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Background:Several studies have reported treatment options for patients with Kawasaki disease refractory to standard immunoglobulin therapy; however, no studies have reported low-dose immunoglobulin therapy for patients with a low risk of Kawasaki disease.Methods:A total of 277 patients with Kawasaki disease were included in this study. We used Kobayashi score and our Less high-risk score to divide the patients into three groups. Patients in the high-risk group (Kobayashi score ≥ 5 points) received 2 g/kg intravenous immunoglobulin and prednisolone. Patients in the moderate-risk group (Kobayashi score < 5 points and Less high-risk score ≥ 2 points) received 2 g/kg intravenous immunoglobulin treatment. Patients in the low-risk group (Kobayashi score < 5 points and Less high-risk score < 2 points) received 1 g/kg intravenous immunoglobulin treatment. The response rate and the incidence of coronary artery lesions at 4 weeks after treatment were evaluated in each group.Results:The treatment response rates in the high-risk (n = 110), moderate-risk (n = 80), and low-risk (n = 87) groups were 74.5, 72.5, and 77.0%, respectively. Coronary artery lesions occurred in 7.3, 3.8, and 2.3% of patients in the high-, moderate-, and low-risk groups, respectively. There were no significant differences between the groups regarding treatment response or coronary artery lesion rate.Conclusion:The therapeutic response rate and the therapeutic effect of low-dose intravenous immunoglobulin in the low-risk group identified with our new scoring were satisfactory. Stratified therapies for patients with Kawasaki disease based on the scoring system may be useful.

Understanding the epidemiology and clinical course of multisystem inflammatory syndrome in children (MIS-C) and its temporal association with coronavirus disease 2019 (Covid-19) is important, given the clinical and public health implications of the syndrome.We conducted targeted surveillance for MIS-C from March 15 to May 20, 2020, in pediatric health centers across the United States. The case definition included six criteria: serious illness leading to hospitalization, an age of less than 21 years, fever that lasted for at least 24 hours, laboratory evidence of inflammation, multisystem organ involvement, and evidence of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) based on reverse-transcriptase polymerase chain reaction (RT-PCR), antibody testing, or exposure to persons with Covid-19 in the past month. Clinicians abstracted the data onto standardized forms.We report on 186 patients with MIS-C in 26 states. The median age was 8.3 years, 115 patients (62%) were male, 135 (73%) had previously been healthy, 131 (70%) were positive for SARS-CoV-2 by RT-PCR or antibody testing, and 164 (88%) were hospitalized after April 16, 2020. Organ-system involvement included the gastrointestinal system in 171 patients (92%), cardiovascular in 149 (80%), hematologic in 142 (76%), mucocutaneous in 137 (74%), and respiratory in 131 (70%). The median duration of hospitalization was 7 days (interquartile range, 4 to 10); 148 patients (80%) received intensive care, 37 (20%) received mechanical ventilation, 90 (48%) received vasoactive support, and 4 (2%) died. Coronary-artery aneurysms (z scores ≥2.5) were documented in 15 patients (8%), and Kawasaki's disease-like features were documented in 74 (40%). Most patients (171 [92%]) had elevations in at least four biomarkers indicating inflammation. The use of immunomodulating therapies was common: intravenous immune globulin was used in 144 (77%), glucocorticoids in 91 (49%), and interleukin-6 or 1RA inhibitors in 38 (20%).Multisystem inflammatory syndrome in children associated with SARS-CoV-2 led to serious and life-threatening illness in previously healthy children and adolescents. (Funded by the Centers for Disease Control and Prevention.).

