NPSAG workshop, Stockholm, March 13, slides total 1

Transcription

1 How Fortum has developed the seismic PSA in the years Doc. Pentti Varpasuo, Aalto University/ Fortum Power and Heat Oy Finland Lecture held at Agenda for NPSAG Seismic PSA Workshop 13/14 March 2013 Radisson Blu Arlandia Hotel, Sweden NPSAG workshop, Stockholm, March 13, slides total 1

2 1. INTRODUCTION For the present the origin of tectonic earthquakes has partly remained unknown. The most extensively favored theory maintains that tectonic earthquakes are caused by slips along geologic faults. NPSAG workshop, Stockholm, March 13, slides total 2

3 However, it is quite clear that theory is incomplete to describe all the tectonic earthquakes. So it can be supposed that different earthquakes are caused by more than one mechanism. NPSAG workshop, Stockholm, March 13, slides total 3

4 Because there is the lack of the information of the geological processes which give rise to earthquakes, a probabilistic approach is widely accepted as one possible way to estimate future earthquakes. NPSAG workshop, Stockholm, March 13, slides total 4

5 A seismic design regionalization map must therefore be presented in the sense of greater or lesser risk, and one acceptable basis for maps of earthquake hazard is the mean return period with which earthquake events may be associated. NPSAG workshop, Stockholm, March 13, slides total 5

6 The results of this lecture has been developed with the aid of computer program EQRISK prepared by Robin McGuire [1] and with the aid of SEISRISK III [2]. The theory of these codes isare based on studies of Cornell and Merz [3], [4]. These programs have been widely used in seismic hazard analyses [5], [6], [7]. NPSAG workshop, Stockholm, March 13, slides total 6

7 The Fennoscandian recorded history of earthquakes dates back to the late 15th century. With Fennoscandia in this study is meant the region of Nordic countries, which include Finland, Sweden, Norway, Baltic countries and Carelian Republic in Russian Federation. NPSAG workshop, Stockholm, March 13, slides total 7

8 Instrumental recording started in 1956 in Finnish territory. During the instrumental period there have been on an average five events yearly, the magnitudes of which are in the order of magnitude of three in Richter magnitude scale. NPSAG workshop, Stockholm, March 13, slides total 8

9 A magnitude of 4.9 relates to the largest earthquake in the vicinity of Finland that occurred off the Estonian coast about 120 km from Helsinki in On the whole, ten Finnish earthquakes with greater magnitude than 4.5 are known. None of these had an epicenter in Southern Finland. It can be said that Finland is one of the quietest seismic regions in the world. NPSAG workshop, Stockholm, March 13, slides total 9

10 An attenuation of Fennoscandian earthquakes is based on historical intensity observations and observations in regions, which are deemed to similar in geology and seismicity. Uncertainties in the various assumptions critical to the analysis of the ground motion characteristics will be taken into account in form of the decision tree. NPSAG workshop, Stockholm, March 13, slides total 10

11 The dependence of ground acceleration on yearly exceedance probability will be presented by a distribution. The given results that are used in nuclear power plant design are defined as median values for a return period of years. NPSAG workshop, Stockholm, March 13, slides total 11

12 2. SEISMIC HAZARD, Update for Loviisa, June 2008 Probabilistic seismic hazard assessment (PSHA) requires input data and a mathematical model. A homogeneous sample of earthquakes having occurred inside a large area around the investigated area is proper input data. Basic steps in mathematical modeling are the following. NPSAG workshop, Stockholm, March 13, slides total 12

13 First step is to delineate source areas of potential future earthquakes. These source areas or zones should be homogeneous with respect to spatial distribution and frequency content of earthquakes and also with respect to their upper magnitudes. NPSAG workshop, Stockholm, March 13, slides total 13

14 At the second step, the probability distribution of the number of earthquakes is determined as a function of magnitude for each zone. This distribution is called magnitude-recurrence relationship. The rate of earthquake occurrence in magnitude-recurrence relationship is estimated with the aid of historical data. The distribution is reliable only in the magnitude range which is covered by occurred earthquakes. NPSAG workshop, Stockholm, March 13, slides total 14

