Study on Seismic Analysis Method of Fast Reactor Plant with Seismic Isolation System

Paper deals with the detailed seismic analysis of powerful high-speed Russian turbine of Nuclear Power Plant. Dozens of patterns of such turbine work reliably since 70’s worldwide. Until last decade only simplified structural analyses were available due to a complicated overall structure and internals of such turbines. The current analysis considers detail geometry of the turbine itself as well as vibration and seismic isolation system within turbine’s pedestal and full range of operational, accident and seismic loads. To solve the problem of the turbine seismic and dynamic qualification the following steps have been done. On the first step detailed finite element models of turbine’s high and low pressure parts and rotor system with bearings were created. Using such models corresponding simplified models were developed to be included into the coupled model of the system: “Building – Vibroisolation Pedestal – Turbine” (BVT). The second step was the analysis of that coupled system. Soil-structure interaction was considered using actual soil conditions. Three components of time history acceleration were used to define seismic excitation. As the result of BVT system analysis a full picture of time history displacements and loads were determined. At the same time a non-linear problem of rotor’s axial and radial bearings behavior and gaps in the system was solved. On the final step determined loads were applied to the detailed model of turbine for seismic and dynamic qualification of the whole structure.

Download Full-text

Core Seismic Experiment and Analysis of Hexagonal Bundle Model for Fast Reactor

Volume 8: Seismic Engineering ◽

10.1115/pvp2017-65354 ◽

2017 ◽

Author(s):

Akihisa Iwasaki ◽

Shinichiro Matsubara ◽

Tomohiko Yamamoto ◽

Seiji Kitamura ◽

Shigeki Okamura

Keyword(s):

Seismic Response ◽

Fast Reactor ◽

Impact Force ◽

Seismic Analysis ◽

Reactor Core ◽

Three Dimensions ◽

Analysis Method ◽

Core Element ◽

Core Elements ◽

Advanced Analysis

To design fast reactor (FR) core components, seismic response must be evaluated in order to ensure structural integrity. Therefore, advanced analysis method must be developed to calculate seismic response of a fast reactor core. The fast reactor core is generally made of several hundred core elements which are hexagonal flexible beams embedded at the lower support plate in hexagonal arrangement. When a big earthquake occurs, large horizontal displacement, vertical displacement (rising) and impact force of each core element may cause a trouble for control rod insertability and core element intensity. Therefore, a seismic analysis method of a fast reactor core considering three-dimensional nonlinear behavior, such as impact, fluid-structure interaction, was developed. 1/1.5 scale 37 core element mock-ups hexagonal-matrix experiment was performed to validate the core elements vibration analysis code in three dimensions (REVIAN-3D). Vertical behavior (rising displacement) and horizontal behavior (impact force) were good agreement with experiments by the validation of REVIAN-3D.

Download Full-text

Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 4 — Aging Properties of a Half Scale Thick Rubber Bearings Based on Breaking Test

Volume 8: Seismic Engineering ◽

10.1115/pvp2016-63105 ◽

2016 ◽

Author(s):

Tomoyoshi Watakabe ◽

Tomohiko Yamamoto ◽

Tsuyoshi Fukasawa ◽

Shigeki Okamura ◽

Takahiro Somaki ◽

...

Keyword(s):

