Fukushima Nuclear Accident Research Articles

Neutron-physical characteristics of UO2 and UN/U3Si2 fuels with Zr, SiC and APMT accident tolerant claddings

H2 production due to zirconium hydration was the primary source of explosion in the Fukushima Daiichi nuclear accident. To improve accident tolerance of the new reactor designs, advanced fuel and cladding materials are being extensively investigated. Neutronic evaluation at both the pin-cell and assembly levels are performed for the conventional UO2 and the candidate UN/U3Si2 fuels with traditional cladding (Zr) as well as the accident tolerant claddings (SiC and advanced powder metallurgic ferritic, APMT). The neutronic performance, plutonium inventory, cycle length, radial and pin power distribution, spectrum distribution, spatial self-shielding analysis, plutonium radial distribution, and reactivity coefficients are evaluated and analyzed. Combination of UN/U3Si2 and APMT produces 68% and 66 % more 239Pu and 135Xe than the UO2 and APMT systems. In overall, the reactivity change versus burnup and other main neutronic parameters of SiC cladding are quite similar to the current Zr cladding. Using SiC resulted in an average increase of 0.85 % in reactivity in comparison to Zr conventional cladding (without any change in the enrichment of the fuel). Compared with the traditionally used UO2 fuel assembly, the UN/U3Si2 fuel assembly exhibit a higher (0.2 % at BOC and 0.4 % at EOC) pin power peak value in an assembly, which should be a concern from safety aspects. The negativity of FTC and MTC for the proposed UN/U3Si2 is higher than that of UO2 fuel. These higher and enhanced FTC and MTC values of UN fuels mean an improved inherent safety feature of UN-like high U density fuels.

Seismic mitigation analysis of three-dimensional base-isolated nuclear structures with soil-dependent isolation system under extreme earthquakes

The Fukushima nuclear accident in March 2011 has raised more stringent requirements for the ability of nuclear power plants (NPPs) to withstand extreme disasters such as extreme earthquakes. To address this challenge, this study proposed a new hybrid multi-dimensional passive control system that combines three-dimensional base isolation and geotechnical seismic isolation. In this system, high-damper rubber bearings were employed to isolate horizontal seismic motions, whereas disc springs, accounting for frictional forces, were used to mitigate vertical seismic motions. Additionally, a geotechnical seismic isolation system arranged under the base mat was leveraged to further reduce the seismic response of the superstructure. Taking a large-scale reactor building in complex layered sites as an example, the effectiveness of the hybrid multi-dimensional isolation system was studied using a wave motion method. The research results indicate that when subjected to extreme earthquakes, hybrid multi-dimensional isolation exhibits superior isolation performance compared with three-dimensional base isolation, which can significantly reduce the three-dimensional dynamic response of nuclear structures without increasing the displacement of the isolation bearings. The proposed hybrid multi-dimensional isolation system offers an effective solution to the challenges faced by three-dimensional isolation systems, thereby enhancing the seismic resistance of nuclear structures against extreme earthquakes.

Extension of Japan’s Prefectural Emission Accounting and Enrichment of Socioeconomic Data from 1990 to 2020

With the continuous increase in carbon dioxide emissions due to human activities and the resulting severe climate issues, there is global concern about energy conservation and emission reduction. However, detailed data on energy consumption and emissions at a fine-grained scale, particularly regarding spatial dimensions and sector-specific emissions, remains insufficient and in need of refinement and timely updates. In Japan, following the Fukushima nuclear disaster, there has been a significant shift from nuclear power generation to reliance on fossil fuels across various sectors, highlighting disparities in emissions data across different regions and industries. Our work extends the emissions time series for Japan’s 47 prefectures, incorporating their socioeconomic characteristics over a broader time frame and with a more detailed sectoral classification. The emissions inventory, covering the period from 1990 to 2020, is based on the consumption of the three main fossil fuels across 32 sectors, with emissions carefully allocated for regional power generation. This dataset, presented in a unified format, is expanded to include longer time scales and more detailed socioeconomic data. It is anticipated to offer crucial insights for establishing regional emission reduction targets and identifying sectoral priorities for decarbonization.

