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Page 1 of 34 DSAR-APPENDIX F Classification of Structures and Equipment and Seismic Criteria Rev 2 Safety Classification:
Usage Level:
Safety Information Change No.:
EC 68812 Reason for Change:
Section being updated to clarify compliance of the Auxiliary Building crane (HE-2) with ASME NOG-1-2004 and NUREG-0554 per the modifications made via EC 68812 Preparer:
D.Sojka Fort Calhoun Station
DSAR-Appendix F Information Use Page 2 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Table of Contents 1.0 CLASSIFICATION OF STRUCTURES AND EQUIPMENT............................................. 5 1.1 Definition of Classes................................................................................................ 5 1.2 Classification of Buildings and Structures................................................................ 5 1.3 Classification of Systems and Equipment................................................................ 5 2.0 SEISMIC CRITERIA, ANALYSIS AND INSTRUMENTATION......................................... 6 2.1 Class I Seismic Criteria........................................................................................... 6 2.1.1 Design and Maximum Hypothetical Earthquakes......................................... 6 2.1.2 Stress and Deformation Criteria.................................................................... 7 2.1.3 Damping Factors........................................................................................ 11 2.1.4 Response Curves....................................................................................... 12 2.1.5 Fuel Handling Equipment........................................................................... 12 2.2 Methods of Analysis for Class I Structures and Components................................ 12 2.2.1 General
................................................................................................. 12 2.2.2 Structures or Equipment Supported In or On Other Structures.................. 13 2.2.3 Auxiliary Building........................................................................................ 18 2.2.4 Fuel Handling Crane................................................................................... 21 2.3 Plant Seismic Instrumentation............................................................................... 22 2.4 Class II Seismic Criteria........................................................................................ 23 2.5 Seismic Design of Equipment and Piping.............................................................. 24 3.0 APPENDIX F REFERENCES........................................................................................ 33
DSAR-Appendix F Information Use Page 3 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria List of Tables Table F Loading Combinations and Primary Stress Limits................................................. 8 Table F Damping Factors................................................................................................. 11 Table F Seismic Responses of Reactor and Auxiliary Buildings Obtained by Modal Analysis Using Response Spectrum Concept..................................................... 25 Table F Seismic Responses of Reactor and Auxiliary Buildings Obtained by Modal Analysis Using Response Spectrum Concept..................................................... 26 Table F Seismic Response of Reactor and Auxiliary Buildings Obtained by Modal Analysis Using Time-History Concept............................................................................... 31 Table F Seismic Response of Reactor and Auxiliary Buildings Obtained by Modal Analysis Using Time-History Concept............................................................................... 32
DSAR-Appendix F Information Use Page 4 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria List of Figures The following figures are controlled drawings and can be viewed and printed from the listed aperture card.
Figure No.
Title Aperture Card F-1 Response Spectra, Design Earthquake................................................... 36758 F-2 Response Spectra, Maximum Hypothetical Earthquake.......................... 36759 F-3 Foundation Spring Constants - Mass Data.............................................. 36760 F-4 Containment Structure - Absolute Accelerations..................................... 36761 F-5 Mode Shape Five Mass System Reactor and Aux Building..................... 36762 F-6 Mode Shape Five Mass System Reactor and Aux Building..................... 36763 F-7 Mode Shape Five Mass System Reactor and Aux Building..................... 36764 F-8 Mode Shape Five Mass System Reactor and Aux Building..................... 36765 F-9 Mode Shape Five Mass System Reactor and Aux Building..................... 36766 F-10 Mode Shape Five Mass System Reactor and Aux Building..................... 36767 F-11 Mode Shape Five Mass System Reactor and Aux Building..................... 36768 F-12 Equipment Responses............................................................................. 36769 F-13 Equipment Responses............................................................................. 36770 F-14 Equipment Responses............................................................................. 36771 F-15 Equipment Responses............................................................................. 36772 F-16 Equipment Responses............................................................................. 36773 F-17 Equipment Responses............................................................................. 36774 F-18 Floor Response Spectrum....................................................................... 36775 F-19 Floor Response Spectrum....................................................................... 36776 F-20 Floor Response Spectrum....................................................................... 36777 F-21 Floor Response Spectrum....................................................................... 36778 F-22 Floor Response Spectrum....................................................................... 36779 F-23 Floor Response Spectrum....................................................................... 36780 F-24 Floor Response Spectrum....................................................................... 36781 F-25 Floor Response Spectrum....................................................................... 36782 F-26 Floor Response Spectrum....................................................................... 36783 F-27 Floor Response Spectrum....................................................................... 36784 F-28 Horizontal and Vertical Absolute Accelerations Induced by Design Earthquake (OBE)............................................................................................ XB-545-S-38 F-29 Horizontal and Vertical Absolute Accelerations Induced by Maximum Hypothetical Earthquake (DBE).................................................... XB-545-S-39
DSAR-Appendix F Information Use Page 5 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria 1.0 CLASSIFICATION OF STRUCTURES AND EQUIPMENT 1.1 Definition of Classes Structures and components including instruments and controls designated as Seismic Class I as specifically defined in this section (not to be confused with ASME Class 1) are those whose failure might cause or increase the severity of an accident which could result in an uncontrolled release of radioactivity. Components and structures vital to supporting SFP Cooling, makeup, and Aux Building and Control Room HVAC are also included in the Class I classification. All other structures and components are classified as Class II.
