super(152)Eu and super(241)Am are the most frequently used radiotracers in the separation studies on trivalent minor actinides and lanthanides. In almost all those studies, the determination of ...super(152)Eu and super(241)Am has been based on measuring their gamma radiation by using a NaI(Tl) scintillation detector and/or a germanium detector. In this study, based on measuring the beta particles and mono-energy electrons from super(152)Eu and the alpha particles from super(241)Am, we provide a new option to simultaneously determine the radioactivities of super(152)Eu and super(241)Am by liquid scintillation counting (LSC) with the aid of alpha / beta discrimination. If the count rate ratio of super(241)Am to super(152)Eu is within the range of 100:1-1:100, the radioactivities of super(152)Eu and super(241)Am in mixed samples can be simultaneously determined by LSC with the errors less than 5 %. In addition, the interferences of super(241)Am on Eu are divided into two parts: inside and outside the super(241)Am region of interest. Only if the count rate ratio of super(241)Am to Eu is more than 10:1, should the latter interference be in consideration.
The retention capacity of natural calcareous gravels used as a filling material between the packages containing radioactive waste materials in the disposal cells was evaluated for Sr, U, Ni, Ag, 14C, ...99Tc, 239Pu, 228Th and 152Eu. The thermodynamic calculations performed considering repository conditions indicated that the chemistry of most of these elements was dominated by neutral or cationic species, this is the case of 238Pu 152Eu, 228Th, Ni and Ag. The studied gravels presented high sorption capacities for these cationic or neutral species, but they are not efficient on retaining anionic species as in the case of 99Tc or Sr, which is already present in the composition of the studied gravels. For those elements where the predominant species are carbonated (14C and U) low distribution coefficients were obtained. A preliminary mechanistic sorption model was developed for each radionuclide considering carbonate (>CO3H) and calcium hydroxide (>CaOH) sites. Our preliminary model allowed to successfully reproduce the experimental trend of the data obtained in this work.
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•The distribution coefficients (Kd) for radionuclides on calcareous gravels were evaluated.•The retention of cationic or neutral species (Pu, Eu, Th, Ni, Ag) was effective.•The retention of anionic species (Tc, Sr) was ineffective.•Low distribution coefficients for carbonated species (C, U).•A preliminary mechanistic sorption model for each radionuclide was proposed.
Synchrotron radiation (SR) based techniques have been utilized with increasing frequency in the past decade to explore the brilliant and challenging sciences of actinide‐based materials. This trend ...is partially driven by the basic needs for multi‐scale actinide speciation and bonding information and also the realistic needs for nuclear energy research. In this review, recent research progresses on actinide related materials by means of various SR techniques were selectively highlighted and summarized, with the emphasis on X‐ray absorption spectroscopy, X‐ray diffraction and scattering spectroscopy, which are powerful tools to characterize actinide materials. In addition, advanced SR techniques for exploring future advanced nuclear fuel cycles dealing with actinides are illustrated as well.
The rapid development of synchrotron radiation (SR) based techniques offers tremendous opportunities for brilliant and challenging research in actinide‐based materials nowadays. This review addresses recent research progresses in actinide related materials by means of various SR techniques, with emphasis on X‐ray absorption spectroscopy, X‐ray diffraction and scattering spectroscopy.
Frontispiece: Covalency in Actinide Compounds Pace, Kristen A.; Klepov, Vladislav V.; Berseneva, Anna A. ...
Chemistry,
April 1, 2021, 2021-04-00, 20210401, Volume:
27, Issue:
19
Journal Article
Peer reviewed
Open access
This frontispiece illustrates two ways of achieving a higher degree of covalency in actinide compounds, one employs orbital energy degeneracy and the other—orbital overlap between the 5f and ligand ...orbitals. For more information see the Concept article by V. V. Klepov, H.‐C. zur Loye et al. on page 5835.
Differential covalency in trivalent actinide versus lanthanide bonding with soft donors can aid separations. In their Research Article on page 9459, Enrique R. Batista, Andrew J. Gaunt, Ping Yang, ...and co‐workers compare electronic structure and bonding with isoradial Am3+ and Nd3+ using hard O‐ and soft Se‐donor ligands. The first structural characterization of molecular Am–Se bonding, along with spectroscopy and ab initio calculations, is used to evaluate f‐orbital involvement for Am3+ versus Nd3+ and explain structural trends. Graphic designed by Josh Smith, Chemistry Division, Los Alamos National Laboratory.
Evaluation of covariance for JENDL was virtually started after the release of JENDL-3.2. The covariance data were obtained for 16 nuclides and compiled to the JENDL-3.2 Covariance File. At the time ...of the JENDL-4.0 development, covariances were much enhanced especially for actinides; covariance data were given for 99 nuclides in total. The latest version JENDL-5 includes covariance data for 105 nuclides by adding new evaluations for light nuclides and structure materials. An overview of the covariance evaluation for JENDL is presented.
Liquid–liquid extraction of actinides and lanthanides by use of ionic liquids is reviewed, considering, first, phenomenological aspects, then looking more deeply at the various mechanisms. Future ...trends in this developing field are presented.
The redox chemistry of the actinide elements plays a central role in many aspects of nuclear fission technology including the reprocessing of spent fuel, safe disposal strategies and in the ability ...to reliably predict the mobility of actinides in natural and engineered environmental conditions. In both aqueous and non-aqueous conditions, the redox chemistry of the actinides can be complicated and diverse and speciation is governed by both the actinide in question and many environmental factors. Although, historically, actinyl(VI) and (V) ions have been the subject of the most in depth research, the study of actinide ions in the +IV oxidation state (principally for U, Np and Pu) is inherently important in governing speciation in all aspects of the nuclear fuel cycle. Importantly, reactions involving reduction, disproportionation and re-oxidation tend to involve actinide ions in the +IV oxidation state leading to complex systems particularly in aqueous solution that control the solubility and migratory behaviour of actinide containing species. In this review, we focus on recent developments in the coordination and redox chemistry of the actinides involving actinide(IV) species in terms of fundamental coordination chemical studies, mineral chemistry, biogeochemistry and the implications of hydrolysis chemistry on the chemical and physical behaviour of actinide(IV) ions in the natural and engineered environment.
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