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  • 1. Bruno, J.
    et al.
    Cera, E.
    Eriksen, Trygve E.
    KTH, Superseded Departments, Chemistry.
    Grivé, M.
    Ripoll, S.
    Modelling experimental results on radiolytic processes at the spent fuel water interface. I. Radiolysis products and U release2004In: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXVII, 2004, p. 397-402Conference paper (Refereed)
    Abstract [en]

    Experimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2 surfaces in poising the redox state of solid/water systems. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions. The collected data so far, indicate that production and fate of radiolysis products follow the same trends independently on the solution composition used in the tests. Hydrogen and oxygen concentrations show an initial increase with time until reaching a constant concentration. The trend observed for hydrogen peroxide is a decrease at short contact times to reach again a constant concentration with time. These steady-states indicate an overall balance of the generated radiolytic species. Modelling work indicates that uranium dissolution is controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase is governed by the precipitation of schoepite. These results are determinant to highlight that reducing conditions are restored in the aqueous phase in relatively short periods of time and at short distances away from the dynamic redox spent fuel/water interface.

  • 2. Cera, E.
    et al.
    Grivé, M.
    Bruno, J.
    Eriksen, Trygve E.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry (closed 20110630).
    Modelling experimental results on radiolytic processes at the spent fuel water interface. II. Radionuclides release2006In: Mater Res Soc Symp Proc, 2006, p. 537-546Conference paper (Refereed)
    Abstract [en]

    Experimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2 surfaces in poising the redox state of solid/water systems as well as the radionuclides release behaviour. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions. Some of the collected data has been previously published [1], specifically those data concerning radiolysis products and dissolution of the matrix. The results and the modelling tasks indicated an overall balance of the generated radiolytic species and that uranium dissolution was controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase was governed by the precipitation of schoepite. This paper is the continuation of a series accounting for the data and modelling work related to investigating the release behaviour of minor radionuclides from the spent fuel. Uranium concentrations as a function of time showed an initial increase until reaching a steady stale, indicating a matrix dissolution control. The same behaviour is observed for neptunium, caesium, strontium, technetium and molybdenum indicating a congruent release of these elements with the major component of the fuel matrix. On the other hand, no clear tendency is observed for plutonium data where additional solubility limiting mechanisms may apply. Kinetic modelling of the trace elements: caesium, strontium, technetium and molybdenum is based on the congruent release of these elements with the major component of the fuel matrix. Rate constants have been determined. Kinetic modelling of neptunium data took also into account the. subsequent precipitation as Np(IV) hydroxide. Finally, measured Pu concentrations may be explained by the precipitation of Pu(IV) and/or Pu(III) solid phases.

  • 3.
    Ekeroth, Ella
    et al.
    KTH, Superseded Departments, Chemistry.
    Jonsson, Mats.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve
    KTH, Superseded Departments, Chemistry.
    Ljungqvist, Kristina
    KTH, Superseded Departments, Chemistry.
    Kovacs, Sandor
    Puigdomenech, Ignasi
    Reduction of UO22+ by H-22004In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 334, no 1, p. 35-39Article in journal (Refereed)
    Abstract [en]

    The reactivity of H, towards UO22+ has been studied experimentally using a PEEK coated autoclave where the UO22+ concentration in aqueous solution containing 2 mM carbonate was measured as a function of time at p(H2) similar to 40 bar. The experiments were performed in the temperature interval 74-100 degreesC. In addition, the suggested catalytic activity of UO2 on the reduction of UO22+ by H-2 was investigated. The results clearly show that H-2 is capable of reducing UO22+ to UO2 without the presence of a catalyst. The reaction is of first order with respect to UO22+. The activation energy for the process is 130 +/- 24 U mol(-1) and the rate constant is k(298K) = 3.6 x 10(-9) l mol(-1) s(-1). The activation enthalpy and entropy for the process was determined to 126 kJ mol(-1) and 16.5 J mol(-1) K-1, respectively. Traces of oxygen were shown to inhibit the reduction process. Hence, the suggested catalytic activity of freshly precipitated U02 on the reduction of UO22+ by H-2 could not be confirmed.