1.2 Classification of Buildings and Structures Class I buildings and structures are listed below. Buildings and structures not listed are Class II; these contain conventional facilities.
- a. Auxiliary building (including the control room, spent fuel storage pool, safety injection and refueling water storage tank, and emergency diesel generator rooms);
- b. Intake structure (up to elevation 1007.5).
1.3 Classification of Systems and Equipment Systems and equipment designated as Class I are listed below. Where necessary the description is amplified to indicate the Class I items. All supports, hangers, etc.,
associated with Class I equipment are also to Class I standards. Systems, equipment and other items not listed are Class II.
Systems and Equipment
- 1.
Control room HVAC inlet ductwork
- 2.
Auxiliary building HVAC system
- 3.
Emergency power - Diesel generators (including starting air from air receivers to air start motors, fuel oil transfer and storage), station batteries
- 4.
Normal station electrical power - switch gear, control boards, control centers, bus ducts, and cables required for Class I systems and equipment
- 5.
Spent fuel pool cooling system
- 6.
Portions of the radioactive liquid waste disposal system
- 7.
Spent Fuel handling equipment
DSAR-Appendix F Information Use Page 6 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria
- 8.
Fire protection system (pump house only)
- 9.
Fuel handling crane
- 10.
Radiation monitoring system in auxiliary building
- 11.
Component cooling water system
- 12.
Safety injection system (alternate route to support Spent Fuel Pool Cooling)
- 13.
Instruments and control devices required for monitoring Spent Fuel Pool per Appendix G
- 14.
Raw water system 2.0 SEISMIC CRITERIA, ANALYSIS AND INSTRUMENTATION 2.1 Class I Seismic Criteria 2.1.1 Design and Maximum Hypothetical Earthquakes The following criteria was applied to components, structures and equipment for the design earthquake and maximum hypothetical earthquake.
Design Earthquake (Operating Basis Earthquake)
All Class I components, systems and structures are designed so that the seismic stresses resulting from the response to a ground acceleration of 0.08g acting in the horizontal direction and two-thirds of 0.08g acting in the vertical direction simultaneously, in combination with the primary steady state stresses, are maintained within the allowable working stress limits accepted as good practice and, where applicable, set forth in the appropriate design standards; e.g., the ASME Boiler and Pressure Vessel Code, B31.1 (1967) and B31.7 (1968) Codes for Pressure Piping, ACI 318 Building Code Requirements for Reinforced Concrete, and AISC Specifications for the Design and Erection of Structural Steel for Buildings.
Maximum Hypothetical Earthquake (Design Basis Earthquake)
All Class I components, systems and structures are designed so that seismic stresses resulting from the response to a ground acceleration of 0.17g acting in the horizontal direction and two-thirds of 0.17g acting in the vertical direction simultaneously, in combination with the primary steady state stresses, are limited so that the function of the component, system or structure is not impaired in such a manner that function is prevented.
DSAR-Appendix F Information Use Page 7 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria 2.1.2 Stress and Deformation Criteria The stress and deformation criteria for piping systems, vessels and supports for the various design load combinations are presented in Table F-1.
Stress and deformation criteria for seismic Class I HVAC systems are available in the Alternate Seismic Criteria and Methodologies (ASCM) (briefly described in Section F.2.2.3) which may be used, provided the analysis is performed in accordance with the caveats, requirements, and methods identified therein. (Reference 3.6) For seismic Class I systems the necessary restraints employed to limit deformations during the maximum hypothetical earthquake are such that stresses will not cause rupture. The natural frequency of each system was determined analytically to ensure proper positioning of these restraints or energy absorbing devices.
