Shaking Table Testing of a Scaled Nuclear Power Plant Structure with Base Isolation

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Introduction
Seismic performance of a nuclear power plant (NPP) under extreme earthquakes is particularly important.Te nuclear power plant system is complicated and requires high seismic resistance.After applying isolation, the standardized design can be achieved during the seismic design of a nuclear power plant [1].Base isolation techniques are innovative strategies to protect structures from seismic and dynamic loadings [2].Low-damping rubber (LDR) and lead-rubber (LR) seismic isolation bearings have been proposed for use in safetyrelated nuclear structures in the United States to mitigate the efects of severe horizontal earthquake shaking.Tey consist of multiple rubber layers in which the top and bottom surfaces are bonded to steel plates to restrict compressive deformation [3].However, the engineering practice of isolation technology in NPP is subject to many limitations, such as the aging of rubber bearings [4].A few large light water reactors were base-isolated in France (Cruas) and South Africa (Koeberg) in the 1980s.Some engineering measures can signifcantly improve the seismic design standards, and enhance the seismic resistance, of the overall structures of nuclear power plants that have adapted isolation technology.
In recent year, seismic isolation has been investigated on the use of isolation technology in NPP to reduce seismic demands on structures, systems, and components.Te U.S. Department of Energy funded a series of studies related to the isolation of advanced reactors.Whittaker et al. [5] discussed the application of isolation technology to NPPs in the United States.Yu et al. [6] used numerical simulation methods to research nuclear facilities on sites located in moderate and high seismic hazard areas, and the results indicated that the isolation system can efectively reduce the seismic risk and capital cost of NPPs.Parsi et al. [7] discussed the pathway of seismic isolation to standardized advanced nuclear reactors.
Te Multidisciplinary Center for Earthquake Engineering Research (MCEER) team in the United States has conducted systematic research on nuclear power isolation systems.For example, Huang et al. [8][9][10] adopted a numerical simulation method to carry out a nonlinear dynamic analysis and evaluate the seismic safety of a base-isolated nuclear power plant and its important internal equipment, and the results were published in Chapter 12 of the ASCE 4-16 standards [11].Te Nuclear Regulatory Commission (NRC) of the United States has also conducted extensive research on the application of isolation technology in nuclear power plants, such as the study of a mechanical model of rubber bearings under ultimate loads [12] and the probabilistic risk analysis of nuclear facilities under base isolation [13], and the results of this research have been summarized in the ASCE 43 standards [14].
Te Korea Atomic Energy Research Institute (KAERI) and the Korea Electric Power Corporation (KEPCO) funded a fve-year research program on the isolation of nuclear power plants and obtained signifcant research results regarding the implementation measures and standards of isolation, the performance standards of pipeline structures, seismic vulnerability, and the risk assessment of isolated plants [15][16][17][18].
However, there has been little research on the base isolation of NPPs, especially considering both structure and equipment.It is obvious that base isolation can improve the seismic margin of the plant and equipment.Terefore, it is necessary to conduct shaking table tests to investigate the efects of base isolation.In this paper, a high-temperature gas-cooled reactor NPP model was made to the base-isolated and nonisolated shaking table tests.Te seismic performances of the structures were analyzed, and the infuences of base isolation on the dynamic response of the plant and its internal main equipment under both design and beyonddesign ground motion were, respectively, investigated.Te results were compared with those of experiments under nonisolated states to verify the efects of the isolators.