Mass balance and economic analysis of volume reduction treatment for final disposal of radiocesium-contaminated incineration residues

This study evaluates the mass balance and economic feasibility of volume reduction treatment for radiocesium-contaminated incineration residues at the Interim Storage Facility for radioactive waste resulting from the accident at TEPCO’s Fukushima Daiichi Nuclear Power Plant accident in 2011. Operational since March 2020, the Volume Reduction Facility employs thermal melting treatment to concentrate the radiocesium, resulting in the production of 42,000 tons of highly radioactive fly ash. Technologies for further volume reduction of the fly ash have been considered as one possible treatment scenario, but there have been no studies evaluating the optimization of this process. This work focuses on evaluating the feasibility of one promising approach: washing, selective adsorption of radiocesium into an adsorbent, and subsequent adsorbent stabilization. Unit costs were set for each step of the volume reduction process, and mass balance and economic evaluation were conducted. The findings reveal the generation of 390 tons of stabilized waste requiring final disposal, along with 10,000 tons of washing residue and 320,000 tons of wastewater. The subtotal cost of fly ash volume reduction was approximately 38 billion yen, with 61% attributed to adsorption treatment. Sensitivity analysis suggested that adsorbents with an adsorption ratio above 5000 could effectively reduce costs. Notably, the cost of adsorption process significantly influences subtotal costs. These insights enhance understanding of the economic viability and efficiency of volume reduction treatment for radiocesium-contaminated incineration residues, contributing to optimized strategies and technologies for volume reduction prior to final disposal.

Survey Analysis of Potential Nuclear Safety Research of Thailand for International Research Collaborative Reinforcement in the 2020s

Abstract To achieve the long-term challenge of nuclear energy public acceptance in Thailand, nuclear safety research needed to be properly determined in both domestic and international directions, especially in the 2020s which was a period passing the Fukushima disaster over 10 years. Thailand Institute of Nuclear Technology (TINT) has studied nuclear safety research after the Fukushima accident to answer technical and social issues of nuclear power. An update of nuclear safety research from domestic experts and international surveys was needed in order to identify potential collaborative research to serve the goal of public acceptance reinforcement. The objective of this study was to survey, assess and rank the importance and knowledge level of nuclear safety research in Thailand among domestic experts in various fields. The survey was extended to collect the opinion of international participants of the ASEAN Network on Nuclear Power Safety Research (ASEAN NPSR) to analyze the similarity of the nuclear research interest for reinforcing the future collaborative project. As a result, the importance and knowledge level showed diverse important research topics with the priority of research scopes on human factor novel reactor technologies, and risk assessment. According to the ASEAN NPSR survey, the nuclear safety research of severe accidents, risk assessment, and novel reactor technologies were listed as potential collaborative projects. Also, the domestic and ASEAN NPSR survey results helped support the new collaborative research extension session in the annual ASEAN NPSR meeting to together discuss the potential nuclear safety research between members for the 2020s.

Use of Modeling as an Enabler for Cross-Topic Knowledge Management and Ontologies to Support Return of Experience and Replicability of Large Nuclear Projects

