Bare Foil Research Articles

A European manufacturing line for monolithic U–Mo bare foil production

The nuclear research reactor Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II), operated by the Technical University of Munich (TUM) in Germany, provides intense thermal neutron beams for the international scientific community. The uranium fuel currently used for the compact core is an assembly of fuel plates composed of dispersed U3Si2 powder with an enrichment up to 93%, dispersed in aluminium (Al) powder and cladded with an Al alloy. Within the international efforts to minimise the usage of HEU (Highly Enriched Uranium), the FRM II aims to convert its compact core to LEU (Low Enriched Uranium), i.e., a fuel with an enrichment in 235U lower than 20%. The most promising candidate is the metallic monolithic uranium–molybdenum alloy (U–Mo) with zirconium (Zr) coating and Al-based cladding. Here, we show the first European pilot line for U–Mo bare foil manufacturing, implemented in collaboration with the European fuel manufacturer Framatome-CERCATM in Romans-sur-Isère, France. This line involves innovative manufacturing processes, including casting, laser welding, hot rolling, and laser cutting. An overview of the bare foil development with the first results is presented, including visual inspections of foils produced from the hot rolling, the laser cutting and the manufacturing tools used. These first depleted uranium (DU) bare foils are analysed to extract the best manufacturing parameters for future industrialisation. This European manufacturing process gives an alternative solution to the US development for U–Mo monolithic bare foil manufacturing. It represents the first step for European monolithic fuel manufacturing, which could push other European research reactors to use the monolithic U–Mo for their conversion.

Effect of shroud on the energy extraction performance of oscillating foil

A shrouded oscillating-foil turbine is proposed to augment the energy extraction performance. The oscillating foil undergoes combined plunging and pitching motion to convert the flow energy. A diffuser is introduced into the oscillating-foil-based turbine as the shroud. The speed-up and energy extraction performance of the turbine were assessed numerically. The effects of three cost-independent geometrical factors, namely shroud entrance width, shroud angle and streamwise distance between shroud and foil, and shroud sectional shape on energy extraction performance were investigated in detail. The optimal motion parameters for the shrouded oscillating-foil turbine were re-explored due to the altered flow field in the shroud. The results demonstrated that the maximum energy extraction efficiency of bare oscillating foil (0.336) can be augmented by 35.8% to 0.456 by appropriate arrangement of the shroud with a relative chord length of 0.8. The optimal motion parameters for the shrouded foil are slightly different from those of bare foil. The re-tuned motion parameters can further improve the efficiency to 0.47. Considering both the manufacturing cost of the shaped sections and their performance, it is more advantageous and attractive to use a flat plate as the shroud in engineering practices.

Suppressing Corrosion of Aluminum Foils via Highly Conductive Graphene-like Carbon Coating in High-Performance Lithium-Based Batteries.

Aluminum foil is the predominant cathodic current collector in lithium-based batteries due to the high electronic conductivity, stable chemical/electrochemical properties, low density, and low cost. However, with the development of next-generation lithium batteries, Al current collectors face new challenges, such as the requirement of increased chemical stability at high voltage, long-cycle-life batteries with different electrolyte systems, as well as improved electronic conductivity and adhesion for new electrode materials. In this study, we demonstrate a novel graphene-like carbon (GLC) coating on the Al foil in lithium-based batteries. Various physical and electrochemical characterizations are conducted to reveal the electronic conductivity and electrochemical stability of the GLC-Al foil in both carbonate- and ether-based electrolytes. Full-cell tests, including Li-S batteries and high-voltage Li-ion batteries, are performed to demonstrate the significantly improved cycling and rate performance of batteries with the use of the GLC-Al foil as current collectors. The cell using the GLC-Al foil can greatly reduce the potential polarization in Li-S batteries and can obtain a reversible capacity of 750 mAh g-1 over 100 cycles at 0.5C. Even with high-sulfur-loading cathodes, the Li-S battery at 1C still maintains over 500 mAh g-1 after 100 cycles. In high-voltage Li-ion batteries, the GLC-Al foil significantly improves the high-rate performance, showing an increased retained capacity by over 100 mAh g-1 after 450 cycles at 1C compared to the bare foil. It is believed that the developed GLC-Al foil brings new opportunities to enhance the battery life of lithium-based batteries.

