ML20129E916
| ML20129E916 | |
| Person / Time | |
|---|---|
| Site: | 05000447 |
| Issue date: | 09/30/1983 |
| From: | GENERAL ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20127A304 | List: |
| References | |
| FOIA-84-175, FOIA-84-A-66 NUDOCS 8506060631 | |
| Download: ML20129E916 (51) | |
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION
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GESSAR II SEISMIC EVENT ANALYSIS GENERAL ELECTRIC COMPANY SEPTEMBER, 1983
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^ f GENERAL ELECTRIC COMPAN PROPRIETARY INFORMATION GESSAR II SEISMIC EVENT ANALYSIS CONTENTS Page EXECUTIVE
SUMMARY
x 1.0. Intr.oduction 1
1.1 Background
2 1.2 Approach 3
1.2.1 Seismic Hazard Curve 3
1.2.2 Seismic Fragi'iity of Structures and Components 4
1.2.3 Seismic Contribution to Core Damage Frequency 5
1.3 -Application to a Specific Plant Site 6
1.4 References 6
(
l 2.0 Seismic Hazard Analysis 8
2.1 Introduction 9
2.2 Approach 12 2.3 Development of GESSAR II Seismic Hazard Curve 14 2.4 References 17 I'
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41 GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION Contents (Continued)
P. age 3.0 Seismic Fragilities 21 3.1 Introduction 22 25 3.2 Structural Fragility 3.2.1 Introduction 25 3.2.2 General Criteria for Development of Structural Fragilities 28-3.2.3 Structural Capacity Factor of Safety 31 3.2.3.1 Load Margin, F 31 s
3.2.3.1.1 Load Margin, F1 31 3.2.3.1.2 Strength Margin, F st 32 3.2.3.1.3 Inelastic Energy Absorption Factor, F 39 p
3.2.3.2 Structu"al Response Factor, F 41 rs 3.2.4 Median Values of Capacity Factors 46 3.3 Component Fragility 47 3.3.1 Introduction 47 ii
L 8-GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION Contents (Continued)
Pa.ge 3.3.2 Component Capacity Factors of Safety 48 3.3.2.1 Code Margin, F 49 c
3.3.2.2 Load Margin, F 49 L
3.3.2.3 Material Response Margin, F 50 R
3.3.2.4 Inelastic Energy Absorbtion Margin, F 50 p
3.3.2.5 Damping Margin, F 50 D
3.3.2.6 Design Response Spectra Margin, F 51 th 3.3.2.7 Analysis Margin, F 51 A
3.3.3 LLNL and PRA Data 52 3.4 References 53 4.0 Evaluation of Seismic Impact on Core Damage Frequency 84 4.1 Introduction 84 i
4.2 Accident Sequence Analysis 85 l
4.3 Calculated Seismic-Induced Core Damage Frequency 89 i
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GENERAL ELECTRIC COMPANY a*
l PROPRIETARY INFORMATION Contents (Continued)
. Pag 5.0 Evaluation of Seismic Impact on Offsite Consequences 109 5.1 ' Introduction 109 5.2 Release Frequency Analysis 109 5.2.1. Release Pathways 109 5.2.2 Flow Splits 111 5.2.3 Failure Rates 112 5.2.4 Release Categories 113 5.2.5 Conditional Release Fractions 115 5.3 Release Category Frequency Summary 116 5.4 Offsite Consequences 117 6.0 Summary and Conclusions 130 Appendix A.
Translation of Return Periods to Annual Frequency of Exceedance A-1 iv
C GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION
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TABLES Table Title Pg 3-1 Dynamic Amplification Factors at 50% and 84.1%
57 Probability Levels 3-2 Capacity Factors of Safety for the Pedestal 58 (Moment) 3-3 Capacity Factors of Safety for the Pedestal 59 (Shear) 3-4 Capacity Factors of Safety for the Drywell (Flexural-tension in rebar) 60 3-5 Capacity Factors of Safety for the Drywell (Flexural-concrete compression) 61 3-6 Capacity Factors of Safety for the Drywell 62-(Shear) 3-7 Capacity Factors of Safety for the Containment Shell in the Suppression Pool (Shear) 63 3-8 Capacity Factors of Safety for the Containment Shell above the Suppression Pool (Buckling) 64 3-9 Capacity Factors of Safety for the Containment Anchor Bolts (Shear) 65 3-10 Capacity Factors of Safety for the Containment Anchor Bolts (Failure in Concrete Bearing) 66 y
1-GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION TABLES (Continued)
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Table Title Page 3-11 Capacity Factors of Safety for the RPV Skirt / Pedestal Connection Bolt (tension produced by moment) 67 3-12 Canacity Factors of Safety for the RPV Skirt / Pedestal Connection Bolt (Shear / Friction) 68 3-13 Capacity Factors of Safety for the Shield Building (tension in rebar-flexural) 69 3-14 Capacity Factors of Safety for the Shield Building (Shear) 70 3-15 Capacity Factors of Safety for Seismic Category I Structures (Shear) 71 3-16 Capacity Factors of Safety for Seismic Category I Structures (Flexural) 72 3-17 Capacity Factors of Safety for Auxiliary Building Foundation Soil (Sliding) 73 3-18 Capacity Factors of Safety for Non-Seismic Category I Structure (Flexural-tension in rebar) 74 3-19 Median Effective Ground Acceleration and Coefficients of Variation for Structures 75 vi
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PROPRIETARY INFORMATION TBLES(Continued)
Table Title h
3-20 Factors of Safety for Piping 76 3-21 Factors of Safety for Pumps 77 3-22 Factors for Safety for Shroud Support 78 3-23 Factors of Safety for CRD Guide Tube 79 3-24 Factors of Safety for RHR Heat Exchanger 80 3-25 Median Capacities of Components 81 4-1 BWR/6 Components / Structures Fragility 90 4-2 Buildings and Effected Systems 91 4-3 Random Independent Failure Data for Accident Mitigating Systems 92 4-4 Boolean Expressions for Safety Systems 93 4-5 Bollean Expressions for Event Tree Sequences 94 5-1 Release Pathways, Barriers and Potential Release Fractions 118 5-2 Bases for Seismic PRA Release Pathway Assessment 120 5-3 Consolidation of Core Damage Sequences into Release Pathway Event Trees 121 5-4 Summary of Release Sequence Frequencies 122 vii
GENERAL ELECTRIC COMPANY 6.'
