Understanding the effects of helium on microstructures and mechanical properties of reduced-activation ferritic-martensitic steels is important to use of these steels in fusion reactor structures. ...The 9Cr-2WVTa steels were doped with 58Ni and 60Ni isotopes at 2 weight percent to control the rate of transmutation helium generation. The samples were irradiated in the High Flux Isotope Reactor to ~24 displacements per atom at nominal temperatures of 300, 400, and 500°C, producing 228 and 7 atomic parts-per-million helium in the 58Ni- and 60Ni-doped samples, respectively. Transmission electron microscopy revealed a variety of precipitates and the radiation-induced dislocation loops and cavities (voids or helium bubbles). Tensile tests of the irradiated samples at the irradiation temperatures showed radiation-induced hardening at 300°C and radiation-induced softening at 400°C. Analysis indicates that the hardening primarily originated from the loops and cavities. The 58Ni-doped samples had greater strengthening contributions from loops and cavities, leading to higher hardening with lower ductility than the 60Ni-doped samples. The greater helium production of 58Ni did not show pronounced reductions in ductility of the samples.
We irradiated four ferritic alloys with energetic Fe and He ions: one castable nanostructured alloy (CNA) containing Ti-W-Ta-carbides, and three nanostructured ferritic alloys (NFAs). The NFAs were: ...9Cr containing Y-Ti-O nanoclusters, and two Fe-12Cr-5Al NFAs containing Y-Zr-O or Y-Hf-O clusters. All four were subjected to simultaneous dual-beam Fe + He ion implantation (650 °C, ∼50 dpa, ∼15 appm He/dpa), simulating fusion-reactor conditions. Examination using scanning/transmission electron microscopy (STEM) revealed high-number-density helium bubbles of ∼8 nm, ∼1021 m−3 (CNA), and of ∼3 nm, 1023 m−3 (NFAs). STEM combined with multivariate statistical analysis data mining suggests that the precipitate-matrix interfaces in all alloys survived ∼50 dpa at 650 °C and serve as effective helium trapping sites. All alloys appear viable structural material candidates for fusion or advanced fission energy systems. Among these developmental alloys the NFAs appear to sequester the helium into smaller bubbles and away from the grain boundaries more effectively than the early-generation CNA.
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This paper addresses certain key feasibility issues facing the application of SiC-matrix microencapsulated fuels for light water reactor application. Issues addressed are the irradiation stability of ...the SiC-based nano-powder ceramic matrix under LWR-relevant irradiation conditions, the presence or extent of reaction of the SiC matrix with zirconium-based cladding, the stability of the inner and outer pyrolytic graphite layers of the TRISO coating system at this uncharacteristically low irradiation temperature, and the state of the particle–matrix interface following irradiation which could possibly affect thermal transport. In the process of determining these feasibility issues microstructural evolution and change in dimension and thermal conductivity was studied. As a general finding the SiC matrix was found to be quite stable with behavior similar to that of CVD SiC. In magnitude the irradiation-induced swelling of the matrix material was slightly higher and irradiation-degraded thermal conductivity was slightly lower as compared to CVD SiC. No significant reaction of this SiC-based nano-powder ceramic matrix material with Zircaloy was observed. Irradiation of the sample in the 320–360°C range to a maximum dose of 7.7×1025n/m2 (E>0.1MeV) did not have significant negative impact on the constituent layers of the TRISO coating system. At the highest dose studied, layer structure and interface integrity remained essentially unchanged with good apparent thermal transport through the microsphere to the surrounding matrix.
