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Final Report: The Crystal Chemistry and Structural Analysis

of Uranium Oxide Hydrates Grant # DE-FG03-95ER14540

Mark L. Mlller & Rodney C. Ewing May 15,1!)95 - December 31,1997

Project Summary sc of this research program was to

dcvclop a t rough undcrstanding of the crystal- chemical and crystal-structural rystematks uf umnyl uxidc hydrates which are the initial corrosion pducts of the UO, in spent nuclcar fuc.f and thc principal phnscs in whrch actinides occur in thc ncw surface environmcnl. The scope of this prograin has been e x p t c d to include all inooynic phases in which U plays a si nificanr stmctunl role: currcnlly 183 phases wit 6 known cryslnl StnlctUreS.

Results During thc first two years of this pmjeui we

have whicvcd significant progress in uncki.staading the crystaf chcniical paramctcrs that constrain thc crystd stmcturer of thesc phases and have appraised b s e pharrcs a! transuranic element hosts. The currcnt data- includes one hundred and cighty-two phews, fifty-seven of which arc naturally occurring mineriils, The cryslal structure dal&a.se includes thc crystal rtructurcs of schocpite, iantbinite, vondcndricsscheite, and "wyartite lr', which have been detcrmined as pait of this nsearch program.

To racilitute this research, we puwhased and instullcd (1 uscd Siemens P3 4-circle difhciometcr. This insliument tnablcd us to collcct x-ray diffraction data for single crystal slructure dctcrminations und rcfinemmts and was critical to the SUCUCC'CSS of this rcscarch pmgrmn. Thc faur-circle difrrwonretcr was purchased with tnatching funds from the Department of Euth & Planetary Scicnces.

A struclural hicrarchy b a d on the pulyiiicrization of polyhcdra of higher band valance has k e n developed to facilitate understanding the crystd chemical controls on the crystal struclure. The crystal structures of

phases that require lf+ arc grouped into phws containing iso!;rlrxl uranyl polyhedra. clusters uT uranyl pulyhtdra. infinite chains of urmyl polyhedra, infinite shea& of irranyl polyhcJrrl, and frmcworks of uranyl polyhedra.

Within Ihc phllses includcd in our dritiibase, u'* usually occurs as part of an appruxiinateIy linear, Ur, uranyl ion (Fig. 1). 'fhc uranyl io11 is cwordinated by 4. 5, or 6 nearly coplmar equatorial anions, kignatcd 4. (0 P 02', OH', Ha). Because thc hnd valence or itie oxygcns of the uranyl ion are nearly d s f i c d by the slmt (0.18 nm) uranyl bond, the apical. uranyf. oxygens are usually bonded to MhCr cations utrly through dativcly weak hydrogen bonds or through Van der WmIr W i n g . uatorLI anions, howevcr, do require bonds to%itionel cations to satisfy thcir bond valence wquircmcnt.. . As a mlt, uranyl polyhedra Loid to pdyiixrize by sharing cquatorid cdges anJ c o ~ c m , anJ of thc 183 structures included in the dotabme. 109 an sheet stwcturcrc. Substitution of monovdlcnt ailions for oxygen ut thc quatorial positions

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This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or use- fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any spe- cific commercial product, proccss, or KMCC by trade name, trademark, manufac- turer, or otherwise does not ncccssarily constitute or imply its endorsement, m m - mendation. or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

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f c d u in dcweascd polymcrizuilun of uranyl polyhcdra. This, along wilh diiution of uranium with nqxct to other cttlions in thc SlNCtUIE produccs thc attucturcs b a d on chains, cfustcm, and isolatcd urdiiyl pofyhcdrii, Fraincworks typically result whcii thc uranyl oxy en atoms are

valence, and frequently chis ~ s u l t s in uranyl ions that do not occur in a single orjcntiltjon with the cryhtal structure.

