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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
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DOE OSTI2024

Challenges and Solutions for Fast Neutron Irradiation of Bulk Material Specimens

Reactor developers continue to recognize opportunities for further enhancing fast spectrum reactor designs with advanced core materials, but all the material test reactors currently available to the United States are thermal spectrum designs. Fortunately, the Advanced Test Reactor and High Flux Isotope Reactor are versatile high flux facilities where spectral modification strategies can be used to reduce undesirable thermal neutron capture transmutation damage and augment fast flux delivered to specimens. New opportunities to leverage high flux regions and specially designed fast flux boosting experiment configurations can be used to achieve meaningful fast fluences on large specimens in ATR. New optimization potentials can be employed to achieve even higher fluences, albeit for smaller specimens, using thermal neutron filters in HFIR test positions. These capabilities, while not true fast reactors, can provide highly relevant environments for researchers needing to study the effects of fast neutron damage in bulk material specimens.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Noble gas constraints on spent fuel irradiation histories

Fission gas isotopic compositions are sensitive to a variety of reactor operating parameters that include the neutron flux, neutron fluence at different neutron energies, and operating temperature. Measurements of fission gas isotopic compositions thus have potential to constrain reactor simulations for nuclear forensics and safeguards applications. In this paper, we present Kr and Xe isotope measurements from a suite of samples obtained from locations that span the axial length a fuel pin with a well-characterized irradiation history and compare these data to spatially resolved reactor simulations. Here, we observed positive correlations between fluence sensitive isotopic ratios and burnup and between a flux sensitive ratio and power, although some discrepancies are observed between the measured data and model predictions. These differences may be due to simplifications in the model and/or inaccuracies in the cross sections. A much broader measurement to model comparison is required to better understand the discrepancies.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Thermally induced dispersive optical bistability in silver nanosuspensions produced by pulsed laser ablation method

The thermally induced optical bistability in prepared silver (Ag) nanosuspensions have been studied experimentally, using Fabry–Perot and Mach–Zehnder interferometry methods. Two Ag nanosuspensions of different sizes were produced by different fluences of pulsed laser ablation method in distilled water. The pulsed Nd:YAG laser of 7 ns pulse width, 1064 nm wavelength and different fluences was employed to produce Ag nanosuspensions. Experimental observations were performed by an ultraviolet–visible–near infrared spectrophotometry. Structure and size of prepared Ag nanoparticles were diagnosed using transmission electron microscope images. Fabry–Perot and Mach–Zehnder interferometry methods were used to carry out the optical bistability process in prepared Ag nanosuspensions. In two considered interferometers, the obtained phase shifts of the hysteresis loops based on the optical bistability are inversely proportional to the nonlinear refractive index of samples and thickness of Ag nanosuspensions cells. Results indicate that the induced thermal effect of the optical bistability can be tuned by modifying parameters such as the nonlinear refractive index and applied interferometry methods. Hence, a desirable situation for the thermo-optical effects of the optical bistability can be easily realized in Ag nanosuspensions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

α Irradiation Response on the Electronic Transport Properties of p -B 12 P 2

B 12 P 2 , a wide bandgap semiconductor, has been previously reported to self-heal from high-energy electron bombardment as determined from transmission electron microscopy. However, the effect of irradiation on the electronic transport properties of B 12 P 2 has not been studied. We report electrical transport measurements on B 12 P 2 after α irradiation. The temperature-dependent Hall effect was measured on p-type B 12 P 2 after successive α irradiation from 210 Po over a fluence range of 1 × 10 11 –1 × 10 13 α/cm 2 to test for self-healing of B 12 P 2 to α bombardment. Prior to irradiation, B 12 P 2 displayed electrical transport characteristics of both hopping and impurity/defect band conduction due to background impurities and growth-induced defects. Fluences of 5 × 10 12 α/cm 2 or greater caused a decrease in the hole mobility and an increase in defect band conduction, suggesting defect accumulation in B 12 P 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2017

The amorphization of 3C-SiC irradiated at moderately elevated temperatures as revealed by X-ray diffraction