Mechanical Properties ◽

Fast Reactor ◽

Seismic Isolation ◽

Hysteresis Loops ◽

Natural Period ◽

Isolation System ◽

Rubber Bearing ◽

Aging Properties ◽

Rubber Bearings ◽

Effects Of Aging

A seismic isolation system composed of a thick rubber bearing and an oil damper has been developed for Sodium-Cooled Fast Reactor. One of the advantages of the isolation system is the use of thick rubber bearings to ensure the longer vertical natural period of a plant, thereby mitigating seismic loads to mechanical components. Based on many previous studies, rubber bearing technology has progressed, but test data regarding the effect of aging is not sufficient. Moreover, there is no data on the limits of linear strain and breaking behavior for thick rubber bearings after aging. This paper focused on the aging properties of thick rubber bearings, such as basic mechanical properties and ultimate strength. An aging test of thick rubber bearings was conducted using 1/2-scale (800mm diameter) and 1/8-scale (200mm diameter) rubber bearings. Aging of the rubber bearings was reproduced using thermal degradation, in which the target of aging periods were 30 and 60 years. The hysteresis loops of the thick rubber bearings after aging were obtained through horizontal and vertical static loading tests, and the effects of aging were evaluated by comparison with the initial mechanical properties. In addition, for the purpose of further research, the effect of scale by aging was clarified to compare the mechanical properties between the 1/2-scale and 1/8-scale rubber bearings.

Download Full-text

Research and Development of Three-Dimensional Isolation System for Sodium-Cooled Fast Reactor: Part 3 — Characteristics for Elements on Basis of Half-Scale Loading Tests

Volume 8: Seismic Engineering ◽

10.1115/pvp2019-93475 ◽

2019 ◽

Author(s):

Takahiro Somaki ◽

Tsuyoshi Fukasawa ◽

Shigeki Okamura ◽

Takayuki Miyagawa ◽

Masato Uchita ◽

...

Keyword(s):

Fast Reactor ◽

Seismic Isolation ◽

Design Method ◽

Three Dimensional ◽

Isolation System ◽

Rubber Bearing ◽

In Series ◽

Loading Tests ◽

Rubber Bearings ◽

Disc Spring

Abstract The authors have been developing the three-dimensional isolation system for a Sodium-cooled Fast Reactor, and reported the details of characteristics of disc springs and vertical oil dampers on the basis of full-scale loading tests [1]. To clarify the fundamental characteristics of the three-dimensional isolation system, the loading tests using a half-scale assembled specimen have been planned, which is composed of a rubber bearing, disc spring units, the horizontal supporting functions, the smoothly sliding elements, and the rotate restraint elements. This paper describes each characteristic of the rubber bearings, disc springs and sliding element before assembling a half-scale specimen of the three-dimensional seismic isolation system by the static or dynamic loading. The applicability of design method, the scaling effect in disc springs, and the dependence on the friction coefficient of the sliding elements were investigated and confirmed. Additionally, the method of minimizing the variation of force-displacement relationships between four disc spring units, each of which has the three disc springs stacked in parallel and six disc springs stacked in series, was studied. It should be noted that this paper is in series from Part 2 [1] held on 2018PVP.

Download Full-text

Seismic Isolation of the IRIS Nuclear Plant

Volume 8: Seismic Engineering ◽

10.1115/pvp2009-78042 ◽

2009 ◽

Cited By ~ 3

Author(s):

Massimo Forni ◽

Alessandro Poggianti ◽

Fosco Bianchi ◽

Giuseppe Forasassi ◽

Rosa Lo Frano ◽

...

Keyword(s):