Bccause structures containing slieets of polyhedra am the dominute class of uranyl- bearing phascs, and because all known SNP corrosron products eiccpt, soddyite, are shcct structures, this hierarchy further classifies sheet stmcwcs hito six slructurd groups. The topology of the quatorial onions or sheet anion topology, SAT, of each shcct i s uscd to classify cuch sheet s1ructure. The SAT is derived from the sheet of uranyl polyhedra in lhe structure by the pwcss diagr-amnicd in figwe 2. ' l k SAT was onalyzed to identil'y the chains prcscnt within it. Each chain is asswiuhd with a single-lcttcr chain descriptor which is uwJ to specify the .wqucnce of chains ihat is rcquircd to construct he toptcrgy.

Each chain is composcd of o. specific number of polyhedra! s h . All at the chains thut have been obscrvcd Lhus Fir arc made up of iriaitgular, rhombic, pentagonal, and Ilcxagonal sites. ThC edges of P topology can also be populated. Fach site is II polcntid site of cation population:

bonded IO inon [hail one cution o f h i g h bond

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tl=l&~c, the sites present in each chain cnnarrain thc chcmislry uf the chain and. thereforc. the topologies that contain it.

Each SAT can bc ppulslled with cations and apical onions in .several ways to produce, sometimes greatly, dit'lcrcnt sheets of polyhedra. Figure 3 shows two populations of the UP SAT (Fig. 3b). hi Figutc 3a, the shcct that occurs in bccquerelite, protasite, a-U& end hillictite is illustratcd. All pentaganal s i lm an populated wirh uranyl iuns, and all triangular hitcs NC vacant. The UP topology ppulation thai occurs in lhe synthetic phases MulcU~MstJ,i,lcHlo),,. K~lrU~,XSO,)sl(HIO),, md HMJ%KSQhMHlOh is illustrated in Figure 3c. I n chis shcel the penta8onaI sites of the P-chains are all vacant. as are thc trinngrilirr sites of the U-chains. The rulfuie tctrahedm populate e d p of the ~cp logy .

Within the hicrarchy. each group of sheet structums contains phases rhri are bawl ott topolo@u t l w ~ are related, in that [by contain a unique clioin type. Furihcnnorc. 1hc topologies within each of four of these groups. can be vicwd as il polytypic wries.

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As ;rn exaniple. ttw urr-uwhead group is mads up of topologies that contain the urrowhand chain. Arrowhead chains are made up of iriangular and pcniagonal si tcs. Euch arrowhead cualains one ptagonal site sliaring ilzl cdge with one triangular sile. In khe arrowhead chain, the tip of one nrrowhed ({he triangular site) shercs corners with the base of the next arrowhead. Arrowhcad chihs are diwliond. that is. they point upwards or downwards. Upward pointing arrowhead chaicis are denoted U-chains; downwvd poiriting chains are &noted D-chsins. Arrowhead chains, in addition to the rhombic, R-chains, ore illustratcd in Figure 2.

Figure 4 demonstrates schrinaticolly the biruclunl rclationships that relaic: rhc incmbcrs of the wowhead group. Thcrc itre two possible expansions of the UD dirin sequence. Thr: rhombic expansion occurs when thc D-chein is Iranshtcd down and away from the U-chain to allow insertion of il R-chain bctwren them, as seen in F i ~ u l r 2. TtK: P-chain expansion requires insening a P-chain, made u of cdge-sharing

chain. This expansion also requixs revcrsing the direction of' the orrowhcad chains subsequent to the P-chain, so that the anowheads iujjaxnt to the P-clrairt are of Lhc wine orientation. AppIicatiun of an odd niimhtr uf P-chain cxpmsions, therefore, cuuws a doubling of the original chain sequence mpcar lenglh.

pmtagtwal sitcs, between the e -chain and ihc D-

In addition to elucidnting the slructurid rlmiliuitier or Jiaparate shcetr, thin UppruitdI provides a mews of predicting the stnrcturc of phascs for which the crystal structure is unknown. By vc~torizing the toplogics that result from the P-choin and R-chain expansions in Figure 4, {he irlwlizcd unit ccll of cach toptogy can bc cslculated from the chain dcscriptm. Fibk I coritains the vector coefficients &rained from idcalized chain gcomctrierr for the chains observed in the arrowhead group. Comparison of the unit ccll dimensions with !how obtained cxpcrimcntrrlly is PISO provided. In this preliminary ht~~lation. IW provisiun has bccn in& to account for variations in street composition, cation sile, vacancy etc. Improvemtn~ in agrccmcnt between observed and predicted valucg will certainly be r e a l i d when thew factors are consitlend.