  • 4.
    Eriksen, Trygve E
    et al.
    KTH, Superseded Departments, Chemistry.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Diffusion of I, CS, and SR2- in compacted bentonite-anion exclusion and surface diffusion1996Report (Other academic)
  • 5.
    Eriksen, Trygve E.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Shoesmith, David W.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Radiation induced dissolution of UO2 based nuclear fuel - A critical review of predictive modelling approaches2012In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 420, no 1-3, p. 409-423Article, review/survey (Refereed)
    Abstract [en]

    Radiation induced dissolution of uranium dioxide (UO2) nuclear fuel and the consequent release of radionuclides to intruding groundwater are key-processes in the safety analysis of future deep geological repositories for spent nuclear fuel. For several decades, these processes have been studied experimentally using both spent fuel and various types of simulated spent fuels. The latter have been employed since it is difficult to draw mechanistic conclusions from real spent nuclear fuel experiments. Several predictive modelling approaches have been developed over the last two decades. These models are largely based on experimental observations. In this work we have performed a critical review of the modelling approaches developed based on the large body of chemical and electrochemical experimental data. The main conclusions are: (1) the use of measured interfacial rate constants give results in generally good agreement with experimental results compared to simulations where homogeneous rate constants are used; (2) the use of spatial dose rate distributions is particularly important when simulating the behaviour over short time periods; and (3) the steady-state approach (the rate of oxidant consumption is equal to the rate of oxidant production) provides a simple but fairly accurate alternative, but errors in the reaction mechanism and in the kinetic parameters used may not be revealed by simple benchmarking. It is essential to use experimentally determined rate constants and verified reaction mechanisms, irrespective of whether the approach is chemical or electrochemical.

  • 6.
    Eriksen, Trygve
    et al.
    KTH, Superseded Departments, Chemistry.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Molera, Mireia
    KTH, Superseded Departments, Chemistry.
    Sorption effects on cation diffusion in compacted bentonite1999In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 54, no 1-2, p. 231-236Article in journal (Refereed)
    Abstract [en]

    Diffusion of Na+. Cs+, Co2+ and Sr2+ in bentonite compacted to a dry density of 1800 kg m(-3) and saturated with groundwaters and aqueous solutions of differing ionic strength have been studied experimentally using the through diffusion technique. Sorption experiments have been carried out under a wide range of pH and concentration of supporting electrolyte. The dependence of the apparent diffusivity of Na+, Cs+ and Sr2+, mainly sorbed by ion exchange, on the sorption intensity is accommodated by a model encompassing diffusion of the sorbed cations within the electrical double layer next to the mineral surface in addition to diffusion in the pore water. The apparent diffusivity of Co2+, sorbed by surface complexation reactions, corresponds to complete immobilization on sorption.

  • 7.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E.
    KTH, Superseded Departments, Chemistry.
    In situ anion diffusion experiments using radiotracers2004In: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009, Vol. 68, no 3-4, p. 183-192Article in journal (Refereed)
    Abstract [en]

    Diffusion experiments in compacted bentonite have been carried out in situ using the borehole laboratory CHEMLAB. The ordinary anion iodide and the redox-sensitive pertechnetate ion have been investigated. In spite of strongly reducing groundwater conditions, technetium was found to diffuse mostly unreduced as TcO4-, although in some spots in the compacted clay, the activity was significantly higher, which may be explained by reduction of some TcO4- by iron-containing minerals in the bentonite. The measured concentration profiles in the clay cannot be accommodated by assuming one single diffusion process. The experimental data are modeled assuming two diffusion paths, intralamellar diffusion and diffusion in external water. The apparent diffusivity for the intralamellar diffusion was found to be 8.6 x 10(-11) m(2) s(-1) for iodide with a capacity factor of 0.1, while the apparent diffusivity for the diffusion in external water was found to be 5 x 10(-14) m(2) s(-1) with alpha = 2.26. The corresponding values for Tc were found to be D-a = 6 x 10(-11) m(2) s(-1), alpha = 0.1 and D-a = 1 x 10(-13) m(2) s(-1), alpha = 0.46, respectively. The diffusion constants and capacity factors obtained in this study are in accordance with data from laboratory experiments.

  • 8.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E
    Anion Diffusion Experiments Using Radiotracers Under Representative Underground ConditionsIn: Journal of Contaminant Hydrology, ISSN 0169-7722, E-ISSN 1873-6009Article in journal (Other academic)
  • 9.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E
    KTH, Superseded Departments, Chemistry.
    CHEMLAB - in situ diffusion experiments using radioactive tracers1998In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 82, p. 153-156Article in journal (Refereed)
    Abstract [en]

    In situ diffusion experiments in bentonite clay have been carried out in the probe CHEMLAB, using the radioactive tracers Co-57, Sr-85 and Cs-134. The measured diffusion profiles for the radionuclides are in good agreement with predicted profiles obtained from modelling based on apparent diffusivities and sorption coefficients obtained in laboratory experiments with corresponding clay density and ground water composition.