Abstract Nuclear projects often produce and consume a large amount of knowledge. Capitalization on this knowledge constitutes a significant way to increase efficiency on subsequent projects for any stakeholder. In this study, modeling is used as a main approach to support this capitalization. It constitutes, through graphical layout, a more reliable and robust way to transfer information. Moreover, the use of an interconnected set of models enables organizations to break the silos between the disciplines. The approach proposed is based on the operational implementation of existing “on-the-shelf” elements to benefit from previous implementations. The presented example illustrates how, on a nuclear project, engineering processes have been modeled from knowledge of previous projects. These components are all interconnected to constitute a self-supporting set of models as a body of knowledge. The use of models as a main base for knowledge management and transfer has been initiated due to (i) increased traceability of design decisions and impact analysis required by ever-increasing safety requirements from 1980s, 1990s, and Fukushima accident for new nuclear and (ii) gradual departures of design teams and lifetime extension of existing power plants requiring efficient ways to pass down knowledge to newcomers. Additionally, transfer of knowledge from document-centric to model-centric has enabled securitization of interfaces (between organizations, between systems) due to more numerous stakeholders and reduction of rework and site works.

Awareness of disaster preparedness between administrative staff and residents in the vicinity of the Genkai and Ikata nuclear power plants following the Fukushima Daiichi nuclear power plant disaster.

When considering disaster preparedness, one challenge is mitigating the health impacts of evacuations. Nuclear disaster preparedness has evolved based on past experiences from numerous disasters, including the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. However, there is a lack of comprehensive reporting on the awareness of administrative staff, medical personnel, and residents in the areas surrounding nuclear power plants (NPPs). This study reports on a survey aimed at gaining insights into the understanding and current state of disaster preparedness and elucidating the differences in perceptions of nuclear disaster preparedness among the relevant stakeholders surrounding NPPs. Interview surveys were conducted from 14 to 16 September 2022 in the area surrounding Kyushu Electric Power's Genkai NPP in Saga Prefecture and from 11 to 13 January 2023 in the area around Shikoku Electric Power's Ikata NPP. The surveys targeted administrative, medical, and nursing care facilities and residents. Responses from 57 participants indicated a lack of awareness of natural and nuclear disasters, challenges in evacuation planning, and a gap between nuclear disaster training and residents' understanding of evacuation protocols. This study highlights inadequacies in nuclear disaster preparedness and the need for a better understanding among residents regarding evacuation procedures. This study identified three key issues: (1) a lack of awareness about disasters, including nuclear disasters; (2) concerns about complex disasters and the difficulties in creating evacuation plans; and (3) a discrepancy between nuclear disaster training and residents' understanding of evacuation procedures. To bridge this gap, it is important to deepen residents' understanding of nuclear disasters, continuously convey the lessons learned from the FDNPP accident, and regularly reassess and update nuclear disaster preparedness strategies.

Basic Performance Evaluation of a Radiation Survey Meter That Uses a Plastic-Scintillation Sensor.

After the Fukushima nuclear power plant accident in 2011, many types of survey meters were used, including Geiger-Müller (GM) survey meters, which have long been used to measure β-rays. Recently, however, a novel radiation survey meter that uses a plastic-scintillation sensor has been developed. Although manufacturers' catalog data are available for these survey meters, there have been no user reports on performance. In addition, the performance of commercial plastic-scintillation survey meters has not been evaluated. In this study, we experimentally compared the performance of a plastic-scintillation survey meter with that of a GM survey meter. The results show that the two instruments performed very similarly in most respects. The GM survey meter exhibited count losses when the radiation count rate was high, whereas the plastic-scintillation survey meter remained accurate under such circumstances, with almost no count loss at high radiation rates. For measurements at background rates (i.e., low counting rates), the counting rates of the plastic-scintillation and GM survey meters were similar. Therefore, an advantage of plastic-scintillation survey meters is that they are less affected by count loss than GM survey meters. We conclude that the plastic-scintillation survey meter is a useful β-ray measuring/monitoring instrument.

Negative Aspects of Self-Imposed Evacuation among Mothers of Small Children Following Japan's Fukushima Daiichi Nuclear Power Station Accident.