PROPRIETARY INFORMATION FIGURES Fioure Title Page 1-1 GESSAR II Seismic Event Analysis 7
2-1 GESSAR II Seismic Hazard Curve 19 2 -GESSAR II Seismic Hazard Curve Compared to Hazard Curves From Other Studies 20 3-1 Effect of Age on Concrete Com'pressive Strength 82 3-2 Response Spectrum for Control Motion 83 4-1 Top Level Seismic Event Tree 96 4-2 Seismic Event Tree for Loss of Offsite Power With Scram 97 4-3 Seismic Event Tree for Loss of Offsite Power Without Scram 98 4-4 Seismic Event Tree for Failure of the Diesel 99 Generator Buildings 4-5 Seismic Evant Tree for the Failure of the Shield 100 or Control Building 101 4-6 Simplified Fault Tree for HPCS System viii
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GENERAL ELECTRIC COMPANY.
-4 PROPRIETARY INFORMATION FIGURES (Continued)
Figure Title Pajgt
'4-7 Simplified Fault Tree for RCIC System 102 4-8 Simplified Fault Tree for ADS 103 4-9 Simplified Fault Tree for LPCS System 104' 4-10 Simplified Fault Tree for LPCI System 105 4 Simplified Fault Tree for RHR System 106 4-12 Simplified Fault Tree for the SCRAM System 107 4-13 Simplified Fault Tree for the SLC System 108 5-1 Seismic Fragility Curves 123 5-2 Release Pathway Event Tree 124 5-3 Release Pathway Event Tree 125 5-4 Release Pathway Event Tree 126 5-5 Release Pathway Event Tree 127 5-6 Release Pathway Event Tree 128 5-7
' Comparison of Risk for the WASH-1400 BWR and BWR/6 129 iX 8
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION EXECUTIVE
SUMMARY
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Background===
The purpose of this submittal is to provide an analysis that demonstrates the capability of the GESSAR II design to accomodate low probability seismic events beyond the Safe Shutdown Earthquake (SSE) design basis.
Consideration of seismic events as accident initiators was not included in the March 1982 Probabilistic Risk Assessment (PRA) of the BWR/6 Mark III Standard Plant design.
This submittal is provided to meet the intent of the NRC draft Policy Statement on Severe Accidents which requires the consideration of seumic and other external events for standard plant certification.
The Seismic Event Analysis The GE assessment of seismic-initiated core damage frequency and offsite risk consists of four principal tasks:
the establishment of a seismic hazard curve; the determination of the seismic capability of critical components and structures; the evaluation of core damage frequency; and the estimate of the offsite consequences.
Current data on seismic hazard and structural and component seismic fragility were utilized in the development of the seismic hazard curve and the fragility curves, respectively.
Fault tree / event tree methodology was employed in the evaluation of seismically-induced accident sequences used to determine x
GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION the seismic-induced core damage frequency.
The accident sequences were analyzed by considering the characteristics which would be important to fission product transport, Fission product release fractions were computed and the offsite consequences were evaluated.
Results The annual seismically-induced core damage frequency evaluated over the
-7 range of the seismic hazard curve (to 0.95g) was 4.0 x 10
, which is 9 percent of the core damage frequency calculated for internal events.
The dominant contributor to core damage in the seismic study was the loss of offsite power caused by failure of ceramic insulators.
The structural fragility evaluuions demonstrated that the containment structure maintains its integrity and function with high probability for the range of seismic conditions evaluated.
In particular, maintenance of the pool scrubbing function resulted in low offsite consequences for the seismic-initiated events.
The CRAC analyses of offsite consequences resulted in no calculated early fatalities (as in the internal event study), and a latent fatality risk of 9 x 10~7 (compared to the internal event value of 1.66 x 10-5).
Seismic-initiated events thus contribute only 5 percent to the total plant risk.
