The frequency dependent response of the electrical impedance of UO2

AC impedance techniques in the frequency range 5 Hz to 5 MHz have been employed to measure dielectric properties of single crystal UO₂ in the form of plate specimens. The dielectric constant has been measured down to 4 K, giving results consistent with previous reports. Both barrier and volume effects have been shown to contribute to the measured impedances. The barrier effects account for the anomalously large capacitances observed in previous attempts to measure the dielectric constant by the conventional plate technique. Activation energies for carriers in both boundary and bulk regions are similar (0.18 to 0.25 eV). The behaviour is consistent with the presence of electronic holes present in the concentrations to be expected from small deviations from stoichiometry.     

The electrical impedance response of steel surface oxide layers in molten lead-bismuth eutectic

Stainless steel 316L samples were preoxidized and then immersed in molten lead-bismuth eutectic (LBE) alloy at 200 °C. The changes in their electrical impedance responses were observed over time. Negligible impedance magnitudes were observed at first, followed by a rapid increase to thousands of ohm-cm². The impedance response is sensitive to changes in the immersed sample area. Micro-indentations on samples caused their impedance magnitudes to decrease initially, but the magnitudes recovered within a few days. SEM analysis showed that the indentations were still present and visible even after the recovery of impedance response, demonstrating that the physical features of the oxide layers which govern the electrical response must be smaller than the micrometer length scale.     

Dissolution of magnetite using an environmentally friendly chelant: an electrochemical impedance spectroscopy study

Ethylenediaminedisuccinic acid (EDDS), a biodegradable substitute for EDTA, was used as a chelant for dissolving magnetite and magnetite formed on iron metal surface. Dissolution was found to increase in presence of ferrous ions and depend on pH of solution, concentration of ferrous ion, EDDS concentration, applied cathodic potential and temperature. The impedance spectrum for the dissolution of magnetite film formed on iron exhibited two time constants. The first at high frequency range is ascribed to the reductive dissolution of magnetite. It is very crucial to carry out the dissolution process at the appropriate temperature to insure complete removal of oxide layer.     

In situ electrochemical impedance spectroscopy of Zr–1%Nb under VVER primary circuit conditions

Oxide layers were grown on tubular samples of Zr–1%Nb under conditions simulating those in VVER-type pressurised water reactors, viz. in near-neutral borate solutions in an autoclave at 290 °C. These samples were investigated using electrochemical impedance spectroscopy which was found to be suitable to follow in situ the corrosion process. A –CPE_oxR_ox– element was used to characterise the oxide layer on Zr–1%Nb. Both the CPE_ox coefficient, σ_ox, and the parallel resistance, R_ox, were found to be thickness dependent. The layer thickness, however, can only be calculated after a calibration procedure. The temperature dependence of the CPE_ox element was also found to be anomalous while the temperature dependence of R_ox indicates that the oxide layer has semiconductor properties. The relaxation time – defined as (R_oxσ_ox)^1/ – was found to be quasi-independent of oxidation time and temperature; thus it is characteristic to the oxide layer on Zr–1%Nb.     

Transverse mode-coupling instability with longitudinal impedance

Transverse mode-coupling instability(TMCI)is a dangerous transverse single-bunch instability that can lead to severe par-ticle loss.The mechanism of TMCI can be explained by the coupling of transverse coherent oscillation modes owing to the transverse short-range wakefield(i.e.,the transverse broadband impedance).Recent studies on future circular colliders,e.g.,FCC-ee,showed that the threshold of TMCI decreased significantly when both longitudinal and transverse impedances were included.We performed computations for the circular electron-positron collider(CEPC)and observed a similar phenom-enon.Systematic studies on the influence of longitudinal impedance on the TMCI threshold were conducted.We concluded that the imaginary part of the longitudinal impedance,which caused a reduction in the incoherent synchrotron tune,was the primary reason for the reduction in the TMCI threshold.Additionally,the real part of the longitudinal impedance assists in increasing the TMCI threshold.     

Characterization of defect accumulation in neutron-irradiated Mo by positron annihilation spectroscopy

Positron annihilation lifetime spectroscopy measurements were performed on neutron-irradiated low carbon arc cast Mo. Irradiation took place in the high flux isotope reactor, Oak Ridge National Laboratory, at a temperature of 80 ± 10 °C. Neutron fluences ranged from 2 × 10²¹ to 8 × 10²⁴ n/m² (E > 0.1 MeV), corresponding to displacement damage levels in the range from 7.2 × 10⁻⁵ to 2.8 × 10⁻¹ displacements per atom (dpa). A high density of submicroscopic cavities was observed in the neutron-irradiated Mo and their size distributions were estimated. Cavities were detected even at a very low-dose of ∼10⁻⁴ dpa. The average size of the cavities did not change significantly with dose, in contrast to neutron-irradiated bcc Fe where cavity sizes increased with increasing dose. It is suggested that the in-cascade vacancy clustering may be significant in neutron-irradiated Mo, as predicted by molecular dynamics simulations.     

