Long term stability of iron for more than 1500 years indicated by archaeological samples from the Yamato 6th tumulus

One of the candidate materials for overpack in the Japanese engineered barrier system for high-level radioactive waste (HLW) is iron and therefore its long-term stability for at least 1000 years is very important for safety analysis of the repository system. Therefore, several of the iron artifacts excavated from the Yamato 6th tumulus (ancient tomb) in Nara prefecture were analyzed using X-ray computed tomography (CT) to determine corrosion depth. The samples analyzed, both of two large and 11 smaller iron artifacts are called ‘Tetsutei’. The thickness of each rust layer was measured from a cross-section image of the sample and the difference in material density between rust and iron was shown by the image density by the X-ray CT. In the case of pitting corrosion in the sample, the depth of the pits was measured directly and estimated as total corrosion depth with general corrosion layer. The corrosion depths are 0.5–2.1 mm. These data indicate conservative predictions for the extrapolations based on experimental studies. Such corrosion data from archaeological samples are useful in analogue studies of high-level radioactive waste disposal as evidence of long-term stability of a waste container.     

Plasma Focus as a High Intensity Flash X-Ray Source for Biological Radiography

A study on X-ray emission from a low energy (3.3 kJ) plasma focus (PF) device operated with hydrogen is reported. X-ray are detected by using an X-ray detector consisting of three Quantrad Si PIN-diodes with differential filtering and with a pinhole camera. The X-ray yield in different energy windows is measured as a function of hydrogen filling pressure. The maximum yield in 4-geometry is found to be 46.6 J and corresponding wall plug efficiency for X-ray generation is 1.40%. In particular, to demonstrate feasibility of the present PF as a high intensity flash X-ray source for good contrast biological radiography, an X-ray radiogram of a fish, is presented. The fine structure of the specimen can be seen in different parts. The PF, because of its high X-ray yield and good reproducibility is particularly suited for this application.     

Immobilization of selenium by biofilm of Shewanella putrefaciens with and without Fe(III)-citrate complex

To investigate the effect of biofilms on selenium migration, we examined selenite reduction by biofilms of an iron-reducing bacterium, Shewanella putrefaciens, under anaerobic conditions. The biofilms were grown under static conditions on culture cover glasses coated with poly-L-lysine. Optical microscopic observation of the biofilms after staining with 0.1% crystal violet solution revealed that the cells were surrounded by filamentous extracellular polymer substances. Exposure of the biofilms to aqueous selenite resulted in the formation of red precipitates, which were assigned to nanoparticulate elemental selenium using X-ray absorption near-edge structure analysis. Micrographic observation showed that the precipitates immobilized at the biofilms. We also examined the selenite reduction in the presence of Fe(III)-citrate complex. In this case, a dark brown precipitate formed at the biofilms. X-ray absorption near-edge structure analysis revealed that the precipitate was a mixed compound with elemental selenium and iron selenide. These findings indicate that biofilms of iron-reducing bacteria in the environment can immobilize selenium by reducing Se(IV) to Se(0), and Fe(III)-citrate complex promotes the reduction of Se(0) to Se(-II).     

EPR Study of Uranium (V) Species in Photo-and Electrolytic Reduction Processes of UO2 NO3)2-2TBP

Abstract

Electron Paramagnetic Resonance (EPR) and optical spectra of uranium(V) species were observed in both processes of photo- and electrolytic reduction of UO₂(NO₃)₂-2tributylphosphate (TBP) in 80%TBP-n-dodecane solution. The formation of U(V) species was detected by an optical spectrum (λ_max: 770, 970 and 1,420 nm). EPR signal with the value of ff-factor –2.3 and a linewidth of approximately 1,100 Gs was observed during the electrolytic reduction. On the other hand, during the photoreduction the signal with the value of fil-factor –1.94 was observed and there was found a superhyperfine structure with the intensity ratio of 1:2:1, that is caused by the superhyperfine coupling with nuclear spin, I=1/2, of the strongly coordinated ³¹P to the central uranium through oxygen atom. The superhyperfine coupling constant was estimated to be 27 Gs. Moreover, the signal with the value of g-factor –2.00 due to an organic radical was observed. The residue after the thermo-gravimetric analysis of UO₂(NO₃)₂-2TBP was identified as α-UP₂O₇ by the powder X-ray diffraction analysis, indicating the strong coordination of TBP to the central uranium atom.     

