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The mutual separation of actinides (An) from lanthanides (Ln), using diethylenetriamine- N,N′,N″-pentaacetic acid (DTPA) or diethylenetriamine- N,N′,N″-triacetic acid-N,N″-bis(diethylacetamide) (DTBA) masking agents in the aqueous phase via diglycolamide (DGA) extraction is focused on the basis of Trivalent Actinide-Lanthanide Separations by Phosphorus-reagent Extraction from Aqueous Complexes (TALSPEAK) method. We also obtained the same separation performance using the commercially available DTPA using DTBA. In this work, we selected lactic acid (LA) of pH buffer from 10 organic acids and ethylenediamine (ED) for the pH adjustment based on the salt-free system. Approximately same D and SF values are obtained in the following conditions: TODGA-DTPA-LA-NaOH, TODGA-DTPA-LA-ED, and TODGA-DTBA-LA, except for different pH conditions (DTPA: pH 1.7–1.71, DTBA: pH 1.15). Experimental results using batchwise multi-stage extractions showed average yields of Ln (La to Gd) and Am to be 3.73% and 98.1% in the aqueous phase using DGA-DTPA-LA-ED, 3.1% and 97.0% using DGA-DTPA-LA-NaOH, and 1.61% and 98.7% using DGA-DTBA-LA. The suitable pH condition for the multi-stage extraction, using DTBA to extract over 95% Am with under 5% coextraction of Ln was limited to 1.14–1.16 throughout this work.

The effects of waste loading in vitrified high-level nuclear waste (HLW) from the reprocessing of high-burnup spent fuel (56 GWd/tHM) on waste volume reduction (i.e., number of HLW canisters produced) and decay heat generation were investigated to minimize the repository footprint. As the waste loading increases, the number of canisters produced decreases; however, the decay heat and subsequent footprint per canister increase. The best estimate waste loading observed was 23 wt% (including 10 wt% Na2O), wherein the repository footprint minimizes to 60.0 m2/tHM. These results are slightly higher than those for standard HLW (55.5 m2/tHM). However, upon comparing the repository footprint with electric power generation, the benefit of optimization was that the footprint for high-burnup HLW (131 m2/TWh) was 13% smaller than that of standard HLW (151 m2/TWh). Graphical abstract Repository footprint of the vitrified HLW as a function of waste loading for different cooling times. a, b Footprint per tons of heavy metal (tHM), c, d footprint per electricity generation (tera watt-hour, TWh). a, c 45 GWd/tHM, b, d 56 GWd/tHM.

(not in the manuscript) Oral reconstruction in fully edentulous patients can be challenging at times. Hence, it is important to offer the most suitable treatment option after a detailed clinical examination and treatment plan. This 14-year long-term follow-up report is the clinical case of a 71-year-old non-smoker who visited the clinic in 2006 and opted for full-mouth reconstruction using Auro Galvano Crown (AGC) attachments. Maintenance was performed twice a year for the past 14 years, and the clinical results were satisfactory, with no signs of inflammation or lack of retention of the superstructures. This was associated with a high level of patient satisfaction, as indicated by the Oral Health Impact Profile (OHIP 14). Compared to the screw-retained implants over dentures, AGC attachments can be a viable and effective treatment option when restoring fully edentulous arches.

Developing the conventional separation method by which minor actinides (MA) such as Am and Cm are separated from lanthanides is important with respect to their recovery and isolation from high-level radioactive waste (HLW). Owing to the chemical behavior of trivalent lanthanide and actinide ions with similar ionic radii, realizing this separation is still challenging. All lanthanides, Am, and Cm can be extracted using diglycolamide (DGA) extractants, and relatively high An/Ln separation efficiencies have been obtained using diethylenetriamine-N,N’,N”-triacetic acid-N,N”-bis(diethylacetamide) (DTBA). Referring to our previous study, where a good separation and a MA recovery of approximately 95% with the co-existence of 5% Nd in the aqueous phase were observed. To improve these results as well as the separation conditions, under modified conditions by adding lactic acid to stabilize pH, the recovery rates observed were as follows: 97.1% for average Ln metals with the co-existence of 1.59% Am in the organic phase and 98.4% for Am with the co-existence of 2.95% Ln in the aqueous phase.

