The New regulatory standards for nuclear power plants (NPPs) in Japan were strengthened, based on the lessons learned from the Fukushima Daiichi accident. At first glance, it seems that they mainly require improvements in the hardware of NPPs. Of course, improving safety by hardware is very important and needs to be continued. However, on the other hand, improving safety by software or human ware is also very important. Therefore, active discussions have been held on software and/or human ware in internatio...
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Can we say that the Safety Measures Taken after the Fukushima Daiichi Accident are Sufficient? (Issues Considered Important for Improving Safety)

The latest trends related to standardization and optimization of US nuclear power plant maintenance are explained as follows, including the history from the past. Standard nuclear performance model (SNPM) of power plants started in the late 1990s. Standardization of maintenance process by TNPO AP-913 "Equipment Reliability" and AP-928 "Work Management" and maintenance optimization by EPRT PM (Preventive Maintenance) Template and PMBD. Critical component reduction and Value Based Maintenance (VBM) as the lat...
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Standardization and Optimization of Maintenance at US Nuclear Power Plants

The core shroud specimens (316L stainless steel) were used to characterize the surface hardening layer introduced by machining and to evaluate the SCC susceptibility in the simulated BWR coolant environment. Based on the results obtained, the effect of the surface hardening layer on the SCC susceptibility and its mechanism are discussed. It is suggested that the wall part has clearly higher SCC susceptibility than the support ring part when compared between the as-received materials (with surface hardening ...
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Evaluation of SCC susceptibility of austenitic stainless steel with surface hardening layer in high-temperature water

While the importance of maintenance of NPP is now being well recognized, standardization on maintenance has been mainly implemented for hardware that is SSCs. The quality of the SSCs in service is ensured not only by recognition of physical characteristic of the SCCs, but also by activities of the organization and personnel for maintenance of the SSCs. This paper presents status of study on the guideline for management of repair activities, which provides a typical example of standardization on management o...
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The Study on the Guideline for Management of Repair Activities

In this study, a new signal-processing method was developed to improve the precision of locating flaw’s position using microwave NDT. The previous processing method is available only for the single-mode microwave, which causes the noise generation in the case that multi-mode microwaves propagate in a metal pipe. In order to reduce the noise, the reflections caused by the propagation of unintended modes were extracted and deducted from the original signal. The result showed the less noise intensity and highe...
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Precision Improvement of a Method to Predict the Flaw Location on an Inner Surface of a Metal Pipe Using Multiple-mode Microwaves

Electromagnetic acoustic transducer (EMAT) is suited to monitoring because of its non-contacting nature. However, a standard EMAT tends to give overestimating results because the estimated thickness is associated with the average of varying thickness over an area under the coil of EMAT. To solve this problem, Point-Focusing EMAT (PF EMAT), which concentrates ultrasonic waves at a certain point, was applied to thickness gauging. This study evaluates the focusing property of PF EMAT and its applicability to l...
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Evaluation of Point Focusing EMAT using ultrasonic wave visualization system and finite element analysis

At nuclear power plants, measures are required for emergency power supply equipment under the condition that high-concentration volcanic ash will continue to fall on the order of several g / m3 for 24 hours. A pre-filter is installed as the main countermeasure, but a lot of manpower is required in anticipation of clogging. Therefore, it is desired to develop a device with a capability to stably remove a large amount of high-concentration volcanic ash from intake air for a long period. In this work, a volcan...
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Development of large flow rate micro differential pressure intake type volcanic ash removal device capable of continuous operation

In the Fukushima Daiichi Nuclear Power Station, it is possible that fuel debris dust, scraps of reactor structural materials, etc. will be mixed into the cooling water during future fuel debris retrieval process. In that case, the thinning mechanism of the cooling system piping may be different from that under liquid single-phase flow. In this study, the final goal is to predict the thinning behavior based on the carbon steel pipe thinning mechanism under solid-liquid mixed phase flow. Then, mass transfer c...
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Piping System, Risk Management based on Wall Thinning Monitoring and Prediction ( ) Mass transfer coefficient evaluation near the wall surface under solid-liquid multiphase flow conditions

In order to clarify the solid particle behavior in a piping flow, especially to that in the vicinity of channel wall, a water-circulation loop was fabricated for the evaluation of solid particle -liquid two-phase flow. Firstly, the inflow condition upstream into an elbow was evaluated by a flow visualization experiment adopting PIV method and almost fully-developed turbulent velocity profiles have been realized by inserting perforated plates in the flow straightener tank installed upstream of the elbow. Hou...
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Piping System, Risk Management based on Wall Thinning Monitoring and Prediction (2) Visualization Experiment of Solid-Liquid Multiphase Flow in a Elbow

The electromagnetic acoustic resonance (EMAR) method with an electromagnetic acoustic transducer (EMAT) is proposed for pipe wall thinning measurement in the previous study. In this study, the Cepstrum method is proposed to process the data obtained by an EMAR method, and it is compared with the previous autocorrelation function (ACF), superposition of nth compression (SNC), multiplication of nth compression (MNC) methods. The Cepstrum method can evaluate the thickness range of the specimen under EMAT. Also...
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Piping System, Risk Management based on Wall Thinning Monitoring and Prediction Data Processing Methods of Pipe Wall Thinning Measurement by Electromagnetic Acoustic Resonance (EMAR)