Determination of the distribution of air and water in porous media by electrical impedance tomography and magneto-electrical imaging

Monitoring the distribution of water content is essential for understanding hydrological processes in the lithosphere and the pedosphere. The movement of water in unsaturated rock formations and in the vadose zone is influenced by different processes (mainly infiltration, evaporation, percolation and capillary flow) which may be rate determining depending on the actual conditions. The interdependence of these processes also strongly influences the transport and distribution of solutes in the pore space. In order to gain a better understanding of the movement and distribution of water in unsaturated media, systematic investigations with non-invasive or minimal invasive methods appear to be most suitable. Studies on the distribution of electrical conductivity can improve risk analysis concerning waste disposals in general and nuclear waste repositories in particular. Induced polarization and magnetic flux density determined with two highly sensitive accessories yield additional information and may allow for better discrimination of coupled flow processes. Electrical impedance tomography (EIT) with 20 current injection and 48 voltage electrodes was used here to monitor the evaporation of tap water from a container filled with sand under laboratory conditions at 20 °C. The results are compared with data obtained by determining spectral induced polarization (SIP) of sand during desaturation in a multi-step outflow equipment. Infiltration processes and evaporation from sand saturated with 0.01 M CaCl₂ were determined by magneto-electrical resistivity imaging technique (MERIT). The results were obtained from a long-term experiment under controlled conditions.     

Ion-induced photon spectroscopy of insulators and application to in-situ diagnostics of nanoparticle formation processes

Ion-induced photon emission under heavy-ion bombardment has been studied over an energy range from near-infrared to vacuum-ultraviolet. Time-resolved optical devices with fast-response CCD cameras detected photons from a-SiO₂ under implantation with negative Cu ions of 60 keV, up to a dose rate of 100 μA/cm². The ion-induced photon spectra consisted of sharp line spectra due to isolated atoms of Si, Cu and a broad band of visible light. The line spectra resulted from an ion-induced glow above the surface and indicated pronounced outward transport of Cu atoms to the vacuum. Intensity of the line spectra and the broad band varied non-linearly with dose and dose rate. The in-situ spectroscopy provided diagnostic information of surface- and intra-solid processes associated with nanoparticle formation at high dose rates. The Cu sublimation reflected from presence of a Cu-depleted zone beneath the surface, which is one of the important factors to form a two-dimensional arrangement of nanoparticles.     

Characterization of heat transfer processes in a melt pool convection and vessel-creep experiment

The results of an integral experiment on melt pool convection and vessel-creep deformation are presented and analyzed. The experiment is performed on a test facility, named Failure Of REactor VEssel Retention (FOREVER). The facility employs a 1/10-scaled 15Mo3-(German)-steel vessel of 400-mm diameter, 15-mm wall thickness and 750-mm height. A high-temperature (1300 °C) oxide melt is prepared in a SiC-crucible placed in a 50 kW induction furnace and is, then, poured into the 1/10th scale vessel. A MoSi₂ 50 kW electric heater is employed in the melt pool to heat and maintain its temperature at 1200 °C. The vessel is pressurized with argon at the desired pressure. In the FOREVER/C1 experiment, the vessel wall, maintained at about 900 °C and pressurized to 26 bars, was subjected to creep deformation in a 24-h non-stop test. The FOREVER/C1 test is the first integral experiment, in which a decay-heated oxidic naturally-convecting melt pool was maintained in long-term contact with the hemispherical lower head of a pressurized, creeping, steel vessel. A sizeable database was obtained on melt pool temperatures, melt pool energy split, heat transfer rates, heat flux distribution on the melt (crust)–vessel contact surface, vessel temperatures and, in particular the vessel wall creep rate as a function of time. The paper provides information on the FOREVER/C1 measured thermal characteristics and analysis of the observed thermal behavior. The coupled nature of thermal and mechanical processes, as well as the effect of other system conditions (such as depressurization) on the melt pool and vessel temperature responses are analyzed.     

Differentiation of illicit drugs with THz time-domain spectroscopy

The terahertz time-domain spectroscopy (THz-TDS) was used for sensing and identifying illicit drugs.The absorption spectra of seven illicit drug samples (morphine and its hydrochloride,cocaine hydrochloride,codeine phosphate,papaverine hydrochloride,pethidine hydrochloride,and thebaine) were studied by THz-TDS at 0.3-2.0 THz at room temperature.The geometric structure and vibration frequencies of morphine were calculated by density functional theory.The four absorption features were dominated by intra-/inter-molecular collective or lattice vibration modes.Each illicit drug has a distinct signature in its THz spectra.The results indicate that the THz-TDS can be used to identify and discriminate illicit drugs by their characteristic fingerprints.     

