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Seismic high-frequency content loads on structures and components within nuclear facilities
KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Sweden is generally considered to be a low seismicity area, but for structures within nuclear power facilities, the safety level demand with respect to seismic events are high and thus, these structures are required to be earthquake-resistant. The seismic hazard is here primarily considered to be associated with near-field earthquakes. The nuclear power plants are further founded on hard rock and the expected ground motions are dominated by high frequencies. The design earthquake considered for the nuclear facilities has an annual probability of 10-5 events, that is, the probability of occurrence is once per 100 000 years. The focus of the study is the seismic response of large concrete structures for the nuclear power industry, with regard not only to the structure itself but also to non-structural components attached to the primary structure, and with emphasis on Swedish conditions. The aim of this licentiate thesis is to summarize and demonstrate some important aspects when the seismic load is dominated by high frequencies. Additionally, an overview of laws, regulations, codes, standards, and guidelines important for seismic analysis and design of nuclear power structures is provided.

The thesis includes two case studies investigating the effect of seismic high-frequency content loads. The first study investigates the influence of gaps in the piping supports on the response of a steel piping system subjected to a seismic load dominated by high amplitudes at high frequencies. The gaps are found in the joints of the strut supports or are gaps between the rigid box supports and the pipe. The piping system is assessed to be susceptible to high-frequency loads and is located within the reactor containment building of a nuclear power plant. The stress response of the pipe and the acceleration response of the valves are evaluated. The second study investigates the effect of fluid-structure interaction (FSI) on the response of an elevated rectangular water-containing concrete pool subjected to a seismic load with dominating low and high frequencies, respectively. The pool is located within the reactor containment building of a boiling water reactor at a nuclear power plant. The hydrodynamic pressure distribution is evaluated together with the stress distribution in the walls of the tank.

From the two case studies, it is evident that the response due to a seismic load dominated by high frequencies and low frequencies, respectively, is different. Although the seismic high-frequency load may be considered non-damaging for the structure, the effect may not be negligible for non-structural components attached to the primary structure. Including geometrical non-linear effects such as gaps may however reduce the response. It was shown that the stress response for most of the pipe elements in the first case study was reduced due to the gaps. It may also be that the inclusion of fluid-structure interaction effects changes the dynamic properties of a structural system so that it responds significantly in the high frequency range, thus making it more vulnerable to seismic loads dominated by high frequencies. In the second case study, it was shown that even for a seismic load with small amplitudes and short duration, but with dominating high-frequency content, as the Swedish 10-5 design earthquake, the increase of the dynamic response as fluid-structure interaction is accounted for is significant.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xii, 52 p.
Series
TRITA-BKN. Bulletin, ISSN 1103-4270 ; 123
Keyword [en]
Nuclear power plant, Earthquake, Seismic high frequencies, Fluid-structure interaction, Piping, Concrete, Pool
National Category
Civil Engineering
Identifiers
URN: urn:nbn:se:kth:diva-145403OAI: oai:DiVA.org:kth-145403DiVA: diva2:718075
Presentation
2014-06-09, Sal B26, Brinellvägen 23, KTH Byggvetenskap, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150519

Available from: 2014-05-19 Created: 2014-05-19 Last updated: 2014-05-19Bibliographically approved
List of papers
1. Piping system subjected to seismic hard rock high frequencies
Open this publication in new window or tab >>Piping system subjected to seismic hard rock high frequencies
2014 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 278, 302-309 p.Article in journal (Refereed) Published
Abstract [en]

This paper addresses the influence of support gaps in the analyses of a piping system when subjected to a seismic hard rock high-frequency load. The system is located within the reactor containment building of a nuclear power plant and is assessed to be susceptible to high-frequency loads. The stress response of the pipe and the acceleration response of the valves are evaluated for different support gap sizes. It is shown that the inclusion of the support gaps in the analyses reduces the stress response for almost all pipe elements. On the other hand, the acceleration response of the valves is not necessarily reduced by the consideration of the gaps.