15 The magnitude-recurrence relationship based on historical data gives only weak estimation of the probability of large magnitudes. The uncertainty relating to the probabilities of the large magnitudes is taken into account by varying the limit value of the upper bound magnitude. NPSAG workshop, Stockholm, March 13, slides total 15

16 Third step is to determine the attenuation functions that describe the ground motion as a function of magnitude and distance between the site and the hypocenter of the event. NPSAG workshop, Stockholm, March 13, slides total 16

17 The contribution of each source area to the estimated ground motion parameter of the site studied is evaluated numerically. All the possible earthquake magnitudes and locations are integrated to get their effect to the estimated ground motion parameter. The results from different source areas are summed up and the total expected number of earthquakes per unit time is obtained. NPSAG workshop, Stockholm, March 13, slides total 17

18 The seismic hazard or the probability that a certain ground motion parameter value will be exceeded is obtained by using Poisson process assumption. Following Poisson process an event can occur at random and at any time or at any point any point in space. Probabilistic seismic hazard assessment assumes that future earthquakes can be estimated by observed seismic history. NPSAG workshop, Stockholm, March 13, slides total 18

19 The maximum magnitude of earthquakes in each source area is also estimated according to historical data. The earthquake energy is not released in a single point but the earthquake is usually a series of fault ruptures or slips which happen in a ruptured zone. The mathematical model used describes energy release by a pointsource model, in which all the energy is concentrated to a single point. The only geometric factor considered is distance between the source and the site. NPSAG workshop, Stockholm, March 13, slides total 19

20 In the uncertainty analysis the parameters are assumed to be stochastic were the earthquake catalog, Gutenberg magnitude-recurrence parameters a and b, the maximum magnitude and the selected attenuation function. Two possible alternatives were given for first three of these parameter sets and four possible alternatives were given to attenuation equation selection. A probability distribution of 32 discrete values was obtained from the decision tree. NPSAG workshop, Stockholm, March 13, slides total 20

21 Loviisa seismic site hazard in terms of PGA is depicted in Figure 1. Olkiluoto seismic site hazard in terms of PGA is depicted in Figure 2. Hanhikivi seismic site hazard in terms of PGA is depicted in Figure 3. NPSAG workshop, Stockholm, March 13, slides total 21

22 Annual frequency of exceedance Distribution of hazard curves for Loviisa site; Seisrisk III analysis,june E-02 1.E-03 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 1.E PGA amplitude (g) 5%fractile median 95%fractile weighted mean uniform mean Figure 1 Loviisa seismic site hazard in terms of PGA, June 2008 NPSAG workshop, Stockholm, March 13, slides total 22

23 Annual frequency of exceedance Distribution of hazard curves for Olkiluoto site; Seisrisk III analysis, April E-02 1.E-03 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 1.E PGA amplitude (g) 5%fractile median 95%fractile Figure 2 Olkiluoto seismic site hazard in terms of PGA, April 2007 NPSAG workshop, Stockholm, March 13, slides total 23

24 Annual frequency of exceedance Distribution of hazard curves for Hanhikivi site; Seisrisk III analysis, October E-02 1.E-03 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 1.E PGA amplitude (g) 5%fractile median 95%fractile Figure 3 Hanhikivi seismic site hazard in terms of PGA, October 2009 NPSAG workshop, Stockholm, March 13, slides total 24

25 3. GROUND MOTION, UPDATE FOR OL3, December 2008 The design seismic ground motion for the nuclear power plants is defined with the aid of design response spectrum, which is formulated in terms of horizontal and vertical ground acceleration. For Finland, the design response spectrum shape is described in the document YVL 2.6 Seismic Analysis and Design of Nuclear Power Plants [8]. NPSAG workshop, Stockholm, March 13, slides total 25