Mechanisms of radiation damage buildup in 3C-SiC remain poorly understood. Here, we use X-ray diffraction in combination with numerical simulations to study depth profiles of radiation-produced strain and lattice damage in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal increased defect recombination with increasing temperature, with a critical amorphization fluence increasing from 0.17 to 0.44 displacements per atom. The amorphization process is found to be correlated with the evolution of lattice strain. We find that, at fluences corresponding to the onset of amorphization, lattice strain is ~2% and is independent of temperature. With continuing bombardment above the onset of amorphization, the strain in the crystal bulk increases and reaches a saturation value that decreases from 7% to 5% with increasing temperature. Based on strain profiles, we compute depth profiles of the effective concentration of point defect clusters in the crystalline phase. Bombardment at higher temperatures results in lower maximum defect concentrations pointing to enhanced defect mobility.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Thermodynamics of an austenitic stainless steel (AISI-348) under in situ TEM heavy ion irradiation

The stability of the face-centred cubic austenite (γ-Fe) phase in a commercial stainless steel (AISI348) was investigated through in situ transmission electron microscopy (TEM) with heavy ion irradiation at 1073 K up to a fluence of 1.3×10 17 ions·cm -2 (corresponding to a dose of 46 dpa). The γ-Fe phase was observed to decompose at a fluence of around 7.8×10 15 ions·cm -2 (3 dpa) when a new phase nucleated and grew upon increasing irradiation dose. Scanning transmission electron microscopy (STEM) with energy dispersive X-ray (EDX) spectroscopy and multivariate statistical analysis (MVSA) were used to characterise the irradiated specimens. The combination of such experimental techniques with calculated equilibrium phase diagrams using the CALPHAD method led to the conclusion that the new phase formed upon irradiation is the body-centred cubic Cr-rich α 0 phase. At the nanoscale, precipitation of M 23 C 6 (τ-carbide) was also observed. The results indicate that ion irradiation can assist the austenitic stainless steel to reach a non-equilibrium state similar to a calculated equilibrium state observed at lower temperatures in which, under conventional conditions, is suppressed due to kinetic restrictions.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Multi-scale structural analysis of swift heavy ion-irradiated ZrO 2 and HfO 2

The radiation-induced monoclinic-to-tetragonal phase transition in ZrO 2 and HfO 2 has been the subject of many investigations, but the transformation pathways and underlying structural mechanisms are still not well understood. In this study, microcrystalline powder samples of ZrO 2 and HfO 2 were irradiated with 946 MeV and 1470 MeV Au ions to a wide fluence range up to 3 × 10 13 ions/cm 2 . To characterize beam-induced structural modifications across all spatial length scales, complementary experimental techniques such as synchrotron X-ray diffraction and spallation neutron total scattering were used. The phase evolution of the tetragonal polymorph with increasing ion fluence is accurately described by a heterogeneous track-overlap model that incorporates both direct- and double-impact processes. These damage accumulation processes are an expression of a core-shell ion track morphology that depends on irradiation conditions and target material. Neutron pair distribution function analysis revealed that ion-beam-induced tetragonal ZrO 2 is merely a configurational average of short-range orthorhombic (Pbcn) domains stabilized by a dense network of domain walls. Furthermore, this knowledge is critical for a better understanding of how crystalline-to-crystalline phase transformations proceed at the atomic scale under extreme conditions.

