Effect of the preparation conditions of zirconium phosphate on the characteristics of Sr immobilization

The proton-type crystalline zirconium phosphate, HZr₂(PO₄)₃, was obtained by a thermal decomposition of NH₄Zr₂(PO₄)₃ at different temperatures from 400 to 800 °C, where NH₄Zr₂(PO₄)₃ was obtained in advance by a hydrothermal synthesis using a mixed solution of ZrOCl₂, H₃PO₄ and H₂C₂O₄ with different processing times from 5 to 72 h. Sr ion was immobilized to HZr₂(PO₄)₃ by treating the mixture of HZr₂(PO₄)₃ and Sr(NO₃)₂ aqueous solution in an autoclave at 250 °C. Immobilizing and leaching performance of St in HZr₂(PO₄)₃ were discussed.     

Alkali Metal Ion and Lithium Isotope Selectivity of HZr2(PO4)3

HZr₂(PO₄)₃ has been synthesized by the heat treatment of NH₄Zr₂(PO₄)₃ and its properties as an ion exchanger have been examined with the main focus on its alkali metal ion and lithium isotope selectivity. The distribution coefficients for alkali metal ions revealed that HZr₂(PO₄)₃ was lithium ion-specific and showed little affinity toward potassium, rubidium or cesium ion. The lithium and sodium ion uptakes from aqueous solutions were monotonously increasing functions of pH. Isotopically, HZr₂(PO₄)₃ was ⁶Li-specific. Contrary to ion uptake, the lithium isotope effect was a monotonously decreasing function of pH; a larger separation factor was observed at a lower pH. This result was consistent with the existence of two different ion exchange sites formed in lithium ion-inserted HZr₂(PO₄)₃.     

Selectivity of Alkali Metal Ion and Lithium Isotopes on Ion Exchangers in H Form Prepared from LiTi x Zr2-x (PO4)3 (x=0, 1)

Inorganic metal (IV) phosphate-based ion exchanges in the hydrogen form, HTi _x Zr_2-x (PO₄)₃ (x =0, 1), have been prepared by leaching lithium ions from the precursors, LTi _x Zr_2-x (PO₄)₃ (x=0, 1), through ion exchange with protons. The degrees of leaching of lithium ion were more than 99%. Both ion exchangers showed high selectivity toward lithium and sodium ions and little affinity to rubidium and cesium ions among alkali metal ions. The lithium ion uptakes from aqueous solutions were monotonously increasing functions of pH. Isotopically, both ion exchangers were ⁶Li-specific like other inorganic ion exchangers so far examined. The ⁷Li-to-⁶Li isotopic single-stage separation factor, S, of HTiZr(PO₄)₃ was larger than that of HZr₂(PO₄)₃ at a given pH-value. The relatively large S-values of 1.022 and 1.042 were found for HZr₂ (PO₄)₃ for HTiZr(PO₄)₃, respectively, at 25°C when the pH of the solution phase was around 5.     

Candidate waste forms for immobilisation of waste chloride salt from pyroprocessing of spent nuclear fuel

Sodalite/glass bodies prepared by hot isostatic pressing (HIPing) at ～850 °C/100 MPa are candidates for immobilising fission product-bearing waste KCl–LiCl pyroprocessing salts. To study the capacity of sodalite to structurally incorporate such pyroprocessing salts, K, Li, Cs, Sr, Ba and La were individually targeted for substitution in a Na site in sodalite (Na vacancies targeted as charge compensators for alkaline and rare earths) and studied by X-ray diffraction and scanning electron microscopy after sintering in the range of 800–1000 °C. K and Li appeared to enter the sodalite, but Cs, Sr and Ba formed aluminosilicate phases and La formed an oxyapatite phase. However these non-sodalite phases have reasonable resistance to water leaching.Pure chlorapatite gives superior leach resistance to sodalite, and alkalis, alkaline and rare earth ions are generally known to enter chlorapatite, but attempts to incorporate simulated waste salt formulations into HIPed chlorapatite-based preparations or to substitute Cs alone into the structure of Ca-based chlorapatite were not successful on the basis of scanning electron microscopy. The materials exhibited severe water leachability, mainly in regard to Cs release. Attempts to substitute Cs into Ba- and Sr-based chlorapatites also did not look encouraging. Consequently the use of apatite alone to retain fission product-bearing waste pyroprocessing salts from electrolytic nuclear fuel reprocessing is problematical, but chlorapatite glass–ceramics may be feasible, albeit with reduced waste loadings. Spodiosite, Ca₂(PO₄)Cl, does not appear to be suitable for incorporation of Cl-bearing waste containing fission products.     