26 The spectral shape to be used to define this motion corresponds to a median (50 percentile) spectrum with the return period of years developed for hard rock sites. The horizontal peak ground acceleration will be assumed at least equal to 0.1g. The vertical spectrum will be assumed equal to 2/3 of the horizontal spectrum NPSAG workshop, Stockholm, March 13, slides total 26

27 The theoretical background for synthetic ground motion simulation following the references [9] and [10] is given in this subsection According to the spectral representation theorem, if the ground motion at a point is a homogeneous mean-square continuous real time process, then it can be expressed as a sum of independent sinusoidal processes as Equation 1 Z(t) = S[A i sin(w i t +f i )] NPSAG workshop, Stockholm, March 13, slides total 27

28 The random number generator is used to produce the phase angles with uniform distribution in the range between 0 and 2p. With a set of phase angles, the array of amplitudes A i in Equation 1 is to be determined. The amplitudes A i are related to the power spectra density function (PSD) Equation 2 PSD(w n )Dw = A n2 /2 In Equation 2 the product PSD(w n )Dw is the contribution of one sinusoid with the frequency of w n to the total power of the motion. NPSAG workshop, Stockholm, March 13, slides total 28

29 The transient character of the motion is represented by the envelope function I(t). The resulting non-stationary motion has the form of Equation 3 X(t) = I(t)S[A i sin(w i t +f i )]. The response spectra corresponding to motion in Equation 3 is calculated. The response spectrum for one chosen damping value (usually 5% damping) is called the target response spectrum, which is then attempted to match by the following iterative procedure. NPSAG workshop, Stockholm, March 13, slides total 29

30 At each cycle of iteration the calculated response is compared with the target at a set of user specified control frequencies. The ratio of the target response to the computed response is obtained at each control frequency and the corresponding value of the power spectral density is modified in proportion to the square of this ratio. Equation 4 PSD(w) i+1 = PSD(w) i [S v (w)/s v (i) (w)] 2. NPSAG workshop, Stockholm, March 13, slides total 30

31 In Equation 4 S v is the target response spectrum value. With the modified spectral density function a new motion is generated and a new response spectrum is calculated. The procedure should not be expected to be convergent at all control frequencies; the response at a control frequency is dependent not only on the spectral density function value for that frequency, but also on other values at frequencies close to the frequency of interest as well. In the following two Figures 4 and 5 the design ground motion in global x-direction generated for the OL3 is given: NPSAG workshop, Stockholm, March 13, slides total 31

32 acceleration (m/s2) time (seconds) Figure 4 TVO OL3 Des Acc time histories x-com, Parabolically base line corrected, December 2008 NPSAG workshop, Stockholm, March 13, slides total 32

33 spectral acceleration (g) E E E E+02 frequency (hz) Figure 5 TVO OL3 Des Acc time histories x-com, target spectrum [YVL 2.6] fit, December 2008 NPSAG workshop, Stockholm, March 13, slides total 33

34 4. STRUCTURAL RESPONSE, Update for Loviisa, July 2010 The reactor building model description for the structural response analysis of the Loviisa Nuclear Power Plant unit one and two is given in this subsection. The analysis of the reactor building has been carried out using the following sequence of calculations and two main computer programs: MSC/PATRAN [14], MSC/NASTRAN [15]. NPSAG workshop, Stockholm, March 13, slides total 34

35 A 3D-model was created for the whole reactor building (see Figure 6). The 3Dmodel consists of the outer containment, the inner containment, the internal structures and the base slab. The FEMmodel was formed along center lines of the concrete structures. NPSAG workshop, Stockholm, March 13, slides total 35

36 Figure 6 The 3D analysis model of Loviisa nuclear power plant reactor building, Update for Loviisa, July 2010 NPSAG workshop, Stockholm, March 13, slides total 36

37 The results of the response spectra calculations for the elevation of are depicted in Figure 7. The horizontal argument axis gives the frequency in Hz in logarithmic scale. The vertical ordinate axis gives the spectral accelerations in g s in linear scale. The plot in Figure 7 gives the response spectra for Y-direction and the maximum value of the scale is 7 m/s 2 or 0.7 g. The plot in Figure 7 contains spectra for damping ratio 0.02, and for median value and for 84 % fractile value. NPSAG workshop, Stockholm, March 13, slides total 37

