Jahrestagung Kerntechnik 2008 Germany
Ermüdungsanalyse des Druckhalterstutzens der VAL IN KKP2
Die Ermüdung von Materialen und Bauteilen ist ein wichtiges, sicherheitsrelevantes Thema bei zyklischen mechanischen und thermischen Belastungen und daher ein wesentlicher Bestandteil eines seriösen Alterungsmanagements. Nur durch eine Ermüdungsanalyse kann die Dauer– bzw. Betriebsfestigkeit gezeigt und nachgewiesen, und somit das Versagen der Komponente auf Grund von Ermüdung ausgeschlossen, werden.
In der vorliegenden Arbeit werden zunächst einige Grundlagen der Ermüdung beschrieben. Im Anschluss wird die Methode der „allgemeinen elastisch–plastische Ermüdungsanalyse“ aus KTA 3201.2 näher aufgezeigt und auf ein konkretes Beispiel, den Druckhalterstutzen der VAL im KKP2, angewendet. Der so ermittelte Erschöpfungsgrad wird schließlich mit den Berechnungsergebnissen anderer Methoden der Ermüdungsanalyse nach KTA 3201.2 bzw. FAMOS–Stufe 3 verglichen und bewertet.
Michael Heyder
Klaus-Dieter Tulke
SECED Conference 2019 London / United Kingdom
Increase of Seismic Resistance by Optimization of the Support Concept
Due to the Fukushima earthquake event in 2011, stress tests for all nuclear power plants were and are still carried out. The result of these tests showed, that a lot of nuclear power plants have to reassess safety-relevant buildings, components and piping systems with respect to earthquake. The first step represents the calculation of new floor response spectra with increased ground acceleration. The seismic proof of the buildings is mostly successful, but the new spectra lead to inadmissible loads on pipe supports and connections to components. For most supports a simple reinforcement, using anchors with a larger diameter, is not possible. The 20 to 30 years old support and anchor concepts do not meet the current codes or the state of the art. Therefor in most cases changes in the hardware, such as anchors and supports were installed. It has to be noticed that the old support concepts were much too rigid due to too many supports. In the progress of analyzing a lot of piping systems, the authors established that computational optimized support concepts require 60 to 70 percent less supports than the original design. Furthermore, the resulting loads on the supports and the building decreases. The new support constructions are lighter and simpler. All in all, the effort and costs are reduced. The success of the optimization concept will be demonstrated using real safety-relevant piping systems of nuclear power plants.
Stefan Riedelmeier
Holger Senechal
Dieter Kollmann
Michael Heyder
26th SMiRT 2021 Berlin / Germany
Probabilistic SSSI Analysis of Reactor and Auxiliary Building without and with Incoherency Effects
The objective of this paper is to compare and discuss selected result quantities from different seismic analyses for two existing nuclear structures: (a) single soil-structure-interaction (SSI) and (b) structure-soil-structure-interaction (SSSI) of two adjacent buildings. The motivation in this context is to examine whether a mutual impact of these buildings can occur during a seismic event. In addition, the paper also investigates the impact of ground-motion incoherency. Seismic result quantities are obtained with the semi-probabilistic approach implementing the Latin Hypercube Sampling (LHS) method to generate a near-random sample of 30 parameter values from a multidimensional distribution.
The existing ACS SASSI calculations of the two individual buildings form the basis. These are merged to a common SSSI model and 30 probabilistic calculations are performed. In a further step, these 30 calculations are repeated considering incoherency for hard rock (Abrahamson, 2007).
The results of the present case study show that the effects of a more sophisticated SSSI, compared with a classical probabilistic SSI, do not affect every seismic result quantity in the same way. The effect on the probabilistic floor response spectra (FRS) due to the mutual influence of the buildings generally leads to a larger broadening of the spectral shape around the fundamental frequency of the structure and a slight shift of the maximum spectral acceleration towards the low-frequency region. In the vertical direction, the effects of SSSI compared with single SSI in the FRS are more evident, especially for the structure with the lower structural mass. Generally, in the high-frequency region the spectral accelerations of SSSI and SSI are in good agreement. This observation also applies to the comparison of the maximum relative displacements of the two seismic analyses, even though the frequency content diverges at the levels of the nodal time histories. It could be shown that effects of incoherency on the seismic results quantities are of minor importance for the presented case study.
