| 1. |
- Andersson, Sofie, 1976, et al.
(författare)
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Berkelium nitrate complex formation using a solvent extraction technique
- 2006
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 94:1, s. 59-61
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Tidskriftsartikel (refereegranskat)abstract
- The extraction of Bk(III) into an organic phase consisting of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine, 2-bromodecanoic acid and tert-butyl benzene as a function of nitrate ion concentration in the aqueous phase was studied in order to determine the stability constants of the formation of Bk nitrate complexes. Increasing the nitrate ion concentration in the aqueous phase will increase the nitrate complex formation and thus the extraction of metal ions will decrease. Measuring this decrease in distribution ratio and fitting the data points with an appropriate model gives the stability constants of the Bk nitrate complex formation. © by Oldenbourg Wissenschaftsverlag.
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| 2. |
- Andersson, Sofie, 1976, et al.
(författare)
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Study of nitrate complex formation with Pm, Eu, Am and Cm using a solvent extraction technique
- 2004
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 92:12, s. 863-867
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Tidskriftsartikel (refereegranskat)abstract
- The separation of actinides and lanthanides is an important question in the treatment of spent nuclear fuel in the transmutation concept. To find an efficient and well functioning separation process it is necessary to study the chemistry of the elements in the two groups in different aqueous media. The stability constants of the nitrate complex formation with Pm, Eu, Am and Cm were determined using solvent extraction. The extraction was studied using the synergistic system of 2,6-bis-(benzoxazolyl)-4-dodecyloxylpyridine and 2-bromodecanoic acid in tert-butyl benzene. As the nitrate ion concentration in the aqueous phase was increased, a decrease in separation between actinides and lanthanides was seen owing to complex formation between the different elements and the nitrate ions.
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| 3. |
- André, Magnus, et al.
(författare)
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Measuring sorption coefficients and BET surface areas on intact drillcore and crushed granite samples
- 2008
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 96:9-11, s. 673-677
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Tidskriftsartikel (refereegranskat)abstract
- In general sorption coefficients, K-d cat ion exchange capacity, CEC, and BET surface areas are measured on crushed rock samples because it is very time consuming to measure K-d and CEC on larger rock pieces as it takes a long time for the sorbing species to penetrate into and equilibrate a large sample. Also conventional sample holders for BET measurements are too small to hold a large sample. We have manufactured large sample holders for BET measurements and modified the equipment so that it is possible to measure BET surface areas on samples with 50 mm diameter and LIP to 100 mm length. Results are presented for intact pieces and compared to results on crushed material from the same drillcore. For K-d and CEC measurements we have developed a technique and equipment by which ions can be made to rapidly intrude into and equilibrate the internal surfaces of the same size samples as mentioned above. The method is based on electro-migration where the sample is placed between two vessels one with an anode and other with a cathode. The electric potential gradient drives the ions into and through the sample very much faster than molecular diffusion does. With Cs as the sorbing ion a few weeks were sufficient to equilibrate the 50 mm long sample. In previous diffusion experiments it took more than a year to equilibrate a 15 mm thick sample. A special mixing technique eliminates the development of low and high PH in the electrode compartments. K-d results from measurements on an intact drillcore are presented and comparison is made with results obtained on crushed material from the same bore core. The results from the sorption experiments are compared with the results from the BET surface area determinations in an attempt to evaluate the use of the BET surface area as a proxy for sorption behaviour.
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| 4. |
- Brown, Paul L., et al.
(författare)
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The aqueous chemistry of radium
- 2022
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 110:6-9, s. 505-513
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Tidskriftsartikel (refereegranskat)abstract
- Available literature data on the aqueous chemistry of radium are compiled. There are limited available experimental data and a significant portion of the data has been estimated using electrostatic techniques, typically based on the corresponding data of barium. The available data are compared with the corresponding data of barium (and strontium) and a methodology for estimating additional radium thermochemical data is described.
