| 1. |
- Amme, Marcus, et al.
(författare)
-
Combined effects of Fe(II) and oxidizing radiolysis products on UO2 and PuO2 dissolution in a system containing solid UO2 and PuO2
- 2012
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 430:1-3, s. 1-5
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
(författare)
-
The relative impact of radiolysis products in radiation induced oxidative dissolution of UO2
- 2006
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 355:1-3, s. 38-46
-
Tidskriftsartikel (refereegranskat)abstract
- 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. |
- Hart, Traver, et al.
(författare)
-
High-Resolution CRISPR Screens Reveal Fitness Genes and Genotype-Specific Cancer Liabilities
- 2015
-
Ingår i: Cell. - : Elsevier BV. - 0092-8674 .- 1097-4172. ; 163:6
-
Tidskriftsartikel (refereegranskat)abstract
- The ability to perturb genes in human cells is crucial for elucidating gene function and holds great potential for finding therapeutic targets for diseases such as cancer. To extend the catalog of human core and context-dependent fitness genes, we have developed a high-complexity second-generation genome-scale CRISPR-Cas9 gRNA library and applied it to fitness screens in five human cell lines. Using an improved Bayesian analytical approach, we consistently discover 5-fold more fitness genes than were previously observed. We present a list of 1,580 human core fitness genes and describe their general properties. Moreover, we demonstrate that context-dependent fitness genes accurately recapitulate pathway-specific genetic vulnerabilities induced by known oncogenes and reveal cell-type-specific dependencies for specific receptor tyrosine kinases, even in oncogenic KRAS backgrounds. Thus, rigorous identification of human cell line fitness genes using a high-complexity CRISPR-Cas9 library affords a high-resolution view of the genetic vulnerabilities of a cell.
|
|
| 4. |
- Hudson, Lawrence N, et al.
(författare)
-
The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project
- 2017
-
Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 7:1, s. 145-188
-
Tidskriftsartikel (refereegranskat)abstract
- The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.
|
|
| 5. |
- Jonsson, Mats, et al.
(författare)
-
Dissolution of UO2 by one- and two-electron oxidants
- 2004
-
Ingår i: Materials Research Society Symposium Proceedings. - 0272-9172 .- 1946-4274. ; 807, s. 77-82
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 6. |
- Jonsson, Mats, et al.
(författare)
-
Radiation induced spent nuclear fuel dissolution under deep repository conditions
- 2007
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 41:20, s. 7087-7093
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 7. |
- Knutsen, Halvor, et al.
(författare)
-
Combining population genomics with demographic analyses highlights habitat patchiness and larval dispersal as determinants of connectivity in coastal fish species
- 2022
-
Ingår i: Molecular Ecology. - : Wiley. - 0962-1083 .- 1365-294X. ; 31:9, s. 2562-2577
-
Tidskriftsartikel (refereegranskat)abstract
- Gene flow shapes spatial genetic structure and the potential for local adaptation. Among marine animals with non-migratory adults, the presence or absence of a pelagic larval stage is thought to be a key determinant in shaping gene flow and the genetic structure of populations. In addition, the spatial distribution of suitable habitats is expected to influence the distribution of biological populations and their connectivity patterns. We used whole genome sequencing to study demographic history and reduced representation (ddRAD) sequencing data to analyze spatial genetic structure in broadnosed pipefish (Syngnathus typhle). Its main habitat is eelgrass beds, which are patchily distributed along the study area in southern Norway. Demographic connectivity among populations was inferred from long-term (~30 year) population counts that uncovered a rapid decline in spatial correlations in abundance with distance as short as ~2 km. These findings were contrasted with data for two other fish species that have a pelagic larval stage (corkwing wrasse, Symphodus melops; black goby, Gobius niger). For these latter species, we found wider spatial scales of connectivity and weaker genetic isolation-by-distance patterns, except where both species experienced a strong barrier to gene flow, seemingly due to lack of suitable habitat. Our findings verify expectations that a fragmented habitat and absence of a pelagic larval stage promote genetic structure, while presence of a pelagic larvae stage increases demographic connectivity and gene flow, except perhaps over extensive habitat gaps.
|
|
| 8. |
- Landis, Susanne H., et al.
