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Monolithic silicon carbide (SiC) to SiC plate joints were fabricated and irradiated with neutrons at 270–310 °C to 8.7 dpa for SiC. The joining methods included solid state diffusion bonding using titanium and molybdenum interlayers, SiC nanopowder sintering, reaction sintering with a Ti-Si-C system, and hybrid processing of polymer pyrolysis and chemical vapor infiltration (CVI). All the irradiated joints exhibited apparent shear strength of more than 84 MPa on average. Significant irradiation-induced cracking was found in the bonding layers of the Ti and Mo diffusion bonds and Ti-Si-C reaction sintered bond. The SiC-based bonding layers of the SiC nanopowder sintered and hybrid polymer pyrolysis and CVI joints all showed stable microstructure following the irradiation.

This paper reports on a nuclear-grade joining material for bonding of silicon carbide-based components. The joint material is fabricated via a hybrid preceramic polymer, chemical vapor infiltration process. The joint is comprised entirely of β-SiC and results in excellent mechanical and permeability performance. The joint strength, composition, and microstructure have been characterized before and after irradiation to 4.5 dpa at 730 °C in the High Flux Isotope Reactor. The hybrid preceramic polymer-chemical vapor infiltrated joint exhibited complete retention of shear strength and no evidence of microstructural evolution or damage was detected following irradiation.

An approach to transform and accelerate nuclear fuel development and qualification is outlined. The approach exploits advanced modeling and simulation at the outset to inform constituent and system selection and to enable integral fuel performance analyses. Analyses using these tools identify and prioritize the most important fuel performance parameters and phenomena for subsequent targeted characterization with separate-effects tests. Separate-effects testing spans out-of-pile and in-pile tests and is meant to iterate with and inform engineering-scale integral fuel performance analyses throughout the development process. Exercising this cycle in an agile fashion will increase confidence in the integral fuel performance predictions while reducing uncertainties. This process sets the stage for executing a much more limited set of well-defined integral irradiation tests designed to validate engineering-scale fuel performance codes and to confirm the performance and safety of the fuel system under prototypic conditions. This approach will reduce the time for development and qualification of a new fuel system, and it will also reduce associated costs.

Nuclear grade silicon carbide fiber (SiCf) reinforced silicon carbide matrix (SiCm) composite is a promising candidate material for accident tolerance fuel (ATF) cladding. A major challenge is ensuring the mechanical robustness of the ceramic cladding under accident conditions. In this work the high temperature mechanical response of a SiCf–SiCm composite tubing is studied using a novel thermo-mechanical test method. A solid surrogate tube is placed within and bonded to the SiCf–SiCm sample tube using a ceramic adhesive. The bonded tube pair is heated from the center using a ceramic glower. During testing, the outer surface temperature of the SiC sample tube rises up to 1274 K, and a steep temperature gradient develops through the thickness of the tube pair. Due to CTE mismatch and the temperature gradient, the solid surrogate tube induces high tensile stress in the SiC sample. During testing, 3D digital image correlation (DIC) method is used to map the strains on the outer surface of the SiC-composite, and acoustic emissions (AE) are monitored to detect the onset and progress of material damage. The thermo-mechanical behavior of SiC-composite sample is compared with that of monolithic SiC samples. Finite element models are developed to estimate stress–strain distribution within the tube assembly. Model predicted surface strain matches the measured surface strain using the DIC method. AE activities indicated a progressive damage process for SiCf–SiCm composite samples. For the composites tested in this study, the threshold mechanical hoop strain for matrix micro-cracking to initiate in SiCf–SiCm sample is found to be ∼300 microstrain.

Silicon carbide (SiC) fiber, SiC matrix composites (SiC/SiC) are being considered as a cladding material for light water reactors in order to improve safety performance. Engineered, multi-layer cladding designs consisting of both monolithic SiC (mSiC) and SiC/SiC have been examined as promising concepts to meet both strength and impermeability requirements. A new model has been developed to calculate stresses and failure probabilities for multi-layer cladding consisting of SiC-based materials in reactor operating conditions. The results show that stresses in SiC-based cladding are dominated by temperature-dependent irradiation-induced swelling, with the largest stresses occurring during the cold shutdown conditions. Failure probabilities are driven by the resulting tensile stresses at the cladding inner wall, while the outer wall is subject to compressive stresses. This indicates that the inner SiC/SiC, outer mSiC concept has the lowest failure probability, as the pseudo-plastic deformation of the composite reduces tensile loading and the compressed monolith provides a reliable, impermeable barrier to fission product release.

