Progress on the development of H-concentration probes in eutectic lead–lithium: Synthesis and characterization of electrochemical sensor materials

Dynamic tritium concentration measurement in lithium–lead eutectic (17% Li–83% Pb) is of major interest for a reliable tritium testing program in ITER TBM and for an experimental proof of tritium self-sufficiency in liquid metal breeding systems. Potentiometric hydrogen sensors for molten lithium–lead eutectic have been designed at the Electrochemical Methods Lab at Institut Quimic de Sarria (IQS) at Barcelona and are under development and qualification. The probes are based on the use of solid state electrolytes and works as Proton Exchange Membranes (PEM).In this work, the following compounds have been synthesized in order to be tested as PEM H-probes: BaCeO₃, BaCe_0.9Y_0.1O_3?δ, SrCe_0.9Y_0.1O_3?δ and Sr(Ce_0.9–Zr_0.1)_0.95Yb_0.05O_3?δ. Potentiometric measurements of the synthesized ceramic elements have been performed at different hydrogen concentrations at 500 °C. In this campaign, a fixed and known hydrogen pressure has been used in the reference electrode. The sensors constructed using the proton conductor elements BaCeO₃, SrCe_0.9Y_0.1O_3?δ and Sr(Ce_0.9–Zr_0.1)_0.95Yb_0.05O_3?δ exhibited quite stable output potential and its value was quite close to the theoretical value calculated with the Nernst equation (deviation less than 100 mV). Unstable measurement was obtained using BaCe_0.9Y_0.1O_3?δ as a solid state electrolyte in the sensor.     

Effect of H+ and O+ implantation on electrical properties of SrBi2Ta2O9 ferroelectric thin films

The effect on the crystalline structure and ferroelectric properties of ion implantation in SrBi₂Ta₂O₉(SBT) ferroelectric thin films has been investigated. 25 keV H⁺, 140 keV O⁺ with doses from 1 × 10¹⁴/cm² to 3 × 10¹⁵/cm² were implanted into the Sol–Gel prepared SBT ferroelectric thin films. The X-ray diffraction patterns of SBT films show that no difference appears in the crystalline structure of as-H⁺-implanted SBT films compared with as-grown films, H⁺ and O⁺ co-implanted SBT films show an obvious degradation of crystalline structure. Ferroelectric properties measurements indicate that both remnant polarization and coercive electric field of H⁺ implanted SBT films decrease with increasing the implantation dose. The disappearance of ferroelectricity was found in the H⁺, O⁺ co-implanted SBT films at room temperature. The great recovery of hydrogen-induced degradation in SBT films was obtained with O⁺ implantation using a heat-target-implantation technique.     

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.     

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.     

Investigation of hydrogen concentration and hardness of ion irradiated organically modified silicate thin films

A study of the effects of ion irradiation of organically modified silicate thin films on the loss of hydrogen and increase in hardness is presented. NaOH catalyzed SiNa_wO_xC_yH_z thin films were synthesized by sol–gel processing from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and spin-coated onto Si substrates. After drying at 300 °C, the films were irradiated with 125 keV H⁺ or 250 keV N²⁺ at fluences ranging from 1 × 10¹⁴ to 2.5 × 10¹⁶ ions/cm². Elastic Recoil Detection (ERD) was used to investigate resulting hydrogen concentration as a function of ion fluence and irradiating species. Nanoindentation was used to measure the hardness of the irradiated films. FT-IR spectroscopy was also used to examine resulting changes in chemical bonding. The resulting hydrogen loss and increase in hardness are compared to similarly processed acid catalyzed silicate thin films.     

