Volume 88, Issue 9-11 - Migration 1999

Large amounts of hydrogen are produced as a result of the anoxic corrosion of iron in the proposed container materials for some geologic repositories. Another hydrogen source, less important than the anoxic corrosion of iron, is the radiolysis of water by the spent fuel radiation. Gas phase formation occurs when the pressure of the hydrogen equals at least the hydrostatic pressure, around 5 MPa at 500 meters depth. The effects of 5 MPa hydrogen pressure on spent PWR fuel leaching and on uranium oxide solubility have been studied in carbonated solutions at 70 °C. The experiments were performed in a 1 liter autoclave, filled with 950 ml of a solution 10 mM NaCl, 2 mM NaHCO 3 and with hydrogen at a pressure of 5 MPa in the remaining 50 ml free volume. The leaching behavior of 2 g PWR spent fuel powder of the 0.25-0.50 mm fraction, placed in a gold basket was studied during several months by analyzing 10 ml solution samples taken after regular time intervals. A few experiments were performed also with unirradiated U(IV) oxide. In both cases extremely low concentrations of uranium (less than 10 -9 M were measured in the solution samples. Furthermore the uranium levels in solution remained practically constant during the whole leaching period (more than one year), indicating the absence of any oxidative dissolution of the spent fuel matrix. The same conclusion is confirmed by the constant (within analytical errors) levels of strontium, cesium, molybdenum, iodine and technetium during the whole leaching period. These results have been compared with the ones obtained during the leaching of a spent fuel pin in anoxic conditions, where the uranium and other radionuclides levels are several orders of magnitude higher. The surface of spent fuel or U(IV) oxide is partially oxidized during storage, giving rise to relatively high levels of U(VI) in solution even during leaching in anoxic conditions. No such effect could be observed in the presence of 5 MPa hydrogen, indicating that this initial amount of U(VI) should have been reduced to U(IV). The experimental study of the influence of various parameters as temperature and pressure is still in progress.

The spent fuel matrix constitutes a dynamic redox system, due to the time-dependent generation of oxidants and reductants at the spent fuel/water interface by alpha, beta and gamma radiolysis. In this context it is critical to understand the main processes and mechanisms that control the radiolytic production of redox components at this interface and their impact on the stability of the UO 2 matrix and in radionuclide release. In order to achieve this, a series of carefully controlled experiments have been carried out in order to determine the time dependence of the radiolytic H 2 , O 2 and H 2 O 2 production and radionuclide release (U, Pu, Np, Tc, Mo, Sr and Cs). These tests have been performed by using PWR Ringhals spent fuel fragments in contact with 10 mM NaHCO 3 solutions in an initially anoxic and closed system. The results of these experiments indicate quite a consistent and reproducible behaviour of the radiolytically generated reductants and oxidants. The results indicate that it is possible to define an equilibrium redox potential for the main redox pairs in the bulk system and that the experimentally determined radionuclide release can be rationalised in terms of the system redox potential.

The solubility of Sn(IV) in cementitious systems is directly related to the presence of dissolved Ca. In the presence of typical Ca concentrations, solid Ca[Sn(OH) 6 ](s) is precipitated, resulting in dissolved tin(IV) concentrations that are about four to six orders of magnitude lower than observed in alkaline, Ca-free systems. From different experiments carried out in initially oversaturated and undersaturated solutions, solubility products have been evaluated. A constant of 10 9.85 at I=0 has been derived for the formation of fresh Ca[Sn(OH) 6 ](precip) according to the reaction Ca 2+ +{Sn(OH) 6 2- ↔ Ca[Sn(OH) 6 ](s). A constant of 10 10.93 has been derived in undersaturation experiments for the equilibrium with crystalline Ca[Sn(OH) 6 ](cr).

After a few hundred years in a geologic repository, α-emissions will dominate the radiation field in and around spent nuclear fuel. In the event of a failure of the spent fuel container, the dissolution of the uranium dioxide matrix in contact with groundwater could be enhanced by α-radiolysis, which could create oxidizing conditions at the fuel surface. The radioactivity (hence the radiolysis) of the irradiated fuel available nowadays is characterized by strong β- and γ-contributions, which are not representative of aged fuel in a repository. A possible way to single out the effects of α-radiolysis on the dissolution behaviour of irradiated fuel is to study unirradiated UO 2 doped with a short-lived α-emitter. UO 2 containing ~0.1 and ~10 wt.% of 238 PuO 2 was fabricated and leached. Previous results of static (batch and sequential) leaching tests on monoliths at room temperature in demineralized water under anoxic atmosphere showed that the amounts of U released were higher in the case of UO 2 containing 238 Pu than in the case of undoped UO 2 . This work presents results of leaching experiments performed under similar conditions on materials of the same composition, but crushed to give samples with two different particle size distributions to investigate the effects of different surface areas. The U release data, normalized to the geometric surface area, showed enhanced U dissolution from α-doped UO 2 also in the case of crushed materials, except for the initial release after 1 h of leaching. Under these experimental conditions, the concentration of U measured in the leachates for the two doped materials did not show a clear dependence on α-activity.

The dehydration of uranyl minerals can affect phase structure and stability. Synthetic autunite hydrates, Ca[(UO 2 )(PO 4 )] 2 · × H 2 O, were studied by X-ray powder diffractometry (XRD) and thermogravimetric analysis (TGA) to address ambiguous or contradictory reports in the literature. Structurally, XRD analysis supported the three well-defined phases commonly reported in the literature, i.e. autunite, metaautunite I, and metaautunite II. In addition, a fourth phase with a basal plane spacing between that of autunite and metaautunite I, designated metaautunite Ia, was identified as an apparent metastable intermediate. TGA analysis confirmed that water loss or accumulation is tolerated to different degrees among the autunite hydrates. Loss of low temperature water appears to initiate collapse of the interlayer spacing from 10 to 9 Å to form metaautunite I and/or Ia, while the lower hydrates accommodate minor water loss and accumulation without significant structural alteration. Our results support previous research indicating the reversibility of the autunite to metaautunite I conversion. The complex dehydration pattern of autunite is not observed in all the 1:1 uranyl phosphates, such as chernikovite (H[(UO 2 )(PO 4 )] · 4 H 2 O).