Characterization of dose delivery in a hard X-ray irradiation facility

The Radiation Bioengineering Laboratory at Seoul National University (SNU) operates a user-constructed hard X-ray irradiation facility for radiation biology and radiation therapy physics studies. The system package of YXLON model 450-D08 operating at the anode voltage of up to 450 kV is a key part of the facility, which enables in vitro cell irradiation and animal irradiation for in vivo studies. In this article, dose delivery in the hard X-ray irradiation facility was characterized in terms of the dose vs. operational parametric combination of the facility. The operational parameters included beam tube anode voltage, beam tube current, irradiation time, and beam exit-to-sample distance. Bremsstrahlung X-rays at energy below approximately 20 keV were filtered out by a 3 mm-thick aluminum plate fitted over the 5 mm-thick beryllium window. Gafchromic EBT films were used as radiation sensor materials in dose measurement. The characterization was validated via experimental observation of the in vitro biological responses of cells to radiation exposure. The biological responses obtained using the new hard X-ray irradiator were highly comparable with those obtained using a commercial gamma-ray irradiator.     

X-ray radiolysis induced formation of silver nano-particles: A SAXS and UV-visible absorption spectroscopy study

We show that X-ray irradiation of metal salt aqueous solutions in the absence of any stabilizer leads to the synthesis of metal nano-particles, similarly to γ-ray irradiation. The chemical route is the reduction of silver metal ions induced by radiolysis of water. Moreover, X-rays used for the synthesis allow following in situ the formation of silver nano-particles by Small Angle X-ray Scattering associated with UV-visible absorption spectroscopy. The synthesized nano-objects appear spherical with a radius of about 14 nm.     

Computational fluid dynamic investigations of partial blockage detection by core-temperature monitoring system of a sodium cooled fast reactor

Thermal hydraulic studies have been carried out to understand temperature dilution suffered by core-temperature monitoring system of a sodium cooled fast reactor. The three-dimensional computational model is validated against experimental results of a water model. Jet mixing phenomenon as predicted by different turbulence models is compared and RNG k–? model is found to be better than other models. A comprehensive parametric study considering: (i) effects of construction/manufacturing tolerances on thermocouple positions with respect to subassembly positions, (ii) thermal/irradiation bowing of subassemblies, and (iii) changes in core power profile during reactor operation cycles has been carried out. The studies indicate the maximum possible dilution in fuel and blanket subassemblies to be 2.63 K and 46.84 K, respectively. Shifting of thermocouple positions radially outward by 20 mm with respect to subassembly centers leads to an overall improvement in accuracy of thermocouple readings. It is also seen that subassembly blockage that leads to 7% flow reduction in fuel subassembly and 12% flow reduction in blanket subassembly can be detected effectively by the core-temperature monitoring system.     

Lattice Parameters of Mixed Oxides in Sm-U-O System

The oxidation-reduction properties of mixed oxides in the system Sm-U-O and the variation of their lattice parameters due to oxidation and reduction were examined by means of thermogravimetry and X-ray diffraction. For mixed oxides Sm_yU_1-yO_2±x prepared in air, the O/M ratio decreased linearly from 2.667 at y= 0 to nearly stoichiometric 2.02 at y=0.5. The 0/M ratios at y>0.5 were on the line connecting 2.667 at y= 0 with 1.50 at y =1. The single phase region of the fluorite structure was between y = 0.5 and 0.6. The lattice parameters of the fluorite phase at ≤0.6 were constant, 5.418×10^?10m. For mixed oxides prepared in hydrogen, the 0/M ratio decreased linearly from 2.00 at y = 0 to 1.84 at y = 0.5, and from 1.84 at y = 0.5 to 1.50 at y = 1. The quenched oxides were single phase compounds except those for y = 0.1, 0.6 and 0.9. The lattice parameter of the fluorite structure decreased from 5.4700 at y = 0 to 5.427 × 10^?10 m of Smo.₄U0.6O_1.854. and was kept constant between y = 0.4 and 0.5, then increased to 5.466 × m at y = 0.7. The Sm-U-O phase diagram at 1,000°C was constructed on the basis of the X-ray diffraction work.     

