x) ( -h~

Report YJT-95-14~~~~~(C~- ~,

SOLUBILITY OF UNIRRADIATED UO2 FUEL INAQUEOUS SOLUTIONS - COMPARISON BETWEENEXPERIMENTAL AND CALCULATED (EQ3/6) DATA

Kaija Ollila

November 1995

VOIMAYHTIOIDEN YDINJATETOIMIKUNTANuclear Waste Commission of Finnish Power Companies

YJT

Report YJT-95- 14

SOLUBILITY OF UNIRRADIATED UO2 FUEL INAQUEOUS SOLUTIONS - COMPARISON BETWEENEXPERIMENTAL AND CALCULATED (EQ3/6) DATA

Kaija OllilaVTr Chemical Technology

November 1995Helsinki

ISSN-0359-548X

IMATRAN VOIMA OY (IVO)

Address Telephone TelexFIN-01019 IVO Nat. (90) 85611 124608 voima tiFINLAND Int. +358 0 85611

TEOLLISUUDEN VOIMA OY (TVO)

Address Telephone TelexAnnankatu 42 C Nat. (90) 61801 122065 tvo fiFIN-00100 HELSINKI Int. +358 0 61801FINLAND

Julkaisila -Published by

a \ VOIMAYHTIOIDEN YDINJATETOIMIKUNTAN)deor 'VMe Commiss of ish Pwer CuM es

YJT

Raportin numero - Reorl codeYJT-95-l14

Julkaisuaika - Date

November 1995

Teklla(t) -Author(s) Toimeksiantala(t) - Commissioned by

Kaija Ollila Teollisuuden Voima OyVTT Chemical Technology

Nimeke -Title

SOLUBILITY OF UNIRRADIATED U0 2 FUEL IN AQUEOUS SOLUTIONS -COMPARISON BETWEEN EXPERIMENTAL AND CALCULATED (EQ3/6) DATA

Timvistelma -Abstract

The solubility behaviour of unirradiated U0 2 pellets was studied under oxic (air-saturated) andanoxic (N2 ) conditions in deionized water, in sodium bicarbonate solutions with varyingbicarbonate content (60 - 600 ppm), in Allard groundwater simulating granitic fresh ground-water conditions, and in bentonite water simulating the effects of bentonite on granitic freshgroundwater (250C). The release of uranium was measured during static batch dissolutionexperiments of long duration (2 - 6 years). A comparison was made with the theoreticalsolubility data calculated with the geochemical code EQ3/6 in order to evaluate solubility (steadystate) limiting factors. Under oxic conditions, various hypotheses for redox control (redoxpotential of the bulk solution or redox potential at the surface) were tested in the EQ3/6 calcu-lations.

Under oxic conditions, the measured concentrations for uranium at steady-state in deionizedwater are equal to the solubility of schoepite (PO2 = 0.2 atm, COMU database). In NaHCO3solutions with lower carbonate concentrations (60 - 120 ppm) and in Allard groundwater, thesteady state concentrations of uranium are close to the calculated solubilities of uranium at theU3 07 /U 308 boundary. In bentonite water, the solution concentration of uranium stabilizes at alower level, suggesting the formation of a secondary phase with a lower solubility. Onlyuranium oxide with a crystal structure of uraninite (U02 - U30 7 ) was identified in all waterswhen analysing particulate material in the solutions.

Under anoxic conditions, the measured concentrations at steady state are at the level of a mixedvalence oxide, U4 09 (UO2 .25 ) solubilities. The water composition had a minor effect on thesolution concentration of uranium.

ISSN ISSN-0359-548X Kieli -LanguageiEnglish

Sivumaara - Number of pages 27 + 22

Jakaja - Distributed by

Teollisuuden Voima OyNuclear Waste ManagementAnnankatu 42 C00100 HELSINKITel. 90-61801

Julkaisila - Published by

. G VOIMAYHTIOIDEN YDINJATETOIMIKUNTAI* Nuder WAste Unmirron of Rwish Poer Cwponies

YJT

Raporlin numero - Report codeYJT-95- 14

Julka)sualka - Date

Marraskuu 1995

Tekija(t) -Author(s) Toimeksiantaia(t) - Commissioned by

Kaija Ollila I Teollisuuden Voima OyVTT Kemiantekniikka

Nimeke - Title

SATEILYTTAMATTOMAN U0 2-POLTrOAINEEN LIUKOISUUS VESILIUOKSISSA -VERTAILU KOKEELLISTEN MITITAUSTULOSTEN JA MALLINNUSTULOSTEN(EQ3/6) VALILLA

Tiivistetma - Abstract

Tassa tyossa on tutkittu sateilyttamantt6mann U0 2 -polttoaineen liukenemista erilaisen kemiallisenkoostumuksen omaavissa vesissa hapellisissa (ilma-kyllastetyt) ja hapettomissa (N 2) olosuh-teissa 25°C:ssa. Uraanin vapautumista mitattiin deionisoidussa vedessa (referenssivesi), nat-riumbikarbonaattiliuoksissa bikarbonaattipitoisuuden funktiona ja synteettisessai pohjavedessa(Allardin vesi, bentoniittivesi) kayttaen staattista batch-liukenemiskoemenetelmaa (2 - 6 a).Liukoisuutta (steady state) rajoittavien tekij6iden arvioimiseksi verrattiin mittaustuloksia EQ3/6-mallinnuksen antamiin tuloksiin. Mallinnuksessa vaihdeltiin redox-olosuhteita saatelevia tekijoita(vesiliuos, U0 2 :n pinta).

Hapellisissa olosuhteissa deionisoidussa vedessa uraanin marn a vesifaasissa tasoittui arvoon(3 - 5 - 10-6 mol/l), joka vastaa mallilla laskettua schoepiitin liukoisuutta (PO2 = 0.2 atm,COMU-tiedosto). Natriumbikarbonaattiliuoksissa matalemmilla bikarbonaattipitoisuuksilla (60 -120 ppm) ja Allardin vedessa (1 - 2 * 10-5 mol/l) uraanin maarat vesifaasissa tasoittuivat arvoi-hin, jotka ovat kertaluokan matalampia kuin schoepiitin liukoisuudet. Mitatut pitoisuudet ovatlahella uraanin teoreettista liukoisuutta, kun liukoisuusmallinnuksessa oletetaan U0 2 :n pinnan(U 307 /U 3 08 ) maaraaviin redox-olosuhteet ja uraanin maarn an vesifaasissa. Bentoniittivedessauraanin maarar vesifaasissa stabiloitui arvoon (1 * 10-6 mol/1), joka viittaa niukkaliukoisenuraanifaasin saostumiseen (esim. uranyylisilikaatti). Mitattu arvo on kolme kertaluokkaa mata-lampi kuin schoepiitin liukoisuus, jonka oletettiin rajoittavan uraanin liukoisuutta TVO-92turvallisuusanalyysissa hapellisissa olosuhteissa. Analysoitaessa mahdollisten sekundaarifaasienmuodostumista identifioitiin kaikissa vesissa ainoastaan uraanioksidi, jonka kiderakenne olisama kuin uraniniitilla (U02 - U307)-

Hapettomissa olosuhteissa uraanin maarat vesifaasissa kaikissa vesissa nayttivat tasoittuvanarvoihin (2 - 4 * 10-8 mol/1), jotka ovat lahella U 40 9 :n (UO2.2 5) teoreettista liukoisuutta. Vedenkoostumuksella oli vaihaiinen vaikutus.

ISSN ISSN-0359-548X Kieli - Language

Sivumaara - Number of pages 27gl+n22

Jakaja -Distributed by

Teollisuuden Voima OyYdinjatehuoltoAnnankatu 42 C00100 HELSINKIPuh. 90-61801

CONTENTS

ABSTRACTTIIVISTELMA

1 INTRODUCTION 1

2 METHODS OF EXPERIMENTS 22.1 Materials 22.2 Waters 22.3 Redox conditions 22.4 Dissolution procedure 32.5 Analytical methods 4

3 METHODS OF CALCULATIONS 5

4 SOLUBILITY OF URANIUM UNDER OXIC CONDITIONS 64.1 Solubility limits of the dissolving matrix 64.2 Comparison between experimental and calculated

uranium data 10

5 SOLUBILITY OF URANIUM UNDER ANOXIC CONDITIONS 185.1 Solubility-limiting solid phase 185.2 Comparison between experimental and calculated

uranium data 19

6 CONCLUSIONS 23

7 ACKNOWLEDGEMENTS 23

8 REFERENCES 25

APPENDICES 1 - 22

I

INTRODUCTION

The spent fuel from the TVO I and TVO II reactors is planned to be

disposed of in a repository to be constructed at a depth of about 500metres in crystalline granitic bedrock. In the concept of the multiple

barriers, the barriers for radionuclide release into the environment arethe granitic bedrock, the backfill, the copper-steel canister and the

fuel itself. The innermost barrier is the limited solubility or dissol-ution rate of the U0 2 fuel and of the radionuclides embedded in the

fuel matrix. The overall objectives of this experimental study are

research on dissolution mechanisms of U0 2 for understanding thedissolution mechanisms of spent fuel U0 2 matrix in granitic ground-water under disposal conditions, and to produce solubility data for

uranium for the TVO safety assessments of spent fuel disposal.

This report presents the results obtained from dissolution experi-ments of unirradiated U0 2 pellets as a function of water compositionunder oxic (air-saturated) and anoxic (nitrogen atmosphere) condi-

tions at 25 'C. Three water-types, deionized water, NaHCO 3 solutions

with varying carbonate content and synthetic groundwaters wereused in the experiments. The synthetic groundwaters included Allard

groundwater which simulates fresh groundwater conditions at great

depths in granitic bedrock, and bentonite water which simulates theeffects of bentonite on fresh granitic groundwater. The experimentalmethod was static batch dissolution procedure. The earlier results of

the oxic experiments have been published by Ollila and Leino-Fors-man /1993/.

A comparison of the experimental data is made with the solubilities

calculated using the geochemical code EQ3/6 in order to evaluatesolubility (steady state) limiting factors. The EQ3/6 is a theoreticalmodel based on the premise of chemical equilibrium conditions. The

solubilities are based on the databases of SKB, of the NEA Thermo-chemical Database Project (TDB) by the OECD Nuclear Energy

Agency), and of the Lawrence Livermore National Laboratory (com-posite, COM). Various hypotheses for redox control under oxic condi-

tions are tested. The controlling factor is assumed to be the redox

potential of the bulk solution (oxygen partial pressure) or the redox

potential at the U02 surface (the transitions between various UO2,x

phases).