We measured the rates of dissolution of pyrochlore, zirconolite, and brannerite in pH-buffered solutions of pH 2, 4, 6, 8, 10, and 12 at temperatures of 25, 50, and 75 °C in flow-through reactors. The dissolution rates for all phases show a minimum near pH 8. Zirconolite dissolves the slowest of the three phases, with a slightly higher rate for pyrochlore and a much higher dissolution rate for brannerite. Brannerite dissolves as much has 30 times faster than zirconolite. The rates increase with temperature, but the magnitude of the increase varies with pH. The calculated average apparent activation energy for dissolution is 6±3 kcal/mole. Dissolution is non-stoichiometric at all pHs. Ti and Hf are released most slowly, and are often below detection limits (1 ppb for Ti, 0.2 ppb for Hf). Releases of Ca, U, Gd, and Ce appear to be stoichiometric below pH 8. At pH 8 and above only U is measurable in solution. Dissolution rates are slow under all conditions, and commonly in the range of 1-100 nm total dissolution/year (between 10 -3.5 and 10 -5.5 g/m 2 /day).

By using 239 Np and/or 237 Np, the complexation of Np(V) with Aldrich humic acid and polyacrylic acid has been studied at the concentration of Np(V) from ~10 -13 to ~10 -4 M by the solvent extraction method using TTA and 1,10-phenanthroline in isoamyl alcohol. By defining the apparent formation constant as β α =[ML]/([M]C R α), where C R is the total concentration of proton exchanging sites and α is the degree of dissociation, [M] and [ML] respectively denote the concentrations of free and bound NpO 2 + , log β α have been obtained at pH 6-7 in 0.1 and 1.0 M NaClO 4 . For both humate and polyacrylate, log β α slightly increased with the degree of dissociation, and slightly decreased with ionic strength. While the variation of Np(V) concentration had no appreciable influence on the log β α of polyacrylate (ranging from 1.8 to 3.0 depending on pH and ionic strength), log β α of humate decreased from 4.7-5.3 (depending on pH and ionic strength) at [M] < 10 -9 M to 2.8-3.1 at [M] = 10 -5 M, indicating the coexistence of weak and strong binding sites in the humic acid.

We investigated the influence of phenolic OH groups on the complexation behavior of humic acid (HA) with UO 2 2+ ions at pH 4. Starting from synthetic HA type M1, natural HA Aldrich, and natural HA Kranichsee, we synthesized modified HAs with blocked phenolic OH groups by derivatization with diazomethane. The partial blocking of phenolic OH groups was confirmed by a radiometric method which quantitatively determined the functional groups and by FTIR spectroscopy. The complexation behavior of the chemically modified and unmodified HAs with UO 2 2+ ions was investigated by time-resolved laser-induced fluorescence spectroscopy. The experimental data were evaluated with the metal ion charge neutralization model. We determined comparable complexation constants for all HAs. Two modified HAs (type M1 and Aldrich) had significantly lower loading capacities for UO 2 2+ ions (10.5 ± 0.9% and 9.7 ± 1.6%, respectively) than the corresponding unmodified HAs 18.0 ± 2.0% and 17.5 ± 1.6%, respectively). This indicates that the blocking of the phenolic OH groups changes the complexation behavior of HAs.

The structure and reaction dynamics in the systems UO 2 2+ -SO 4 2- and UO 2 2+ -SO 4 2- -OH - were investigated using EXAFS and 17 O-NMR spectroscopy. Uranium L III edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Å. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Å. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO 2 2+ + SO 4 2- ⇔ UO 2 SO 4 (k 1 ), (2) U * O 2 2+ + UO 2 SO 4 ⇔ U * O 2 SO 4 + UO 2 2+ (k 2 ), (3) UO 2 2+ + UO 2 (SO 4 ) 2 2- ⇔ 2 UO 2 SO 4 (k 3 ), and (4) UO 2 SO 4 + SO 4 2- ⇔ UO 2 (SO 4 ) 2 2- (k 4 ). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their 17 O chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.

The speciation of tetravalent technetium has been studied in HCl solutions ranging from 1.0 to 6.0 M. Tc(IV) exists in 6.0 M HCl as the well characterized TcCl 6 2- chloride complex. In 1.0 M HCl, the chloride ligands of TcCl 6 2- are slowly substituted by other ligands such as H 2 O, OH - or O 2- . So TcCl m O n (OH) p (H 2 O) q (4-m-2n-p)+ compounds may form with (m + n + p + q) = 6. Several speciation techniques such as UV-visible and Raman spectrometries, X-ray absorption spectroscopy and electrochemistry have enabled to get an insight into this problem. All the results have indicated two most likely species of Tc(IV) after aging for about ten days in 1.0 M HCl to be aquo-chlorocomplexes of technetium and not oxo-chorocomplexes: TcCl 5 · H 2 O - and TcCl 4 · 2 H 2 O.

The hydrolysis of uranium(VI) has been investigated in 0.10 and 1.0 mol dm -3 Na 2 SO 4 using the potentiometric titration technique. Analysis of the data indicates the presence of the following uranyl hydrolysis species: (UO 2 ) 2 (OH) 2 2+ , (UO 2 ) 3 (OH) 4 2+ , (UO 2 ) 4 (OH) 7 + and (UO 2 ) 5 (OH) 8 2+ in both media, and additionally, UO 2 OH + and (UO 2 ) 3 (OH) 5 + in the lower ionic strength only. The data were used to calculate stability constants for ternary uranyl hydroxo-sulfate complexes. These constants were found to be in excellent agreement with those found in an earlier study at a higher Na 2 SO 4 concentration (1.5 mol dm -3 ).

For the quantitative description of the interaction of metal ions with humic substances, it is necessary to clarify the effects of both polyelectrolyte and heterogeneous nature of humic substances. To estimate the polyelectrolyte effect separately, polyacrylic acid (MW = 90000) has been selected as a representative of well-defined, homogeneous polymeric weak acids, and its interaction with Eu(III) has been investigated by a solvent extraction method using 152 Eu (~10 -8 M) with TTA and TBP in xylene. By defining the apparent complex formation constant as β α = [ML]/([M][R]), where [M] = [Eu 3+ ], [ML] is the concentration of Eu(III) associated with polyacrylic acid and [R] = C R α (C R is a total concentration of proton exchanging sites and α is a degree of dissociation determined by potentiometric titration), the apparent constants have been obtained at several pcH and ionic strength (0.1 M and 1.0 M NaClO 4 ). The constants increased with pcH and decreased with an increase of ionic strength, that is, the values of log β α varied from 6.0 (at pcH = 4.7) to 7.6 (pcH = 5.5) at 0.1 M NaClO 4 and from 4.8 (pcH = 4.4) to 6.5 (pcH = 5.4) at 1.0 M. The plots of log β α versus log α revealed almost linear relationship both at 0.1 and 1.0 M NaClO 4 .