Density functional theory calculation is applied to predict the stability constants for Eu3+ and Am3+ complexes in aqueous solution for molecular modelling of novel separation agents for minor acti...

The impact of disposal of mixed oxide (MOX) fuel from light water reactors (LWRs) has been considered from the viewpoint of the thermal properties and the number of the vitrified waste for various ...

To achieve trichotomic separation of light lanthanides (Ln), heavy Ln, and Am, batchwise multi-stage extractions using N,N,N′,N′-tetraoctyl-diglycolamide (TODGA) extractant from organic acids are studied. This technique has the advantages of both solvent extraction and chromatography, which enable successive separation and management of large volumes of aqueous solutions. Malonic acid (M-Acid) is used as the main component of the aqueous phase. It is clear that the separation factor for Nd/Am from M-Acid and that for La/Am from M-Acid + HNO3 are both around 30, thus we plan to conduct these separations.

As a result of the Fukushima nuclear power plant accident in March 2011, massive amounts of soil were contaminated with radioactive Cs. To remediate the contaminated soil, we are developing a desor...

Lanthanide (Ln) extractions from organic acids to n-dodecane by N,N,N′,N′-tetraoctyl-diglycolamide (TODGA) were conducted. Four organic acids (lactic acid, malonic acid, tartaric acid, and citric a...

An N-isopropylacrylamide(NIPA) gel can swell and shrink in response to temperature and pH, and metal ion adsorption using NIPA gel containing N,N,N’,N’-tetrakis(2-methylpyridyl)ethylenediamine(TPEN...

To investigate the effective separation of actinides (Ans) from lanthanides (Lns), single-stage batch extraction experiments were performed with a novel extractant, tetradodecyl-1,10-phenanthroline-2,9-diamide (TDdPTDA) with various diluents such as 3-nitrobenzotrifluoride (F-3), nitrobenzene, and n-dodecane for Am, Cm, and Lns. The extraction kinetics with TDdPTDA was rapid enough to perform continuous extraction experiments using mixer-settler extractors. The slopes of the distribution ratio versus the TDdPTDA concentration and the distribution ratio versus the nitric acid concentration were similar for F-3 and nitrobenzene systems, but different from the n-dodecane system. These differences were attributed to the characteristics of the diluents. This study revealed high distribution ratios of Am (DAm) and Cm (DCm) for TDdPTDA, with the high separation factors (SFs) of Am from Lns enough for their separation.

Separation of Cs and Sr from high-level liquid waste (HLLW) contributes to reducing heat generation and correspondingly to minimizing the required use of space in geological disposal repositories for high-level radioactive waste. To maximize the impact of Cs and Sr separation on reducing the occupied area of a repository, it is necessary to consider both the front-end and back-end stages of the nuclear energy system. Therefore, we quantitatively surveyed factors that potentially affect the reduction in the occupied area – that is, the area required for disposal of one waste package – when introducing Cs and Sr separation. From an evaluation using the Comprehensive Analysis of Effects on Reduction of Disposal Area (CAERA) index, we found that in case of a 15-year cooling period of spent nuclear fuel (SNF) after discharge, which is the current operational condition at the Rokkasho Reprocessing Plant, a maximum reduction of 30% in occupied area was achieved for 25 and 30 wt% waste-loaded vitrified waste with Cs and Sr separation. In that case, separation of more than 70% of Cs and Sr was required based on the current reference case for the Japanese geological disposal concept (the so-called H12 Report). In addition, the effectiveness of Cs and Sr separation for reducing the occupied area was drastically decreased if the cooling period after discharge was extended beyond 15 years; for instance, vitrified waste with a more than 40-year cooling period showed almost no reduction in occupied area. This was because the amount of 241Am, which is generated from the beta decay of 241Pu, and the contribution of 241Am to heat generation in vitrified waste increased as the cooling period became longer. The results suggested that the cooling period of the SNF, the waste loading of the vitrified waste, the Cs and Sr separation ratio and the occupied area of the waste were key factors governing the effectiveness of Cs and Sr separation for geological disposal area reductions.

