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[en] The seismic analysis of nuclear components is characterized today by extensive engineering computer calculations in order to satisfy both the component standard codes such as ASME III as well as federal regulations and guides. The current nuclear siesmic design procedure has envolved in a fragmented fashion and continues to change its elements as improved technology leads to changing standards and guides. The dominant trend is a monotonic increase in the overall conservation with time causing a similar trend in costs of nuclear power plants. Ironically the improvements in the state of art are feeding a process which is eroding the very incentives that attracted us to nuclear power in the first place. This paper examines the cause of this process and suggests that what is needed is a realistic goal which appropriately addresses the overall uncertainty of the seismic design process. (Auth.)
[en] This paper is based on i) the recent input of the authors for the Underground Containment Sub-Section of the Seismic Task Group Report of the ASCE Committee for Nuclear Structures and Materials, and ii) parametric studies carried out by the first author on the principal undergound concepts. The extensive work on aseismic design of above-ground reactors and recent studies on missile impact effects, aircraft impact, blast effects due to chemical explosions, reactor core melt-down and tornadoes indicate the advantages of underground siting with inherent general reduction to complexity of seismic amplification and benefits of structural and biological integrity. Other advantages are possibilities of urban siting, ecological considerations, reduced effects on the landscape, ability to design three-dimensionally, separation of component facilities, support capability to equipment, reduced power transmission costs, increased number of acceptable units and power capability from a single location, and reduction of decommissioning problems. In view of the limited actual experience in the structural design of underground containments (only four European reactors), the proposals are based on a) the transposition of applicable design specifications, constraints and criteria from existing surface nuclear power plants to underground, and b) the use of many years of experience in the structural design of large underground cavities and cavity complexes for other purposes such as mining, hydropower stations etc. (Auth.)
[en] Highlights: • Conducted vector-valued PSHA for the first time in nuclear power industry. • Demonstrated the advantages of the innovative fragility method. • Demonstrated the applicability of the innovative fragility method to SMA and SPRA. - Abstract: This study presents an application of the innovative fragility method proposed in companion paper (Part I) to a horizontal heat exchanger in Darlington nuclear generating station. To illustrate the advantages of the proposed method, seismic fragility curves and High Confidence of Low Probability of Failure seismic capacity of the heat exchanger are calculated by the conventional and proposed fragility methods. The results show that, by using two ground motion parameters, the median seismic capacity of the heat exchanger has remarkable 53.9% increase, and the High Confidence of Low Probability of Failure seismic capacity is increased by 25.0%. These increases come from the reduction of conservatism of the median seismic demand by incorporating the correlation between two ground motion parameters. Although applications of components mounted on supporting structures are not presented, seismic capacities of components are expected to increase as long as the effect of structural dominant modes on seismic responses are captured by employing the proposed method. For critical structures, systems, and components that limit the plant seismic capacity, the proposed fragility method should be implemented to evaluate their seismic capacities.
[en] The heat removal alternatives are: (1) subcooled flow boiling (SFB) with water, (2) high velocity helium gas convection (HGC), and (3) liquid metal (LM) heat transfer in the presence of a transverse magnetic field (TM). Advantages and disadvantages of each technique are delineated. Each heat removal technique is examined for a case study applicable to near-term fusion components such as limiters and divertors. Comparisons are made for the selected case study involving heat removal from a 1.5 m long, 1.0 cm diameter (inside) coolant channel which is subjected to a unifirm steady-state heat flux of 0.5 kW/cm2. The results show that SFB has the greatest heat removal capability, with the lowest coolant channel wall temperature and pumping power, followed by HGC and LMTM. Critical research and development needs for each technique are also summarized. (orig./HP)
[en] New methods have been developed and applied to better quantify and increase the reliability, safety, and availability of electric power plants. Present and potential problem areas have been identified both by development of an improved computerized data base of malfunctions in nuclear power plants and by detailed metallurgical and mechanical failure analyses of selected problems. Significant advances in the accuracy and speed of structural analyses have been made through development and application of the boundary integral equation and influence function methods of stress and fracture mechanics analyses. The currently specified flaw evaluation procedures of the ASME Boiler and Pressure Vessel Code have been computerized. Results obtained from these procedures for evaluation of specific in-service inspection indications have been compared with results obtained utilizing the improved analytical methods. Mathematical methods have also been developed to describe and analyze the statistical variations in materials properties and in component loading, and uncertainties in the flaw size that might be passed by quality assurance systems. These new methods have been combined to develop accurate failure rate predictions based upon probabilistic fracture mechanics. Improved failure prevention strategies have been formulated by combining probabilistic fracture mechanics and cost optimization techniques. The approach has been demonstrated by optimizing the nondestructive inspection level with regard to both reliability and cost. (Auth.)