On the study of catalytic membrane reactor for water detritiation: Membrane characterization

Tritium waste recycling is a real economic and ecological issue. Generally under the non-valuable Q₂O form (Q = H, D or T), waste can be converted into fuel Q₂ for a fusion machine (e.g. JET, ITER) by isotope exchange reaction Q₂O + H₂ = H₂O + Q₂. Such a reaction is carried out over Ni-based catalyst bed packed in a thin wall hydrogen permselective membrane tube. This catalytic membrane reactor can achieve higher conversion ratios than conventional fixed bed reactors by selective removal of reaction product Q₂ by the membrane according to Le Chatelier's Law.This paper presents some preliminary permeation tests performed on a catalytic membrane reactor. Permeabilities of pure hydrogen and deuterium as well as those of binary mixtures of hydrogen, deuterium and nitrogen have been estimated by measuring permeation fluxes at temperatures ranging from 573 to 673 K, and pressure differences up to 1.5 bar. Pure component global fluxes were linked to permeation coefficient by means of Sieverts’ law. The thin membrane (150 μm), made of Pd–Ag alloy (23 wt.%_Ag), showed good permeability and infinite selectivity toward protium and deuterium. Lower permeability values were obtained with mixtures containing non permeable gases highlighting the existence of gas phase resistance. The sensitivity of this concentration polarization phenomenon to the composition and the flow rate of the inlet was evaluated and fitted by a two-dimensional model.     

129I AMS at 0.5 MV tandem accelerator

The ¹²⁹I measurement program has been established at the 0.5 MV ‘Tandy’ accelerator of the PSI/ETH Zürich AMS facility. This development was made possible by using a SiN window instead of Mylar one in a gas ionization detector. The setting up of the ¹²⁹I measurement at Tandy is simple, the acquired performance is stable and reliable, and the quality of results is equal to or better than at our larger EN-tandem. With this setup, high sample throughput, which is required in many ¹²⁹I studies, can be easily achieved. The measurements are performed in the +3 charge state. At this charge state the major difficulty in the ¹²⁹I⁺³ identification is caused by a highly abundant 43⁺¹ (m = 43, q = +1) molecule interference. This is a positive molecular ion, because its intensity reduces exponentially with an increase in gas stripper pressure. We conclude that this molecule is ²⁷Al¹⁶O⁺ (m/q = 43/1 = 129/3) and comes from the break-up of (Al₂O₃ + Al)^? (m = 129) precursor at the terminal: (Al₂O₃ + Al)^? → ²⁷Al¹⁶O⁺. The expected isobaric interferences ⁴³Ca⁺¹ and ⁸⁶Sr⁺², which also originate from the break-up of molecules in the stripper, were found to be low and do not disturb the ¹²⁹I⁺³ measurements. The best repeatable performance with our standard sample material was achieved at 0.14 μg/cm² Ar gas stripper pressure with machine blanks showing ～6 × 10^?14 normalized ¹²⁹I/I ratio and 9% transmission through the accelerator. However, high ²⁷Al¹⁶O⁺ molecular rates were observed from the user samples, and in order to destroy these molecules we had to increase the stripper pressure to ～0.22 μg/cm². This increase in the stripper pressure degraded the machine blank values to ～9 × 10^?14 and reduced transmission to 8%. Nevertheless, the achieved measurement conditions are sufficient for measurement of nearly all ¹²⁹I samples that have been submitted to PSI/ETH over the last few years.     

Erbium environment on Er-doped silica and alumino-silicate glass films: An EXAFS study

Er-doped dielectric films are characterized by the emission of a photoluminescence signal at λ = 1.54 μm, the main used in the optical telecommunications. The efficiency of the radiative emission is strongly related to the characteristics of the Er³⁺ environment. Er-doped SiO₂ films (synthesized by rf-magnetron co-sputtering) and 87SiO₂:10Al₂O₃:3Na₂O silicate glass films doped with 0.5 mol% of Er (prepared by sol–gel route and subsequently doped with silver by Ag⁺ ? Na⁺ field-assisted solid-state ion exchange) were studied by extended X-ray absorption fine structure spectroscopy performed at Er L_III-edge (Italian beamline GILDA of the ESRF). In the silica samples the Er coordinates about 4.5 O atoms at a short distance (R = 2.07–2.13 Å), similar to the one observed in Er-doped glasses when the preparation conditions are far from the thermodynamical equilibrium. In alumino-silicate samples the first shell of atoms is formed of 5.5–7.5 O atoms at a distance of about 2.31 Å, showing a local structure similar to other Er-doped sol–gel glasses and glass–ceramics. A comparison between the first shell structure around Er ions and the different intensity of the photoluminescence emission suggests that the increase of the radiative emission upon thermal annealing is mainly related to the decrease of the defects number in the glass structure as a consequence of the annealing.     