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GENERAL ELECTRIC COMPANT PROPRIETARY INFORMATION These results are not unexpected in that the GESSAR II design has incorporated an envelope approach in the specification of critical site and plant parameters.
This approach provides for location of the standard plant on most U.S. sites.
Also, as a result of utilization of the envelope approach, excess capability exists to withstand events beyond the design basis.
Conclusions The GESSAR II plant design provides substantial capacity for seismic events well beyond'the SSE.
This is substantiated by:
.1)
The core damage frequency from seismic-initiated events is approximately 9 percent of the internal event core damage frequency.
2)
Seismic initiated events account for a sm. 1 percentage (s 5%) of the total plant risk.
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i GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION-
' 1. 0 INTRODUCTION This section provides the background and describes the approach utilized in-the GESSAR II seismic event analysis.
The application of the analysis to a specific plant site is also explained.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION
1.1 BACKGROUND
In March 1982, a Probabilistic Risk Assessment (PRA) of the BWR/6 Mark III Standard Plant design was provided to the NRC to aid in the NRC Staff evaluation of that design relative to severe accident issues.
The PRA did not consider the effects of external events, such as earthquakes, fires or floods in the evaluation of plant risk.
The capability of the GESSAR II design to accommodate seismic events is presented in this seismic risk evaluation which should be considered as supplementary to the internal events analysis.
It is provided to meet the intent of the NRC draft policy statement on Severe Accidents (1) which includes the consideration of seismic and other external events as requirements for standard plant certifi~ cation.
Chapter 3 of the GESSAR II FSAR describes the deterministic analyses performed to verify the Nuclear Island Design relative to seismic events within the design basis envelope.
Since the GESSAR II plant is designed for a nominal 0.3g SSE on all soil conditions, considerable margin exists relative to any particular site.
It is this design margin that allows the plant to accommodate seismic events far beyond the design basis without significant risk to the public health and safety.
The risk assessment presented in the following sections quantifies the design margin and confirms the low risk from seismic-initiated events.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 1.2 APPROACH The assessment.of seismic-initiated core damage frequency and offsite risk consists of four primary tasks:
the establishment of a seismic hazard curve, the determination of the seismic capability of critical
-components and structures, an assessment of the core damage frequency, and an estimate of the offsite risk.
The chronology and interrelation-ships among these tasks is illustrated in Figure 1-1.
The following paragraphs describe the technical approach taken to accomplish these tasks.
1.2.1 Seismic Hazard Curve In establishing the GESSAR II seismic hazard curve, it was desirable to establish a single seismic hazard curve that would reasonably bound potential GESSAR II sites.
This approach parallels the utilization of tiie GESSAR siting envelope for deterministic considerations of seismic i
and other external events.
The single curve was chosen, however, so as not to unduly bias the results of the seismic event analysis relative to the consideration of internal events included in the GESSAR II Probabilistic Risk Assessment (PRA).
Available published information of annual frequency of exceedance of peak ground acceleration was reviewed and a reasonable upper bound was established for potential GESSAR II sites in the United. States.
The data base included hazard information from several site-specific probabilistic risk 3
GENERAL ELECTRIC ~ COMPANY PROPRIETARY INFORMATION assessments and the USGS Open-File Report 82-1033.
The details of the development of the seismic hazard curve are given in Section 2.0.
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The GE seismic hazard curve is equal to or greater than the median centered hazard curves for all proposed GESSAR II sites.
Thus, it is not considered to be a bounding curve.
It is considered to be a best estimate for the highest seismicity GESSAR II sites, although, its application to low seismic GESSAR II sites would be conservative.
1.2.2 Seismic Fragility of Structures and Components The seismic fragility expresses the cumulative conditional probability of failure of a structure or component given ground motion accele*ation of a certain magnitude.
For the structures and components such as those found in the GESSAR II plant design, there exists a minimal database.
Therefore, fragilities of structures and components were developed primarily from extrapolation of design analyses supplemented by qualified engineering judgment and available test data.
In addition to the independent seismically-induced failures of components and structures, the failure of a component due to failure of a nearby structure was also analyzed.
Therefore, the locations of critical components were determined from plant arrangement drawings.
In order to preclude a detailed structural assessment of each structure within a building, it was conservatively assumed that structural failure of one part of a building lead to loss of all components within that building.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION Section 3.0 describes the quantification of the fragility of structures and components as a function of ground motion acceleration.
1.2.3 Seismic Contribution to Core Damage Frequency i
The seismic contribution to core damage frequency, described in Section 4.0, was estimated by a fault tree / event tree methodology similar to that employed in the internal event PRA.
The internal even PRA system fault trees were modified to include seismic failures in addition to random failures Seismically-induced accident sequences were determined and core d'
) event trees were constructed.
Finally, core damage frequencies were computed combining the system and structural failure probabilities with the seismic hazard frequency over the range of ground motion acceler-ation.
1.2.4 Offsite Consequences and Risk The accident sequences were analysed in terms of their characteristics which would be important to fission product transport.
Special event trees were developed to account for unique common mode failures, such as building failures, not present in the internal events PRA, but which impact fission product transport.