2

2 METHODS OF EXPERIMENTS

2.1 Materials

All the dissolution experiments of this report have used unirradiated

sintered polycrystalline U0 2 fuel in pellet form. The pellets had anaverage mass of 9.8 grams and a geometrical surface of 4.5 10' mi2 .The surfaces of the pellets were not pretreated by polishing prior to

the start of the experiments.

2.2 Waters

The waters used in the experiments were deionized water as thereference water, sodium bicarbonate solutions with varying bicarbon-

ate contents (0.98 - 9.83 mmol/l, 60 - 600 mg/i) and two types of

synthetic groundwater (App. 1). Synthetic granitic groundwater by

Allard et al /1981/, so-called Allard groundwater, represents naturalfresh groundwater conditions at great depths in granitic bedrock.Synthetic bentonite water by Snellman /1986/ simulates the effects of

bentonite on fresh granitic groundwater.

2.3 Redox conditions

The dissolution experiments were carried out in the different waters

listed above both under oxic and anoxic conditions. The oxic experi-ments were carried out in Schott Duran flasks under air-saturatedconditions at 25 'C. The flasks were loosely closed during dissolution

periods in order to allow the access of air into the solution. The

anoxic conditions of deep groundwater were simulated in an anae-robic glove box. Each pellet was immersed in deaerated water (nitro-

gen) in polypropylene bottles inside the anaerobic box. The oxygen

concentration in the box was kept low by using high-purity nitrogen

gas (99.999 % N2), which was continuously recirculated in a closedcircuit and purified by the filters (adsorbers: molecular sieve, CuO

catalyst). The oxygen concentration in the atmosphere of this box

normally stayed below 1 ppm (- 0.1 ppm). The carbon dioxide

content was undetectable. All the experiments under anoxic condi-

tions were performed at 27-29 'C, the ambient temperature of the

anaerobic box.

3

2.4 Dissolution procedure

The oxic experiments were performed as batch-without-replenishmentexperiments. In these experiments, four U0 2 pellets were immersed

in 1 liter of water in Schott Duran flasks of I liter total volume. Addi-tionally, a ten-fold ratio of pellet surface area to water volume was

applied in one series of tests in Allard groundwater (ten pellets/250ml of water). Small aliquots (5-10 ml) were taken periodically for

further analysis. These aliquots were replaced with fresh water whichhad similar composition. The amounts of uranium in microfiltered

(sample 1, membranes of 0.45 pm pore size) and ultrafiltered (sample

2, membranes of 3 to 4 nm pore size, nominal cut-off value of 50 000

M) aliquots were measured.

For the experiments under anoxic conditions, the waters were pre-pared as follows: All components but NaHCO3 were dissolved in

deionized water under atmospheric conditions. The solution was

deaerated with N2, and transferred into the anaerobic box. Sodium

bicarbonate was added to the solution in the glove box. The waterswere allowed to equilibrate in the glove box for at least one week

prior to the start of the dissolution experiments. As under oxicconditions, the experiments were performed in batch-without-replen-

ishment fashion. Each U0 2 pellet was immersed in 1 liter ofequilibrated water in polypropylene bottles of I liter total volume.

Small aliquots (2 ml), which were replaced with fresh water, were

taken periodically from the solutions for further analysis. Theamounts of uranium in unfiltered and microfiltered aliquots (mem-branes of 0.45 pm pore size) were analysed. Ultrafiltration (mem-branes of 3 to 4 nm pore size, nominal cut-off value of 50 000 M) was

used instead of microfiltration after the experimental time of 150

days.

Prior to the start of the dissolution experiments under anoxic condi-

tions, a predissolution was carried out for the pellets in the glove

box, in an attempt to remove a more soluble oxidized layer on thesolid surface that might have been present on the surface of the U0 2pellets due to the earlier manipulation of the pellets in air. Each pelletwas immersed in 100 ml of equilibrated water in polypropylene

bottles of 125 ml, the water compositions being similar to those used

later in the dissolution experiments. The duration of this predisso-

4

lution period with daily changing of water was ten days. The amount

of uranium released into the water phase per day was followed.

2.5 Analytical methods

The uranium contents in the oxic experiments were analysed byepithermal neutron activation analysis (INAA). Inductively coupled

plasma mass spectrometry (ICP-MS) was used in analysing the

solutions of the last four samplings. The uranium contents in theanoxic experiments were analysed by ICP-MS in order to reach lower

detection limits. The microfiltration of the solutions was carried outusing the Millex-HV 0.45 pm filter units of Millipore and the

ultrafiltration of the solutions was carried out using the Model 3micro-volume and the Model 8010 Amicon Ultrafiltration Cells

(Amicon Diaflo membranes, XM 50). The anions and cations of the

solutions were analysed by ion chromatography (IC) at the end of theexperimental time. The carbonate equilibrium of the solutions was

analysed using the SFS 3005 Standard method for the determinationof alkalinity and acidity in water (Metrohm titrator).

The oxidation state of uranium was preliminarily determined in thesolutions after the contact with the pellets at the end of the experi-

mental time. The method was based on the separation of the tetra-valent and hexavalent states by ion-exchange chromatography in HCO

medium /Hussonnois et al 1989/. The uranium contents of eachfraction were analysed by ICP-MS. The development and testing ofthis method for our experimental conditions is reported elsewhere

/Ollila et al 1995/.

The presence of possible secondary phases of uranium on the surface

of the pellets or in the solutions was examined with X-ray diffrac-

tometry (XRD), Debye - Scherrer camera and X-ray photoelectron

spectroscopy (XPS). The XPS analyses were performed in the Univer-

sitat Politecnica de Catalunya (UPC) in Spain.

5

3 METHODS OF CALCULATIONS

The EQ3/6 package (EQ3NR: versions 3245 R111 and 7.1 R125, EQ6:versions 3245 R104, 7.1 R121) developed by the Lawrence LivermoreLaboratory /Daveler and Bourcier 1989ab, Wolery and Daveler 1989,

Wolery 1992, Wolery and Daveler 1992/ was used to calculate ura-

nium solubilities under experimental conditions.

The EQ3/6 code is a theoretical model based on the premise of

chemical equilibrium conditions. The EQ3NR code is based both onthe charge-balance equation, and on the mass-balance equations forall elements except hydrogen and oxygen. The EQ6 code is based onthe mass-balance equations for all elements including oxygen andhydrogen. In the case of solid solubility calculations with the EQ3NRprogram, the alternative constraint of phase equilibrium with a

mineral substitutes the mass-balance equation for uranium. The redox

constraint used was either oxygen fixed gas fugacity, Eh, or redoxpotential was assumed to be determined by the transitions between

different U02+,x phases on the surface of U02. The activity coefficientswere calculated with the B-dot equation /Helgeson et al 1969/. Theactivity coefficients are in this option treated as functions of the ionicstrength but not of the specific aqueous solution composition. This isrealistic in dilute solutions where the ionic strength is less than orequal to 1.0 molal /Daveler and Bourcier 1989a/.

The thermodynamic databases were the SKBU database (Data

0.3245S02) by Puigdomenech and Bruno /1988/, the NEA database

(NEAU, DataO.NEA.R16) which is based on Grenthe et al /1992/,and the COM (composite) database (COMU, DataO.com.R16) byLawrence Livermore National Laboratory /Daveler and Wolery1992/. The SKBU database has been validated for use in the EQ3/6code package /Puigdomenech and Bruno 1988/.

6

4 SOLUBILITY OF URANIUM UNDER OXIC CONDITIONS

4.1 Solubility limits of the dissolving matrix

Concentrations(moUL)

1 e-4 +

1 e-5 +

+ 0

le-7 & &

le-8

1e-90 500 1000 1500 2000 2500 3000

Cumulative contacttime (days)

|+ BWR 0 PWR A BWR DIW 0 PWR DIW

Figure 4-1. Uranium concentration in deionized water and Allard groundwater in spentfuel dissolution experiments under oxic conditions as a function of cumu-lative contact time IForsyth and Werme 1992/.

A general result from spent fuel dissolution experiments performedin the presence of atmospheric oxygen is that the solution concentra-

tion of uranium reaches a constant value after short time periods. The

concentrations obtained for uranium in the dissolution tests of spent

fuel in synthetic Allard groundwater and deionized water /Forsyth

and Werme 1992/ are plotted against cumulative contact time in

Figure 4-1. Over the first week of contact, the concentration increased

to 4 * 104 mol/l and remained constant at that level for 500 days. At

longer cumulative contact times, after some thousand days, the

concentration increased to 2 * 10- mol/l. The solution concentrationappears to be controlled with respect to some kind of oxidized phase.

Initial attempts to identify the solubility-controlling phase seemed to

indicate that the solution concentration was in close agreement with

the solubility limit of schoepite, U0 2(OH)2 * H 20 (s) /Bruno et al

1984/. Hovewer, when the refined thermodynamic data for schoepite

and for U(VI) hydroxo complexes /Bruno and Sandino 1989/ were

used, it was observed that uranium concentrations were about afactor of 10 - 30 lower than given by the solubility of schoepite

7

/Grambow 1989, Forsyth and Werme 1992/. If the constant uraniumconcentration is not due to the saturation effects of dissolving solid,other reasons could be steady state controlled by the rates of dissol-

ution and of precipitation, or steady state controlled by the solubility

of a secondary alteration product.

Under oxic conditions in groundwater, U0 2 is not thermodynamically

stable, but oxidizes to form a higher uranium oxide (e.g. U3 07 , U308 ,U03 * 2H20) or forms a secondary solid phase of uranium as analteration product, depending on the availability of oxygen or other

oxidizing agents and the composition of the water. The dissolving

solid under oxidizing conditions is essentially U307, which forms by

solid-state oxygen diffusion through the U0 2 surface. The U3 07surface will remain unstable with respect to schoepite or other U(VI)

phases if the concentration of oxidants in solution is sufficiently high

/Grambow 1989/. The U0 2/U 3 07 matrix is unlikely to achieve asolubility limit, although the alteration products do. The solubility of

uranium increases until saturation with respect to the alteration

product is reached. The mechanism of dissolution is highly depend-ent on the extent of oxidation. For very small extents of oxidation asolubility-limited dissolution model may still be applicable.

