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  • 1. Amme, Marcus
    et al.
    Pehrman, Reijo
    Deutsch, Rudolf
    Roth, Olivia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Combined effects of Fe(II) and oxidizing radiolysis products on UO2 and PuO2 dissolution in a system containing solid UO2 and PuO22012In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 430, no 1-3, p. 1-5Article in journal (Refereed)
    Abstract [en]

    The stability of UO2 spent nuclear fuel in an oxygen-free geological repository depends on the absence of oxidizing reaction partners in the near field. This work investigates the reactions between the products of water radiolysis by alpha radiation and Fe(II) an the effect on UO2 dissolution. Solid (PuO2)-Pu-238 powder and UO2 pellet were allowed to react in Fe(II) solution in oxygen-free batch reactor tests and kinetics of the subsequent redox reactions were measured. Depending on the concentration of Fe(II) (tests with 10(-5) and 10(-4) mol L-1 were made), the induced redox reactions took place between 20 and 400 h. Dissolved uranium concentrations went first through a minimum caused by reduction, followed by a maximum caused by radiolytic oxidation, and eventually reached another minimum, probably due to sorption on precipitated Fe(III). Plutonium concentrations were decreasing steadily after going through a maximum about 70 h from the start of the experiments. The results show that in the presence of the strong alpha-radiolytic field induced by the presence of solid Pu-238, the behavior of the system is largely governed by Fe(II) as it controls the H2O2 concentration, reduces U(VI) in solution and drives the Fenton reaction leading to the oxidation of Pu(IV).

  • 2.
    Ekeroth, Ella
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Roth, Olivia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    The relative impact of radiolysis products in radiation induced oxidative dissolution of UO22006In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 355, no 1-3, p. 38-46Article in journal (Refereed)
    Abstract [en]

    The relative impact of radiolysis products in radiation induced oxidative dissolution Of UO2 has been studied experimentally. The experiments were performed by y-irradiating an aqueous solution containing HCO3 and a UO2-pellet. The U(VI) concentration in the solution was measured as a function of irradiation time. The aqueous solution was saturated with Ar, N2O, N2O/O-2 (80/20), air and O-2 in order to vary the conditions and the initial oxidant yields. The measured rate of oxidation was significantly higher for the O-2- and air saturated systems compared to the other systems. Using oxidant concentrations derived from numerical simulations of the corresponding homogeneous systems and previously determined rate constants for oxidation Of UO2, the relative trend in rate of oxidation in the different systems was reproduced. The results from the simulations were also used to estimate the relative impact of the oxidative radiolysis products as a function of irradiation time, both for gamma- and alpha-irradiated systems. For 7-irradiated systems saturated with Ar, air or 02, the most important oxidant is H2O2 while for N2O- and N2O/O-2-saturated systems the most important oxidant is CO3.-. For a-irradiated systems the most important oxidant was found to be H2O2.

  • 3.
    Jonsson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Ekeroth, Ella
    KTH, Superseded Departments, Chemistry.
    Roth, Olivia
    KTH, Superseded Departments, Chemistry.
    Dissolution of UO2 by one- and two-electron oxidants2004In: Materials Research Society Symposium Proceedings, ISSN 0272-9172, E-ISSN 1946-4274, Vol. 807, p. 77-82Article in journal (Refereed)
    Abstract [en]

    In this work, the efficiency of one- and two-electron oxidants in oxidative dissolution Of UO2 has been investigated. This was accomplished by measuring the U(VI)-concentration in solution after exposing UO2-powder to controlled amounts of oxidants in aqueous solution. The oxidants used in this study are H2O2, IrCl62-, CO3.- and OH..H2O2 acts as a two-electron oxidant while the remaining three oxidants are one-electron oxidants. CO3.- and OH. were generated using gamma-radiolysis. The results clearly show that the dissolution yields for one-electron oxidants (per electron pair) are lower than the yields for two-electron oxidants. Furthermore, the yields for one-electron oxidants increase with increasing amount of oxidant (especially at low amounts of oxidant). The rationale for this is that U(VI) is the main soluble species which is formed directly upon two-electron oxidation. For one-electron oxidants the primary oxidation product is U(V) which can form U(VI) upon reaction with a second oxidant. The probability for a second oxidation is however low at low concentrations of oxidant.