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| 5. |
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| 6. |
- Fawzy Abdel-Magied, Ahmed
(författare)
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Solid phase extraction of uranium from phosphoric acid : kinetic and thermodynamic study
- 2017
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 105:10, s. 813-820
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Tidskriftsartikel (refereegranskat)abstract
- There is a high interest to develop suitable solid phase extractants for uranium separation from aqueous solutions in order to reduce cost and enhance the efficiency. This paper describes solid phase extraction of uranium(VI) from aqueous phosphoric acid solution using MCM-41 based D2HEPA-TOPO organophosphorous extractants. The mixture of D2HEPA (di-2-ethyl-hexylphosphoric acid) and TOPO (tri-n-octylphosphine oxide) was impregnated into the pores of MCM-41 and the synthesized sorbent was fully characterized. The influences of different factors such as synergistic mixture ratio, phosphoric acid concentration, mixing time and temperature were investigated. The results showed that 90% of uranium(VI) extraction can be achieved within 5 min, using D2HEPATOPO@MCM-41 (mass ratio 2: 1 w/w) from 1 M phosphoric acid containing 64 ppm of uranium at room temperature. High adsorption capacity of uranium(VI) have been achieved at the mentioned conditions. The rate constant for the chemical adsorption of uranium(VI) was 0.988 g mg. 1 min. 1 calculated by the pseudo-second order rate equation. The obtained thermodynamics parameters showed that uranium(VI) adsorption from H-3 PO4 is an exothermic and spontaneous process.
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| 7. |
- Fermvik, Anna, 1978, et al.
(författare)
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Radiolysis of C5-BTBP in cyclohexanone irradiated in the absence and precence of an aqueous phase
- 2012
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 100:4, s. 273-282
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Tidskriftsartikel (refereegranskat)abstract
- Spent nuclear fuel contains many highly ra-dioactive species; hence solvents used in reprocessing willbe subjected to radiolysis. In this study, solvents containingone of the BTBP molecules intended for the separation oftrivalent actinides and lanthanides, the so called C5-BTBP,have been subjected to radiolysis and hydrolysis. We presenthere that this compound shows a dramatic decrease in bothdistribution ratios and separation factor when irradiated withhigher doses up to 50 kGy; particularly in the presence ofan aqueous phase. Furthermore, fast hydrolytic degradation isobserved, which significantly contributes to the overall degreeof decomposition. This is supported by speciation studies per-formed by HPLC and LC-MS methods. Proposed structuresof the highest-yield degradation products are presented andthey seem to confirm previously drawn structures for theseproducts. From these studies it can be concluded that thepresence of nitric acid or nitrate during irradiation leads tohigher content of species containing keto groups.
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| 8. |
- Hedström, Hanna, 1983, et al.
(författare)
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Radon capture with silver exchanged zeolites
- 2012
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 100:6, s. 395-399
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Tidskriftsartikel (refereegranskat)abstract
- To enable laboratory work with larger amounts of Ra-226 and its decay products, e.g., Rn-222 and its daughters, these need to be captured in order to avoid unnecessary alpha contamination of the laboratory work space and ventilation systems. In this study, radon gas was pumped through a column filled with the silver exchanged zeolite called "silver exchanged molecular sieves 13X" (Ag84Na2[(AlO2)(86)(SiO2)(106)]. xH(2)O). After exposure to radon, the radioactivity of the zeolite was measured repeatedly using high resolution gamma spectrometry. It was shown that radon was captured and retained in the silver exchanged zeolite. The zeolites' ability to retain radon was decreased by formation of metallic silver, caused by ionizing radiation. However, the zeolite was regenerated by heating and its radon capture ability was restored. The daughters of radon are not in gas phase and will hence stay on the column.
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| 9. |
- Hill, C., et al.
(författare)
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Assessment of ligand extraction properties: an intercomparison campaign amongst EUROPARTners
- 2008
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 96:4-5, s. 259-264
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Tidskriftsartikel (refereegranskat)abstract
- An intercomparison campaign was organized at the beginning of the European FP6 EUROPART Integrated Project, among the partners involved in the assessment of the extracting properties of novel ligands, in order to check their accuracy and reliability when determining metal cation distribution ratios. Three different extracting systems, presenting various selectivity and affinity towards trivalent actinides were selected: (i) CMPO, (ii) TPTZ and (iii) BTP. Although some differences could be pointed out in the implementation of liquid-liquid extraction tests, the distribution ratios measured by the nine partners were fairly reproducible (
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| 10. |
- Jansson, Mats, et al.