Silicon carbide (SiC) is being investigated for accident tolerant fuel cladding applications due to its high temperature strength, exceptional stability under irradiation, and reduced oxidation compared to Zircaloy under accident conditions. An engineered cladding design combining monolithic SiC and SiC–SiC composite layers could offer a tough, hermetic structure to provide improved performance and safety, with a failure rate comparable to current Zircaloy cladding. Modeling and design efforts require a thorough understanding of the properties and structure of SiC-based cladding. Furthermore, both fabrication and characterization of long, thin-walled SiC–SiC tubes to meet application requirements are challenging. In this work, mechanical and thermal properties of unirradiated, as-fabricated SiC-based cladding structures were measured, and permeability and dimensional control were assessed. In order to account for the tubular geometry of the cladding designs, development and modification of several characterization methods were required.

Spark plasma sintering (SPS) is an emerging powder consolidating technique which promises high potential capabilities to process refractory ceramics with properties previously unattainable. As the first step in studying the applicability of this technique to the processing of tailored ceramic structures, the validity of SPS to consolidate refractory carbides with controllable porosity is investigated. Vanadium carbide (V 8 C 7 ) is chosen as a studied material. The structure, thermal and mechanical properties of the V 8 C 7 powder pellets produced by SPS are analyzed and discussed in the paper. The attained properties of the processed ceramic material are in particular suitable for applications where high electrical conductivity and strength at high melting temperatures, low thermal conductivity and low thermal expansion coefficient are needed.

SiC fiber-reinforced SiC matrix composites (SiC/SiC) are under consideration as a structural material for a range of nuclear applications. While these materials have been studied for decades, recently new small scale materials testing techniques have emerged which can be used to characterize SiC/SiC materials from a new perspective. In this work cross section nanoindentation was performed on SiC/SiC composites revealing that both the hardness and Young’s modulus was substantially lower in the fiber compared to the matrix despite both being SiC. Using scanning electron microscopy it was observed that the grain growth of the matrix during formation was radially out from the fiber with a changing grain structure as a function of radius from the fiber center. Focused ion beam machining was used to manufacture micro-cantilever samples and evaluate the fracture toughness and fracture strength in the matrix as a function of grain orientation in the matrix. Additionally microstructural characterization techniques like Raman spectroscopy, X-ray diffraction, and microtomography were used to evaluate differences in the matrix and fibers of the composite.

The use of silicon carbide (SiC) composites as structural materials in nuclear applications necessitates the development of a viable joining method. One critical application for nuclear-grade joining is the sealing of fuel within a cylindrical cladding. This paper demonstrates cylindrical joint feasibility using a low activation nuclear-grade joint material comprised entirely of β-SiC. While many papers have considered joining material, this paper takes into consideration the joint geometry and component form factor, as well as the material performance. Work focused specifically on characterizing the strength and permeability performance of joints between cylindrical SiC–SiC composites and monolithic SiC endplugs. The effects of environment and neutron irradiation were not evaluated in this study. Joint test specimens of different geometries were evaluated in their as-fabricated state, as well as after being subjected to thermal cycling and partial mechanical loading. A butted scarf geometry supplied the best combination of high strength and low permeability. A leak rate performance of 2 × 10 −9 mbar l s −1 was maintained after thermal cycling and partial mechanical loading and sustained applied force of 3.4 kN, or an apparent strength of 77 MPa. This work shows that a cylindrical SiC–SiC composite tube sealed with a butted scarf endplug provides out-of-pile strength and permeability performance that meets light water reactor design requirements.

Silicon carbide (SiC) and silicon carbide fiber reinforced composites (SiC/SiC f ) are currently being evaluated as a high temperature material for use in nuclear reactors. While methods to determine the mechanical properties of SiC/SiC f on planar test specimens are well established, mechanical testing methods for tubular SiC/SiC f are still being developed. In this study the C-ring test is evaluated for use with nuclear grade SiC/SiC f as a method of measuring hoop strength. For the samples tested in this work, hoop strengths from C-ring testing are shown to agree within 6% to those obtained using expanding plug testing and analysis shows that the expected composite behavior is observed during testing. While other techniques may give more accurate values for hoop stress, the small specimen requirements and ease of testing makes C-ring testing a valuable tool.