Oxide dispersion strengthened (ODS) steels have been developed as accident tolerant fuel cladding materials because of their excellent high temperature oxidation resistance as well as high temperature mechanical properties. 12Cr–6Al-ODS steel specimens with electron-beam (EB) weld line were irradiated with neutron in high flux isotope reactor (HFIR) at 300 °C to 2.6 dpa. Irradiation hardening was measured by Vickers hardness (HV) method. The irradiation resulted in a hardening of ∼95 HV in the base metal and ∼140 HV in EB weld line. The post-irradiation microstructures including the stability of the oxide nanoparticles was examined by transmission electron microscopy (TEM). The dispersion morphology of oxide particles in base metal was rather stable under present irradiation condition as no significant change was observed with respect to their average size and number density. As for the oxides in EB weld line, a similar trend with base metal was recognized. The 1/2 and type dislocation loops formed in both base metal and EB weld line after neutron irradiation. The average size of dislocation loops was measured to be 7.6 ± 3.8 and 10.0 ± 3.8 nm in base metal and EB weld line, respectively. Meanwhile, the total number density was estimated to be (1.6 ± 1.0) × 1022 and (2.2 ± 0.5) × 1022 m−3 in base metal and EB weld line, respectively. Oxide/matrix interface may act as a trapping site for irradiation induced defects, leading to the smaller loop size and number density in base metal than in EB weld line. Dispersed barrier hardening (DBH) model indicated that the irradiation hardening could be attributed to the formation of dislocation loops.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, Accepted: 2017-06-01, 資料番号: PA1820003000

Randomly oriented strand composites are promising materials for complex-shaped parts, especially in the aerospace and automotive industries. However, test data from small specimens tend to have a high level of scatter as these materials contain several centimetres of chopped carbon fibre strands. In this study, we investigated the mechanical properties of ultra-thin chopped carbon fibre tape reinforced thermoplastics (UT-CTT), which contain chopped thermoplastic thin-ply prepreg tapes produced using a paper-making technique. We propose a model for accurately evaluating the flexural modulus and its scatter, which was verified by comparison with experimental data. The predictions of the model showed excellent agreement with the experimental results. This method makes it possible to quantify the scatter of the flexural modulus and is useful for designing geometries of, not only standard test specimens, but also complex parts for actual applications.

Chemical effects of Mo and B on the Cs chemisorption onto stainless steel (SS) were predicted using a chemical equilibrium calculation based on an assumed model. A step reaction model for the Cs chemisorption process considering surface oxide layer formed on SS was assumed based on a literature review. Resultant major Cs compounds by Cs chemisorption were calculated for the two types of SS having different oxide surface layer structures. It is seen that Mo has induced the formation of Cs2MoO4 as a major Cs compound. On the other hand, little effects were observed for B. Cs-Si-O compounds were major resultant compounds regardless of Mo or B existence, indicating the stability of Cs-Si-O compounds. The results suggest that Cs-Mo-O in addition to Cs-Si-O compounds should be considered for further investigation on Cs chemisorption.

Light-water reactor (LWR) fuel cladding shall retain the performance as the barrier for nuclear fuel materials and fission products in high-pressure and high-temperature coolant under irradiation conditions for long periods. The cladding also has to withstand temperature increase and severe loading under accidental conditions. As lessons learned from the accident at the Fukushima Daiichi nuclear power station, advanced cladding materials are being developed to enhance accident tolerance compared to conventional zirconium alloys. The present paper reviews the progress of the development and summarizes the subjects to be solved for enhanced accident-tolerant fuel cladding, focusing on performance degradation under various corrosive environmental conditions that should be considered in designing the LWR fuel.

This study experimentally investigates the damage behaviour of a quasi-isotropic (QI) laminate of carbon fibre reinforced thermoplastics and chopped carbon fibre tape reinforced thermoplastics (CTT) under lightning strikes. Simulated lightning strike tests were performed and the damage was evaluated using a high-speed camera, ultrasonic testing, and optical microscopy of cross-sectioned samples. The shape of the vaporized resin and projected damage area resulting from the joule heating was dependent on the electrical anisotropy of composite surfaces; the shape of the vaporized resin was circular for QI laminate with thinner prepreg and CTT materials. In addition, the damage could be categorized into three modes: fibre sublimation, resin vaporization, and delamination. Finally, the application of thin-ply prepreg suppressed the projected damage area and the removal of the composite surface due to fibre sublimation and resin vaporization in both samples. Our findings clearly demonstrate the reduction of lightning damage when using thin-ply prepreg.