(författare)
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CHEMLAB - in situ diffusion experiments using radioactive tracers
- 1998
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Ingår i: Radiochimica Acta. - 0033-8230 .- 2193-3405. ; 82, s. 153-156
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Tidskriftsartikel (refereegranskat)abstract
- In situ diffusion experiments in bentonite clay have been carried out in the probe CHEMLAB, using the radioactive tracers Co-57, Sr-85 and Cs-134. The measured diffusion profiles for the radionuclides are in good agreement with predicted profiles obtained from modelling based on apparent diffusivities and sorption coefficients obtained in laboratory experiments with corresponding clay density and ground water composition.
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| 11. |
- Langrock, G., et al.
(författare)
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Digital liquid-scintillation counting and effective pulse-shape discrimination with artificial neural networks
- 2015
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 103:1, s. 15-25
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Tidskriftsartikel (refereegranskat)abstract
- A typical problem in low-level liquid scintillation (LS) counting is the identification of alpha particles in the presence of a high background of beta and gamma particles. Especially the occurrence of beta-beta and beta-gamma pile-ups may prevent the unambiguous identification of an alpha signal by commonly used analog electronics. In this case, pulse-shape discrimination (PSD) and pile-up rejection (PUR) units show an insufficient performance. This problem was also observed in own earlier experiments on the chemical behaviour of transactinide elements using the liquid-liquid extraction system SISAK in combination with LS counting alpha-particle signals from the decay of the transactinides could not be unambiguously assigned. However, the availability of instruments for the digital recording of LS pulses changes the situation and provides possibilities for new approaches in the treatment of LS pulse shapes. In a SISAK experiment performed at PSI, Villigen, a fast transient recorder, a PC card with oscilloscope characteristics and a sampling rate of 1 giga samples s(-1) (1 ns per point), was used for the first time to record LS signals. It turned out, that the recorded signals were predominantly alpha, beta-beta and beta-gamma pile up, and fission events. This paper describes the subsequent development and use of artificial neural networks (ANN) based on the method of "back-propagation of errors" to automatically distinguish between different pulse shapes. Such networks can "learn" pulse shapes and classify hitherto unknown pulses correctly after a learning period. The results show that ANN in combination with fast digital recording of pulse shapes can be a powerful tool in LS spectrometry even at high background count rates.
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| 12. |
- Liu, Jinsong, et al.
(författare)
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Coupled transport/reaction modelling of copper canister corrosion aided by microbial processes
- 2004
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 92:11-sep, s. 849-854
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Tidskriftsartikel (refereegranskat)abstract
- Copper canister corrosion is an important issue in the concept of a nuclear fuel repository. Previous studies indicate that the oxygen-free copper canister could hold its integrity for more than 100 000 years in the repository environment. Microbial processes may reduce sulphate to sulphide and considerably increase the amount of sulphide available for corrosion. In this paper. a coupled transport/reaction model is developed to account for the transport of chemical species produced by microbial processes. The corroding agents like sulphide would come not only from the intruding groundwater, but also from the reduction of sulphate near the canister. The reaction of sulphate-reducing bacteria and the transport of sulphide in the bentonite buffer is included in the model. The local depth of copper canister corrosion is calculated by the model.
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| 13. |
- Moll, Henry, et al.
(författare)
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Neptunium(V) complexation by natural pyoverdins and related model compounds
- 2010
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230. ; 98:9-11, s. 571-576
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Tidskriftsartikel (refereegranskat)abstract
- Ubiquitous fluorescent Pseudomonas species secrete bacterial pyoverdin-type siderophores. These bioligands have great potential to bind and transport actinides in the environment due to their hydroxamate and catechol functionalities. We investigated the unknown interaction of the neptunyl cation (NpO2+) with pyoverdins (PYO) released by Pseudomonas fluorescens (CCUG 32456) cells and with simple hydroxamate (salicylhydroxamic acid: SHA and benzohydroxamic acid: BHA) and catechol (2,3-dihydroxynaphthalene: NAP) ligands using near-infrared (NIR) absorption spectroscopy over a wide pH range. NpO2+-bioligand species of the MxLyHz type were identified from the spectrophotometric titrations in all four systems. The 1 : 1 : 2, 1 : 1 : 1, and 1 : 1 : 0 complexes were determined with the pyoverdins. In addition to 1 : 1 species, SHA, BHA, and NAP also form 1 : 2 : 0 species with NpO2+. The stability constants of these neptunyl(V)-bioligand complexes and their individual spectroscopic properties are reported. Our findings indicate that NpO2+ has a stronger affinity to the catechol functionality of the pyoverdin molecule. The identified NpO2+-PYO species belong to the strongest NpO2+ complexes with organic material reported so far.