Shaking Table Test
2.1.Prototype Structure.China's Huaneng Shidaowan hightemperature gas-cooled reactor nuclear power plant is the frst demonstration project in the world to successfully commercialize fourth-generation nuclear power technology and comprises a reactor plant, a nuclear auxiliary plant, and a spent-fuel plant.Te structure is irregular in both horizontal and vertical arrangements.Te plane is L-shaped; the reactor is located in the corner, and the spent-fuel plant and the nuclear auxiliary plant are located on either side of the reactor.Te thickness of the reinforced concrete shear wall at the reactor and the auxiliary plant is 1000 mm, and the thickness of the shear wall at the spent-fuel plant is 1500 mm.Te thickness of the reinforced concrete protecting tube at the pressure vessel is 2400 mm.Te elevation of the foundation is −15.55 m and that at the top of the reactor plant is 44.10 m.Te elevations at the top of the spent-fuel plant and the auxiliary plant are 36.08m and 21.60 m, respectively.Te structure of NPP is illustrated in Figure 1.

Design of the Test Specimen
2.2.1.NPP Model.Te scale of the plant model was determined to be 1/20 by considering the payload and size of the shaking table.Te model was constructed of particulate concrete material, and the mix proportion of cement, yellow sand, lime, and water was 1 : 0.5 : 0.6 : 1.88 [19].Te compressive strength of the concrete cube was 8.6 MPa.Te density of the microconcrete was similar to that of the prototype concrete, so the similitude parameter of density was set as 1.Te elastic modulus similitude parameter was set as 1/4, and the scales of each physical quantity are listed in Table 1.
To ensure the accuracy of the experiments, the specimen was as least simplifed as possible.Te models of the reactor plant and the spent-fuel plant were made according to the prototypes, and the openings of the foor and stairs were retained.Te nuclear auxiliary plant model had a simplifed wall according to equivalent stifness, and its internal wall was simplifed as two crossed walls, as illustrated in Figure 2.
Te internal template was made of foam and had little efect on the strength of the structure; the internal structure of the test model was complicated with many openings and internal walls, and it was a closed structure, leading to the impossibility of dismantling the inner template.Te method of layered construction was adopted for the concrete specimen; after the completion of each layer of construction and maintenance, the next layer of the template was created.Te construction of the concrete model is illustrated in Figure 3.

Isolator.
Te raft foundation was used on the prototype nuclear power plant, and 329 lead-rubber bearings (LRBs) were designed for the isolation layer under the foundation.LRB1100, LRB900, and LRB800 were selected to efectively avoid structural torsion and meet the requirements of isolation.In the model test, the stifness similarity ratio compared to the prototype was adopted to the isolator.Considering the fabrication of isolation bearing and the connection between the bearing and shaking table, four LRB220 were applied as the isolation bearing of the model.Te basic parameters of the isolators are listed in Table 2, and the hysteresis curve of a single lead-rubber bearing is presented in Figure 4.
Te isolators were placed under the foundation slab.Te same model was tested with and without isolation bearings, it was necessary to consider the installation and removal of the isolators.Terefore, they were arranged at the corner of the foundation slab, as shown in Figure 5.To ensure that the isolators could be successfully installed and removed, round Science and Technology of Nuclear Installations steel columns were placed under the isolators to increase clearance.Te lower portions of the steel columns were connected to the shaking table by steel sheets, the upper portions were connected with the lower steel sheets of the isolators by bolts, and the upper steel sheets of the isolators were connected with the base plate of the specimen.Te assembly of the isolators is illustrated in Figure 6.
To ensure the accurate positioning and installation of the isolators, the model was made on a simulation table with the same size as that of the shaking table, and the isolators were installed in advance.Reinforcements on the steel sheets of isolation bearings were implanted into the bottom plate of the model to fx both the model and isolation bearings.Te on-site installation of the isolation bearings is depicted in Figure 7.   8.

Science and Technology of Nuclear Installations
Te method adopted to fx the equipment was the use of welded steel bars to simulate the lateral and vertical supports of the two pieces of equipment.One end of the steel bar was welded to the equipment, and the other end was embedded in the wall cylinder and foor of the pressure vessel and bound with the steel bars of the wall cylinder and foor.Finally, the concrete is poured outside the steel framework (see Figure 9).