Seismic Isolation ◽

Seismic Analysis ◽

Wide Spectrum ◽

Seismic Excitation ◽

Fragility Analysis ◽

Pressurized Water ◽

Isolation System ◽

Order Of Magnitude ◽

Safety Features ◽

The Impact

The safety-by-design™ approach adopted for the design of the International Reactor Innovative and Secure (IRIS) resulted in the elimination by design of some of the main accident scenarios classically applicable to Pressurized Water Reactors (PWR) and to the reduction of either consequences or frequency of the remaining classical at-power accident initiators. As a result of such strategy the Core Damage Frequency (CDF) from at-power internal initiating events was reduced to the 10−8/ry order of magnitude, thus elevating CDF from external events (seismic above all) to an even more significant contributor than what currently experienced in the existing PWR fleet. The same safety-by-design™ approach was then exported from the design of the IRIS reactor and of its safety systems to the design of the IRIS Nuclear Steam Supply System (NSSS) building, with the goal of reducing the impact of seismically induced scenarios. The small footprint of the IRIS NSSS building, which includes all Engineered Safety Features (ESF), all the emergency heat sink and all the required support systems makes the idea of seismic isolation of the entire nuclear island a relatively easy and economically competitive solution. The seismically isolated IRIS NSSS building dramatically reduces the seismic excitation perceived by the reactor vessel, the containment structure and all the main IRIS ESF components, thus virtually eliminating the seismic-induced CDF. This solution is also contributing to the standardization of the IRIS plant, with a single design compatible with a variety of sites covering a wide spectrum of seismic conditions. The conceptual IRIS seismic isolation system is herein presented, along with a selection of the preliminary seismic analyses confirming the drastic reduction of the seismic excitation to the IRIS NSSS building. Along with the adoption of the seismic isolation system, a more refined approach to the computation of the fragility analysis of the components is also being developed, in order to reduce the undue conservatism historically affecting seismic analysis. The new fragility analysis methodology will be particularly focused on the analysis of the isolators themselves, which will now be the limiting components in the evaluation of the overall seismic induced CDF.

Download Full-text

Development on Rubber Bearings for Sodium-Cooled Fast Reactor: Part 2 — Fundamental Characteristics of Half-Scale Rubber Bearings Based on Static Test

Volume 8: Seismic Engineering ◽

10.1115/pvp2015-45263 ◽

2015 ◽

Cited By ~ 2

Author(s):

Tsuyoshi Fukasawa ◽

Shigeki Okamura ◽

Tomohiko Yamamoto ◽

Nobuchika Kawasaki ◽

Takahiro Somaki ◽

...

Keyword(s):

Fast Reactor ◽

Static Loading ◽

Seismic Isolation ◽

Linear Strain ◽

Isolation System ◽

Rubber Bearing ◽

Strain Limit ◽

Seismic Force ◽

Loading Tests ◽

Rubber Bearings

This paper described the results of the static loading tests using a half-scale thick rubber bearing to investigate the fundamental characteristics such as horizontal and vertical restoring force of a rubber bearing applied to a Sodium-cooled-Fast-Reactor (SFR). Since the SFR has thin-walled component structures, a seismic isolation system is employed to mitigate the seismic force. A rubber bearing with thick rubber layers is used for the seismic isolation system applied to the SFR, it was developed aiming for isolation of not only horizontal response acceleration, but also vertical response acceleration. The thick rubber bearing of 1600 mm in diameter full-scale was designed to provide about a 10000 kN rated load with a horizontal natural period of 3.4 s and a vertical one of 0.125 s. Moreover, a linear strain limit of the thick rubber bearing was designed to accept a horizontal displacement of 700 mm or more in order to ensure a double safety margin for response displacements against a design basis ground motion. The static loading tests were performed using a half-scale thick rubber bearing with a diameter of 800 mm to investigate the horizontal/vertical stiffness, damping ratio, a linear strain limit in horizontal direction and a tensile yield stress in the vertical direction. The fundamental characteristic of rubber bearings employed to the SFR and the validity of a design formula became clear through the static loading tests.

Download Full-text

Application of Seismic Isolation to the STAR-LM Reactor

10th International Conference on Nuclear Engineering, Volume 1 ◽

10.1115/icone10-22506 ◽

2002 ◽

Cited By ~ 1

Author(s):

B. Yoo ◽

R. F. Kulak

Keyword(s):

Seismic Isolation ◽

Design Research ◽

Seismic Analysis ◽

Three Dimensional ◽

Base System ◽

Two Dimensional ◽

Isolation System ◽

Fixed Base ◽

Initial Work ◽

Isolation Systems

This paper presents findings from our initial work in developing a seismic isolation system for the STAR-LM reactor design. Research and development was carried out to determine the characteristics of the isolator device. The heavy weight and small footprint presented a challenge in bearing design and bearing placement. Results are also presented from a study on the use of three-dimensional seismic isolation devices to the full-scale reactor. Both two-dimensional (i.e., one device for horizontal isolation only) and integral (i.e., one device for horizontal and vertical) concepts were explored. The seismic analysis responses of the two-dimensional and the three-dimensional isolation systems for the STAR-LM are compared with that of the conventional fixed base system. Finally, results are presented from a study on the effects of the levels of vertical and horizontal damping on the seismic response of STAR-LM.