38 Figure 7 Probabilistic Floor response spectra in Y-direction for elevation for Loviisa NPP reactor building, July 2010 NPSAG workshop, Stockholm, March 13, slides total 38

39 5. THE SEISMIC FRAGILITY OF THE FEED WATER TANKS IN LOVIISA PLANT, JULY 2008 The seismic fragility of a component is defined as the conditional probability of its failure given a value of peak ground acceleration. Using the lognormal-distribution assumption, the fragility (i.e., the probability of failure, f') at any non-exceedance probability level Q can be derived as Equation 5 f = [(ln(a/a) + U -1 (Q))/ R ] In Equation 5 Q = P(f < f' a) is the probability that the conditional probability f is less than f' for a peak ground acceleration a. A is the median ground acceleration capacity, R is the logarithmic standard deviation representing the inherent randomness about A, and U is the logarithmic standard deviation representing the uncertainty in the median value. The quantity (.) is the standard Gaussian cumulative distribution function, and -1 (.) is its inverse. NPSAG workshop, Stockholm, March 13, slides total 39

40 The median value A for the feed water tank is obtained from failure criteria of 8% for the work equivalent plastic strain in the anchor bolts of the center support of the four feed water tanks modeled explicitly in global finite element model and the coefficients R and U are derived as in the following Table 1: Capacity Factor Equipment Response Factor Structural Response Factor Ground Acceleration Capacity Table 1 The derivation of logarithmic standard deviations R =0.28 for randomness and U = 0.38 for uncertainty in Equation 5 Using the median peak ground acceleration capacity of 0.28g and logarithmic standard deviations R = 0.28 for randomness and U =0.38 for uncertainty the graphical presentation of the fragility definition of the Equation 5 can be depicted as follows in Figure 8: NPSAG workshop, Stockholm, March 13, slides total 40 R U

41 Snapshot of the strutural model to estimate the feedwater tank fragility NPSAG workshop, Stockholm, March 13, slides total 41

42 Figure 8 The updated fragility of the feed water tanks showing the median failure capacity of 0.28g in PGA and the logarithmic standard deviations R = 0.28 for randomness and U =0.38 for uncertainty NPSAG workshop, Stockholm, March 13, slides total 42

43 Plot of Loviisa plant primary circuit model NPSAG workshop, Stockholm, March 13, slides total 43

44 Loviisa unit the distribution of seismic core melt risk for plant components NPSAG workshop, Stockholm, March 13, slides total 44

45 6. EQUIPMENT QUALIFICATION, August 2007 In the following subsection the equipment qualification program carried out with shaking table testing during the automation renewal project of the Loviisa NPP is described [22]. Five different typical electrical equipment categories were tested. The categories to be tested were: (1) Rectifier cabinet with the equipment identification notation of EK; (2) 400VAC alternate current switch cabinet with the equipment identification notation of 22FV13VO012; (3) 24VDC direct current switch gear cabinet with the equipment identification notation of DS; (4) the alternate current switchgear cabinet for air conditioning with the equipment identification notation of 22FV08J0022; (5) the battery fuse box with the equipment identification notation of 20EK86. NPSAG workshop, Stockholm, March 13, slides total 45

46 In the following only the rectifier tests are described in detail. In the tests of the EK rectifier neither electric interference nor structural damages was observed so the rectifier passed the test acceptably. After the seismic tests the device was sent for further functional testing to the manufacturer. The aim of these additional factory tests was to investigate if any changes had been taken place in the electric properties of the rectifier. The factory tests did not indicate any changes in the electric properties of the rectifier. A schematic sketch showing the rectifier, the test directions and the locations of the response accelerometers is given in Figure 9. The acceleration responses of the test specimen were measured by tri-axial piezoelectric accelerometers with signal conditioner units and by single axis piezoelectric accelerometers with signal conditioner units. The acceleration signals were sampled by a data acquisition system built into the control system of the testing system console. The photograph of the EK rectifier test specimen is given in Figure 10. NPSAG workshop, Stockholm, March 13, slides total 46