The thorium (Th) fuel cycle is attracting attention again because of its potential merits over the uranium (U) fuel cycle, but the associated back-end technology remains insufficiently mature compa...

We have investigated the uptake mechanism of palladium (Pd: one of the most important elements in industry used as a catalyst) ions into Prussian-blue nanoparticles (PBNPs) in a nitric acid solution via high-resolution electron transmission microscopy, inductively coupled plasma atomic emission spectroscopy, powder X-ray diffraction, and ultraviolet-visible-near infrared spectroscopy in combination with first principles calculations. Comparison of the structural and electronic properties of PBNPs between before and after a 24 h sorption test reveals that the Pd2+ ions incorporated into PBNPs by the substitution of Fe2+ ions of the PB framework while maintaining the crystal structure, and the substitution efficiency is estimated to be 87% per PB unit cell. This implies that 0.30 g of Pd can be recovered by using 1 g of PB having the chemical formula KFe(III)[Fe(II)(CN)6]. The present finding suggests that PB (or its analogues) can be applied to recycle noble and rare metals from electronic and nuclear wastes.

Nuclear Material Balance code version 4.0 (NMB4.0) has been developed through collaborative R&D between TokyoTech&JAEA. Conventional nuclear fuel cycle simulation codes mainly analyze actinides and are specialized for front-end mass balance analysis. However, quantitative back-end simulation has recently become necessary for considering R&D strategies and sustainable nuclear energy utilization. Therefore, NMB4.0 was developed to realize the integrated nuclear fuel cycle simulation from front- to back-end. There are three technical features in NMB4.0: 179 nuclides are tracked, more than any other code, throughout the nuclear fuel cycle; the Okamura explicit method is implemented, which contributes to reducing the numerical cost while maintaining the accuracy of depletion calculations on nuclides with a shorter half-life; and flexibility of back-end simulation is achieved. The main objective of this paper is to show the newly developed functions, made for integrated back-end simulation, and verify NMB4.0 through a benchmark study to show the computational performance.

Reprocessing of spent nuclear fuels generates high-level liquid waste (HLLW) which undergoes vitrification into borosilicate glass before final geological disposal. To ensure the quality of the gla...

High-level liquid waste (HLLW) contains more than 30 kinds of nitrates which consist of fission products. A series of such phenomena as evaporation, melting and thermal decomposition of HLLW takes ...

Looking ahead to final disposal of high-level radioactive waste arising from further utilization of nuclear energy, the effects of high burn-up of light-water reactors (LWR) with UO2 and MOX fuel a...

A novel hydrophobic ionic liquid including N,N,N′,N′-tetrakis(2-pyridylmethyl)-1,3-diaminopropane-2-amido structures ((IL-TPTNA)+NTf2−) was successfully synthesized. Its extraction performance of Eu3+ from nitric acid solution was investigated by dissolving in a low viscosity ionic liquid (C6mim)+NTf2−. As a result, it was found that the extraction percentage of Eu3+ varied with the pH value. The stripping of extracted metals from (C6mim)+NTf2− into a receiving phase was successfully achieved under 1.0 M nitric acid conditions. Slope analysis confirmed that (IL-TPTNA)+NTf2− formed a 1:3 complex with Eu3+ in the (C6mim)+NTf2− system. Furthermore, (IL-TPTNA)+NTf2− showed greater preference to heavier lanthanides than lighter ones.

Extraction with multiple theoretical stages by a single contactor is possible when a liquid–liquid countercurrent centrifugal contactor with Taylor vortices (TVs) is used. A series of TVs inside th...

In light of the widespread Cs pollution that may follow nuclear disasters, the decontamination of post-accident soil has earned much attention due to the difficulty of Cs removal for its super-retention in micaceous minerals. Herein, we successfully used solvated Mg2+ to desorb Cs from Cs-saturated vermiculitized biotite (VB) to clarify the microscale mechanism underlying a Cs removal process, and we applied this new method to actual radioactive soil to validate the practical remediation effect. The results revealed that sorbed Cs was uniformly fixed in the collapsed interlayers of VB crystals and thus was poorly and slowly desorbed by ambient treatment with Mg2+ regardless of the treating concentration, duration time, and number of cycles. However, almost all Cs was effectively and efficiently removed by hydrothermal treatment at 250°C. Further characterizations of treated Cs-VB confirmed that Mg2+ indeed diffused into Cs collapsed interlayers from the edge-side to the interior central region with the increase of the treating temperature, and the substituted anhydrous Cs+ ensuing interlayer decollapsed. Similarly, a negligible amount of Cs was removed from the radioactive soil by treatment with Mg2+ at 60 °C, whereas nearly complete Cs removal was achieved at 250 °C, which clearly validated the desorption process as achieved for Cs-VB and definitely reinforced the applicability of the current reported pathway for practical Cs decontamination with soil remediation.