In-line determination of the degree of crosslinking of ethylene vinyl acetate in PV modules by Raman spectroscopy

In photovoltaics, the quality of the polymeric solar cell embedding material is of key importance for the long-term durability and performance of the PV modules. For the most common encapsulant, elastomeric ethylene vinyl acetate (EVA), the degree of crosslinking is a key issue in this respect. Raman spectroscopy was researched as a fully contact-free, truly non-destructive optical method to measure the degree of EVA crosslinking of bare EVA film samples as well as in-situ inside assembled PV modules. The method relies on evaluating subtle but characteristic spectral differences in the CH-stretching vibration region (3.000–2.800cm−1) that correlate directly, unambiguously and reliably to the crosslinking state of the EVA encapsulant. With measurement times below one second per analysis point, the method is suitable for real-time, in-line quality control. Using a self-referencing data evaluation approach, the method could be designed to be widely immune to real-world effects, including different sample reflectivity and instrument drifts. Involving the reaction kinetics of the curing reaction, the Raman data can be converted into crosslinking readings that equal the traditional, Soxhlet-derived gel content values. The method has been successfully validated for bare foils, glass–backsheet and glass–glass modules with three different EVA types and deployed in-line in a commercial PV module manufacturing line. Using Raman spectroscopy, it is thus possible to determine the degree of crosslinking of the EVA encapsulant inside assembled modules in-line and with high accuracy, even on moving modules.

Reevaluation of neutron flux characterization parameters for NIST RT-2 facility

It has been difficult to characterize the thermal to epithermal neutron flux ratio (f) and the measure of the nonideal epithermal neutron flux distribution (α) for the RT-2 pneumatic rabbit facility at the NIST National Bureau of Standards Reactor (NBSR). In a previous paper, only cadmium-covered irradiations yielded physically reasonable parameters. New measurements were performed using chromium, manganese, cobalt, zinc, zirconium, molybdenum, antimony, gadolinium, lutetium, and gold. The neutron temperature (T n ) in RT-2 measured using bare lutetium and gold foils gave unphysical values. The bare foil methods for measuring f and α gave inconsistent results. The underlying reasons are demonstrated via MCNP simulation results for cumulative reaction rates of selected isotopes. To determine expected intervals for f, α and T, parametric methods were explored. Measured reaction rate probability per target atom (R p ) values for the listed elements were fitted to a modified Westcott curve using an iterative least-squares method to verify consistency of measurements and nuclear data. An advanced parametric approach using a detailed MCNP model of the NBSR was used to calculate neutron flux characterization parameters.

Fast electron propagation in Ti foils irradiated with sub-picosecond laser pulses at Iλ2>1018 Wcm−2μm2

We have studied the propagation of fast electrons through laser irradiated Ti foils by monitoring the emission of hard X-rays and K-{\alpha} radiation from bare foils and foils backed by a thick epoxy layer. Key observations include strong refluxing of electrons and divergence of the electron beam in the foil with evidence of magnetic field collimation. Our diagnostics have allowed us to estimate the fast electron temperature and fraction of laser energy converted to fast electrons. We have observed clear differences between the fast electron temperatures observed with bare and epoxy backed targets which may be due to the effects of refluxing.

MO-D-T-617-03: Secondary Neutron Spectra From High Energy IMRT and Conventional Treatment Plans Using Bonner Spheres and Au-197 Activation Foils