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| 14. |
- Moll, H., et al.
(författare)
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Solution coordination chemistry of uranium in the binary UO22+-SO42- and the ternary UO22+-SO42--OH- system
- 2006
-
Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 88:11-sep, s. 559-566
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Tidskriftsartikel (refereegranskat)abstract
- The structure and reaction dynamics in the systems UO22+-SO42- and UO22+-SO42--OH- were investigated using EXAFS and O-17-NMR spectroscopy. Uranium Lm edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Angstrom. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Angstrom. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO22++SO(4)(2-)reversible arrow UO2SO4(k(1)), (2) U*O-2(2+)+UO(2)SO(4)reversible arrowU*O2SO4+UO22+(k(2)), (3) UO22++UO2(SO4)(2)(2-)reversible arrow 2UO(2)SO(4)(k(3)), and (4) UO2SO4+SO42-reversible arrowUO2(SO4)(2)(2-)(k(4)). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their O-17 chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.
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| 15. |
- Moll, H., et al.
(författare)
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The hydrolysis of dioxouranium(VI) investigated using EXAFS and O-17-NMR
- 2000
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 88:7, s. 411-415
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Tidskriftsartikel (refereegranskat)abstract
- The structure of dioxouranium(VI) as a function of pH at different (CH3)(4)N-OH concentrations has been investigated with the aid of U L-III-edge EXAFS. Polynuclear hydroxo species were identified by an U-U interaction at 3.80(8) Angstrom at pH = 4.1. The precipitate formed at pH = 7 has a schoepite like structure. In solution at high pH [0.5 M (CH3)(4)N-OH], the EXAFS data are consistent with the formation of a monomeric four coordinated uranium(VI) hydroxide complex UO2(OH)(4)(2-) of octahedral geometry. The first shell contains two O atoms with a U=O distance of 1.83(o) Angstrom, and four O atoms were identified at a U-O distance of 2.26(5) Angstrom. In strong alkaline solutions [>1 M (CH3)(4)N)-OH],O-17-NMR spectra indicate the presence of two species, presumably UO2(OH)(4)(2-) and UO2(OH)(5)(3-), the latter in low concentration, which are in rapid equilibrium with one another at 268 K in aqueous solution.
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| 16. |
- Muuri, E., et al.
(författare)
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Behavior of Cs in Grimsel granodiorite: sorption on main minerals and crushed rock
- 2016
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230 .- 2193-3405. ; 104:8, s. 575-582
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Tidskriftsartikel (refereegranskat)abstract
- In this study the sorption of cesium was investigated on four different minerals; quartz, plagioclase, potassium feldspar and biotite as well as granodiorite obtained from the Grimsel test site in Switzerland. The experiments were conducted in the presence of the weakly saline Grimsel groundwater simulant by determining the distribution coefficients using batch sorption experiments and PHREEQC-modelling across a large concentration range. In addition, the purity of the minerals was measured by XRD and the specific surface areas by BET method using krypton. The distribution coefficients of cesium were largest on biotite (0.304 +/- 0.005 m(3)/kg in 10(-8) M). Furthermore, the sorption of cesium on quartz was found to be negligibly small in all investigated concentrations and the sorption of cesium on potassium feldspar and plagioclase showed similar behavior against a concentration isotherm with distribution coefficients of 0.0368 +/- 0.0004 m(3)/kg and 0.18 +/- 0.04 m(3)/kg in 10(-8) M. Finally, cesium sorption behavior on crushed granodiorite followed the trend of one of its most abundant mineral, plagioclase with distribution coefficient values of 0.107 +/- 0.003m(3)/kg in 10-8 M. At low concentrations (< 1.0 . 10(-6) M) cesium was sorbed on the frayed edge sites of biotite and once these sites are fully occupied cesium sorbs additionally to the Type II and Planar sites. As a consequence, the sorption of cesium on biotite is decreased at concentrations > 1.0 . 10(-6) M. Secondly cesium sorption on potassium feldspar and plagioclase showed similar non-linear behavior with varying concentration. The results were used to assist the interpretation of cesium diffusion process in the 2.5 year in-situ experiment carried out in the underground laboratory at Grimsel test site in Switzerland (2007-2009).