Test Device.
Te experiments were conducted in three directions on a 5 × 5 m shaking table at the Institute of Engineering Mechanics, China Earthquake Administration.Te specifc parameters were as follows: a table size of 5 × 5 m, a maximum load of 30 t, a maximum overturning moment of 80 t•m, maximum strokes of ±500 mm along the x-and y-directions and ±200 mm along the z-direction, a maximum full-load acceleration of 2.0 g along the x-and ydirections, a no-load acceleration of 3.0 g, a maximum fullload acceleration of 2.0 g along the z-direction, a no-load acceleration of 2.0 g, maximum speeds of 1.5 m/s along the x-and y-directions and 1.2 m/s along the z-direction, and an operating frequency of 0.1-100 Hz.
Te test specimen on the shaking table is depicted in Figure 10.Dynamic acquisition systems made by Jing Ming Technology Co., Ltd (Yangzhou, China) were adopted to collect the test data.Te acquisition frequency of this test was set as 1000 Hz, and 64-channel acceleration and displacement signals and strain signals of 64 channels were collected synchronously (see Figure 11).

Measuring Point Arrangement.
Tree-component acceleration sensors (A1-A7) were used to measure the acceleration response of the structure, and Figure 12 illustrates the arrangement of the acceleration sensors.Sensor A1 was placed on the foundation foor, sensor A2 was placed at the vertical support of the pressure vessel, sensors A3-A5 were located at the foors of the key equipment, sensor A6 was positioned at the concrete roof of the top pressure vessel barrel, and sensor A7 was located on the top plate.Pull-onthe-rope displacement sensors were employed to measure the displacement of the isolators and each layer.Due to the closed structure of the nuclear power plant model, sensors A2-A10 were prearranged during the construction process.Regarding the two sensors not shown in Figure 12, sensor A11 was placed on the top of the spent-fuel plant and sensor A12 was placed on top of the auxiliary plant.
Pull-on-the-rope displacement sensors were respectively arranged along the x-and y-directions to measure the relative displacement of the isolators and the displacement of the test model.Te x-direction displacement sensors were arranged at diferent elevations of the reactor plant and the   According to the shape of the plant, the concrete at the junction of the reactor plant and the nuclear auxiliary plant was prone to damage.Terefore, six sets (three in each    Science and Technology of Nuclear Installations group) of strain gauges were placed along the height of the easily damaged position with angles of 45 °between each of the strain gauges.Te installation of the sensors is presented in Figure 13.

Selection of Ground Motions.
Tree artifcial earthquake motions and two historical earthquake records were used in the tests.Te artifcial earthquake motions were, respectively, generated by the uniform hazard spectrum (UHS), RG1.60, and SL-2 spectra.UHS was generated by a specifc site condition [20].Te SL-2 spectrum called ultimate safety earthquake spectrum was obtained from the safety evaluation report of the nuclear power plant.Te RG1.60 spectrum was obtained from Regulatory Guide1.60 [21].To explore the infuence of the uniform hazard spectrum (UHS) on the seismic and isolation performances of the structure, the historical records of Parkfeld and San Fernando were selected according to the shape of UHS.Te peak acceleration of the fve motions was adjusted to be the same as that of the SL-2 spectrum, and the response spectrum curves are illustrated in Figure 14.
Te test was carried out in two stages; the frst was the isolation test, and the isolators were then removed for the nonisolation test.Te two tests were both carried out with bidirectional and tridirectional ground motion.Te peak value increased gradually from 0.85 g to 1.7 g.After each magnitude was complete, white noise was input for frequency sweeps.According to the similitude relationships of time, the ground motions were input by a scale of 0.1.

