Seismic isolation for nuclear power plants: Technical and non-technical aspects in decision making

Technical aspects of seismic isolation systems show merit for their use in nuclear power plants. Less quantifiable non-technical aspects must be evaluated in the decision to employ a seismic isolation system.First, non-technical aspects are discussed. An historical and applications perspective is given, and it is suggested that the number of applications of seismic isolation systems is correlated with the amount of research activity in this area. For nuclear plants, it is suggested that application of seismic isolation systems is in part related to standardized plant designs in high seismic regions. Also, for nuclear plants, it is suggested that direct capital cost, enhanced seismic safety, regulatory licensing and unknown locations of nearby active faults are all factors which can weigh in favor and/or not in favor for seismic isolation application.Second, technical aspects are discussed. The technical results show that seismic isolation reduces building response, and reduces floor response spectra/equipment response. These results combine in application to reduce seismic risk and thus enhance safety for nuclear plants.     

Seismic safety of nuclear power plants in eastern Europe

This paper summarizes the work performed by the International Atomic Energy Agency in the areas of safety review and applied research in support of programmes for the assessment and enhancement of seismic safety in Eastern Europe and in particular, WWER type nuclear power plants during the past seven years. Three major topics are discussed; engineering safety review services in relation to external events, technical guidelines for the assessment and upgrading of WWER type nuclear power plants, and the Coordinated Research Programme on "Benchmark study for the seismic analysis and testing of WWER type nuclear power plants". These topics are summarized in a way to provide an overview of the past and present safety situation in selected WWER type plants which are all located in Eastern European countries. The main conclusion of this paper is that even though there is now a thorough understanding of the seismic safety issues in these operating nuclear power plants, the implementation of seismic upgrades to structures, systems and components are lagging behind, particularly for those cases in which re-evaluation indicated the necessity to strengthen the safety related structures or install new safety systems.     

Seismic protection technology for nuclear power plants: a systematic review

Seismic protection systems (SPS) have been developed and used successfully in conventional structures, but their applications in nuclear power plants (NPPs) are scarce. However, valuable research has been conducted worldwide to include SPS in nuclear engineering design. This study aims to provide a state-of-the-art review of SPS in nuclear engineering and to answer four significant research questions: (1) why are SPS not adopted in the nuclear industry and what issues have prevented their deployment? (2) what types of SPS are being considered in nuclear engineering research? (3) what are the strategies for location of SPS within NPPs? and (4) how may SPS provide improved structural performance and safety of NPPs under seismic actions? This review is conducted following the procedures of systematic reviews, where possible.

The issues concerning the use of SPS in NPPs are identified: cost, safety, licensing and scarcity of applications. NPPs demand full structural integrity and reactor's safe shutdown during earthquake actions. Therefore, horizontal isolation may be insufficient in active seismic zones and isolation in the vertical direction may be required. Based on the results in this review, it is likely that next generation reactors in seismic zones will include state-of-the-art SPS to achieve full standardised design.     

Issues in seismic isolation of nuclear power plants

The paper covers the issues involved in considering seismic isolation for nuclear plants. The application of isolation techniques to non-nuclear installations is discussed. Its potential application to nuclear components and plants is considered and the lack of actual, experimental verification of novel techniques is portrayed. Finally a cost comparison, based on certain preliminary assumptions of isolated and non-isolated nuclear plants is made.     

Seismic re-evaluation of nuclear facilities worldwide: overview and status

Existing nuclear facilities throughout the world are being subjected to severe scrutiny of their safety in the event of an earthquake. In the United States, there have been several licensing and safety review issues for which industry and regulatory agencies have cooperated to develop rational and economically feasible criteria for resolving the issues. Currently, all operating nuclear power plants in the United States are conducting an Individual Plant Examination of External Events, including earthquakes beyond the design basis. About two-thirds of the operating plants are conducting parallel programs for verifying the seismic adequacy of equipment for the design basis earthquake. The U.S. Department of Energy is also beginning to perform detailed evaluations of their facilities, many of which had little or no seismic design. Western European countries also have been re-evaluating their older nuclear power plants for seismic events often adapting the criteria developed in the United States. With the change in the political systems in Eastern Europe, there is a strong emphasis from their Western European neighbors to evaluate and upgrade the safety of their operating nuclear power plants. Finally, nuclear facilities in Asia are also being evaluated for seismic vulnerabilities. This paper focuses on the methodologies that have been developed for re-evaluation of existing nuclear power plants and presents examples of the application of these methodologies to nuclear facilities worldwide.     

