| 1. |
- Aneheim, Emma, 1982, et al.
(författare)
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Extraction experiments after radiolysis of a proposed GANEX solvent - the effect of time
- 2012
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Ingår i: Procedia Chemistry. - : Elsevier BV. - 1876-6196. ; 7, s. 123-129
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Konferensbidrag (refereegranskat)abstract
- In a solvent intended for use within group actinide extraction CyMe4-BTBP and TBP are combined together in cyclohexanone. After irradiating the solvent in acid contact a latency period before extraction reduced the extraction capability of plutonium. This reduction was larger when the solvent was kept in contact with the acid after irradiation. The decrease in plutonium extraction could be an effect of both a reduced extraction performance of CyMe4-BTBP caused by hydrolysis as well as a shift in oxidation state of the plutonium as it was shown that oxidizing Pu(IV) to Pu(VI) decreased the extraction by the solvent. (C) 2012 Elsevier B. V. .. Selection and/or peer-review under responsibility of the Chairman of the ATALANTE 2012 Program Committee
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| 2. |
- Bauhn, Lovisa, 1981, et al.
(författare)
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A micro hot test of the Chalmers-GANEX extraction system on used nuclear fuel
- 2013
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Ingår i: International Nuclear Fuel Cycle Conference, GLOBAL 2013: Nuclear Energy at a Crossroads. ; 1, s. 335-340
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Konferensbidrag (refereegranskat)abstract
- In the present study, a "micro hot test" has been performed using the Chalmers-GANEX (Group ActiNide EXtraction) system for partitioning of used nuclear fuel. The test included a pre-extraction step using N,N-di-2- ethylhexylbutyramide (DEHBA) in n-octanol to remove the bulk part of the uranium. This pre-extraction was followed by a group extraction of actinides using the mixture of TBP and CyMe4-BTBP in cyclohexanone as suggested in the Chalmers-GANEX process, and a three stage stripping of the extracted actinides. Distribution ratios for the extractions and stripping were determined based on a combination of γ- and α-spectrometry, as well as ICP-MS measurements. Successful extraction of uranium, plutonium and the minor actinides neptunium, americium and curium was achieved. However, measurements also indicated that co-extraction of europium occurs to some extent during the separation. These results were expected based on previous experiments using trace concentrations of actinides and lanthanides. Since this test was only performed in one stage with respect to the group actinide extraction, it is expected that multi stage tests will give even better results.
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| 3. |
- Bauhn, Lovisa, 1981
(författare)
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Homogeneous radiolysis studies using 238Pu
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Used nuclear fuel contains radiotoxic elements with lifetimes in the range of 100 000 years. Although possibilities for recycling of the fuel exist, a final storage for the ultimate high-level waste will be necessary. In Sweden, a deep geologic repository will be constructed, in which the used fuel will be protected from ground water contact by different barriers. However, considering the extensive time scale, scenarios of barrier failures and ground water intrusion are a necessary part of the safety assessment. In such a scenario, the possible release of radiotoxic elements into the environment will be governed by the solubility of the UO2 matrix, which may be altered by oxidative radiolysis products formed in the water. In this work, a method has been developed for the study of homogeneous α-radiolysis under final repository conditions, with the intention to determine the effect of dissolved bromide on the radiolytic yield of oxygen. To enable this study, a high activity 238Pu solution was stabilized at neutral pH, and a method for mass spectrometric measurement of oxygen gas at the ppm level was developed. Contrary to expectations, a qualitative evaluation of the measurement data indicated a consumption of oxygen in the radiolysis experiment. It was however concluded that the experimental procedure will require further improvements before any radiolytically produced, or consumed, oxygen could be quantified.
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| 4. |
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| 5. |
- Bauhn, Lovisa, 1981, et al.
(författare)
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The fate of hydroxyl radicals produced during H2O2 decomposition on a SIMFUEL surface in the presence of dissolved hydrogen
- 2018
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 507, s. 38-43
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Tidskriftsartikel (refereegranskat)abstract
- Over geologic timescales hydrogen peroxide will be one of the most important radiolytic oxidants challenging the spent fuel integrity in a deep repository. Consequently, the reaction between hydrogen peroxide and different kinds of UO 2 based materials has been the subject of several studies over recent decades. Parts of these studies have investigated the effect of dissolved hydrogen on this reaction, as large amounts of hydrogen are expected to be produced by anoxic corrosion of iron in the deep repositories. In some of the studies hydrogen has been shown to offset the radiolysis-driven oxidative dissolution of the fuel despite the expected inertia of hydrogen at repository temperatures. However, the underlying mechanism is primarily based on the effect of the metallic particles contained in the spent fuel. One clue to the mechanistic understanding is whether or not a reaction takes place between dissolved hydrogen and hydroxyl radicals adsorbed to a fuel surface resulting from the decomposition of H 2 O 2 . In the study presented here this reaction could be confirmed in an autoclave system with SIMFUEL, a hydrogen peroxide spiked solution, and deuterium gas. The results show that the studied reaction does not only occur, but accounts for a substantial part of the hydrogen peroxide consumption in the system. Only a very minor part, 0.02%, of the total consumed hydrogen peroxide caused oxidative dissolution of the SIMFUEL. The conclusion is supported by quantitative measurements of HDO, dissolved U in solution and O 2 in the gas phase.