Theoretical critical angels of ion channeling in carbon nanotubes

We have developed a mass- and charge-dependent equation to predict theoretical critical angles for ion channeling in carbon nanotubes. We focus M (ion mass) effects how to reduce Ze (ion nucleus charge) effects on Ψ_C (critical angles). As an instance, we give theoretical critical angels of He, Ne, Ar, Kr, Xe and Rn ion channeling in carbon nanotubes. We find that for (10, 10) single-wall carbon nanotubes, Ψ_C(He) ≈ Ψ_C(Ne) ≈ Ψ_C(Ar) ≈ Ψ_C(Kr) ≈ Ψ_C(Xe) ≈ Ψ_C(Rn) ≈ 23.3 (keV/E)^1/2 deg. This is because (Z/M)^1/2 ≈ 0.66 [amu]^?1/2.     

Ion beam analysis of high pressure deposition of epitaxial PZT thin films

Epitaxial thin films of Pb(Zr_0.53Ti_0.47) (PZT) ferroelectric ceramic were successfully grown on Sr(Nb)TiO₃ (SNTO) single crystal substrates by an high-pressure RF sputtering technique. Pure O₂ was used as working gas at a pressure above 1 Torr. The crystalline films properties were evaluated by θ–2θ DRX scans. From these measurements we concluded that the PZT layers were single crystalline and c-axis oriented with a (001)PZT||(001)SNTO crystallographic relationship. Film composition and film–substrate interface characteristics were studied by bombardment of the samples with a 2560 keV ³He⁺ beam. Rutherford Backscattering (RBS) technique was applied to fit the experimental spectra in order to deduce the elemental depth concentration profile of the films. The high-pressured technique represents a useful and capable method to obtaining in situ epitaxial ferroelectric thin film with high quality structural, compositional and dielectric properties, without post deposit treatment.     

Low-temperature immobilization of actinides and other components of high-level waste in magnesium potassium phosphate matrices

The magnesium potassium phosphate (MPP) matrices formed by the room-temperature reaction of MgO and KH₂PO₄ solution were used for immobilization of simulated liquid alkaline high-level waste (HLW) containing actinides, fission and corrosion products. Novel procedures of solidification of HLW simulants were developed to increase stability of the MPP matrices to leaching radionuclides (Pu, Np, Am, Cs, Sr, Tc, I and Se), matrix-forming (K, Mg and PO₄) and admixture components (NO₃, NO₂, Na and others) as well as hazardous elements (Pb, Cr, Zn and others) according to the ANS, PCT, TCLP standards. Density (∼1.7 g/cm³), compressive strength (>20 MPa), radiation resistance of the matrices and chemical yield of radiolytic hydrogen (0.004 molecule H₂/100 eV) were determined. The phase composition of the matrices and distribution of radionuclides were studied by XRD and autoradiography correspondingly.     