Keyword
Piping, Hard rock high frequencies, HRHF, Seismic, Earthquake, Support gap
National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-145400 (URN)10.1016/j.nucengdes.2014.07.009 (DOI)000343839300030 ()2-s2.0-84906761669 (Scopus ID)
Note

Updated from manuscript to article.

QC 20141128

Available from: 2014-05-19 Created: 2014-05-19 Last updated: 2017-12-05Bibliographically approved
2. Stresses in water filled concrete pools within nuclear facilities subjected to seismic loads
Open this publication in new window or tab >>Stresses in water filled concrete pools within nuclear facilities subjected to seismic loads
2014 (English)In: Nordic Concrete Research, ISSN 0800-6377, no 51, 43-62 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a study on water filled pools within nuclear facilities subjected to seismic loads. The type of structure studied is an elevated rectangular concrete tank, supported by the reactor containment, which is a high cylindrical concrete structure. Seismic analysis is performed using finite element models, accounting for fluid-structure interaction (FSI) between the water and the concrete structure. The stresses in a concrete pool are calculated, also investigating the changes in stresses as additional cross-walls are added. The effects from earthquakes dominated by low and high frequencies are evaluated, representative for conditions at the West coast of North America and Northern Europe, respectively. It is shown that the coupled fluid-structure systems have more significant modes in the high frequency range compared to the models without water, that is, for frequencies at which the Northern European type earthquake has significant energy compared to the Western North American earthquake. The seismic analyses show that the relative increase of hydrodynamic pressure is higher when the outer walls of the pool are stiffened due to the inclusion of additional cross-walls. With the inclusion of additional cross-walls, modes with lower natural frequencies, although still relatively high, become more important for the hydrodynamic pressure response. Leading to a higher stress response in the outer walls of the pool for models including the additional cross-walls compared to models without cross-walls. The study indicates that the effect from fluid-structure interaction is of great importance also for seismic loads with relatively high-frequency content.

National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-145402 (URN)
Note

QC 20150211. Updated from manuscript to article in journal

Available from: 2014-05-19 Created: 2014-05-19 Last updated: 2017-12-05Bibliographically approved
3. Interaction between structure and water in seismic analyses of nuclear facilities
Open this publication in new window or tab >>Interaction between structure and water in seismic analyses of nuclear facilities
Show others...
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The objective of this paper is to evaluate different approaches to account for fluid-structure interaction (FSI) in seismic analyses of nuclear facilities. Different methods to account for FSI, from simplified to highly advanced numerical methods, are briefly reviewed and some important concepts are discussed. A benchmark example of a simple tank sloshing problem is included to evaluate the use of different FSI methods.

The main conclusion from the study is that it is of great significance to first of all include the effect of FSI. When considering the response of a tank subjected to a load of periodic nature, as in the benchmark example, the hydrodynamic effects are very important, since they increase the load effect on the structure. It is also observed that the simplified methods, in which the hydrodynamic effects are included as a mass-spring system, results in much higher stresses in the structure than if the fluid is included as continuum elements. However, the more advanced methods lead to extra computational time and also require more from the analyst. With the focus of this project being the global response of the structure, most methods describe the fluid unnecessarily complicated and phenomena such as splashing and turbulence are of little interest. The main aspects that influence the structure are the mass and inertia of the fluid along with the surface waves, the sloshing. Considering this, simplified methods such as elements with acoustic equations, and even mass-spring systems, to represent the fluid, often give results that are accurate enough.

National Category
Infrastructure Engineering
Identifiers
urn:nbn:se:kth:diva-129557 (URN)
Conference
22nd Conference on Structural Mechanics in Reactor Technology, San Francisco, California, USA, August 18-23, 2013
Note

NV 20140430

Available from: 2013-10-02 Created: 2013-10-02 Last updated: 2014-05-19Bibliographically approved

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