Electrochemical impedance spectroscopic study of passive zirconium

Spent, unreproccessed nuclear fuel is generally contained within the operational fuel sheathing fabricated from a zirconium alloy (Zircaloy 2, Zircaloy 4, or Zirlo) and is then stored in a swimming pool and/or dry storage facilities until permanent disposal in a licensed repository. During this period, which begins with irradiation of the fuel in the reactor during operation, the fuel sheathing is exposed to various, aggressive environments. The objective of the present study was to characterize the nature of the passive film that forms on pure zirconium in contact with an aqueous phase [0.1 M B(OH)₃ + 0.001 M LiOH, pH 6.94] at elevated temperatures (in this case, 250 °C), prior to storage, using electrochemical impedance spectroscopy (EIS) with the data being interpreted in terms of the point defect model (PDM). The results show that the corrosion resistance of zirconium in high temperature, de-aerated aqueous solutions is dominated by the outer layer. The extracted model parameter values can be used in deterministic models for predicting the accumulation of general corrosion damage to zirconium under a wide range of conditions that might exist in some repositories.     

Nondestructive assay of spent nuclear fuel with gamma-ray spectroscopy

An important issue in nuclear safeguards is to verify operator-declared data of spent nuclear fuel. Various techniques have therefore been assigned for this purpose. A nondestructive approach is to measure the gamma radiation from spent nuclear fuel assemblies. Using this technique, parameters such as burnup and cooling time can be calculated or verified.     

屏蔽电缆转移阻抗的测量

介绍了一种快速有效地测量电缆转移阻抗的方法,给出了SYVZ－9综合电缆转移阻抗的测试结果,从测试结果可以看出,在低频下,转移阻抗为电缆屏蔽层的直流电阻,随着频率的增加,转移阻抗迅速增加。     

一种复合屏蔽电缆的转移阻抗

给出一种复合屏蔽电缆转移阻抗的测试方法和结果,从测试结果可看出．在低频下．转移阻抗为电缆屏蔽的直流电阻;在高频段(大于30MHz)．转移阻抗随着频率的增加而增加．其屏蔽性能优于单层屏蔽结构的电缆。     

Radiation stability of prototype ITER-type resistive bolometers with improved electrical contacts

We present the results for reactor irradiation of prototype ITER-compatible resistive radiation hardened bolometers up to a total dose of ∼0.01 dpa (thermal/fast [E > 0.1 MeV] neutron fluence of 5.2/0.8 ×10¹⁹ n/cm²). The prototype bolometer has a 100 nm thick Pt meander deposited on an alumina ceramic substrate. Connection of the delicate meander with external wiring is provided via special binding posts placed on the substrate. The binding post consist of a Pt ring attached to the substrate using melted glass, with a laser welded 0.1 mm diameter Pt wire. A vacuum capsule with a special bolometer holder was designed and fabricated to allow reactor irradiation at ∼400 °C in vacuum. The desired temperature was obtained by balancing the radiation heat generation and thermal energy losses via radiation and conductive heat transfer. The resistance of the Pt meander was measured in the course of 19 days irradiation in the BR2 material testing reactor of the SCK·CEN. Immediately after insertion of the bolometer into the reactor a significant decrease of the meander resistance was observed. The resistance then stabilized after several days of irradiation. The meander resistance measurements were stable during the first week of irradiation, but then the electrical contact was lost. Post-irradiation inspection showed that the binding posts remained attached to the substrate while one of the Pt wires detached from the Pt ring most probably due to a bad laser weld.     

Room temperature, high-resolution X-ray spectroscopy with silicondrift chambers

The development of detectors for high resolution room temperature X-ray spectroscopy represents a relevant progress in many fields of application, mainly in out-of-laboratory environments. A new type of silicon detector, the semiconductor drift chamber (SDC), allows one to obtain at room temperature, or with a moderate cooling, a resolution comparable to that obtained at liquid nitrogen temperature with traditional detectors of the same active area. The key feature of the SDC's is the very low output capacitance (about 100 fF) independent of the active area of the device. This feature, together with a good capacitive matching between the detector and the first stage of amplification, leads to high values of the resolution at short shaping times. We tested a simple 6-mm² cylindrical SDC at room temperature and at -20°C (easily obtainable with electrical cooling), by using a specifically designed, low capacitance, JFET as the input transistor of the preamplifier. With a ⁵⁵Fe source, we measured an equivalent noise charge (ENC) of 34 e^- RMS and 27 e^- RMS at room temperature and at -20°C respectively. To our knowledge these are presently the best values obtained for the same active area near room temperature     

Transient processes with delayed neutrons in a heterogeneous reactor

Institute of Theretical and Experimental Physics. Translated from Atomnaya Énergiya, Vol. 70, No. 1, pp. 8–12, January, 1991.