Carbon fiber reinforced thermoplastics (CFRTP) have been developed to realize excellent formability and mechanical properties. Specifically, discontinuous CFRTP (DCFRTP) are promising candidates for decreasing production cost and for application to mass production. Polyamide 6 (PA6) is a promising matrix for CFRTP due to its good adhesion properties with carbon fibers (CFs). However, the degradation of the mechanical properties of CFRTP due to the hygroscopic properties of PA6 is an area of concern. Thus, an investigation of the effects of water absorption on the mechanical properties of discontinuous CF reinforced PA6 is necessary. Additionally, a theoretical prediction of the degradation in mechanical properties is useful to clarify the effect of the absorbed water. Therefore, in this study, the influence of water absorption on the mechanical properties of CFRTP was investigated by measuring the mechanical properties using a three-point bending test. In addition, the flexural modulus was calculated using the Timoshenko beam equation to predict the degradation due to water absorption.

In the current study, new advanced oxidation-resistant FeCrAl oxide dispersion strengthened (ODS) alloys were developed via the control of composition-processing conditions for nuclear energy systems. For the first time, a single-crystal like recrystallized FeCrAl ODS alloy was achieved with a unique crystallographic texture of (110) 〈211〉 and a high number density of fine nanoscale oxide particles. Evaluation of yield strengths at different temperatures showed higher values in transverse direction than longitudinal direction. The orientation dependence of yield strength up to 800 °C was attributed to lower value of Schmid factor in transverse direction. Accordingly, the critical resolved shear stress of this practical class of advanced materials was calculated in various temperatures.

This study concerns the development of a reliable method to measure the volume resistivity of ultra-thin chopped carbon fiber tape reinforced thermoplastics (UT-CTT) made by tow spreading technology. It was found that, by using vises with aluminum foil and silver paste, resistivity can be accurately evaluated and the in-plane volume resistivity of UT-CTT decreased with increasing tape length and decreasing tape thickness. However, an increase in tape thickness led to a decrease in out-of-plane resistivity. The resistivity also had smaller coefficient of variation (CoV) in UT-CTT specimens that included a greater number of chopped tapes for a given volume. This makes it possible to achieve a volume resistivity in UT-CTT that is close to that of quasi-isotropic laminates, despite the discontinuity of the carbon fiber, with potential applications improving lightning resistance and electromagnetic interference (EMI) shielding.

Cesium (Cs) and iodine (I) vapor species formed just after release from degraded fuels were predicted by means of the chemical equilibrium calculation with focuses on the effects of boron (B) release kinetics. Modified equations for the release kinetics of Cs, I and molybdenum (Mo) were utilized for evaluation of atmospheric dependences of their releases fractions. The B release kinetics was evaluated considering the formation of iron (Fe)–B–O–H compounds. The release of B was enhanced above approximately 2250 K with the vapor species of CsBO2 under steam atmosphere, while the formation of CsBO2 was limited under steam-starvation atmosphere due to the much lower release of B by the formation of low volatile Fe–B compounds. This limitation on CsBO2 formation under steam-starvation atmosphere would have resulted in a lesser formation of gaseous hydrogen iodine, HI, and of high volatile atomic I.

Ultra-thin chopped carbon fiber tape-reinforced thermoplastics, which belong to a class of randomly oriented strands and are characterized by enhanced strength, stiffness, and formability properties, have been prepared via a paper-making method from ultra-thin thermoplastic prepregs. The failure of ultra-thin chopped carbon fiber tape-reinforced thermoplastics under static tensile loading was studied in detail using various observation techniques, such as high-speed camera imaging, thermography, and optical microscopy. The obtained results revealed that the tensile fracture of ultra-thin chopped carbon fiber tape-reinforced thermoplastics exhibited three main patterns: fiber breakage, splitting of chopped tapes, and pulling out of chopped tapes. In contrast to conventional randomly oriented strands, the utilization of ultra-thin prepregs decreased the tensile strength scattering. An increase in the ultra-thin prepreg tape length resulted in an increase in the strength average magnitude, reaching saturation at a length of 18 mm. The results of this study can be used for constructing tensile strength prediction models and expanding the ultra-thin chopped carbon fiber tape-reinforced thermoplastics application range.