This study clarified the negative aspects of the self-imposed evacuation of mothers of small children seeking to avoid radiation exposure from the Fukushima Daiichi Nuclear Power Station accident on 11 March 2011. We conducted semi-structured interviews with 27 mothers, employing open-ended inquiries based on an interview guide. Our analysis of their responses using the Ka-Wakita-Jiro (KJ) method categorized the results into eight distinct groups comprising 142 labels. These categories included continued anxiety about the health effects of radiation, differences in risk perception, changes in spousal relationships, the inability to make friends and find support, living as a single parent, financial concerns, the unfamiliar feel of the area to which they evacuated, and uncertainty about the future. Despite their hardships, the mothers continued their self-imposed evacuation to avoid radioactivity. Our findings underscore that their anxieties about radiation exposure persisted even after self-imposed evacuation, leading to deteriorated relationships with key individuals who would have been involved in raising their children. These results offer valuable insights into the challenges experienced by the indirect victims of the nuclear accident, such as the mothers of small children.

Deciphering decadal observation of Fukushima-derived radiocesium in the most polluted port near the Fukushima Daiichi Nuclear Power Plant: from seawater to marine fish

The biological concentration effect of radionuclides in marine fish has exacerbated public anxiety about seafood security in the context of Fukushima nuclear-contaminated water discharged into the ocean. However, the most polluted port near the Fukushima Daiichi Nuclear Power Plant (FDNPP) has seldom been investigated, especially for radioactivity in marine fish. In this study, decadal observations of radiocesium in marine fish and seawater from the most polluted port were simultaneously established after the Fukushima Nuclear Accident. We found a generally decreasing trend of historical 137Cs activity in seawater, with seasonal variations modulated by precipitation. Seasonal variations were elucidated with finer detail and divided into exponential decline in the dry season and steady variation in the wet season. A novel method was proposed to estimate the continuing source term of 137Cs derived from the FDNPP, which was 3.9 PBq in 2011 and 19.3 TBq between 2012 and 2022 on the basis of historical 137Cs. The biological concentration effect of marine fish is quantitatively emphasized according to the higher ratio of over-standards for radiocesium in marine fish relative to that in seawater. Long-term observation and analysis of radiocesium in marine fish and seawater from the most polluted port would provide insights into the scientific evaluation of the effectiveness of the decommissioning of the FDNPP in the past and share lessons on the fate of Fukushima-derived radionuclides in the future.

Radionuclides in marine sediment

Abstract Most contaminants in the sea originate from land sources. Radionuclides in sea water are transported by sea currents. Marine sediment is a physical trap for pollutants that are introduced to the environment and play an important role in radiological studies. Radionuclides from seawater bound to particulates sink to the seabed. Their resuspension causes the reintroduction of pollutants to the water column. Remobilization and horizontal/vertical transport by various processes may occur. Long-lived radionuclides become buried in sub-surface sediment. Grain size sediment classification and sediment geochemical composition all play a significant role in the development of the radionuclide content of marine sediment. Atmospheric fallout from the Chernobyl and the Fukushima accidents, atmospheric nuclear weapon testing, releases from nuclear industry plants, river runoff, and to a lesser extent directed and submarine groundwater discharges are the major sources of radionuclides in the marine environment.

Multi-unit PSA based risk evaluation framework for utilizing cross-tie systems for nuclear power plants

The Fukushima accident showed that the safety of multiple nuclear power plants (NPPs) at the same site could be jeopardized simultaneously. Since then, many studies have focused on developing strategies to prevent the spread of multi-unit accidents, with numerous countries establishing strategies to use mobile equipment. However, mobile equipment strategies are inherently accompanied by a high degree of uncertainty regarding operation success and duration because multiple organizations and personnel interact in various ways during multi-unit accident situations. Furthermore, supplementing current fixed equipment with additional mobile equipment requires extra resources. Therefore, cross-tie strategies that use currently installed fixed equipment can provide additional means to manage site risk with relatively few additional costs. This study proposes a multi-unit probabilistic safety assessment–based risk evaluation framework for utilizing cross-tie systems in NPPs and a modeling methodology to quantify the effectiveness of the cross-tie strategies. A case study was conducted to evaluate the risk reduction from using cross-tie strategies for emergency diesel generators and alternate AC diesel generators, which are power systems utilized in multi-unit loss of offsite power initiating events. It is expected that the developed framework and methodology can be utilized for other types of cross-tie strategies as well.

