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- El Jamal, Sawsan, et al.
(författare)
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On the Stability of Uranium Carbide in Aqueous Solution-Effects of HCO3- and H2O2
- 2021
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 6:37, s. 24289-24295
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Tidskriftsartikel (refereegranskat)abstract
- Uranium carbide (UC) is a candidate fuel material for future Generation IV nuclear reactors. As part of a general safety assessment, it is important to understand how fuel materials behave in aqueous systems in the event of accidents or upon complete barrier failure in a geological repository for spent nuclear fuel. As irradiated nuclear fuel is radioactive, it is important to consider radiolysis of water as a process where strongly oxidizing species can be produced. These species may display high reactivity toward the fuel itself and thereby influence its integrity. The most important radiolytic oxidant under repository conditions has been shown to be H2O2. In this work, we have studied the dissolution of uranium upon exposure of UC powder to aqueous solutions containing HCO3- and H2O2, separately and in combination. The experiments show that UC dissolves quite readily in aqueous solution containing 10 mM HCO3- and that the presence of H2O2 increases the dissolution further. UC also dissolves in pure water after the addition of H2O2, but more slowly than in solutions containing both HCO3- and H2O2. The experimental results are discussed in view of possible mechanisms.
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- El Jamal, Sawsan
(författare)
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Stability of Alternative Nuclear Fuel Materials in Aqueous Systems
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nuclear power produces a large portion of the electricity worldwide. It has been the largest low-carbon energy source for more than 30 years and has played an essential role in the security of energy supplies for many countries. However, despite its advantages, its future is unknown mainly because of accidents that can happen under reactor operation and the high radioactivity of the fuel after use. Therefore, Generation IV nuclear power has been introduced as it promises a sustainable and economical way of producing energy and reduces some of the risks observed in current reactors. UC and UN have advantageous properties compared to conventional UO2-based fuel which makes them promising fuel candidates for Generation IV nuclear reactors. Even though the fuel for Generation IV reactors is planned to be reprocessed, unexpected political decisions may change these plans, and the used fuel could end up in a geological repository. Therefore, the behavior of these new fuel materials must be understood in accident scenarios in reactors as well as under deep geological repository conditions. The radioactivity of the used fuel will induce radiolysis of water that comes in contact with it. This will lead to oxidative dissolution of the fuel and this is one of the potential routes for radionuclide release in the environment.In the first part of this thesis, UC and UN have been investigated in aqueous solutions under anoxic conditions, and under the influence of external γ-radiation and H2O2, the latter mimicking the impact of α-radiolysis. The hydrolysis of these materials in aqueous systems resulted in matrix dissolution which is not observed for UO2. The oxidative dissolution induced by H2O2 is more prominent than hydrolysis in water with or without added HCO3- where higher concentrations of dissolved uranium can be detected. In addition, the differences in reactivity are discussed for these materials and H2O2 is most reactive towards UN followed by UC and finally UO2, yet the dissolution yield is the lowest for UN. The change in UC and UN behavior with consecutive exposure to H2O2 was attributed to a change in surface reactivity where catalytic decomposition of H2O2 becomes possible. As it was observed for H2O2 additions, radiation induced oxidative dissolution also dominates over hydrolysis. Unexpectedly high concentrations of H2O2 were observed in the irradiated systems. This was found to be due to formation of nano-particulate studtite that could not be separated from the solutions samples by filtration. Hence, it turned out to be impossible to determine the free U(VI) and H2O2 concentrations in these systems.Finally, the stability of pure and ZrN containing UN pellet fragments was investigated in aqueous system under external γ-radiation or H2O2 exposure. The behavior of these pellet fragments was similar to the UN powder where the dissolution of uranium was enhanced under oxidizing conditions if compared with anoxic conditions (hydrolysis). Consecutive exposures of UN pellet fragments to H2O2 showed a change in surface reactivity. This change is attributed to the formation of an oxide layer on the surface of UN, as UO2 is less reactive towards H2O2 and UO2 pellets display lower dissolution yields than UN pellets. In addition, the impact of ZrN as a stabilizing additive to UN pellets was studied. The addition of ZrN to UN is expected to stabilize the UN matrix and thus render a more accident tolerant fuel. Interestingly, it was shown that under oxidizing conditions, ZrN did not have a significant impact on the stability of UN pellets in aqueous systems
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- Hansson, Niklas, 1992, et al.
(författare)
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Geometrical aspects of alpha dose rates from UO2 based fuels
- 2022
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Ingår i: Radiation Physics and Chemistry. - : Elsevier BV. - 0969-806X .- 1879-0895. ; 199, s. 110336-
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Tidskriftsartikel (refereegranskat)abstract
- Models for calculating dose rates of spherical particles as well as in fuel cracks are important for radionuclide source term estimations. Dose rates from UO2 based fuels were calculated for planar, spherical, and crack geometries. The escape probability for a-particles in spherical UO2 particles was derived as a continuous equation. The dose rate increased with increasing spherical radius due to the decreasing relative volume of the surrounding water layer. The model produced escape probabilities that were closely predicted by the theoretical derivation. It was shown that the dose rate in water filled fuel cracks with width smaller than the range of an alpha-particle led to dissolution rates that were lower per unit surface area.
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- Puranen, Anders, 1977-, et al.