Holger Senechal
Philipp Linneweber
Davide Kurmann
Dan. M. Ghiocel
26th SMiRT 2021 Berlin / Germany
Seismic Reevaluation of a Fuel Storage Rack considering FSI and Friction Effects
The subject of the paper is the seismic reevaluation of a fuel storage rack considering FSI (FluidStructure Interaction) and friction effects. Due to new earthquake hazard, new acceleration-timehistories for the fuel pool were determined. A non-linear transient Finite Element Analysis is performed, at which various accelerations-time-histories are considered. Although, the new maximum accelerations are nearly 3 times higher than for the design of the fuel storage rack, for each acceleration-time-history, no collisions with the pool wall or other racks occur. The maximum relative displacements are even smaller than for the design calculation. Additionally, no severe tilting is observed and the maximum stresses are below the allowable stresses.
Stefan Riedelmeier
Holger Senechal
14th International Conference on Pressure Surges 2023 Eindhoven / Netherlands
Reduction of surge loads by the application of optimised hydraulic dampers for non-return valves in the extraction lines of steam turbines
In case of a full load rejection of a steam turbine, large pressure transients are generated. Due to the low pressure in the turbine, steam streams from auxiliary heat exchangers towards the turbine. When the non-return valves (NRVs) in the extraction lines close, high steam hammer loads are generated. This also includes a high impact when the valve disc hits the seat. In order to minimise the loads hydraulic dampers are applied. The damper geometry is optimised for short closing times and minimum impact velocities. The effectiveness of the damper is demonstrated with 1D simulations using a NRV model with and without damper.
Stefan Riedelmeier
Dieter Kollmann
27th SMiRT 2024 Yokohama / Japan
Transferring SSI into Time Domain
In nuclear engineering, ACS-SASSI is a time and cost-efficient tool for seismic calculations in the complex frequency domain. However, recent discussions and developments focus on the alternative time domain-based Domain Reduction Method (DRM). The DRM especially introduces the possibility to incorporate nonlinearities, yet albeit by an increase in computation time. Additionally, in a first step the domain reduction method has to be calibrated with a preliminary SASSI calculation.
In response to the evolving landscape, ACS-SASSI has introduced Option A-AA [Ghiocel, D. M., Saremi M. (2017)], a feature list that combines the frequency domain efficiency of ACS-SASSI with the time domain variability of ANSYS. Basically, it enables users to extract seismic calculation results and apply them as boundary conditions in ANSYS.
This paper investigates a practical implementation of this approach, wherein time history displacements extracted from an ACS-SASSI seismic calculation are employed as boundary conditions in a Finite Element Method (FEM) Solver, here ANSYS. This implementation is motivated by the desire to combine the established numerical efficiency of ACS-SASSI Soil-Structure Interaction (SSI) calculations, achieved through mode superstition in the frequency domain, with the capabilities of ANSYS in performing nonlinear calculations in the time domain. The approach retains the original size of the model and avoids the introduction of additional elements in the soil area.
A simple model is used in a first step to verify the basic idea and the implementation. The influence of the damping parameter is investigated. The gathered knowledge is then tested in a more sophisticated model. In line with the need for absolute displacements for the calculations a baseline correction is introduced and validated by the approach ACS-SASSI uses to obtain absolute displacements.
Results from the presented case study demonstrate the reproducibility of ACS-SASSI results in an ANSYS environment, validating both ACS-SASSI and the utilized baseline correction from [J. Yang, J.B. Li, G. Lin (2005)].
Philipp Linneweber
Holger Senechal
Yigit Isbiliroglu
Davide Kurmann
27th SMiRT 2024 Yokohama / Japan
On the Application of probabilistic Soil-Structure-Interaction Analysis Response Quantities for the subsequent seismic Analysis of Systems and Components
The US Standard ASCE 4-16 provides methods for performing seismic analysis to obtain seismic response quantities (e.g. displacements, accelerations, in-structure response spectra), which are used in the design or re-evaluation of safety-related structures, systems, and components (SSCs). Among others, the standard describes a probabilistic method to perform soil-structure-interaction (SSI) and systematically treat sources of uncertainties.
Our technical contribution compares the different seismic response quantities at the subsystem level – by means of a decoupled analysis – due to alternative applications of the motion quantities arising from a single probabilistic SSI analysis. The complexity of the different approaches ranges from simple response spectra analysis to a more complex time-history analysis. They are applied to three different beam models: a Control Cabinet (Model 1), a Diesel Generator (Model 2) and a simple Pipe System (Model 3).
Our study confirms that the calculation with the response spectrum method provides satisfactory, accurate and – in general – conservative results, when compared with more complex timehistory analyses. Exceptions may be observed at models, where non-linear behavior of specific elements (i.e. bearing systems) is captured by equivalent-linear approximation techniques in response spectra analyses (i.e. Diesel Generator).
Calculation techniques that use time-history analyses are more sophisticate and request more attention in the modeling set-up. This comment is particularly correct, when performing muti-model analyses with variation of the constitutive modeling parameters by means of LHS techniques.
Davide Kurmann
Holger Senechal