  • 10.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Eriksen, Trygve E
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Wold, Susanna
    KTH, Superseded Departments, Chemistry. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    LOT: in situ diffusion experiments using radioactive tracers2003In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 23, no 1-4, p. 77-85Article in journal (Refereed)
    Abstract [en]

    An experiment series at Aspo Hard Rock Laboratory, called "Long Term Test of Buffer Material", LOT, are carried out at Aspo Hard Rock Laboratory to validate models of clay buffer performance at standard KBS-3 repository conditions and to quantify clay buffer alteration processes at adverse conditions. In conjunction with the tests of the bentonite, cation diffusion tests using caesium and cobalt are performed. Each test contains 38 cylindrical blocks of bentonite clay with a hole in the middle which are placed around a copper rod in a vertically drilled hole at a depth of 450 m. In each test, four identical cylindrical bentonite plugs, doped with 1 MBq Co-57 and Cs-134, respectively, are inserted in the fifth block from the bottom. The system was left to be saturated with ground water before heating of the central copper rod started to simulate the thermal activity of radioactive waste. The experiments continued for 14 months before the bentonite blocks were drilled out using over-core drilling technique. The lowest blocks were cut up, sparsely in the outer layer, and in cubic centimeters, big samples closer to where the activity was inserted. All samples were analyzed using a gamma spectrometer to get a three-dimensional picture of the activity distribution. The system was then fitted to a diffusion model to obtain apparent diffusivities for the two cations. The apparent diffusivity for cobalt agrees well with those obtained in other in situ experiments and in laboratory studies, while the value for caesium is lower than expected. This can be due to that the clay was not fully water saturated during the experiment.

  • 11.
    Jonsson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Nielsen, Fredrik
    KTH, Superseded Departments, Chemistry.
    Ekeroth, Ella
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E.
    KTH, Superseded Departments, Chemistry.
    Modeling of the effects of radiolysis on UO2-dissolution employing recent experimental data2004In: / [ed] Oversby, VM; Werme, LO, 2004, Vol. 807, p. 385-390Conference paper (Refereed)
    Abstract [en]

    This study examines the effect of water radiolysis on the dissolution of uranium dioxide. A model is created to describe the system of uranium dioxide fragments in water, and the production and reactions of radiolysis products (using recent kinetic data). The system is evaluated under different conditions using MAKSIMA-CHEMIST. Conditions examined include presence of carbonate in the water and effects of hydrogen. The simulations are compared to experimental results on spent fuel dissolution. Surprisingly, the simulated U(VI)-release agrees within a factor of three with the experimentally found U(VI)-release. The inhibiting effect of hydrogen is clearly demonstrated by the simulations. From the results of the simulations we are also able to conclude that the main inhibiting effect of H-2 is the reaction with OH* and not the reduction of U(VI) to U(IV).

  • 12. Karnland, O
    et al.
    Sandén, T
    Johannesson, L-E
    Eriksen, Trygve
    KTH, Superseded Departments, Chemistry.
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Wold, Susanna
    KTH, Superseded Departments, Chemistry.
    Pedersen, K
    Rosborg, B
    Long term test of buffer material: Final report on the pilot parcels2000Report (Other academic)
  • 13.
    Molera, Mireia
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Anion diffusion pathways in bentonite clay compacted to different dry densities2003In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 23, no 1-4, p. 69-76Article in journal (Refereed)
    Abstract [en]

    Diffusion of the anions Cl- and I- in MX-80 compacted bentonite has been studied at different ionic strengths (0.01, 0.1 M NaClO4) and clay density (0.4, 0.8, 1.2, 1.8 g cm(-3)) at the buffered pH of bentonite 8.2 using a through-diffusion technique with measurement of breakthrough curves and concentration profiles in the bentonite. Apparent diffusivities and capacity factors (alpha=epsilon+rhoK(d)) are obtained from diffusion simulations using the computer code ANADIFF. Two diffusion processes, both with density and ionic strength dependent apparent diffusivities and capacity factors, were observed. The diffusion processes observed are ascribed to diffusion in intralayer and interparticle water. The experimental data indicate that intralayer water constitutes the dominating part of water in bentonite compacted to dry the densities 0.4-1.8 g cm(-3) studied in this work.

  • 14.
    Nielsen, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Ekeroth, Ella
    Studsvik Nuclear AB, Nyköping.
    Eriksen, Trygve E.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Simulation of radiation induced dissolution of spent nuclear fuel using the steady-state approach. A comparison to experimental data2008In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 374, no 1-2, p. 286-289Article in journal (Refereed)
    Abstract [en]

    Using the recently developed steady-state model for simulation of radiation induced dissolution of spent nuclear fuel in water we have estimated the rate of dissolution for relatively fresh fuel to 1.64 x 10(-9) Mol m(-2) s(-1). A series of experiments have been performed on fuel fragments in deoxygenated water containing 10 mM HCO3-. The dissolution rates obtained from these experiments range from 2.6 x 10(-10) to 1.6 x 10-9 Mol m(-2) s(-1). The leaching time in the experiments is 40 days or less and during this time the amount of released uranium increases linearly with time which indicates that the system has reached steady-state. The excellent agreement between the estimated dissolution rate and the dissolution rates obtained from the spent nuclear fuel leaching experiments indicates that the steady-state approach can indeed be used to predict the rate of spent nuclear fuel dissolution.

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