Purpose: The purpose of this work is to measure and compare secondary neutron spectra both in‐field and out‐of‐field from the delivery of high energyIMRT and conventional radiation therapy. Direct measurement of neutron spectra in phantom for IMRT has received little attention. Studies are needed to demonstrate the strength of the assumption that the spectra are the same for IMRT and conventional radiation therapy.Method and Materials: 197 Au activation foils are placed on the surface of a special holder which is inserted into different Bonner Spheres. Seven levels of moderation were used: the bare foil holder and the holder inside 2″, 3″, 5″, 8″, 10″, and 12″ spheres. Net counts of the 411keV gamma peak were measured for each foil using a high purity Germanium detector with spectral analysis capabilities. The activity at the end of irradiation, and the production rate per unit mass of target (Bqs−1g−1) were calculated. Data were unfolded with MXD_FC33 algorithm, PTB (Germany) with a response matrix specifically calculated for this measurement system using MCNPX. The response matrix was verified by unfolding 197 Au ‐Foil Bonner Sphere system data from irradiations with 252 Cf . Results: The unfolded neutron spectra and neutron flux are evaluated. Ambient Dose Equivalent, H*(10) is calculated from spectral data. The data show an increase in the secondary neutron flux and H*(10) for IMRT compared to conventional radiotherapy. The IMRT spectra show a small shift to lower energies. Ratios of in‐field to out‐of‐field flux for 18MV fall off approximately with the inverse square. The ratios of 18MV to 15MV IMRT and conventional out of field flux are 2.13 and 2.6, respectively. Conclusion: 197 Au activation foils inside Bonner spheres technique for the measurement of neutron spectra inside the treatment room is an effective tool for the determination of neutron spectra from IMRT and conventional radiation delivery.

Kαyields from Ti foils irradiated with ultrashort laser pulses

We have studied the emission of Kalpha radiation from Ti foils irradiated with ultrashort (45 fs) laser pulses. We utilized the fundamental (800 nm) light from a Ti:sapphire laser on bare foils and foils coated with a thin layer of parylene E (CH). The focusing was varied widely to give a range of intensities from approximately 10(15) - 10(19) W cm(-2). Our results show a conversion efficiency of laser to Kalpha energy of approximately 10(-4) at tight focus for both types of targets. In addition, the coated targets exhibited strong secondary peaks of conversion at large defocus, which we believe are due to modification of the extent of preformed plasma due to the dielectric nature of the plastic layer. This in turn affects the level of resonance absorption. A simple model of Kalpha production predicts a much higher conversion than seen experimentally and possible reasons for this are discussed.

Chemical Solution Deposition of PLZT Films on Base Metal Foils

ABSTRACTIn an effort to develop cost effective, volumetrically efficient, high charge density and high energy density capacitors, Pb(Zr,Ti)O3 and La-doped Pb(Zr,Ti)O3 films were deposited by chemical solution deposition on nickel and alloy foils. PZT films deposited on bare foils exhibited lower permittivity and more electric field hysteresis compared to films deposited on platinized silicon substrates, due to the formation of low capacitance interfacial layers and/or diffusion of foil elements into the PZT. However, an ultimate dielectric breakdown strength of approximately 1.35 MV/cm was obtained for a film thickness of 1.8 μm, corresponding to a withstand voltage of 245 V. A reduced temperature dependence of capacitance was observed with decreasing film thickness. In order to improve the dielectric response, barrier layers of LaNiO3, Ru, or Ir were deposited on top of the metal foils used as substrates. The barrier improved relative permittivity and reduced hysteresis in relative permittivity as a function of dc bias.

H + emission by MeV-ion impact: Charge state dependence of energy and angular distributions

A linear time-of-flight mass spectrometer equipped with two acceleration grids and a position sensitive stop detector was used to measure the initial energies and emission angles of H + ions as a function of the charge state of the incident heavy ion beam. For this purpose, three different targets – a bare gold foil, a bare carbon foil and a 1500 A ̊ thick glycine film deposited on a gold foil – were irradiated by a 127 MeV I q+ beam ( q=17–32) under an angle of incidence of 55° against the surface normal. The measurements were performed at a pressure of about 10 −7 mbar. The results are axial, radial and total energy distributions and corresponding mean energies and emission angles. As in previous experiments, the axial energy distribution of H + measured for the glycine sample is shifted to shorter flight times, i.e. larger energies compared to the distributions obtained with the bare foils. This shift is not charge state dependent. The mean total energy increases with the charge state as 0.14, 0.21 and 0.25 eV per charge unit, respectively, for the gold, carbon and glycine targets. The angular distributions are generally asymmetric; we observed that the H + ions are ejected preferentially backwards along the line-of-incidence of the primary ions. This effect is much more expressed for the glycine film than for the bare foils. The results are discussed in the frame work of available models of H + production and desorption.