In a patient with cardiofaciocutaneous syndrome complicated by intractable infantile spasms (West syndrome), cardiac hypertrophy developed during adrenocorticotropic hormone treatment. Various types of antiepileptic drugs, intravenous immunoglobulin, thyrotropin releasing hormone, and a ketogenic diet were ineffective in this case. However, vigabatrin both decreased clinical seizures and improved electroencephalogram findings. Although vigabatrin has not been approved for use in Japan, the results in the present case suggest that this drug should be considered as an alternative therapy for cases of infantile spasms associated with syndromes involving cardiomyopathy or its potential risk factors, such as cardiofaciocutaneous syndrome.

Oxide dispersion strengthened (ODS) steels are promising accident tolerant fuel (ATF) cladding alternatives because of their excellent oxidation resistance and mechanical properties at high temperatures. Coupons of 12Cr–6Al-ODS steel with an electron-beam (EB) weld line were irradiated with 6.4 MeV Fe3+ ions at 300 °C to nominal doses of 2.6, 7.9 and 13.0 dpa at 600 nm depth below the irradiated surface. Transmission electron microscopy (TEM) and nano-indentation tests were performed after ion irradiation to investigate the post-irradiation microstructures including the stability of oxide nanoparticles and the irradiation induced hardening, respectively, with special attention paid to the comparison between base metal and EB weld line. Oxide nanoparticles in base metal were stable under present irradiation conditions as no significant change was observed with respect to the average diameter and number density. A similar trend was recognized for the oxides in EB weld line. As for irradiation-induced dislocation loops, EB weld line exhibited larger average diameter and higher number density than base metal. And the average diameter of dislocation loops increased with increasing irradiation dose, while the number density appeared to peak at an intermediate dose of 7.9 dpa, irrespective of in base metal or EB weld line. Irradiation hardening was estimated by two different methods, so called bulk hardness by Nix-Gao model and the reference depth hardness at an indentation depth of 225 nm. Both methods showed a higher irradiation hardening in EB weld line than in base metal irrespective of irradiation dose, and hardening saturation was noted in EB weld line. The estimated hardening by dispersed barrier hardening (DBH) model was consistent with the measured hardening, suggesting that the irradiation hardening could be mainly attributed to the formation of dislocation loops with different Burgers vector.

Oxide dispersion strengthened (ODS) FeCrAl ferritic steels are being developed as potential accident tolerance fuel cladding materials for the light water reactors (LWRs) due to significant improvement in steam oxidation by alumina forming scale and good mechanical properties up to high temperatures. In this study, the microstructural characteristics and tensile properties of the two FeCrAl ODS cladding tubes with different extrusion temperatures of 1100 °C and 1150 °C were investigated during processing conditions. While the hot extruded sample showed micron sized elongated grains with strong α-fiber in texture, cold pilger rolling process change the microstructure to submicron/micron size grain structure along with texture evolution to both α-fiber ( texture) and γ-fiber ({111} texture) via crystalline rotations. Subsequently, final annealing resulted in evolution of microstructure to large grain recrystallized structure starting at recrystallization temperature of ~810–850 °C. Two distinct texture development happened in recrystallized cladding tubes, i.e., only large elongated grains of (110) texture following extrusion temperature of 1100 °C; and two texture components of (110) and {111} following higher extrusion temperature of 1150 °C. The different texture development and retarding of recrystallization progress in 1100°C-extruded cladding tubes were attributed to higher distribution of oxide particles. Furthermore, the ring-tensile test properties of recrystallized FeCrAl ODS cladding tubes were evaluated in the temperature range of 25–800 °C and showed a very good combination of strength-ductility with a lower strength and higher ductility for 1150 °C extruded tube up to ~500 °C and opposite properties at higher temperatures.

We have launched a new research program for evaluation of fission product and actinide release behaviour under severe accident conditions, focusing on their chemical forms. In this research program, the fission product and actinide release models incorporated in the severe accident analysis code will be improved by implementing effects of chemical forms that are to be obtained by an experimental investigation on the fission product and actinide release behaviour from irradiated fuels. A novel in-situ measurement method of chemical forms of fission products and actinides just after their release as well as an off-line analysis method will be employed as the experimental means for evaluating the chemical forms at the release and their stability after release.

