When an abnormal situation occurs in a nuclear power plant (NPP), operators must properly diagnose the event among hundreds of possible abnormal events. To do so, they monitor changes in plant ...parameters and confirm the correct abnormal operating procedure when the parameters match the entry conditions described in that procedure. In this process, operators are burdened with a lot of information. The purpose of this study is to optimize the number of main parameters to be monitored for abnormal state diagnosis in NPPs by clarifying the classification process with a deep learning model. To increase the transparency of the trained convolutional neural network model in the diagnosis of 10 different NPP states, we applied three explanation techniques: saliency mapping, guided gradient-weighted class activation mapping, and deep learning important features + Shapley values. These techniques can highlight the particular input parameters that are the most influential to the classification. Each transparency result confirmed that the parameters selected by these techniques can be a key rationale in NPP abnormal state diagnosis. By averaging the results of the two methods with the highest transparency performance, it was possible to intuitively classify all 10 NPP states with only 6 optimized monitoring parameters.
•Optimization of the number of main parameters by interpreting a deep learning model for abnormal state diagnosis in NPPs.•Transparency increase of the model by applying three explanation techniques: saliency mapping, Guided Grad-CAM, and Deep SHAP.•Successful diagnosis for 10 plant states using only 6 optimized parameters, out of 944 parameters.
Japan recently announced plans to discharge over 1.2 million tons of radioactive water from the Fukushima Daiichi Nuclear Power Plant (FDNPP) into the Pacific Ocean. The contaminated water can poses ...a threat to marine ecosystems and human health. To estimate the impact of the plan, here, we developed a three-dimensional global model to track the transport and dispersion of tritium released from the radioactive water of the FDNPP. The pollution scenarios for four release durations (1 month, 1 year, 5 years, and 10 years) were simulated. The simulation results showed that for the release in short-duration scenarios (1 month and 1 year), the peak plume with high tritium concentration shifted with the currents and finally reached the northeastern Pacific. For the long-duration scenarios (5 years and 10 years), the peak plume of the contaminated water was confined to coastal regions east of Japan.
•The spatiotemporal transport of tritium seawater released from FDNPP is simulated.•Radioactive seawater arrives at the Pacific coast of North America within 4 to 5 years.•The released tritium seawater expands into the China Seas in 2–3 years.
A contaminated zone elongated toward Futaba Town, north-northwest of the Fukushima Daiichi Nuclear Power Plant (FDNPP), contains highly radioactive particles released from reactor Unit 1. There are ...uncertainties associated with the physio-chemical properties and environmental impacts of these particles. In this study, 31 radioactive particles were isolated from surface soils collected 3.9 km north-northwest of the FDNPP. Two of these particles have the highest particle-associated 134+137Cs activity ever reported for Fukushima (6.1 × 105 and 2.5 × 106 Bq per particle after decay-correction to March 2011). The new, highly-radioactive particle labeled FTB1 is an aggregate of flaky silicate nanoparticles with an amorphous structure containing ~0.8 wt% Cs, occasionally associated with SiO2 and TiO2 inclusions. FTB1 likely originates from the reactor building, which was damaged by a H2 explosion, after adsorbing volatilized Cs. The 134+137Cs activity in the other highly radioactive particle labeled FTB26 exceeded 106 Bq. FTB26 has a glassy carbon core and a surface that is embedded with numerous micro-particles: Pb–Sn alloy, fibrous Al-silicate, Ca-carbonate or hydroxide, and quartz. The isotopic signatures of the micro-particles indicate neutron capture by B, Cs volatilization, and adsorption of natural Ba. The composition of the micro-particles on FTB26 reflects the composition of airborne particles at the moment of the H2 explosion. Owing to their large size, the health effects of the highly radioactive particles are likely limited to external radiation during static contact with skin; the highly radioactive particles are thus expected to have negligible health impacts for humans. By investigating the mobility of the highly radioactive particles, we can better understand how the radiation dose transfers through environments impacted by Unit 1. The highly radioactive particles also provide insights into the atmospheric conditions at the time of the Unit 1 explosion and the physio-chemical phenomena that occurred during reactor meltdown.
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•New type of radioactive particles discovered 3.9 km NNW of Fukushima Daiichi.•Particles consist of glassy carbon with other micro-particles embedded into the surface.•Isotopic analysis indicates volatilization of Cs before the H2 explosion.•The human health effects of the particles are expected to be minimal owing to their large size (>500 μm).
ABSTRACT
In the wake of the Fukushima Daiichi Nuclear Power Plant accident in 2011, radiation and its potential health effects have become a central concern, shaping debates on the nuclearity of ...Fukushima. However, residents living in the former evacuation zone often challenged the centrality of nuclearity to their experiences of the nuclear fallout. Taking seriously their efforts to move beyond nuclearity, this article elucidates their varied concerns for the ways in which social and ecological relations—or what I call “ecologics”—have been rearranged after the fallout in the name of their biological and economic well‐being. By challenging practices that imposed market logics of containment and equivalence on their living environment, these residents enacted alternatives cultivating socioecological relations that facilitated trust and care in their communities. I argue that residents negotiated partial boundaries not only against radiation but also against socioecological arrangements that tore apart their relationships of mutual support and further reappropriated their land for political economic projects.