核电组织错误的表现与类型

通过访谈和事件再分析的方法，对影响核电安全的组织因素-组织错误进行探索。根据访谈记录和事件分析报告的编码，将得到的数据进行聚类分析，得到影响核电安全的5类组织因素。它们分别为：技术管理因素、非技术管理因素、信息界面、全局思想缺乏和组织计划。研究同时发现，相对于技术管理因素．非技术管理因素对系统安全的影响较大，因此，非技术培训对于系统的安全不可或缺。     

Seismic design of nuclear power plants — an assessment

This paper presents a review and evaluation of the design standards and the analytical and experimental methods used in the seismic design of nuclear power plants with emphasis on United States practice. Three major areas were investigated: (a) soils, siting, and seismic ground motion specification; (b) soil-structure interaction; and (c) the response of major nuclear power plant structures and components. The purpose of this review and evaluation program was to prepare an independent assessment of the state-of-the-art of the seismic design of nuclear power plants and to identify seismic analysis and design research areas meriting support by the various organizations comprising the ‘nuclear power industry’. Criteria used for evaluating the relative importance of alternative research areas included the potential research impact on nuclear power plant siting, design, construction, cost, safety, licensing, and regulation.Three methods were used in the study herein. The first involved the review of current literature, focusing primarily on publications dated later than 1970. This review included the results of numerous studies, of which those of Japanese origin and those presented in recent international conferences were predominant. The second method entailed a review of international experience in the dynamic testing of nuclear power plant structures and components, and related experience with scaled and model tests. Included in this experience, in addition to the questions of analysis, design, and measurement of dynamic parameters, are related efforts involving a review of responses obtained during measured earthquake response and investigations into appropriate methods for backfitting or upgrading older nuclear power plants to meet new seismic criteria.The third approach was to obtain the opinions and recommendations of technically knowledgeable individuals in the US ‘nuclear industry’; the survey results are shown in the Appendix.     

Philosophy and practice of the aseismic design of nuclear power plants — Summary of the guidelines in Japan

Aseismic design is considered to be one of the most important factors for the safety of the nuclear power plants built in zones of high seismicity such as Japan. All structures, equipment and piping are classified in accordance with the importance of their radioactive safety to the plant, and the dynamic analysis and/or factored seismic coefficient analysis are applied accordingly. Site and ground conditions, as well as seismicity, should be studied thoroughly in order to estimate the intensities of the design earthquake and the safety margin check earthquake. Dynamic analyses of buildings and structures are performed using the multi-lumped-mass-system supported by soil springs with time history analysis conceptions. This idea is also applied to the design of equipment and piping by coupled system to the major structure or by the floor response spectra criteria. Tolerances are applied to damping factors although some experiments show more realistic results. Allowable stresses of ferrous metals for equipment and piping during earthquakes are more scientifically precise.

This report summarizes a guideline for aseismic design of nuclear power plants. The guideline was prepared by the Japan Electric Association in April, 1970, after three years laborious work.

In sect. 1, the philosophy and criteria are described. All components of a plant should be classified into three classes in accordance with their contributions to reactor safeties. Design to earthquake loadings should be based on “design basis earthquake” which is decided in consideration of local seismicity.

In sect 2, site selection and review for ground are described in the sense of seismic aspects.

In sect 3, deciding the earthquake motion for design is discussed. In Japan, semi-statistical approaches are used in normal practice.

In sect. 4, design philosophy and practice of building structures and containment vessels are described. They are designed under statical seismic forces, and the design of the class “A” structures should be checked by a dynamic response technique.