47 Figure 9 A schematic sketch of the electrical rectifier cabinet showing the test directions and the locations of the response accelerometers NPSAG workshop, Stockholm, March 13, slides total 47

48 Figure 10 The rectifier cabinet on the shaking table for testing in the Side-to-Side & Vertical directions In the following Figures 11, 12 and 13 are shown the excitation spectra in side-to-side and vertical direction used in the rectifier cabinet tests as well as the measured cabinet response during the tests. NPSAG workshop, Stockholm, March 13, slides total 48

49 Spectral acceleration (g) Horizontal excitation spectrum (g) frequency (HZ) Figure 11 The rectifier cabinet excitation spectrum for the shaking table in the horizontal direction NPSAG workshop, Stockholm, March 13, slides total 49

50 Spectral acceleration (g) Vertical excitation spectrum (g) Frequency (HZ) Figure 12 The rectifier cabinet excitation spectrum for the shaking table in the vertical direction NPSAG workshop, Stockholm, March 13, slides total 50

51 spec. acc. (g) EK rectifier; side to side excitation; seismic qualification results freq (HZ) hor exc spec ver exc spec hor top res ver top res hor main transf res ver main transf res hor base res ver base res Figure 13 Seismic qualification test results for EK rectifier cabinet in graphical form; Excitation direction side to side NPSAG workshop, Stockholm, March 13, slides total 51

52 7. CONCLUSION In this paper the following task of nuclear power plant design and analysis were described: 1) The seismic hazard assessment; 2) The design ground motion development for the site. The following steps are needed for the seismic hazard assessment and design ground motion development: 1.1) The development of regional seismic model; 1.2) The development of strong motion prediction equations; 1.3) Logic three development for taking into account uncertainties and seismic hazard quantification; 1.4) The development of uniform hazard response spectra for ground motion at the site; 2.1) Simulation of acceleration time histories compatible with uniform hazard response spectra. The whole compendium of tasks forming the hazard and ground motion part is also called the seismic site characterization. The structural and equipment fragility part includes the following steps: 1) Development of structural models of the plant buildings; 2) Development of the soil model underneath the plants buildings for soilstructure interaction response analysis 3) Determination of in-structure response spectra for the plant buildings for the equipment response analysis; 4) Designing and analyzing the structures and equipment so that they can withstand the seismic load combined with all other relevant loads. NPSAG workshop, Stockholm, March 13, slides total 52

53 8. REFERENCES [1] R. K. McGuire, 'Fortran computer program for seismic risk analysis', USGS Open File Report, No , [2] Bender B. & Perkins D. M SEISRISK III: A Computer Program for Seismic Hazard Estimation, U. S. Geological Survey Bulletin 1772, United States Governement Printing Office; Washington. [3] C. A. Cornell, 'Engineering seismic risk analysis', Bull. seism. soc. Am., 58, (1968). [4] H. A. Merz and C. A. Cornell, 'Seismic risk analysis based on a quadratic magnitude-frequency law', Bull. seism. soc. Am., 63, (1973). [5] R. Yarar et al., 'A preliminary probabilistic assessment of the seismic hazard in Turkey', Proc. 7th world conf. earthquake eng., Istanbul, 1 (1980). [6] J. G. Anderson, 'Consistency of probabilistic seismic risk methods', Proc. 7th World Conf. Earthquake Eng., Istanbul, 1 (1980). [7] R. Saegesser et al., `Seismic risk maps of Switzerland', 4th SmiRT conf., San Francisco, K1/3 (1977). [8] STUK Radiation and Nuclear Safety Authority, Maanjaristysten huomioon ottaminen ydinvoimalaitoksissa, OHJE YVL 2.6/ , ISBN NPSAG workshop, Stockholm, March 13, slides total 53