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| 17. |
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| 18. |
- Tietze, Sabrina, 1986, et al.
(författare)
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Synthesis of I-131 labelled iodine species relevant during severe nuclear accidents in light water reactors
- 2013
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230. ; 101:10, s. 675-680
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Tidskriftsartikel (refereegranskat)abstract
- Methods for the small scale synthesis of I-131 labelled iodine species relevant to severe nuclear accidents in light water reactors have been developed. The introduced methods allow the synthesis of impurity free, volatile, inorganic elemental iodine and volatile, organic iodides such as methyl-and ethyl iodide, as well as butyl iodide, chloroiodomethane, allyl iodide and benzyl iodide with ease. The radioactive iodine containing products are sufficiently stable to allow their storage for later use. Due to their volatility the liquid species can be easily converted into gaseous species and thus can be used in research in liquid and gaseous phase. The primary motivation for the development of these synthesis methods is to study the behaviour of volatile iodine species under the conditions of a severe nuclear accident in a light water reactor. Thus, the chemicals involved in the synthesis are chosen in a way to not generate impurities (chlorine and organic solvents) in the products which interfere with competing reactions relevant during a severe nuclear accident. Teknopox Aqua VA epoxy paint, which is used in Swedish light water reactor containments, and its reactions with the produced iodine species are described. The synthesised iodine species undergo chemisorption on paint films. Different to elemental iodine, the organic iodides are non-reactive with copper surfaces. The sorbed iodine species are partly re-released mainly in form of organic iodides and not as elemental iodine when the exposed paint films are heat treated. The partitioning and hydrolysis behaviour of gaseous methyl-and ethyl iodide between containment gas phase and water pools is found to be similar. The methods have been designed to minimise the use of harmful materials and the production of radioactive waste.
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| 19. |
- Tolmachev, Vladimir, et al.
(författare)
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Radiobromination of closo-dodecaborate anion. Aspects of labelling chemistry in aqueous solutions using Chloramine-T
- 2002
-
Ingår i: Radiochimica Acta. - 0033-8230 .- 2193-3405. ; 90:4, s. 229-235
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Tidskriftsartikel (refereegranskat)abstract
- Closo-dodecaborate dianion is a three-dimensional aromatic inorganic molecule, which can be easily halogenated forming a stable halogen-boron bond. Derivatives of closo-dodecaborate were considered as a convenient chemical form of delivery of enriched 10B to malignant tumors for boron neutron capture therapy (BNCT). Some properties of closo-dodecaborate (hydrophilicity, strength of halogen-boron bond, charge at lysosomal pH) make it attractive as a potential prosthetic group for attachment of radioactive halogens to tumor-targeting proteins. Bromine radioisotopes possess a variety of useful nuclear characteristics, and can be used in different areas of clinical diagnostics and therapy. In this work, a basic chemistry of closo-dodecaborate radiobromination was studied. It was found, that di(triethylamonium) dodecahydro-closo-dodecaborate can be labelled in high yield, more then 90%, in a wide pH range. By decreasing the pH, the bromination can be directed to closo-dodecaborate in the presence of phenolic compounds. The results of the study indicate a possibility of using the radioactive bromine label for investigation of pharmacokinetics of boronated compounds for BNCT.
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| 20. |
- Ekberg, Christian, 1967, et al.