Study on spent fuel heatup during spent fuel pool complete loss of coolant accident

Abstract After years of operation, nuclear power plants accumulate a substantial amount of spent fuel stored in spent fuel pools. Prior to the completion of dry storage facilities, this spent fuel remains in the spent fuel pools for several decades. The progression of accidents in spent fuel pools leading to fuel damage typically spans several days or even weeks, which may lead people to overlook the importance of spent fuel pool safety. However, accidents involving spent fuel pools have a characteristic of low probability but high consequences. Their significance has been reemphasized, especially after the Fukushima accident. This study conducts an analysis of the scenario where a spent fuel pool experiences a complete loss of water. A plant equipped with a BWR-4 reactor and a MARK-I containment structure is used as the reference plant. The analysis utilizes the MAAP5 code to assess the impact of different fuel cooling times and ventilation flow rate of secondary containment building on the fuel temperature variation, considering only air circulation for cooling. Based on the analysis results, the plant utilizes the normal ventilation system of the reactor building, which can maintain the fuel temperature below 565 °C with a cooling time of 1 year. Additionally, it was found in the study that adequate ventilation flow rates and sufficient cooling time can ensure that the fuel temperature remains below 565 °C, thereby preserving fuel integrity.

The local economic impacts of mega nuclear accident: A synthetic control analysis of Fukushima

The economic impacts of mega accidents are complex, and accurately quantifying these impacts poses a formidable challenge. Traditional methods often fall short in capturing the extensive consequences of such infrequent disasters, which may go beyond immediate damages to include long-term economic disruptions and indirect costs. This study sheds a light on the economic aftermath of the Fukushima nuclear disaster. Utilizing the synthetic control method (SCM), our analysis reveals a significant, albeit temporary, downturn in the economic performance of the affected region. Specifically, the prefectural per capita income of Fukushima declines by up to 14.4% in the two years following the disaster. This decrease is linked to the composition of Fukushima's GDP and a reduction in labor supply. Our findings demonstrate the effectiveness of SCM as a potent tool for performing counterfactual analyses of mega accidents, offering essential insights into their economic impacts and the pathways to recovery.

Time in DNB experimental study on Cr coated zircaloy cladding

Since the Fukushima-Daiichi accident effort has been put in by the nuclear community to develop Accident Tolerant Fuel (ATF) cladding materials to reduce the risk of clad oxidation and, consequently, hydrogen generation and potential major accidents. Among designed materials, the use of a chromium coating on top of zirconium-alloy cladding showed reasonable results in preliminary tests, being a favorable cladding solution for Pressurized Water Reactors. This paper provides highly detailed temperature data obtained during time in departure from nucleate boiling (DNB) experiments under prototypical reactor conditions of temperature, pressure, mass flux, and heat flux profile on a Cr-coated zirconium-alloy cladded heater rod simulating the fuel pin. Data were obtained at mass fluxes from 1300 to 1700 kg/m2s, pressure of 16 MPa, and inlet temperature of 333 °C (subcooling degree of 14.4 °C). The change in dry time was obtained by increasing the spike in wall temperature necessary to shut down the power. These tests showed that increasing the spike in temperature to characterize the critical heat flux from 50 °C to 400 °C resulted in variations of the departure from nucleate boiling measured value within the uncertainty range of their measurements, hence, validating the use of a spike of 50 °C, a commonly used value in this kind of study, as an indicator of the critical heat flux. Within the dry region, the temperature was found to increase along the direction of the flow for a very short length, reaching a peak, from which it reduces linearly until the surface reaches a temperature that is no longer able to sustain a dry patch. It was noticed that the dry region can grow against the flow direction due to the cosine profile of the heat flux, and that small dryout events can occur without leading to departure from nucleate boiling, i.e., being fully suppressed. However, two consecutive events may sum up and cause the critical heat flux. Rewet time was found to increase with peak cladding temperature and decrease with mass flux. A maximum peak cladding temperature of 844 °C was found, with the surface remaining dry for approximately 14.1 s. The minimum film boiling temperature was measured during the rewet process, showing absolute values of around 580 °C, and difference between wall and inlet temperatures of about 240 °C. A post-inspection using microscope and X-ray images showed no damage to the cladding and heater structure, differently than what was noticed for the bare zircaloy in a previous study. This indicated that the presence of chromium coated cladding can improve the oxidation resistance of the cladding not only in short critical heat flux transients but also in longer events associated with major accidents, like a Loss of Coolant Accident.