hriotlrtr hcncfit of exprulding the rcop of lhis rescarcb mgmm is thmt wc have betn ahle to ineludc &sa of g m compositional diversity. This has made clear thc ability nf uranyl shocts to include cations other than uranium. Analysis of thc ctystfl styturcs in our database shows Ihat CaZ+, Pb +, Sr + Na* uccur with umnium in the pentagonal sites of several to 1 ~ b E . Catiops includin Cu +bMgz+l Ti", S-.% , Ma"'', Nb-' AS$+, &, V occur in Lhe rhocbic sites: Triqular sitcs c p rrccommocfate Si , S6', B'+; whcmm, only Ma has becn found to wcupy the

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hcxaganal nib%. It is importunt to note chat all ul these cations accur in sites tlim are similar or irlcnticd to those populated with uranium in ather stmcturcs based on the SBI~K SAT.

Comparison with the crystal smctures adopled by transurantc elcmeni pliabcs irirlicrrks h a t pcntavafcnt and hexavoleiit transuranic elements will substirure for uranium occupying pentagonal or hexagunal des. The tctravalcnt species will likely substitute prcfercntially far urilnmm occupying rhombic sites.

Coinpcnration lor variations in cation charge can be accoinplihhed in several ways. Mechanisms that havc bccn observed in this etudy include: 02--OH suhstituQon at thc equatorial anion positions; 0"-Hfi subsgitutiun at the apical anion position; increasing cation coordination by thc introduction of additional a ical anions (as obncrved in wyartitdl. in which

ici tlre rhombic sitc shrms an edge wirh a COB triangle directed into the. interlayer); or by compensating cation substitution in the intcrlayer.

Summary Analysis of the slml anion toplogics

underlying the crysld sfructures of the kmwn uranyl sheet Ir'trucLures and cnmparhn of ihcsc struclurcs with S~NC~U~VS of ofher aclinide- bearing phascs has allowcd:

Dcvelopmcnt of a classification of crystal slructurca of uranyl phascs based on the

d c g m of polymcrization of polytiedra of highcr bond valence. ldeniificaiicln of stmctural elcmnls which make up the sheets of uranyl plyhcdra in the

Idealifiicat ion of zlructunl FchUionship that occur amongst the various uranyl-bewitlg shccts lhnt mcur in the crystal stmclures of umyt-bearing ph'lses. klcntificatian of polytypic ur expansion series that exist within the targcr class of sheet scrwlurrs @.g, clcvcn of thc twenty-nine obsuvcd topologies can bc rcprescntcd as cxpmsions of a single kplogy, using only two types of expansion chuiiik). Prediction of the unit cclls and constraint or the shat coinpositions for unubservcd topolo@es tlnd topology populations. This is of part~culirr vdue in the dctcrmination of the cryrrial rlmctumrs for yliases fnr which thc SINC~UCCS arc currently unknown. Rediction of the ability of uranyl-bearing

to accommodate trnnsurmic elements. hcsc dictions are based on comparisons p t with t e ujrrsumic clctncnl coordination

geometries observed in transuranic clcntcnt- W i n g phases for which the crystal suuclurrs iue known and on other crystal chemical c~nsidcntions e.g. valence, bond strength sums, cation radii.

crystal structures.