要旨
東京電力福島第一原子力発電所事故後の被災地での生活は、放射性物質による
汚染と健康への影響を中心に議論されてきた。本論文では、福島県の避難指示 解除区域で行った参与観察やインタビューをもとに、帰還した住民の原発事故
後の考え方を考察した。その結果、住民の多くが、地域に降り注いだ放射性物質
に注意を向けているだけでなく、これまで暮らしてきた土地や自然、人との関わり
(ecologics)の中で現状に合ったより良い生活を模索していることが分かった。ま
た、放射性物質による汚染に着目した外部からの関わりにより、原発事故の被害
が明らかになり、責任を追求することが可能となった一方で、図らずも、開発主義
が助長され、その土地に根差した生き方が疎外されてしまう側面をも持っているこ
とを示した。公害、災害、環境破壊などの研究や政策においては、「被害」や「汚
染」を検証する科学的・医学的視点だけでなく、ecologicsの概念を導入すること
で、住民がその土地やコミュニティとの関わりを再構築する過程で、健康を守りな
がらより良い生活を実現していく方法を見出せることが期待できる。東京電力福
島第一原子力発電所事故; 帰還住民; 健康; ecologics; 地元学; コミュニティ
再生; 折り合い; 放射能汚染; 開発主義
•We present a comprehensive survey and assessment of the state of current knowledge in multi-unit probabilistic risk assessment (MUPRA).•The research and development activities of MUPRA are ...summarized, including scholarly publications, workshops, proceedings, projects, and case studies.•The MUPRA literature is synthesized and discussed in three facets: multi-unit event characterization, MUPRA methodological development, and site-based risk metrics and risk aggregation.•We discuss the research progress, challenges, and gaps for MUPRA to highlight possible research and development needs.
A growing concern regarding probabilistic risk assessments (PRA) is the impact of dependencies among reactor units co-located at a nuclear power site, especially after the March 2011 Fukushima Daiichi accident. To address these dependencies and identify the critical contributors to the entire site risk, multi-unit probabilistic risk assessment (MUPRA) has been actively developed by various research and regulatory agencies. However, possible inter-unit dependencies in MUPRA have led to some technical issues and challenges associated with the development and modeling of initiating events, accident sequences, end states, and risk metrics relevant to multi-unit sites. This paper provides a comprehensive survey and assessment of the state of current knowledge in MUPRA. The critical recent literature is synthesized and discussed, focusing on three facets: multi-unit event characterization, MUPRA methodological development, and site-based risk metrics and risk aggregation. This survey aims to identify the key issues addressed and challenges faced by the research and development activities of MUPRA, and identifies gaps and opportunities for future research and developments.
This investigation is to review advanced technologies for modeling and control of reactor cores in nuclear power plants for electricity generation. A reactor core in a nuclear power plant is the key ...part as the hot source with radioactivity nuclear fuel, which possesses security risks and economic potential. Incapacity of a nuclear power plant to carry out desired control of its core can result in either higher operating costs or a reduction in system security and reliability, and the implementation of desirable control for the core can improve security and effectiveness of the nuclear power plant. Generally speaking, the reactor core control contains the power (or coolant temperature) control and axial power difference (namely power distribution) control of the core. The core power control is to regulate the core power, and the core load following control is to regulate the core power and axial power difference simultaneously. Modeling reactor cores is the inevitable preliminary work for research of reactor core control. Over the decades, continuous work has been devoted to the research of including modeling, power and load following control for reactor cores. In this paper, the review on advanced technologies for modeling, power and load following control of reactor cores is presented. Modeling approaches for reactor cores are reviewed such as the point reactor core modeling. Power control methods for reactor cores are reviewed such as the feedback control with a state observer. Load following control techniques for reactor cores are reviewed such as Mode A, Mode G, Mode T, Mechanical Shim and advanced control methods of containing multivariable frequency control, etc. The review in this paper can contribute to comprehend the past work with respective advantages, and then exploit novel research directions for development of nuclear power plants.
