~ m~ed wlth 15 we~ght percent o~ a
powdered ~or~ Or ~ ~mulated metal o~lde nuclear ~ st~ and
melted ln a platinu~ cruclble at temperature~ between 800
and 1050C. rOr 3 hour~. Se~ Table II for th~ composit-
ionR. The compositions of th~ lead-iron phosphate host
~las~ ~tud~ed are g~ven in Tablc I~ The molten glas~ wa~
t~èn poured ~n~o a hented mold Or spectro3copicall~ pur~
carbon, annealed at 450C. ror 2 hours and cooled to roo~
temperature over th~ ~p8C~ O~ a few hour~. All o~ ~h~
component~ Or the wa~te wera readil~ dl~solved ~n a ~hort
lS t~e a~ 1050C., and all Or tho componentJ e~cept A1203 and
2rO2 ~ere d~olved at t~mperature~ bet~een 800 and 900C.
Th~ lead-iron pho~phato gla~s ~aJtetorms prepsred at 800
to 900C. in ~h~ch A1203 and ZrO2 ~ero not completelg
dl~aolved, ho~ever, were a~ corroJ~on re~tant aa tho
lead~ron phoJphate waaterorms prepared at 1050C. All or
tho lead-~ron phoJphate gla~e~ loade~ w~th the ~mulate~
- nu~lear ~aJte had a blac~ appesran¢o that r~embled that Or
wa~to-loaded boroo~l~cate gla~. Th~ l~ad-iron phoapha~
gla~scs that ~era heated to b~t~e~n loooa and 1050C. ~er~
25 ver~ homo~eneou~. -
22 123~33
Corro~on ~e~t~ o~ ~ho ~yp~ (MCC~l) developed by th~
Materlsls Characterlzatlon Center located at Battelle
Nort~west Laboratorie~ were u~ed to compare the corroslon
behavior Or the lead-lron phocphate nucle~r wa~te~orm wlth
that Or an ~dentically loaded boro ilicate glas~ nuclear
wasteform. Each wasteform wa~ corroded ~or one month ln
diYtilled water at 90C. The re~ult~ are ~hown ln Flgure
1. The data ~how that the net relea~e Or all o~ the
element~ rrom the lead-iron phospha~e wa~terorm wa3 at
10 lca9t 100 to 1000 timeq smaller th~n the corre~pondlng
amount~ relea~ed by the boro~lllcate wa~terorm (ths~
Frit 131 plu5 29 percent of the rirst simulated nuclear
wa~te composltlon - see Table II ror the exact
composition~). The concentration~ o~ all Or the element~
pre3ent ln the lead-lron phosphate leachate were below the
detectable limlt~ Or the standard analyt~cal chemical
technique~ employed (in thi~ case, inductively coupled
pla~ma emisslon analy~is - ICP~ atomic ab~orpotion, and
~luorlmetry). The pre~ence Or iron (a component Or the
nuclear waste materlsl) ia primarlly re~ponJlble ~or the
very hlgh corro~ion re~l~tance Or ~he nuclear ~a~te gla~s
relatlve to that Or pure lead pho3phat~ gla~.
In ~ore detall, Plgure 1 ~ho~ the 30-da~ corro~lon
r~te~ at 90C. in dl~tllled H20 ~or lead-lron phoaphate
tPb(P03)2 plu~ 15 weight percent o~ tho ~lr~t ~lmul~ted
,.,~ ' '.
12~3~3g
nuclear ~aate] and boro~illcat~ (Prlt 131 p1ua 29 welght
percent ot the f~r~t ~mulated nuclear waste) nuclear waate
glaase~. The lead-lron phosphate and boro~llicate nuclear
waste gla~es had the ~ame waate per volume loadlng.
The erfecta Or the pH o~ the corroding 301utlon on the
corroslon rate of the lead-~ron phosphate waaterorm wa~
alao lnveaSlgated (aee Fi~ure 2) and compared to the
behavlor Or a boroallicste glass wa~tefor~. The lead-lron
pho~phate wasterorm was comprised Or 50 weight percent o~
PbO and 50 wei~ht percent Or P205 plua 15 weigh~ percent Or
the r~rst aimulated nuclear waste (see Table Ir). The
wa~te welght percentagea ror the lead-lron phosphate glaa3
versua boroaillcate gla~a yleld comparable waate per volume
ractora due to the higher den~lty o~ th~ lead-iron
pho~phate glasa (l.e., 5 ~ 0.1 g/cm3) relatlve to
borosillcate glaas (2.6 g/cm3). The boros~licate gla~s W~9
comprlaed Or Frlt 131 plu~ 9 ~elght percent Or the rlrYt
almulated nuclear waste (~ee Table Il). In the neutral pH
reg1Ona (i.e., ror pH Yalue~ between 5 and 9) which
encompass the pH range Or moat natural ground watera, the
corroslon rate Or the lea~-lron phoaphate ~a~tcrorm ~aa lOO
to 1000 tlmes maller than the corresponding corroalon
rateJ of the ~oroailicate glaas waaterorm. At thc pH
e~treme~ Or 2 to 12, th~ corroa~on rate Or th~ lead-iron
phosphate ~asteror~ appro~ches but doe~ not e~ceed that o~
the boros11lcate glasJ ~aaterorm (see Plgure 23.