Complexation of Ni(II) and Co(II) by unfractionated humic acid (HA) was measured in 0.3 to 5.0 m NaCl solutions at pH 6 and 20 °C, using a solvent extraction technique. The dissociation constants and capacities of the humic acid were investigated in 0.1 to 5.0 m NaCl solutions at 25 °C using potentiometric titration methods.

The tetravalent actinide humate complexation was investigated for types of bonding between Th(IV) and humic acid. The Th(IV)-humate was prepared in solution, separated by ultrafiltration and analyzed by X-ray photoelectron spectroscopy (XPS). The stability of humic acid against X-ray induced degradation was verified by high-resolution XPS during long-term irradiation. The Th 4f 7/2 line of Th(IV)-humate can be fitted by one Gaussian-Lorentzian function, indicating that one type of bonding is mainly involved in the complexation. The Th 4f spectrum of Th(IV)-humate is, as compared to those of other Th(IV)-compounds, similar to the Th(IV)-complex with an ion exchanger containing carboxylic functional groups only. The present XPS study corroborates EXAFS results, according to which Th(IV) is predominantly bound to carboxylic groups of humic acid and demonstrates the applicability of the XPS technique for the characterization of metal-humate complexes.

Uranium L III -edge extended X-ray absorption fine structure (EXAFS) analysis was carried out on aqueous uranium(VI) complexes with monomeric intermediates of the natural wood-degradation process such as protocatechuic acid (3,4-dihydroxybenzoic acid), catechol (2-hydroxyphenol), pyrogallol (1,2,3-trihydroxybenzol), and vanillic acid (4-hydroxy-3-methoxybenzoic acid). The structural parameters of the 1:1 complexes with protocatechuic acid and vanillic acid in weakly acidic solution indicate that the carboxylic group coordinates the uranyl cation in a bidentate mode in the equatorial plane. Based on the identical structural parameters observed for protocatechuic acid, catechol and pyrogallol in alkaline media, we conclude that the coordination with uranium occurs via the neighboring OH groups of the phenols under formation of a five-membered ring.

First and second apparent stability constants for cobalt(II) with oxalate ion have been determined using solvent extraction. Data were collected in 0.3 m to 5.0 m NaCl aqueous solutions. The logarithms of first stability constant ranged from 3.30 ± 0.03 to 3.57 ± 0.03 and second stability constant ranged from 5.49 ± 0.05 to 6.02 ± 0.06. The data were modeled using the Pitzer equations. For the 1:1 complex, values of the μ 0 /RT = -20.3 and the single neutral-ion interaction parameter λ 0 CoOx-Cl - = -0.161 were determined. For the 1:2 complex, a value for the μ 0 /RT = -12.4 was calculated from literature data and the Pitzer parameters β 0 Co(Ox)2 2- -Na+ = -0.628; β 1 Co(Ox)2 2- -Na+ = 1.74 and c Φ = 0.251 were determined. Standard chemical potential values are based on a model for oxalate deprotonation reported in an earlier study. Stability constants determined in this work are compared to available values from the literature.

Fluorescence spectroscopy was used to study the Ca 2+ /UO 2 2+ /CO 3 2- solution system at different ionic strengths. Fluorescent titrations confirmed formation of Ca 2 UO 2 (CO 3 ) 3 complex for which the values of log β 213 were measured at 0.1, 0.3, 0.7, 1.0 and 3.0 m (NaClO 4 ) at pcH = 8.1. Specific Interaction Theory (SIT) was used to correlate the log β 213 values as a function of ionic strength. The value obtained for log β 0 213 (I = 0) was 29.8 ± 0.7, indicating that Ca 2 UO 2 (CO 3 ) 3 was the predominant specie at the pH 8 in calcium rich, oxic waters.

The migration behavior of Np(IV/V) is investigated by column experiments using a sandy sediment with groundwater rich in humic substances. NIR spectroscopy, redox speciation by TTA extraction and ultrafiltration are used for the Np speciation in the groundwater prior to its introduction into the column and after elution. Np is found to be transported as humic colloid-bound species which are eluted slightly faster than the water flow velocity. The fraction of humic colloid-borne Np increases with the reduction progress of Np(V) to Np(IV), because the interaction of Np(IV) with humic substances is much stronger than Np(V). The results demonstrate the importance of the speciation of redox sensitive actinides in natural aquifers for the assessment of the humic colloid facilitated migration.

The reduction of Pu(V) by humic acid in the presence of divalent cations (calcium and magnesium) was investigated. Tracer concentrations of 238 Pu were used (ca. 10 -10 M). Experiments were run in 5 m NaCl in the dark at pcH values of 6 and 8 with humic acid concentrations between 0 and 10 ppm. The redox speciation of plutonium was determined by solvent extraction methods. The reduction of Pu(V) by humic acid in the absence of divalent cations was investigated also with samples exposed to light prior to or after the introduction of plutonium. The presence of divalent cations, as well as light exposure increased the reduction of Pu(V), compared to when experiments were run in the dark without divalent cations.

The water of a mine drainage gallery was investigated for its contents of colloid-borne heavy metals with emphasis on uranium. About 1 mg/L of colloid particles of 100 to 300 nm were found. They consist of a matrix of Fe and Al oxyhydroxides and are formed when anoxic slightly acidic shaft waters mix with oxic near-neutral gallery water. The colloid particles bear toxic trace elements such as As, Pb, and Cu. Almost 100% of the As and Pb and about 70% of the Cu contained in the water are colloid-borne. Carbonato complexes prevent the uranyl from being adsorbed on the colloids in the unaltered gallery water. Acidification destroys these complexes: up to 50% of the uranium is attached to the colloids in the slightly acidic pH region. Further acidification converts the uranyl again to a ‘non-colloidal’ form.