A novel hydrophobic ionic liquid including an N,N,N′,N′-tetrakis(2-methylpyridyl)-1,2-phenylenediamine-4-amido structure ((IL-1,2-tpbd)+NTf2−) was successfully synthesized. (IL-1,2-tpbd)+NTf2− combined one amido (O-hard donor) and four pyridine (N-soft donor) groups. Its Cd2+ and Zn2+ separation behavior in nitric acid solution was investigated as a function of the extraction time, effect of pH etc. by dissolving (IL-1,2-tpbd)+NTf2− in a room temperature ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ((C6mim)+NTf2−). The extraction kinetics were fairly fast and could reach equilibrium within 4 h. When pHeq ≥ 1.8, the extraction percentage of Cd2+ and Zn2+ remained constant and the maximum separation factor was calculated as 12.78 at pHeq = 3.1; when pHeq < 1.8, the extraction percentage of Cd2+ and Zn2+ decreased drastically due to the protonation of the pyridine groups. Complete stripping of the extracted Cd2+ and Zn2+ from the ionic liquid phase into an aqueous phase was successfully achieved under highly acidic conditions ([HNO3] = 2 M) without adding any other metal complex forming agents. The extraction mechanism was summarized as a cation exchange due to the independence of nitrate ions in the extraction process. Additionally, the results of the slope analysis and UV-vis titration revealed the formation of a 1 : 2 complex. Furthermore, (IL-1,2-tpbd)+NTf2− showed a higher preference for Cd2+ even under the interference of various co-existing metal ions.

A hydrophilic N-isopropylacrylamide (NIPA) gel copolymerized with a hexavalent nitrogen donor ligand, N,N,N’,N’-tetrakis(4-propenyloxy-2-pyridylmethyl)ethylenediamine (TPPEN), adsorbs soft metals s...

Separation of platinum-group metals (PGMs: Ru, Rh, Pd) and Mo from high-level liquid waste (HLLW) makes the vitrification process more stable. Aluminum ferrocyanide (AlHCF) has been synthesized, and it is suitable for the simultaneous recovery of PGMs and Mo from HLLW. In this study, an adsorption experiment onto AlHCF was conducted in a spent fuel solution prepared from an irradiated MOX fuel. An adsorption experiment in a simulated HLLW with 26 elements was also conducted as reference. As a result, both Pd and Mo have been successfully adsorbed on AlHCF in both the spent fuel solution and the simulated HLLW. Americium was not adsorbed onto AlHCF as tri-valent lanthanide ions were.

The reversibility of cesium adsorption in contaminated soil is largely dependent on its interaction with micaceous minerals, which may be greatly influenced by various cations. Herein, we systematically investigated the effects of NH4+, K+, Mg2+, and Ca2+ on the adsorption/desorption of Cs+ into different binding sites of vermiculitized biotite (VB). Original VB was initially saturated by NH4+, K+, or Mg2+; we then evaluated the adsorption of Cs+ on three treated VBs, and the desorption by extraction with NH4+, K+, Mg2+, or Ca2+ was further evaluated. Our structural analysis and Cs+ extractability determinations showed that NH4+ and K+ both collapsed the interlayers of VB, resulting in the dominant adsorption of Cs+ to external surface sites on which Cs+ was readily extracted by NH4+, K+, Mg2+, or Ca2+ irrespective of their species, whereas Mg2+ maintained the VB with expanded interlayers, leading to the overwhelming adsorption of Cs+ in collapsed interlayer sites on which the Cs+ desorption was difficult...