  • 4.
    Jonsson, Mats
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Nielsen, Fredrik
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Roth, Olivia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Ekeroth, Ella
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Nilsson, Sara
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Hossain, Mohammad Mohsin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Radiation induced spent nuclear fuel dissolution under deep repository conditions2007In: Environmental Science and Technology, ISSN 0013-936X, Vol. 41, no 20, p. 7087-7093Article in journal (Refereed)
    Abstract [en]

    The dynamics of spent nuclear fuel dissolution in groundwater is an important part of the safety assessment of a deep geological repository for high level nuclear waste. In this paper we discuss the most important elementary processes and parameters involved in radiation induced oxidative dissolution of spent nuclear fuel. Based on these processes, we also present a new approach for simulation of spent nuclear fuel dissolution under deep repository conditions. This approach accounts for the effects of fuel age, burn up, noble metal nanoparticle contents, aqueous H-2 and HCO3- concentration, water chemistry, and combinations thereof. The results clearly indicate that solutes consuming H2O2 and combined effects of noble metal nanoparticles and H-2 have significant impact on the rate of spent nuclear fuel dissolution. Using data from the two possible repository sites in Sweden, we have employed the new approach to estimate the maximum rate of spent nuclear fuel dissolution. This estimate indicates that H-2 produced from radiolysis of groundwater alone will be sufficient to inhibit the dissolution, completely for spent nuclear fuel older than 100 years.

  • 5.
    Pehrman, Reijo
    et al.
    European Commission, Joint Research Centre, Institute for Transuranium Elements.
    Amme, Marcus
    European Commission, Joint Research Centre, Institute for Transuranium Elements.
    Roth, Olivia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Ekeroth, Ella
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Oxidative dissolution of actinide oxides in H2O2 containing aqueous solution: A preliminary study2010In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 397, no 1-3, p. 128-131Article in journal (Refereed)
    Abstract [en]

    Oxidative dissolution Of Spent nuclear fuel is an important issue in the safety assessment of a future geological repository for Spent nuclear fuel. Although UO2 Constitutes, in terms of mass, the majority of the spent fuel material, its main radiotoxicity is (after extended storage times) contained in actinides with half lives shorter than that of 238-uranium, such as isotopes of Np and Pu. Relatively little information is available on the dissolution behavior of Np and Pu in comparable environments. This work investigates the oxidative dissolution of NpO2 and PuO2 in non-complexing aqueous solutions containing H2O2 and compares their behavior with that of UO2. We have found that oxidative dissolution takes place for all three actinides in the presence of H2O2. Based on the obtained dissolution rates, we Would not expect the dissolution of the actinides to be congruent. Instead, in a System Without complexing agent, the release rates of Np and Pu are expected to be lower than the U release rate.

  • 6.
    Roth, Olivia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Physical and Chemical Aspects of Radiation Induced Oxidative Dissolution of UO22006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The general subject of this thesis is oxidative dissolution of UO2. The dissolution of UO2 is mainly investigated because of the importance of the UO2 matrix of spent nuclear fuel as a barrier against radionuclide release in a future deep repository. U(IV) is extremely insoluble under the reducing conditions prevalent in a deep repository, whereas U(VI) is more soluble. Hence, oxidation of the UO2-matrix will affect its solubility and thereby its function as a barrier. In this thesis the relative efficiency of one- and two electron oxidants in dissolving UO2 is studied. The oxidative dissolution yield of UO2 was found to differ between one- and two-electron oxidants. At low oxidant concentrations the dissolution yields for one-electron oxidants are significantly lower than for two-electron oxidants. However, the dissolution yield for one-electron oxidants increases with increasing oxidant concentration, which could be rationalized by the increased probability for two consecutive one-electron oxidations at the same site and the increased possibility for disproportionation.

    Furthermore, the relative impact of radical and molecular radiolysis products on oxidative dissolution of UO2 is investigated. Experiments were performed where the amount of dissolved U(VI) was measured in γ-irradiated systems dominated by different oxidants. We have found that the UO2 dissolution rate in systems exposed to γ-irradiation can be estimated from oxidant concentrations derived from simulations of radiolysis in the corresponding homogeneous systems and rate constants for the surface reactions. These simulations show that for all systems studied in this work, the molecular oxidants will be the most important oxidants for long irradiation times (>10 hours). Similar simulations of α-irradiated systems show that in systems relevant for a deep repository for spent nuclear fuel, only the molecular oxidants (mainly H2O2) are of importance for the dissolution of the fuel matrix.

    The effect on UO2 reactivity by irradiation of the material is of importance when predicting the spent fuel dissolution rate since the fuel, due to its content of radionuclides, is exposed to continuous self-irradiation. The effect of irradiation on the reaction between solid UO2 and MnO4- in aqueous solutions was studied. It was found that irradiation of UO2 at doses >40 kGy increases the reactivity of the material up to ~1.3 times the reactivity of unirradiated UO2. The increased reactivity remains after the irradiation and can possibly be attributed to permanent changes in the material. This issue must be taken into account when predicting the reactivity of spent nuclear fuel since the fuel is exposed to doses >40 kGy after only a few days in the reactor.