Irradiation-induced void denuded zone (VDZ) formation near grain boundaries was studied to clarify the effects of minor alloying elements on vacancy diffusivity during irradiation in practical PNC316 stainless steel developed for nuclear reactor core materials. The test materials were Fe–15Cr–15Ni steel without additives and PNC316 stainless steel; the latter contains minor alloying elements to improve the void swelling resistance. These steels were neutron-irradiated in the experimental fast reactor JOYO at temperatures from 749 K to 775 K and fast neutron doses of 18–103 dpa, and electron irradiation was also carried out using 1 MeV high voltage electron microscopy at temperatures of 723 K and 773 K and doses up to 14.4 dpa. VDZ formation was analyzed by TEM microstructural observation after irradiation by considering radiation-induced segregation near the grain boundaries. VDZs were formed near random grain boundaries with higher misfit angles in both Fe–15Cr–15Ni and PNC316 steels. The VDZ widths in the PNC316 stainless steel were narrower than those for the Fe–15Cr–15Ni steel for all neutron and electron irradiations. The VDZ width analysis implied that the vacancy diffusivity was reduced in PNC316 stainless steel as a result of interaction of vacancies with minor alloying elements.

An oxide dispersion strengthened (ODS) austenitic stainless steel was developed by mechanical alloying (MA) of advanced SUS316 stainless steel. A nano-characterization was performed to understand details of the effect of minor alloying elements in the distribution of dispersoids. It is shown that Y2O3 particles dissolve into the austenitic matrix after the MA for 6 h. Annealing at 1073 K or higher temperatures result in a distribution of fine oxide particles in the recrystallized grains in the ODS austenitic stainless steel. Additions of Hafnium or Zirconium led to the distribution of finer oxide particles than in samples without these elements, resulting in an increase in the hardness of the samples. The most effective concentration of Hf and Zr to increase the hardness was 0.6 and 0.2–0.3 wt%, respectively.

Addition of minor elements to a base alloy is often applied with the aim of mitigating void swelling by decreasing the vacancy diffusivity and flux which influence vacancy accumulation behavior. However, the comparative evaluations of parameters, such as the diffusivity and flux, between a base alloy and modified alloys with specific additives have not been studied in detail. In this study, type 316 austenitic stainless steel as a base alloy and type 316 austenitic stainless steels modified with vanadium (V) or zirconium (Zr) additions were used to perform evaluations from the changes of widths of the void denuded zone (VDZ) formed near a random grain boundary during electron irradiation because these widths depend on vacancy diffusivity and flux. The formations of VDZs were observed in in-situ observations during electron irradiation at 723K and the formed VDZ widths were measured from the transmission electron microscopic images after electron irradiation. As a result, the VDZs were formed in both steels without and with V, and respective widths were ³119 and ³100nm. On the other hand, the VDZ formation was not observed clearly in the steel with Zr. From the measured VDZ widths in the steels without and with Vaddition, the estimated ratio of the vacancy diffusivity in the steel with V to that in the steel without V was about 0.50 and the estimated ratio of the vacancy flux in the steel with V to that in the steel without V was about 0.71. This result suggests that the effect of additional minor elements on vacancy accumulation behaviors under electron irradiation could be estimated from evaluations of the VDZ width changes among steels with and without minor elements. Especially, because void swelling is closely related with the vacancy diffusion process, the VDZ width changes would also be reflected on void swelling behavior. [doi:10.2320/matertrans.MD201309]

In this study, identification of the crystal structure and analysis of the orientation relationship of oxide particles in an oxide dispersion strengthened austenitic stainless steel was carried out. High resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy showed that most of the oxide particles had a faceted shape and consisted of a complex oxide, the anion-deficient fluorite structure Y2Hf2O7. Selected area diffraction patterns and HRTEM indicated that the faceted oxide particle has a cube-on-cube orientation relationship with the surrounding matrix. In addition, strain fields were observed around the oxide particle with given reflection conditions, indicating that it surrounds the oxide particle. The observed strain fields would affect glide dislocation pinning and the migration of irradiation-induced point defects.