Grambow /1989/ made a comparison of calculated U solubility (EQ3)with Swedish spent fuel dissolution experiments in synthetic Allard

groundwater and deionized water under oxic conditions. He used

electrochemical arguments to predict solubility at saturation. It wassuggested that the controlling factor is the redox potential at the U0 2surface (corrosion potential) rather than the redox potential of thebulk solution (Eh). The redox potential at the surface may differsubstantially from the overall Eh in solution. The measured corrosion

potentials in the presence of dissolved 02 and in the presence of H202/Shoesmith et al 1986a/ are compared in Figure 4-2 with the resultsof thermodynamic calculations of the stability fields of various

uranium oxides and of schoepite using the SKBU database /Bruno

and Puigdomenech 1989/. Also given are the surface analysis results(XPS) of U02 electrodes at certain applied potentials.

8

10 02 600

5 ~ tnZ Schoepite5 E -U 66 (XPS U03 IXPS) 300

pe ~~~~~~~~~~~mV0.0

H2i-- 02.33(XPS)JO.2 (fue U307

-5 ~ > . -3000 2 4 6 8 10 12 14

pH

Figure 4-2. Comparison of the measured corrosion potentials of U0 2 in the presence ofdissolved °2 and in the presence of H202 with the stability fields of variousuranium oxides and schoepite iGrambow 19891.

Grambow /1989/ used three hypotheses for Eh control in his calcula-

tions:

1) The Eh was assumed to be given by the measured corrosion

potentials.2) The Eh was assumed to be given by the U30 7/U 3Og bound-

ary.

3) The Eh was assumed to be given by the U 3 07 /schoepiteboundary.

This interpretation of U saturation in solution means that no overall

thermodynamic equilibrium is reached, but steady state. True ther-

modynamic equilibrium under oxidizing conditions would require

complete conversion of U02 (U307) to a higher oxide. The best agree-ment of calculated U solubilities and measured U concentrations in

spent fuel dissolution experiments in Allard groundwater was

obtained when the above hypothesis 2) was used, see Figure 4-3.

9

0.0001

Usequ0.00001 * stat

Conc U [mol] * repi

0.000001 * LBSFA PWR

0.00000010 500 1000 1500 2000 2500

Cumulative exposure time [di

Figure 4-3. Measured uranium concentrations in spent fuel dissolution experiments inAllard groundwater versus cumulative contact time. Comparison withcalculated U solubility at the U3 07LU308 boundary at pH 8.2. Upper line:calculated for constant carbonate content, lower line: carbonate control byequilibrium with air (sequ= sequential, stat= static, repl= replenishment,LBSF= low burnup fuel) lGrambow 1989/.

In the following paragraph, the measured solubilities of U in thedissolution experiments of U02 pellets in deionized water, NaHCO3solutions and synthetic groundwaters under oxic conditions (air-saturated) are compared with the theoretical solubilities given by the

calculations using the EQ3/6 code. In the EQ3/6 simulations varioushypotheses for Eh control were tested. The redox potential wasassumed to be controlled by the oxygen partial pressure or equilibriabetween different uranium oxides:

1) the oxygen partial pressure (Po2 = 0.2 atm),

2) the U3 07/U 308 boundary or3) the U3 07 /schoepite boundary.

In the latter two EQ3/6 simulations equilibrium between differenturanium oxides fixes the oxygen partial pressure. This also deter-

mines the concentration of dissolved uranium. The redox potential ismuch lower than the redox potential calculated from the oxygenpartial pressure.

10

4.2 Comparison between experimental and calculated uranium data

The measured concentrations of uranium after the dissolution periodsof U0 2 pellets in deionized water under air-saturated conditions are

given in Figure 4-4. The cumulative contact time was 2200 days (6years). The amount of uranium increases slowly and attains a steadystate at the concentration of 3 - 5 . 104 mol/l, being one order of

magnitude higher than the concentrations measured in the dissol-ution experiments of spent fuel by Forsyth and Werme /1992/ (Fig-ure 4-1, p. 5).

10-3

0EC

a)C)0

Schoepite (SKBU)

Schoepite (COMU)

Schoepite (NEAU)

U307/U308 (NEAU, SKBU)* sample 1

10 \A sample 20 500 1000 1500

Time [days]

2000 250

Figure 4-4. Measured concentrations of uranium in deionized water after the dissolutionperiods of U02 pellets under air-saturated conditions, pH= 5.8 (batch-without-replenishment method, sample I and 2: U in micro- and ultra-filtered solutions, respectively, p. 3). The dashed lines represent the solubil-ities of schoepite (P02= 0.2 atm) and the uranium solubility at theU307/U308 boundary (EQ3/6). Equilibrium with air was assumed (see App.2).

The oxidative dissolution mechanism of U0 2 in deionized waterinvolves phase alteration, in which U0 2 alters to the particulate form

of U03 hydrate, if sufficient oxygen is available. The U03 hydratesabsorb on the surface of U0 2 or precipitate elsewhere /Shoesmith etal 1986b/. The concentration of uranium in solution is not controlled

11

by the solubility of dissolving U0 2 (U307) but by U(VI) containingsolid alteration product. The stable phase at 25 IC is schoepite,

U0 2 (OH)2 * H 20 (chemically equivalent to U0 3 - 2H20). Schoepite ora closely related compound (dehydrated schoepite, U0 3 * 0.8 H20)has been identified in long-term leaching experiments of spent fuel in

deionized water /Forsyth et al 1990, Stroes-Gascoyne et al 1986/.Schoepite was also identified, probably as a secondary phase, in the

agitated U02 powder dissolution experiments under oxic (air-satu-

rated) conditions in deionized water, in NaHCO3 solution (120 ppmHC03-) and in synthetic groundwaters (Allard groundwater,

bentonite water) /Ollila and Leino-Forsman 1993/. In those experi-

ments, the surface of the U0 2 powder was allowed to oxidize in air

prior to the start of the dissolution experiments.

The results of the solubility calculations (EQ3/6) in deionized water

are given in App. 2 and a comparison with the measured data ismade in Figure 4-4. The solubility of schoepite was calculated assum-ing the oxygen partial pressure (0.2 atm) to determine the redoxpotential. Alternatively, the Eh was assumed to be controlled by the

U3 07/U 3 08 or U 3 07 /schoepite boundary. This also determines theconcentration of dissolved uranium in solution. The redox potential

in the latter case is considerably lower than the redox potential givenby the oxygen partial pressure (see App. 2). Equilibrium with air

(Pco2= 10-35 atm) was assumed. Best agreement between the measured

data at steady state and the calculations was obtained when thesolubility of schoepite was calculated at PO2= 0.2 atm using the

COMU database. The reason for the lower solubility given by theNEAU database is the aqueous species U0 2(OH)2 (aq) in the COMUdatabase, which has not been included in the NEAU database. Thesolubility given by the SKBU database is considerably higher. Thereis a different value of the solubility product of schoepite in the SKBU

and NEAU (COMU) databases (log K= 5.6 and 4.8, respectively). Thecalculated solubility at the U307/U 308 boundary is one order of

magnitude lower than the measured concentrations at steady state.

The solubilities at the U 3 07 /schoepite boundary are equal to thesolubilities of schoepite at PO2= 0.2 atm (App. 2). The dominating

aqueous species are included in the table of App. 2.

The presence of particulate, crystalline material in deionized water at

the end of the experimental time was shown by analysing with the

12

XRD and Debye-Scherrer camera of a membrane filter after the

filtration of the water phase. It seemed to be uranium oxide with a

crystal structure of uraninite (U0 2 - U3 07 ), App. 3. Schoepite was not

observed. The small amount of material retained on filter madeanalysing difficult. A new attempt to identify the particulate material

on the filter was made with XPS. It was not possible to identify anysecondary phase. The composition of the UO2 pellet surface was,

according to the XPS determination, 100 % U(IV), App. 4.

A comparison between the measured concentrations of uranium in

NaHCO3 solution (120 ppm HCO3-) after dissolution periods of U0 2pellets under air-saturated conditions, and the calculations is given inFigure 4-5. The results for another series of experiments as a function

of bicarbonate concentration are presented in Figure 4-6. This series

was performed as batch-with-replenishment experiments, in which

10-4

13

the water was changed between the dissolution periods /Ollila andLeino-Forsman 1993/. The detailed results of the calculations are

listed in Apps. 5 - 8. The U solubilities were calculated in two differ-

ent ways:

1) measured pH: The U solubilities were calculated at the

measured pH values of the solutions at the end of the experi-

mental time.

2) theoretical pH: the U solubilities were calculated assumingthe equilibrium with air (pco2= 10 5 atm).

As can be seen from Figure 4-5, the amount of uranium in NaHCO3solution (120 ppm HCO3-) seems to attain a steady state at the solu-bility of uranium at the U3 07/U 308 boundary. The solubility ofschoepite is clearly higher (see App. 6). Only uranium oxide with a

crystal structure of uraninite (U0 2 - U3 07 ) was identified in thematerial retained on the membrane filter after the filtration of the sol-ution at the end of the dissolution experiment. The XPS determina-tion of the U0 2 pellet surface showed 100 % U(IV). There is a differ-

ence between the two databases. The solubility calculated using theNEAU database is increased by the presence of the mixed(UO2 )2(CO3)(OH)3- complex. This complex is not included in the SKBU

database.

In the series of experiments as a function of bicarbonate content,

Figure 4-6, the uranium concentrations measured after the last dissol-ution period of 900 days agree with the results for the U3 07/U 308boundary at lower carbonate concentrations (60 - 120 ppm). At highercarbonate concentrations, the measured concentrations are lower. One

explanation for this is that the solutions with high carbonate concen-

trations are not saturated. These experiments used the batch-with-replenishment method, in which successive dissolution periods were

carried out, leading to a very long cumulative experimental time. The

duration of the longest dissolution period is 900 days, and in the test

series with the carbonate content of 120 ppm using the batch-with-

out-replenishment method (Figure 4-5), the solution concentrationstill increases after the experimental time of 900 days. Unfortunately,

the batch-without-replenishment method was applied only in the test

series in NaHCO3 solution with a carbonate content of 120 ppm.

14

When comparing the measured pH values at the end of the last

dissolution periods (batch-with-replenishment method) with thetheoretical pH values at equilibrium with air, the measured values

were somewhat lower (see Apps. 5 - 8).

1 0-2 I

10-30E

C~~.~10-s/

P 1°04 i zz 9 *U series I (s 1)

8 !0 series I (s 2)10-5 A series 11 (s 1)

^ series II (s 2)I U30yU308 (NEAU)

X10-6 , l U307/U30, (SKIBU)0 100 200 300 400 500 600 700

HCO3 concentration [ppm]

Figure 4-6. Measured concentrations of uranium in NaHCO3 solution as a function ofbicarbonate content after the dissolution periods (900 days) of U02 pelletsunder air-saturated conditions (pH in Apps. 5 - 8, batch-with-replenishmentmethod, two parallel test series, s 1 and s 2: U in microfiltered and ultrafil-tered solutions, respectively 1Olila and Leino-Forsman 1993/). The dashedlines as mentioned above.