A new experimental method is presented for the determination of solubility data, which is based on the laser-induced breakdown detection (LIBD). The method is capable of monitoring the initial colloid generation when the metal ion concentration reaches or just exceeds the solubility at given pH. The application is made to determine the solubility of Th(IV) in acidic solutions at I = 0.5 M (NaCl) and 25 °C. The initial colloid formation is determined as a function the H + concentration in a series of 2.8 × 10 -2 - 8.9 × 10 -5 M thorium solutions. The conditional solubility product (log K´ sp = -49.54 ± 0.22) obtained in this study corresponds to an equilibrium between solution and colloidal thorium dioxide particles. The solubility product at I = 0 (log K° sp = -52.8 ± 0.3) is calculated with the SIT coefficients of the NEA-TDB. It corresponds to the known value for crystalline ThO 2 (cr), in particular if the small particle size of about 20 nm is taken into account. The present results indicate that the high thorium solubilities measured in the previous studies for amorphous Th(IV) hydroxide or hydrous oxide are primarily caused by the inclusion of polynuclear species or Th(IV) colloids of very small size.

X-ray absorption fine structure (XAFS) spectroscopy is a powerful tool for obtaining basic molecular-level information, which is required for a better understanding of the mechanisms responsible for radionuclide transport in the environment. A unique experimental station dedicated to the study of actinides and other radionuclides by XAFS spectroscopy has become operational at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. The main characteristics of the Rossendorf Beamline, ROBL, and its radiochemistry end station and selected results obtained on Tc and Np solutions are presented.

Sorption of Hf(IV) onto amorphous silica at pH values between 1 and 7 is investigated by extended X-ray absorption fine structure (EXAFS) and time differential perturbed angular correlation (TDPAC) spectroscopies. Hafnium(IV) is studied as a chemical analogue for understanding the speciation of tetravalent actinides. In addition, 181 Hf is a frequently investigated TDPAC probe nuclide. Spectra obtained from both techniques show that there is a change in Hf-species with sample preparation pH. Results from TDPAC measurements show that two similar surface binding sites exist for Hf(IV) on the silica surface at low pH values. At a pH above 3, a third, unspecific surface binding site for Hf(IV) begins to dominate. EXAFS investigations do not detect the presence of polynuclear surface species. Both TDPAC and Hf L3 edge EXAFS spectra of the sorption samples differ from that of a Hf(IV) solution or a Hf(IV) hydrolysis product. This indicates that the sorbed species are different from solution or simple hydrolysis species. Short Hf-O distances are obtained from theoretical fits to the EXAFS oscillations for all samples. This suggests that the primary interaction of Hf(IV) with the silica surface occurs via silanol groups. Differences in the electric field gradient surrounding sorbed Hf(IV) cations as a function of pH, observed in the TDPAC spectra, must result from changes in overall species geometry rather than a change in the primary Hf-silica surface interaction.

The generation of Eu(III) precipitation and the Eu sorption on TiO 2 particles in aqueous solution were studied using laser-induced breakdown spectroscopy (LIBS). The plasma emission intensity vs. the Eu concentration plot showed a good linearity in the concentration range of 6.6 × 10 -3 M - 1.3 × 10 -2 M for Eu aqueous solution at pH 1.1 and 6.6 × 10 -5 M - 6.6 × 10 -4 M for Eu 2 O 3 suspension at pH 5.0. It was found that the generation of Eu precipitation was detected through a drastic increase of plasma emission intensity of Eu. The results suggested that LIBS is useful for analyzing the particles and the precipitation of Eu in aqueous solution, even if the Eu ion concentration is higher by orders of magnitude. Furthermore, we could measure the plasma emission of Eu ions sorbed on TiO 2 particles under the conditions where the plasma emission of Eu ions could not be detected in the absence of TiO 2 . Hence, LIBS technique is considered to be useful to study the colloid generation of Eu.

Migration behavior of Np(V) in sandy soil and granite media was studied in the presence of humic substances using a column method. Two kinds of naturally occurring fulvics were isolated from groundwater at the Chalk River Laboratories of AECL (hereafter, CRL-fulvics) and at the Underground Research Laboratory of AECL (hereafter, URL-fulvics). The commercial humics from Aldrich Co. (hereafter, Aldrich-humics) was also used to compare the influence of humics from different origin on the migration behavior of Np(V). The dominant molecular size of these humic substances was under 5,000 daltons for the fulvics, and in the range from 30,000 to 100,000 daltons for Aldrich-humics. An enhanced elution of Np(V) from the sandy soil column under coexistence of CRL-fulvics at 20 mg/L was observed in comparison with the studies in the absence of humic substances. On the other hand, Np(V) under coexistence of Aldrich-humics was retarded. The difference in the effects of the humic substances on the migration behavior of Np(V) may be caused by the difference in the molecular size distribution of the humic substances. That is, the CRL-fulvics, being smaller in size, has lower sorption ability on the sandy soil than the Aldrich-humics, and thereby Np-fulvics complexes may be able to easily migrate through the sandy soil column. In the case of granite column experiments, again an enhanced elution of Np(V) under the coexistence of URL-fulvics was found and this observation was similar to that found with the CRL-fulvics. From these observations, it is likely that the migration behavior of Np(V) is influenced by the presence of humic substances.

In a high level waste repository in which temperatures are elevated due to waste decay, concrete structures will be subjected to hydrothermal conditions that will alter their physical and chemical properties. Virtually no studies have examined the interaction of hydrothermally altered concrete with radionuclides. We present the results of experiments in which soluble and colloid-associated U and Np, were eluted into a fractured, hydrothermally altered concrete core. Although the fluid residence time in the fracture was estimated to be on the order of 1 minute, U and Np in the effluent from the core were below detection (10 -9 - 10 -8 M), for both soluble and colloid-associated species. Inorganic colloids and latex microspheres were similarly immobilized within the core. Post-test analysis of the core identified the immobilized U and Np at or near the fracture surface, with a spatial distribution similar to that of the latex microspheres. Because hydrothermal alteration followed fracturing, the growth of crystalline calcium silicate hydrate and clay mineral alteration products on, and possibly across the fracture, resulted in a highly reactive fracture that was effective at capturing both soluble and colloidal radionuclides. Comparison of results from batch experiments [1] with these experiments indicate that partitioning of U and Np to the solid phase, and equilibration of the incoming fluid with the concrete, occurs rapidly in the fractured system. Transport of U through the concrete may be solubility and/or sorption limited; transport of Np appears to be limited primarily by sorption.