(författare)
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Complexation of thorium with phosphate
- 2011
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230. ; 99:1, s. 31-35
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Tidskriftsartikel (refereegranskat)abstract
- Using liquid-liquid extraction and the AKUFVE-technique developed by the Nuclear Chemistry Department at Chalmers University of Technology, Sweden, the complex formation equilibria of hydrogen phosphate (HPO 4 2- ) with thorium have been studied at different temperatures (15, 25 and 35 °C), varying pH (7, 8 and 8.7) and in 1 M (Na, H)ClO 4 . Evaluation of the acquired solvent extraction data indicated the formation of the ThHPO 4 2+ , Th(HPO 4 ) 2 (aq) and Th(HPO 4 ) 3 2- complexes. For Th(HPO 4 ) 2 (aq) and Th(HPO 4 ) 3 2- , the logarithm of the stability constants obtained at 25 °C were 17.0 ±3.5 and 23.7 ±0.2, respectively. Only an estimate of the stability of ThHPO 4 2+ could be obtained. Enthalpies and entropies of the complex formation reactions have been determined: Th(HPO 4 ) 2 (aq) (ΔH = 698 ± 27kJmol -1 , ΔS = 2669±91 Jmol -1 K -1 ) and Th(HPO 4 ) 3 2- (ΔH = 499 ±4kJmol -1 , ΔS = 2137 ± 12 Jmol -1 K -1 ). © by Oldenbourg Wissenschaftsverlag, München.
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| 21. |
- Fermvik, Anna, 1978, et al.
(författare)
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Influence of dose rate on the radiolytic stability of a BTPB solvent for actinide(III)/lanthanide(III) separation
- 2009
-
Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230. ; 97:6, s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- The recently developed ligand MF2-BTBP dissolved in cyclohexanone is a promising solvent for the group separation of trivalent actinides(III) from the lantha-nides(III). Its high stability against nitric acid has been demonstrated recently. Since the solvent is also exposed to a continuously high radiation level in the counter current process, the radiolytic stability of the solvent was examined in this study. Irradiation experiments were carried out up to an absorbed dose of 100 kGy and the effect of the dose rate was investigated. The extraction behaviour for An(III)/Ln(III) separation was studied after radiolysis for evaluation. It was found that during high dose rate irradia-tion the extraction efficiency for both Am(III) and Eu(III) decreased significantly with increasing absorbed dose, whereas during the low dose rate irradiation the extraction efficiencies remained more or less at the same level.
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| 22. |
- Fermvik, Anna, 1978, et al.
(författare)
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Semi-quantitative and quantitative studies on the gamma radiolysis of C5-BTBP
- 2011
-
Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230. ; 99:2, s. 113-119
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Tidskriftsartikel (refereegranskat)abstract
- An industrial liquid liquid extraction process for reprocessing of spent nuclear fuel will inevitably lead to radiolysis of the phases, since the process streams contain highly radioactive species. Solvents containing one of the BTBP (6,6'-bis(5,6-dialkyl-[1,2,4]-triazin-3-yl)-2,2'-bipyridine) molecules intended for the separation of trivalent actinides (An) from lanthanides (Ln), the so called C5-BTBP, have shown a dramatic decrease in both distribution ratios and An/Ln separation factor when irradiated; hence, the molecule is highly unstable towards radiolysis. HPLC-, APCI(+)-MS and LC-MS analyses were performed on irradiated solvents containing initially 0.005 M C5-BTBP dissolved in either hexanol or cyclohexanone. The decrease in concentration of starting molecule as well as the increase in concentration of various degradation products were studied with quantitative and semi-quantitative measurements. Structures were suggested for the degradation products produced in highest yields and these were compared to previously proposed structures for the same products.
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| 23. |
- Holgersson, Stellan, 1964, et al.
(författare)
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Diffusion of HTO and cement pore fluids through host rock
- 2002
-
Ingår i: Radiochimica Acta. - 0033-8230. ; 90, s. 99-108
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Tidskriftsartikel (refereegranskat)abstract
- In the post-closure period of a deep disposal facility for low- to intermediate-level radioactive waste, highly alkaline pore-fluids chemically equilibrated with cementious components of the engineered barriers will migrate into the surroundings. Primary minerals in the host rock could dissolve and secondary calcium silicate hydrate (CSH) phases might be formed in the micro pore system of the rock and change the available porosity for radionuclides and hence the permeability. Since the retardation of radionuclides in the host rock depend on sorption and matrix diffusion, the study of the mineral reactions are of importance. Experiments with diffusion of HTO and synthetic cementitious pore-waters through 1 cm thick discs of Äspö diorite have been made in a nitrogen-flushed glovebox facility. Synthetic cementitious pore-waters representative of fresh and leached concrete were used. For the fresh pore-water the results show that hydroxide ion diffusion is retarded relative to HTO tracer, indicating that reactions between hydroxide and host rock take place. The result can be interpreted as hydroxide sorption in the rock. Al and Si did also accumulate on the sampling side which was attributed to mineral dissolution. For the evolved pore-water no through-diffusion of hydroxide ions or accumulation of other elements in the sampling cell were observed during the sampling period, indicating that the through-diffusion of hydroxide is hindered by this type of pore-water.