54 [9] "Simulated Earthquake Motions Compatible with Prescribed Response Spectra." Gasparini, D, Vanmarkcke, E., MIT Department of Civil Engineering Research Report R76-4, Order No. 527, January [10] Xu J.,Philippacopoulas A. J., Miller, C. A., Constantino C. J., CARES (Computer Analysis for Rapid Evaluation of Structures 1.0, NUREG/CR-5588,BNL-NUREG-52241,Vol. 1-3, Brookhaven National Laboratory, May [11] Seismic Hazard assessment of Tianwan Nuclear Power Plant Site in China, Pentti Varpasuo, Proceedings of the International Conference on Structural Constructions in 21st Century, Moscow, Russian Federation, November 21-23, [12] Safety Guide on Earthquakes and Associated Topics in Relation to NPP Siting, HAF0101. Approved jointly by NNSB and SSB. A Collection of Safety Guides for NPP, NNSB. Law Publisher of China, [13] The Development of the Floor Response Spectra using large 3D model, Pentti Varpasuo, Proceedings of the 7th International Symposium "Current Issues related to Nuclear Power Plant Structures Equipment and Piping", c.c. David Tung (ed.), Raleigh, North Carolina, December, 1-4, [14] MSC/PATRAN, Version 7.5. Release Guide, The MacNeal-Schwendler Corporation, Los Angeles, California, January [15] MSC/NASTRAN Linear Static Analysis. User's Guide, Version 69+, The MacNeal- Schwendler Corporation, Los Angeles, California, July [16] Välikangas, P., IVODIM, Description of Design Programs for Reinforced Concrete Structures, Internal Report, IVO International Ltd, Civil Engineering. NPSAG workshop, Stockholm, March 13, slides total 54

55 [17] SNiP Betonnie i zchelezobetonnie konstruktsii. M. Gostroi SSSR [18] ASCE STANDARD Seismic Analysis of Safety-Related Nuclear Structures and Commentary on Standard for Seismic Analysis of Safety Related Nuclear Structures. Approved September [19] Ivanov P.L. Grunti i osnovanija gidrotehnicheskih sooruzchenij. ( Soils and foundations for hydrotechnical constructions), M. Visshaja Shkola [20] U.S. Atomic Energy Commission, Regulatory Guide 1.60, Design Response Spectra for Seismic Design of Nuclear Power Plants, Version 1, December [21] Transactions of 15th International Conference on Structural Mechanics in Reactor Technology (SMIRT15), Seoul, Korea, August 15-20, 1999, Paper K6-A2-FT, Time History Analysis of Global 3D Reactor Building Model to establish Seismic Supports for Equipment, Varpasuo P., IVO Power Engineering Ltd., Finland. [22] Proceedings of 19th International Conference on Structural Mechanics in Reactor Technology, , Toronto, Canada, Seismic Qualification of the Equipment for Loviisa Plant Automation Renewal Project, P. Varpasuo, Fortum Nuclear Services Ltd., Espoo, Finland. [23] Proceedings of OECD NEA Workshop on SSI Knowledge and Effect on the Seismic Assessment of NPP s, Sep. 2010, Ottawa, Canada, The Simulation of the KK7 Reactor Building Structural Response for NCO 2007 Event using different Modeling and Analysis Techniques, Pentti Varpasuo, Jukka Kähkönen, Mari Vuorinen and Sampsa Launiainen, Fortum Power and Heat Ltd, Finland. [24] Japan Nuclear Energy Safety Organization (JNES), Seismic Safety Division, "Seismic Safety Reevaluation of existing-npps based on the New Seismic Design Review Guide and Experience of The Niigataken Chuetsu-oki Earthquake " International Atomic Energy Agency, Extra-Budgetary Project on Seismic Safety of Existing Nuclear Power Plants 3rd Steering Committee meeting, September 25, 2009, Vienna NPSAG workshop, Stockholm, March 13, slides total 55