(författare)
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A study on the immobilization of selenium oxyanions by H2/Pd(s) in aqueous solution : Confirmation of the one-electron reduction barrier of selenate
- 2010
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Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 116:1-4, s. 16-23
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Tidskriftsartikel (refereegranskat)abstract
- Selenium is a trace element of concern in several geochemical contexts, due to the potentially high mobility of the selenium oxyanions and the narrow range between deficiency and toxicity of the element. For high level nuclear waste repositories the long-lived fission product 79Se has been identified as a potential key dose contributor for the long-term safety. This paper deals with the catalytic effect of Pd(s) on the H2 reduction of selenium oxyanions which was studied experimentally in aqueous solutions containing bicarbonate and chloride. Pd-catalysts and hydrogen have been proposed for the remediation of various groundwater contaminants and can also serve as a model substance for catalytic noble metal inclusions present in spent nuclear fuel. In this study selenite (SeO32−) was found to adsorb on Pd. In the presence of hydrogen the rate of selenite removal increased yielding elemental Se. However, no adsorption or reduction of selenate (SeO42−) was observed. A simple radiation chemical experiment revealed a notable barrier towards stepwise one-electron reduction of selenate to selenite. This provides an explanation for the lower reactivity of selenate in systems where reductive immobilization of selenite as well as selenate is thermodynamically favorable.
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- Yang, Yi, et al.
(författare)
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Gamma-radiation induced synthesis of freestanding nickel nanoparticles
- 2021
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 50:1, s. 376-383
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Tidskriftsartikel (refereegranskat)abstract
- A versatile method to produce metallic nickel nanoparticles is demonstrated. Metallic Ni nanoparticles have been synthesized from aqueous solution of NiCl2 using gamma-radiation induced reduction. To prevent Ni re-oxidation, post-irradiation treatment was elaborated. Structural and compositional analyses were executed using X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. These studies reveal that the synthesized material consists of fcc Ni particles having size of 3.47 +/- 0.71 nm. The nanoparticles have a tendency to agglomerate to the larger clusters. The latter are partially oxidized to form thin amorphous/poor-crystalline Ni(OH)(2)/NiO layers at the surface. Magnetization measurements demonstrate that the nanomaterial exhibit ferromagnetic-like behaviour with magnetization 30% lower than that in bulk Ni. The large active surface area (ECSA, 39.2 m(2) g(-1)) and good electrochemical reversibility, confirmed by the electrochemical studies, make the synthesized material a potential candidate as an active component for energy storage devices.
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- Ahlsson, Fredrik, 1967-, et al.
(författare)
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Adipokines and their relation to maternal energy substrate production, insulin resistance and fetal size
- 2013
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Ingår i: European Journal of Obstetrics, Gynecology, and Reproductive Biology. - : Elsevier BV. - 0301-2115 .- 1872-7654. ; 168:1, s. 26-29
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE:The role of adipokines in the regulation of energy substrate production in non-diabetic pregnant women has not been elucidated. We hypothesize that serum concentrations of adiponectin are related to fetal growth via maternal fat mass, insulin resistance and glucose production, and further, that serum levels of leptin are associated with lipolysis and that this also influences fetal growth. Hence, we investigated the relationship between adipokines, energy substrate production, insulin resistance, body composition and fetal weight in non-diabetic pregnant women in late gestation.STUDY DESIGN:Twenty pregnant women with normal glucose tolerance were investigated at 36 weeks of gestation at Uppsala University Hospital. Levels of adipokines were related to rates of glucose production and lipolysis, maternal body composition, insulin resistance, resting energy expenditure and estimated fetal weights. Rates of glucose production and lipolysis were estimated by stable isotope dilution technique.RESULTS:Median (range) rate of glucose production was 805 (653-1337)μmol/min and that of glycerol production, reflecting lipolysis, was 214 (110-576)μmol/min. HOMA insulin resistance averaged 1.5±0.75 and estimated fetal weights ranged between 2670 and 4175g (-0.2 to 2.7 SDS). Mean concentration of adiponectin was 7.2±2.5mg/L and median level of leptin was 47.1 (9.9-58.0)μg/L. Adiponectin concentrations (7.2±2.5mg/L) correlated inversely with maternal fat mass, insulin resistance, glucose production and fetal weight, r=-0.50, p<0.035, r=-0.77, p<0.001, r=-0.67, p<0.002, and r=-0.51, p<0.032, respectively. Leptin concentrations correlated with maternal fat mass and insulin resistance, r=0.76, p<0.001 and r=0.73, p<0.001, respectively. There was no correlation between maternal levels of leptin and rate of glucose production or fetal weight. Neither were any correlations found between levels of leptin or adiponectin and maternal lipolysis or resting energy expenditure.CONCLUSION:The inverse correlations between levels of maternal adiponectin and insulin resistance as well as endogenous glucose production rates indicate that low levels of adiponectin in obese pregnant women may represent one mechanism behind increased fetal size. Maternal levels of leptin are linked to maternal fat mass and its metabolic consequences, but the data indicate that leptin lacks a regulatory role with regard to maternal lipolysis in late pregnancy.
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| 10. |
- Ahlstrand, Christina, 1957, et al.
(författare)
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Reliabilitetstestning av Purdue Pegboard® (finmotoriktest).
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I MQ-FAS studien, vars syfte var att ändra muskelspänningsmönstret hos kvinnor med kroniska nackbesvär, ingick ett besticktorkningsmoment som en standardiserad arbetsuppgift i hemmet. För validering av denna besticktorkning har en pilotstudie genomförts, 12 personer torkade bestick vid två tillfällen. I studien, som utfördes av 2 testledare, ingick även ett finmotorikstest (Purdue Pegboard), ansträngningsskattning (Borg RPE-skalan) samt ett frågeformulär. Detta test kan med vissa justeringar troligen vara användbart som ett mått på arbetsförmåga av övre extremiteter vid utförande av arbetssyssla i hemmet, och jämföra individ med sig själv, för att mäta om funktionsnedsättning eller ökning har skett. Dock skall poängteras att detta var en pilotstudie och ytterligare studie av reliabilitet och validitet rekommenderas innan testet används i stor utsträckning för att mäta om funktionsnedsättning eller ökning har skett.
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