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| 6. |
- Bauhn, Lovisa, 1981
(författare)
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The interaction of dissolved hydrogen with α-radiolytic oxidants during nuclear fuel dissolution
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Used nuclear fuel contains radiotoxic elements that will need to be kept isolated from the biosphere over a time period of 100 000 years. The KBS-3 geological storage concept aims to prevent the migration of radionuclides into the environment by different engineered barriers. As a complement to these engineered barriers, the low solubility of UO2 in water will limit the release of radiotoxic elements from the fuel in the event of groundwater intrusion. However, the strong radiation field from the used fuel will result in radiolysis of any intruding water, creating H2O2 and other oxidative species. Although radiolytic oxidants have the ability to alter UO2 dissolution behaviour, hydrogen gas formed in the anoxic corrosion of iron in the canisters has been shown to protect the fuel from radiation-induced dissolution.In this research, the interaction of dissolved hydrogen with oxidants produced in the radiolysis of water subjected to α-radiation was studied. The studies were performed experimentally by means of homogeneous α-radiolysis, as well as leaching of SIMFUEL and a high activity MOX fuel. The possible inhibition of the hydrogen effect by the presence of bromide in groundwater was also investigated. Preparations for the studies included oxidation and neutralization of a 238Pu solution, as well as method development for low concentration oxygen measurements by gas mass spectrometry.The results suggest that the presence of dissolved bromide does not affect the production of α-radiolytic oxidants. It was further shown that the consumption of α-radiolytic oxidants by hydrogen does not occur in the bulk solution, which confirms the role of fuel surfaces in the activation of hydrogen. In the leaching of SIMFUEL in water with added H2O2, only 0.02% of the H2O2 consumption could be related to fuel dissolution by oxidation of uranium, while the main part was shown to decompose on the fuel surface. Formation of semi-heavy water (HDO) during leaching in a deuterium atmosphere indicated that a reaction may occur between dissolved hydrogen and hydroxyl radicals from the hydrogen peroxide decomposition. It was also shown that the protective effect of hydrogen on the radiation-induced dissolution of the fuel is maintained even at α-activities comparable to those of fresh spent fuel.
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| 7. |
- Bauhn, Lovisa, 1981, et al.
(författare)
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The interaction of molecular hydrogen with α-radiolytic oxidants on a (U,Pu)O2 surface
- 2018
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 505, s. 54-61
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Tidskriftsartikel (refereegranskat)abstract
- In order to assess the impact of α-radiolysis of water on the oxidative dissolution of spent fuel, an un-irradiated, annealed MOX fuel pellet with high content of Pu (∼24 wt%), and a specific α-activity of 4.96 GBq/g MOX , was leached in carbonate-containing solutions of low ionic strength. The high Pu content in the pellet stabilizes the (U,Pu)O 2 (s) matrix towards oxidative dissolution, whereas the α-decays emitted from the surface are expected to produce ∼3.6 × 10 −7 mol H 2 O 2 /day, contributing to the oxidative dissolution of the pellet. Two sets of leaching tests were conducted under different redox conditions: Ar gas atmosphere and deuterium gas atmosphere. A relatively slow increase of the U and Pu concentrations was observed in the Ar case, with U concentrations increasing from 1·10-6 M after 1 h to ∼7 × 10-5 M after 58 days. Leaching under an atmosphere starting at 1 MPa deuterium gas was undertaken in order to evaluate any effect of dissolved hydrogen on the radiolytic dissolution of the pellet, as well as to investigate any potential recombination of the α-radiolytic products with dissolved deuterium. For the latter purpose, isotopic analysis of the D/H content was carried out on solution samples taken during the leaching. Despite the continuous production of radiolytic oxidants, the concentrations of U and Pu remained quite constant at the level of ∼3 × 10-8 M during the first 30 days, i.e. as long as the deuterium pressure remained higher than 0.8 MPa. These data rule out any oxidative dissolution of the pellet during the first month. The un-irradiated MOX fuel does not contain metallic ε-particles, hence it is mainly the interaction of ra diolytic oxidants and dissolved deuterium with the surface of the mixed actinide oxide that causes the neutralization of the oxidants. This conclusion is supported by the steadily increasing levels of HDO measured in the leachate samples.
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| 8. |
- Fleischer, Siegfried, 1938-, et al.
(författare)
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Dark oxidation of water in soils
- 2013
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - Hoboken, NJ : Wiley-Blackwell. - 0280-6509 .- 1600-0889. ; 65:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the release of oxygen (O2) under dark conditions in aerobic soils. This unexpected process is hidden by respiration which constitutes the dominating reversal O2 flux. By using H218O in different soils, we confirmed that 16O18O and 18O2 released under dark soil conditions originated from added H218O. Water is the only large-scale source of electrons for reduction of CO2 in soils, but it has not been considered as an electron donor because of the very strong oxidation system needed. A high share of soil inorganic material seems to favor the release of O2. © 2013 S. Fleischer et al.
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