Fission product releases fractions were computed and each accident sequence was assigned to a release category for evaluation of the offsite consequences.
The same site characteristics that were utilized in the internal event PRA, were used to assess the risk from seismic-initiated core damage events.
The risk evaluation is described in Section 5.0.
GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 1.3 Application to a Specific Plant Site As specified in the Safety Evaluation Report, an applicant referencing GESSAR II is required to provide confirmation of a number of site param5ters.
For utilization of the GESSAR II Seismic Event analysis, GE proposes that the applicant also provide a site specific assessment of seismic hazard.
The site specific hazard evaluation can then be compared to the curve utilized in the GE hazard analysis to determine if the seismic portion of the GESSAR II PRA is applicable to that site.
For cases where deviations are identified beyond the hazard level employed in the Seismic Event Analysis, a reeval'uation of the impact of seismic events on plant risk parameters may be required.
This approach in the utilization of the seismic hazard curve is consistent with the treatment of other site unique parameters in the context of the standard plant design approach.
It also facilitates consideration of seismic events relative to severe accidents for a standard plant design.
1.4 References
- 1. Proposed Commission Policy Statement on Severe Accidents, Federal Register Volume 48,No.72, April 13,1983.
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PROPRIETARY INFORMATION i
Figure 1-1 1
GESSAR II SEISf1IC EVENT ANALYSIS IDENTIFY SYSTEMS IMPORTANT TO CORE DAMAGE o
IDENTIFY COMPONENTS IMPORTANT TO SYSTEM FUNCTION n
PLANT-CONFIGURATION t
IDENTIFY STRUCTURE TtlAT CONTAINS THE COMPONENTS o
o COMPONENT STRUCTURAL FRAGILITY SEISMIC FRAGILTlY HAZARD s
P CORE DAMAGE PROBABILITY
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2.0 SEISMIC HAZARD ANALYSIS h
This section of the report presents the basis and development of the
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seismic' hazard curve used in the evaluation of the impact of seismic events on the potential for core damage and offsite consequences.
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PROPRIETARY INFORMATION
2.1 INTRODUCTION
In a seismic hazard analysis, the focus is to obtain a complementary cumulatice distribution function (CCDF) defining the annual probability of occurrence of an earthquake with magnitude greater than a specified ground motion parameter (e.g., peak ground acceleration, effective peak ground acceleration, sustained peak ground acceleration, etc.).
This CCDF is also known alternatively as the seismic hazard curve.
This probability, P[A>a], when evaluated over a series 9
GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION of ground motion values, is the discrete CCDF sought in a deterministic seismic hazard analysis, in which the uncertainties in the seismic parameters are not explicitly considered.
In a Baysian approach (l'5), the uncertainties in the seismic parameters are accounted for methodologically as the prior estimates, which are essentially the subjective probability assignments by seismologists and geologists knowledgeable in the seismic parameters under consideration.
These prior estimates represent judgment of the probability of occurrence of the given seismic parameters.
Conjugating these prior estimates, with the available data as sample likelihood functions, results in a family of CCDF's each of which has a probability weight associated with it.
The Baysian weighted CCDF is then obtained by summing the products of each of the CCDFs by the probability weight associated with that CCDF.
If the seismic parameters were known with certainty, the deterministic approach and the Baysian approach should be identical.
In contrast, the deterministic approach tends to have a conservative bias, in order to account for the uncertainties in the underlying seismic parameters.
The Baysian appraoch, on the other hand, attempts to address the uncertainty issue explicitly via judgment.
Given the evolutionary nature of our understanding of the earthquake phenomena, and the paucity of available quality earthquake data, it is prudent to exercise discretion in using this judgmental information.
That is, it is important not to derive a false sense of security in the analysis that incorporates this information.
In the study in 10
GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION Reference 6, expert's estimates of low probability earthquakes around the contiguous United States can differ by several orders of magnitude.
In consideration of the preceding information, it was decided that a single hazard curve kould be established which would reasonably bound potential GESSAR II sites.
The resulting curve is not con-sidered to be an absolute b'ounding curve in that it represents a best estimate for the highest seismicity GESSAR II sites.
It is recognized, however, that its application to low seismic GESSAR II sites would be conservative.
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GENERAL = ELECTRIC COMPANY PROPRIETARY INFORMATION
- 2. 2 TECHNICAL BASIS To develop a realistic, upper-bound seismic hazard curve that will envelope a majority of the potential nuclear plant sites in the United States, at a consistent probability level, two separate, ideal approaches can be utilized.
The first is known as the " Demand" approach and the second, the " Capacity" approach.
In the Demand approach, the bounding seismic hazard curve is obtained by repeating the deterministic or Baysian process outlined in Section 2.1 for a number of strategic site locations to generate the necessary site-specific seismic hazard curves.
The envelope of these site-specific curves defines the bounding curve to be used.
In this manner, a family of bounding curves, at various probability levels can also be established using Baysian_ techniques.
In the " Capacity" approach, the seismic hazard demand is increased incrementally until the system capacity is exceeded.
In this case, the bounding seismic hazard curve is represented by the most limiting seismic hazard demand placed upon the system and is definitely site-independent.