Irradiation behavior of ODS steel cladding tubes was evaluated for the further progress in understanding of the neutron-irradiation effects on ODS steel. Two types of ODS (9Cr–ODS_F/M, 12Cr–ODS_F) steel cladding tubes with differences in basic compositions and matrix phases were irradiated in JOYO. Post-irradiation examination data concerning hardness, ring tensile property, and microstructure were obtained. Hardness measurement after irradiation showed that there was an apparent irradiation temperature dependence on hardness for 9Cr–ODS_F/M steel whereas no distinct temperature dependence for 12Cr–ODS_F steel. Also, there was no significant change in tensile strengths after irradiation below 923 K, but those above 1023 K up to 6.6 × 10 26 n/m 2 ( E > 0.1 MeV) were decreased by about 20%. TEM observations showed that the radiation-induced defect cluster formation during irradiation was suppressed because of high density sink site for defect such as initially-existed dislocation, and precipitate interfaces. In addition, oxide particles were stable up to the maximum doses of this irradiation test.

For Fe–Ni alloy involving the metastable γ″-Ni3Nb precipitates in the standard chemical composition of Fe–43Ni–15Cr–2W–1Mo–3.8Nb–0.1V–0.1Ti–0.28Al–0.1Zr–0.04C (mass%), hardness measurement and TEM analyses were performed during aging at temperatures 650–750 °C up to 200 h after 20% cold-rolling. The hardness increases due to coherent γ″-Ni3Nb precipitate, but longer aging induces hardness decrease due to its coarsening and dislocation recovery. Aging at 800 °C for 200 h leads to transformation to the stable δ-Ni3Nb. Based on these data, an appropriate aging condition is considered to be at the temperature 700–750 °C for 8 h in order to distribute finely intra-granular γ″ precipitates at the final stage of manufacturing.

Four experimental fuel assemblies (EFAs) containing 9Cr-ODS steel cladding fuel pins were previously irradiated in the BOR-60 to demonstrate the in-reactor performance of 9Cr-ODS steel for use as fuel cladding tubes. One of the EFAs achieved the best data, a peak burn-up of 11.9at% and a neutron dose of 51 dpa, without any microstructure instability or any fuel pin rupture. On the other hand, in another EFA (peak burn-up, 10.5at%; peak neutron dose, 44 dpa), peculiar irradiation behaviors, such as microstructure instability and fuel pin rupture, occurred. Investigations of the cause of these peculiar irradiation behaviors were carried out. The detection sensitivity in an ultrasonic inspection test was shown to be low for the metallic Cr and metallic Fe inclusions. The peculiar microstructure change reappeared with high-temperature thermal-aging of the 9Cr-ODS steel containing metallic Cr inclusions. The strength and ductility of the defective part containing metallic Cr inclusions were appreciably lower t...

The behavior of radiation-induced segregation (RIS) and intergranular corrosion at random grain boundaries and Σ3 coincidence site lattice (CSL) boundaries in proton-irradiated 316L stainless steel was examined. The frequency of the CSL boundaries was enhanced up to 86.6% by grain boundary engineering treatment prior to irradiation. Significant nickel enrichment and chromium depletion were induced at the random grain boundary owing to the RIS. At faceted Σ3 CSL boundaries, chromium depletion occurred at the asymmetrical boundary facet plane whereas no RIS was observed at the coherent twin boundary. After the electrochemical etching test, an intergranular corrosion groove was found along the random grain boundaries because of the low chromium concentration (∼12%) at the boundaries. At the faceted Σ3 CSL boundaries, the discontinuous groove along the asymmetric facet plane was completely disrupted by the non-corrosive coherent twin boundary.

As the number of people going to public facilities such as stations and airports visitors increases, the facilities become increasingly congested. To maintain personal safety and comfortableness, we have developed a dynamic guide signs system we call "Projection Sign" to control pedestrian flow. It enables signs and their information to be changed on a situational basis. This paper reports how we tested the system at Haneda Airport to examine its effectiveness. We found that users' age and the language they use affect the signs' visual attractiveness. We also found that the signs' information changes user flow trends. We use these results to discuss ways to make guide signs in public spaces more effective.

The effects of fast neutron irradiation on ring tensile properties of oxide dispersion strengthened (ODS) steel claddings for fast reactor were investigated. Specimens were irradiated in the experimental fast reactor Joyo using the material irradiation rig at temperatures between 693 and 1108 K to fast neutron doses ranging from 16 to 33 dpa. The post-irradiation ring tensile tests were carried out at irradiation temperatures. The experimental results showed that there was no significant change in tensile strengths after neutron irradiation below 923 K, but the tensile strengths at neutron irradiation above 1023 K up to 33 dpa were decreased by about 20%. On the other hand, uniform elongation after irradiation was more than 2% at all irradiation conditions. The ring tensile properties of these ODS claddings remained excellent within these irradiation conditions compared with conventional 11Cr ferritic/martensitic steel (PNC-FMS) claddings.