[en] Highlights: • A model is developed to simulate flooding due to rainfall, wave overtopping and tide. • The discharge exchange between overland flow and pipe flow is considered. • The computed discharge agrees well with the experimental results. • The numerical model is applied to a coastal nuclear power plant. - Abstract: Modelling the flooding inundation in coastal nuclear plants under external hazards is critical for risk assessments associated with nuclear safety. In this paper, a coupled model is developed to simulate the flood process in a coastal nuclear power plant under the combined action of extreme rainfall, wave overtopping, and tidal flow, based on the storm water management model, SWMM and the overland flooding model, TELEMAC-2D. Discharge exchange between the overland flow and the drainage network flow is calculated by a weir equation and an orifice equation, if the water level of a node in the underground network is lower than the elevation of ground surface corresponding to the node, while it is calculated by SWMM through a water level boundary condition. An experiment is performed to observe flow patterns between the drainage network and ground surface and to test the reliability of the numerical model. Three typical flow patterns, i.e. pressure flow, spiral flow and weir flow, are observed, and the computed flow discharge is in good agreement with experimental results. The mathematical model is then applied to a scenario analysis of flooding inundation in a nuclear power plant under the combination of wave overtopping, tidal flow and an extreme rainfall. Results show that the most dangerous scenario near nuclear power units occurs when the rainfall peak arises later than the peak of wave and tide; the wave wall, revetments and pipe system play an important role on weakening the accumulated water depth. The coupled model developed in this paper is likely to supply a useful tool for nuclear power risk assessments associated with flooding inundation, and further work should examine the validation and reliability of the model with field data.
[en] This paper concerns the comprehensive problems of underground nuclear power plants (UNPP) with regard to increased safety considerations. This constructional concept is not new, but has not yet been realized, for commercial facilities it is again a matter for discussion. Recently numerous studies (especially in the USA and the Federal Republic of Germany) have been elaborated and they come to considerably different conclusions - already concerning partial subdivisions. It is the aim of this contribution to critically analyse these studies, especially with regard to the principal question of different basis design criteria, constructional concepts and impacts as well as problems of licensibility and operation. Due to the size of these analyses and first of all due to the lack of in situ experiences it seems too early to give at this time period final (pro or con) recommendations concerning the undergrounding of nuclear facilities. (orig.)
[en] This paper was prepared for SMiRT-10, 1989, and produced to show the evolution of fusion technology in the light of interactions between the SMiRT Conferences and the fusion programmes. It describes the present status of fusion in general, and then concentrates on a description of the advances of those fusion technologies which have particular relevance to SMiRT topics. These are first wall and high heat flux components, magnets and their support structure, breeding blankets, remote maintenance, and structural materials. It turned out that fission oriented developments discussed at SMiRT Conferences are of high relevance also for fusion applications, indeed, but it also became apparent that the electro-magnetic properties of a fusion reactor make their immediate application impossible. (orig.)
[en] The simulation of the three components of seismic motion at a point are often needed in earthquake engineering risk studies. In addition, synthetic accelerograms should be compatible with all known features of the causative fault. In the paper, a procedure to simultaneously generate the two horizontal and the vertical components of the acceleration-time-history of a seismic event is proposed. Base functions, which may appear in the three components, are defined in terms of frequency, time of arrival and duration, regarded as random variables. These variables are related to the geometric fault parameters and to the velocities of wave propagation. The unknown amplitudes are finally determined by matching the resulting spectra to specified target functions. Although in its present stage of development the approach requires additional research, it is shown that satisfactory results have already been obtained. (orig.)
[en] Highlights: • Lists implementations of seismic isolation of nuclear facilities in Europe. • Compiles and distils information on seismic isolation in the modern era. • Identifies recent developments and best practice in seismic protective systems. • Identifies future opportunities and technical needs. - Abstract: Seismic isolation of nuclear power plants is in its infancy, with only a small number of applications worldwide. This outcome is due in part to the construction of only a small number of new build nuclear power plants since base-isolation technology became mainstream in the 1990s, perceived concerns regarding the long-term mechanical properties of isolation bearings, and a lack of guidance, codes and standards related to isolation of safety-related nuclear facilities. This paper charts the history of seismic isolation, identifies the research that led to the first implementation of isolation for buildings and bridges in the modern era, summarizes the first applications of the technology to nuclear facilities, and describes important research and developments, including the writing of nuclear standards, in the past 20 years. Future research and development needs are identified.