Test Results and Analysis
3.1.Acceleration Response.Figure 15 presents the acceleration amplifcation factor of the NPP model with the peak was 0.85 g.Te amplifcation factor was about 0.1 and 0.2∼0.4 at the base and top of the model, respectively.Te results were less than the results of Tagliaferro et al. [22] and Zhu et al. [23], where amplifcation factors were about 0.3 and 0.5, respectively.It can be seen that the structure with isolators can reduce the acceleration response of the upper structure.Te acceleration of the structure with isolators was more evenly distributed in the horizontal direction, and the diference between the motions was small.However, there was an obvious amplifcation efect on the top layer, and the amplifcation efect in the y-direction was greater than that in the x-direction, and this occurred because of the ydirection, as the weak-axis direction of the structure, making the dynamic response of the structure more evident.In the horizontal direction of the structure without isolators, the diference of the amplifcation efect among the motions was large.Along the x-direction, the amplifcation of UHS and RG1.60 was particularly obvious.Tis may be the main frequency content of the motions close to the natural frequency of the model.Along the y-direction, the amplifcation factor of RG1.60 was the greatest, and those of the two historical earthquake records were the smallest.Meanwhile, the amplifcation factor of UHS and SL-2 was placed in the middle.
In the vertical direction of the structure, the vibration of the foundation slab caused by the isolation layer was large, and the acceleration changed greatly in the vertical direction of the foundation plate.In the middle of the structure, acceleration was small, and the amplifcation on the top of the structure changed was relatively obvious.Due to the small diferences between the vertical stifness of the isolation layer and the NPP model, the horizontal isolators had less efect on the vertical isolation of the structure, and the amplifcation factor of each layer in the structure was greater than that of the table.For the structure without isolators, the acceleration amplifcation factor was greater, and the amplifcation efect of the top layer was more obvious.
Figure 16 presents the respective acceleration amplifcation factors of the structure with isolators with the peak accelerations were 1.28 g and 1.70 g.With an increase in the foor height, the acceleration amplifcation factor of the structure increased.Under a peak value of 1.28 g, the amplifcation factor in the upper layer structure was within 0.3 along the x-direction, which in the middle layers was between 0.1 and 0.3 along the y-direction.At the top of the structure, the amplifcation factor was 0.47.Under a peak value of 1.7 g, the maximum amplifcation factor of the structure along the x-direction was 0.43 and that along the ydirection was less than 0.25.Terefore, the isolated structure could still maintain a good isolation efect under overdesign ground motion.
Figure 17 presents the acceleration time-history curve and the corresponding Fourier spectra of the pressure vessel support (measuring point A2) under the isolated and nonisolated actions (the peak value was 0.85 g).In the isolated state, the peak acceleration in both directions was approximately 0.1 g, which was less than the input value.As can be observed in the spectrogram, the frequency distributions of UHS in the x-and y-directions were wide, and the distribution was uniform within 10 Hz.Te SL-2 spectrum exhibited a peak in the y-direction, while the RG1.60   Science and Technology of Nuclear Installations spectrum exhibited peaks in both the x-and y-directions.
Te distributed range of each spectrum in the y-direction was wider than that in the x-direction, which was related to the strong and weak axis of the structure.In the nonisolated test, the acceleration time history of the measurement point was greater than the input value, indicating that the acceleration at point A2 was amplifed.Compared with the isolation tests, the nonisolated frequency had a relatively backward range, and the peak frequencies of the spectrogram under diferent motions had diferent ranges.Tis indicated that the responses of the structure to diferent motions were quite diferent.
To investigate the efects of the horizontal isolators on vertical motions, Figure 18 presents the acceleration response and corresponding Fourier spectrum of the pressure vessel support (measurement point A2) when the input peak value was 0.85 g.It can be concluded from the time history that, except for the San Fernando motion, the horizontal isolators had little efect on the peak acceleration of this point.Due to the existence of the isolators, the waveforms of the same ground motions were quite diferent from that in the nonisolated test, and the performance of the artifcial ground motion was more obvious.In the nonisolated test, the vibration caused by ground motions SL-2 and RG1.60 basically stopped after 3 s, while the vibration of the measuring point in the isolated test stopped after 4 s.It is evident from the spectrogram that, in the isolated tests, the spectrum of the measuring point was concentrated at about 20 Hz, whereas in the nonisolated state, the frequency range of the measuring point was between 30 and 40 Hz.Tis indicates that the horizontal isolators had an impact on the vertical motion of the structure and that the vertical stifness of the isolated layer was weaker than the overall stifness of the structure.
Figure 19 presents the three-direction acceleration timehistory curve at the middle part of the equipment (A9), and the isolation efect of the base isolation bearings on the equipment was obvious.Due to the impact of the isolators, the vibration time of the structure under isolation was longer, but the amplitude was very small, and the peak acceleration under all conditions was approximately 0.1 g.Te horizontal frequency was concentrated around 10 Hz, and the vertical frequency was around 20 Hz.In the structure without isolators, the peak accelerations all exceeded 1 g, and the peak values of the artifcial earthquake motions generated by the UHS and RG1.60 spectra were larger than those of others.Te horizontal spectra were concentrated between 10 and 30 Hz, and the vertical spectra were mostly concentrated after 30 Hz. Tis implies that the vertical stifness of the structure was large.
Figure 20 presents the acceleration amplifcation factor of measuring point A9 in the middle of the pressure vessel under the action of a seismic wave of 0.85 g.Te seismic isolators greatly reduced the peak acceleration response of the equipment.When the structure was not equipped with isolators, the amplifcation coefcients of the acceleration in the two directions were quite diferent; the amplifcation coefcients of the San Fernando and SL-2 waves along the xdirection were 1.04 and 1.1, respectively, and therefore, the amplifcation efect along the x-direction was small.In contrast, the amplifcation coefcients of the acceleration of the two waves along the y-direction were 1.27 and 2.07,  Science and Technology of Nuclear Installations respectively, and therefore, the amplifcation efect was signifcant.Te efect of the isolators on UHS was particularly obvious; the x-direction amplifed coefcient of UHS was 1.89 in the nonisolated state and 0.13 in the isolated state.