The Lovasjärvi intrusion (SE-Finland) contents a high percentage of ferrous olivine (> 65%). This material has been suggested as a redox-active backfill-additive in deep nuclear waste repositories, due to the large Fe(II) proportion in its mineral composition. In order to understand the processes involved in the redox buffering capacity of this material the transport of uranium (VI) through olivine columns was studied. The results showed considerable retardation factor for the U(VI), particularly in carbonate-free media. The experimental data were simulated by means of reactive transport modeling. The best agreement between the experimental and calculated data was obtained considering that the interaction of U(VI) with the olivine surface occurred at two different types of sorption sites. One type accounts for the sorption capacity of the olivine mineral, and a second type accounts for the sorption on amorphous Fe(OH) 3 (s) formed at expenses of the oxidative dissolution of olivine.

The sorption behavior of aqueous Pu(IV) on brucite (Mg(OH) 2 ) in the presence and absence of citrate was investigated by a combination of wet chemical batch sorption experiments and X-ray photoelectron spectroscopy (XPS). Sorption occurs rapidly at near 100% levels from pH 8 to pH 13, and is not affected by the presence of citrate. XPS results indicate that Pu was incorporated in the subsurface in the cases studied.

The sorption behavior of Cs + , and Ba 2+ on natural clay was investigated using ToF-SIMS, XPS, and XRD. The natural clay was composed mainly of chlorite and illite in addition to quartz and calcite. Depth profiling up to 70 Å was performed at 10 Å steps utilizing ToF-SIMS to study the amount of sorbed Cs + and Ba 2+ as a function of depth in the clay matrix. The results suggest that Cs + and Ba 2+ ions were sorbed primarily by ion exchange coupled with hydrolytic sorption. According to ToF-SIMS and XPS results, the total sorbed amount of Ba 2+ was larger than that of Cs + . Quantitative determination of the primary cations within the analyzed clay before and after sorption indicated that for Ba 2+ sorption, Ca 2+ , Mg 2+ and for Cs + sorption Ca 2+ , K + were the major exchanging ions. The XRD spectra of Ba-sorbed clay contained new peaks that were identified as BaCO 3 .

Component additivity (CA) and generalised composite (GC) approaches to deriving a suitable surface complexation model for description of U(VI) adsorption to natural mineral assemblages are pursued in this paper with good success. A single, ferrihydrite-like component is found to reasonably describe uranyl uptake to a number of kaolinitic iron-rich natural substrates at pH > 4 in the CA approach with previously published information on nature of surface complexes, acid-base properties of surface sites and electrostatic effects used in the model. The GC approach, in which little pre-knowledge about generic surface sites is assumed, gives even better fits and would appear to be a method of particular strength for application in areas such as performance assessment provided the model is developed in a careful, stepwise manner with simplicity and goodness of fit as the major criteria for acceptance.

A simple method of evaluating the distribution coefficient (K d ) of radioactive Ni was examined. The method is based on the measurement of the solid-liquid concentration distribution ratio (f d ) of background stable Ni. To verify the method, the K d ´s of both the radioactive Ni and stable Ni were simultaneously measured by using three different samples through batch sorption experiments in which radioactive Ni with a constant concentration and stable Ni with various concentrations coexisted. The f d of background stable Ni was then measured by extraction with 0.1 N CH 3 COONH 4 and 0.1 N HCl solutions to compare f d with K d . The results showed that the K d ´s of radioactive Ni agreed with those of stable Ni, and that the f d corresponded to the K d when the liquid-phase concentration of stable Ni approached the background level. This indicates that the method of evaluating K d by using f d is applicable to Ni within the experiment.

The effect of adsorption of Gd(III) on the electrokinetic potential of silica (Aerosil, 390 m 2 /g) was studied at various Gd(III) concentrations (ranging from 10 -6 to 10 -2 mol dm -3 ) and at four different solid to liquid ratios (ranging from 0.05 to 8% of silica by weight). Up to some critical concentration of trivalent cations, their effect on the electrokinetic potential of silica is negligible and the sign is negative over the entire studied pH range. This critical concentration increases when the solid to liquid ratio increases. When Gd(III) concentration exceeds the critical value, the magnitude of the negative electrokinetic potential of silica is reduced. This effect is substantial at pH 6 but it is rather insignificant when the pH is very high (pH > 8) or very low (pH < 4). When the Gd(III) concentration is even higher, the sign of the electrokinetic potential is reversed to positive over certain pH range, which depends on the solid to liquid ratio and Gd(III) concentration. The shape of experimental electrokinetic curves of silica in the presence of trivalent cations often shows maximums and double isoelectric points, thus, it is very complex in comparison with the shape of the percentage of uptake vs. pH curves. Therefore, a test of an adsorption model based on electrokinetic curves is much more demanding than a test based merely on uptake vs. pH curves. The parameters of surface complexation model (SCM) derived from analysis of a large set of uptake curves were used to predict the course of electrokinetic curves. The calculated and experimentally observed maximums and isoelectric points do not exactly match (a difference up to one pH unit), but the model curves qualitatively reflect the trends observed in electokinetic experiments.

Sorption equilibrium and kinetics of NpO 2 + on dispersed particles of Na-montmorillonite were experimentally investigated by using a°batch technique and a°spectroscopic method, respectively. Considering the heterogeneity of sorption sites, we investigated the affinity spectra for the sorption of NpO 2 + . It was found that the spectrum for NpO 2 + was monomodal but asymmetrical and that the half-width at half-maximum of the spectrum was relatively broad, indicating that the sorption sites of surface of Na-montmorillonite are strongly heterogeneous. From the kinetic spectrum for NpO 2 + , two sorption processes could be distinguished. It was considered that the fast process is attributable to the sorption of NpO 2 + on the easily accessible outer surface of Na-montmorillonite particles and that the slower process is assigned to the sorption on the interlayer surface. Mean apparent activation enthalpies for the fast and the slow processes were evaluated as 19 ± 2 kJ/mol and 23 ± 3 kJ/mol, respectively.

