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Journal Articles

Research and examination of seismic safety evaluation and function maintenance for important equipment in nuclear facilities

Furuya, Osamu*; Fujita, Satoshi*; Muta, Hitoshi*; Otori, Yasuki*; Itoi, Tatsuya*; Okamura, Shigeki*; Minagawa, Keisuke*; Nakamura, Izumi*; Fujimoto, Shigeru*; Otani, Akihito*; et al.

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 6 Pages, 2021/07

Since the Fukushima accident, with the higher safety requirements of nuclear facilities in Japan, suppliers, manufacturers and academic societies have been actively considering the reconstruction of the safety of nuclear facilities from various perspectives. The Nuclear Regulation Authority has formulated new regulatory standards and is in operation. The new regulatory standards are based on defense in depth, and have significantly raised the levels of natural hazards and have requested to strengthen the countermeasures from the perspective of preventing the simultaneous loss of safety functions due to common factors. Facilities for dealing with specific serious accidents are required to have robustness to ensure functions against earthquakes that exceed the design standards to a certain extent. In addition, since the probabilistic risk assessment (PRA) and the safety margin evaluation are performed to include the range beyond the design assumption in the safety improvement evaluation, it is very important to extent the special knowledge in the strength of important equipment for seismic safety. This paper summarizes the research and examination results of specialized knowledge on the concept of maintaining the functions of important seismic facilities and the damage index to be considered by severe earthquakes. In the other paper, the study on reliability of seismic capacity analysis for important equipment in nuclear facilities will be reported.

Journal Articles

Development of level-1 PSA method applicable to Japan Sodium-cooled Fast Reactor

Kurisaka, Kenichi; Sakai, Takaaki; Yamano, Hidemasa; Fujita, Satoshi*; Minagawa, Keisuke*; Yamaguchi, Akira*; Takata, Takashi*

Nuclear Engineering and Design, 269, p.268 - 280, 2014/04

 Times Cited Count:5 Percentile:43.74(Nuclear Science & Technology)

This paper describes a study to develop the level-1 probabilistic safety assessment (PSA) method that is applicable to the Japan Sodium-cooled Fast Reactor (JSFR). This study aims to provide a new evaluation method of (1) passive safety architectures related to internal events and (2) an advanced seismic isolation system related to a seismic event as a representative external event in Japan. Regarding the internal events evaluation, a quantitative analysis on the frequency of the core damage caused by reactor shutdown failure was conducted. A failure in passive reactor shutdown was taken into account in the event tree model. The failure rate of sodium-cooled fast reactor (SFR) specific components was evaluated based on the operating experience in existing SFRs by applying the Hierarchical Bayesian Method, which can consider a plant-to-plant variability. By conducting an uncertainty analysis, it was found that the assumption about the correlation of the probability parameters between the main and backup reactor shutdown systems is sensitive to the mean value of the frequency of the core damage caused by reactor shutdown failure. As for the seismic event evaluation, seismic response analysis and sensitivity analysis of a seismic isolation system were carried out. As a result, it was confirmed that nonlinear properties of rubber bearings have influence on response of the building and inner equipment.

Journal Articles

Behavior of the energy of vibration failure experiment by using a 2-mass system model

Seki, Hajime*; Fujita, Satoshi*; Minagawa, Keisuke*; Kitamura, Seiji; Watakabe, Tomoyoshi

Dynamics and Design Conference 2013 (D&D 2013) Koen Rombunshu (USB Flash Drive), 8 Pages, 2013/08

When we study the behavior of the pipes during an earthquake, the most important damage doesn't come from the maximal load by itself, but from the accumulation of the fatigue damage caused by the repetition of the cyclic load. Therefore, from the point of view of seismic design evaluation methods, techniques that can quantitatively assess the probability of fatigue failure of mechanical structures are needed. The relationship between failure and energy is evaluated, and examined by focusing on the Energy Balance Method said to be effective as an earthquake response analysis technique in the present. This study carries out failure experiments using 2-mass system model based on Energy Balance Method. Furthermore, we focus on the strain from the vicinity of broken point as local response.