Floor Response Spectrum.
Due to the signifcance of the nuclear power equipment, the foor response spectrum at the equipment support is of importance.Terefore, the threedirection foor response spectrum was converted to the prototype according to the scale used for comparison in this Science and Technology of Nuclear Installations work, and the results are presented in Figure 21.In the horizontal direction, the frequency of the response spectrum of the isolated foor was between 0.3 and 0.7 Hz, while that of the nonisolated foor was between 1 and 5 Hz; thus, the peak frequency of the foor response spectrum was efectively reduced by the isolators.Te foor response spectrum of the structure with seismic isolators was primarily a single peak, the value of which did not exceed 0.1 g; in contrast, that of the structure without seismic isolators was primarily double peaks, and the peak values mostly exceeded 1 g.Terefore, horizontal isolation efectively reduced the peak value of the foor response spectrum.Te amplitude of the seismic wave generated by UHS in the isolated state was higher over the entire range of frequencies.In the nonisolated state, the peak frequency of the artifcial wave generated by UHS was lower and that of the Parkfeld wave was higher.Te frequency of the nuclear power equipment was primarily distributed after 7 Hz, which averted the peak of the foor response spectrum.However, the amplitude of the foor response spectrum resulting from the artifcial earthquake motions generated by UHS and RG1.60 in this frequency band was relatively large and should be fully considered when the equipment is seismically resistant.Under the condition of horizontal isolation, the vertical foor response spectra of various working conditions exhibited large peaks at 2 Hz, while that in the nonisolated state was relatively fat without a prominent peak.Base isolators could therefore signifcantly reduce the horizontal foor response spectrum of a nuclear power plant, which is conducive to the seismic safety of the internal equipment of the plant and can increase the safety reserves of the structure and equipment.Te adoption of base isolators can also greatly expand the site requirements of nuclear power plants.