In the context of the Korean Peninsula, North Gyeongsang Province stands out as a focal point for increased seismic activity, housing notable nuclear power plants (NPPs) such as Hanul and Wolseong. ...This study meticulously undertook an assessment of seismic hazard, ground response, and liquefaction potential specific to the North Gyeongsang region. These multifaceted evaluations served as foundational components intricately interwoven to construct an advanced microzonation map. The genesis of this microzonation map is tied to the Seismic Hazard Index ((Sindex), a sophisticated framework discerning sites in the southern and southeastern regions, including Pohang, Yeongdeok, Bulguksa, and Yangdong Folk Village, as predisposed to an elevated seismic threat. A noteworthy observation noted as both aforementioned NPPs fall within this identified zone of intense seismic vulnerability. The microzonation outcomes laid the groundwork for a thorough examination of the seismic vulnerability inherent to NPPs. This scrutiny, in turn, facilitated the derivation of intricate risk matrices, serving as a cornerstone in the structure of comprehensive risk assessment. Broadening the scope, a dedicated seismic risk assessment was executed specifically for the Wolseong NPP. The results of this assessment are presented artfully across three distinct post-earthquake functional scenarios, achieved through the integration of a meticulously derived site-specific intensity-response relationship for assumed damage states. Simultaneously, the exposure of health, safety, and operational risks for each damage state enriched the narrative. This study provided the foundational elements intricately woven together to craft the inaugural advanced microzonation map for North Gyeongsang in South Korea. This entire compendium serves as a first guiding, shedding light on the pathway toward the pioneering development of earthquake-resistant designs for NPPs in South Korea.
•Microzonation map by assessing seismic hazard and liquefaction potential.•Seismic risk assessment for the Wolseong Nuclear Power Plant using risk matrices.•Health, safety, and operational risks for Wolseong Nuclear Power Plant.•Functionality mappings will be useful for evaluating future Nuclear Power Plants.
The commissioning of a nuclear power plant (NPP) is a high-intensity job with severe consequences in the event of accidents. Commissioning workers are exposed to both mentally and physically ...demanding conditions, factors that may impose an elevated probability of human errors. This study aimed to explore the relationship between occupational stress (OS) and human error (HE) among commissioning workers in NPPs and verify whether anxiety mediates this relationship. A cross-sectional, descriptive and analytic study was carried out among 215 commissioning workers across three NPP commissioning sites in China, three questionnaires were used to collect data on OS, anxiety, and HE. The analyses were performed using the Process 3.0 macro in SPSS to verify the mediation effect. This study highlights the need for individual stress and anxiety management by providing managers with insight into the mechanism of anxiety in relation to OS and HE, which can effectively reduce the probability of HE and improve the safety of nuclear power systems.
Thermal desalination is an energy intensive process that satisfies its requirement from conventional fossil fuel sources. Current research efforts aim at finding alternatives for fossil fuels to ...power thermal desalination. Nuclear energy offers a feasible option for power cogeneration and production of fresh water due to the significant amount of recovered useful heat. The heat is exploited to produce steam and generate electricity on-site to power thermal and membrane desalination facilities. Large or small/medium nuclear reactors (SMR) can be used. This paper reviews the various aspects of nuclear desalination, the different nuclear reactors that have been coupled with desalination processes, and the hybrid desalination systems coupled with nuclear reactors. It also discusses the safety and public acceptance for the nuclear desalination practices as well as the latest economic studies and assessments for on –site nuclear desalination power plants. Ten main projects around the world are primarily operated as nuclear desalination plants. The major desalination processes coupled with nuclear SMRs are MSF, MED and RO. The cost of water production using nuclear desalination was estimated to range from 0.4 $/m3 to 1.8 $/m3 depending on the type of reactor and the desalination process used.
•Latest advances and technical features of nuclear desalination plants are reviewed.•Nuclear SMR reactors are promising for powering large scale desalination plants.•Hybrid nuclear systems are promising alternatives in the power and water future challenges.•Techno-economic analysis of various nuclear desalination systems provide great potential.•The safety of nuclear desalination systems can be enhanced by reinforcing engineering design.
•Developed BN approach estimates system seismic fragility accounting for dependency•BN approach performs better than Reed-McCann method estimating system fragilities•BN approach can be used in ...single-unit and multi-unit seismic PRAs
The importance of modeling dependency between seismic failures of multiple components in a nuclear power plant (NPP) probabilistic risk assessment (PRA) has been discussed since the 1980s. In NUREG/CR-7237, Budnitz et al. found the Reed-McCann method to be the most promising method for modeling dependent seismic failures in NPP PRA. However, there are issues with the Reed-McCann method's quantification of the seismic fragility of a system of multiple components. To address this issue and to facilitate an overall realism increase in modeling dependencies in seismic PRA, this paper proposes a Bayesian network (BN) approach to model dependent seismic failures. To illustrate the proposed approach, we calculate the fragility of a parallel system and a series system using the Reed-McCann method, the BN approach, the First-Order Reliability Method (FORM) and Monte Carlo simulation (MCS). Then, we compare the system fragility results from these four approaches/methods to the lower and upper bounds of the system fragility. We found that the BN approach performed better than the Reed-McCann method with respect to providing results that stay within the lower and upper bounds of the system fragility. Further, the BN approach gives similar results to FORM and MCS. This paper proposes a BN approach because, in combination with our previous work about extending a probabilistic seismic hazard analysis to account for the spatial variability of ground motion at an NPP hard-rock site, it can be used to simultaneously and realistically account for dependent seismic failures and spatial variability of ground motion in both single-unit and multi-unit seismic PRAs.
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