Journal Articles

Analytical study on seismic response of isolated structure considering nonlinear properties of rubber bearing

Minagawa, Keisuke*; Fujita, Satoshi*; Yamaguchi, Akira*; Takata, Takashi*; Kurisaka, Kenichi

Nihon Kikai Gakkai Rombunshu, C, 79(804), p.2684 - 2693, 2013/08

Journal Articles

Seismic response analysis of isolation system considering coupling effect between horizontal and vertical deformation of rubber bearings

Minagawa, Keisuke*; Fujita, Satoshi*; Yamaguchi, Akira*; Takata, Takashi*; Kurisaka, Kenichi

Transactions of 22nd International Conference on Structural Mechanics in Reactor Technology (SMiRT-22) (CD-ROM), 9 Pages, 2013/08

Application of seismic isolation system using rubber bearings into nuclear power plants has been expected. Generally, rubber bearings have nonlinear characteristics in case of large deformation. In addition, the horizontal nonlinear characteristics depend on vertical load. Therefore it is important to consider these nonlinearity and coupling effect. Authors have already reported results of seismic response analysis of an isolated reactor building considering the nonlinearity of rubber bearings. In this paper, seismic response analysis considering the coupling effect of horizontal and vertical deformation of rubber bearings is investigated by numerical simulations. The summaries of the simulations are as follows. The vertical motion affected the start displacement of hardening, so that the coupling effect decreased isolation performance of horizontal direction. However the isolation system is still effective to reduce seismic force even if the nonlinearity and the coupling effect were considered.

Journal Articles

Development of level-1 PSA method for sodium-cooled fast reactor

Kurisaka, Kenichi; Sakai, Takaaki; Yamano, Hidemasa; Nishino, Hiroyuki; Fujita, Satoshi*; Minagawa, Keisuke*; Yamaguchi, Akira*; Takata, Takashi*

Proceedings of Probabilistic Safety Assessment and Management Topical Conference; In light of the Fukushima Dai-ichi Accident (PSAM 2013) (USB Flash Drive), 10 Pages, 2013/04

This study includes a level-1 PSA related to internal events and a seismic event as a representative external event for Japan sodium-cooled fast reactors with passive safety features and a seismic isolation system. For the internal events, it is necessary to evaluate the passive safety features, of which reliability depends on uncertainties of related physical phenomena. In order to consider the reliability of the passive natural circulation, accident sequences leading to core damage result from natural circulation failure were developed, and the annual frequency of the accident sequences was evaluated for the PSA method study. In respects of seismic event, we developed response analysis method considering the coupling effect of horizontal and vertical shaking on the horizontal seismic isolation characteristics, and developed a fragility evaluation model including the effect of seismic non-linearly for the seismic isolation system.

Journal Articles

Seismic response of isolated nuclear power plant considering nonlinear restoring force characteristics of rubber bearings

Fujita, Satoshi*; Minagawa, Keisuke*; Yamaguchi, Akira*; Takata, Takashi*; Kurisaka, Kenichi

Proceedings of 15th World Conference on Earthquake Engineering (WCEE-15) (USB Flash Drive), 9 Pages, 2012/09

Journal Articles

Development of level-1 PSA method applicable to Japan sodium-cooled fast reactor, 1; Research plan and internal event evaluation related to reactor shutdown failure

Kurisaka, Kenichi; Sakai, Takaaki; Yamano, Hidemasa; Fujita, Satoshi*; Minagawa, Keisuke*; Yamaguchi, Akira*; Takata, Takashi*

Transactions of 21st International Conference on Structural Mechanics in Reactor Technology (SMiRT-21) (CD-ROM), 8 Pages, 2011/11

This paper describes a study to develop the level-1 probabilistic safety assessment (PSA) method that is applicable to the Japan Sodium-cooled Fast Reactor (JSFR). This study has been started since August 2010 and aims to provide a new evaluation method of (1) passive safety architectures related to internal events and (2) an advanced seismic isolation system related to a seismic event as a representative external event in Japan. However, after the nuclear accident at Fukushima Dai-ichi Nuclear Power Plant on March 11 2011, the research-period was shortened from four to two years by political reason, and only a limited scope of the research subject will be performed in the two years. Regarding the internal events evaluation, a quantitative analysis on the frequency of the core damage caused by reactor shutdown failure was conducted. A failure in passive reactor shutdown was taken into account in the event tree model. The failure rate of sodium-cooled fast reactor (SFR) specific components was evaluated based on the operating experience in existing SFRs by applying the Hierarchical Bayesian Method, which can consider a plant-to-plant variability. By conducting an uncertainty analysis, it was found that the assumption about the correlation of the probability parameters between the main and backup reactor shutdown systems is sensitive to the mean value of the frequency of the core damage caused by reactor shutdown failure.