Combined Rietveld refinement of Zn2SiO4:Mn2+ using X-ray and neutron powder diffraction data

The behavior of Mn²⁺ ions doped into the crystal lattice of Zn₂SiO₄ is closely related to the luminescent properties of Zn₂SiO₄:Mn²⁺ as a color-emitting phosphor. The combined Rietveld refinement using X-ray and neutron powder diffraction was used to determine the site preference and the amount of Mn²⁺ ions in Zn₂SiO₄:Mn²⁺. Of possible cation-disorder models, the best Rietveld refinement was obtained from the model that Mn²⁺ ions partially substituted for Zn²⁺ ions in two crystallographically non-equivalent Zn sites. The final converged weighted R-factor, R_wp, and the goodness-of-fit indicator, S (=R_wp/R_e) were 8.12% and 2.28, respectively. The occupancy of Mn²⁺ ions for the two non-equivalent Zn sites was 0.034(4) and 0.003(2), respectively. The refined model described the crystal structure in space group R?3 (No. 148) with Z = 18, a (=b) = 13.9612(1) Å, c = 9.3294(1) Å and γ = 120°.     

A calorimetric study of high temperature phase stability in Fe–U alloys

A differential scanning calorimetry study of high temperature phase equilibria and phase transformation kinetics in Fe_100?xU_x binary alloys, with x varying from 0 to 95 mass% U is undertaken. Accurate measurement of transformation temperatures pertaining to: (i) α-Fe → γ-Fe → δ-Fe polymorphic phase change, (ii) UFe₂ + γ-Fe → L and U₆Fe + UFe₂ → L transformations and (iii) melting has been made as a function of uranium concentration. The measured transformation temperatures are used to construct the binary Fe?U phase diagram, which showed general agreement with the latest assessment. The L → UFe₂ + γ-Fe eutectic reaction is found to occur at 1357 ± 5 K, with the eutectic composition of 47 mass%. The heat of transformation associated with this invariant reaction is estimated to be 19,969 ± 1736 J mol of atoms^?1. The L → U₆Fe + UFe₂ reaction occurs at 89 mass%, and at 1001 ± 5 K, with a heat of transformation 20,250 ± 2113 J mol of atoms^?1. The heat of melting of stoichiometric UFe₂ is estimated to be 20,983 ± 2098 J mol of atoms^?1, which is higher than the currently assessed value by 30%. A non-faceted microstructural morphology is found to accompany the eutectic solidification process of all the alloy compositions.     

Ohmic contacts on n-type layers formed in GaN/AlGaN/GaN by dual-energy Si ion implantation

Electrical properties of Si-implanted n-type GaN/AlGaN/GaN layers and contact resistances of ohmic electrodes (TiAl) formed on these layers have been examined. Experimental results have clearly shown that ohmic electrodes with a low specific-contact resistance of 1.4 × 10^?7 Ω cm² can be fabricated on the n-type layer having a low sheet resistance of 145 Ω/sq, which has been formed by the dual-energy Si ion implantation (80 keV:1.01 × 10¹⁵/cm² + 30 keV:1.6 × 10¹⁴/cm²) and subsequent annealing at 1200 °C for 2 min using a Si₃N₄ layer as an encapsulant.     

Investigation on a corrosion product deposit layer on a boiling water reactor fuel cladding

Recent investigations on the complex corrosion product deposits on a boiling water reactor (BWR) fuel cladding have shown that the observed layer locally presents unexpected magnetic properties. The magnetic behaviour of this layer and its axial variation on BWR fuel cladding is of interest with respect to non-destructive cladding characterization. Consequently, a cladding from a BWR was cut at elevations of 810 mm, where the layer was observed to be magnetic, and of 1810 mm where it was less magnetic. The samples were subsequently analyzed using electron probe microanalysis (EPMA), magnetic analysis and X-ray techniques (μXRF, μXRD and μXAFS).Both EPMA and μXRF have shown that the observed corrosion deposit layer which is situated on the Zircaloy corrosion layer consists mostly of 3-d elements’ oxides (Fe, Zn, Ni and Mn). The distribution of these elements within the investigated layer is rather complex and not homogeneous. The main phases identified by 2D μXRD mapping inside the layer are hematite and spinel phases with the common formula M_xFe_y(M_(1?x)Fe_(2?y))O₄, where M = Zn, Ni, Mn. It has been shown that the solid solutions of these phases were obtained with rather large differences between the parameter cell of the known spinels (ZnFe₂O₄, NiFe₂O₄ and MnFe₂O₄) and the investigated material. The comparison of EPMA with μXRD analysis shows that the ratio of Fe₂O₃/MFe₂O₄ (M = Zn, Ni, Mn) phases in the lower sample equals ～1/2 and in the higher one ～1/1 within the analyzed volume of the samples. It has been shown that this ratio, together with the thickness of the corrosion product deposit layer, effect its magnetic properties.     