Seismic Class I equipment is capable of functioning during and following a maximum hypothetical earthquake. Analyses were made to provide assurance that elements would not come into contact because of displacements occurring during the seismic disturbance. Where necessary, clearances were increased accordingly.
GIP-3 (Reference 3.12) may be used as an alternative method for showing that systems and equipment will not be adversely affected by potential seismic interactions with nearby equipment and structures. See Section F.2.2.2 for a description of the caveats and requirements for this alternative seismic qualification method.
DSAR-Appendix F Information Use Page 8 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Table F Loading Combinations and Primary Stress Limits Primary Stress Limits Loading Combinations Vessels Piping (e)
Supports (f)
- 1.
Design Loading +
PM < SM PM < 1.2Sh Working Design Earthquake Stress PB + PL < 1.5SM PB + PM < 1.2Sh
- 2.
Normal Operating PM < SD PM < SD Within Loadings + (Maximum Yield Hypothetical Earthquake 1.5 1
2
4 cos
2 x
+ (Fluid Transient Loadings) (g))
(b)
(c)
DSAR-Appendix F Information Use Page 9 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Table F Loading Combinations and Primary Stress Limits (Continued)
NOTES:
(a)
These stress criteria are not applied to a piping run within which a pipe break is considered to have occurred.
(b)
Loading combinations 2 and 3, stress limits for vessels, are also used in evaluating the effects of local loads imposed on vessels and/or piping, with the symbol PM changed to PL.
(c)
The tabulated limits for piping are based on a minimum "shape factor". These limits are modified to incorporate the shape factor of the particular piping being analyzed.
(d)
Not Used (e)
As an alternative to USAS B31.7, 1968, Class 3, piping analysis may also be performed in accordance with ASME III, 1980 Edition (no Addenda). Material properties shall be from the original code of record (i.e., USAS B31.7, 1968).
Associated stress limits shall be in accordance with ASME III, 1980 Edition (no Addenda) for Service Levels as shown below:
Load Combination Service Level A: Design Loading (Pressure, Weight, Other Mechanical Loadings, and Thermal where applicable)
Service Level B: Design Loading + Design Earthquake Service Level C: Normal Operating Loadings + (Maximum Hypothetical Earthquake + (Fluid Transient Loading) (g))
(f)
Support analysis will continue to be performed in accordance with the existing licensing basis (i.e., Seventh Edition, AISC, American Institute of Steel Construction).
(g)
Square-Root-Sum-of-the-Squares may be used to combine loads.
DSAR-Appendix F Information Use Page 10 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Table F 1 - Loading Combinations and Primary Stress Limits (Continued)
Legend PM = Calculated Primary Membrane Stress The following typical values are selected to illustrate the conservatism of this approach for PB = Calculated Primary Bending Stress establishing stress limits. Units are 103 lbs/sq.in.
PL = Calculated Primary Local Membrane Stress Material SY (1)
Su SD SL SM = Tabulated Allowable Stress Limit at A-106B 25.4 60.0 (2) 25.4 36.9 Temperature from ASME Boiler and Pressure Vessel Code,Section III.
SA-533B 41.4 80.0 (2) 41.4 54.3 SY = Tabulated Yield at Temperature, ASME Boiler 304 SS 17.0 54.0 (3) 18.35 29.3 and Pressure Vessel Code,Section III 316 SS 18.5 58.2 (3) 22.2 31.7 Sh = Tabulated Value at Temperature from USAS B31.7 (1)
From ASME Boiler and Pressure Vessel Code,Section III, 1968 Revision, at 650°F.
SD = Design Stress (2)
Minimum value at room temperature which is
= SY (for ferritic steels) approximately the same at 650°F for ferritic materials.
= 1.2SM (for austenitic steels)
(3)
Estimated.
SL = SY + 1 (Su - SY) 3 Su = Tensile Strength of Material at Temperature
DSAR-Appendix F Information Use Page 11 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Piping runs are designed with sufficient flexibility to accept differential movement between structures without exceeding the allowable stress criteria presented in Table F-1. However, the containment and auxiliary building are on a common mat and, therefore, movement between these structures is not significant in contributing to piping stress levels. Estimates of these displacements are available in Reference 3.6. In addition, seismic anchor motion (SAM) displacements between the Auxiliary Building and the Turbine Building, which are significant were calculated. These displacements can be used for analysis of piping, such as Raw Water, which pass between the two structures. (Reference 3.6) 2.1.3 Damping Factors Damping factors used in the design of seismic Class I components and structures are shown in Table F-2. Alternatively, the damping factors of Reference 3.6 may be used, provided the analysis is performed in accordance with the caveats, requirements, and methods described for the ASCM. Another alternative which may be used for mechanical and electrical equipment is to use the damping factors in GIP-3 (Reference 3.12), provided the evaluation is performed in accordance with the caveats, requirements and methods described in Reference 3.10. See Section F.2.2.2 for a discussion of the use and limitations of GIP-3.