Monoclinic-to-tetragonal phase transformation↗
DOE OSTI2021

Search for low-energy neutrinos from astrophysical sources with Borexino

We report on searches for neutrinos and antineutrinos from astrophysical sources performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso in Italy. Electron antineutrinos ( $\bar{ν}_e$ ) are detected in an organic liquid scintillator through the inverse β -decay reaction. In the present work we set model-independent upper limits in the energy range 1.8-16.8 MeV on neutrino fluxes from unknown sources that improve our previous results, on average, by a factor 2.5. Using the same data set, we first obtain experimental constraints on the diffuse supernova $\bar{ν}_e$ fluxes in the previously unexplored region below 8 MeV. A search for $\bar{ν}_e$ in the solar neutrino flux is also presented: the presence of $\bar{ν}_e$ would be a manifestation of a non-zero anomalous magnetic moment of the neutrino, making possible its conversion to antineutrinos in the strong magnetic field of the Sun. We obtain a limit for a solar $\bar{ν}_e$ flux of 384 cm -2 s -1 (90% C.L.), assuming an undistorted solar 8 B neutrinos energy spectrum, that corresponds to a transition probability pνe→$\bar{ν}_e$< 7.2 ×10-5 (90% C.L.) for E $\bar{ν}_e$ > 1.8 MeV.At lower energies, by investigating the spectral shape of elastic scattering events, we obtain a new limit on solar 7 Be- ν e conversion into $\bar{ν}_e$ of pνe→$\bar{ν}_e$< 0.14 (90% C.L.) at 0.862 MeV. Last, we investigate solar flares as possible neutrino sources and obtain the strongest up-to-date limits on the fluence of neutrinos of all flavor neutrino below 3–7 MeV. Assuming the neutrino flux to be proportional to the flare’s intensity, we exclude an intense solar flare as the cause of the observed excess of events in run 117 of the Cl-Ar Homestake experiment.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2023

A novel method for quantifying irradiation damage in nuclear graphite using Raman spectroscopy

Raman spectroscopy has long been used in studying irradiation damage in carbon/graphite materials. It is however unclear if the measurements from different types of materials are directly comparable. Further, decoupling the contribution from irradiation temperature and fluence to the total damage in nuclear graphite possessing irradiation damage gradient is currently not readily feasible as it requires a complete set of test reactor irradiation experiments over the relevant temperature and fluence range. A novel methodology has therefore been proposed and developed to quantify total irradiation damage evolution at crystal level based on graphite Raman G-band position shift. Specifically, G-band positions derived from a large number of spectra collected from the fractured surface of microfine-grained POCO ZXF-5Q graphite possessing proton irradiation damage gradient were plotted with open literature Raman data on HOPG, BEPO (AXGP graphite), PCEA and IG-110 graphite as a function of dpa. The total damage level within 2σ beam radius in this POCO graphite was estimated to be equivalent to ~2–5 dpa at ~350–370 °C. Derived G-band positions were then mapped to the three-stage amorphization trajectory model indicating beam centre area has entered the second stage, i.e., transitioning from nanocrystalline graphite into amorphous carbon. G-band position relative shift (ΔG) curve with a ‘turn-around’ peak as a function of total damage can be used for in-service lifetime prediction. Importantly, the developed methodology has the potential to ‘unify’ total damage levels across different grades of nuclear graphite caused by ion, neutron and proton irradiation at different temperatures.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Effects of in-situ UV irradiation on the uniformity and optical properties of GaAsBi epi-layers grown by MBE

In-situ UV illumination influences the incorporation dynamics of bismuth adatom in GaAs. Here we use the inherent variation of the fluence across the sample to explore the role of the incident irradiation. With illumination it is found that steady state growth processes are achieved more quickly resulting in more abrupt interfaces, as well as uniform GaAs 1-x Bi x epi-layers. Comparisons of low temperature photoluminescence spectra show an increasing density of clusters of incorporated bismuth atoms with decreasing incident fluence.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

High-dose temperature-dependent neutron irradiation effects on the optical transmission and dimensional stability of amorphous fused silica

The primary concern for implementing amorphous fused silica (a-SiO 2 ) fiber optic sensors in a nuclear environment is the radiation-induced attenuation (RIA) of the light signal due to the formation of radiation-induced color centers. In addition, Bragg grating sensors drift under irradiation due to radiation-induced compaction of the a-SiO 2 structure. This work provides new data regarding RIA and radiation-induced compaction of a-SiO 2 samples irradiated to a fast neutron fluence of 2.4 × 10 21 n/cm 2 at temperatures of 95, 298, and 688 °C. Results show that RIA may be approaching saturation for the range of photon energies evaluated in this paper and that the hydroxyl content has a significant impact on RIA when the irradiation temperature is increased to 688 °C. Furthermore, a model was developed for predicting radiation-induced compaction, and the resulting signal drift for Bragg grating sensors, as a function of neutron fluence and temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Enhanced backscatter and unsaturated blue wavelength shifts in F-doped fused silica optical fibers exposed to extreme neutron radiation damage