Finally, the measured concentrations of uranium in the syntheticgroundwaters after the dissolution periods of U0 2 pellets under air-

saturated conditions, together with the results of the solubility calcu-

lations are given in Figures 4-7, 4-8 and 4-9. The detailed results of

the EQ3/6 calculations are listed in Apps. 9 and 10. The calculationswere carried out in the same way as in the case of the NaHCO3solutions, using alternatively the measured pH values at the end of

the experimental time (6 years) as input data, or assuming the equi-

librium with air. The experimental data for uranium in Allard

groundwater include the results of two series of dissolution experi-

ments, both using the batch-without-replenishment method. The

difference in those series was the ratio of pellet surface area to water

volume (SA/V, see p. 3). The test series of Figure 4-8 used a ten-fold

ratio compared to the test series of Figure 4-7.

15

10-4

C

ii'4

i

_._._._._._._._._._._._._._._._. U307/U308 (COMU)

_ _ _ __ U307/U308 (SKBU)

1 -El

° 10-6

U sample 11 0-7 A sample 2

0 500 1000 1500 2000 2500

Time [days]

Measured concentrations of uranium in Allard groundwater after thedissolution periods of U02 pellets under air-saturated conditions, pH= 8.4(batch-without-replenishment method, sample I and 2: U in micro- andultrafiltered solutions, respectively, p. 3). The dashed lines represent theuranium solubilities at the U3071U 30, boundary. Equilibrium with air wasassumed.

Figure 4-7.

1 0-4 I I II

…----------- ----------- U3071U308 (COMU)

0E

0

a,C.D

00

10-5

10-6I I II

U30 7/U30, (SKBU)

U

AA

test series I (s 1)test series I (s 2)test series 11 (s 1)test series 11 (s 2)

Figure 4-8.

0 500 1000 1500 2000 2500

Time [days]

Measured concentrations of uranium in Allard groundwater after thedissolution periods of U02 pellets (tenfold SA/V ratio) under air-saturatedconditions, pH= 8.1 (two parallel test series, batch-without-replenishmentmethod, s I and 2: U in micro- and ultrafiltered solutions, respectively,p. 3). The dashed lines as mentioned above.

16

1 0-5 l l

______________. Haiweeite

E 10-6C.0 g75

0o 1 0-7_0

* sample 1

1 0-8 A , sample 20 500 1000 1500 2000 2500

Time [days]

Figure 4-9. Measured concentrations of uranium in bentonite water after the dissolutionperiods of U02 pellets under air-saturated conditions, pH= 9.0 (batch-without-replenishment method, sample 1 and 2: U in micro- and ultrafil-tered solutions, respectively, p. 3). The dashed line represents the solubilityof haiweete (PO2= 0.2 atm, SKBU database).

The amount of uranium in Allard groundwater attains a steady stateat a concentration of 1 - 2 *10-5 mol/l, being in good agreement with

the results of spent fuel dissolution experiments by Forsyth and

Werme /1992/, Figure 4-1 (p. 6). The agreement between the test

series of Figures 4-7 and 4-8 is also good. The concentration at steady

state is close to the solubility at the U307 /U3 08 boundary given bythe SKBU database. The solubility given by the COMU database is

higher due to the presence of the mixed complex, (UO2)2(CO3)(OH)3-.

The solubility of schoepite (see App. 9) is one order of magnitude

higher. The COMU data file was used for groundwaters instead of

the NEAU data file because of a wider range of minerals, includinge.g. calcite. Both Allard groundwater and bentonite water are oversa-

turated with calcite under air-saturated conditions. In bentonite

water, a steady state is attained at a concentration of one order of

magnitude lower, 1 - 10' mol/l, regardless of the high carbonate

content of the water (600 ppm). It is three orders of magnitude belowthe solubility of schoepite and the solubilities of uranium at the

U307/U 308 or U 307 /schoepite boundaries, see App. 10. This suggeststhe formation of a secondary phase with a lower solubility. The

uranyl silicates are known to be the most stable long-term phases in

17

oxidizing siliceous groundwater /Finch and Ewing 1989/. Thesolubility of one such phase, haiweeite, Ca(U02)2(Si2 05 )3 * 5 H20 hasbeen presented for comparison in Figure 4-9.

The attempts to identify possible secondary phases in the solutions atthe end of the experimental time were only partly successful becauseof the small amount of material retained on membrane filters. As indeionized water and the NaHCO3 solution (120 ppm HC0 3-), ura-nium oxide with a crystal structure of uraninite (U02 - U30 7 ) wasidentified in both synthetic groundwaters (XRD, Debye-Scherrercamera). Calcite was identified in bentonite water. The compositionof the U02 pellet surface was, according to the XPS determinations,92 % U(IV) and 8 % U(IV) after the contact with Allard groundwater,and 100 % U(JV) after the contact with bentonite water. Analysing ofthe composition of the solutions after the dissolution experimentsdoes not show any remarkable change in Allard groundwater com-pared to the situation at the beginning, App. 11. In bentonite water,App. 12, the silica (SiO 2) and calcium (magnesium) contents of thesolution are lower at the end of the experiment.

18

5 SOLUBILITY OF URANIUM UNDER ANOXIC CONDITIONS

5.1 Solubility-limiting solid phase

Under reducing conditions, i.e. in the redox regime where U(IV) is

the predominant oxidation state, U02 or U409 is the stable uraniumsolid. The dissolution reaction:

UO 2 + 4H+ -- > U9 + 2H2O

will attain equilibrium in the absence of oxidants. U4' will be hydrol-

yzed or complexed in solution. The uranium concentrations in equi-

librium are extremely low. The complex formation of uranium with

carbonate affects the relative stabilities of the oxidation states of ura-

nium. This makes U(VI) stable in more reducing conditions than inthe absence of carbonate and increases solubility. The relative

amounts of the U(VI)- carbonate complexes and the U(IV)- hydroxidecomplex depend on carbonate concentration, pH and Eh /SKI Project-90 1991/.

The solubility of U0 2 depends on the crystallinity and particle size of

the solid. In the SKBU and NEAU databases three oxides of U(IV):U0 2 (c) (uraninite), U0 2(fuel) and U0 2(am) in the order of increasingsolubility, have been included. UO2(fuel) has not been included in the

NEAU database. Uraninite corresponds to a well-crystallized solid.

The data for U0 2(am) reflects the properties of a hydrous and X-ray

amorphous solid that is obtained by precipitation in alkaline aqueous

solutions. U0 2(fuel) is an intermediate solid (particle size of 1-5 pm),

which corresponds to the average particle size of U02 in spent fuel/Puigdomenech and Bruno 1988/. In the following paragraph, the

solubilities of uranium measured under anoxic conditions (nitrogenatmosphere) in the dissolution experiments of U0 2 pellets are com-

pared with the theoretical (EQ3/6) solubilities of the U(IV) oxides.

Additionally, the solubilities of the mixed valence oxide, U4 09(UO2.25 ), were calculated. This phase is formed by diffusion of oxygeninto the U0 2 matrix /Garisto and Garisto 1985/. U409 has been found

as an oxidation product in grain boundaries in spent fuel at 140 to

225 °C /Woodley et al 1988/. The redox constraint used in the

calculations of the anoxic conditions was Eh.

19

5.2 Comparison between experimental and calculated uranium data

The results of the predissolution periods, which were carried out

prior to the start of the dissolution experiments in order to removepossible oxidized layer on the surface of the pellets, are given in theform of U dissolution rates in App. 13. The duration of the predisso-

lution with daily changing of water was ten days (see p. 3). The

amount of uranium released per day into the aqueous phase

decreased during that time period by 1 - 2 orders of magnitude.

The measured concentrations of uranium after the dissolution periodsof U0 2 pellets in deionized water, in NaHCO 3 solutions and in

synthetic groundwaters under anoxic conditions are given in Apps.14 - 20. Several parallel samplings were made in order to test theaccuracy of ICP-MS in the analysing of low contents of uranium. Thelower figures in the Apps. give the standard deviations of the filteredsamples. The uranium contents found in unfiltered and filtered

samples show some difference. This difference would seem todecrease towards the end of the experimental time in all waters butin deionized water, when steady state has been reached. Possibly the

formation of colloids or precipitates occurred. Sorption onto filtermembranes cannot be excluded. On the other hand, successivesampling with filtration using the same membrane produced small

differences in the uranium contents of the solutions.

The concentrations measured for uranium in deionized water leveloff at the solubility of 6 - 9 * 10- mol/I (App. 14, lower figure), beingbetween the theoretical solubilities of the well-crystallized solid,uraninite, U0 2 (c), and of U0 2(fuel), Figure 5-1. These concentrationsrepresent the uranium contents found in the filtered solution. Theconcentration at steady state is equal to the solubility of a mixed

valence oxide, U409(c) (UO2 .2). There are, however, some indicationsin the literature that the formation of U409 (c) at room temperaturewould be kinetically hindered /Grambow 1989/. The higher concen-

trations measured in the unfiltered solution suggest the occurrence ofprecipitation phenomena.

20

10-7- -- -. . ... .. _..-- .-- .- U02(uel) (SKBU)

10-8 sA A U4 09 (c) (SKBI)

U0 2 .2. (NEAU)

0E 10-9

__… U0 2(c) (NEAU)

10-10 U02(c) (SKBU)

10-11 l l0 100 200 300 400

Time [days]

Figure 5-1. Measured concentrations for uranium in deionized water after the dissol-ution periods of U0 2 pellets under anoxic conditions. The dashed lines givethe calculated (EQ316) solubilities of uranium oxides (pH= 7.0).

The steady-state concentrations obtained for uranium in NaHCO3 sol-

utions as a function of HC03 content vary 2 - 4 * 10' mol/l, Apps. 15- 18 (lower figures). Under strongly reducing conditions, the car-

bonate content should not have an effect on the solubility of uranium,

the neutral hydroxide complex of U(IV), U(OH)4 , being the dominat-

ing species. The effect of the carbonate complexation of U(VI)increases solubility under mildly reducing conditions, especially at

high carbonate concentrations. There is only a minor increase in the

solubility of uranium as a function of carbonate content under the

studied experimental conditions. The measured concentrations at

steady state are again at the level of U409 (c) (UO2.2) solubility given

by the NEAU database, see Figure 5-2. The solubilities were calcu-lated at the pH value measured at the end of the experimental time,

which was identical for all NaHCO3 solutions (9.1).