In sect. 5, design philosophy and practice of piping, vesels and equipment are described. Those which belong to class “A” items should be designed in a dynamic sense. Several programs for dynamic analyses of these items are prepared. Allowable stress under earthquake conditions is discussed in relation to other codes, for example, ASME Section III.

The greater part of the philosophy and design criteria have been adopted to all nuclear power plants which have been and are currently being built in Japan.     

Seismic analysis and design of electrical cable trays and support systems

Most cable trays in nuclear power plants are classified as seismic category I components. Current safety requirements dictate that all such components be adequately designed in order to remain functional during and after the most severe possible earthquake, so that a safe and orderly plant shut-down can be ensured. The design aspects of electrical cable trays and support systems are discussed from the seismic and structural standpoint. The effects of the inherent flexibility of commonly used cable trays is considered. A procedure for the selection of trays and the design of their support structure is recommended. The dynamic characteristics of typical trays are determined analytically and also from test results. The advantages of a rigid support system are discussed. Two procedures are presented for the design of the support systems, namely, static loading and spectral analysis. The interaction between trays and supports is discussed.     

Speech of B. Estève “EPR deployment shifting into high gear”

Economics of nuclear power has been assessed by various European studies. Of particular interest in the Finnish study which supported the decision to build Finland's 5th nuclear power unit.Sensitivity studies, as well as the 2005 update of this study, demonstrate the robustness of nuclear competitiveness compared to other electricity generation means.EPR is AREVA's generation 3+ reactor: a large evolutionary power reactor with improved safety. EPR is being built at the Finnish site of Olkiluoto. It is being launched in France at Flamanville and it is licensed in the USA in view of its deployment on that market. It has also been offered to China in response to the Generation 3 international invitation to bid.     

集散控制系统在核电站保护系统中的应用

在核电站保护系统中应用基于数字化技术的安全级DCS已替代模拟技术成为主流,因为核电站的安全性要求很高,所以DCS技术的可靠性至关重要。为了确保应用DCS技术设计的可靠性,通过分析相关法规、标准的要求,总结了安全级DCS设计须进行的质量鉴定项及软件验证和确认过程,并结合当前主要应用的几个安全级DCS产品的技术特点,提出了安全级DCS设计开发中应考虑的控制器、智能IO模块、优选驱动模块以及通信等关键技术的要点。     

Seismic isolation in New Zealand

Bridges, buildings, and industrial equipment can be given increased protection from earthquake damage by limiting the earthquake attack through seismic isolation. A broad summary of the seismic responses of base-isolated structures is of considerable assistance for their preliminary design. Seismic isolation as already used in New Zealand consists of a flexible base or support combined with some form of energy-dissipating device, usually involving the hysteretic working of steel or lead. This paper presents examples of the New Zealand experience, where seismic isolation has been used for 42 bridges, 3 buildings, a tall chimney, and high-voltage capacitor banks.Additional seismic response factors, which may be important for nuclear power plants, are also discussed briefly.     

Loose-parts monitoring: Present status of the technology, its implementation in U.S. reactors, and some recommendations for achieving improved performance

At the request of the U.S. Nuclear Regulatory Commission (NRC), an assessment of the technical development status of loose-parts monitoring systems (LPMS) and their performance record to date in commercial light-water-cooled nuclear reactor plants was made during the spring of 1977, using an on-site personal interview and equipment demonstration approach. Our study revealed that while presently demonstrated LPMS technology does indeed provide a capability for detecting the presence of those relatively massive loose parts that would likely constitute a serious operational or safety hazard to the plant, it unfortunately affords little information useful to the determination of the parts' safety significance and has not yet attained the levels of sophistication and reliability ordinarily associated with safety systems. We also found a definite need for specification of the functional requirements for LPMS, in the form of a clear and comprehensive statement of NRC policy regarding the formulation and implementation of safety-oriented, yet operationally practicable, loose-parts monitoring programs for both existing and future nuclear generating stations so that overall objectives of both the utilities and the regulatory agency might be satisfied simultaneously.

While it is our best technical judgment that loose-parts monitoring programs providing reliable detection (but not characterization) capabilities could be implemented with today's technology, the path on which the nuclear utility industry should proceed in order to meet NRC expectations is not completely clear. A Regulatory Guide entitled “Loose Part Detection Program for the Primary System of Light-Water-Cooled Reactors,” soon to be issued for public comment, constitutes a first step towards satisfying this need for guidance and goal establishment.     