Table F Damping Factors Percent Damping Maximum Design Hypothetical Component or Structure Earthquake Earthquake Steel Assemblies Bolted or Riveted 2.0 2.0 Welded 1.0 1.0 Vital Piping Systems 0.5 0.5 Rigid Vault Type Concrete Structures 2.0 5.0 Framed Concrete Structures 5.0 7.0 Auxiliary Building Crane 4.0 7.0
DSAR-Appendix F Information Use Page 12 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria 2.1.4 Response Curves Response curves are shown in Figures F-1 and F-2 for the design and maximum hypothetical earthquakes respectively and were used for the design of seismic Class I components and class I structures.
The response spectrum concept provides a conservative approach which has been found generally to be satisfactory for other sites with similar sub-surface conditions. The spectra conform to the average spectra developed by Housner (and presented in Reference 3.1) for frequencies higher than about 0.33 cycles per second. The spectra for frequencies lower than about 0.33 cycles per second were prepared utilizing data presented by Newmark (Reference 3.2).
The spectra have been 'normalized' to a horizontal ground acceleration of eight percent of gravity for the design earthquake and seventeen percent of gravity for the maximum hypothetical earthquake.
2.1.5 Fuel Handling Equipment All fuel handling equipment is designed for a seismic loading of 0.09g vertical and 0.19g horizontal applied simultaneously. The stress under the combined deadweight live and seismic loads will not exceed the allowable stress of the material. Furthermore, the equipment will withstand a simultaneous vertical acceleration of 0.13g and a horizontal acceleration of 0.27g in conjunction with normal loads without exceeding material minimum yield stresses. Guide rollers restrict lateral movement of the fuel handling machine and the spent fuel handling machine on their rails and have been designed for seismic loads in excess of the above values. In addition, because of its high center of gravity, the spent fuel handling machine is provided with keepers to prevent overturning under seismic shock conditions.
2.2 Methods of Analysis for Seismic Class I Structures and Components 2.2.1 General The following methods of analysis were applied to Class I structures, systems and equipment:
- a. The natural frequency of vibration of the structure or component was determined.
- b. The response acceleration of the component to the seismic motion was taken from the response spectrum curve at the appropriate natural frequency and damping factor.
DSAR-Appendix F Information Use Page 13 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria
- c. Stresses resulting from the combined influence of normal loads and the additional load from the design earthquake were calculated and checked against the limits imposed by the design standard.
- d. Stresses and deflections resulting from the combined influence of normal loads and the additional loads from the maximum hypothetical earthquake were calculated and checked to verify that deflections would not prevent functional performance and that stresses would not produce rupture.
2.2.2 Structures or Equipment Supported In or On Other Structures Structures or equipment supported in or on other structures are classified into three groups based on their natural frequency and the frequency of the supporting structure as follows:
- a. Rigid Group: fn/f > 2.0
- b. Resonance Group: 0.7 < fn/f < 2.0
- c. Flexible Group: fn/f < 0.7 Where: fn is the natural frequency of the structure or equipment, and f is the frequency of the supporting structure in the corresponding location.
Rigid Group The analysis of equipment in the rigid group was based on applying a static load at its center of gravity. The load assumed was equal to the mass of the equipment multiplied by the maximum acceleration at the floor level on which the equipment was mounted.
Resonance Group If a structure or item of equipment was found to fall in the resonance group, the supporting structure or equipment was modified to alter the frequency and prevent resonance wherever possible. If the resonance condition could not be avoided the possibility of large amplitudes is avoided by the use of stops or damping devices. Dynamic design considering resonance vibration was performed when this was not possible. If the restriction of vibration was such as to make the element rigid, an examination assuming rigid behavior was also carried out.
Flexible Group Flexible elements were designed using induced accelerations corresponding with their frequencies. A careful check was made for elements which could come into contact because of excessive displacements.
DSAR-Appendix F Information Use Page 14 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Piping and Equipment The B31.7 piping design to be analyzed for seismic effects has been previously defined by:
- a. Pipe routing based on flow diagrams, equipment arrangement, accessibility, radioactivity considerations, drainage, venting, and other considerations.