    It has earlier been suggested that the rate of a heterogeneous liquid-solid reaction depends on the size of the solid particles. This was investigated for UO2 particles in this thesis. Experimental kinetic parameters are compared to the previously proposed equations for UO2 powder of four size fractions and a UO2 pellet. We have found that the particle size dependence of the second order rate constant and activation energy for oxidation of UO2 by MnO4- is described quite well by the proposed equations.

  • 7.
    Roth, Olivia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Redox Chemistry in Radiation Induced Dissolution of Spent Nuclear Fuel: from Elementary Reactions to Predictive Modeling2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The focus of this doctoral thesis is the redox chemistry involved in radiation induced oxidative dissolution of spent nuclear fuel and UO2 (as a model substance for spent nuclear fuel). It is shown that two electron oxidants are more efficient than one electron oxidants in oxidative dissolution of UO2 at low oxidant concentrations. Furthermore, it is shown that H2O2 is the only oxidant that has to be taken into account in radiation induced dissolution of UO2 under deep repository conditions (granite groundwater dominated by α-radiolysis). Previously determined rate constants for oxidation of UO2 by H2O2 and O2, and rate constants for dissolution of U(VI) from the surface are successfully used to reproduce numerous UO2 dissolution rates reported in the literature. The impact of reactive solutes (Fe(II)(aq), 2-propanol and chloride) and Pd-inclusions (as a model for ε-particles) in combination with H2, on radiation induced oxidative dissolution of UO2 is investigated. It is shown that both the studied reactive solutes (under oxygen free conditions) and the combination of Pd inclusions and H2 inhibit the dissolution. Calculations (based on the fuel inventory) show that 1 µM Fe(II)(aq) decreases the dissolution rate by a factor of ~50 and that 1 ppm surface coverage of ε-particles is sufficient to completely stop the dissolution of 100 year old fuel (assuming 40 bar H2).The dissolution behavior of NpO2 and PuO2 in H2O2 containing aqueous solution without complexing agent is studied and compared to UO2. Based on the measured dissolution rates, we would not expect the dissolution of the actinides to be congruent. Instead, in a system without complexing agent, the rates Np and Pu are expected to be lower than the U release rate. The effect of ionizing irradiation on the UO2 reactivity is studied in order to elucidate the effect of self-irradiation on the reactivity of the spent fuel matrix. It is shown that a threshold dose must be achieved before any effect of irradiation can be seen. Beyond the threshold the reactivity seems to increase with increasing dose. Furthermore, the effect appears to be permanent. The effect of particle size on the reactivity of UO2 powder is studied in view of proposed theories suggesting a particle size dependence of both the pre-exponential factor and the activation energy for redox reactions. The rate constant and activation energy for oxidation of UO2 by MnO4- seems to agree with the proposed equations. The radiation chemical synthesis of UO2 nanoparticles is studied. It is shown that U(VI) released by dissolution of spent nuclear fuel could be reduced to UO2 nanoparticles.These particles could, due to their high reactivity towards H2O2, act as oxidant scavenger in a future deep repository for spent nuclear fuel.

  • 8.
    Roth, Olivia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Bönnemark, Tobias
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    The influence of particle size on the kinetics of UO2 oxidation in aqueous powder suspensions2006In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 353, no 1-2, p. 75-79Article in journal (Refereed)
    Abstract [en]

    Previous studies have indicated that the rate of a heterogeneous liquid-solid reaction depends on the size of the solid particles. It has been suggested that both the pre-exponential factor and the activation energy depend on the particle size. The processes involved in dissolution of UO2 have been extensively studied because of their importance for the safety analysis of a future deep repository for spent nuclear fuel and in many of these studies powder suspensions of UO2 are used as a model system. Therefore, it is of importance to investigate and quantify the particle size effect on the kinetics of UO2 oxidation in order to enable comparison of data from studies oil different solid substrates. In this work the influence of particle size on the second order rate constant and on the activation energy of the reaction between MnO4- and UO2 was studied using aqueousUO(2)-particle suspensions of four different size distributions. A comparative study of the activation energy for the reaction using a UO2 pellet was also performed.