Amorphous fused silica (a-SiO 2 ) optical fibers, with and without inscribed Bragg gratings, were interrogated using infrared (~1550 nm) optical backscatter reflectometry during ~25 days of intense neutron irradiation to a fast (energy > 0.1 MeV) neutron fluence of ~10 21 n/cm 2 , or ~1.5 atomic displacements per atom. The reflected light amplitudes in Ge-doped core telecommunications fiber dropped below detection limits (>15 dB attenuation) within 3 days of irradiation (~10 20 fast n/cm 2 ). Here, amplitudes from a pure silica core, F-doped silica cladding fiber reached equilibrium levels ~1.5–2 dB higher than pre-irradiation values, whereas Bragg gratings inscribed in the same fiber using a femtosecond laser (point-by-point method) suffered > 45 dB attenuation. Blue wavelength shifts were initially consistent with previous radiation-induced compaction models but increased linearly with increasing neutron fluence (no evidence of saturation) beyond 10 20 n/cm 2 and exceeded 0.6%, which corresponds to >1,000 °C drift if used to measure temperature changes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Thermal stability of helium bubble superlattice in Mo under TEM in-situ heating

Although the temperature window of He ion irradiation for gas bubble superlattice (GBS) formation was found to be in the range of approximately 0.15 – 0.35 melting point, the thermal stability of He GBS has not been fully investigated. This work reports the experiment using an in-situ heating holder in a transmission electron microscope (TEM). A 3.0 mm TEM disc sample of Mo (99.5% pure) was jet-polished and then irradiated with 40 keV He ions at 300°C to a fluence of 1.0E+17 ions/cm 2 , corresponding to a peak He concentration of approximately 10 at.%, in order to introduce He GBS. In-situ heating was conducted with a ramp rate of ~ 25°C/min, hold time of ~ 30 min, and temperature step of ~ 100°C up to 850°C (0.39T m ). The result shows exceptional thermal stability of He GBS in Mo with no noticeable change on GBS lattice constant and ordering. The implication of this unique and stable ordered microstructure on mechanistic understanding of GBS and its advanced application will be discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Stored energy release in neutron irradiated silicon carbide

The purpose of this investigation is to experimentally quantify the stored energy release upon thermal annealing of previously irradiated high-purity silicon carbide (SiC.) Samples of highly-faulted polycrystalline CVD β-SiC and single crystal 6HSiC were irradiated in a mixed spectrum fission reactor near 60 °C in a fluence range from 5 × 10 23 to 2 × 10 26 n/m 2 (E > 0.1 MeV), or about 0.05–20 dpa, in order to quantify the stored energy release and correlate the release to the observed microscopic swelling, lattice dilation, and microstructure as observed through TEM. Within the fluence of this study the crystalline material was observed to swell to a remarkable extent, achieving 8.13% dilation, and then cross a threshold dose for amorphization at approximately 1 × 10 25 n/m 2 (E > 0.1 MeV) Once amorphized the material attains an as-amorphized swelling of 11.7% at this irradiation condition. Coincident with the extraordinary swelling obtained for the crystalline SiC, an equally impressive stored energy release of greater than 2500 J/g at the critical threshold for amorphization is inferred. As expected, following amorphization the stored energy in the structure diminishes, measured to be approximately 590 J/g. Generally, the findings of stored energy are consistent with existing theory, though the amount of stored energy given the large observed crystalline strain is remarkable. The overall conclusion of this work finds comparable stored energy in SiC to that of nuclear graphite, and similar to graphite, a stored energy release in excess of its specific heat in some irradiation conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of irradiation temperature on the response of CeO2, ThO2, and UO2 to highly ionizing radiation