The present paper describes the surface complexation behaviour of trivalent metal ions, Am(III) and Eu(III), on well characterised γ-alumina. Experiments are conducted at different pH (4-8) and ionic strength (0.001 - 0.1 M NaClO 4 ) either in the presence or absence of CO 2 . By varying the metal ion concentration from 10 -9 to 10 -4 mol/L, the sorption isotherm is established under each given experimental condition. Different surface complexation models are applied to the experimental results to interpret and appraise the surface sorption processes under different experimental conditions. A comparison of the present results is made with the Eu(III) sorption onto the hematite mineral surface investigated previously. It has been shown that sorption properties of hematite and γ-alumina seem to be quite similar. For both systems, a good agreement is found between experimental data and modelling, once using the two site surface complexation model and the same complexation constants for the respective monodentate surface complex. The Eu(III) sorption reaction is additionally studied in-situ by time resolved laser fluorescence spectroscopy (TRLFS). Formation of inner-sphere complexes can be deduced from the emission spectra. The continuous increase of the fluorescence life time with increasing pH starting from pH = 5.0 indicates that surface complexation is accompanied by a decreasing number of hydration water in the first coordination sphere.

Sorption coefficients of Am(III) and Cm(III) on kaolinite were determined at pH from 3.5 to 10 and humic acid (HA) concentrations of 0 to 20 ppm at ionic strength of 0.1 M (NaClO 4 ) at 298 K with N 2 bubbling. The sorption ratio of HA on kaolinite was also measured under the same experimental conditions. The sorption coefficients of Am(III) and Cm(III) in the absence of HA increased with pH over the whole pH range. The presence of HA enhanced sorption coefficients at pH values up to around 5, above which the sorption coefficients were lowered by introducing HA. The effects of HA on sorption coefficients were interpreted by the use of a linear additive model, modified for metal-humate complex formation in the aqueous phase. The model was found to be in fairly good agreement with the experimental data.

We studied the influence of humic acid (HA) on the uranium(VI) sorption onto the rock material phyllite and onto its main mineral constituents quartz, muscovite, chlorite, and albite at an ionic strength of 0.1 M in the pH range of 3.5 to 9.5 under aerobic conditions. The uranium(VI) concentration was 1 × 10 -6 M and the HA concentration was 5 and 60 mg/L, respectively. The solid/solution ratio was 12.5 g/L. Furthermore, we studied the uranium and HA sorption on ferrihydrite (3 × 10 -4 M Fe) and compared the results to the sorption behavior of phyllite. The study showed that the uranium sorption onto phyllite and onto its mineral constituents is influenced by the pH-dependent sorption behavior of the HA. Due to high HA sorption onto the solids in the acidic pH range the uranium uptake is enhanced compared to the uranium uptake in the absence of HA. A high concentration of dissolved HA in the near-neutral pH range reduces the uranium sorption due to formation of aqueous uranyl humate complexes. Furthermore, we could show that the high uranium and HA sorption on phyllite is primarily caused by minor amounts of the secondary mineral ferrihydrite that is formed due to weathering of phyllite. Thus, the ferrihydrite predominates the contributions of the main minerals quartz, muscovite, chlorite, and albite, that are naturally present in the rock material phyllite.

Partition coefficients (K d ) of U(VI) and Np(V) on untreated and hydrothermally altered concrete were measured in 0.01 M NaCl and 0.01 M NaHCO 3 solutions as functions of concentration of the radionuclides, pH, and time. The partition coefficients for both U(VI) and Np(V) on hydrothermally altered concrete are significantly lower than those on untreated concrete. The partition of both U(VI) and Np(V) are pH dependent, although the pH dependence does not appear to reflect precipitation of U and Np-bearing phases. Both sorption and precipitation are likely processes controlling partitioning of U to concrete; sorption is the most likely process controlling the partitioning of Np to concrete. The presence of 0.01 M carbonate species in solution decreases K d of U(VI) for both hydrothermally altered and untreated concrete from ≥ 10 4 mL/g to ~400 to 1000 mL/g indicating a significant impact on U(VI) sorption. In contrast, the presence of carbonate only reduced the K d of Np(V) by one order of magnitude or less. X-ray absorption spectroscopy analysis of U/concrete mixtures at different pHs and times indicate that uranyl ions are partitioned as monomeric species on untreated concrete, but oligomeric species on hydrothermally altered concrete. Similar analysis of Np/concrete mixtures shows that about half of the partitioned Np(V) is reduced to Np(IV) over a period of 6 months.

Uraninite and associated alteration products from the Colorado Plateau were studied by optical microscopy, electron microprobe analysis (EMPA), scanning electron microscopy (SEM) and backscattered electron (BSE) imaging in order to determine the behavior and fate of trace elements, such as Pb, Ca, Si, Th, Zr, and REE, during corrosion under oxidizing conditions. The long-term alteration products and processes of uraninite may provide insight into the corrosion of the UO 2 in spent nuclear fuel. Uraninite, schoepite, calciouranoite, uranophane, fourmarierite, a Fe-rich uranyl phase, and coffinite were identified. The primary uraninites and alteration phases generally have low trace element contents, except for coffinite from Caribou Mine, Colorado that has Y 2 O 3 as high as 0.88 wt%. The highest Zr, Ti, Th and REE values of the uraninite are ThO 2 0.17, Y 2 O 3 0.28, La 2 O 3 0.03, Ce 2 O 3 0.10, Pr 2 O 3 0.02, Nd 2 O 3 0.14, Sm 2 O 3 0.12, Eu 2 O 3 0.04, Gd 2 O 3 0.08, ZrO 2 0.93, and TiO 2 0.54 wt%, which are in general lower than the corresponding components in secondary uranyl phases (the highest values are ThO 2 0.21, Y 2 O 3 0.88, La 2 O 3 0.05, Ce 2 O 3 0.15, Pr 2 O 3 0.05, Nd 2 O 3 0.18, Sm 2 O 3 0.14, Eu 2 O 3 0.11, Gd 2 O 3 0.08, ZrO 2 2.11, and TiO 2 2.74 wt%), suggesting that trace elements preferentially enter the structures of these secondary uranyl phases (Table 2). A compositional profile of a concentric structure in schoepite shows that, with increasing alteration, UO 2 , PbO and ZrO 2 decrease, and SiO 2 , TiO 2 , CaO and P 2 O 5 increase. Alteration causes loss of U, Pb and Zr and incorporation of Si, Ti, Ca and P into uranyl phases. The Ca-rich calciouranoite from Grants, New Mexico, indicates an interaction between the limestone host rock and uranium minerals. Texturally, concentric structures and micro-fractures are common. Concentric structures are usually composed of both uraninite and uranyl phases, while micro-fractures are common in the secondary phases.