In other words, no matter where the nuclear plant site is located, so long as it is constructed according to the GESSAR requirements, the seismic hazard capability, represented here as a seismic hazard curve, is unique.
Ilowever, neither of these approaches is considered to be practical in view of the general lack of quality earthquake data and quality structural and component fragility data.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION
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2.3 DEVELOPMENT OF GESSAR II SEISMIC HAZARD CURVE As discussed in sections 2.1 and 2.2, a single seismic hazard curve was established for the evaluation of the impact of seismic events on the potential for core damage and offsite consequences.
This section provides information and the methodology employed in the development of the seismic hazard curve.
As noted in Section 2.2, available published information on the annual frequency of exceedance of levels of ground motion acceleration was reviewed.
This information included several site specific probabilistic risk assessments as well as the USGS open-file report 82-1033(11)
From this review, observations noted in the following paragraphs were made and utilized in the development of the GESSAR II seismic hazard curve.
2.3.1 DEFINITION OF GROUND MOTION ACCELERATION In most recent hazard analyses, the annual frequency of exceedance is expressed in terms of the damage effective or effective peak ground accelerations (EPGA's).
Another figure of merit used was the sustained ground acceleration or third highest peak in the acceleration time-history.
The use of other than the peak ground acceleration results from a concensus that for structures and components whose fundamental frequen-cies are within the range of predominant frequency contents of the ground motion, several-cycles of ground motion at a given amplitude level must be susta..ed in order to result in structural or component damage.
The
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o GENERAL ELECTRIC COMPANY PROPRIETAP.Y INFORMATION relationship used for converting peak ground acceleration (PGA) values to EPGA is of the form PGA = (K)(EPGA) where the constant K ranged from 1.23 to 1.25.
The GESSAR II seismic hazard curve is defined in terms of EPGA.
2.3.2 ANNUAL FREQUENCY OR EXCEEDANCE AT HIGH g LEVEL It was also noted that for the hazard analyses utilizing EPGA, upper bound cutoff values were used for a given earthquake source and intensity.
This is generally understood to be an attempt to correlate the historical earthquake data in Modified Mercalli Intensity (MMI) to EPGA. In the information presented in reference 10, the upper bound EPGA is conserva-Other PRAs tively estimated to be no more than 0.8g for MMI scale of IX.
have followed the concept of defining an upper bound cutoff.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 2.3.3 ANNUAL FREQUENCY OF EXCEEDANCE, 0.lg-0.8g 2.3.4 COMPARISON WITH USGS DATA Reference 11 provides recent national seismic hazard information.
Even though there may be disagreements with information provided in Reference 11, it provides an information base to compare to a generic hazard curve.
The seismic hazard information in Reference 11 was presented as a set of three isoacceleration zone maps.
Using the potential GESSAR sites identified in Reference 13, maximum ground accelerations were identified for each of the time isoacceleration maps representing 10, 50 and 250 year return periods.
The return periods were translated into an annual frequency of exceedance using the approach described in Appendix A.
Thus for annual frequencies of exceedance greater than 4.2x10 4, the seismic hazard curve in Figure 1-1 is expected to bound more than 80% of the potential GESSAR sites identified in Reference 13.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 2.4-REFERENCES 1.
Yegian, M.K.,." State-of-the-Art for Assessing Earthquake Hazards in the United States - Report 13 on Probabilistic Seismic Hazard Analysis", Department of Civil Engineering, Northeastern University, July 1979.
2.
Cornell., C.A., " Engineering Seismic Risk Analysis", Bulletin of the Seismological Society of American, Vol. 58, pp. 1583-1606, October 1968.
3.
McQuire, R.K., " Evaluation of Earthquake Risk to Site", USGS Open-File Report 76-67,.1976.
4.
Bernreuter, D.L., " Seismic Hazard Analysis - Review Panel, Ground Motion and Feedback Results", NUREG/CR-1582, Vol. 5.
5.
Benjamin, J.R. and Cornell, C. A., " Probability Statistics, and Decision for Civil Engineers", McGraw-Hill Book Company, 1970.
6.
Okrent, D., "A Survey of Expert Opinion on Low Probability Earthquake",
UCLA - ENG - 7515, February 1975.
7.
201, " Reactor Safety Study - An Assessment of Accident Risks
'in U.S. Commercial Nuclear Power Plant", U.S. Nuclear Regulatory Commission, WASH-1400, NUREG-75/014, October 1975.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 8.
Zion Probabilistic Safety Study, " Seismic Ground Motion at Zion Nuclear Plant Site", prepared by Dames and Moore.
'9.
Report No. 4161, " Severe A'ccident Risk Assessment - Limerick Generating Station", prepared by NUS Corporation for Philadelphia Electric Company, April 1983.
10.
Kennedy, R.P., Cornell, C.A., Campbell, R.D., Kaplan, S. and Perla, H.F., "Probabilistic Seismic Safety Study of an Existing Nuclear Power Plant", Nuclear Engineering and Design, 59 (1980), North-Holland Publishing Company.
11.
Algerwissen, S.T., Perkins, D.M., Thenhaus, P.C., Hanson, S.L., and Bender, B.L., "Probabilistic Estimates of Maximum Acceleration and Velocity in Rocks in the Contigous United States", USGS Open-File Report 82-1033, 1982.