Download Full-text

Seismic Analysis of Conventional and Isolated LNG Tanks Using Mechanical Analogs

Earthquake Spectra ◽

10.1193/1.2945293 ◽

2008 ◽

Vol 24 (3) ◽

pp. 599-616 ◽

Cited By ~ 28

Author(s):

Ioannis P. Christovasilis ◽

Andrew S. Whittaker

Keyword(s):

Seismic Isolation ◽

Seismic Analysis ◽

Numerical Models ◽

Base Shear ◽

Isolation System ◽

Analysis And Design ◽

Mechanical Analog ◽

Wave Heights ◽

Overturning Moment ◽

Lng Tank

The seismic response of a conventional and an isolated vertical, cylindrical, Liquefied Natural Gas (LNG) tank is computed using a mechanical analog and a finite element code to judge the utility of the analog for preliminary design and of the effectiveness of seismic isolation. Data reported and statistically sorted include base shear, global overturning moment, and wave height in the tank. The results obtained from the two numerical models are in good agreement and demonstrate that the mechanical analog can be used with confidence for the preliminary analysis and design of conventional and isolated LNG tanks that have similar dimensions to the sample tank of this study. The base shear and overturning moment in the seismically isolated LNG tank are 10% to 15% of the values computed for the conventional tank; the wave heights are unaffected by the introduction of a seismic isolation system.

Download Full-text

Development of seismic analysis method of fast reactor core

Transactions of the JSME (in Japanese) ◽

10.1299/transjsme.16-00093 ◽

2016 ◽

Vol 82 (839) ◽

pp. 16-00093-16-00093

Author(s):

Akihisa IWASAKI ◽

Kazuo HIROTA ◽

Masatsugu MONDE ◽

Iwao IKARIMOTO

Keyword(s):

Fast Reactor ◽

Seismic Analysis ◽

Reactor Core ◽

Analysis Method

Download Full-text

Development of a Core Seismic Analysis Method for a Fast Reactor

Volume 8: Seismic Engineering ◽

10.1115/pvp2016-63454 ◽

2016 ◽

Author(s):

Akihisa Iwasaki ◽

Kazuo Hirota ◽

Masatsugu Monde ◽

Shinichiro Matsubara ◽

Iwao Ikarimoto

Keyword(s):

Fast Reactor ◽

Seismic Analysis ◽

Reactor Core ◽

Great Earthquake ◽

Analysis Method ◽

Core Element ◽

The Core ◽

Vibration Behavior ◽

Core Elements ◽

Core Seismic Analysis

A fast reactor core consists of several hundreds of core assemblies, which are hexagonal flexible beams embedded at the lower support plate in a hexagonal arrangement, separated by small gaps, and immersed in a fluid. Core assemblies have no support for vertical fixing in order to avoid the influence of thermal expansion and swelling. These days, in Japan, it has become necessary to postulate huge earthquakes in seismic evaluations. If a great earthquake occurs, the large displacement and impact force in each core assembly may cause problems with control rod insertability and core assembly strength. So, it is necessary to grasp the vibration behavior of the core elements during an earthquake in order to appropriately design the core support structures and core elements of a fast reactor. Thus, considering horizontal and vertical forces (impact forces and fluid forces) acting on the core elements during an earthquake, a core seismic analysis method has been developed to evaluate 3D core vibration behavior considering fluid structure interaction and vertical displacements (rising). This paper summarizes the details of the core element vibration analysis code in 3D (REVIAN-3D) that has been developed.

Download Full-text