Both advanced fission reactor concepts and fusion energy systems demand materials that can survive extremely harsh operating environments having persistent high temperature and high neutron flux conditions. Silicon carbide fiber/silicon carbide matrix (SiC–SiC) composites have shown promise for these applications, which include fuel cladding and reactor structural components. However, the composite fabrication process is time consuming and the fabrication of complicated geometries can be difficult. In this work, SiC–SiC and carbon fiber–SiC composite samples were fabricated using chemical vapor infiltration (CVI), and the mechanical and thermal properties of samples with a range of densities and total infiltration times were characterized and compared. Both sample density and the reinforcing fiber material were found to have a very significant influence on the composite mechanical and thermal material properties. In particular, internal porosity is found to have a significant effect on the mechanical response, as can be observed in the crack propagation in low density samples. In order to better understand the densification of the composites, a computer model is being developed to simulate the diffusion of reactants through the fiber preform, and SiC deposition on the fiber surfaces. Preliminary modeling has been correlated with experimental results and shows promising results.

We present measurements of the chlorine K-alpha emission from reduced mass targets, irradiated with ultra-high intensity laser pulses. Chlorinated plastic targets with diameters down to 50 μm and mass of a few 10−8 g were irradiated with up to 7 J of laser energy focused to intensities of several 1019 W/cm2. The conversion of laser energy to K-alpha radiation is measured, and high-resolution spectra that allow observation of line shifts are observed, indicating isochoric heating of the target up to 18 eV. A zero-dimensional 2-temperature equilibration model, combined with electron impact K-shell ionization and post processed spectra from collisional radiative calculations reproduces the observed K-alpha yields and line shifts, and shows the importance of target expansion due to the hot electron pressure.

The inertial confinement fusion community is actively preparing for the transition from kilojoule- to megajoule-class lasers. To assess laser and target performance, a sophisticated array of diagnostics that can operate in increasingly harsh environments is required. In this paper, we overview some of the needs and challenges related to performing X-ray spectroscopy with very intense and highly energetic X-ray sources. To illustrate issues that will be broadly applicable to diagnostics at high energy density facilities, we relate lessons learned during early testing of the high-energy electronic X-ray spectrometer (HENEX), a core-level diagnostic commissioned by the National Ignition Facility. A spectrometer design employing symmetric Laue diffraction has proven to be particularly well suited for the high energy density environment and will extend existing diagnostic techniques to high-Z, K-shell spectroscopy.

Laser-Produced plasmas at subcritical densities have proven to be efficient sources for X-ray production. In this context, we obtain experimental results from Kr and Xe gas-filled targets that were irradiated by the OMEGA (Laboratory for Laser Energetics, University of Rochester) laser. Nearly 40% of the laser energy was converted into X-rays in the L-shell-photon-energy range (≥ 1.6 keV) by a Kr-filled target. The conversion efficiency measurements were correlated with time-resolved plasma-temperature measurements done by means of a Thomson-scattering diagnostic. The measured range of temperatures, between 2-3.5 keV, is in good agreement with LASNEX radiation-hydrodynamics simulations. X-ray-cooling rates and charge-state distributions were computed using detailed atomic data from the HULLAC suite of codes. X-ray yields predicted by the cooling-rate calculations are compared to measured spectra, and good agreement is found for predictions made with highly-detailed atomic models. We find that X-ray conversion efficiency in Kr-filled targets is a strong function of temperature, and has an optimum density near 15% of the laser's critical density. © 2005 Elsevier Ltd. All rights reserved.

Thin-walled gold halfraums are a common choice for producing X-ray drives in experiments at high-power laser facilities. At the Omega Laser, we use 10 kJ of laser energy in a two-pulse sequence to generate halfraum drive temperatures of 160–190 eV for ∼3 ns. This type of drive is well characterized and reproducible, with characterization of the drive radiation temperature typically performed using the Dante diagnostic, a 10-channel array of filtered X-ray diodes. Additionally, photoconductive diamond detectors (PCDs) have been calibrated to the Dante, and can now be used in place of the Dante to measure the drive. Measurements of halfraum drives from both Dante and PCDs are compared with calculations, with good agreement. This agreement lends the calculations a predictive capability in designing further experiments utilizing halfraum drives.

Outstanding discrepancies between data and calculations of laser-produced plasmas in recombination have been observed since the 1980s. Although improvements in hydrodynamic modeling may reduce the discrepancies, there are indications that non-LTE atomic kinetics may be the dominant cause. Experiments to investigate non-LTE effects were recently performed at the NIKE KrF laser on low-density Ti-doped aerogels. The laser irradiated a 2 mm diameter, cylindrical sample of various lengths with a 4-ns square pulse to create a volumetrically heated plasma. Ti L-shell spectra spanning a range of 0.47–3 keV were obtained with a transmission grating coupled to Si photodiodes. The diagnostic can be configured to provide 1-dimensional spatial resolution at a single photon energy, or 18 discrete energies with a resolving power, λ / δ λ of 3–20. The data are examined and compared to calculations to develop absolute emission measurements that can provide new tests of the non-LTE physics.