Decline in the Conception Rate of Wild Japanese Monkeys after the Fukushima Daiichi Nuclear Power Plant Accident

We examined the conception rate of wild Japanese monkeys (Macaca fuscata) in Fukushima City that were exposed to radiation as a result of the Fukushima Daiichi Nuclear Power Plant accident in March 2011. The conception rate in the year of delivery from 2009 to 2022 was estimated by dissecting individuals that were euthanized by the government for population control as a countermeasure against crop damage. To evaluate the effects of exposure, the cumulative exposure dose for each individual was calculated using the concentration of radiocesium deposited in the soil at the capture site and the concentration of radiocesium in muscle estimated from the aggregated transfer factor. There were no significant differences in conception rates across all age classes over time. In terms of conception rates by age class, there was a significant decrease post-exposure compared with pre-exposure in the age class ≥ 8 years, but no significant differences in the age class 5–7 years. The non-ovulation rate did not significantly differ between the pre- and post-exposure periods for any age class. Body fat index, which can affect fertility, was compared between the pre- and post-exposure periods, and no significant differences were found in either age class. In contrast, the median total cumulative exposure (cumulative internal exposure + cumulative external exposure) was significantly higher in the age class ≥ 8 years compared with the age class 5–7 years. These results suggest that the total cumulative exposure dose may be one of the reasons for the lower conception rate in the post-exposure period among the age class ≥ 8 years.

Surrogate Model of Solved Poisson Kriging Method for Radiation Field Reconstruction

Reverse reconstruction methods for the radiation field do not require information on the radioactive source and are capable of constructing the radiation field using a small amount of monitoring data, showing huge significance for radiation protection. However, in previous studies, inverse reconstruction methods have given less consideration to variations in the time dimension. Herein, the principle of the Poisson Kriging method solved by the surrogate model has been analyzed, and the Poisson Kriging method has been applied to the inverse reconstruction of two-dimensional radiation fields at different moments. On this basis, this work also investigated the effects of the principal function and correlation coefficient model on the objective function, the results of which demonstrate that the quadratic polynomial principal function and the Gaussian model correlation coefficient have good stability and convergence. Compared with the inverse distance weighting methods and the radial basis function methods, the Poisson Kriging method has smaller errors, showing that it is more suitable for reconstructing complex radiation fields. Finally, the Poisson Kriging method was applied to the Fukushima nuclear accident radiation field calculation. The Pearson correlation coefficient of its results was r = 0.49, reflecting the validity of this method. Our work provides a calculation method for the spatial distribution and trend of the radiation field in the early stages of a nuclear accident, which is helpful for furthering radiation protection and emergency responses to nuclear accidents.