The microstructures, prior and posterior to volumetrically remarkable swelling, of heavily neutron-irradiated specimens of compositionally-modified SUS316 based steel were carefully studied and characterized by using transmission electron microscope(TEM) and high resolution TEM to make clear an onset mechanism of radiation-induced swelling as well as an effect of neutron irradiation on microstructure. As the results of TEM study, it was demonstrated that the microstructural evolutions, including radiation-induced swelling, depended strongly on the irradiation condition. The relationship between the onset of swelling and microstructural evolution is quite complicated but the effects of irradiation temperature on microstructural changes appear to be relatively large. The onset mechanisms of swelling at a specific temperature or temperature range are discussed from the viewpoint of microstructure in this paper.

Excellent high-temperature strength and resistance to radiation damage of 9Cr Oxide Dispersion Strengthened (9Cr-ODS) martensitic steel have been realized by nano-size Y–Ti–O complex oxide particles dispersed in the matrix and a dual phase structure consisting of α′-martensite and δ-ferrite. These are produced by mechanically alloying Fe–Cr–Ti powders with Y 2 O 3 followed by a hot-consolidation process. Therefore, the hot-consolidation process is the issue to be clarified for the formation of nano-size oxide particle and δ-ferrite. The temperature dependence of the formation and development of nano-size oxide particles and δ-ferrite using mechanically alloyed 9Cr-ODS raw powder were investigated applying X-ray Diffraction and Small Angle X-ray Scattering measurement at SPring-8 and by Electron Probe Micro Analysis. In situ heating measurement techniques with XRD and SAXS enabled real-time observation of phase transformations and allowed correlation between formation of nano-size oxide particle and δ-ferrite.

Austenitic stainless steel PNC316 was subjected to grain boundary engineering (GBE). It was found that the grain boundary engineered PNC316 (PNC316-GBEM) had a coincidence site lattice (CSL) fraction of 86% and that the network of random grain boundaries was perfectly divided by the CSL boundaries. The thermal stability and the void swelling behavior of PNC316-GBEM were investigated by means of SEM and TEM analyses. After thermal aging at 973 K for 100 h, structural changes were observed neither in the grain boundary networks of PNC316-GBEM nor in another sample of PNC316-GBEM subjected to 20% additional cold rolling, PNC316-GBEM20%CW. PNC316-GBEM showed a higher void swelling rate than as-received PNC316 (PNC316-AS). However, with additional 20% cold rolling after GBE, the void swelling rate decreased to as low as that of PNC316-AS.

The in-reactor creep rupture tests of 11Cr–0.5Mo–2W, V, Nb F/M steel were carried out in the temperature range from 823 to 943 K using materials open test assembly in the fast flux test facility and tensile and temperature-transient-to-burst specimens were irradiated in the experimental fast reactor JOYO at temperatures between 693 and 1013 K to fast neutron doses ranging from 11 to 102 dpa. The results of post-irradiation mechanical tests showed that there was no significant degradation in tensile and transient burst strengths even after neutron irradiation below 873 K, but that there was significant degradation in both strengths at neutron irradiation above 903 K. On the other hand, the in-reactor creep rupture times were equal or greater than those of out-reactor creep even after neutron irradiation at all temperatures. This creep rupture behavior was different from that of tensile and transient burst specimens.

Eleven Cr ferritic/martensitic steels with improved high temperature properties (PNC-FMS) were thermally-aged and neutron-irradiated. To understand the thermal-aging and the irradiation effects on their microstructural developments, microstructural observation was made. From the detailed observations and microchemical analyses, the following points were obtained. (1) When irradiated at 400–450 °C to doses up to 94.6 dpa, both dislocation loops and cavities formed in the ferrite phase region. But void swelling was estimated as 0.05% at the most. (2) When irradiated at moderate temperatures of 500–600 °C, M23C6 and M6C grew and entirely covered the prior austenite grain (PAG) boundaries, suggesting that carbide precipitation on the PAG boundaries contributed to the extended time periods of recovery of martensite laths. (3) When irradiated at high temperatures above 650 °C, formation and growth of equi-axial grains occurred in addition to the complete recovery of martensite laths and the huge growth of carbides.