High-resolution X-ray spectra were recorded by the High-Energy Electronic X-ray (HENEX) spectrometer from a variety of targets irradiated by the Omega laser at the Laboratory for Laser Energetics. The HENEX spectrometer utilizes four reflection crystals covering the 1–20 keV energy range and one quartz(1 0 −1 1) transmission crystal (Laue geometry) covering the 11–40 keV range. The time-integrated spectral images were recorded on five CMOS X-ray detectors. In the spectra recorded from krypton-filled gasbag and hohlraum targets, the helium-like K-shell transitions n = 1 – 2 , 1–3, and 1–4 appeared in the 13–17 keV energy range. A number of additional spectral features were observed at energies lower than the helium-like n = 1 – 3 and n = 1 – 4 transitions. Based on computational simulations of the spectra using the FLYCHK/FLYSPEC codes, which included opacity effects, these additional features are identified to be inner-shell transitions from the Li-like through N-like krypton charge states. The comparisons of the calculated and observed spectra indicate that these transitions are characteristic of the plasma conditions immediately after the laser pulse when the krypton density is 2×1018 cm−3 and the electron temperature is in the range 2.8–3.2 keV. These spectral features represent a new diagnostic for the charge state distribution, the density and electron temperature, and the plasma opacity. Laboratory experiments indicate that it is feasible to record K-shell spectra from gold and higher Z targets in the >60 keV energy range using a Ge(2 2 0) transmission crystal.

A series of experiments to explore Ge opacity at temperatures where the M-shell is almost filled will be discussed. Data are obtained at lower temperatures than previously explored and allow us to investigate the role of atomic structure calculations and their impact on opacity scalings. The experiment uses the Nova laser to irradiate a gold hohlraum within which a CH-tamped Ge sample is radiatively heated. A Nd backlight probes the sample 2 ns later to produce Ge spectral absorption features in the 1.2-1.5 keV energy range. Temperature is monitored by the use of an Al dopant and density is monitored by measuring the edge-on expansion of the sample. Temporal resolution of about 200 ps is obtained by using a short pulse backlight. Calculations in this photon energy region show significant changes in the spectral features.

In this paper we present time-resolved temperature measurements of a radiatively heated, thin tamped foil via Kα absorption spectroscopy. The sample foil was 1500 A MgO, tamped on both sides with 1000 A paralyene, and was heated by soft x-rays transmitted through the back side of a separate laser-irradiated 1500 A Au foil. The resulting plasma was then backlit by a separate laser-irradiated front-surface U foil, providing a time-resolved K -shell absorption spectrum over the duration of the heating phase. We compare the resulting data to synthetic spectra obtained from detailed simulations of the heating and expansion of the tamped foils, and find poor agreement. Much better agreement is obtained when we determine the temperatures through best-fit absorption spectra which assume temperatures ∗> 35% higher than predicted; the reason for this discrepancy is not yet understood.

Apart from their intrinsic interest, plasma physics processes are important because they affect the coupling of the laser energy into laser-irradiated targets. Recently, new gas-filled targets have been developed to create large mm-size plasmas for the study of stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). We present x-ray images and x-ray spectra to characterize these targets, which show that the plasmas are homogeneous, have electron densities of ~10 21 cm −3 , and attain electron temperatures of ~3 keV. We also give SBS measurements to demonstrate how systematic studies of physical phenomena can be performed using these targets.

High-resolution absorption spectra of radiatively-heated low-Z foils (CH and BN) have been recorded at the Nova II laser facility by a grazing-incidence spectrograph. Using a calibration curve for Kodak 101 photographic plates, the plate density was converted to relative intensity transmitted by the foil. Absorption spectra are presented for the elements B, C, and N. The absorption features near the nickel L edge in the wavelength region 11–15 A are also presented.

The experiments reported in this paper were undertaken to measure the rear x-ray flux of foils having different thicknesses. The targets were burnthrough foils, planar free-standing Au foils and CH supported Au foils, that were nearly entirely ablated during the laser pulse. The x-ray flux from the non-irradiated rear side is of sufficient intensity that it can serve as an x-ray heating source, backlight, or photon pump. The foils were irradiated with one smoothed beam of Nova which provided ∼ 3300 J of 2ω0 light in a 1 nsec square pulse. The primary diagnostics measured absolute flux and transmitted laser light. The time-dependent absolute flux measurements, the total-integrated energy of the x-ray spectrum, and the temporal evolution will be discussed.