First-principles study of hydrogen adsorption and permeation in reconstructed cubic erbium oxide surfaces

Understanding surface properties of Er₂O₃, especially in relation to adsorption and permeation of atomic hydrogen, is of considerable importance to the study of tritium permeation barriers. In this work, hydrogen diffusion pathways through the low-index (1 0 0), (1 1 0), and (1 1 1) surfaces of cubic Er₂O₃ have been calculated using density functional theory within the GGA (PBE) + U approach. The dependence of the effective U parameter on lattice constants, bulk moduli, and formation energies of Er₂O₃ has been investigated in detail. The energetics of hydrogen penetration from the surfaces to the solution site in bulk Er₂O₃ were defined using the optimum effective U value of 5.5 eV. For a low surface coverage of hydrogen (0.89 × 10¹⁴ H/cm²), a penetration energy of at least 1.7 eV was found for all the low-index erbium oxide surfaces considered. The results of the present study will provide useful guidance for future studies on modeling defects, such as grain boundaries and vacancies, in tritium permeation barriers.     

An advance process of aluminum rich coating as tritium permeation barrier on 321 steel workpiece

We have proposed an advance three-step process, Al-electroplating in ionic liquid followed by heat treating and selectively oxidation, preparing aluminum rich coating as tritium permeation barrier (TPB). In present work, the advance process was applied to 321 steel workpieces. In the Al-electroplating, pieces were coated by galvanostatic electrodeposition at 20 mA/cm² in aluminum chloride (AlCl₃)–1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid. The Al coating on those pieces all displayed attractive brightness and well adhered to surface of pieces. Within the aluminizing time from 1 to 30 h, a series of experiments were carried out to aluminize 321 steel pieces with Al 20 μm coating at 700 °C. After heat treated for 8 h, a 30 μm thick aluminized coating on piece appeared homogeneous, free of porosity, and mainly consisted of (Fe, Cr, Ni)Al₂, and then was selectively oxidized in argon gas at 700 °C for 50 h to form Al₂O₃ scale. The finally fabricated aluminum rich coating, without any visible defects, had a double-layered structure consisting of an outer γ-Al₂O₃ layer with thickness of 0.2 μm and inner (Fe, Cr, Ni)Al/(Fe, Cr, Ni)₃Al layer of 50 μm thickness. The deuterium permeation reduction factor, PRF, of piece (Φ 80 × 2, L 150 mm) with such coating increased by 2 orders of magnitude at 600–727 °C. The reproducibility of the process was also showed.     

Overall Conductivity and Electromotive Force of SrZr0:9Yb0:1O3–a Cell System Supplied with Moist CH4

A proton-conducting ceramic cell for recovering tritium from process streams was investigated for its application to a fusion reactor system. The ceramic cell tested here was composed of a SrZr_0:9Yb_0.1O_3–a tube, one end of which was closed, and Ni/SiO₂ and NiO/SiO₂ porous electrodes. Its anode was supplied with moist CH₄ or H₂ and its cathode with moist O₂. All of the j-V curves obtained by a direct-current method were correlated to the relation V = E ₀ ? jd/σ at 600–700°C regardless of the two different conditions of the CH₄ + H₂O and H₂ + H₂O supply. The rate-controlling step of charged hydrogen ion transfer was determined from the dependences of the overall conductivity σ and the electromotive force E ₀ on the anode H₂O partial pressure and temperature. The E ₀ value under the condition of the CH₄ + H₂O supply was affected by the diffusion of reaction products of CH₄ + H₂O = CO + 3H₂ through the porous anode. On the other hand, the σ value was limited by the oxygen reduction rate at the cathode interface between the ceramic and the Ni electrode regardless of the different conditions between CH₄ + H₂O and H₂ + H₂O. These results were consistent with our results obtained by an alternating-current method. The activation energy of the overall conductivity was 60 kJ/mol.     

