Fundamental Study of Tandem Electron Beam Welding for Nuclear Fusion and Fission Reactors

As the important part of the life extension program for nuclear fission reactors and that of the maintenance scheme of blanket of fusion reactors, repair welding technique of neutron damaged materials is recognized to be one of the most urgent subjects to be established. This work provides the potentiality and the critical issues of "Tandem electron beam welding technique" when it is applied to heavily neutron damaged materials. Where mechanical property degradation due to the displacement damage and helium production from (n, α) reaction makes it very difficult to produce sound welded joint. This paper presents the preliminary results to see the elementary characteristics of the welded joints produced by Tandem electron beam welding technique. Not only for the stainless steel nor high-nickel alloys, also for stainless steel to high-nickel alloy welded joints were studied. The tandem electron beam welding was done at JWRI, Osaka University. By optimizing the drilling effect from the leading electron beam and the weld defect suppression effect from the secondary electron beam , weld defect free welded joints were obtained with the excellent joint strength and ductility. The weld bead shape and penetration characteristics are also provided. The present results are quite promising to apply "Tandem electron beam welding" to heavily neutron damaged metallic structures and components

Effect of Interfacial Shear Strength on Mechanical Property of SiC/SiC

In order to quantitatively evaluate mechanical properties of fibers, matrices and their interfaces in fiber reinforced SiC/SiC composites, nano-indentation tests have been carried out. Using the same technique, fiber push-out test was performed. The specimens were analyzed by means of scanning electron microscopy (SEM), before and after indentation tests. From the indentation load vs. displacement relations, the fiber pushed out process has been discussed and the initiation loads of interfacial debonding and those of interfacial sliding were defined and were discussed in comparison with the C/C composites. The load of interfacial debonding initiation was likely to increase in proportion to the fiber circumference. The initiation load of interfacial sliding increased with increment of contact area between fiber and matrix. The relation between bending strength and interfacial shear strength of SiC_/SiC_ is preliminary postulated together with crack initiation and propagation characteristics and microstructural characteristics of the composites

High speed formation of pyro-carbon coat on silicon carbide fiber by continuous chemical vapor deposition furnace

In order to develop a practical process for the carbon coating on SiC fiber, high-speed and continuous pyrocarbon (PyC) coating process are under development by using a continuous CVD furnace with open-ends structure. The effects of process gas and winding speed have been investigated. It was revealed that the growth rate of PyC is in proportion to winding speed and the flow rate of process gas. PyC growth rate was reached up to 250 nm/min, which is several hundred higher than those of conventional CVI/CVD methods This results indicates that the mass production of PyC coated SiC fiber without unexpected residual deformation (torsion and curvature) is possible. And, the mass production and practical use of SiC/SiC using PyC coated SiC fiber will be largely promoted

TENSILE PROPERTIES OF JPCA AND JFMS IRRADIATED IN JMTR BY MEANS OF MINIATURIZED SPECIMEN TESTING

In the research and development of miniaturized specimen technology, consideration of specimen size effect is the key issue. In this work, tensile tests were studied with variations of specimen size around the standard mini-tensile specimen in the Japanese fusion materials program. The materials used were JPCA (modified 316 SS) and JFMS (modified 10Cr-2Mo dual phase steel). Microstructure has been controlled to clarify the effect of grain size for the former and the effect of ferrite/martensite ratio for the latter. Neutron irradiations of post-irradiation deformation response, microstructure prior to and after deformation were examined by transmission electron microscopy. The effects of specimen thickness and aspect ratio(thickness/width) on tensile properties are studied. New scaling equations to evaluate valid yield strength and tensile strength from small specimens with thickness less than the critical thickness, t_c, are proposed. The origins of specimen size effects from a microstructural viewpoint are also discussed

RADIATION EFFECTS ON METAL MATRIX COMPOSITES BY FISSION NEUTRONS FROM JMTR AND JOYO

Ceramics fiber reinforced composites are expected to be potential candidates as fusion reactor structural materials. Aluminum matrix composites reinforced with C or SiC fibers are investigated. The objectives of this investigation are to evaluate potential of Al matrix composites as low activation fusion reactor materials and to develop them for fusion applications. Mechanical properties were measured by three point bending test and mini size specimen tensile test for composite materials and mono-filament tensile test. Microstructure was inspected by means of SEM and TEM. The effects of radiation were studied using fission neutrons of JOYO(FBR) and JMTR(BWR) and 1 MeV electrons from a HVEM. Al matrix composites showed excellent stability under irradiation up to a certain fluence, named threshold fluence. For SiC fibers in the composites, increment of tensile strength and Young\u27s modulus and crystallization of amorphous SiC were observed below the threshold fluence. But at above the threshold fluence, strength drastically dropped. Alloying of Ni and Si to matrix aluminum alloys was suggested to be unfavorable for SiC/Al composite materials used under nuclear reactor environments

Effects of Impurities on an Al Grain Boundary

The atomic and electronic structures of the Al AE ¼ 9 tilt grain boundary with segregated impurity atoms have been calculated by the firstprinciples pseudopotential method based on the local density functional theory. Effects of impurities of group I (Na), group II (Ca), group IV (Si) and group VI (S) have been examined. For the Na and Ca segregation cases, the impurity-Al interactions seem to have metallic characters. However, the boundary expands substantially and the charge density decreases significantly over the boundary. Thus these impurities should cause weaker intergranular adhesion. For both the Si and S segregation cases, the charge density increases around the impurity atom. The Si atom forms the covalent-metallic character mixing bonds with neighboring Al atoms. Such strong and directional bonds should prevent the rearrangement of atoms under stresses. However, the S atom forms such a strong bond with only one neighbor, differently from the Si case. It can be said that each impurity has various effects on the local atomic and electronic structure of an Al grain boundary according to the nature of each species, which seems to dominate the mechanism of embrittlement

Clinical, Radiological, and Pathological Investigation of Asbestosis

By the radiological examination, differential diagnosis of asbestosis from chronic interstitial pneumonia such as IPF/UIP is difficult. The pathological features of asbestosis show the peribronchiolar fibrosis which suggest that asbestos fibers cause the inflammation of bronchioli. Therefore, the criteria for pathological diagnosis of asbestosis in 2010, contain the finding of peribronchiolar fibrosis again. Chest CT scanning including HRCT for total of 38 cases clinically diagnosed asbestosis were reviewed by 3 radiologists and one pulmonologist. On the other hand, the histology of lung tissues obtained by surgery or autopsy were examined by 4 pulmonological pathologists. Furthermore, the content of asbestos bodies in the lung was counted by phase-contrast microscopy. Thirteen cases were definitely diagnosed of asbestosis in the image including HRCT and 17 cases were diagnosed by the histopathological examination showing lung fibrosis with peribronchiolar fibrosis. Only 10 cases were indicated asbestosis by both the radiological and histopathological examinations. The mean value of asbestos bodies for these cases, was 2,133,255 per gram of dry lung tissue