Measurements of magnetic minor hysteresis loops have been performed in martensitic stainless steel subjected to tensile creep test at 120 MPa and 873 K. The minor-loop coefficients as well as coercivity, which are indicators of internal stress, sharply increase at the primary creep and show a very s low increase at the secondary creep, followed by the steady increase at the ternary creep. A good correlation of the coefficients with creep strain cl early shows that magnetic method using minor hysteresis lo...
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Changes of Magnetic Hysteresis Properties due to Creep Damage in Martensitic Stainless Steel

For the commercialization of fast breeder reactors (FBR), it is essential to enhance the economic competitiveness by reduction of total cost by elongation of plant service period. For this reason, it is needed to establish the aged weld joint integrity assessment method for future FBR compon ents. Additionally, since it is expected to employ the repair weld for aged structural components, it is essential to investigate the effect of repair weld. To investigate the influence of high temperature-long service...
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Basic investigation of aging weld joint and repair weld joint integrity assessmentusing neutron residual stress measurement method

Magnetic properties derived from major hysteresis loops are sensitive to the microstructures of iron-based steels and have therefore been used for nondestructive evaluation of degradation in ferromagnetic materials contained in structural components. A permeability obtained from ac small field excitation may be a more us eful parameter than one obtained from a major hysteresis loop from the viewpoints of electricity consumption and real-time measurement. In this paper, the relati on between the ac permeabi...
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Evaluation for Mechanical Properties of Ferromagnetic Steels by AC Permeability

This study provides an application of the risk evaluation of a nuclear power plant to the improvement of the plant operation and maintenance activities. The risk p rofiles for assumption of not only single but also double outage of safety systems, obtained from the risk importance analysis, show that the risk increase from si ngle outage of the supporting systems is generally higher than that of the frontline systems, and that the risk increase from double system outage depends on the combination of the o...
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Study on the Risk Evaluation for Safety Systems Outage at Nuclear Power Plant

When a crack is detected in nuclear reactor core internals, it is important to survey details of a crack. In this study, to survey nuclear reactor core in ternals simply, new electrolytic etching method that applies “Gel Electrode” and underwater microscope were developed. To apply “Gel Electrode”, we can see fusion boundary and grain boundary after electrolytic etching. To use underwater microscope, we can see surface figures of nuclear reactor core internals directly without taking boat samples or repli...
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Development of Underwater Remote Inspection Technique for Nuclear Reactor Core Internals

A diffraction spot trace method (DSTM) was developed to measure internal stresses of materials with coarse grains. The DSTM was applied to light metals, such as aluminum alloy and magnesium alloy. In this study, validity of the DSTM was examined using high energy synchrotron X-rays of 70 keV. The specimen was a welded plate of austenitic stainless steel (SUS316L). The thickness of the specimen was 9 mm. The improved rotating slit-system was used, and PILATUS was used as an area detector. It was diffi...
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Evaluation of Welding Residual Stresses in Austenitic Stainless Steel Using Diffraction Spot Trace Method

A diffraction spot trace method (DSTM) was developed to measure internal stresses of materials with coarse grains. The DSTM was applied to light metals, such as aluminum alloy and magnesium alloy. In this study, validity of the DSTM was examined using high energy synchrotron X-rays of 70 keV. The specimen was a welded plate of austenitic stainless steel (SUS316L). The thickness of the specimen was 9 mm. The improved rotating slit-system was used, and PILATUS was used as an area detector. It was difficu...
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Evaluation of Welding Residual Stresses in Austenitic Stainless Steel Using Diffraction Spot Trace Method

This study demonstrates the possibility of applying magnetic methods to pressure vessel surveillanc e at nuclear power plants. Magnetic hesteresis-minor-loop measurement and TEM observation were pref ormed on thermally aged Fe-1.0wt%Cu model alloys. Minor loop parameters decreased with increasing a ging time. The mechanism is discussed in terms of Cu precipitation behaviors of cold-rolled alloys....
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Relation between Precipitation Behaviors and Magnetic Properties in Cold-rolled FeCu Model Alloys

This study demonstrates the possibility of applying magnetic methods to pressure vessel surveillance at nuclea r power plants. Charpy impact test and magnetic hysteresis-loop measurement were preformed on Fe-1.0wt%Cu model alloys. The ductile-brittle transition temperature and the coercivity increased by cold-rolling and thermal agi ng. This correlation originates from an increase in the dislocation density and a formation of Cu precipitates....
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Magnetic Properties of FeCu Model Alloys Embrittled by Cold-rolling and Thermal Aging

Anchor bolts have been used to fix components in nuclear power plant to concrete structure. Bolt thinning is supposed to occur under long term operation of nuclear power plant in corrosive environments and requires a development of nondestructive inspection method. We have begun some internal researches since 2009 and developed a unique PA-UT method using delayed echoes. Additional works were conducted recently to show its performance such as a detectable maximum defect length and depth, which are rep...
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Development of inspection method for thinned bolts by PA-UT (2)