Addition versus radiolytic production effects of hydrogen peroxide on aqueous corrosion of UO2

The effects of hydrogen peroxide, H₂O₂, on UO₂ corrosion is investigated in aerated deionized water in two types of situations. The H₂O₂ species is either added to water or produced by radiolysis at UO₂/H₂O interfaces. The concentrations vary in the range 10⁻⁵–10⁻¹ mol l⁻¹. The radiolysis is induced by irradiating the UO₂/H₂O interfaces with a He²⁺-beam emerging from the UO₂ discs into the solutions. Both the evolution of the aqueous solutions and the UO₂ surfaces are characterised. In both types of experiments, the alteration of UO₂ results in the formation of the same secondary phase, an hydrated uranium peroxide called studtite (UO₂(O)₂ · 4H₂O). However, the uranium release at the interface differs strikingly. It is much higher when H₂O₂ is produced by irradiation than when it is simply added. Furthermore, it varies in opposite direction as a function of the H₂O₂ concentration. This gives evidence that the chemistry at the UO₂ interface under irradiation differs significantly from the chemistry induced by simply adding H₂O₂ to the solution. Rutherford backscattering spectrometry is used to determine the growth rate of the corrosion layer. For H₂O₂ addition, the layer thickness increases with increasing leaching time, although as time increases, the U release tends towards zero. It is possible to establish the first empirical equation relating the corrosion rates to the added H₂O₂ concentrations. For H₂O₂ radiolytic production, the growth is continuous as irradiation time increases but the growth rate seems to decrease as the layer grows and to reach a limit.     

Effect of yttria addition on the stability of porous chromium oxide ceramics in supercritical water

Porous chromium oxide (Cr₂O₃) ceramics were prepared by oxidizing highly porous chromium carbides that were obtained by a reactive sintering method, and were evaluated at temperatures ranging from 375 °C to 625 °C in supercritical water (SCW) environments with a fixed pressure of 25–30 MPa. Reactive element yttrium was introduced to the porous oxide ceramic by adding various amounts of yttria of 5, 10 and 20 wt.%, respectively, prior to reactive sintering. The exposure in SCW shows that the porous chromium oxide is quite stable in SCW at 375 °C. However, the stability decreased with increasing temperature. It is well known that chromium oxide can be oxidized to soluble chromium (VI) species in SCW when oxygen is present. Adding yttria increases the stability of chromium oxide in SCW environments. However, adding yttria higher than 5 wt.% increased the weight loss of porous chromium oxide samples because of the direct dissociation of Y₂O₃ in SCW.     

Formation of diffusion barrier coating on superalloy 690 substrate and its stability in borosilicate melt at elevated temperature

Aluminized and thermally oxidized superalloy 690 substrates forming Al₂O₃ layer on (NiCr)Al + Cr₅Al₈ types aluminides and bare substrates were exposed in sodium borosilicate melt at 1248 K for 192 h. SEM–EDXS analysis along the cross-section of bare substrate with adhered glass revealed formation of a continuous, thick Cr₂O₃ layer at the substrate/glass interface due to its low solubility in borosilicate melt. XRD on aluminide coated and thermally oxidized specimen revealed existence of Al₂O₃ along with NiAl and Cr₅Al₈ type phases after the exposure in borosilicate melt. SEM–EDXS analysis along the cross-section of aluminide coated and thermally oxidized sample with adhered glass indicated good stability of coating in borosilicate melt without any phase formation at the coating/glass interface. However, some Al enrichment in glass phase adjacent to interface was noticed without any significant Ni or Cr enrichment.     

The solid film lubrication by carbon ion implantation into α-Al2O3

Improvement in tribological performance by C⁺110 keV implantation can be achieved by having a more graphite-like carbon structure on Al₂O₃. It was shown that fracture toughness and critical peeling load increased for a fluence of 5 × 10¹⁷C⁺/cm² because of residual compression stress and amorphism of surface. The testing in a different implantation dose indicated that the friction and wear mechanism in Optimol fretting wear machine (SRV) was a combination of surface structure and its abrasive wear. Raman shift shows that the amorphous graphite with 5 × 10¹⁷–1 × 10¹⁸ C⁺/cm² implantation dose was formed on Al₂O₃ surface, so that it reduced friction coefficient and wear of Al₂O₃, also it is noticed that the failure of lubrication due to graphite-like film wear is much earlier in the implantation sample with 1 × 10¹⁷C⁺/cm² dose.     