The CO2 content in the atmosphere of the anaerobic box is notknown. It is low, below the detection limit of the analyzer (Fuji

electric infrared gas analyzer). In order to study the stability of the

carbonate content in the solutions under N2 atmosphere, the contentsof the HC03- and C032 -ions were measured using the standard

21

method (SFS 3005) for the determination of the alkalinity in water.

The titrations were carried out for the solutions (without pellets) after

two months' equilibration, and for the solutions (with pellets) after

one year's experimental time. All the titrations were made under N2atmosphere in the box. The results of the analyses show that there isonly a small decrease in the contents of the HCO3 and C032 - in the

NaHCO3 solutions over one-year experimental time, see App. 21. The

experimental vessels were tightly closed between the samplings.

1 0-71 - - - - - -- U02(fuel) (SKBU)

% 7- -i < -z _U0 2 -25 (NEAU)

1 0-8..U 40,(c) (SKBU)

E 10-9_ _ … U02(c) (NEAU)

10-10 U0 2(c) (SKBU)

0 NaHCO3 -60

1 0-1 ____________________________________ _ A NaHCO 3-1200 100 200 300 400 500 600 700 ° NaHCO3-275

SoNaHC0,3-6600Time [days]

Figure 5-2. Measured concentrations for uranium in NaHCO3 solutions after thedissolution periods of U02 pellets under anoxic conditions. The dashed linesgive the calculated (EQ3/6) solubilities of uranium oxides (pH= 9.1, Eh=-0.3 V).

Finally, the measured concentrations of uranium after the dissolution

periods of U02 pellets in synthetic groundwaters under anoxic

conditions are shown in Apps. 19 - 20. Comparison of the measured

data with the calculated solubilities, Figure 5-3, shows that the

measured data at steady state in groundwaters (2 - 3 10' mol/1)

seem to be equal to the solubility of U4 09 (C) (U02 .25) given the NEAUdatabase (Eh= -0.3 V), which was also the case in the other solutions.

The solubilities were calculated using the measured ph values (see

22

Figure 5-3) at the end of the experimental time. There is only a little

increase in the solubility in bentonite water, regardless of the high

carbonate content (see also App. 21).

1 0 -7 I I I I I I0-7. ..... _ _. ...... .. _.. . - U0 2(fuel) (SKBU)

lo-8 -yQ---o--g--- U0 225 (NEAU)10-8

. S- ---------------------.................. U40 9 (c) (SKBU)

E 10-9

… _ _ _ U02(c) (NEA)

1 -10' __…U0 2(c) (SKBU)

A Allard groundwater10-1 0O Bentonite water

0 100 200 300 400 500 600 700

Time [days)

Figure 5-3. Measured concentrations for uranium in synthetic groundwaters after thedissolution periods of U02 pellets under anoxic conditions. The dashed linesgive the calculated (EQ3/6) solubilities of uranium oxides (Allard ground-water: pH= 9.0, bentonite water: pH= 8.9, Eh= -0.3 V).

An attempt to investigate the speciation of uranium in aqueous phase

was made by determining the oxidation state of uranium in thesolutions after the contact with the pellets at the end of the experi-

mental time. The method included the separation of the hexavalentand tetravalent states by anion exchange in HCl medium and the

analyses of the uranium contents of each fraction by ICP-MS. The

sample solution in 4.5 M HCI was added to a chromatographiccolumn filled with anionic resin. Under these conditions U(VI) is

fixed at 95 - 100 %, while U(IV) flows through the column. Then theU(VI) was recovered by elution with 0.1 M HCI. The detailed analy-

ses and development of the method for our experimental conditions

are reported in ref /Ollila et al 1995/. The results of the analyses

show that uranium was mainly at the U(VI) state (91 - 99 %), App.

22.

23

6 CONCLUSIONS

The solubility behaviour of unirradiated U0 2 pellets was studied as

a function of water composition under oxic (air-saturated) and anoxic

(N) conditions at 25 'C. The waters included deionized water as

reference water, sodium bicarbonate solutions with varying bicarbon-ate content, Allard groundwater representing granitic fresh ground-

water conditions, and bentonite water simulating the effects of

bentonite on fresh granitic groundwater. The experimental methodwas a static batch dissolution procedure. Comparison was made with

the theoretical solubility data (EQ3/6, the SKBU, NEAU and COMUdatabases) in order to evaluate solubility (steady state) limiting

factors.

In the EQ3/6 calculations, various hypotheses for redox control weretested under oxic conditions. The controlling factor was assumed to

be given by the redox potential of the bulk solution (oxygen partial

pressure, Po2= 0.2 atm), or the redox potential at the U0 2 surface (the

U3 07 /U3 08 or U 3 07 /schoepite boundaries). In the latter case, the

redox constraint also determines the concentration of uranium in sol-ution. The measured data at steady state in deionized water is equal

to the solubility of schoepite at P0 2= 0.2 atm given by the calcula-tions (the COMU database). In sodium bicarbonate solutions, the

solution concentration of uranium is close to the calculated uranium

solubilities at the U307/U 3 0 8 boundary at lower carbonate concentra-

tions (60 - 120 ppm). This is also the case also in Allard groundwater.In bentonite water, the results suggest a different solubility control,

e.g. the formation of a secondary phase with a lower solubility. Themeasured concentrations of uranium at steady state in bentonitewater were three orders of magnitude below the solubility of schoe-

pite or the solubility at the U307 /U3 08 boundary. Schoepite wasassumed to limit the solubilities of uranium in the TVO-92 safety

assessment /Vieno et al 1992/. The identification of the possiblesolubility-limiting secondary phases of uranium was made difficult

by the small amount of particulate material collected from the sol-

utions. Only uranium oxide with a crystal structure of uraninite (UO2

- U307) was identified in all the waters.

Under anoxic conditions, the measured concentrations at steady state

are at the level of U4 09 (UO2 2 .) solubilities, being clearly higher than

24

the solubilities of well-crystallized uraninite and below the solubilities

of U0 2(fuel). The water composition had a minor effect on the sol-ution concentration of uranium. Additional solubility experiments, in

which solution equilibrium is approached from oversaturation, areneeded to confirm the solubility-limniting phases.

7 ACKNOWLEDGEMENTS

Teollisuuden Voima Oy is gratefully acknowledged for financial

support. The author takes pleasure in thanking Ms. R. Zilliacus andDr. R. Rosenberg (VTT Chemical Technology, Molecular structure

and Chemical Analytics) for performing the ICP-MS analyses and Mr.

K. Lindqvist (Geological Survey of Finland) for performing the XRDanalyses. The author wishes to thank Dr. Joan de Pablo and Dr. E.

Torrero (Universitat Politecnica de Catalunya) for the XPS analyses.The contribution of K. Helosuo also deserves acknowledgement.Thanks are also due to Dr. M. Olin for helping with the EQ3/6modelling.

25

8 REFERENCES

Allard B., Larson S.A., Albinsson Y., Tullborg E.L., Karlsson M.,

Andersson K. and Torstenfelt B. (1981), Minerals and precipitates infractures and their effects on the retention of radionuclides in crystal-

line rocks, in: Near-Field Phenomena in Geologic Repositories for

Radioactive Waste, Seattle, 1981, pp. 93 - 101.

Bruno J., Forsyth R.S. and Werme L.O. (1984), Spent U0 2-fuel dissol-ution. Tentative modelling of experimental apparent solubilities, in:

Scientific Basis for Nuclear Waste Management VIII (eds. C.M. Jant-

zen, J.A. Stone and R.C. Ewing), Mat. Res. Soc. Symp. Proc., 1984, pp.

413 - 420.

Bruno J. and Sandino A. (1989), The solubility of amorphous and

crystalline schoepite in neutral to alkaline aqueous solutions, in:Scientific Basis for Nuclear Waste Management XII (eds. W. Lutze

and R.C. Ewing), Mat. Res. Soc. Symp. Proc., 1989, pp. 871 - 878.

Daveler S. and Bourcier B. (1989a), EQ3NR - Input file user's guide,Lawrence Livermore National Laboratory, University of California,Livermore, California, 1989.

Daveler S. and Bourcier B. (1989b), EQ6 - Input file user's guide,

Lawrence Livermore National Laboratory, University of California,Livermore, California, 1989.

Finch R.J. and Ewing R.C. (1989), Alteration of natural U0 2 underoxidizing conditions from Shinkolobwe, Katanga, Zaire: A naturalanalogue for the corrosion of spent fuel, SKB Technical Report 89-37,

Stockholm, Sweden, 1989.

Forsyth R.S., Eklund U-B., Mattsson 0. and Schrire D. (1990), Examin-

ation of the surface deposit on an irradiated PWR fuel specimensubjected to corrosion in deionized water, SKB Technical Report 90-

04, Stockholm, Sweden, 1990.

Forsyth R.S. and Werme L.O. (1992), Spent fuel corrosion and dissol-

ution, Journal of Nuclear Materials 190 (1992), pp. 3 - 19.

26

Garisto F. and Garisto N.C. (1985), A U02 solubility function for the

assessment of used nuclear fuel disposal, Nucl. Science and Engineer-

ing 90 (1985), pp. 103 - 110.

Grambow B. (1989), Spent fuel dissolution and oxidation. An evalu-ation of literature data, SKB Technical Report 89-13, Stockholm,

Sweden, 1989.

Grenthe I., Fuger J., Konings R.J.M., Lemire R.J., Muller A.B., Ngu-

yen-Trung Cregu C. and Wanner H. (1992), Chemical thermody-

namics of uranium, Nuclear Energy Agency, 1992, 715 p.

Helgeson H.C., Carrels R.M. and Mackenzie F.T. (1969), Evaluation of

irreversible reactions in geochemical processes involving minerals and

aqueous solutions - II. Applications, Geochim. Cosmochim. Acta 33

(1969), pp. 455 - 481.

Hussonnois M., Guillaumont R., Brillard L. and Fattahi M. (1989), Amethod for determining the oxidation state of uranium at concentra-tion as low as 1010 M, in: Scientific Basis for Nuclear Waste Manage-

ment XII (eds. W. Lutze and R.C. Ewing), Mat. Res. Soc. Symp. Proc.,1989, pp. 979 - 985.

Ollila K., Helosuo K. and Lipponen M. (1995), Testing of a method

for determining the oxidation state of uranium in solution underanoxic (N2) conditions, to be published in the YJT-series of Nuclear

Waste Commission of Finnish Power Companies 1995.