Microstructures in high purity β-SiC irradiated with fast neutrons (up to ∼9.6
×
10
25
n/m
2, in HFIR) at very high temperatures (1130, 1300, and 1460
°C) were studied by transmission electron ...microscopy. Cavities and dislocation loops were generally observed in irradiated samples. The cavities were preferentially formed at grown-in stacking faults, and were spherical in shape below 1300
°C and mainly faceted with {1
1
1} planes at 1460
°C. Estimated volume fractions of observed cavities were much smaller than macroscopic densitometer swelling recently reported, which implies other defects cause the swelling in this temperature regime. Larger Frank loops (>25
nm in radius) formed at 1460
°C were identified as interstitial type using the inside/outside method. Unfaulting of the loops was not observed or was very rare. Rapid loop growth and density decrease were observed in the temperature range of 1300–1460
°C concurrently with the rapid cavity growth. The limited growth rate of dense loops at lower temperature was discussed in terms of high sink density estimated from a grain-boundary-loop-denuded zone formed at 1130
°C.
Ovarian cancer is one of the most aggressive female reproductive tract tumors. Paclitaxel (PTX) is widely used for the treatment of ovarian cancer. However, ovarian cancers often acquire ...chemotherapeutic resistance to this agent. We investigated the mechanism of chemoresistance by analysis of microRNAs using the ovarian cancer cell line KFr13 and its PTX-resistant derivative (KFr13Tx). We found that miR-31 was downregulated in KFr13Tx cells, and that re-introduction of miR31 re-sensitized them to PTX both in vitro and in vivo. miR-31 was found to bind to the 3'-UTR of mRNA of MET, and the decrease in MET correlated to higher sensitivity to PTX. Furthermore, co-treatment of KFr13Tx cells with MET inhibitors sensitized the tumor cells to PTX both in vitro and in vivo. In addition, lower levels of miR31 and higher expression of MET in human ovarian cancer specimens were significantly correlated with PTX chemoresistance and poor prognosis. This study demonstrated miR31-dependent regulation of MET for chemoresistance of ovarian cancer, raising the possibility that combination therapy with a MET inhibitor and PTX will increase PTX efficacy.
This paper presents results from a neutron irradiation campaign on CVD SiC carried out in the High Flux Isotope Reactor. Materials were irradiated in a range of temperature from 200 to 1500
°C and ...from a fraction of a dpa to ∼6
dpa. Data on swelling and room temperature thermal conductivity are presented. The swelling behavior below ∼800
°C agrees well with the literature values. Data in the range of 1000–1600
°C indicates that swelling increases as the dose is increased from 2
dpa to 6
dpa, at higher-swelling with increasing irradiation temperature. Any peak in void swelling apparently occurs at irradiation temperature >1500
°C (>0.6
T
m). In the 1100–1200
°C temperature range, volumetric swelling is apparently at a minimum though increases from ∼0.2% to ∼0.4% as dose increases from ∼2
dpa to ∼6
dpa. The maximum swelling was found to be ∼1.5% at the maximum dose and temperature of this study, ∼6
dpa and ∼1500
°C. Room temperature thermal conductivity data over the entire temperature range are presented and a direct correlation between the thermal defect resistance and swelling is seen for materials irradiated at temperature less than 800
°C. Above 1000
°C the correlation between swelling and thermal defect resistance breaks down indicating a changing microstructure at high temperature to a microstructure less effective at scattering phonons on a swelling-normalized basis.
The initial results of a post-irradiation examination study conducted on a SiC-SiC tubular specimen irradiated under a high radial heat flux are presented herein. The elastic properties of the ...specimen were evaluated before and after the irradiation using the resonant ultrasound spectroscopy (RUS) technique. The composite tubular specimen was considered as an orthotropic elastic with nine elastic constants (Young's moduli, shear moduli and Poisson's ratios—three components of each) for representing its full elastic deformation behavior. All the elastic moduli decreased after irradiation; the reduction was as high as 35% in one of the moduli. The significant decrease in the moduli indicates the presence of microcracks. The results from a computational study show significant stress development in the specimen due to irradiation, primarily caused by differential swelling across the thickness of the specimen. The evaluated stresses exceed the proportional limit stress of the material, indicating the likelihood of matrix microcracking, and thus corroborating the results obtained from RUS. X-ray Computed Tomography (XCT) study confirmed the presence of cracks in the irradiated specimen. These cracks occurred at the inner region of the specimen and propagated in axial and hoop directions. These XCT results are in agreement with the RUS results and stress distribution results from the computational study.