The effect of grain boundary engineering on the oxidation behavior of INCOLOY alloy 800H in supercritical water

Grain boundary engineering (GBE) was applied to INCOLOY alloy 800H by means of thermomechanical processing. The oxidation behavior of GBE-treated alloy 800H exposed in supercritical water (SCW) with 25 ppb dissolved oxygen at 500 °C and 25 MPa was significantly improved as compared to 800H in the annealed condition. Gravimetry, optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) were employed in this study to analyze the oxidation behavior of control (annealed) and GBE-treated samples. GBE improves the protective oxidation behavior by enhancing spallation resistance and reducing oxidation rate. Spallation resistance correlates with a reduction in texture of the oxide layers.     

Low Exposure X-ray Transmission Measurements for Contrast Media Detection with Filtered X-rays

A feasibility study of X-ray transmission measurements for contrast media with less exposure using filtered X-rays and their energy information is described. Based on measurements of the energy spectra of La-filtered X-rays, sensitivity to the contrast media and the relative quantity of dose exposure of filtered X-rays as the ratio to white X-rays are shown. The dose exposure for the measurement of iodine contrast media is reduced by more than 50% with a 400/xm thick La filter. By using a filter with atomic number close to that of iodine such as Cs and Ba, a greater reduction in dose exposure with a smaller increase in the current of the X-ray tube is expected.     

Response of reinforced concrete structures to macrocell corrosion of reinforcements. Part II: After propagation of microcracks via a numerical approach

Investigation of response of reinforced concrete (RC) structures due to axisymmetric macrocell corrosion of rebars is of concern after propagation of microcracks within the concrete medium. The geometry, boundary and interfaces conditions of the present problem are identical to those stated in part I. As seen in the companion paper, the exact solution to the boundary value problem corresponding to the uncracked steel–rust–concrete composite was possible. After appearance of the microcracks the concrete behavior becomes nonlinear anisotropic with post-cracking softening, and the associated problem is analytically intractable. Therefore, it is proposed to employ a novel meshless method, namely gradient reproducing kernel particle (GRKPM), in the cylindrical coordinates. The analytical and numerical solutions pertinent to the uncracked concrete are in good agreement. Subsequently, the effects of the parameters associated with the mechanical behavior of concrete and properties of rust on the time of surface cracking, the maximum values of consumed rebar per unit area of anode and crack width openings at the time of surface cracking, and the maximum value of radial stress at the rust–concrete interface are scrutinized in some detail.     

Metal location and thickness in a multilayered sheet by measuring Kα/Kβ, Lα/Lβ and Lα/Lγ X-ray ratios

When a multilayered material is analyzed by means of energy-dispersive X-ray fluorescence analysis, then the X-ray ratios of Kα/Kβ, or Lα/Lβ and Lα/Lγ, for an element in the multilayered material, depend on the composition and thickness of the layer in which the element is situated, and on the composition and thickness of the superimposed layer (or layers).Multilayered samples are common in archaeometry, for example, in the case of pigment layers in paintings, or in the case of gilded or silvered alloys. The latter situation is examined in detail in the present paper, with a specific reference to pre-Columbian alloys from various museums in the north of Peru.     

Numerical Experiments on Soft X-ray Emission Optimization of Nitrogen Plasma in 3 kJ Plasma Focus SY-1 Using Modified Lee Model

The X-ray emission properties of nitrogen plasmas are numerically investigated using corona plasma equilibrium model. The X-ray emission intensities of nitrogen Ly _α , Ly _β and He _α , He _β lines are calculated. The optimum plasma temperature for nitrogen X-ray output is concluded to be around 160 eV. The Lee model is modified to include nitrogen in addition to other gasses (H₂, D₂, He, Ne, Ar, Xe). It is then applied to characterize the 2.8 kJ plasma focus PF-SY1, finding a nitrogen soft X-ray yield (Ysxr) of 8.7 mJ in its typical operation. Keeping the bank parameters and operational voltage unchanged but systematically changing other parameters, numerical experiments were performed finding the optimum combination of pressure = 0.09 Torr, anode length = 7.2 cm and anode radius = 2.58 cm. The optimum Ysxr was 64 mJ. Thus we expect to increase the nitrogen Ysxr of PF-SY1 sevenfold from its present typical operation; without changing the capacitor bank, merely by changing the electrode configuration and operating pressure.     