Validation of 134Cs, 137Cs and 154Eu single ratios as burnup monitors for ultra-high burnup UO2 fuel

A measurement station has been built for the non-destructive investigation of burnt fuel rod segments through high-resolution gamma spectrometry. Four UO₂ pressurised water reactor fuel rod segments with different burnup levels between 50 and >100 GWd/t and ⩽10 year cooling time have been experimentally characterised using gamma-ray spectrometry to determine ¹³⁴Cs, ¹³⁷Cs and ¹⁵⁴Eu and their corresponding concentration ratios. Experimental errors of ∼2% (1σ) for the ¹³⁴Cs/¹³⁷Cs ratio were obtained for most of the segments. In parallel, pin cell depletion calculations have been performed for each segment using the deterministic code CASMO-4. Measured and calculated ratios have then been compared with the purpose of deriving and validating pin-averaged single-ratio burnup indicators for very high burnups. It is shown that the ¹³⁴Cs/¹³⁷Cs ratio, frequently used as a burnup monitor, is considerably less precise for values exceeding 50 GWd/t; discrepancies of ∼16% are found between measured and calculated values, increasing with burnup up to ∼23%. The ratios built with the ¹⁵⁴Eu concentration show even much larger discrepancies, essentially because this isotope is rather poorly predicted as revealed by just using different basic cross section data.     

Gamma irradiation induced damage creation on the cation distribution,structural and magnetic properties in Ni–Zn ferrite

Ferrite of system, namely Ni_1?xZn_xFe₂O₄ with x = (0.0, 0.2, 0.4, 0.6, 0.8, 1.0), have been prepared by solid state reaction to investigate the effect of gamma rays irradiations using Co⁶⁰ source on the cation distribution, structural and magnetic properties. The unirradiated and irradiated samples were then subjected to characterization techniques such as X-ray diffraction, magnetization and AC susceptibility. The results of these characterizations are found to be different for irradiated from that of the pristine sample. The modifications in respect of irradiated samples are explained in terms of the ion-induced disorder. The important result of γ-irradiation on the cation distribution, structural and magnetic properties is the change of ratio Fe²⁺/Fe³⁺. Possible reasons on the results are proposed.     

Cerium and neodymium co-precipitation in molten chloride by wet argon sparging

Co-precipitations of cerium (III) and neodymium (III) at 10 wt.% in LiCl–CaCl₂ (30-70 mol%) molten salt at 705 °C have been achieved using an original way of precipitation, wet argon sparging. Several CeCl₃/NdCl₃ ratios have been studied, and the isolated powders were analyzed using different characterization methods including XRD investigations. The lanthanides precipitation yields have been determined around 99.9% using ICP-AES analysis. XRD demonstrated that the precipitates mainly contained mixed oxychloride (Ce_1?xNd_x)OCl and a small amount of the mixed oxide Ce_1?yNd_yO_2?0.5y. Calcination of these precipitates has resulted in the cerium and neodymium mixed oxides. For the precipitation with a Ce/Nd = 50/50 ratio, an hydroxychloride Ln(OH)₂Cl and the oxychloride Ce^IV(Nd_0.7Ce_0.3)^IIIO₃Cl have been identified as unexpected intermediate compounds.     