The nucleation of a mineral crystal and its growth in groundwater carrying fractures 300 m above the Palmottu uranium deposit provide an impressive example of geochemical selectivity of uranium. Fracture-filling material was collected from a 3 mm thick fracture at depth 74.8 - 75 m (drillcore R348). SEM and EDS analyses on a thin section of the original fracture-filling show that the fracture filling is heterogeneous, composing mineral crystal particles and very porous clay-rich aggregates. The results of INAA on millimetre-sized single mineral crystals and aggregates selected from grinded fracture-filling show that porous aggregates (composed of clays and micrometer sized mineral particles) contain up to 1000 ppm U, which is higher than the average of the whole fracture-filling (400 ppm) and host rock related millimetre sized mineral particles (18 - 100 ppm). 233 U/ 238 U isotope exchange proves that a large fraction of the uranium in the fracture-filling is not easily exchanged with uranium in the solution. The amount of 238 U released in the isotope exchange experiment is too high to be explained by reversible U(VI) sorption. Oxidation state analyses show that 30% of the uranium exists as U(IV). Laboratory batch experiment at anoxic conditions proved that pyrite can immobilise U(VI).

We studied the fluorescence properties of 120 uranium minerals in order to provide a data base of potential secondary solids that may form in the flooding process of defunct uranium mines. This data base may provide a link of the fluorescence spectra of the minerals to solution spectra containing so far unknown tertiary and quaternary solution complexes in environmental uranium(VI)-containing waters. In our initial effort to establish the data base, we are focusing on phosphate- and arsenate-containing uranium(VI) minerals. Except for chernikovite [(H 3 O) 2 (UO 2 ) 2 (PO 4 ) 2 · 6H 2 O], these minerals show intensive fluorescence emissions bands with a bathochromic shift of up to 18 nm compared to the fluorescence of the uranyl ion in solution. We found hypsochromic shifts of the fluorescence emission for the uranyl phosphates and bathochromic shifts for the uranyl arsenates. The band spacing of the fluorescence emissions from the 20502 cm -1 level are comparable to the vibrational frequency available from IR-data. Using these data we estimated the axial U-O bond lengths. The decrease of the vibration frequency from 813 cm -1 (saleiite, [Mg(UO 2 ) 2 (PO 4 ) 2 · 10(H 2 O)]) to 794 cm -1 (uranocircite, [Ba(UO 2 ) 2 (PO 4 ) 2 · 12(H 2 O)]) is related to a slight increase of the U-O bond length by 3 pm. In both series, the fluorescence lifetime decreases with decreasing crystal water. This is different compared to solution spectra where the lifetime increases as water is displaced from the inner coordination shell. Comparing the fluorescence data of the mineral troegerite [H 2 (UO 2 ) 2 (AsO 4 ) 2 · 8(H 2 O)] with the fluorescence spectra of uranyl arsenate solutions, we identified one of the three uranyl arsenate complexes in solution as HUO 2 (AsO 4 )(aq.).

Occurrence of natural U in fracture smectite (main mineral component of bentonite) was studied as an analogue to radionuclide behaviour in the near-field of spent nuclear fuel repository. Elevated U content (57 ppm) was observed in fracture smectite sampled from the surface of water-carrying fracture in granite pegmatite at a depth of 70 m. The current groundwater conditions are oxidising at the sampled point. The U-234/U-238 activity ratio (AR) measured in the bulk U and in its sequentially extracted phases, displays unusually low value (around 0.30). Low AR indicates preferential loss of the U-234 isotope from the system. Because the U-234 loss can also be seen in the Th-230/U-234 activity ratio (clearly over 1), the selective removal of the U-234 isotope must have taken place more recently than what is needed to equilibrate Th-230/U-234 pair (i.e. 350000 a). To explain the selective U-234 loss from the smectite we postulate that bulk U is in reduced +4 form and a considerable part of the U-234 isotope in easily leachable oxidised +6 form. This study suggests that the long-term chemical stability of the bulk U in the smectite is due to irreversible fixation of U in the reduced +4 form.

Microorganisms may affect the long-term stability and mobility of radionuclides disposed of in deep geological formations. Of particular concern is the association of radionuclides with subterranean microbial cells and their subsequent transport as biocolloids. We characterized the total microbial populations in two groundwater samples: one from the Culebra dolomite member of the Rustler Formation at the Waste Isolation Pilot Plant (WIPP), NM, and the other from the granitic formation at the Grimsel Test Site (GTS), Switzerland. Culebra groundwater (ionic strength 2.8 M, pH 7) contained 1.51 ± 1.08 × 10 5 cells ml -1 , with a mean cell length of 0.75 ± 0.04 μm and width of 0.58 ± 0.02 μm. In contrast, low ionic-strength GTS groundwater (0.001 M, pH 10) contained 3.97 ± 0.37 × 10 3 cells ml -1 , with a mean cell length of 1.50 ± 0.14 μm and width of 0.37 ± 0.01 μm. Adding appropriate electron donors and acceptors to the groundwaters facilitated the growth of aerobic, denitrifying, fermentative, and acetogenic microorganisms. Uranium biosorption was studied in two isolates from these groundwaters, as well as several pure cultures from saline and non-saline environments. Halophilic and non-halophilic bacteria exhibited differences in the amount of U associated with the cells. Plutonium uptake by Acetobacterium sp. isolated from GTS varied from 30 - 145 pg of Pu mg -1 dry weight of cells.

Humic material from several soils was fractionated using both gel chromatographic and gel electrophoretic techniques. The distribution of uranium amongst fractions obtained by both methods was determined using ICP-MS. Humic material isolated from electrophoretic fractions was characterised using FTIR and UV-vis spectroscopy, base titration, Sephadex G200 size fractionation and CHN elemental analysis. Both size and chemical separation occurred during electrophoretic fractionation with the smaller, more hydrophilic molecules being more electrophoretically mobile. The gel chromatographic and gel electrophoretic studies showed that the association of U in soils was skewed towards the larger humic molecules but that some association with certain smaller humic molecules warrants further work to characterise the behaviour of these complexes under varying environmental conditions.