有关核电厂主给水系统设计的探讨

介绍了目前核电厂主给水系统隔离的几种设计方案，从事故进程和核电厂运行事件两个方面阐明了每种设计方案的优劣，得出了符合核安全原则的设计方案，这一分析对核电厂的设计和改造有一定的借鉴作用。     

浮动核电站跨界转运的安全和法律问题初步研究

浮动核电站具有模块化、多用途、可移动、运行灵活、适应性强等优势,受到了国际社会的广泛关注,具有广阔的应用前景和发展空间。然而,浮动核电站由于特殊的海外部署场景和可移动特性,不可避免地面临着跨越主权边界转运的安全和法律问题。结合浮动核电站不同的海外部署场景,重点对浮动核电站在不同部署场景下跨界转运可能面临的安全和法律问题进行梳理总结和讨论分析,并从法律、安保和应急层面提出可能的解决方案建议,对浮动核电站跨界转运相关的国际公约和规则制定具有一定参考意义。     

Nuclear Power Plant Compliance with the Principle of Power-System Indepedence from Safety Systems Operation

The purpose of this paper is to show that during the operation of safety systems at nuclear power plants the principle of independence from the power system, which is one of the basic principles inocrporated in the design of safety systems, is not satisfied and the power system, especially if it is deficient, cannot guarantee the required electricity and protection for safety systems from general failures. To satisfy the independence principle, guarantee the required quality of electricity, and protect the safety systems in nuclear power plants from general failures, it is proposed that the presently operative algorithm for starting up diesel generators be reexamined. When the safety systems at nuclear power plants perform their required functions, they should operate from autonomous diesel generators at the nuclear power plant, which are equipped with electricity quality regulators (frequency and voltage), and not from the power system. It is also suggested that the variant of the algorithm where diesel generators are started up as a preventative measure when the quality of the electricity in the power system drops below admissable limits be reexamined.     

不同法规关于核电厂设计地震动合成的技术要求比较

详细介绍了我国核电厂地震安全评价及抗震分析与设计中用到的多部国内外的法规、标准和导则的技术规定,对其技术背景和要求进行了深入比较和分析,结合工程实践给出了相关的评述和应用建议.     

New Zealand seismic base isolation concepts and their application to nuclear engineering

This paper describes recent New Zealand experience with seismic base isolation, and in particular, the distinguishing feature of the New Zealand system - that of using mechanical energy dissipators to control response.There are presently 22 structures in New Zealand which use base isolation concepts for seismic protection. Nuclear power plants are not used in New Zealand, but the principles adopted for the above buildings and bridge structures are appropriate for nuclear structures and, as shown by use of hypothetical examples, significant benefits can be achieved for these structures also. The most important is a marked reduction for the in-structure acceleration spectra with consequential implications for the enhanced safety of secondary structures and equipment.The paper also reviews the experimental and analytical studies undertaken to validate the technique and addresses the issues of reliability and cost.     

Recent tendency of the practice of soil-structure interaction design analysis in Japan and its theoretical background

Many methods of soil-structure interaction analysis for design calculations of nuclear power plants are available. The validity of methods has often been examined by their application to simulation analysis of shaker tests or seismic observations of nuclear power plant buildings, and forced vibration tests of large-scale foundation blocks. In this paper, such simulation analyses performed in Japan are reviewed and discussed for their practical applications.     

美国核电厂GALL报告解读

GALL报告是美国NRC颁布的用于指导审查核电厂执照更新申请的技术文件,它采用表单化形式,从具体的构筑物与部件层面出发,详细记录了材料、环境、老化效应与机理、老化管理大纲间逐一对应的关系。基于文献调研与分析,从开发背景、发展历史、内容框架、应用情况等方面介绍了GALL报告的基本信息,应是我国对该文件的首次全面解读,对我国建立核电厂老化管理大纲及有关核电厂延寿的核安全监管法规具有重要参考价值。