The effect of pulsed irradiation on the swelling of 316 stainless steel in fusion reactors

A time-dependent rate theory formulation has been used to study the effects of pulsed irradiation on point defect and void behavior at elevated temperatures. It is found that point defects in pulsed tokamaks, θ-pinchs and inertial confinement fusion reactors (ICFR) display non-steady-state behavior. The pulsed nature of the irradiation has been shown to produce considerable deviations from steady-state void growth behavior at high temperatures (0.3 T_m to 0.5 T_m). In particular, the amount of swelling in the first-wall can be reduced for ICFR pulsing conditions and pulse widths ranging from a nanosecond to a microsecond. The amount of reduction increases with increased pellet yield at a fixed operating temperature, geometry and ICFR plant power output.     

Electrochemical Properties of Uranyl Ion in Ionic Liquids as Media for Pyrochemical Reprocessing

We have proposed a new reprocessing process by using ionic liquids (ILs) instead of molten salts of alkali chlorides in pyrochemical process. In the proposed process, spent nuclear fuels are dissolved in ILs by using Cl₂ as an oxidant, and UO₂ ²⁺ and PuO₂ ²⁺ ions in ILs are recovered as UO₂ and PuO₂ by electrochemical reduction. In order to examine applicability of ILs as media for reprocessing, we have studied electrochemical behavior of UO₂ ²⁺ in 1-butyl-3-methylimidazolium chloride (BMICl), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄), and 1-butyl-3-methylimidazolium nonafluorobutanesulfonate (BMINfO). Electrochemical properties of uranyl chloride dissolved into ILs were examined by cyclic voltammetry. In BMICl, an almost reversible redox couple was observed, and the formal potential and the diffusion coefficient were evaluated as _0:758V vs. Ag/AgCl and 4:8 × 10^?8 cm²s^?1, respectively. On the other hand, the electrochemical reactions of UO₂ ²⁺ in BMIBF₄ and BMINfO were irreversible. In BMINfO, some reduction peaks and one sharp oxidation peak were observed in the range of ?0:6～–0:2V and around 0.85V vs. Ag/AgCl, respectively. The reduction and oxidation peaks were assigned to multi step reduction of UO₂ ²⁺ to U(IV) via U(V) and/or direct reduction of UO₂ ²⁺ to U(IV), and the oxidative dissolution of the resulting U(IV) compounds, respectively. The electrochemical reduction of UO₂ ²⁺ in BMINfO at ?1:0V vs. Ag/AgCl produced the deposits on a carbon electrode as a cathode. Analyses of the deposits with the scanning electron microscope and the energy dispersive X-ray spectrometer indicated that the deposits are compounds containing uranium, oxygen, and chlorine. As a result, it is expected that the UO₂ ²⁺ in IL can be recovered electrolytically as uranium compounds such as UO₂ and uranium oxychlorides.     

Effect of Cathode Designs on Radiation Emission of Compact Diode (CD) Device

A comparative study on the radiation emission such as X-ray yield and efficiency has been carried out in compact diode device. Two different designs of cathode having sharp-edged razor blade (of 0.5 mm thickness with width 2 mm) and a sewing machine needle (of 0.5 mm diameter at tip with length of 39 mm) have been tested for this study. The radiation emission (X-ray yield) was determined by employing two set of PIN diodes at fixed positions. The maximum X-ray yield depends on cathode designs and electrodes separation in few mm. The yield of X-ray is small in the case of sharp-edged razor blade cathode than the sewing machine needle cathode. The X-ray yield, measured by 4π-geometry, shows its dependence on the cathode designs. The maximum X-ray yield is found to be 939.2 ± 65.7 mJ with efficiency of 0.4142 ± 0.0289%. This study indicates that the compact diode device could be optimized to a great extent for optimal X-ray yield by using an appropriate cathode design.     