This study evaluated the clinical outcomes of immediately loaded maxillary anterior single implants placed in fresh extraction sockets. A patient cohort that was treated 1.5 years earlier was recalled, and 18 patients (6 men, 12 women) with 21 implants were included. Clinical photographs and periapical radiographs were taken at follow-up and baseline to determine the bone loss and change in esthetics. No marginal bone loss was detected at follow-up (mean bone level ± standard deviation = 0.32 ± 0.82 mm). Immediate implant placement and loading resulted in predictable clinical and esthetic outcomes, with soft and hard tissue levels remaining stable over time.

Density-functional theory calculations were applied to mo lecular structure and complex formation reaction modelings of metal ion complexes with diethylenetriaminepentaacetic acid (DTPA) and its bisamide (DTPABA) chelates to understand the metal ion selectivity between Am3+ and Eu3+. The calculated complexes with DTPA and DTPABA chelates reproduced the coordination geometries of experimental crystal structures. Calculated Gibbs free energies of the complex formation reactions indicated that Am3+ ion forms higher stable complexes with both chelates than Eu3+ ion, being consistent with the experimental results. The higher Am3+ selectivity over Eu3+ was suggested to originate in the larger bond overlap between Am3+ 5 f-orbital and N 2s, 2p-orbital. This means that the covalent contribution between the metal ion and donor atoms differentiates the complex formation stabilities, leading to the Am3+/Eu3+ selectivity. We expect that this study contributes to systematize the origin of metal ion selectivity and to accelerate novel ligand exploration.

To investigate the effective separation of actinides (Ans) from lanthanides (Lns), single-stage batch extraction experiments were performed with a novel extractant, tetradodecyl-1,10-phenanthroline-2,9-diamide (TDdPTDA) with various diluents such as 3-nitrobenzotrifluoride (F-3), nitrobenzene, and n-dodecane for Am, Cm, and Lns. The extraction kinetics with TDdPTDA was rapid enough to perform continuous extraction experiments using mixer-settler extractors. The slopes of the distribution ratio versus the TDdPTDA concentration and the distribution ratio versus the nitric acid concentration were similar for F-3 and nitrobenzene systems, but different from the n-dodecane system. These differences were attributed to the characteristics of the diluents. This study revealed high distribution ratios of Am (D

Sorbed Cs on vermiculitized biotite in saturation amount was desorbed by extractions with 1M K+ and Mg2+ at varied temperatures. At room temperature, Cs+ was readily desorbed by leaching with K+ (~100%) but not by Mg2+ (~50%). However, contrary was true for desorption at high temperature, in which Mg2+ desorbed far more Cs+ (~100%) than that by K+ (~25%). XRD analysis of Cs depleted samples suggested that the contrary abilities of K+ and Mg2+ for Cs desorption at low and high temperatures were attributed to their induced interlayer collapse or expansion during extraction.

The adsorption and desorption of cesium (Cs) on clays of contaminated soil in a rhizosphere zone can be greatly affected by various biogeochemical processes, the timespans of which are usually months to years. Herein, we present several representative scenarios of the binding of Cs on diverse sites of vermiculitized biotite by controlled Cs adsorption to particles of different sizes. We investigated whether and how the fixed Cs in the different scenarios is desorbed by ambient and hydrothermal treatments with several low-molecular-weight organic acids (LMWOAs). The results showed that the sorbed Cs was discriminatively retained in the un-collapsed, partially collapsed, and thoroughly collapsed structures of vermiculites. The desorption of the sorbed Cs by hydrothermal LMWOAs extractions was easily realized in the un-collapsed structure, but was limited or minimal in the partially collapsed and thoroughly collapsed structures. The Cs desorption varied in accord with the LMWOA species applied and increased with the acid concentration, temperature, and number of treating cycles. The analysis of Cs-desorbed specimens confirmed their partial destruction and interlayer expansion, suggesting that the underlying mechanism of Cs removal by LMWOAs involves not only acid dissolution and complexation but also the accelerated weathering of clays within a short time under hydrothermal conditions. Our findings contribute novel insights into the mobility, bioavailability, and fate of Cs in contaminated soils and its removal from these soils for environmental restorations.