Analysis of hydrogen control in a Small Modular Reactor during TLOFW severe accident

During the Fukushima Daiichi nuclear accident in 2011, hydrogen explosions occurred in all units from Unit 1 to Unit 3. Consequently, one of the lessons learned from the Fukushima Daiichi accident is the necessity of implementing hydrogen control and mitigation strategies for most Nuclear Power Plants (NPPs). This paper focuses on the incorporation of Passive Autocatalytic Recombiners (PARs) during the design phase of a small modular Pressurized Water Reactor (SMR-PWR) project. The numerical analyses are conducted using the MELCOR v. 2.2 code. Two scenarios are compared: the Total Loss of Feed Water (TLOFW) severe accident with and without PARs. Saphiro’s diagram is utilized to investigate whether the mixture's composition (hydrogen, air, steam) is flammable for both scenarios. It has been observed that the inclusion of PARs leads to a reduction in hydrogen risk (detonative or deflagrative) as the final hydrogen concentration values fall below the flammability limit. This study is preliminary, and further research is required.

Investigation of sorption behavior of 137Cs in a river–sea system boundary area after the Fukushima Dai-ichi nuclear power plant accident

The radiocesium (137Cs) distribution between dissolved and particulate phases was examined in river water and coastal seawater as a function of the 137Cs sorption behavior on suspended particles. Dissolved 137Cs activity concentrations in the Tomioka River (salinity <0.1), about 10 km south of Fukushima Dai-ichi Nuclear Power Plant, and in coastal seawater at Tomioka fishery port (salinity >30), Fukushima Prefecture, from June 2019 to October 2021 were 3.6–20 Bq/m3 (geometric mean 11 Bq/m3) and 2.4–86 Bq/m3 (13 Bq/m3), respectively. Although the suspended particle concentration was lower in the river than in seawater, the mean 137Cs activity on suspended particles was 11,000 Bq/kg-dry in the river versus 3200 Bq/kg-dry in seawater. Proportions of ion-exchangeable, organically bound, and refractory fractions of 137Cs on suspended particles were determined by sequential extraction. The ion-exchangeable fraction accounted for 0.3–2.0% (average: 1.2%) and 0.4–1.3% (0.8%) at the river and port sites, respectively. The organically bound fraction accounted for 0.3–4.8% (1.8%) and 0.1–5.5% (2.1%) at the river and port sites, respectively. In both areas, the refractory fraction accounted for >90% of 137Cs. Therefore, the small labile 137Cs fraction on suspended particles in coastal seawater indicates that the mobility of 137Cs to marine biota is quite low. SynopsisThis study is the first to examine radiocesium sorption forms on suspended particles in coastal seawater near the Fukushima Dai-ichi Nuclear Power Plant. It suggests immobility of 137Cs in suspended particles being incorporated to marine biota.

Study on Dynamic Post-Buckling Stability of Thin-Walled Cylinders Subjected to Horizontal Vibration

Abstract As a lesson learned from the Fukushima nuclear accident, the importance of accident mitigation for beyond design basis events (BDBEs) is recognized. Excessive earthquake is a typical BDBE. During such events, the fast reactor main vessel (FRMV) is vulnerable to buckling because of its thin-walled cylindrical structure. Buckling deformation without causing immediate collapse should not be considered as a limit state in BDBEs. Instead, the objective is to achieve a stable post-buckling state. In the present study, dynamic post-buckling behavior of thin-walled cylinders under intense horizontal vibration is experimentally studied, which simulates loop-type FRMV design. Finite element method (FEM) simulation is also conducted and validated by experimental data. Based on results analysis, a global response stability after buckling is confirmed. The buckled model shows resilience to withstand catastrophic collapse even when intense excitation continues to apply. Using equivalent linear response method, dynamic mechanisms behind the stability are revealed. Due to substantial degradation of structural stiffness, the post-buckling response shifts into the out-of-phase domain such that response divergence is prevented. Meanwhile, the response is notably delayed from the input, which impedes the conversion of input energy into kinetic energy, reducing the inertial impact to the structure. These mechanisms are found to be independent of input waveforms and can be applied to a general seismic scenario. Moreover, the limit for global response stability after buckling and the effect of input frequency on the post-buckling behavior are clarified.