Displacement Response.
Figure 22 presents the maximum displacement of the upper foor of the structure under isolation relative to the shaking table under the action of a 0.85 g seismic wave.Under the action of diferent seismic waves, the main relative displacement of the model occurred in the isolated layer and that of each layer of the 16 Science and Technology of Nuclear Installations superstructure was small.Te relative displacement of the structure along the x-direction under the artifcial wave generated by the RG1.60 spectrum had a maximum amplifcation factor of 5.07.Under the action of Parkfeld and SL-2 waves, the relative displacements of the structure along the y-direction changed little.In contrast, the relative displacements of the middle part of the structure under San Fernando and RG1.60 waves were quite diferent, and the displacement at the top of the structure in the y-direction was increased, indicating that the amplifcation efect in the y-direction was greater than that in the x-direction.
Te displacement time history of the reactor top relative to foundation under diferent seismic waves is presented in Figure 23.Te displacement of the model structure in the isolated state was small.For the structure with isolators, the peaks of the displacement in the x-and y-directions generated by the UHS seismic wave were only 0.99 mm and 1.11 mm, respectively, whereas, in the nonisolated state, the peak values of displacement were 2.17 and 1.87 mm, which were, respectively, 2.19 and 1.68 times the values in the isolated state.Tis indicates that the isolators efectively limited the relative displacement between superstructures.

Science and Technology of Nuclear Installations
Of the fve displacement time histories, the peaks caused by the San Fernando and SL-2 seismic waves were relatively small, namely, slightly greater than 0.5 mm in the isolated state, and the peaks of the other three waves were all greater than 1 mm.In addition, the diference in the peak values of the structure along the x-and y-directions was small.Tis was mainly due to the large stifness of the structure itself and the small displacement after the scale reduction of the seismic wave.
Te displacement time-history diagram of the isolation bearing was obtained (see Figure 24) by arranging displacement sensors on the shaking table and the base plate.Due to the small similar relation of the dynamic time for the structure and the large compression of the seismic waves, the  Science and Technology of Nuclear Installations displacement time-history range of the seismic waves was small.Te displacements of the isolators caused by diferent seismic waves in the two horizontal directions were diferent.Te maximum relative displacement of the isolators under the action of the artifcial wave generated by RG1.60 along the x-direction was 5.04 mm, while that generated by SL-2 was the smallest with a value of 2.07 mm.Te maximum relative displacement of the isolators along the y-direction was 2.9 mm under the action of the Parkfeld wave, and the minimum displacement peak was 2.14 mm under the action of the SL-2 artifcial wave.Te design displacement of the isolators was 100 mm, so the displacement of the isolators  Science and Technology of Nuclear Installations 21 under a peak acceleration of 0.85 g was far less than the design displacement, and the isolators were in a linear state.

Stress Analysis.
Te stress response of the structure was determined through the data processing of the strain gauges arranged in the structure.In the test for the models with seismic isolators, due to the small changes in the strain gauge data of the structure and the great dispersion, only the stress time-history diagrams at the junction of the reactor plant and the spent-fuel plant under the action of 0.85 g and 1.28 g seismic waves in the nonisolated state were investigated, as presented in Figure 25.Te stress of the concrete on the outer wall of the structure was small, and it was mainly tensile stress.

Conclusions
In this research, a 1/20 scale model of a high-temperature gas-cooled reactor nuclear power plant in China was designed and manufactured, and lead-rubber isolators were designed.Shaking table tests on a scale model with and without isolators were, respectively, carried out, and the dynamic response and the isolation efect of the structure were investigated.Te following conclusions can be drawn from the present study: (1) It was determined from the frequency-domain analysis that diferent seismic waves had diferent efects on the dynamic response of the structure and the isolation efect.For diferent types of ground motion, the isolators efectively reduced the dominate frequency of the structure, exhibited a relatively good isolation efect, and ensured the seismic capacity of the nuclear power plant under "extreme safety" ground motion.(2) Te isolators efectively weakened the peak values of the foor response spectra and reduced the range of the peak value of the frequency.Under the action of diferent seismic waves, the amplitude of the foor response spectrum corresponding to the artifcial earthquake motions generated by UHS was more prominent, which had a greater impact on the seismic resistance of the structures and equipment.(3) Under the nonisolated state, the amplifcation factor of structural acceleration under the action of artifcial earthquake motions generated by UHS increased notably with the increase in the layer height, and the peak value of the vertex displacement was large.Tese results indicate that UHS generated based on-site conditions had a great infuence on the structure and should be used as the necessary auxiliary verifcation basis for the seismic calculation of nuclear power plants.