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Professional Actlvlfiee Thc following prsonnel have participated in this project during the first cightccn month3 of [his

progre in:

1. Dr. Mark L. Miller nccivd his Ph.D. In Mineralogy from IIK University of Now Mexico and h3s hupivised, and piuiiciputd actively in, all aspccls of the research program. He h a actively puticipated in chc acquisition and installation and upgrade of the 4-circlt diffractorwler. HC has devclopud the ioplogrc approach itsen in this program lo describe and classify uranyl-boring crystal unrciurtu. He is currently dcveloying qpiicwions of this mehad of structural dcscriflion. He rcceivcd 6.0 monlhs of salary support p r year, and is in charge of the x-ray JiffrHction lobordory in the Department of Earth & Ptanciary Scicnces for which hc iwcives 4.0 months pccc ycar of salary suppn. In ;tdJitioii, he has made thc following presentations:

A. "Dcscripiion and Classification of Uranium Oxide Hydroit Sheet Tapalagics: Toward Devcbprnent ot it Stmciurd Madcl for the Esiiiiution of Themdynamic Pur;lmters" Geological Sociciy of Arncrica Annud Meeting, Ncw Orleans. Novcmbcr 9, 199s.

B. "tkscription and Clasifimiiun UC Uranium Oxirk: Hydretc Sheer Topolo~ia" Materials Rcscarch Socicly, Annual Fall Mating, Boston. November 29, 1995.

C. *'The P-R-Arrowkd Expansion Scries: Cllusificntion of Uranyl Sheet Anion Topologies Bnwd on the SLakirrg of Structural Chains" Geological Association of CanadumAincnhgical Associalion of Conado Annual Meeting. Winnipeg, Conads May 4, 1996

D. Mirik L. Miller, Robert J. Finch, Peter C. Bums and Rodney C. Ewing (1996) Transuranic clcnicnt incorporarim into the P-U.,OS uranyl .qhcct. The Geological Society of Amcrica Annual Meeting, Denver, CO, Oclober 3 1, J996.

E. Mark L. Miller, Peler C. Bums and Rodncy C. Ewing (1996) Transuranic ekment incorporation into fhc fl-U108 uranyf sheet. Materials Rcscarch Society, Annual Fall Meeting, Boston, MA, Ihcember 2,1996.

F. Pcteer C. Bums, Mark L. Milkr and Rodney C. Ewing ( IYYb). A elnrcturol hierarchy af urunyl- bewing minerals. Malerials Research Society, Annual Fall Meeting, Bostan, MA, Deccnibcr 2,1996.

11. Prof. Rodney C. Ewlng w i v e d 1.0 months of salary support ;md is Co-Principal fnvestigaor of the research project. Ewing's main effort has bccn in the pcrforrnance usessmnt of the im nct of the corrosion of waste f m s and the subsquent rclcpse of Winidcs and fission pmducts. fie llas made the folfowing presentationr:

A. "Observations on the Corrosion of Oklo Uminifcs": Find meeting of the CEC-CENIQSN "oklo ils a Natural Analogue" program 1991-1995, Saclay. France, June 22. 1995.

B. "Radiation-Induced Amorphization in Nuclrar Wmtc Forms": Annual mceting of !he Amencan Crystallographic Aswcidion, Montreal, Canda, March 29, 1995.

C. " R a d h t h Effects in Nuclear Waste Forms": IVEM Workshop on Major Juvucs in 1rr;di;ltim Ekcts Rtscarch urgiiizcd by the Electron Microscopy Ccnlcr for Marerials Science at Argnnne National Laboratory, October 25, 1995.

D. "When is the Matcrids Science in Nuclear Waste Forms?'? Sympsium X, "Fmntierr; jn Materials Sciedrce", Materials Rcsc~rch Swiety Annual Fall Meeting. Boston, MA, Novembcr 29, 1995.

E. "Thc Role of Wastc Forms in the Performance Asscssmeni of N~lclcar Wuie Repitories": Advisory Committee on Nuclear Wnste of the Nuclcar Regulatory Cornmimion, Wlbahington. D.C.. January 26, 1996.

F. "Where is the Matcrirls Science in Radioactive Wasw Disposdl" Invitcd Iccture, CEA, S ~ l u y . Scrvicc de Chimie Mol&ufnirc, France, Novctnber 19. 1%.

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G. -Whe= i s ib Mo&ri&j &iswc in Radioiclivr waste Disposd?" lnvilcd ICcCUrC, SChcrmr Inslirute, Villigcn. Switzerland. November 22, 1996.

H, *&where i s the Ma&& Science in Radioactive Waste Disposal?" DOE office of Bakic Energy Sciences, Germantown, Maryland, Dccernbcr 6, 1996.