The effects of fast neutron irradiation conditions have been investigated by focusing on the mechanical properties of 11Cr-0.5Mo-2W, Nb, V ferritic/martensitic (F/M) stainless steel (PNC-FMS) and 10.5Cr-1.5Mo, Nb, V F/M stainless steel (HT9M) claddings, especially tensile and transient burst properties. These two F/M claddings were irradiated at temperatures from 693 to 833K to 42.5 dpa (displacement per atom) in the experimental fast reactor JOYO using the PFB090 fuel test subassembly. Post-irradiation tensile and temperature-transient-to-burst tests were carried out for defueled cladding specimens. The results of mechanical tests for the PNC-FMS cladding showed that there was no significant degradation in tensile and transient burst strengths even after fast neutron irradiation. On the other hand, the strength of the HT9M cladding tended to shift to lower values than those of as-received specimens. The differences in tensile and transient burst strengths between the two claddings were attributed to mart...

Microstructural observation was performed on a neutron-irradiated oxide dispersion strengthened (ODS) ferritic steel with emphasis on oxide behavior, including phase stability under irradiation at elevated temperature (∼973 K). Transmission electron microscopy observation of the Y–Ti complex oxide particles showed they were fine (∼40 nm) whereas the Ti-oxide particles were relatively coarse (∼300 nm). Dispersion parameters of oxide particles, such as mean size and number density, changed due to irradiation. This implies recoil resolution of the oxide particles. When irradiated at 973 K, some Y–Ti complex oxides survived and interacted with the dislocation structures, which delayed the dislocation recovery and stabilized the elongated grain structure. It is considered that oxide particles could be effective pinning points of dislocations in motion under irradiation to a dose of ∼100 dpa.

The effects of fast neutron irradiation on tensile and transient burst properties of advanced ferritic/martensitic steel claddings for fast breeder reactors were investigated. Specimens were irradiated in the experimental fast reactor JOYO using the material irradiation rig at temperatures between 773 and 1013 K to fast neutron doses ranging from 11 to 102 dpa. The post-irradiation tensile and temperature-transient-to-burst tests were carried out. The results of mechanical tests showed that there was no significant degradation in tensile and transient burst strengths after neutron irradiation below 873 K. This was attributed to grain boundary strengthening caused by precipitates that preferentially formed on prior-austenite grain boundaries. Both strengths at neutron irradiation above about 903 K up to 102 dpa decreased due to radiation enhanced recovery of lath martensite structures and recrystallization.

For understanding the microstructual details of nano-size oxide particles, three types of ODS ferritic and austenitic steels were examined by high voltage electron microscopy, EDS and AP-FIM. The oxide included Y, Ti and O and showed a shell-like structure with different composition. The shell-like structure depends on crystal structure of the matrix during fabrication process. To evaluate the irradiation stability of the oxide particles, the electron irradiation was carried out to 47 dpa in the temperature range between room temperature and 923 K. During the irradiation, the oxide particles did not show obvious change in size. The irradiation behavior is discussed comparing with the results recently reported.

For basic understanding of how to produce a homogeneous distribution of nano-scale oxide particles, we have applied dual ion-implantation to make a super-saturation of oxide-forming elements. Y+ and O+ ions were implanted into ferritic alloys at room temperature. Both in situ annealing in an electron microscope for thin samples and conventional annealing for bulk samples were carried out at 300–1300 K. Nano-particles of Y2O3 precipitated during annealing, where the starting temperatures for the nucleation and growth depended on the annealing methods. In thin specimens the growth and nucleation of Y2O3 started at 573 and 613 K. In bulk specimens, the growth and nucleation shifted to higher temperatures. Compared with conventional Mechanical Alloying, it is concluded that dual ion-implantation can produce much finer distributions of nano-scale oxides. In order to explain these results, we emphasize the roles of super-saturated elements and lattice defects.