This paper illustrates the coupling of Neutron Activation Analysis (NAA), Proton Induced X-ray Emission (PIXE) and X-ray Photoelectron Spectroscopy (XPS) to quantify iodine contents in natural humic substances from different geochemical origins and to determine its chemical environment. Non negligible contents of iodine from some hundreds of μg/g to more than one weight per cent have been quantified in the humic substances, and iodine seems to be attached to the organic matter by covalent bonds.

A method for quantitative characterisation of the radiocaesium availability to plants in forest ecosystems has been developed. For this purpose an expression has been proposed to calculate the radiocaesium availability factor in soils, which is a combination of key soil characteristics: radiocaesium exchangeability, exchangeable calcium in soil and effective selectivity coefficient. The experimental dependencies of the radiocaesium soil to plant concentration factors for fern and bilberry, on the availability factor calculated by the above equation were satisfactory described by linear function. The advantage of this method to characterise bioavailability of radiocaesium and to estimate site-specific values of concentration factor is that the necessary soil characteristics may be taken from the reference literature, evaluated by experts or determined with a simple experimental procedure. The method can be used in development of a radioecological Geographic Information Systems.

Knowledge of the partitioning of actinides to sediments in natural systems is essential for modeling their environmental fate. Using two different sequential extraction methods, we have studied the partitioning of U and Pu to an acidic, sandy lake sediment that was contaminated due to nuclear production activities. We find that both methods yield similar partitioning information, and that much of the U is associated with insoluble phases, whereas the majority of the Pu is extracted with oxidizable phases, defined to be predominantly organic matter. Our study suggests that U in this ecosystem is of natural origin. Although Pu and Fe in this system are known to cycle from the sediments to the water column during periods of anoxia, only a low percentage of Pu is extracted from the phases that are reducible, which are operationally defined as amorphous Fe oxides. Although this sediment is low in organic matter, our results suggest that natural organics dominate the partitioning of Pu in this system.

Distribution coefficients (K d values) for Cs and U(VI) on soils from an arid region of Australia were measured under a range of conditions. The K d values for trace 137 Cs in 0.02 M NaCl were typically around 10 4 mL/g, and were not affected by the pH. However, the K d decreased with increasing ionic strength, and was strongly dependent on the total Cs concentration. Much lower K d values (around 10 2 mL/g) were measured in systems containing total Cs of 1 mmol/L in a background electrolyte of 0.10 M NaCl. The main factor determining the sorption behaviour of U(VI) in systems equilibrated with air was the pH, with the K d decreasing from above 10 3 mL/g at pH 7 to around 10 mL/g at pH 9.

Radionuclide distributions in undisturbed forest and bog soils, mostly situated in Saxony, Germany (Erzgebirge), were studied. Low concentrations of naturally-occurring U and Th decay series nuclides, including 210 Pb, and artificial radioisotopes ( 125 Sb, 134 Cs, 137 Cs, 241 Am) were determined using low-level γ-spectrometry. In addition, the activities of 238 Pu and 239,240 Pu were determined by radiochemical separation and α-spectrometry. 14 C and excess 210 Pb dating methods were used to date the sampled bog profiles. The different radionuclides show characteristic depth distributions in the forest and bog soil horizons, which were sub-sampled as thin slices. 125 Sb, 241 Am, 238 Pu and 239,240 Pu are strongly fixed in soil organic matter. In spruce forest soils, the influence of soil horizons with distinct properties dominates the vertical time-dependent distribution. In ombrotrophic bogs, the peak positions correlate with the year of maximum input of each nuclide. The Sb, Am and Pu “time markers“ and the 14 C and 210 Pb dating results correspond very well. Although Cs seems to be relatively mobile in organic as well as mineral forest soil horizons, it is enriched in the organic material. In ombrotrophic bogs, Cs is very mobile in the peat deposit. In Sphagnum peat, Cs is translocated continuously towards the growing apices of the Sphagnum mosses, where it is accumulated.

A high-uranium phosphate rock from the Itataia deposit, located in the state of Ceará, Brazil, was milled in a pilot plant for wet-process phosphoric acid production. Further processing with solvent extraction (DEHPA/TOPO) was used aiming to recover uranium from the phosphoric acid. The distribution of natural radionuclides with long physical half-life of the 238 U and 232 Th decay series involved in these operations was evaluated. The radionuclides 226 Ra, 228 Ra and 210 Pb were found to predominate in the phosphogypsum, while 228 Th, 230 Th and 232 Th in the uranium-free phosphoric acid.

A new semi-empirical approach is presented for the prediction of actinide complexation constants with inorganic ligands and applied to mononuclear carbonate complexes. The approach is based on an energy term describing the inter-ligand electrostatic repulsion. For a given metal ion M and ligand L, the formation constants log β° n of the complexes ML n are related by: log β° n = n log β° 1 - rep E L (ML n ) / RT ln 10 The electrostatic ligand repulsion term rep E L is derived from the charge and inter-distance of ligands involved in a given complex and their angular distribution. Semi-empirical parameters are required to describe the effective electrostatic shielding between complexing ligand ions with the metal ion and hydration water molecules between them. These shielding coefficients are specific for the ligands, but independent of the actinide ion and its oxidation state. The shielding coefficients for carbonate ligands are determined from the known formation constants of Am(III) and Cm(III) carbonate complexes, and then used to calculate carbonate complexation constants for other actinides of different oxidation states. Excellent agreement is found between the calculated and experimental values for Np(V), U(VI), Pu(VI), and even for the transition metals Fe(II) and Cu(II). Based on known constants log β° 4 and log β° 5 for U(IV) and Pu(IV), the unknown constants log β° 1 , log β° 2 and log β° 3 are estimated.

The Swedish Fuel and Waste Management Co, SKB, is at present preparing a Performance Assessment (PA) exercise of its HLNW repository concept. The determination of solubility limits of the main radioelements contained in the spent nuclear fuel is a necessary work to understand their potential migration in both the near and far fields. The calculated solubilities are compared to experimental data from relevant spent nuclear fuel dissolution tests and field observations from natural systems, particularly Natural Analogue study sites. This work discusses the main uncertainties associated to the calculated solubilities, particularly those related to the variability of groundwater composition, redox conditions and temperature of the system. The results of the sensivity analysis indicate that although the solubility of some radioelements, such as Th, is not dramatically affected by the uncertainty in the determination of the physico-chemical parameters mentioned above, most of the elements are strongly influenced by this variability, specially Am, U, Np, Pu and Tc.