Figure 1 :
Figure 1: NPP layout.(a) Top view.(b) Elevation view of the reactor and spent-fuel direction.(c) Elevation view of the reactor and auxiliary direction.

Figure 2 :Figure 3 :
Figure 2: Design drawing of the concrete specimen.(a) Plane; (b) sectional view of the reactor and the spent-fuel plant.

Figure 7 :
Figure 7: On-site installation of isolation bearings.(a) Isolation bearings and steel column; (b) reinforcement.

Figure 12 :
Figure 12: Sensors arrangement.(a) Acceleration sensors; (b) pull-on-the-rope displacement sensors (the number was the model elevation).

Figure 13 :
Figure 13: Sensor installation diagram.(a) Acceleration sensor of equipment outer wall; (b) strain gauges on wall.

Figure 16 :Figure 17 :
Figure 16: Acceleration amplifcation factor of isolation structure.(a) 1.28 g along the x-direction; (b) 1.28 g along the y-direction; (c) 1.70 g along the x-direction; (d) 1.70 g along the y-direction.

Figure 17 :
Figure 17: Horizontal acceleration response at pressure vessel support (A2).(a) Structure with isolations along the x-direction; (b) structure with isolations along the y-direction; (c) structure without isolations along the x-direction; (d) structure without isolations along the ydirection.

Figure 18 :Figure 19 Figure 19 :
Figure 18: Vertical acceleration response at pressure vessel support (A2).(a) Structure with isolations along the z-direction; (b) structure without isolations along the z-direction.

Figure 19 :
Figure 19: Response of acceleration in the middle of the pressure vessel (A9).(a) Structure with isolations along the x-direction; (b) structure with isolations along the y-direction; (c) structure with isolations along the z-direction; (d) structure without isolations along the xdirection; (e) structure without isolations along the y-direction; (f ) structure without isolations along the z-direction.

Figure 21 :
Figure 21: Floor response spectrum of the pressure vessel support (A2) (conversion to the prototype).(a) Structure with isolations along the x-direction; (b) structure without isolations along the x-direction; (c) structure with isolations along the y-direction; (d) structure without isolations along the y-direction; (e) structure with isolations along the z-direction; (f ) structure without isolations along the z-direction.

Figure 22 :
Figure 22: Displacement peak under isolation (relative table).(a) Structure with isolations along the x-direction; (b) structure with isolations along the y-direction.

Figure 23 :Figure 24 :
Figure 23: Time history of the top reactor plant relative to foundation.(a) Structure with isolations along the x-direction; (b) structure with isolations along the y-direction; (c) structure without isolations along the x-direction; (d) structure without isolations along the y-direction.

Table 1 :
Similarity law of the NPP model.

Table 2 :
Rubber bearing performance parameters.
2.2.3.Equipment Models.Te pressure vessel and the steam generator of the nuclear power plant were selected for investigation.Te scale of the equipment model was 1/20, which was consistent with the scale of the NPP model.Wall thickness was determined by a stifness similarity ratio.Te outer diameter of the pressure vessel model was 299 mm with a thickness of 12.3 mm, and the outer diameter of the steam generator model was 194 mm with a thickness of 6.3 mm.Te equipment installations of the pressure vessel and the steam generator are illustrated in Figure