Ollila K. and Leino-Forsman H. (1993), The dissolution of unirra-

diated U0 2 fuel pellets under simulated disposal conditions, Report

YJT-93-04, Helsinki, Finland, 1993.

Puigdomenech I. and Bruno J. (1988), Modelling uranium solubilities

in aqueous solutions: Validation of a thermodynamic data base forthe EQ3/6 geochemical codes, SKB Technical Report 88-21, Stock-

holm, Sweden, 1988.

Shoesmith D.W., Sunder S., Johnson L.H. and Bailey M.G. (1986a),Oxidation of CANDU U0 2 fuel by the alpha-radiolysis products of

water, in: Scientific Basis for Nuclear Waste Management IX (ed. L.O.

27

Werme), Mat. Res. Soc. Symp. Proc., 1986, pp. 309 - 316.

Shoesmith D.W., Sunder S., Bailey M.G. and Wallace G.J. (1986b),Mechanism of oxidation and dissolution of CANDU fuel oxidation,in: 2nd International Conference on Radioactive Waste Management,

Conf. Proc., Canadian Nuclear Society, 1986, pp. 674 - 679.

SKI Project-90 (1991), Swedish Nuclear Power Inspectorate, SKI TR

91:23, Stockholm, Sweden, 1991.

Snellman M. (1986), Chemical conditions in a repository - experimen-tal and modelling studies, in: Third Finnish - German Seminar on

Nuclear Waste Management, 1986, pp. 146 - 168.

Stroes-Gascoyne S., Johnson L.H., Beeley P.A. and Sellinger D.M.

(1986), Dissolution of used Candu fuel at various temperatures andredox conditions, in: Scientific Basis for Nuclear Waste Management

IX (ed. L.O. Werme), Mat. Res. Soc. Symp. Proc., 1986, pp. 317 - 326.

Vieno T., Hautojdrvi A., Koskinen L. and Nordman H. (1992), TVO-92

Safety analysis of spent fuel disposal, Report YJT-92-33 E, Helsinki,Finland, 1992.

Wolery T.J. and Daveler S.A. (1989), A computer program for reactionpath modeling of aqueous geochemical systems: User's guide and

documentation, Lawrence Livermore National Laboratory, Universityof California, Livermore, California, 1989.

Wolery T.J. (1992), EQ3NR, a computer program for geochemicalaqueous speciation-solubility calculations: Theoretical manual, user's

guide, and related documentation (version 7.0), 1992.

Wolery T.J. and Daveler S.A. (1992), EQ6, a computer program for

reaction path modeling of aqueous geochemical systems: Theoretical

manual, user's guide, and related documentation (version 7.0), 1992.

Woodley R.E., Einziger R.E. and Buchanan H.C. (1988), Measurement

of the oxidation of spent fuel between 140 and 225 'C by thermogra-

vimetric analysis, Westinghouse Hanford Company, WHC-EP-0107,

1988.

App. 1

Composition of the synthetic groundwaters, mmoll (mg/I).

HCOj

so42 -

Cl-

HP0 42-

Si4 ,

K+

Na'ca2.

Mg2 -

(Fe,0,)

Ionic strength

PHoiX ()

PHanoxic (**)

synthetic graniticgroundwater

(Allard et al [1])

2.01 (123)

0.10 (9.6)

1.97 (70)

0.13 (3.7)

0.10 (3.9)

2.28 (52)

0.45 (18)

0.18 (4.3)

0.005 (0.3)

0.005

8.20

8.71

synthetic bentonitewater

(Snellman [2])

9.83 (600)

0.62 (59.6)

2.26 (80)

0.40 (7.5)

0.0042 (0.4)

0.27 (7.5)

0.10 (3.9)

11.8 (272)

0.45 (18)

0.18 (4.3)

0.005 (0.3)

0.014

8.42

8.77

Composition of the NaHCO3 solutions, mmolll (mg/I).

NaHCO3 -60 NaHCO3 -120 NaHCO 3-275 NaHCO3-600

HCO; 0.98 (60) 1.97 (120) 4.51 (275) 9.83 (600)

Na 0.98 (23) 1.97 (45) 4.51 (104) 9.83 (226)

(Fe,.,) 0.005 (0.3)

C- 0.011 (0.4)

pH..i,(*) 7.80 8.10 8.30 8.40

PHanoxic(**) 8.80 8.85 8.87 8.87

(Feto0 )(*)(**)

ferrous chloride was added to solutions under oxic conditionspH measured for fresh solutions under oxic conditionspH measured for fresh solutions under anoxic conditions (N2 atmosphere)

EQ3/6 calculationsuranium - deionized water

Thermodynamic U and redox U solubility (moltl) Dominantdatabase controls measured pH= 5.8* species (> 5%)

NEAU schoepite 1.54 10-6 U0 2(OH)-,P02= 0.2 atm (pH= 5.8/Eh= 0.875 V)** (UO2)3(OH)5+,

U022 ,

(UO 2 )2 (CO 3 )(OH)3-

SKBU 1.34 . 104 (UO2)3 (OH)5+,(pH= 5.8/Eh= 0.875 V) (UO2)4(OH)7 '

COMU 4.77- 104 U0 2(OH)2(aq),(pH= 5.8/Eh= 0.875 V) UO2OH+,

(UO 2 )3(OH)5'

NEAU U3 07/U 30 8 - 2.32 * 10-7 U0 2(OH)Y,equilibrium (pH= 5.8/Eh= 0.220 V) UOJ22+

SKBU 2.16. 10-7 UO2(OH),(pH= 5.8/Eh= 0.230 V) UO22,, U0 2(OH)2

NEAU U307 /schoepite - 1.54 . 106 U0 2OH', UO2 2 ,equilibrium (pH= 5.8/Eh= 0.252 V) (UO2)3(OH)5 ,

(UO 2 )2 CO 3 (OH) 3

SKBU 1.34 . 10-4 (UO2 )3(OH)5+(pH= 5.8/Eh= 0.290 V) (UO2)4(OH) 7+

* measured pH: pH measured for the solution at the end of the experimental time** pH and Eh at equilibrium with uranium phase

k)

lq~qmnlp identification: PAPFPT 25-Nov-1994 8 28I�Thmn1 � iH�nfuification: PAPERI 25-Nov-1994 8 28[counts]3

2 5c 0 0

1 600 -

900 I

400 l

I 0 0 - ' ' I ,#b

1 00195 8.5 5.5 4'.0 3',0 25 2.0 1.5[]

PAPERT RD ;1ThAYt. ai

App. 4

50000 -

40000

q 30000

CUCbC 200000C.)

10000 -

0-

Data:Pellet 5Model: GaussChiA2 = 7.9937E5yO 0xcI 380.6 0.135WI 1.940 0.0181Al 1.075E5 1.4E4xc2 382.0 0.298w2 2.379 0.541A2 2.754E4 1.36E4

U-peak

20% U(VI) 80% U(NV)

384 386I , I * I . I

376 378 380 382

Binding Energy (eV)

40000- U-peak

30000 -

-20000--.6C

0O 10000-

374 376

Data: pellet 1Model: GaussChl^2 = 1.9032E6yO 0xci 380.2 0.0206WI 2.124 0.0293Al 1.063E5 1.06E3

100% U(IV)

I I I

378 380 382

Binding Energy (eV)384 386

X-ray photoelectron spectroscopy detennination of U02 pellet surface before (upper figure) andafter the contact with deionized water under oxic, air-saturated conditions, pH= 5.8 (lowerfigure).

EQ3/6 calculationsuranium - NaHCO. (60 ppm HCO)

Thermodynamic U and redox U solubility (mol/l) Dominantdatabase controls species (> 5%)

measured pH= 7.8* theoretical pH (pCO2 = 10-3i5 atm)

NEAU schoepite 6.69 10W 7.18 * 10r (UO2 )2C0 3(OH)3;po2= 0.2 atm (pH= 7.8/Eh= 0.755 V)** (pH= 8.27/Eh= 0.730 V)** U02(CO3)22;1

UO2 (CO3)3 4

SKBU 3.80. 10W 4.54 * 10 U0 2(CO3)22(pH= 7.8/Eh= 0.755 V) (pH= 8.24/Eh= 0.730 V) UO2(CO3)34

NEAU U307/U 30 8 - 7.04 * 104 8.62 - 104 U0 2(CO3)22-,

equilibrium (pH= 7.8/Eh= 0.105 V) (pH= 8.30/Eh= 0.075 V) (UO2)2Co3(OH)3-,UO 2 (CO3 )34-

SKBU 1.68 * 104 2.31 * 104 U0 2(CO3)22-,

(pH= 7.8/Eh= 0.110 V) (pH= 8.29/Eh= 0.080 V) UO2(CO3)34

NEAU U3 07 /schoepite- 6.69 . 104 7.18 . 10- (UO2)2 CO3(OH)3-,equilibrium (pH= 7.8/Eh= 0.135 V) (pH= 8.27/Eh= 0.105 V) U0 2(CO3)22-

________________________________ U 02 (C O3)34-

SKBU 3.80 - 10- 4.54* 1W0 U0 2(CO3)22;(pH= 7.8/Eh= 0.170 V) (pH= 8.24/Eh= 0.145 V) UO2(CO3)34

* measured pH: pH measured for the solutions after the last dissolution period (900 days)** pH and Eh at equilibrium with uranium phase

(J1

EQ3/6 calculationsuranium - NaHCO. (120 ppm HCOJ

Thermodynamic U and redox U solubility (mol/l) Dominantdatabase controls species (> 5%)

measured pH= 8.2* theoretical pH (pCO2 = lo" atm)

NEAU schoepite 1.86 . 104 2.11 . 104 (UO2)2CO3(OH)3-;P02= 0.2 atm (pH= 8.2/Eh= 0.735 V)** (pH= 8.51/Eh= 0.715 V)** U0 2(CO3)34-,

U0 2 (C03 )2 2-

SKBU 1.80. 0 2.10 *104(pH= 8.2/Eh= 0.735 V) (pH= 8.44/Eh= 0.720 V) U0 2(CO3)22-

NEAU U307/U308 - 3.35 * 10-5 4.94 - 10-5 U0 2(CO3)3 ,equilibrium (pH= 8.2/Eh= 0.080 V) (pH= 8.57/Eh= 0.060 V) U02(CO )22,