12.
Hsieh, T., Okrent, D. and Apostolakis, G.E., "On the Average Probability Distribution of Peak Ground Acceleration in the U.S. Continent Due to Strong Earthquakes", Annals of Nuclear Energy, Vol. 2, pp. 615 to 624, 1975.
4 13.
Gilbert, W.D. and Quirk, J.F., " Siting Envelope for Standardized Plants", Nuclear Technology, Vol. 25, April 1975.
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_ GENERAL ELECTRIC COMPANY j
PROPRIETARY INFORMATION 3.0 SEISMIC FRAGILITIES This section of the report provides a general discussion of seismic fragilities and their bases.
Also included is a detailed consideration of the structural and component fragilities used in the GESSAR II seismic event analysis.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION
3.1 INTRODUCTION
The seismic fragility of a structure or component is defined as the cumulative conditional probability of its failure for ground motion acceleration less than or equal to the acceleration value under con-sideration.
For relatively complex structures and components such as those found in nuclear power plants, there is generally a minimal comprehensive seismic fragility data base.
Therefore, the fragilities of structures and components must be developed primarily from extrapolation of design analyses supplemented by qualified engineering judgment and available test data.
To facilitate this type of evaluation, a lognormal proba-bility distribution is used to define the seismic fragilities.
The two parameters that define the shape of the lognormal probability distribution arethemediangroundmotionacceleration,A,andthelogarithmicstandard deviation, p.
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 3.2 STRUCTURAL FRAGILITY 3.2.1.
Introduction In this section, the structural fragility evaluation (i.e. the probability of structural failure as a function of peak effective ground acceleration) for safety related structures is developed for the Mark III Standard Plant.
The results of the structural fragility evaluation together with the annual frequency of exceedance of effective peak ground acceleration will be used in the event tree and fault tree system models to determine the probability of core damage and radioactivity release.
The Mark III Standard Plant was designed in the late 1970's in accordance with criteria and codes in effect at that time.
The plant was designed to withstand both an operating basis earthquake (OBE) and a safe shutdown earthquake (SSE).
The structural design input for the SSE was based on 0.3g and the OBE was based on 0.15g peak horizontal ground accelerations for all seismic Category I structures.
The plant structures are divided into two categories according to their function and the degree of integrity required to protect the public.
These categories are seismic Category I and non-Category I.
Seismic Category I includes those structures, equipment, and components whose failure or malfunction might cause or increase the 25
GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION l
severity of an accident which would endanger the public health and l
safety.
Seismic Category I structures include the following:
Reactor Pressure Vessel pedestal Drywell Wall Containment Vessel Shield Building Auxiliary Building Fuel Building Non-Category I includes those structures, equipment, and components which are important to reactor operation, but are not essential for preventing an accident which would endanger the public health and safety, and are not essential for the mitigation of the consequences of these accidents.
Examples of non-Category I structures are the turbine building and radwaste building upper structure.
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.o GENERAL ELECTRIC' COMPANY PROPRIETARY INFORMATION
3.4 REFERENCES
1.
Probabilistic Seismic Safety Study of an Existing Nuclear Power Plant R. P. Kennedy, C. A. Cornell,
'R. D. Campbell and H. F. Perla,"
Nuclear Engineering and Design, 39 (1980) pp. 315-338.
2.
"PRA Procedures Guide", US Nuclear Regulatory Commission NUREG/CR-2300, p. 11-27.
3.
" Seismic and Soil-Structure Interaction Analysis of the BWR/6 Mark III System", Appendix 3A, 238 Nuclear Island General Electric -
Standard Safety Analysis Report (GESSAR II), Docket No. STN 50-447.
4.
" Seismic Design Parameter, Standard Review Plan 3.7.1, US Nuclear Regulatory Commission, July 1981.
5.
233 Nuclear Island General Electric Standard Safety Analysis Report (GESSAR II) Docket No. STN 50-447.
6.
" Risk-Based Evaluation of Design Criteria" B. R. Ellingwood and A.H-S. Ang, J. of the Structural Division, ASCE Sept. 1974.
7.
" Conditional Probabilities of Seismic Induced Failures for Structures and Components for the Zion Nuclear Generating Station,"
Wesley, D. A., Campbell, R. D., Hashimoto, P. S., Hardy, G. S.,
SMA 12901.02, October 1980.
53
GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 8.
" Lessons Learned from Seismic PRA Studies," Ravindra, M.
K.,
Kennedy, R.
P., Transactions of the 7th SMIRT Conference, Chicago, Illinois, 1984.
9.
" Composition and Properities of Concrete", G. E. Troxell, H. E. Davis and J. W. Kelly.
McGraw-Hill, 1968.
10.
" Report on Quantification of Uncertainties", Report of Seismic Analysis Main Committee (ASCE), March 15 1983.
11.
" Variability of Mechanical Properties of Reinforcing Bars," 5. A.
Mirza, M. Hatzinikolas and J. G. MacGregor J. of the Structural Division, ASCE, May 1979.
12.