Y(BD4)3, an efficient store of deuterium,and impact of isotope effects on its thermal decomposition

Y(BD₄)₃, which stores as much as 16.6 wt.% and 252 kg/m³ D, has been synthesized via high-energy disk milling. The thermal decomposition of Y(BD₄)₃ has been investigated using thermogravimetric and calorimetric analyses combined with the spectroscopic evolved gas analysis. Two major endothermic events corresponding to thermal decomposition could be distinguished in the DSC profile up to 400 °C at ca. 231 and 285 °C, preceded by a phase transition (at ca. 198 °C) from the low-temperature Pa-3 form to a high-temperature polymorph of Y(BD₄)₃ (F-43c). The high-temperature phase forming at the onset of thermal decomposition may be prepared quantitatively by heating of the low-temperature phase to ca. 216 °C followed by rapid quenching.Effects of isotope H→D substitution on various properties of yttrium borohydride have been analyzed. Y(BD₄)₃ constitutes a very efficient low-temperature source of deuterium gas on the laboratory scale.     

Ion-beam densification of hydroxyapatite thin films

The goal of this study is to demonstrate the feasibility of using ion irradiation to densify a porous ceramic film. Ion irradiation is a room-temperature process, and thus may be preferable to the use of conventional high temperature sintering, which is typically performed at temperatures in excess of 1000°C. Thin films of the bio-ceramic hydroxyapatite (HA), Ca₁₀(PO₄)₆(OH)₂, were deposited on silicon substrates using a sol–gel technique. The films processed in this study were 600 nm thick and had a density of 36% of fully dense HA, after drying at 620°C for 3 min. The dried films were irradiated with 1 and 2 MeV Si⁺⁺ ions with fluences ranging from 10¹⁴ to 6 × 10¹⁵ ions/cm². Samples irradiated with the largest fluence reached densities of 83% of that of fully dense HA. Rutherford backscattering spectrometry was used to verify the HA stoichiometry of the films and to obtain the areal density. Scratch testing showed that implantation led to a substantial improvement in scratch resistance. Nano-indentation was also used to characterize the mechanical properties of the films. The hardness was increased by a factor of 15 by the irradiation. X-ray diffraction was used to characterize the crystalline phases present in the film. Ion irradiation caused some decrease in the already small degree of crystallinity of the film. The advantage of ion-implantation over high temperature sintering is shown as no secondary crystalline phases appear after densification.     

Study on flow instability for feasibility of a thin liquid film first wall

This study proposes a probability of the evaporated gas that agitates a growing instability wave in a thin liquid film first wall. The liquid first wall was considered to be in vacuum and the effect of the ambient gas was neglected but the evaporated gas by the high energy fluxes is a probable cause of unstable wave agitation. The criterion is approximately expressed by the density ratio (Q₂) and the Weber number (We) as Q₂ × We^0.5 ≈ 5 × 10⁻⁴. Performed indirect experimental supported this criterion. For a case study of liquid Pb-17Li film with a velocity of 10 m/s, the evaporated gas pressure must be below 6.2 × 10³ Pa to maintain stable conditions. By recent study, this pressure is generated at 1600 K temperature and it is believed to be attainable by the energy fluxes on the first wall. This result is so far not confirmed so the full verification by experimental is to be performed.     

A simple way to analyze infrared reflectivity spectra of p-type Hg0.78Cd0.22Te implanted in various conditions

Different ion-implanted p-type Hg_0.78Cd_0.22Te samples were analyzed by infrared reflectivity in the 2–20 μm wavelength range. We show how to derive some characteristic values of the free carriers induced by ion implantation from simple models of the implanted samples. For low energy implantations (Al (320 keV)) an excess of electrons with concentration n⁺ ≈ 5 × 10¹⁷ cm⁻³ for doses 10¹² and 10¹⁴ ions cm⁻² is observed between the surface and the projected range R_p of the ions, in agreement with the well-known change of type of the free carriers induced by the ion implantation in this kind of samples. High energy α particle (0.8 and 2 MeV, 10¹⁴ ions cm⁻²) implantations lead to a pronounced inhomogeneous concentration of free electrons with n⁺ ≈ 9.2 × 10¹⁶ cm⁻³ between the surface and R_p where a negligible amount of defects due to the nuclear energy loss is formed, and n⁺ ≈ 1.6 × 10¹⁷ cm⁻³ between R_p and R_p + ΔR_p, ΔR_p being the longitudinal straggling, where the defect production rate through the nuclear energy loss mechanism is maximum.     