I , "Dcsign of Advanced Nuclear Waste Forms" Annual Mating of the AAAS, symposium on "Rcscawh Fruniiws dad Challcngcs in Envirunnientd Sciences, Seattle. Warhinglon, February 15, 1997.

11I.Ur. Pder C. D u m is a visiting scholar on a NoturaJ Science and Engintwring Research Council of Cilnada fcllowship. IIc weivcd 5.0 months salary support (4 months in the form of a stipend) and was inslrumcntd in girltrclicrg data used to dcvclup the structural hierarchy and 1he analysis of the crystal struciurcr. His intctpretationr of the crystal cheinislry crf the,= ph&ws has Icd to the nnalysis of the likelihood of uranyl-kiujng Nilscs acting ils actinide hosl-phases which form during the Corrosion of spcm r~uclcor fucl. Peter also uctively participated in thc installation of the 4.cirr;le diffrxionlcicr ad Lhc sufutiort of the ianthinitc crystal hlructure. Peter has acceptcd n psi t iuc l ilt the Univcrshy of lllinois in 19%. and 1s now at Notre Dam Uiiiversity.

A. Peter C. Burns, Mark L. Miller and ROJnry c'. Ewing (i996). A smcruraf hierarchy of uianyt- bearing minerals. The Cicological Associalion of CaniddMirKrcIogicsl Association of Cnnnda Annual Mceling, Winnipcg, Canada, May 4. 19%

B. Peter C. Burns. Mslrk L. Miller and Rodncy C. Ewing (1996). A structural hicrarchy of uranyl- ph,lses: applications io tllr: disposal of spent nuclear fuel. The Geological Society uf Airicrica Annual Meeliiig, Dcnvcr, CO, Octobcr 31, 1996.

1V.b. Mostsf. Fay& rcccnfly finished hi6 Ph,D. a1 the University of Saskatchcwnn a d joined nur rcscwh group as a visiting scholar. Dr. Fayck is also supportcd by a Natiiril Science and Engineering Rrscwch Council of Canada fellowship. Although he rcceives no salary sitpprt from BES, his research on uraninite-water interactions is supported by, ond is of direct rclcvance to, lliis research program.

A. Mostah Fayck, Pckr C. Bums, Yongxinng Guo, und Kodncy C. Ewing (1996) Micro-struclut-es aid gcochcinical consequences associlrird with uraninite altcrotion. Gcofogical Sacicly of Amcrica Annuul Meeting, Dcnvcr, CO, Octobcr 3 I, 1W.

B. Mosliafa Fsyck, 7'. Kurt Kyser, Rodncy C. Ewlrig (1996) Uraninite-watcr intcractionr in an oxidizing environmcnc. Mawridr Research Saiety Annwl roll Meeting, Boston, MA. December 5.19%.

Research publicSt~on8 resulting from this program: Journals (refcreed) A. Mark L. Millcr. Robert 1. Finch. Peter C. Burns and Rodney C. Ewiny (1996) Description and

cl;lssification of uranium oxide hydraie s k t lopologies. Joumul of Mulet ink Reseumh. 1 I (! 2).

B. PckI' C. Bums, Mark L. Miller and Rodney C. Ewing (1996) Uranyl minerals ;md inorganics: a corn arlson and hierarchy of crystal structures. Canadian Minerulqp'xt, 34, 845-880. (ffeccivprl t!te I99fHmulty McdA! rgthe Miricmlogird Associntinn tfcantda.)

e. Kobcfl J. FirKli, Mark A. Coopcr, Frank C. Hawthorne and Rodmy C. Ewing (19961. The crystd ~tructurc of schmpite, [(UO2)nO2(OH),211H30),1- Crmzdia#r Minerubgivi, 34, 107 1- 1088.

D. Janusz Jallcczek, Rodney C. Ewing, Virginia M. Ovcmby, WIJ h s 0. Wcmc (in prr,ps) Ilraninite and UUZ in rpnt nuclear fucl: A comparison. Jnirmal ofivuclear Matcricrls.