The effective and efficient removal of radioactive Cs from contaminated soil is highly urgent for the nuclear post-accident remediation. In present study, we achieved rapid Cs desorption from both a typical micaceous clay (i.e., vermiculitized biotite, VB) and actually contaminated soil by high-speed ion exchange through temperature-controlled continuous leaching with Mg-solutions in a column reactor. Cs-sorbed VB was firstly employed as a soil surrogate to explore the macro-Cs desorption process and micro-mechanism in detail. Results showed that VB sandwiched the adsorbed Cs to its interlayers within collapsed structure (10.7 A) and prevent Cs release even by abundant extraction with H2O at 250 °C or Mg2+ at 25 °C. However, Mg2+-extracted Cs desorption boosted significantly with elevating temperatures and 100 % of sorbed-Cs was removed from Cs-VB leached above 150 °C. Further structural and composition analysis of the leached specimen ensured that solvated Mg2+ preferentially entered into Cs+-collapsed interlayers at 150 °C than K+-interlayers above 200 °C, leading to prior complete Cs removal over K from VB at lower temperatures. By contrast, the Cs-contaminated soil reduced by ∼39 % but ∼82 % of its initial radioactivity after equally leaching with same volumes of Mg2+-solution at 150 and 200 °C, respectively. These temperature-controlled Cs desorption validated that radioactive Cs in actual soil indeed be tightly trapped by micaceous clays nearly in the Cs-K co-collapsed interlayers, to which its extraction by other cations can conditionally occur above enough high leaching temperatures. These superior features would inspire new insights for the design of novel practical technologies for treatment and decontamination of the nuclear post-accident soils.

We have investigated chemical forms of rhodium (Rh) ion in nitric acid solution by using spectroscopic and first-principles methods, in order to develop the disposal of high-level radioactive nuclear liquid wastes (HLLW). The electronic structure of Rh complexes in both pure water and nitric acid solutions was investigated using ultraviolet-visible (UV-vis) absorption spectroscopy. Comparison with many-electron calculations indicates that Rh ion forms an octahedral bidentate complex coordinated with three nitrate ions, [Rh(NO3)3], in both pure water and nitric acid solutions. This is consistent with thermodynamic prediction. Since the overall feature of UV-vis spectra of the Rh complex remained unchanged in a range of 0-3 M nitric acid solutions, the structure of the Rh complex was found to be stable in the range. In addition, since no significant changes in UV-vis spectra of Rh complex were observed under γ-ray radiation, the Rh complex, [Rh(NO3)3], can be expected to be stable in actual HLLW.

We introduce a new granulation method for Prussian blue (PB) based on thin-film polymer gel coating. PB particles were strongly supported on a hydrophilic polymer gel porous carrier. Scanning electron microscope (SEM) images confirmed that the PB supported on silica (PBS) samples was thinly covered with the polymer gel containing PB, whereas electron probe microanalysis (EPMA) confirmed that the PB particles mainly existed on the PBS surface. PBS is suitable as a column material for adsorbing low concentrations of Cs.

Cesium ions (Cs+) strongly intercalated in vermiculite clay (Verm) had been effectively removed using sea water for its free utility, totally environmental friendly feature, and within containing n...

The reversibility of cesium adsorption in contaminated soil is largely dependent on its interaction with micaceous minerals, which may be greatly influenced by various cations. Herein, we systematically investigated the effects of NH

We have developed a liquid-liquid countercurrent centrifugal extractor that induces Taylor vortices in the annular fluid region. To demonstrate extraction of multiple species (Nd/Sm/Eu/Gd/Dy) with N,N,N′,N′-tetraoctyl diglycolamide (TODGA), additional chemical agents, such as a surfactant (sodium bis(2-ethylhexyl) sulfosuccinate (AOT)), a synergist (nonanoic acid) and a masking agent (N,N,N′,N′-tetraethyl-3,6-dioxaoctane-1,8-diamide (DOODA(C2))) were employed. When only TODGA was utilized, extraction performance was not effective due to the insufficient dispersion even under a high rotating speed. By combining TODGA and other chemical agents, the separation performance was improved considerably in the countercurrent flow of aqueous and organic phases due to the synergistic effect and improved dispersion.