Seismic Design Basis

Seismic design basis for the reactor vessel (including attachments, pressure boundary, and CRD and internals). 

Seismic design basis for the main coolant loop piping and pumps, and for typical category I piping, e.g., the auxiliary feedwater line. 

For nuclear power plants built according to earlier standards and for many of die WWER NPPs, die seismic design basis (i.e. seismic input parameters) is generally not in accordance witii current international practice. The as-built status of NPP structures, components and distribution systems have to be checked against the site specific seismic loads in the event of an earthquake of the design basis level. 

The Temelin NPP had an original seismic design basis value 0.06 g. In order to follow IAEA recommendation 1, the recommendation of the IAEA expert mission to Temelin in 1992, and the IAEA Safety Guides 50-SG-Sl and 50-SG-D15, the safe shutdown earthquake (SL2) and operational basis earthquake (SLI) values have been re-evaluated as follows ... 

A.309. Information that is used to establish the seismic design basis, such as earthquake return frequency and ground motion, shall be presented in this section, as well as information for ... 

Design basis events are postulated in each safety analysis report for external events such as earthquakes, tornados, floods, accidents at nearby industrial facilities, etc. The approach to designing against many potential ex-plant (external) accident initiators can be illustrated by considering the seismic design basis. 

Seismic zone basis must be specified for structural design. Soil data is important, especially for cases where extensive use of foundation piling is required with major cost impact. Availability of aggregate or natural pond stabilization materials near the site will not be considered for early cost estimates, but can be kept in mind for future planning if the project is given the green light. 

The Reactor System, including the core and its support components, and portions of the the neutron control systems must perform, with a high degree of confidence, lOCFRlOO-related radionuclide control functions under design basis conditions. Since the seismically induced forces on these components from an QBE or an SSE could potentially affect the safe operation and safe shutdown of the reactor, the criteria and methods described below are aimed at providing assurance that these components can be adequately designed to assure their continued functionality during and after these events. 

Design Basis is the design inputs, the design constraints, and the design analysis and calculations, It includes topical areas such as seismic qualification, fire protections, and safe shutdown, It encompasses consideration of such factors as plant availability, plant efficiency, costs, and maintainability, and that subset that relates to safety and the authorization basis. 

AH structures and equipment required to fulfil level FI safety functions shall be seismic category I. Such structures and equipment shall be qualified to withstand the effects of a design basis earthquake (DBF) (i.e. to remain structurally intact, leaktight in the case of fluid retaining equipment, and functionally operable to the extent required by its safety role). 

Gonceptual design report has been prepared except chapters on I G, plant layout and civil structures. Various plant design data viz. plant life, design basis events, safety classification, seismic categorisation, applicable design and construction codes, computer codes, material data and site data have been compiled. 

The supports are designed to accept normal, seismic, and Branch Line Pipe Break loads. Irradiation effects are addressed in the fracture mechanics analysis of columns, in combination with the design basis loads, to ensure that structural integrity will be maintained. 

Various safety related systems and safety support systems are designed to appropriate safety class specifications depending on the functional importance. In addition, systems are seismically designed for two different intensities of earthquake. The operating basis earthquake (ODE) represents the intensity of earthquake for which the systems are designed to remain functional during and after the event. The safe shutdown earthquake (SSE) considers the maximum earthquake potential of the site and only those systems which are required to ... 

The requirement of compressed air for safety related systems on a continuous basis is supplied by a separate set of dedicated compressors located in seismically designed buildings. The distribution is also done through, separate, dedicated, seismically designed piping system. 

HMS components in containment are capable of sustaining normal operation and seismic loads. The HMS is not required to function in a design basis accident and is not safety-grade. However the system is expected to mitigate the effects of a degraded core accident and is designed to withstand the appropriate... 

After the Three Mile Island Unit 2 accident, the NRC reviewed auxiliary feedwater system designs with respect to timely initiation, as described in 10 CFR 50, Appendix A, (GDC 20), (Reference 3). Upon completion of the review, the NRC determined that new guidance identified in NUREG-0737, (Reference 4) was necessary in order to assure a timely start of the AFW system after a design basis event (e.g., loss of main feedwater). Among this new guidance was automatic system initiation, environmental and seismic equipment qualification, and single failure criterion. 

The structures of Buildings 105-Is 105P are not susceptible to ilure during design basis earthquakes, tornadoes, and high winds, however, during seismic and shipping cask drop... 

Regardless of the exposure to seismic hazard, an SI 2 design basis earthquakes should be adopted for every nuclear power plant for the design of safety classified items. The minimum level should correspond to a peak ground acceleration of O.lg (zero period of the design response spectrum), to be considered at the free field. A unified, site compatible spectrum should be associated with this peak ground acceleration value. In this case SL-1 may be assumed to be coincident with SL-2. 

For the seismic design of SSCs, external events such as floods or fires assumed to occur at the site as a consequence of an earthquake should be taken into account. They should be defined on the basis of probabilistic considerations. These loadings as a consequence of an earthquake should be combined with either SL-1 or SL-2 loadings, with due account taken of event timing and duration. 

Structural joints, particularly in reinforced concrete structures, should be designed to provide a high ductility and a capability to accommodate large displacements and rotations this provision should be consistent with the acceptance criteria specified in the seismic categorization, but is intended also to take into account considerations relating to beyond design basis events. 

The floor response spectra, typically used as the seismic input for equipment, should be obtained on the basis of the structural response to the design basis ground motion. Natural or artificial time history motions that can be shown to generate response spectra at least as conservative as the response spectra for the design basis ground motion should be used as input to the structural analysis. 

In a test, the item should be subjected to conservatively derived test conditions in order to produce effects at least as severe as those of the design basis seismic event concurrently with other applicable operating or design conditions. Deviations should be evaluated on a case by case basis. 

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