(författare)
-
Behavioral adjustments of a pipefish to bacterial Vibrio challenge
- 2012
-
Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 66:10, s. 1399-1405
-
Tidskriftsartikel (refereegranskat)abstract
- Animals can profit from increasing temperatures by prolonged breeding seasons and faster growth rates. However, these fitness benefits are traded off against higher parasite load and increased virulence of temperature-sensitive pathogens. In thermally stratified habitats, behavioral plasticity can allow hosts to choose the optimal temperature to enhance individual fitness and to escape parasite pressure. To test this idea, we performed a temperature choice experiment with the host-parasite system of the sex-role reversed broad-nosed pipefish (Syngnathus typhle) and its bacterial pathogen Vibrio spp. In this species, pregnant males are expected to face a trade-off between shortening their brooding period in warm water and decreasing the effect of the infection in cold water. We found that exposure to Vibrio changed the temperature preference for both pregnant and nonpregnant males, as well as females compared to nonchallenged fish that tended to prefer warm water. This study shows that behavioral plasticity is one option for avoidance of higher bacterial prevalence, as expected due to rising ocean temperatures.
|
|
| 9. |
- Landis, Susanne H., et al.
(författare)
-
Female pipefish can detect the immune status of their mates
- 2015
-
Ingår i: Behavioral Ecology and Sociobiology. - : Springer Science and Business Media LLC. - 0340-5443 .- 1432-0762. ; 69:12, s. 1917-1923
-
Tidskriftsartikel (refereegranskat)abstract
- Given the ubiquity of the parasites and their important fitness consequences on mate and offspring condition, selection for the ability to distinguish healthy from parasitized potential mates is a key process to enhance Darwinian fitness. In this study, we experimentally evaluated how the immunological experience of two potential partners influences mate choice, using the sex-role-reversed pipefish Syngnathus typhle. We exposed S. typhle to immune challenges with heat-killed Vibrio bacteria and investigated whether the activation of the immune system determined mate preferences. Our results demonstrate that the immune status of the potential partners influenced female mate preference, such that females that were exposed to an immune challenge became choosy and favored unchallenged males. Males, however, did not show any preferences for female immune status. In this context, we discuss mate choice decisions and behavioral plasticity as a complex result of immune challenge, severity of infection, as well as trans-generational effects.
|
|
| 10. |
|
|
| 11. |
- Pasin, Chloé, et al.
(författare)
-
Sex and gender in infection and immunity : addressing the bottlenecks from basic science to public health and clinical applications
- 2023
-
Ingår i: Royal Society Open Science. - 2054-5703. ; 10:7
-
Tidskriftsartikel (refereegranskat)abstract
- Although sex and gender are recognized as major determinants of health and immunity, their role is rarely considered in clinical practice and public health. We identified six bottlenecks preventing the inclusion of sex and gender considerations from basic science to clinical practice, precision medicine and public health policies. (i) A terminology-related bottleneck, linked to the definitions of sex and gender themselves, and the lack of consensus on how to evaluate gender. (ii) A data-related bottleneck, due to gaps in sex-disaggregated data, data on trans/non-binary people and gender identity. (iii) A translational bottleneck, limited by animal models and the underrepresentation of gender minorities in biomedical studies. (iv) A statistical bottleneck, with inappropriate statistical analyses and results interpretation. (v) An ethical bottleneck posed by the underrepresentation of pregnant people and gender minorities in clinical studies. (vi) A structural bottleneck, as systemic bias and discriminations affect not only academic research but also decision makers. We specify guidelines for researchers, scientific journals, funding agencies and academic institutions to address these bottlenecks. Following such guidelines will support the development of more efficient and equitable care strategies for all.
|
|
| 12. |
- Pehrman, Reijo, et al.
(författare)
-
Oxidative dissolution of actinide oxides in H2O2 containing aqueous solution : A preliminary study
- 2010
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 397:1-3, s. 128-131
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 13. |
- Roth, Olivia, et al.
(författare)
-
Factors influencing the rate of radiation-induced dissolution of spent nuclear fuel
- 2009
-
Ingår i: Research on chemical intermediates (Print). - : Springer Science and Business Media LLC. - 0922-6168 .- 1568-5675. ; 35:4, s. 465-478
-
Tidskriftsartikel (refereegranskat)abstract
- 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. |
- Roth, Olivia, et al.
(författare)
-
On the impact of reactive solutes on radiation induced oxidative dissolution of UO2
- 2009
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 385:3, s. 595-600
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 15. |
- Roth, Olivia, et al.