  • 9.
    Roth, Olivia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Hasselberg, Hanna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Radiation chemical synthesis and characterization of UO2 nanoparticles2009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 383, no 3, p. 231-236Article in journal (Refereed)
    Abstract [en]

    In a deep repository for spent nuclear fuel, U(VI)(aq) released upon dissolution of the fuel matrix could, in reducing parts of the system, be converted to U(IV) species which might coalesce and form nanometersized UO2 particles. This type of particles is expected to have different properties compared to bulk UO2(s). Hence, their properties, in particular the capacity for oxidant consumption, must be investigated in order to assess the effects of formation of such particles in a deep repository. In this work, methods for radiation chemical synthesis of nanometer-sized UO2 particles, by electron- and gamma-irradiation of U(VI) solutions, are presented. Electron-irradiation proved to be the most efficient method, showing high conversions of U(VI) and yielding small particles with a narrow size distribution (22-35 nm). Stable colloidal suspensions were obtained at low pH and ionic strength (pH 3, I = 0.03). Furthermore, the reactivity of the produced UO2 particles towards H2O2 is investigated. The U(IV) fraction in the produced particles was found to be similar to 20% of the total uranium content, and the results show that the UO2 nanoparticles are significantly more reactive than micrometer-sized UO2 when it comes to H2O2 consumption, the major part of the H2O2 being catalytically decomposed on the particle surface.

  • 10.
    Roth, Olivia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    On the impact of reactive solutes on radiation induced oxidative dissolution of UO22009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 385, no 3, p. 595-600Article in journal (Refereed)
    Abstract [en]

    The impact of 2-propanol (100 mM), NaCl (0.1 - 2 M) and Fe(II)(aq) (10 mu M) on the radiation induced oxidative dissolution of UO2 is investigated experimentally by gamma-irradiating a UO2 pellet immersed in aqueous solution containing 10 mM HCO3- together with one of the studied solutes and measure the U(VI) concentration in solution as a function of irradiation time. The solution was saturated with one of the following gases; Air, N2O, inert gas (N-2 or At) in order to vary the experimental conditions and/or avoid the influence of oxygen. The results show that, in the presence of oxygen, 2 M chloride decrease the rate of UO2 dissolution whereas the dissolution rate increases somewhat in the presence of 100 mM 2-propanol. Under oxygen-free conditions both 2 M chloride, 100 mM 2-propanol and 10 mu M Fe(II)(aq) decrease the rate of UO2 dissolution. The trends in dissolution rates were reproduced by calculations based on previously determined rate constants for UO2 oxidation and oxidant concentrations obtained from numerical simulation of radiolysis in the corresponding homogeneous systems (taking reactions between the different solutes and the products of water radiolysis as well as changes in oxygen solubility into account). However, the results indicate that we cannot fully account for the G-values in 2 M chloride solution or all reactions involving CI- in the aqueous phase. This calls for further studies of the chloride system.

  • 11.
    Roth, Olivia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Oxidation of UO2(s) in aqueous solution2008In: Central European Journal of Chemistry, ISSN 1895-1066, Vol. 6, no 1, p. 1-14Article in journal (Refereed)
    Abstract [en]

    In this review the kinetics and mechanism of oxidative dissolution of UO2(s), mainly under conditions of relevance for the safety assessment of a deep geological repository for spent nuclear fuel, are discussed. Rate constants for the elementary processes involved (oxidation of UO2 and dissolution of oxidized UO2) are used to calculate the rates of oxidative UO2(s) dissolution under various conditions (type of oxidant, oxidant concentration and HCO3-/CO32- concentration) for which experimental data are also available. The calculated rates are compared to the corresponding experimental values under the assumption that the experimental numbers reflect the steady-state conditions of the system. The agreement between the calculated rates and the corresponding experimental ones is very good, in particular for the higher rates. In general, the calculated rates are somewhat higher than the experimental numbers. This can be due partly to the use of initial concentrations rather than steady-state concentrations in the calculations. The kinetic data are also used to quantitatively discuss the dynamics of spent nuclear fuel dissolution under deep geological repository conditions.

  • 12.
    Roth, Olivia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Nilsson, Sara
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Radiation enhanced reactivity of UO22006In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 354, no 1-3, p. 131-136Article in journal (Refereed)
    Abstract [en]

    Pure UO2 is often used as a model compound when studying reactions of importance in a future deep repository for spent nuclear fuel. The reactivity of pure UO2 is not expected to be identical to the reactivity of the UO2-matrix of spent nuclear fuel for several reasons. One reason is that the spent fuel, due to the content of radionuclides, is continuously being self-irradiated. The aim of this study is to investigate how irradiation of solid UO2 surfaces affects their reactivity towards oxidants. The effect of irradiation (gamma or electrons) on the reaction between solid UO2 and MnO4- in aqueous solutions containing carbonate has been studied. It was found that irradiation with high doses (> 40 kGy) increased the reactivity of the UO2 to about 1.3 times the reactivity of unirradiated UO2.

