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  • 1.
    Horne, Gregory P.
    et al.
    Idaho Natl Lab, Ctr Radiat Chem Res, POB 1625, Idaho Falls, ID 83415 USA..
    Zarzana, Christopher A.
    Idaho Natl Lab, Ctr Radiat Chem Res, POB 1625, Idaho Falls, ID 83415 USA..
    Grimes, Travis S.
    Idaho Natl Lab, Ctr Radiat Chem Res, POB 1625, Idaho Falls, ID 83415 USA..
    Rae, Cathy
    Idaho Natl Lab, Ctr Radiat Chem Res, POB 1625, Idaho Falls, ID 83415 USA..
    Ceder, Joakim
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Chemical Engineering. Idaho Natl Lab, Ctr Radiat Chem Res, POB 1625, Idaho Falls, ID 83415 USA..
    Mezyk, Stephen P.
    Calif State Univ Long Beach, Dept Chem & Biochem, Long Beach, CA 90804 USA..
    Mincher, Bruce J.
    Idaho Natl Lab, Ctr Radiat Chem Res, POB 1625, Idaho Falls, ID 83415 USA..
    Charbonnel, Marie-Christine
    Univ Montpellier, CEA, DEN, DMRC, Marcoule, France..
    Guilbaud, Philippe
    Univ Montpellier, CEA, DEN, DMRC, Marcoule, France..
    Saint-Louis, George
    Univ Montpellier, CEA, DEN, DMRC, Marcoule, France..
    Berthon, Laurence
    Univ Montpellier, CEA, DEN, DMRC, Marcoule, France..
    Effect of chemical environment on the radiation chemistry of N,N-di-(2-ethylhexyl)butyramide (DEHBA) and plutonium retention2019In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 38, p. 14450-14460Article in journal (Refereed)
    Abstract [en]

    N,N-di-(2-ethylhexyl)butyramide (DEHBA) has been proposed as part of a hydro-reprocessing solvent extraction system for the co-extraction of uranium and plutonium from spent nuclear fuel, owing to its selectivity for hexavalent uranium and tetravalent plutonium. However, there is a critical lack of quantitative understanding regarding the impact of chemical environment on the radiation chemistry of DEHBA, and how this would affect process performance. Here we present a systematic investigation into the radiolytic degradation of DEHBA in a range of n-dodecane solvent system formulations, where we subject DEHBA to gamma irradiation, measure reaction kinetics, ligand integrity, degradation product formation, and investigate solvent system performance through uranium and plutonium extraction and strip distribution ratios. The rate of DEHBA degradation in n-dodecane was found to be slow (G = -0.31 +/- 0.02 mu mol J(-1)) but enhanced upon contact with the oxidizing conditions of the investigated solvent systems (organic-only, or in contact with either 0.1 or 3.0 M aqueous nitric acid). Two major degradation products were identified in the organic phase, bis-2-ethylhexylamine (b2EHA) and N-(2-ethylhexyl)butyramide (MEHBA), resulting from the cleavage of C-N bonds, and could account for the total loss of DEHBA up to similar to 300 kGy for organic-only conditions. Both b2EHA and MEHBA were also found to be susceptible to radiolytic degradation, having G-values of -0.12 +/- 0.01 and -0.08 +/- 0.01 mu mol J(-1), respectively. Solvent extraction studies showed: (i) negligible change in uranium extraction and stripping with increasing absorbed dose; and (ii) plutonium extraction and retention exhibits complex dependencies on absorbed dose and chemical environment. Organic-only conditions afforded enhanced plutonium extraction and retention attributed to b2EHA, while acid contacts inhibited this effect and promoted significant plutonium retention for the highest acidity. Overall it has been demonstrated that chemical environment during irradiation has a significant influence on the extent of DEHBA degradation and plutonium retention.

  • 2.
    Winberg-Wang, Helen
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Chemical Engineering.
    Water density impact on water flow and mass transport in rock fractures2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    One way of taking care of spent nuclear fuel is to place it in a geological repository. In Sweden, a three-barrier system is planned. The system is based on encapsulating the fuel in copper canisters. These are surrounded by bentonite clay and buried under 500 m of bedrock. As a part of the safety assessment, the Q-equivalent model is used to quantify the possible release of radioactive material. This model also describes the rate at which corrosive agents carried by seeping water in rock fractures can reach the canisters, which may affect the longevity of the canisters.

    The aim of this thesis was originally to develop an experimental, phys- ical model to visualize and validate the Q-equivalent model. However, the overarching theme of this work has been to study the effect of minor density differences that might be overlooked in experiments, both concentration- dependent and density-difference induced by light absorption.

    In the initial diffusion and flow-experiment and associated calculations and simulations, it was found that simple Q-equivalent can describe and quantify the mass transport in both parallel and variable aperture fractures. However, this is the case only if the density difference between seeping water and clay pore water is insignificant. It was found in experiments with dyes used to visualise the flow and diffusion patterns that even minimal density differences could significantly alter the flow pattern. Density differences can result from concentration gradients or be induced by light absorption. TheQ-equivalent model was extended to account for density-induced flow. The importance of density-induced flow due to concentration gradients at the setting of a long-term repository for nuclear waste was evaluated. It was found that concentration gradients are able to induce rapid vertical up- or downward flow. This could increase the overall mass transport of radioactive material up to the biosphere or carry it downward to larger depths.

  • 3.
    Winberg-Wang, Helen
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Chemical Engineering.
    Visualisation of mass transfer between source and seeping water in a variable aperture fracture-Impact of tracer densityManuscript (preprint) (Other academic)
    Abstract [en]

    An experiment with a vertical slot with horizontally seeping water with a dye diffusing from below was performed to help validate and visualise the Q-equivalent model, which describes the mass transfer rate from a source into flowing water such that in a repository for nuclear waste. The Q-equivalent model is used for quantifying mass transport in geological repositories. However, the tracer propagated much slower and to a lesser extent than predicted by the model. It was found that the tracer gave rise to a small density gradient, which induced buoyancy-driven flow, overwhelming that driven by the horizontal hydraulic gradient. This dramatically changed the mass transfer from the dye source into the water in the slot. For the release of contaminants, this can have detrimental as well as beneficial effects, depending on positive or negative buoyancy is induced. These observations led to an analysis of when and how density differences in a repository can influence the release and further fate of escaping radionuclides in waste repositories. This and other experiments also showed that laboratory experiments aimed to visualise flow and mass transfer processes in fractures could be very sensitive to the heating of the dye tracers by the lighting in the laboratory. 

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