[en] The second harmonic generated by a relativistic annular electron beam propagating through a cylindrical waveguide immersed in a strong axial magnetic field is investigated on the basis of the relativistic hydrodynamic equations for cold electrons. The efficiency of second harmonic generation is calculated separately for the pump by the TM electromagnetic wave and for the pump by the slow space-charge wave, by assuming that the electron beam is thin and of low density and the pump wave is azimuthally symmetric. It is shown that, in the case of slow space-charge wave pump, an appreciably large efficiency of second harmonic generation is achieved in the high frequency region, whereas the efficiency by the TM electromagnetic wave pump is relatively small over the whole frequency range.(author)

[en] Carbon steel corrosion near waterline under gamma-ray irradiation has been investigated. Under irradiation, the corrosion of carbon steel at the waterline is accelerated by the superposition of the water film effect and the irradiation effect. The results of the long-term prediction assuming that the corrosion of carbon steel under irradiation environment follows the power law, the average depth of corrosion at the water line was estimated to be about 10 mm under the aerated environment for 40 years

[en] Pipe wall thinning due to flow accelerated corrosion (FAC) is one of the most important degradation modes which can take place in nuclear power plants. Potential area of FAC is widespread in piping systems and probability of pipe failure due to FAC is relatively high compared to other causes. FAC is a complex phenomenon, where mass transfer under turbulent flow, chemical reactions at interfaces, and mass diffusion in oxide scales cooperatively or competitively interact. Among a number of influencing parameters for FAC rate, this paper focuses on Cr in carbon steels and pH of water. pH is the primary water chemistry parameter to manage FAC susceptibility of the whole piping systems. Small amount of Cr has a significant effect for improving resistance of the carbon steels to FAC. This fact offers an effective countermeasure for FAC mitigation by using Cr modified steels, but, at the same time, the Cr dependence could give difficult problems, when we manage pipe wall thinning with thickness inspections. In a procedure to sample piping lines and locations of thickness measurement, we may need to take into account Cr content of the pipes picked up for the inspection. We also need to pay attention on difference in Cr content between pipes and weld filler metal, even though the absolute Cr levels of the both steels are minor. In the cases that Cr content of weld metal is lower than that of pipe materials, circumferential grooving may form along the weld. Basically, effects of those material and water chemistry factors can be attributed to oxide scale properties, such as solubility to water, porosity, semiconductor property, etc. This paper briefly reviews experimental data of Cr, Ni, Cu effects and of pH effects, including both widely recognized 'historical' data and recent data on combined effects of Cr content and pH obtained by the authors. Characteristics of oxide scales formed in the FAC experiments, such as defect characteristics and Cr enrichment distribution, and their relation to FAC rate are also described. (author)

[en] Austenitic stainless steel weld metal used in boiling water reactor (BWR) is mainly austenitic, but contains up to around 15% of ferrite. Abe et. al. examined aging properties of type 316 low-carbon stainless steel weld metal at 335degC and suggested that thermal hardening due to spinodal decomposition potentially occur even at lower temperature such as BWR operating temperature (288degC). To evaluate the rate of thermal embrittlement of type 316 low-carbon stainless steel weld metal at BWR operating temperature, aging test at 310degC, 335degC, and 440degC was carried out. It is revealed that hardening with aging at 310degC was result of spinodal decomposition. Comparing thermal hardening behavior, hardening rate at 288degC was discussed. (author)

[en] Highlights: • Effect of cold work on oxidation kinetics was clearly observed for 15Cr–20Ni SS. • The tube-shaped 15Cr–20Ni SS showed very good oxidation resistance. • The machined layer by cold drawing has a significant role to mitigate oxidation. - Abstract: Oxidation behavior of austenitic stainless steels as fuel cladding candidate materials for supercritical-water-cooled reactor (SCWR), including three types of 15Cr–20Ni stainless steels (1520 SSs), in the temperature range of 700–780 °C superheated steam have been investigated. Effect of temperature, dissolved oxygen (DO), degree of cold work (CW), and machined layer by cold drawing process on the oxidation kinetics assuming power-law kinetics are discussed. Characteristics of oxide layers and its relation to oxidation behaviors are also discussed. The effect of DO on the weight gain behavior in superheated steam at 700 °C was minor for all specimens at least up to 200 ppb DO. The tube-shaped specimens of 1520 SSs showed very good oxidation resistance at 700–780 °C. There was no clear difference in the oxidation kinetics among the three investigated types of 1520 SSs. The machined layer formed at the tube surface has a significant role to mitigate oxidation in superheated steam. A fine-grained microstructure near the surface due to recrystallization by cold drawing process is effective to form the protective Cr₂O₃ layer. It has been suggested that since Cr diffusion in the outside surface of tubes is accelerated as a result of an increased dislocation density and/or grain refinement by cold drawing, tube specimens show very slow oxidation kinetics. Breakdown of the protective Cr₂O₃ layer and nodule oxide formation were partly observed on the tube-shaped specimens of 15Cr–20Ni SSs. The reliability of Cr₂O₃ layer has to be carefully examined to predict the oxidation kinetics after long-term exposure

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[en] Effects of Cr content on flow accelerated corrosion (FAC) of carbon steels have been evaluated and their relation to oxide scale characteristics based on detailed oxide layer characterizations using transmission electron microscope with X-ray analyzer have been discussed. There is no 'threshold' concentration of chromium below which there is no effect of Cr content on the corrosion rate. Time dependency to chromium effect has also been not observed. Thickness of oxide layer does not affect the FAC rate in this experiments. (author)

[en] Oxidation behavior and cracking susceptibility of the Ni-Cr alloys (Ni-14Cr, Ni-22Cr and Ni-30Cr) under extremely-low oxygen partial pressure have been investigated by experiments used as plate specimen and Reverse U-Bend (RUB) specimen for 750 hours at 400degC in two kinds of gas system (inert gas and dry steam) under various oxygen potential (Ni stable, Ni/NiO equilibrium and NiO stable). The Ni-Cr alloys cracked along grain boundary both in inert gas system (with trace O₂, without H₂O) and in hydrogenated steam. The cracking susceptibility was confirmed in near Ni/NiO equilibrium in hydrogenated steam as contrasted with higher oxygen potential in inert gas system. This result shows that potential range for the cracking susceptibility seemed to be different between the two kinds of gas system. Cracking severity was highest for Ni-14Cr and lowest for Ni-30Cr both in inert gas and steam. But even Ni-30Cr was not immune to IG cracking in steam near Ni/NiO equilibrium. (author)

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