(författare)
-
Oxidation of UO2(s) in aqueous solution
- 2008
-
Ingår i: Central European Journal of Chemistry. - : Walter de Gruyter GmbH. - 1895-1066. ; 6:1, s. 1-14
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 16. |
- Roth, Olivia, 1978-
(författare)
-
Physical and Chemical Aspects of Radiation Induced Oxidative Dissolution of UO2
- 2006
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Denna licensiatavhandling behandlar oxidativ upplösning av UO2. Upplösning av UO2 studeras huvudsakligen då UO2-matrisen hos använt kärnbränsle förväntas fungera som en barriär mot frigörande av radionuklider i ett framtida djupförvar. Lösligheten av U(IV) är mycket låg under i djupförvaret rådande förhållanden emedan U(VI) har betydligt högre löslighet. Oxidation av UO2-matrisen kommer därför att påverka dess löslighet och därmed dess funktion som barriär. I denna avhandling studeras den relativa effektiviteten av en- och två-elektronoxidanter för upplösning av UO2. Vid låga oxidantkoncentrationer är utbytet för upplösningen för en-elektronoxidanter signifikant lägre än för två-elektronoxidanter. För en-elektronoxidanter ökar dock utbytet med ökande oxidanthalt, vilket kan förklaras av den ökade sannolikheten för två konsekutiva en-elektronoxidationer av samma reaktionssite och den ökade möjligheten till disproportionering. Radikaler och molekylära radiolysprodukters relativa inverkan på oxidativ upplösning av UO2 studeras också i denna avhandling genom mätning av mängden upplöst U(VI) i γ-bestrålade system som dominerades av olika oxidanter. Dessa studier visade att upplösningshastigheten av UO2 kan uppskattas från oxidantkoncentrationer framtagna genom simuleringar av radiolys i motsvarande homogena system och hastighetskonstanterna för ytreaktionerna. Simuleringarna visar att de molekylära oxidanterna kommer vara de viktigaste oxidanterna i alla system i denna studie vid långa bestrålningstider (>10 timmar). Vid liknande simuleringar av α-bestrålade system fanns att vid förhållanden relevanta för ett djupförvar för använt kärnbränsle, är det endast de molekylära oxidanterna (i huvudsak H2O2) som är av betydelse för upplösningen av bränslematrisen. Då använt kärnbränsle innehåller en mängd radionuklider som utsätter UO2-matrisen för kontinuerlig bestrålning, är det av vikt att undersöka hur bestrålning påverkar reaktiviteten av UO2. Bestrålningseffekten på reaktionen mellan UO2 och MnO4- studerades. Dessa försök visade att bestrålning av UO2 vid doser >40 kGy leder till att reaktiviteten ökar upp till 1.3 gånger reaktiviteten av obestrålad UO2. Den ökade reaktiviteten kvarstår efter bestrålningen och effekten kan därför möjligen tillskrivas permanenta förändringar i materialet. Vid uppskattning av reaktiviteten hos använt kärnbränsle måste hänsyn tas till denna effekt då bränslet redan efter ett par dagar i reaktor blivit utsatt för doser >40 kGy. Det har tidigare föreslagits att hastigheten för en heterogen västka/fast-fas reaktion är beroende av partikelstorleken hos det fasta materialet, vilket har studerats för UO2-partiklar i denna avhandling. Experimentellt bestämda kinetiska parametrar jämförs med de föreslagna ekvationerna för fyra storleksfraktioner av UO2-pulver och en UO2-pellet. Studien visade partikelstorleksberoendet av andra ordningens hastighetskonstant och aktiveringsenergin för oxidation av UO2 med MnO4- beskrivs relativt väl av de föreslagna ekvationerna.
|
|
| 17. |
- Roth, Olivia, et al.
(författare)
-
Radiation chemical synthesis and characterization of UO2 nanoparticles
- 2009
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 383:3, s. 231-236
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 18. |
- Roth, Olivia, et al.
(författare)
-
Radiation enhanced reactivity of UO2
- 2006
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 354:1-3, s. 131-136
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 19. |
- Roth, Olivia, 1978-
(författare)
-
Redox Chemistry in Radiation Induced Dissolution of Spent Nuclear Fuel : from Elementary Reactions to Predictive Modeling
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 20. |
- Roth, Olivia, et al.
(författare)
-
The influence of particle size on the kinetics of UO2 oxidation in aqueous powder suspensions
- 2006
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 353:1-2, s. 75-79
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 21. |
- Sundin, Sara, et al.
(författare)
-
H2O2 and radiation induced dissolution of UO2 and SIMFUEL in HCO3- deficient aqueous solution
- 2013
-
Ingår i: Journal of Nuclear Materials. - : Elsevier. - 0022-3115 .- 1873-4820. ; 443:1-3, s. 291-297
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 22. |
- Trummer, Martin, et al.
(författare)
-
H2 inhibition of radiation induced dissolution of spent nuclear fuel
- 2009
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 383:3, s. 226-230
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