Journal Articles

Development of level-1 PSA method applicable to Japan sodium-cooled fast reactor, 2; Seismic response analysis considering characteristics of the advanced seismic isolation system

Minagawa, Keisuke*; Fujita, Satoshi*; Yamaguchi, Akira*; Takata, Takashi*; Kurisaka, Kenichi

Transactions of 21st International Conference on Structural Mechanics in Reactor Technology (SMiRT-21) (CD-ROM), 8 Pages, 2011/11

We carried out fundamental seismic response analysis that considers both horizontal and vertical nonlinearity of rubber bearing. In this study, the horizontal nonlinearity was considered independently from vertical response in order to construct accurate nonlinear analytical model of rubber bearing. That is to say, the coupling effect was not considered. Both horizontal and vertical nonlinear characteristics of rubber bearing were explained by multi-linear model. Analytical model of building for horizontal direction consists of 3 mass points that is the isolation layer, lower and upper layer of the building. It for vertical direction consists of 4 mass points, that is ground layer, the isolation layer, lower and upper layer of the building. At first, nonlinear seismic response analysis was executed in order to confirm nonlinear characteristics of analytical model of rubber bearing. Influence of nonlinearity of rubber bearing upon response of building was also investigated by the analysis. After that, sensitivity analysis was executed. Parameters of rubber bearing, oil damper and building were fluctuated, and influence of variation of these parameters upon response of building was investigated.

Journal Articles

Study on seismic response of isolated nuclear power plant based on probabilistic assessment, 1; Modeling considering nonlinearity of rubber bearings

Fujita, Satoshi*; Minagawa, Keisuke*; Yamaguchi, Akira*; Takata, Takashi*; Kurisaka, Kenichi

Dynamics and Design Conference 2011 (D&D 2011) Koen Rombunshu (CD-ROM), 7 Pages, 2011/09

The response to the input more than assumption is requested in the seismic response analysis used for the Probabilistic Safety Assessment. Rubber bearings used as the isolation system cause nonlinearity in the restoring force when the input more than assumption is received. However, the seismic response analysis method for considering nonlinear of the rubber bearing has not been established. Therefore, this study aims at the development of the seismic response analysis method of an isolated nuclear power plant based on the probabilistic safety assessment. In this paper, isolated building model that the nonlinearity of the rubber bearing is considered is made, the seismic response analysis is done, and the influence that it gives respond was verified. As a result, in horizontal direction, it was confirmed that the increasing tendency of the response acceleration was remarkable because of the increase of the earthquake size. In vertical direction, it was confirmed that the increasing tendency of the response displacement was remarkable.

Journal Articles

Study on seismic response of isolated nuclear power plant based on probabilistic assessment, 2; Sensitivity analysis on parameter of isolated nuclear power plant model

Minagawa, Keisuke*; Fujita, Satoshi*; Yamaguchi, Akira*; Takata, Takashi*; Kurisaka, Kenichi

Dynamics and Design Conference 2011 (D&D 2011) Koen Rombunshu (CD-ROM), 10 Pages, 2011/09

It is necessary to consider the change in the response by the difference of the physical properties value and the material characterizations of an isolation layer and a building in Probabilistic Safety Assessment. Then, in this paper, the sensitivity analysis of the parameter of the isolated building model that the nonlinearity of rubber bearing is considered used for the seismic response analysis done by the first report is done. The response when an arbitrary parameter is set to the upper limit or the lower limit by the logarithm standard deviation is compared with the response when all parameters are set to the median, and the error ratio is examined as sensitivity. As a result, in the earthquake size in which the nonlinearity is caused, the difference of the parameter of the building, the isolation layer such as the displacement that hardening begins and the load that softening begins of the rubber bearing shows high sensitivity, and it has a bad influence for the building response. Therefore, it was confirmed that the parameter that showed high sensitivity had to examine the difference in detail.