1233~339
Table I
Lead-iron pho~phst2 hos~ glas~ compo~ition~ T~e
nuclear wa~te glas3 1~ ~ormed by meltin~ the lead-iron
phosphate ho~t gla~s together wlth a powdered rorm Or the
nuclear waste.
Compound Welght %
PbO 40-66
25 30-55
~e2o3 1 0~10
10 Note~ Amount Or iron oxide added depends cn type Or
hlgh-level nuclear wa~te.
2s ~ 839
0
_,
~, C
~ o_
z _ ~ ~ ~ ~ c ~ r ~ o
o ~ o ~ , o ~ U~ ~ ~ ~ ~ ~ ~ ~ _ _ U~
o.
_ E c~
0 -' o
O E t~ ~
C~, ~
E U~ Q~ bO
O
C~ ~ 0
O~ 0 3_ ~ )o t~ J O a:~ O O O O U~
o o ~ o o ~ o c~ ~u N ~ O O O O
~ a~ 0
6q 0
O
C~ C
O--
. Z ~O CO ~ ~ ~ ~ ~ ~ O
V ~ O h
0 0
O
k~ q~ E C~
J~ ~ C
:a 0 ~ Q~ ~
S O ~ ~ :J
E~ _~ v oo a~ ~ ~ O o
_I ~ 0 ~ O O ~ ~ '1 0 C~
h 3-- ~ 1 0 0 O O O ~J C~l O
_~ V ~ 0 ~ 0
m C^
o
~ ~ ~ o~ o o U~ U~
S~ . O~
0 ~ v ~ U~ o o
0 0 G
O ~ C
O ~ u
h 3~ ~ ~10 0 ~ C-~
~æ O O ~ ~ O O 0 0~
0
U~ O
c~ ~ ~n
0.,_ l l l
~v o o o
'29 2 ~
0 E~
0 J~ C
0
4'4 0
U~ o
E~ 0--~ O O
C D
26 ~;~3~839
Ot~er te~t~ lndic~ted that thR corrodlon behavior o~
t~ lead-iron p~o3phate ~a~e~orm was not ~ected bg lsrge
do~e~ or gamma radlat~on, nor wa~ t~e materlal unusuall~
su~ceptible to corrosion at a hlgher tempcrsur~, e.g.,
135C.
In th~ 800~ to 1050C. temperatur~ range, th~
~13co~it~ Or th~ molten lead-lron pho~phst~ wa~teror~ ~B
much le3~ thsn ~he prototype borosilicate ~la~J ~a~teror~,
a~ evidenced b~ the ~sct that the lead-~ron phosphate could
be ea~lly poured at 800C. In splt~ o~ the lo~ vlsco~
for th~ lesd-iron pho~ph~te betw~en 800~ to 1000C., th~
pho~phat~ gla~ w ~t~rorm sortened at
600C. ~hich ~a~ about 25C. hi~h~r than the ~o~tening
poln~ Or the boro~illcat~ gla a ~sst~or~.
A lead-~ron pho~phate ~a~teror~ ~a~ expo3ed to air at
550C. ~or 60 hours in order to determln~ i~ there ~a~ any
rapld tendenc~ to de~itr~rg-. No obviou~ devitPl~ication Or
the wn3terorm wa~ detected u~ing X-ray dirfraction
analy~lJ, ~nd a subJequent corro~lon teJt on tho ~amplo
~ho~ed no degradatlon in corro~lon re~l~tancc. ~ aimilAr
te~t of boro~ilic~to 61a~ treated at 500G. for 60 houro
indi¢ated that th~ boro~ilieat~ glas~ corro~on rate ~a~
~oasurably hiBher rollo~in th~ heat treatment.
3~nc~ higher te~per~tur~a aro needed to ¢ompletel~
di~Jol~e the ~1203 present in DO~ ra~loactlv~ nuslear
27 1;233839
w~atec, an alum~num ba~e allog can be e~ployed as a
cannlster materlal. A lead-lron phosphate 61as~ wasteror3
Or the lnvent~on wa3 melted at ~00C. in accordance with
thls invent~on and poured lnto a pure alumlnum conta~ner
(aluminum melts at 660C.). The alumlnum container dld not
melt.
The foregolng descriPtlon of prererred embodlment3 o~
the inventlon has been pre~ented ror purpo3e~ of
~llustration and de~crlpt~on. It i not lntended to be
exhau~t~ve or to limlt the inventlon to the preciQe form
discloqed, and obviously many modlflcstlon~ and varlations
are pos~ible ln light Or the above teaching~0 The
embodiment~ were chosen and descrlbed ln order to be~t
explain the prlnciple~ Or the inventlon and its practlcal
appllcatlon to thereby enable other~ ~killed in the art to
best utlllze the lnvention in variou~ embodlments and wlth
varlous modlrlcatlon~ a~ re ~ui~ed to the partlcular use
contemplated. It is intended that the ~cope Or the
lnvention be de~ned by the clalms appended hereto.
,t','~ ;,