Structural, thermal and optical behavior of 84 MeV oxygen and 120 MeV silicon ions irradiated PES

In order to study structural, thermal and optical behavior, thin flat samples of polyethersulfone were irradiated with oxygen and silicon ions. The changes in properties were analyzed using different techniques viz: X-ray diffraction, thermo-gravimetric analysis, Fourier transform infrared, UV-visible and photoluminescence spectroscopy. A noticeable increase in the intensity of X-ray diffraction peaks was observed after irradiation with 84 MeV oxygen ions at low and medium fluences, which may be attributed to radiation-induced cross-linking in polymer. Fourier transform infrared and thermo-gravimetric analysis corroborated the results of X-ray diffraction analysis. No noticeable change in the Fourier transform infrared spectra of oxygen ion irradiated polyethersulfone were observed even at the highest fluence of 1 × 10¹³ ions cm⁻², but after irradiation with silicon ions, a reduction in intensity of almost all characteristic bands was revealed. An increase in the activation energy of decomposition of polyethersulfone was observed after irradiation with 84 MeV oxygen ions up to medium fluences but degradation was revealed at higher fluences. Similar trends were observed by photoluminescence analysis.     

Effect of swift heavy ion irradiation on spray deposited CdX (X = S, Te) thin films

Cadmium sulfide and cadmium telluride thin films are irradiated with high energy heavy ion beam to study the irradiation induced effects in these films. The polycrystalline thin film samples deposited by spray pyrolysis are irradiated with 60 MeV Oxygen ions using tandem Pelletron accelerator. The X-ray diffraction patterns exhibit a reduction in peak intensities in both CdS and CdTe films. The grain size decrease with fluence is observed for both CdS and CdTe films, with more decrease for CdTe films. The AFM results support this observation. The films show opposite trend in the variation of electrical resistivity with irradiation fluence. A decrease in resistivity is observed for CdS films due to an increase of carrier concentration arising by the creation of sulfur vacancies during the irradiation. The creation of sulfur vacancies is confirmed by XPS studies. The stoichiometric changes seen from XPS studies support this observation. An enhancement of grain boundary scattering due to the reduction of grain size leads to the increase of electrical resistivity for CdTe films.     

铀浓缩厂放射性废物管理与最小化实践

介绍了某铀浓缩厂含铀放射性废物管理现状及放射性废物最小化方面的应用实践。放射性废物分类收集,集中处置,减少放射性废物的体积及产生量是基本要求。采用5%的Na₂CO₃和30% H₂O₂混合液以及清水对放射性污染管道、阀门等进行清洗,使α表面污染≤0.4 Bq/cm²,清洗液厂内循环利用。通过除锈清洗液再利用、水压试验水再利用及容器清洗工艺优化改进等措施,单台容器平均废液产生量减少35%左右,从源头上控制了含铀废液的产生量。小容器处理工艺由湿法改为干法,废水产生量减少了90%;大容器清洗过程中,除锈液可重复利用5次,可使得除锈废液的产生量减少80%左右。提高吸附尾液循环利用比,减少了废水的产生量。采用钙盐联合沉淀法处理废水,废渣年产生量平均减少20%,废水处理合格率大大提高。在此基础上,介绍了实现含铀放射性废物最小化的几点思路,并提出相关措施。     

Pinch Current and Soft X-Ray Yield Limitations by Numerical Experiments on Nitrogen Plasma Focus

The modified version of the Lee model code RADPF5-15a is used to run numerical experiments with nitrogen gas, for optimizing the nitrogen soft X-ray yield on PF-SY1. The static inductance L ₀ of the capacitor bank is progressively reduced to assess the effect on pinch current I _pinch. The experiments confirm the I _pinch, limitation effect in plasma focus, where there is an optimum L ₀ below which although the peak total current, I _peak, continues to increase progressively with progressively reduced inductance L ₀, the I _pinch and consequently the soft X-ray yield, Ysxr, of that plasma focus would not increase, but instead decreases. For the PF-SY1 with capacitance of 25 μF, the optimum L ₀ = 5 nH, at which I _pinch = 254 kA, Ysxr = 5 J; reducing L ₀ further increases neither I _pinch nor nitrogen Ysxr. The obtained results indicate that reducing the present L ₀ of the PF-SY1 device will increase the nitrogen soft X-ray yield.