  • 13.
    Roth, Olivia
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Trummer, Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Factors influencing the rate of radiation-induced dissolution of spent nuclear fuel2009In: Research on chemical intermediates (Print), ISSN 0922-6168, E-ISSN 1568-5675, Vol. 35, no 4, p. 465-478Article in journal (Refereed)
    Abstract [en]

    Several countries plan to store spent nuclear fuel in deep geological repositories. Accurate prediction of the spent fuel dissolution rate is a key issue in the safety assessment of a future deep repository. A reliable quantitative model for radiation-induced spent fuel dissolution must be based on an accurate description of the dose distribution around the spent fuel and fundamental knowledge about the elementary processes involved. In this paper, we discuss factors influencing the rate of radiation-induced dissolution of spent nuclear fuel, focusing on solutes (H-2, HCO3 (-), Fe(II) and organic substances affecting the H2O2 concentration and factors influencing the reactivity of the fuel surface towards H2O2. Taking these factors into account, we have also simulated dissolution of spent nuclear fuel under realistic deep repository conditions.

  • 14.
    Sundin, Sara
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Dahlgren, Björn
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Roth, Olivia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    H2O2 and radiation induced dissolution of UO2 and SIMFUEL in HCO3- deficient aqueous solution2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 443, no 1-3, p. 291-297Article in journal (Refereed)
    Abstract [en]

    Understanding UO2 matrix dissolution is of major importance for the safety assessment of a future deep geological repository. Oxidative dissolution of UO2 and SIMFUEL pellets have been extensively studied in HCO3- solutions, while less is known about systems with no or very low HCO3- concentrations. The aim of this work is to elucidate the oxidative dissolution of UO2 and SIMFUEL pellets in HCO3- free solutions by studying the dissolution of U (VI) and consumption of H2O2 over time. The results are compared with previous experiments performed in HCO3- solutions. The oxidative dissolution rate is higher for the UO2 pellet in HCO3- compared to the other systems. It is evident that the kinetics of the reaction with H2O2 is qualitatively different for SIMFUEL in comparison with pure UO2. For the UO2 pellet in pure water, the presence of a secondary phase (meta) studtite, on the surface of the pellet is confirmed by Raman spectroscopy. The kinetic impact of the secondary phase is evaluated in separate UO2 powder experiments. The (meta) studtite (surface) precipitation leads to a slower release of uranium into the solution. Numerical simulations using experimentally determined rate constants are used to evaluate a simple mechanism of surface precipitation. The numerical results are in fair agreement with the experimental observations given certain criteria. In addition, the γ-radiation induced dissolution of UO 2 and SIMFUEL pellets were investigated in pure water, and compared with HCO3- systems. Also here the dissolution rate of uranium is higher for UO2 in HCO3- compared to pure water, while for SIMFUEL longer irradiation times are needed to observe any difference between pure and HCO3- containing water.

  • 15.
    Trummer, Martin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Roth, Olivia
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Hinhibition of radiation induced dissolution of spent nuclear fuel2009In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 383, no 3, p. 226-230Article in journal (Refereed)
    Abstract [en]

    In order to elucidate the effect of noble metal clusters in spent nuclear fuel on the kinetics of radiation induced spent fuel dissolution we have used I'd particle doped UO2 pellets. The catalytic effect of Pd particles on the kinetics of radiation induced dissolution Of UO2 during gamma-irradiation in HCO3- containing solutions purged with N-2 and H-2 was studied in this work. Four pellets with Pd concentrations of 0%, 0.1%, 1% and 3% were produced to mimic spent nuclear fuel. The pellets were placed in 10 mM HCO3- aqueous solutions and gamma-irradiated, and the dissolution of UO22+ was measured spectrophotometrically as a function of time. Under N-2 atmosphere, 3% I'd prevent the dissolution of uranium by reduction with the radiolytically produced H-2, while the other pellets show a rate of dissolution of around 1.6 x 10(-9) mol m(-2) s(-1). Under H-2 atmosphere already 0.1% Pd effectively prevents the dissolution of uranium, while the rate of dissolution for the pellet without Pd is 1.4 x 10(-9) mol m(-2) s(-1). It is also shown in experiments without radiation in aqueous solutions containing H2O2 and O-2 that epsilon-particles catalyze the oxidation of the UO2 matrix by these molecular oxidants, and that the kinetics of the catalyzed reactions is close to diffusion controlled.

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