E. Rokn J . Fiwh, Friink C. Hawthorne. and Rodney C. Ewing (in prcss) Calcutaid X-ray wwder- d i f f r a c h ~ for schmpile, [(UO;~)U~(~H)II~(H~O),~. and coiaparisnn with rcportcd powder piiltems. Porcvicr Diffraction.

3048-3056.

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P. Robcn 1. Fiadt, Rank C. Ilnwlhorno, und Rodney C. Ewing (submitted) Phase trarrsfnrmaficsns and crystaflograpliic relations among schoepite, mtaschocpitc and drhydrotcd schmpite. Cnafftlir~fi Min cruiog ist .

G. Roben J. Finch and Rodney C. Ewing (in prcss) Clarkeite: JWW chemical and structural drttn, A mrricrrn Mineralogist.

H. Pcccr C. Burns, Murk I.,. M'ller and R d i c y C. Ewing ( 1996) Incorporation of iacrinidc clernenls trttn the crystal siruclures of &-bearing phases during thc oxidation of spcnl iiuclear fucl. Jfnsrnul of Nttcleur Mukriiils, 245, 1-9.

I. P c k r C. Burns, Robcrt 1. Finch, Frank C, Hawthorne. Mark L. Millcr and R d n e y C. Ewiiiy (in press) TIK crystal structure of ianthlnlte, [U~(U02)~0~(0~1)r(N10),J(H10)s: A pssihlc p h m for pu4+ incorporation during tlie orridation of spent nucicar tiel. Ctittutdian Minertdofiisr.

1. Mark L. Miller and Rodney C, Ewing (suuhmiltcd) Claasificalion of U6+ shcct union topologies. Attterirm Minerdog lst.

K. Mostaf'a Payek. Pcter C. B u m , Yongxiang CUO. and Rodney C. Ewing (submitted) Micro-structures and geachemical consequences ilsliOCi&d with urininirc alteration: Applied (ieochmisrry.

L. Mobid'a Fuyck, lilnu~z fancczck, und Rdncy C. Ewing (in press) Mineral chcmistry and oxygen isotopic ;uralysts of uraninite, pitchblende ;urd uranium ahemtion mitterds from the Cigar Lake dcposit , Saskrrtchcwon, Canada. Applied Grrochemisfty.

Symposia Proceedings (refereed) A. Mark L. MiHcr, Robcn J. Pinch, Peter C. Bums and Rodney C. Ewing (i996) Description and

classification of uranium oxide hydrate sheer topologies. Scienlifio Busis for Nuc1e;u Wrwtc Miknagemnt XIX. William M. Mur y mJ Dieter A. Knccht, eds., Muterials Research Society

B. Robcn J. Pinch, Frank C. Hawthorne and Rodney C. Ewing (I%). Schac ite and dehydnrcd schocpitc. Scientific Busis for Nuclear Waste Management XIX. William M. J urphy and Dielcr A. Kiaechr. ds.. Materials Research Society Symposium Proceedings 4 12 p- .

C. M d c L. Millcr, Pctcr C. Bums and Rudricy C. Ewhg (I 9%) Tnnsuranic elemcnt iiicorpration into thc ~MJ.IO~ uranyl shctt. Scientific Basis for Nuclear Wastc Muriapncnt XX. Walter Gray and hex Triity, ds., Proceedings of h FaII meting of the Matctials Research Society (in press),

D. Petcr C. Burns, Roben J . Finch, Mark L. Millcr and Rodney C. E w i q (1996) The crystal htntctun of ianihinie. Sclcniific Basis for Nuclear Waste Management XX. Walter Gray and lncr Trisy, cds.. Proceeding of the Fall mecling of the Materials Rescarch Sociery (in press).

E. Moscafa Poyck, T. Kun Kyser, Rodney C. Ewing. and Mark L. Millcr (1%) Cieorherni-l consequenccs or uraninite-water iritcroction in an oxidizing environrncnt: Scicalific Basis for Nuclear Wzlstc Managersent XX. Walter Gray rrnd Inex Trioy, 4 s . . Proceeriings of the Fall rtlerting of the Materials Rcsciuch Society (in press).