Oxidation of Zircaloy-4 by oxygen and the production of water

The interaction of isotopic oxygen (¹⁸O₂) with Zircaloy-4 (Zry-4) at 150 and 300 K has been studied using Auger electron spectroscopy (AES) and temperature-programmed desorption (TPD) methods. AES reveals the oxidation of the Zry-4 surface, reflected in shifts of the Zr(MNV) and Zr(MNN) features by about 5.5 and 3.0 eV, respectively, for both adsorption temperatures. The O(KLL)/Zr(MNN) Auger peak-to-peak height ratios as a function of exposure show the same trends at both temperatures. Following ¹⁸O₂ adsorption at 150 or 300 K, TPD experiments show hydrogen desorption near 400 K that is attributed to the presence of a surface-stabilized form of hydrogen. Additionally, water (H₂¹⁸O and H₂¹⁶O) desorption below 200 K and above 700 K is observed after 150 K oxygen adsorption. However, after oxygen adsorption at 300 K the only significant desorption features are from isotopic water (H₂¹⁸O). These findings indicate that mass transport involving the near-surface region contributes to the observed desorption, and that this behavior is dependent on the original adsorption temperature. Charging experiments using D₂ prior to and after ¹⁸O₂ adsorption were also performed and support our conclusions about the role of surface–subsurface mass transport in this system.     

Study and optimization of boronization in Alcator C-Mod using the Surface Science Station (S3)

A Surface Science Station (S³) on the Alcator C-Mod tokamak is used to study and optimize the location and rate of boron film deposition in situ during electron cyclotron (EC) discharge plasmas using 2.45 GHz radio-frequency (RF) heating and a mixture of helium and diborane (B₂D₆) gasses. The radial profile of boron deposition is measured with a pair of quartz microbalances (QMB) on S³, the faces of which can be rotated 360° including orientations parallel and perpendicular to the toroidal magnetic field B_T ～0.1 T. The plasma electron density is measured with a Langmuir probe, also on S³ in the vicinity of the QMBs, and typical values are ～1 × 10¹⁶ m^?3. A maximum boron deposition rate of 0.82 μg/cm²/min is obtained, which corresponds to 3.5 nm/min if the film density is that of solid boron. These deposition rates are sufficient for boron film applications between tokamak discharges. However the deposition does not peak at the EC resonance as previously assumed. Rather, deposition peaks near the upper hybrid (UH) resonance, ～5 cm outboard of the EC resonance. This has implications for RF absorption, with the RF waves being no longer damped on the electrons at the EC resonance. The previously inferred radial locations of critical erosion zones in Alcator C-Mod also need to be re-evaluated. The boron deposition profile versus major radius follows the ion flux/density profile, implying that the boron deposition is primarily ionic. The application of a vertical magnetic field (B_V ～0.01 T) was found to narrow the plasma density and boron deposition profiles near the UH resonance, thus better localizing the deposition. A Monte Carlo simulation is developed to model the boron deposition on the different QMB/tokamak surfaces. The model requires a relatively high boron ion gyroradius of ～5 mm, indicating a B⁺¹ ion temperature of ～2 eV, to match the deposition on QMB surfaces with different orientation to B_T. Additionally, the boron ion trajectories become de-magnetized at high neutral gas throughput (～0.5 Pa m³ s^?1) and pressure (～2 Pa) when the largest absolute deposition rates are measured, resulting in deposition patterns, which are independent of surface orientation to B_T in optimized conditions.