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| 24. |
- Holgersson, Stellan, 1964, et al.
(författare)
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Effects of gluco-isosaccharinate on Cs, Ni, Pm and Th sorption onto, and diffusion into cement
- 1998
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Ingår i: Radiochimica Acta. - 0033-8230. ; 82, s. 393-398
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Tidskriftsartikel (refereegranskat)abstract
- The conditions in the Swedish design for a repository of intermediate to low level radioactive waste include a high alkalinity buffer from the concrete construction in combination with cellulose materials in the waste. Experiments have been undertaken in order to quantify the effects of cellulose degradation products on the radionuclide retention capability of the concrete enclosure. Studies of the sorption of Cs, Ni, Pm and Th onto crushed cement and the diffusion of Cs, Ni and Pm in cement and concrete discs of 2 cm thickness were made in a nitrogen-flushed glovebox facility, using different cellulose degradation product additives to the alkaline pore-water. Samples of the liquid phases were taken during a period of 12 months and the sorption and diffusion behaviour was evaluated by radioanalytical methods. In the experiments of alkaline degradation of cellulose the major constituent was found to be D-gluco-isosaccharinate, a potential metal complexing agent, which was synthesized as its Ca salt and used as a 5mM additive in sorption and diffusion experiments. The other additives were leachates of 5 kg/m3 and 100 kg/m3 cellulose in alkaline water. The results show that the additives caused a significant, but transient reduction of the sorption of Pm and Th. The sorption of Cs and Ni were not influenced. The diffusion of D-gluco-isosaccharinate itself was also studied and this indicates that its apparent diffusivity in cement is low, probably due to its strong sorption on cement. This would explain the transient reduction of the radionuclide sorption.
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| 25. |
- Holgersson, Stellan, 1964, et al.
(författare)
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Interactions of cement pore fluids with host rock and the effects on HTO, Na and Cs diffusion
- 1998
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Ingår i: Radiochimica Acta. - 0033-8230. ; 82, s. 197-203
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Tidskriftsartikel (refereegranskat)abstract
- In the post-closure period of a deep disposal facility for low- and intermediate-level radioactive waste, pore-fluids chemically equilibrated with cementious components of the engineered barriers will migrate into the surroundings. Secondary calcium silicate hydrate (CSH) phases might be formed in the micro pore system of the rocks and change the available porosity for radionuclides and hence permeability. Since the retardation of radionuclides in host rock is dependent on the sorption and matrix diffusion, these chemical reactions are of concern. Experiments have been undertaken to react discs of Äspö diorite with alkaline cement porewaters. These experiments provided aged material for through diffusion experiments and samples for studies of chemical reactions. 1 cm thick discs of Äspö diorite were reacted with waters representative for fresh and leached concrete at 70C in nitrogen filled vessels for six months. Analysis of the waters indicates dissolution of primary minerals and precipitation of secondary CSH phases. HTO, Na and Cs diffusion experiments were then undertaken with both reacted and unreacted discs in a nitrogen-flushed glovebox facility. The effects of alkaline degradation of Äspö diorite on tracer through-diffusion was found to be small and of the same order of magnitude as natural variations in rock heterogenity between undegraded samples.
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| 26. |
- Jakobsson, Anna-Maria, 1970, et al.