" Severe Accident Risk Assessment - Limerick Generating Station" NUS Report, April 1983.
13.
" Shear Strength of Low-Rise Walls With Boundary Elements," F. Barda, J. M. Hanson and W. G. Corley.
ACI Symposium on Reinforced Concrete Structures in Seismic Zones, ACI, Detroit, Michigan, 1976.
14.
" Design of Multistory Reinforced Concrete Buildings for Earthquake Motions," J. A. Blume, N. M. Newmark and L. H. Corning, Portland Cement Association, Chicago, Illinois 196 54
GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 15.
" Inelastic Design of Nuclear Reactor Structures and Its Implication on Design of Critical Equipment," N. M. Newmark SMIRT Paper K4/1, 1977 SMIRT conference, San Francisco, California 1978.
16.
" Earthquake Resistant Structural Walls - Tests of Isolated Walls -
Phase II" Construction Technology Laboratories, (Division of PCA),
Skokie, Illinois, Oct.1979.
17.
" Nonlinear Structural Response Characteristics of Nuclear Power Plant Shear Wall Structures," SMIRT Paper K8/7, 1981 SMIRT Conference, Paris, France.
18.
" Structural Analysis and Design of Nuclear Plants Facilities Committee on Nuclear Structures and Materials of the Structural Division, ASCE 1976.
19.
" Design Response Spectra for Seismic Design of Nuclear Power Plants" Regulatory Guide 1.60, 2/5 Nuclear Regulatory Commission, Oct. IS73.
20.
" Damping Values for Seismic Design of Nuclear Power Plant,"
Regulatory Guide 1.61, US Nuclear Regulatory Commission, Oct. 1973.
21.
"Develcpment of Criteria for Seismic Review of Selected Nuclear Power Plant", N. M. Newmark and W. J. Hall, NUREG/CR-0098, 1978.
22.
" Seismic System Analysis," Standard Review Plan 3.7.2, US Nuclear Regulatory Commission, July 1981.
55
i GENERAL ELECTRIC COMPANY.
+
PROPRIETARY INFORMATION 23.
" Preliminary Strong-Motion Results from the San Fernando Earthquake ofFebruary9,1971,"R.P.MaleyandW.K. Cloud,beologicalSurvey Professional Paper 733.
24.
NUREG/CR-2405, " Subsystem Fragility - Seismic Safety Margins Research Program (Phase I)," February 1982.
25.
Zion Probabilistic Safety Study, " Seismic Ground Motion at' Zion Nuclear Plant Site," prepared by Dames and Moore.
56
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION 4.0 EVALUATION OF SEISMIC IMPACT ON CORE DAMAGE FREQUENCY This section describes the methodology used to estimate the annual core damage frequency for the GESSAR II plant due to seismically-induced accident initiators.
The general procedure was to integrate the seismic hazard analysis (section 2.0) and the plant structure and component fragility data (sections 3 and 4) and assess the plant system response.
4.1 Introduction 84
GENERAL ELECTRIC COMPANY
.- er.
PROPRIETARY INFORMATION A numerical estimation of equation (1) was used to compute the core damage frequencies.
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- PROPRIETARY INFORMATION 4.3 Calculated Seismic-Induced Core Damage Frequency The results of the GESSAR II seismic analysis are provided in Figure 4-1.
The total core damage frequency due to earthquake initiators is 3.98x10 7/
year.
This is about 9% of the total core damage frequency due to internally initiated events.
The majority (67%) of the total seismically-induced core damage frequency is due to the loss of offsite' power initiator because of failure of ceramic insulators.
The remaining 33% is primarily due to structural failures and diesel generator common mode failures.
t 89
GENERAL ELECTRIC COMPANY 3.-.f a PROPRIETARY INFORMATION 5.0 EVALUATION OF SEISMIC IMPACT ON OFFSITE CONSEQUENCES This section describes the methodology used to assess the fission product transport and release to the environment for the seismic initiated events. Offsite consequences are evaluated and the results are presented in this section.
5.1 Introduction This section describes the potential fission product transport pathways for the seismic initiated core damage sequences determined in Section 4.0.
The various release pathways are combined with accident sequence characteristics such as timing and flow rates resulting in accident specific release sequences.
These release sequences are further grouped into the appropriate release category which is input to the consequence analysis code to determine potential health effects.
Results of the offsite consequence evaluation are also presented in terms of a risk curve and mean risk value for internally and externally initiated core damage events.
5.2 Release Frequency Analysis 5.2.1 Release Pathways 109
GENERAL ELECTRIC COMPANY
't
- PROPRIETARY INFORMATION 5.4 Offsite Consequences The offsite consequences from seismic events were determined using the CRAC code as described in Appendix F of GESSAR II 150.3.
As in the internal event PRA, there were no calculated early fatalities for the release categories and meteorological conditions analyzed.
The risk curve for latent effects from both internal and external events is given in Figure 5-7.
The mean annual risk from all initiators was 1.75 x 10 s compared to the internal initiator risk of 1.66 x 10 s.
Therefore, the externally initiated core damage events contributed 5 percent to the GESSAR II plant risk.