- b. Preliminary thermal analysis for hot lines confirmed the routing.
Preliminary design was in accordance with B31.1.
- c. Pipe thickness based on B31.1. This selection usually allows a margin over required thickness according to B31.7.
- d. Piping details based on the appropriate code. For example, B31.7 Class I does not permit branches to intersect at angles less than 60 degrees.
- e. Hanger locations were determined in accordance with the appropriate codes.
The first step in seismic analysis of piping was to position seismic restraints closely enough to ensure that the natural frequency of piping in the auxiliary building and containment building was 6 hertz horizontally and 18 hertz in the vertical direction. A proprietary nomogram was developed to calculate the required restraints spacing. The weights of valves were also taken into consideration in spacing of the restraints. This ensures that the piping is in the rigid range when compared to the building in which it is situated. The response of the building to the seismic ground motion was determined as discussed in Section F.2.2.3, the resulting accelerations of which are shown on Figure F-4. Values based on the ASCM are available and can be used in analyses which adopt the ASCM as design basis (Reference 3.6). To simplify the piping analysis, the maximum accelerations obtained, those of the uppermost level of the structure, were used in all subsequent calculations. These accelerations are considered to act at the anchors and seismic restraints of the piping. In order to obtain the response of the piping between restraints, the building accelerations were multiplied by a magnification factor giving the design acceleration of the piping. The magnification factor was derived from the response spectra of Figures F-1 and F-2 normalized for the maximum building acceleration and using 0.5%
damping and a natural frequency of 6 hertz horizontally and 18 hertz vertically.
DSAR-Appendix F Information Use Page 15 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria The design thus determined was put into a proprietary computer program developed by the A.D. Little Company and modified to suit Gibbs & Hill requirements. This code was entitled ADL pipe. It calculated stresses in accordance with equations (9), (10) and (11) of B31.7. The following comments apply to ADL pipe as used by Gibbs & Hill:
- a. The final combination of stresses was done manually.
- b. Stresses are combined at the stress level, rather than moment level as permitted by B31.7.
- c. Seismic displacement of support points was considered in the following cases.
- 1. Part of the pipe was supported by the containment shell and part by the containment internal structure.
- 2. Part of this pipe was supported by the containment shell and part by the auxiliary building structure.
In all other cases, piping support points were considered fixed with respect to one another.
- d. Movement of pipe supports were considered when necessary. For example, the movement of the main steam line supports due to containment post tensioning was taken into account.
- e. The program did not include cyclic loading or thermal gradient thru the wall as required in equations 10 and 11.
B31.1 piping in the auxiliary building received the same attention with regard to selection of hangers and restraints as the B31.7 piping. Seismic stresses were combined with longitudinal stress due to pressure, weight and other sustained loads and limited to Sh (allowable stress in hot condition). Starting in 1979, in response to NRC IE Bulletins numbered 79-02, 79-04, 79-07, 79-14, and 81-01 and NRC Generic Letter No. 81-14, a complete seismic verification of all Critical Quality Element (CQE) piping systems, as defined in the Fort Calhoun Station's CQE list (except those portions of the system that were inaccessible), was initiated. The initial part of the verification process consisted of identifying where adequate documentation existed to demonstrate the seismic qualification of each CQE system. Where adequate documentation did not exist, those systems 2-1/2" in diameter and larger were reanalyzed using the stress criteria identified in Section F.2.1 with a newer, more sophisticated dynamic loading model than previously described.
The net result of the reverification program has been that in some cases, piping systems were determined to be in the resonance group. Piping in the
DSAR-Appendix F Information Use Page 16 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria resonant group was reviewed to determine if excessive displacement or stress was present. If stresses were within allowables and no interference due to the deflection is created the piping is adequate. The piping that did not meet these criteria was modified by use of stops and dampers to adequately prevent large amplitude deflections or an attempt was made to increase the systems natural frequency to 6 Hz horizontal and 18 Hz vertical by adding additional restraints.
Special seismic restraints were provided on control valve mechanisms to prevent overstress when the control mechanism forms a mass center outside the pipe center line and generates over 1500 psi bending stress on the piping system due to earthquake G loading.
The waste disposal tanks are fitted with horizontal restraints at the upper and lower ends, to avoid overloading the equipment support under seismic loading.
Special seismic restraints were installed on the electrical cable trays. The cable trays were supported vertically and horizontally so as to meet the stress criteria under all conditions including the postulated earthquakes.