Symposium Proceedings 4 t 2 p. 369-3 ? 6.

Abstracts A. Mark 1,. Millcr and Rodnc C. Ewing (1995) Description and ctassification of uranium oxide

hydrate sheet to logics: 4 owud Devclopnicnt of a Structural Model for the Estimation OF Thennodynamic F" aameteers. Abstracts and Program, 'I'he Geological Society of A m & AIinuri Mceling, NCW Orleans, LAl Novrriilcr 6 - Novcmbcr 9. lW5.

B. Mark L. Miller and Rodney C. Ewing (lW5) Description and classification uf' uranium axidb hydrm sheer rirpologies. Materials Research Society Annual Full Meeting, Boston, MA. Dcccmher 2-6, 1996, p. 579.

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c. Rodmy c. Ewcn (1995) Wlacfc IS tho malurials science in nuclear wilslc disposal'? (invited) Symposium X - # ronlicrs of Malerials Scicncc. Materials Research Society Aiitrual Fati Mccting, Boston, MA, November 27 - December I, 1995, p- 637.

D. Mark L. Millcr, Pclcr C. Burns and Rodney C. Ewing (1996). The P-R-Arrowhcad Expansion Series: Clasificution of Uranyl Sheet Anion Topologies Based on the Slacking of SlrUCtWiIl Chains. Thc Gcolu r i d Association 01 Cfuinda&fineritlugkal Association of Canruln A i ~ t i ~ a l Meeting.

E. R&y C, Ewing (J996) Mineralogy and Materials Scicnce: Conlribuliona to Radioactive WzW Disposal, The Geological Associatiai of Cmadil/Minerulugical Association of Canada Atinual Mceling, Winnipeg, Canada, May 4, 1996.

F. Peter 0. Burns, Mark L. Miller and Rodney C. Ewing (IY16). A slructurd hierarchy of uranyl- bearing niinenls. The Geological Association of Canad;r/Mincralogicitl Association of Canada Annual Mceiing, Winnipeg. Cdlldi% May 4, 1996

G. Mark L. Miller, Robcn J . Finch, Pckr C. Bums and Rodney C. Ewing (1996) Transtirunic clctnent incorporarion into the ~ - U ~ C h urariyl sheet. Abstracts with Program, 7hc Geological Socicty of Amrica Annual Meeting, Denver, eo, October 28 - 3 I , 1996. p. 454.

H. Peter C. Bums, Mark L. Millct and Rdncy C. Ewing (IW6). A structural hierarchy of unmyl- ases: applicatiotis to the disposal of spent nuclear fual. Absrracrs with Program, Tlrc Gmlogicd !? ocicty of Amcrica Aiinual Meeting, Dcnvcr, CO, October 28 - 3 1, 1Y)6, p. 454.

1. Mostofu Fuyuk, Puter C. Durns, Yongxinng Guo. i d Rndncy C. Ewina (19961 Micra-stnictures and geochemical ccwwquertccs ;Lwxiilted with uraninite alteration: Absinlcts with Program. Cccrlogical Society of America, 1996 Annual Meeting, Denver, Colorado, v. 27 p.454.

J. Mark L. Miller, Peter C. Bums and Rodney C. Dwing ( 1996) Transuranic clemcnr inuorprtliion into [he B-UJOII uranyl sheet. Abstract,,, Murerials Rcseorch Society Annual Fall Mccting, Boston, MA, December 2-6, 1996, p. 756.

K. Peler C. Burns. Robert J. Finch, Mark L. Miller a d Rodncy C. Ewing (1996) The crystal S~NCIUTC of imthinite. Materials Research Society Annuel Fall Mctrlng, Boston, MA. DC0cd.w 2-6. 1996. p. 755.

L. Mostalil Fayek, T. Kurt Kyser, Kodney C. Ewing (1996) Uraninite-water intcrractims in itn oxidizing enwronmenr. Materials Rescarch Society Aniwd Fall Meeting, Boston, MA, Jhczi~rber 2-6. 1996, p. 778.

Winnipeg, k anada, May 4, 1996.

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