The amount and type of metallic transmutants produced in SiC/SiC when used in magnetic (MFE) and inertial (IFE) confinement fusion systems are determined and compared to those obtained following ...irradiation in fission reactors. Up to ∼1.3% metallic transmutants are generated at the expected lifetime of the fusion blanket. Irradiation in fission reactors to the same fast neutron fluence produces about an order of magnitude lower metallic transmutation products than in fusion systems. While the dominant component in fusion systems is Mg, P is the main transmutation product in fission reactors. The impact on the SiC/SiC properties is not fully understood. The results of this work will help guide irradiation experiments in fission reactors to properly simulate the conditions in fusion systems by possible ion implantation. In addition, the results represent a necessary input for modeling activities aimed at understanding the expected effects on properties.
Tungsten-copper laminate composite has shown promise as a structural plasma-facing component as compared to tungsten rod or plate. The present study evaluated the tungsten-copper composite after ...irradiation in the High Flux Isotope Reactor (HFIR) at temperatures of 410–780 °C and fast neutron fluences of 0.02–9.0 × 1025 n/m2, E > 0.1 MeV, 0.0039–1.76 displacements per atom (dpa) in tungsten. Tensile tests were performed on the composites, and the fracture surfaces were analyzed with scanning electron microscopy. Before irradiation, the tungsten layers had brittle cleavage failure, but the overall composite had 15.5% elongation at 22 °C. After only 0.0039 dpa this was reduced to 7.7% elongation, and no ductility was observed after 0.2 dpa at all irradiation temperatures when tensile tested at 22 °C. For elevated temperature tensile tests after irradiation, the composite only had ductile failure at temperatures where the tungsten was delaminating or ductile.
•Fusion reactors need a tough, ductile tungsten plasma-facing material.•The unirradiated tungsten-copper laminate is more ductile than tungsten alone.•After neutron irradiation, the composite has significantly less ductility.•The tungsten behavior appears to dominate the overall composite behavior.
The Magnetospheric Multiscale (MMS) spacecraft observed many enhancements of electromagnetic ion cyclotron (EMIC) waves in an event in the late afternoon outer magnetosphere. These enhancements ...occurred mainly in the troughs of magnetic field intensity associated with a compressional ultralow frequency (ULF) wave. The ULF wave had a period of ∼2–5 min (Pc5 frequency range) and was almost static in the plasma rest frame. The magnetic and ion pressures were in antiphase. They are consistent with mirror‐mode type structures. We apply the Wave‐Particle Interaction Analyzer method, which can quantitatively investigate the energy transfer between hot anisotropic protons and EMIC waves, to burst‐mode data obtained by the four MMS spacecraft. The energy transfer near the cyclotron resonance velocity was identified in the vicinity of the center of troughs of magnetic field intensity, which corresponds to the maxima of ion pressure in the compressional ULF wave. This result is consistent with the idea that the EMIC wave generation is modulated by ULF waves, and preferential locations for the cyclotron resonant energy transfer are the troughs of magnetic field intensity. In these troughs, relatively low resonance velocity due to the lower magnetic field intensity and the enhanced hot proton flux likely contribute to the enhanced energy transfer from hot protons to the EMIC waves by cyclotron resonance. Due to the compressional ULF wave, regions of the cyclotron resonant energy transfer can be narrow (only a few times of the gyroradii of hot resonant protons) in magnetic local time.
Key Points
Electromagnetic ion cyclotron wave enhancements were detected in a compressional ultralow frequency (ULF) wave
Troughs of magnetic field intensity of the ULF wave are preferential locations for the cyclotron resonant energy transfer
Due to compressional ULF wave, regions of the cyclotron resonant energy transfer can be narrow in magnetic local time
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