._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ (U O2 )2 Co 3 (O H )3-

SKBU 1.23 *10-5 2.04 * 10-5 U0 2(CO3)34-,(pH= 8.2/Eh= 0.085 V) (pH= 8.57/Eh= 0.065 V) U0 2(CO3)22

NEAU U30 7/schoepite - 1.86 .104 2.11 104 (UO2)2CO3(OH)3-;equilibrium (pH= 8.2/Eh= 0.145 V) (pH= 8.51/Eh= 0.090 V) UO2(CO3)3$,

U02(C03 )22-

SKBU 1.80 *104 2.10 *104 U0 2 (CO3 )34,(pH= 8.2/Eh= 0.145 V) (pH= 8.44/Eh= 0.135 V) U0 2(CO3 )22-

* measured pH: pH measured for the solutions after the last dissolution period (900 days)** pH and Eh at equilibrium with uranium phase :>

EQ3/6 calculationsuranium - NaHCO, (275 ppm HCO3)

Thermodynamic U and redox U solubility (moVI) Dominantdatabase controls species (> 5%)

measured pH= 8.5* theoretical pH (pCO2= lo`'5 atm)

NEAU schoepite 7.99 *104 8.51 . 104 U0 2(CO3)341 ,Po2= 0.2 atm (pH= 8.5/Eh= 0.716 V)*** (pH= 8.66/Eh= 0.705 V)** U02(CO3)22 ,

(UO 2 )2C0 3 (OH)3 -

SKBU 8.90 - 104 9.09 . 104 U0 2(CO3)34-,(pH= 8.5/Eh= 0.716 V) (pH= 8.56/Eh= 0.710 V) U02(CO3)22-

NEAU U3 07/U 30 8 - 3.46 . 104 4.62 . 104 U0 2(CO3)34 ,equilibrium (pH= 8.5/Eh= 0.064 V) (pH= 8.79/Eh= 0.050 V) U02(CO3)22-

SKBU 1.90 _ 104 2.98 .104 UO 2(CO3)34,(pH= 8.5/Eh= 0.068 V) (pH= 8.83/Eh= 0.050 V) U0 2(CO3)22-

NEAU U3 07/schoepite- 7.99 *104 8.51 *104 UO 2(CO3)34,equilibrium (pH= 8.5/Eh= 0.092 V) (pH= 8.66/Eh= 0.080 V) (UO2)2CO3(OH)3 ,

U0 2 (C03 )2 2-

SKBU 8.90 * 104 9.09 *104 UO2(CO3)34,(pH= 8.5/Eh= 0.131 V) (pH= 8.56/Eh= 0.125 V) U0 2(CO3)22

* measured pH: pH measured for the solutions after the last dissolution period (900 days)** pH and Eh at equilibrium with uranium phase 3>

N1CI

EQ3/6 calculationsuranium - NaHCO. (600 ppm HCOJ

Thermodynamic U and redox U solubility (molIl) Dominantdatabase controls species (> 5%)

measured pH= 8.8* theoretical pH (pCO2= 10-3'i atm)

NEAU schoepite 2.56 * 10-3 2.53 *10-3 U02(CO3)34-,P02= 0.2 atm (pH= 8.8/Eh= 0.700 V)*** (pH= 8.71/Eh= 0.705 V)** (UO2)2CO3(OH)3-,

UO2(CO3)22-

SKBU 2.69 . 10-3 2.61 _ 10-3 UO2(CO3)34,(pH= 8.8/Eh= 0.700 V) (pH= 8.59/Eh= 0.710 V) U02(CO3) 22 -

NEAU U30 7/U 30 8 - 1.94. 10-3 1.98 _ 10-3 UO2(CO3)34equilibrium (pH= 8.8/Eh= 0.050 V) (pH= 8.86/Eh= 0.045 V)

SKBU 1.56 10-3 1.66 . 10-3 UO2(CO3)34(pH= 8.8/Eh= 0.050 V) (pH= 8.92/Eh= 0.045 V)

NEAU U307/schoepite- 2.56 10-3 2.534 *0- U0 2(C03)3tequilibrium (pH= 8.8/Eh= 0.075 V) (pH= 8.71/Eh= 0.080 V) (UO2)2CO3(OH)3-,

U0 2 (CO 3 ) 22

SKBU 2.69 . 10-3 2.61 10- UO2(CO3)31,(pH= 8.8/Eh= 0.115) (pH= 8.59/Eh= 0.125 V) U02(CO3)

* measured pH: pH measured for the solutions after the last dissolution period (900 days)** pH and Eh at equilibrium with uranium phase

EQ3/6 calculationsuranium - Allard groundwater

Thermodynamic U and redox U solubility (mol/1) Dominantdatabase controls species (> 5%)

measured pH= 8.4* theoretical pH (pCO2 = 10'3 atm)

COMU schoepite 2.06- 104 2.17 - 104 (UO2)2CO3(OH)3-;P02= 0.2 atm (pH= 8.4/Eh= 0.725 V)** (pH= 8.48/Eh= 0.715 V)** UO2(CO3)3,

U02(C03)22-

SKBU 2.23 . 104 2.31 - 104 UO2(CO3)34,(pH= 8.4/Eh= 0.725 V) (pH= 8.42/Eh= 0.720 V) U0 2(CO3)22

COMU U307/U3 08 - 4.35 * 10-5 5.31 1-5 UO2(CO3)3'-,equilibrium (pH= 8.4/Eh= 0.070 V) (pH= 8.54/Eh= 0.060 V) U0 2(CO3)2 ,

(UO 2 )2 Co 3 (OH)3'

SKBU 1.90* 10-5 2.55 . 10-5 UO2(CO3)34,(pH= 8.4/Eh= 0.075 V) (pH= 8.56/Eh= 0.065 V) U02 (CO3)22

COMU U307/schoepite- 2.06 10-4 2.17. 104 U0 2(CO3)34-1equilibrium (pH= 8.4/Eh= 0.100 V) (pH= 8.48/Eh= 0.090 V) (UO2)2CO3(OH)3-;

U0 2 (C03 )22SKBU 2.23 * 104 2.31 . 104 UO2(CO 3)3 ,

(pH= 8.4/Eh= 0.140) (pH= 8.42/Eh= 0.135 V) U0 2(CO3)22

* measured pH: pH measured for the solution at the end of the experimental time** pH and Eh at equilibrium with uranium phase

EQ3/6 calculationsuranium - bentonite water

Thermodynamic U and redox U solubility (mol/l) Dominantdatabase controls species (> 5%)

measured pH= 9.0* theoretical pH (pCO2= 10i' atm)

COMU schoepite 2.62 -10- 2.49 * 10-3 U0 2(CO3)3tP02= 0.2 atm (pH= 9.0/Eh= 0.685 V)** (pH= 8.69/Eh= 0.705 V)** (UO2)2CO3(OH)3-,

I_____________________ U0 2 (C03 )2 2 -

SKBU 2.77- 10-3 2.63 * 10-3 U0 2(CO3)34-(pH= 9.0/Eh= 0.685 V) (pH= 8.57/Eh= 0.710 V)

COMU U307/U308 - 2.07- 10-3 1.94 - 10-3 U0 2(CO3)341equilibrium (pH= 9.0/Eh= 0.030 V) (pH= 8.83/Eh= 0.045 V)

SKBU 1.79 .10-3 1.70 - 10-3 U0 2(CO3)34-(pH= 9.0/Eh= 0.035 V) (pH= 8.90/Eh= 0.045 V)

COMU U307 /schoepite- 2.62 * 10-3 2.49 . 10-3 UO2(CO3)34,equilibrium (pH= 9.0/Eh= 0.060 V) (pH= 8.69/Eh= 0.080 V) U02(CO3)2 ,

(UO 2 )2 CO 3 (OH)3-

SKBU 2.77- 10-3 2.63 . 10-3 U02(CO3)(pH= 9.0/Eh= 0.100) (pH= 8.57/Eh= 0.125 V) U0 2(CO3 )22

* measured pH: pH measured for the solution at the end of the experimental time** pH and Eh at equilibrium with uranium phase

V10

App. 1 1

The composition of Allard groundwater before (I) and after (II) the contact with UO2pellets under oxic (air-saturated) conditions (figure 4-7, p. 15). The anionic andcationic analyses were carried out by ion chromatography.

|__________ [ (before)Ion concentrations (ppm)I (before) | I (after)

unfiltered microfiltered ultraf iltered(0.45 pm) (- 3-4 nm)

pH 8.20 8.36 8.28

HCO3- 122.9 122.1 124.2

C032- 4.0 3.3

SiO2 8.0 8.7 8.5

Na 52.4 55.0 55.3

K 3.9 5.3 5.6

Ca 17.9 18.4 17.3

Mg 4.3 3.3 3.5

Cl 70 58A 59.6

S0 4 9.6 8.4 74

U (ICP-MS) 3.250 3.000 3.210

App.12

The composition of bentonite water before (I) and after (II) the contact with U0 2pellets under oxic (air-saturated) conditions (figure 4-9, p. 16). The anionic andcationic analyses were carried out by ion chromatography.

I (before) Ion concentrations (ppm)

| I (before) _II (after)

unfiltered microfiltered ultrafiltered(0.45 pm) 3-4 nm)

pH 8A2 9.03 9.00

HCo3- 600 500.7 491.6

CO32 28.1 26.0

SiO2 16 5.3 3.5

Na 271.5 280.3 282.7

K 3.9 4.8 4.7

Ca 17.9 2.0 2.2

Mg 4.3 2.9 2.9

Cl 80 72A 72.7

S04 59.6 61.7 61.6

U (ICP-MS) 0.190 0.185 0.195

App. 13

10-4 . l

-b

E

,o

.:5

*+[- I

I I

Deionized water

**

10-4

1 0-5 -

('4

E-5E0)

CU

0

-oS

10-5

IXN ' ' 0 * HCO 3 - 600 * HCO3- 12C

A HCO 3 - 275V HCO 3 - 60C

IA v

A

I I I I I

I

10-6 II .- .

0 2 4 6 8 10 1210-6

0 2 4 6 8 10 12

Time [days]

10-4

Time [days]

-bC,

-5E

10-5

10-6

0 2 4 6 8 10 12

Time [days]

Dissolution rates of uranium from U02 pellets during the predissolution periods under anoxicconditions. The rates were calculated per the geometric surface area of the pellet.