Journal Articles

Fundamental study on shape dependency of input energy for failure

Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki

Proceedings of 2009 ASME Pressure Vessels and Piping Division Conference (PVP 2009) (CD-ROM), 7 Pages, 2009/07

Journal Articles

Dynamic strength evaluation of straight pipe using energy balance method

Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki

Proceedings of 2008 ASME Pressure Vessels and Piping Division Conference (PVP 2008) (CD-ROM), 6 Pages, 2008/08

Journal Articles

Fracture prediction of piping using energy balance method

Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki

Transactions of 19th International Conference on Structural Mechanics in Reactor Technology (SMiRT-19) (CD-ROM), 7 Pages, 2007/08

Although mechanical structures have sufficient seismic safety margin, comprehending the ultimate strength is very important in order to improve the seismic safety reliability in unexpected severe earthquake. The energy balance is adequate to investigate the influence of cumulative load because it includes cumulative information. The vibration experiments using simple single-degree-of-freedom experimental model are carried out in order to confirm a calculation technique of energy and to investigate behavior of energy in elasto-plastic region. The vibration failure experiments that lead experimental model to fatigue failure are carried out in order to investigate the relationship between input energy and fatigue failure.

Journal Articles

Study on dynamic strength evaluation method of mechanical members based on energy balance

Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki

Proceedings of 2007 ASME Pressure Vessels and Piping Division Conference/8th International Conference on Creep and Fatigue at Elevated Temperatures (PVP 2007/CREEP-8) (CD-ROM), 6 Pages, 2007/07

This paper describes the dynamic strength evaluation of piping installed in nuclear power plants from a viewpoint of energy balance. In this study, ultimate strength of a simple single degree of freedom model is investigated from a viewpoint of energy balance equation that is one of valid methods for structural calculation. The investigation is implemented by forced vibration experiment. In the experiment, colored random wave having predominant frequency similar to natural frequency of the experimental model is input. Stainless steel and carbon steel are selected as material of experimental model. As a result of the experiment, it is confirmed that input energy for fracture increase with an increase of time for fracture. In other words, more input energy for fracture is needed in case of small input level. Additionally it is confirmed that input energy for fracture depend on the material.

Oral presentation

Study on dynamic strength evaluation method of piping systems, 1; Behavior of energy at elasto-plastic region

Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki

no journal, , 

In this research, The strength evaluation technique for paying attention into energy is examined for the equipments and the piping in the nuclear power plant during the earthquakes. In this report, the shaking table tests for the one mass model were conducted, and the behavior of energy was examined.

Oral presentation

Study on dynamic strength evaluation method of piping systems, 2; Example application to evaluation of piping elbow tests

Kitamura, Seiji; Okamura, Shigeki; Minagawa, Keisuke*; Fujita, Satoshi*

no journal, , 

The dynamic strength evaluation method that pays attention into energy is examined so that the equipment and piping in the nuclear power plant may clarify the condition to plasticity/destruction. It reports on the result of applying the idea of the energy evaluation to the dynamic excitation examination result of the Elbo element.

Oral presentation

Study on dynamic strength evaluation method of piping systems, 3; Behavior of energy at vibration fatigue breakdown

Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki

no journal, , 

It proposes a dynamic strength evaluation method of the piping systems, and the effectiveness of this method is examined. In this report, the behavior of the energy at the vibration fatigue failure by the one mass model was examined.

Oral presentation

Study on dynamic strength evaluation method of piping systems, 4; Relationship between energy and fracture on vibration fatigue fracture

Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki

no journal, , 

Mechanical structures installed in nuclear power plants such as piping are usually designed staically in elastic region. Although these mechanical structures have sufficient seismic safety margin, comprehending the ultimate strength is very important in order to improve of the seismic safety reliability in unexpected severe earthquake. The ultimate strength of piping is investigated from the viewpoint of energy balance method in this research. Vibration fracture experiments that lead one mass model to fatigue fracture are carried out in order to investigate the relationship between input energy and fracture.

Oral presentation

Study on dynaminc strength evaluation method of piping systems, 5; Application of energy balance equation to straight pipe model

Minagawa, Keisuke*; Fujita, Satoshi*; Kitamura, Seiji; Okamura, Shigeki

no journal, , 

In this research, it has aimed to develop the dynamic strength evaluation of the piping system by using the energy balance equation. The relation between the fatigue failure and energy by the vibration has been investigated by having used one mass model up to now. The vibration experiment by the straight piping model was executed and it reports on the result of the arrangement by energy.

29 (Records 1-20 displayed on this page)