Comparative study of transient current induced in SiC p+n and n+p diodes by heavy ion micro beams

N⁺p and p⁺n diodes were fabricated on p- and n-type 6H–SiC substrates with epitaxial layers, respectively. The charge induced in the diodes by 9 MeV oxygen (O) and nickel (Ni) ions was measured using Transient Ion Beam Induced Current (TIBIC) to clarify the capability of these diodes as particle detectors. As a result of the TIBIC measurements using 9 MeV O, the Charge Collection Efficiency (CCE) of around 83% was obtained for both p⁺n and n⁺p diodes. Since the CCE value includes the consumption of incident ion energy in an Al electrode and the n⁺ (p⁺) region as well as the decay of charge in the measurement system, the CCE value obtained in this study indicates that SiC n⁺p as well as p⁺n diodes are suitable for particle detectors. On the other hand, in the case of 9 MeV Ni ion irradiation, the CCE for both n⁺p and p⁺n diodes decreases due to the Auger recombination in dense electron–hole pairs.     

Carbon film growth and hydrogenic retention of tungsten exposed to carbon-seeded high density deuterium plasmas

Tungsten (W) targets have been exposed to high density (n_e ? 4 × 10¹⁹ m^?3), low temperature (T_e ? 3 eV) CH₄-seeded deuterium (D) plasma in Pilot-PSI. The surface temperature of the target was ～1220 K at the center and decreased radially to ～650 K at the edges. Carbon film growth was found to only occur in regions where there was a clear CII emission line, corresponding to regions in the plasma with T_e ? 2 eV. The maximum film thickness was ～2.1 μm after a plasma exposure time of 120 s. ³He nuclear reaction (NRA) analysis and thermal desorption spectroscopy (TDS) determine that the presence of a thin carbon film dominates the hydrogenic retention properties of the W substrate. Thermal desorption spectroscopy analysis shows retention increasing roughly linearly with incident plasma fluence. NRA measures a C/D ratio of ～0.002 in these films deposited at high surface temperatures.     

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.     

Point defects induced in ion irradiated 4H–SiC probed by exciton lines

The defects produced in 4H–SiC epitaxial layers by irradiation with a 200 keV H⁺ ion beam in the fluence range 6.5 × 10¹¹–1.8 × 10¹³ ions/cm² are investigated by Low Temperature Photoluminescence (LTPL–40 K).The defects produced by ion beam irradiation induce the formation of some sharp lines called “alphabet lines” in the photoluminescence spectra in the 425–443 nm range, due to the recombination of excitons at structural defects.From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P₁ lines (e, f, g) and the P₂ lines (a, b, c, d) that exhibit different trends with the ion fluence. The P₁ group normalized yield increases with ion fluence, reaches a maximum at 2.5 × 10¹² ions/cm² and then decreases. The P₂ group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5 × 10¹² ions/cm² and decreases at higher fluence, reaching a value of 50% of the maximum yield.The behaviour of P₁ and P₂ lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.     

Application of a boron doped diamond (BDD) electrode as an anode for the electrolytic reduction of UO2 in Li2O–LiCl–KCl molten salt

A boron doped diamond thin film electrode was employed as an inert anode to replace a platinum electrode in a conventional electrolytic reduction process for UO₂ reduction in Li₂O–LiCl molten salt at 650 °C. The molten salt was changed into Li₂O–LiCl–KCl to decrease the operation temperature to 550 °C at which the boron doped diamond was chemically stable. The potential for oxygen evolution on the boron doped diamond electrode was determined to be approximately 2.2 V vs. a Li–Pb reference electrode whereas that for Li deposition was around ?0.58 V. The density of the anodic current was low compared to that of the cathodic current. Thus the potential of the cathode might not reach the potential for Li deposition if the surface area of the cathode is too wide compared to that of the anode. Therefore, the ratio of the surface areas of the cathode and anode should be precisely controlled. Because the reduction of UO₂ is dependent on the reaction with Li, the deposition of Li is a prerequisite in the reduction process. In a consecutive reduction run, it was proved that the boron doped diamond could be employed as an inert anode.