CA1233839A - Lead-iron phosphate glass as a containment medium for the disposal of high-level nuclear wastes - Google Patents

Abstract

LEAD-IRON PHOSPHATE GLASS AS A CONTAINMENT MEDIUM
FOR THE DISPOSAL OF HIGH-LEVEL NUCLEAR WASTES

ABSTRACT OF THE DISLOSURE
Lead-iron phosphate glasses containing a high level or Fe2O3 for use as a storage medium for high-level radioactive nuclear waste. By combining lead-iron phosphate glass with various types of simulated high-level nuclear waste, a highly corrosion resistant, homogeneous, easily proceased glass can be formed. For corroding solution at 90°C., with solution pH values in the range between 5 and 9, the corrosion rate or the lead-iron phosphate nuclear waste glass is at least 102 to 103 times lower than the corrosion rate or a comparable borosilicate nuclear waste glass. The presence or Fe2O3 in forming the lead-iron phosphate glass is critical. Lead-iron phosphate nuclear waste glass can be prepared at temperatures as low as 800°C., since they exhibit very low melt viscosities in the 800 to 1050°C. temperature range. These waste-loaded glasses do not readily devitrify at temperatures as high as 550°C. and are not adversely affected by large doses of gamma radiation in H2O at 135°C. The lead-iron phosphate waste glasses can be prepared with minimal modification or the technology developed for processing borosilicate glass nuclear wasteforms.

Description

~ 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 ~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.

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 , .

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 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 ~e2o3 1 0~10 10 Note~ Amount Or iron oxide added depends cn type Or hlgh-level nuclear wa~te.

2s ~ 839 _, ~, 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 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 O ~ C
O ~ u h 3~ ~ ~10 0 ~ C-~
~æ O O ~ ~ O O 0 0~

U~ O
c~ ~ ~n 0.,_ l l l ~v o o o '29 2 ~
0 E~

0 J~ C

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','~ ;,

Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A modified lead phosphate glass resulting from the melting of, in weight percent, 40-66% PbO, 30-55% P2O5 and the balance of a corrosion-inhibiting concentration of up to 10% Fe2O3.

2. A nuclear containment composition resulting from the solidification of a melt of (1) a lead phosphate glass consisting essentially of, in weight percent, 45-66% PbO, 34-55% P2O5, (2) a radioactive metal oxide mixture incorporated in said glass, and (3) an effective corrosion-inhibiting concentration up to 9% Fe2O3 incorporated in said glass, based on the total weight of said composition.

3. The composition of claim 2 in which the metal oxide mixture content by weight is up to 20% of the lead-phosphate glass.

4. An improved process for the containment of radioactivity comprising:
(a) forming a melt, at a temperature in the range of 800°C to 1,500°C, of a lead glass composition consisting essentially of 45-66% PbO, 34-55% P2O5 or a compound readily decomposable to P2O5 and an effective corrosion-inhibiting concentration of up to 9% Fe2O3; and (b) incorporating up to 20%, based on the weight of the glass composition of a radioactive metal oxide mixture and then solidifying the melt.