117
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100 10 102 i0 10 105 1
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LATENT F ATALITIES PER YE AR IX) rigure 5-7:
Comparison of Risk for the WASH-1400 BWR and BWR/6 129
GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION
~
e, a
6.0
SUMMARY
AND CONCLUSIONS The objective of the seismic analysis was to estimate the contribution to the GESSAR II plant risk from earthquake-induced core damage sequences.
The analysis consisted of several tasks:
- 1) a seismic hazard analysis,
- 2) structural and component fragility estimates, 3) seismic fault tree and event tree development and 4) fission product transport and offsite consequence analysis.
The output of the above tasks was the contribution to core melt frequency and offsite risk from seismically initiated accidents.
In order to establish the annual frequency of ground acceleration of a specific magnitude, a seismic. hazard curve was developed.
This single hazard curve is expected to reasonably bound the curves for potential GESSAR II sites.
The GESSAR II seismic hazard curve provides the annual frequency of exceedance of peak ground acceleration from values of 0.1 to
~3
-8 0.95 g with corresponding frequencies of exceedance of 10 to 10 per year.
Fragility data for components and structures important to safety in the GESSAR II plant have been estimated based on an extrapolation of design analyses supplemented by engineering judgement and available test data.
Median values of capacity factor and thus the median ground acceleration level corresponding to failure were determined for various failure modes.
Median capacity factors for structures ranged from 0.57 g (non-seismic Category I structures) to 30.9 g (RPV pedestal).
For components, the median capacity factors *anged from 0.20 g (ceramic insulators) to 4.62 g 130
GENERAL ELECTRIC COMPANY
- ~7*
PROPRIETARY INFORMATION (piping).
Seismic event trees were constructed to define accident sequences which could result in core damage.
Fault trees were defined which included seismic failures to evaluate system and component availa-
' bility in order to quantify the event trees.
The core damage frequencies were computed as a function of ground acceleration and multiplied by the frequency of occurrence of that ground accleration.
Finally, the core damage frequencies were summed over the hazard curve range.
The resulting
-7 annual core damage frequency was 4.0x10 The dominant contributor was loss of offsite power caused by failure of ceramic insulators.
The seismic accident sequences were grouped and analyzed according to the characteristics which are important to fission product release, i.e.,
pathways, flow rates, timing, retention mechanisms.
Sequences were combined into the appropriate release category for input to the offsite consequence evaluation.
The dominant release categories (Table 5-4) were associated with transients with loss of containment integrity at the time of RPV failure, ATWS, and transients with loss of heat removal which result in a long time to containment failure.
The suppression pool scrubbing function was maintained for the majority of the events and provided substantial fission product retention.
The long time to containment failure and pool scrubbing resulted in low offsite consequences for the seismic-initiated events.
The CRAC analyses U
of offsite consequences showed a total latent fatality risk of 9x10
-5 compared to the internal event riser of 1.66x10 Seismic-initiated core damage events contribute only 5 percent to total plant risk.
131
GENGRAL ELECTRIC COMPANY PROPRIETARY INFORMATION z7
- This small contribution to the risk is not unexpected for GESSAR II.
In the GESSAR II analysis, a conditional probability of 1 has been taken for containment failure given a core melt for both internally and externally-initiated accident sequences. Therefore, it would be expected that the.
risk contribution from seismic would be approximately proportional to the core damage frequency from seismic. events.
Other PRA's have assumed a very low conditional probability of containment failure for internal events compared to the conditional probability of containment failure for external events.
Therefore, for those analyses the contribution from external events dominates the results and is not proportional to the core damage frequency.
From the preceeding analysis it was concluded that the GESSAR II plant i
design:
1) provides substantial capacity for seismic events beyond the SSE.
2) the dominant contributors to seismic-initiated core damage events are failures of the ceramic insulators and structural failures 3) the core damage frequency from seismic events is a small fraction (9 percent) of the internal event core damage frequency 4) seismic initiators are an insignificant contributor to the GESSAR II plant risk.
132
'I
f GENERAL ELECTRIC COMPANY PROPRIEIARY INFURMA110N yo e
Appendix A Translation of Return Periods to Annual Frequency of Exceedance In order to translate the return periods of the USGS Open File Report to annual frequency of exceedance, the Binominal Probability Law was utilized as described in this Appendix.
Given that the probability of exceeding a given acceleration in a given year is P, from the Binominal Probability Law, the probability of exceeding that 4.cceleration y times in n years is given as P (y) = (") Py (1_p)n y (7) n where if = 0, 1, 2...
n = Y,T+1, (+2...
n n!
(y\\= !(n y)!
1 y The 90% probability of exceedance in 10 years is 10(0)=0.90=h0)po (y_p)10- 0 P
This can be interpreted as the probability of no earthquake (i.e., y=0) producing an acceleration greater than the acceleration level shown in the map in 10 years (i.e., n=10) is 0.90.
Then (1-0)10 = 0.90
~#
or p = 1.1x10 A-1
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GENERAL ELECTRIC COMPANY PROPRIETARY INFORMATION st y ";
- similarly for n=50 and n=250,
-3 p = 2.1x10 for n=50
~4 p = 4.2x10 for n=250 t
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