An alternative method for the measurement of thermal neutron flux (modified cadmium ratio method)

An alternative method of approach has been developed for the measurement of thermal neutron flux. The method depends only on the activity of the bare foil if the cadmium ratio at the irradiation position is known. The method has been tested on the GHARR-1 facility at the Ghana Atomic Energy Commission using gold and indium foils for the measurement of the thermal neutron flux in the flux range of 1010–1012 n·cm−2·s−1 and the results compare very well with those obtained using the conventional method (cadmium separation method).

Contribution of plated-out 218Po and 214Po to measurements of airborne 222Rn and daughters with plastic (CR-39) nuclear track detectors

The fraction of alpha-particle tracks due to radioactivity plated out on its surface was measured for CR-39 nuclear track detector foils used to determine working level values in air. Bare foils were exposed to known concentrations of airborne 222Rn and its short-lived daughters in a calibration chamber. The amounts of 218Po and 214Po on the foil surface were measured with a calibrated diffused junction detector-spectrometer system immediately after the foils were removed from the chamber. Deposition was mostly by 218Po, with some 214Pb but essentially no 214Bi. The track density due to the plated-out radionuclides and the 222Rn, 218Po, and 214Po in chamber air was calculated and compared to the value measured by electrochemical etching. The calculated values generally were slightly above the measured values. On the basis of these calculations, the deposited radioactivity contributed slightly less than one-half of the total tracks in one test and slightly more than two-thirds in another. This effect complicates calibration of the detector relative to airborne radon daughters.

The Oxide-Forming Role of Water in Aluminum Electrolytic Capacitors

The effect of the water content of several electrolytic solutions on their ability to form dielectric oxide films on aluminum was examined. Anhydrous electrolytes were found to be incapable of forming such films, but the addition of small amounts of water made it possible for these solutions to perform as normal oxide-film formers. The anodizing behavior of an anhydrous electrolyte composed of methyl cellosolve and ammonium picrate was investigated in detail in both experimental aluminum anodizations and in finished capacitors, in an attempt to correlate the behavior of the electrolyte as an anodizer of bare foil with the aging and life test characteristics of capacitors containing that electrolyte. The results tend to support the conclusion that water is essential to the proper performance of electrolytic capacitors.

An Accurate Determination of the Cadmium Ratio of Neutron Capture Rates in 238U in Slightly Enriched Uranium

An experimental method of determining the ratio of the epicadmium 238U neutron-capture rate to the subcadmium 238U capture rate in a fuel rod, (ρ28), is presented. The precision is ∼0.3% on the cadmium ratio. The relative 239Np and fission-product activities induced in a representative cross section of the fuel material (a thin bare foil of natural uranium) are compared with those induced in a cadmium-covered identical foil in a “flux symmetric” position in the rod. The 239Np gamma activity is counted by a coincidence method with and without the application of chemical separation. The results from the coincidence method are compared with two single-channel and one hundred-channel analyzer results obtained by chemical separation.

Thermal-Neutron Transmission Through Plane Cadmium Covers

The transmission of thermal neutrons through cadmium covers as a function of cadmium thickness was measured in a graphite stack at various heights above the thermal column of the AE-6 water-boiler reactor. Both dysprosium-alloy and indium-alloy foils were used as detectors and were beta-counted. Because the thermal flux incident on a cadmium cover is depressed relative to the flux incident on a bare foil, a foil with a thick cadmium cover on one side only was used for the zero-thickness measurement and its activity was doubled. The resultant thermal activities for a thin detector were consistent with the exponential integral 0.930 2(dΣα) a cadmium thickness greater than 0.025 cm, where and a value of 2450 barns was used for the absorption cross section of cadmium.