(författare)
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Measurement and Modelling of Pm Sorption onto TiO2 and goethite
- 2004
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Ingår i: Radiochimica Acta. - 0033-8230. ; 92, s. 683-689
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Tidskriftsartikel (refereegranskat)abstract
- The sorption of Pm (1 x 10(-9) M) onto TiO2 and goethite has been studied as a function of pH and Ionic strength (0.01, 0.1 M NaClO4) at ambient temperature under N-2 atmosphere. For both minerals studied there is no effect of the different ionic strengths and the sorption (log K-a vs. pH) increases with a slope of similar to2. At the same pH sorption is lower on the more positively (or less negatively) charged goethite (pH(pzc) = 8.4) than on the TiO2 (pH(pzc) = 6.2). A comparison to other trivalent cations sorbed on different substrates (made by extracting values from %-sorbed curves and calculating these to K-a) indicate a similar pH-dependence. The results have been fitted using a 1-pK basic Stern model with FITEQL [1]. An a priori restriction was that only one sorption reaction stoichiometry at a time was to be used to keep the number of parameters as small as possible. Outersphere and mono-, bi- and tri-dentate inner-sphere complexes were fitted. For each fit the value of the capacitance was varied to find the value that provided the best fit. Two different site densities were used: 1 site/nm(2) and 2.31 sites/nm(2). For the low site density the reaction which provides the best tit was: drop SOH0.5- + Pm+3 drop SOHPm2.5+for both minerals. At the high site density the same reaction fits for TiO2 while there are several reactions that are equivalent in the fit for goethite.
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| 27. |
- Magnusson, Daniel, 1978, et al.
(författare)
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Investigation of the radiolytic stability of a CyMe4-BTBP based SANEX solvent
- 2009
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230. ; 97:9, s. 497-502
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Tidskriftsartikel (refereegranskat)abstract
- The radiolytic degradation of the 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazin-3-yl )-[2,2']-bipyridine (CyMe4-BTBP) based SANEX (selective actinide extraction) solvent has been investigated. As the solvent used in the extraction process is designed to separate trivalent actinides from lanthanides, the radiolytic degradation is mainly due to alpha decay of extracted minor actinide isotopes. A calculation of dose-rates was done by estimating the concentration of minor actinides in the solvent by fuel burn-up calculations and assumptions on dilutions in the subsequent reprocessing steps. The calculations showed that the main isotopes responsible for the dose-rate are Cm-242, Cm-244 and Am-241. Cm-242 is short-lived and has an impact only at short cooling times before reprocessing of the spent fuel. The dose-rates to a SANEX solvent in the reprocessing of standard spent LWR fuels are burn-up dependent and range from at least 0.03-0.2 kGy/h for UO2 fuels and from 0.4 to 0.8 kGy/h for MOX fuels. Fast reactor fuels yield dose-rates over 1 kGy/h. Based on these results, several radiolysis experiments were carried out in order to compare the effect of low LET external gamma radiation (0.2 kGy/h) and internal alpha radiation with different dose-rates (0.05, 0.2 and 1.0 kGy/h). Significant radiolytic degradation was shown in the gamma radiolysis and in the alpha radiolysis experiment at a dose-rate of 1 kGy/h. These experiments were continued up to an absorbed dose similar to 1200 kGy and >300 kGy, respectively. Comparing the alpha radiolysis results for 0.2 kGy/h and 1.0 kGy/h, up to an absorbed dose of similar to 120 kGy, no significant difference in the degradation for the different dose rates could be seen. The radiolytic degradation rate for gamma radiation was 40% higher than for alpha radiation.
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| 28. |
- Magnusson, Daniel, 1978, et al.
(författare)
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Towards an optimized flow-sheet for a SANEX demonstration process using centrifugal contactors
- 2009
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Ingår i: Radiochimica Acta. - : Walter de Gruyter GmbH. - 0033-8230. ; 97:3, s. 155-159
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Tidskriftsartikel (refereegranskat)abstract
- The design of an efficient process flow-sheet requires accurate extraction data for experimental set-up used. Often this data is provided as equilibrium data. Due to the small hold-up volume compared to the flow rate in centrifugal contactors the time for extraction is often too short to reach equilibrium D-ratios. In this work single stage kinetics experiments have been carried out to investigate the D-ratio dependence of the flow rate and to compare this with equilibrium batch experiments for a SANEX system based on CyMe4-BTBP. The first centrifuge experiment was run with spiked solutions while in the second a genuine actinide/lanthanide fraction from a TODGA process was used. Three different flow rates were tested with each set-up. the results show that even with low flow rates, only around 9% of the equilibrium D-ratio (Am) was reached for the extraction in the spiked test and around 16% in the hot test (the difference is due to the size of the centrifuges). In the hot test the lanthanide scrubbing was inefficient whereas in the stripping both the actinides and the lanthanides showed good results. Based on these results improvements of the suggested flow-sheet is discussed.
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| 29. |
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| 30. |
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