In 2018, Tokai Reprocessing Plan (TRP) shifted from operation stage to the decommissioning stage. In order to proceed with steady decommissioning work, TRP effort to enhance project management function. This paper describes an establishment and role of the Decommissioning Project Management Office, effectiveness of applying the project management tool and its utilization concept, and method of materialize the equipment dismantling plan....
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Project management Efforts in the decommissioning project of Tokai Reprocessing Plant

The five post-irradiation examination facilities in the Oarai Research and Development Institute of the Japan Atomic Energy Agency have been operated for over 40 years in order to investigate the irradiation performance and physicochemical characteristics of nuclear fuels and materials for fast reactors. The equipments associated with these facilities have been managed to maintain secure from the problems that occurred in the process of aging. Therefore, we established a safety assessment method for aging f...
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Development of risk assessment method to cope with an aging degradation for the facilities using nuclear material. (1) Risk assessment flow of equipments

We propose acceleration schemes for self-evolving atomistic kinetic Monte Carlo (SEAKMC), which is a promising technique for meso-timescale simulations while maintaining atomistic fidelity. The significant acceleration by a factor of up to ~100 is achieved through the acceleration schemes. Further, the accelerated SEAKMC is applied to the meso-timescale evolution of a cluster of irradiation-induced defects, and we observed the transformation process of the cluster into an energetically stable configuration ...
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Multi-timescale modeling of structural materials while maintaining atomistic fidelity

A dissolver which is a device for dissolving spent fuel is composed of one slab and two barrels (stainless steel 310s). The fuel basket (stainless steel 304L) installed in the barrel is a device for taking out of the insoluble fuel cladding from the dissolver. The inside of the dissolver become high corrosive environment because dissolution is carried out under high temperature and high acid concentration. We developed the remote handling maintenance device and carried out the periodical thickness measureme...
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Remote wall thickness measurement of the fuel basket of the dissolver

Our aim is to develop a technology to suppress the expansion of accident damage by improving the reactor structural resilience as a solution to the problem of restoring the safety function of structures after destruction, which has been an issue since the Fukushima Daiichi Nuclear Power Plant accident. In this research, the visualization method of resilience of nuclear structures was proposed in order to visualize the capacity to mitigate and to recover safety function loss by applying and improving the res...
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Visualization of resilience improvement effect by fracture control technology using resilience index

This paper covers the recent decisions made by Osaka and Saga district courts, respectively, for Nos. 3 and 4 reactors at the Ohi NPP and Nos. 3 and 4 reactors at the Genkai NPP, and discusses the disputed points in determination of design basis ground motions to be used for seismic safety checking, which are regulated in Nuclear Regulatory Authority (NRA) review guide. In the paper, the points in these decisions are clarified and the authors’ view regarding those points are presented, and finally the sugge...
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Scientific Rationality and Engineering Decision Towards Risk-informed Decision Making

An evaluation of failure probability for facilities in a real plant subjected to tornado missiles was introduced based on simple calculation. Impact speeds of the tornado missiles to the plant facility were calculated, assuming several initial locations for them and Rankine's model or Fujita's model as a tornado vortex model. Failure probability of each facility subjected to the tornado missiles was quantitatively evaluated, taking account of probabilities of tornado strike to the plant, number of missiles ...
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Failure probability of plant facilities subjected to tornado missiles - An evaluation for a real plant based on simple calculation -

The authors analyzed the outlines of the OOI NPP judgment and the Nuclear Regulation Authority's (NRA’s) explanation materials on the judgment. In addition, the outline of the related guidelines of the NRA related to both was also analyzed. Based on these analysis results, the authors identified six issues, and analyzed and examined them. We proposed improvement to the guidelines. The five issues are as follows; handling of uncertainty of seismic evaluation in NRA guides, specific examples of reflections of...
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A study on the Trial Case about OOI NPP -Proposal for Improvement of Seismic-related Guidelines in New Regulatory Guide-

We have been investigating the issues of the nuclear power plant suspension trial. Many of the recent issues are related to the validity of seismic assessments. Our study group has clarified what is the technical issue. and is working to show appropriate responses to technical issues that have not been explained in the trial. This report outlines the latest concept of seismic evaluation and clarifies the issues regarding the uncertainty of evaluation....
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A study on the Trial Case about OOI NPP －New Regulatory Guide for Seismic Evaluation of Nuclear Power Plants－

The conventional purpose in the field of structural strength has been to prevent damage to design basis events (DBE). For beyond design basis events (BDBE), it is necessary to mitigate the impact on safety on the premise that damage will occur. The authors propose a mitigation method that suppresses the consequence into a fracture mode with a large impact by reducing the load due to a fracture with a small impact on safety. We will introduce the research results for individual component, extend the applicab...
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New approach to beyond design basis events in structural strength field