Microcrystalline CeO 2 , ThO 2 , and UO 2 were irradiated with 198 MeV 132 Xe ions to the same fluence at temperatures ranging from 25°C to 700°C then characterized by synchrotron X-ray diffraction and X-ray absorption spectroscopy. All samples retain crystallinity and their nominal fluorite-type phase at a fluence of 1.5x10 13 ions/cm 2 . Both CeO 2 and ThO 2 display defect-induced unit cell expansion after irradiation at room temperature (~0.15% and ~0.10%, respectively), yet as irradiation temperature increases, the maximum swelling produced decreases to ~0.02%. Alternatively, UO 2 shows an initial contraction in unit cell parameter (approximately -0.05%), for room temperature irradiation most likely related to irradiation-enhanced annealing or irradiation-induced oxidation. At higher temperatures (above 200°C), UO 2 begins to swell, surpassing its unit cell parameter prior to irradiation (~0.05%), an effect which could be attributed to minor reduction in uranium oxidation state in vacuum. However, while CeO 2 irradiated at room temperature undergoes partial reduction, both UO 2 and ThO 2 exhibit no measurable change in cation oxidation state as evidenced by X-ray absorption spectroscopy. All samples display a decrease in irradiation-induced heterogeneous microstrain as a function of increasing irradiation temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Proton irradiation effects in Molybdenum-Carbide-Graphite composites

The High Luminosity upgrade of the Large Hadron Collider (HL-LHC) has prompted the investigation of novel materials for beam-intercepting devices, and in particular for the collimators responsible for protecting the machine from beam losses. The HL-LHC collimation system will inevitably experience increased levels of radiation damage and undergo changes in their crucial physio-mechanical properties. Graphite-matrix composite materials containing molybdenum carbide particles, along with small amounts of titanium carbide, were developed with the objective of enhanced in-beam performance and tested under proton irradiation. The physical degradation observed in early grades of molybdenum carbide compounds, even after modest proton fluences, has prompted the development of advanced compounds. In this work, we examine the effects of proton irradiation on the microstructural and thermophysical properties of new grades of Molybdenum-carbide-graphite compounds up to fluences of ~2 × 10 20 p/cm 2 . Here, we employ a combination of precision dilatometry and high-energy X-ray diffraction to quantify the dimensional stability and crystallographic phase evolution both pre- and post-irradiation. Our results reveal that these new compounds exhibit superior resilience to radiation damage than their predecessors.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optical transmission and dimensional stability of single-crystal sapphire after high-dose neutron irradiation at various temperatures up to 688 °C

The use of single-crystal sapphire optical fibers has been considered to extend fiber-optic sensing to the extreme temperature (>1000 °C) environments encountered in nuclear applications. However, before these sapphire fiber–based sensors can be deployed, their optical transmission and dimensional stability (which impacts drift of some sensors) must be characterized under representative testing conditions. Data regarding the optical transmission of sapphire following high-dose neutron irradiation at temperatures >100 °C is extremely limited. This work provides measurements of optical density (i.e., attenuation) and directional dimensional changes in bulk single-crystal sapphire materials irradiated to a fast neutron fluence of 2.4 × 10 21 n/cm 2 (3.5 displacements per atom) at temperatures ranging from 95 to 688 °C. Optical density measured after irradiation at 95 and 298 °C showed ultraviolet and visible absorption bands corresponding to known defect centers and temperature trends that were generally consistent with previous ex situ and in situ measurements made at much lower neutron fluence. However, optical density measured after irradiation at 688 °C was as much as two orders of magnitude higher, indicating that the fundamental mechanism for radiation-induced attenuation changes at this irradiation temperature. Additional analysis and comparison with previous works suggest that the attenuation may result from void formation, leading to increased Rayleigh scattering losses in the material and increased swelling that would also result in drift of Bragg grating-based sensors in sapphire fibers. These results pose serious questions regarding the feasibility of sapphire fiber–based sensors for high-temperature nuclear applications.

36 MATERIALS SCIENCE↗