App. 14

14

12-

10 _

8~~~~~~C-

6 IA 8 sample 1

4 AA * A A sample 2

o ~~~0 sample 32 i sample 4

0 A sample 50 100 200 300 400

Time [days]

2x108-Deionized water

1xI104- _

0ED 10-8

A,

5x1 0-9

+~~~~~~~ I

0 100 200 300 400

Time [days]

Uranium concentration (anoxic conditions) in deionized water versus contact time. The upperfigure gives the measured contents in the unfiltered 11 and 21 and filtered f3, 4 and 5;

microfiltration (0.45 ym pore size) up to 150 days, ultrafiltration (- 3-4 nm pore size) after 150days) samples. The lower figure gives the average concentrations and standard deviations of thefiltered samples.

App. 15

14

12

10

060Q

0A

0

A

sample 1

sample 2

sample 3

sample 4

sample 500 100 200 300 400 500 600 700

Time [days]

5.Oxl 0-8

4.5x1 0-8

4.Oxl 0-8

3.5x1 0-

3.Oxl 0-8

2.5xl 0-8

0E

2.Oxl 0-8

1.5x 10-8

10-8

5.Oxl o-90 100 200 300 400 500 600 700

Time [days]

Uranium concentration (anoxic conditions) in NaHCO3 solution, IHCO3-J= 60 ppm, versuscontact time. The upper figure gives the measured contents in the unfiltered 11 and 2] andfiltered 13, 4 and 5; microfiltration (0.45 jum pore size) up to 150 days, ultrafiltration (- 3-4nm pore size) after 150 days] samples. The lower figure gives the average concentrations andstandard deviations of the filtered samples.

App. 16

14

12

10

0.C.

0A

0

A

sample I

sample 2

sample 3

sample 4

sample 5

0 100 200 300 400 500 600 700

Time [days]

5.Ox1 0-8

4.5x1 04

4.0x10-8

3.5x1 0-8

0E

3.Ox1 0-

2.5x1 0-8

2.Oxl 0-8

1.5x`10-8

10-8

5.Oxl o-90 100 200 300 400 500 600 700

Time [days]

Uranium concentration (anoxic conditions) in NaHCO3 solution, [HCO3jl= 120 ppm, versuscontact time. The upper figure gives the measured contents in the unfiltered [1 and 21 andfiltered (3, 4 and 5; microfiltration (0.45 Itm pore size) up to 150 days, ultrafiltration (- 3-4nm pore size) after 150 days] samples. The lower figure gives the average concentrations andstandard deviations of the filtered samples.

App. 17

14

12

10

a.a-Q)

8

6

4

0A

0

0

A

sample 1

sample 2

sample 3

sample 4

sample 500 100 200 300 400 500 600 700

Time [days]

5.Ox1 o

4.5x1 0-8

4.Ox1 0-8

3.5x1 0-Q

-- 3.Ox1O-8

2.5x1 0-a

2.Ox1 0

1.5x10-8

5.0x10-

0 100 200 300 400 500 600 700

Time [days]

Uranium concentration (anoxic conditions) in NaHCO3 solution, [HCOj31= 275 ppm, versuscontact time. The upper figure gives the measured contents in the unfiltered [1 and 21 andfiltered [3, 4 and 5; microfiltration (0.45 jim pore size) up to 150 days, ultrafiltration (- 3-4nm pore size) after 150 days] samples. The lower figure gives the average concentrations andstandard deviations of the filtered samples.

App. 18

14

12

10

0.0.

8

6

4

2

0

5.0x1 0-8

4.5x1 0-8

0

A

0

C

A

sample 1

sample 2

sample 3

sample 4

sample 5

0 100 200 300 400 500 600 700

Time [days]

4.0x10-8I

3.5x104 1

02

3.Ox1O-8 I

I I I f I I

NaHCO 3 (600 ppm HC03)

~/Iv :

t_ I I I I I I

2.5x1 0-8

2.0x10-8

1.5x10-8

10-8

5.0x1 0-9() 100 200 300 400 500 600 700

Time [days]

Uranium concentration (anoxic conditions) in NaHCO3 solution, IHCO3-I= 600 ppm, versuscontact time. The upper figure gives the measured contents in the unfiltered O and 2] andfiltered [3, 4 and 5; microfiltration (0.45 ,ym pore size) up to 150 days, ultrafiltration (- 3-4nm pore size) after 150 days] samples. The lower figure gives the average concentrations andstandard deviations of the filtered samples.

App. 19

8

6

F0.0C 4

2

0

3.Ox1 0-8

2.5x 1 0-

2. Ox 1 0-8

1.5x1 0-8

10-9

5.0x1 0 9

0

A

0

A

sample 1

sample 2

sample 3

sample 4

sample 5

0 100 200 300 400 500 600 700

Time [days]

cE

0 100 200 300 400 500 600 700

Time [days]

Uranium concentration (anoxic conditions) in Allard groundwater versus contact time. Theupper figure gives the measured contents in the unfiltered IN and 21 and filtered [3, 4 and 5;microfiltration (0.45 Am pore size) up to 150 days, ultrafiltration (- 3-4 nm pore size) after 150days) samples. The lower figure gives the average concentrations and standard deviations of thefiltered samples.

App. 20

10

8

60F0L~Q

4

2

10

4.Ox1 04

3.5x1 0-8

3.Ox1 0-8

A

0

0A

A

sample 1

sample 2

sample 3

sample 4

sample 50 100 200 300 400 500 600 700

Time [days]

2.5x1 04 I0

E

I I I I I IBentonite water

I - I I I I I I

2.Ox1 0-8

1.5x10-8 I

1 0-8

5.0x10-9

0 100 200 300 400 500 600 700

Time [days]

Uranium concentration (anoxic conditions) in bentonite water versus contact time. The upperfigure gives the measured contents in the unfiltered [1 and 21 and filtered [3, 4 and 5;microfiltration (0.45 pm pore size) up to 150 days, ultrafiltration (- 3-4 nm pore size) after 150days] samples. The lower figure gives the average concentrations and standard deviations of thefiltered samples.

Results of the analyses of the HCO3 and CO,'- contents in the solutions in the glove box (N.). These analyses were carried out using the SFS3005 Standard method for the determination of alkalinity and acidity in water.

Nominal [HCOA1 The contents of the HCO3-- and CO32- ions(ppm) in the solutions after two months' | in the solutions after one

l________________ equilibration (ppm) 1 year's experimental time (ppm)pH [HCO 3-] j c032-1 pH T [HCO3 -1 [C0 32 -1

NaHCO3-60 60 8.79 50.8 3.0 9.05 52.3 3.5

NaHCO3-120 120 8.85 113.7 4.9 9.05 107.1 6.1

NaHCO 3-275 275 8.88 258.8 9.4 9.06 245.3 13.5

NaHCO 3-600 600 8.87 572.2 20.6 9.06 536.5 28.7

Allard 123 8.71 113.6 5.7 8.96 105.4 8.3groundwater

Bentonite 600 8.77 560.5 23.5 8.92 500.5 25.2water L

App. 22

Oxidation state of uranium in the solutions at the end of the dissolution experimentsunder anoxic (N2) conditions. The results are the averages of two parallel samplings.

Fraction U (VI)(%)

Fraction U (IV)(%)

Deionized water 99.2 0.8

NaHCO3 -60 96.8 3.2

NaHCO3 -120 96.8 3.2

NaHCO3 -275 96.8 3.2

NaHCO3 -600 98.2 1.8

Allard groundwater 91.4 8.6

Bentonite water 96.9 3.1

LIST OF REPORTS I (3)

LIST OF YJT REPORTS PUBLISHED IN 1995

YJT-95-01 Distribution of Pa-231 and Ra-226 in rock - an indicator of rockmatrix diffusionLeena Saarinen, Juhani SuksiDepartment of RadiochemistryUniversity of HelsinkiFebruary 1995

YJT-95-02

YJT-95-03

YJT-95-04

YJT-95-05

YJT-95-06

Technetium, neptunium and uranium in simulated anaerobicgroundwater conditionsMartti HakanenDepartment of RadiochemistryUniversity of HelsinkiAntero LindbergGeological Survey of FinlandMarch 1995

Sorption of alkaline-earth elements Sr, Ba and Ra from groundwateron rocks from TVO investigation areasSeija Kulmala, Martti HakanenDepartment of RadiochemistryUniversity of HelsinkiAntero LindbergGeological Survey of FinlandMarch 1995

Hydraulic and tracer experiments in the TVO Research Tunnel 1993-1994Aimo Hautojarvi, Mikko Ilvonen, Timo VienoVTT EnergyPekka ViitanenVTI' Chemical TechnologyApril 1995

Evaluation of phenomena affecting diffusion of cations in compactedbentoniteArto Muurinen, Jarmo LehikoinenVTT Chemical TechnologyApril 1995

Feasibility study and technical proposal for the use of microseismicmethods in the long-term observation of bedrock stabilityJouni SaariIVO International OyApril 1995

LIST OF REPORTS 2 (3)

YJT-95-07

YJT-95-08

Final disposal of spent nuclear fuel - basis for site selectionPekka AnttilaIVO International OyMay 1995(In Finnish)

Thermal conductivity of rocks at the TVO investigation sites Olkiluoto,Romuvaara and KivettyIlmo Kukkonen, Antero LindbergGeological Survey of FinlandMay 1995

YJT-95-09

YJT-95-10

YJT-95- 11

YJT-95-12

Study of rock porosity by impregnation with carbon-1 4-methylmethacrylateMarja Siitari-Kauppi, Sakari LukkarinenUniversity of HelsinkiDepartment of ChemistryAntero LindbergGeological Survey of FinlandMay 1995

Surface complexation modelling applied to the sorption of nickel onsilicaMarkus OlinVTT Chemical TechnologyOctober 1995

Rock mechanical analyses of in situ stress/strength ratio at the TVOinvestigation sites Kivetty, Olkiluoto and RomuvaaraPasi ToippanenHelsinki University of TechnologyLaboratory of Rock EngineeringErik Johansson, Matti HakalaSaanio & Riekkola Consulting EngineersOctober 1995

Surface complexation modelling: experiments on the sorption of nickelon quartzEsa PuukkoMartti HakanenUniversity of HelsinkiDepartment of ChemistryOctober 1995

YJT-95-13 Investigation of porosity and microfracturing in a disturbed zone withthe 14CPMMA method based on samples from full-scale experimentaldeposition holes of the TVO Research TunnelMarja Siitari-KauppiUniversity of HelsinkiDepartment of ChemistryNovember 1995

LIST OF REPORTS 3 (3)

YJT-95- 14 Solubility of unirradiated U0 2 fuel in aqueous solutions - comparisonbetween experimental and calculated (EQ3/6) dataKaija OllilaVTT Chemical TechnologyNovember 1995