Spacing of vertical supports is sufficiently close to maintain the lowest vertical dominant natural frequency of the cable trays above 18 Hz, which is double the dominant natural frequency of the building. Where multiple tray arrangements make determination of the natural frequencies unfeasible the system has been analyzed for a resonant condition, using a time-history approach. The cable trays are braced horizontally at a spacing to ensure a minimum natural frequency of 6 Hz, double the dominant horizontal natural frequency of the building. The stresses due to the resulting seismic response are maintained within the allowable limits.
In 1980, the NRC initiated an Unreviewed Safety Issue (USI) A-46 to review the seismic adequacy of equipment in certain operating nuclear power plants against seismic criteria not in use when these plants were licensed. Fort Calhoun Station was identified as one of the A-46 plants which must be reviewed. OPPD joined the Seismic Qualification Utility Group (SQUG) which published the Generic Implementation Procedure, Revision 2 (GIP-2)
(Reference 3.7) for evaluating these plants. The NRC accepted the SQUG procedure for resolving USI A-46 in Supplementary Safety Evaluation Report No. 2 (SSER No. 2) (Reference 3.8). OPPD used GIP-2 in its entirety, including the clarifications, interpretations, and exceptions identified in SSER No. 2, as clarified by the August 21, 1992, SQUG letter (Reference 3.9), to evaluate the seismic adequacy of selected safe shutdown equipment in the Fort Calhoun Station (Reference 3.10). The NRC issued a Safety Evaluation Report to OPPD on July 30, 1998, which accepted the results of the USI A-46 program for Fort Calhoun Station, including the approach used to resolve the outliers (Reference 3.11).
DSAR-Appendix F Information Use Page 17 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria SQUG issued Revision 3 of the GIP (GIP-3) on May 16, 1997, to include additional restrictions and certain editorial and typographical changes to GIP-2 (Reference 3.12). The NRC accepted these changes in Supplemental Safety Evaluation Report No. 3 (SSER No. 3) (Reference 3.13).
The elements of the OPPD submittal for resolution of USI A-46 are maintained using the GIP (Reference 3.10). This is used no longer used for safe shutdown and is used to support the defueled condition and the functional requirements of the spent fuel pool and cooling systems.
The GIP-3, including the clarifications, interpretations and exceptions identified in SSER No. 2, as clarified in Reference 3.9 and in SSER No. 3 (Reference 3.13), may be used as an alternative method for seismic qualification of mechanical and electrical equipment, electrical relays, and cable and conduit raceway systems, and portions thereof. The use of GIP-3 is optional (i.e., the original design basis may continue to be used). This method can apply to the re-analysis or modification of existing items and to new or replacement items (except as noted below) and will be documented, therein, by reference to GIP-3 as the design basis for those calculations.
The GIP-3 was originally developed for resolution of USI A-46. As such, portions of this document contain administrative, licensing, and documentation information which is only applicable to the USI A-46 program.
Therefore, only the sections of GIP-3 listed below will be used to perform seismic qualification evaluation of equipment and systems. These sections will be used in their entirety, i.e., all the applicable criteria and methods defined in GIP-3 for an item of equipment or system will be used.
- a.
Part I, Section 2.3.4, Future Modifications and New and Replacement Equipment.
- b.
Part II, Section 2, Seismic Evaluation Personnel.
- c.
Part II, Section 4, Screening Verification and Walkdown.
i NOTE i
For new installations and for newly designed anchorages in modified or replaced items, the anchorage criteria in GIP-3, Part I, Section 2.3.4 will be used.
- d.
Part II, Section 6.4, Comparison of Relay Seismic Capacity to Seismic Demand, and Section 6.5, Relay Walkdown.
i NOTE i
It is not necessary to identify "essential relays" as defined in other parts of GIP-3, Part II, Section 6.
DSAR-Appendix F Information Use Page 18 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria
- e.
Part II, Section 8, Cable and Conduit Raceway Review.
i NOTE i
The additional evaluations and alternative methods for resolving raceway outliers in subsections 8.4.1 through 8.4.8 may be used. However, the generic methods for resolving outliers in GIP-3, Part II, Section 5 will not be used.
- f.
Part II, Section 10, References.
- g.
Appendix B, Summary of Equipment Class Descriptions and Caveats.
- h.
Appendix C, Generic Equipment Characteristics for Anchorage Evaluations.
- i.
Appendix D, Seismic Interaction.
- j.
Appendix G, Screening Evaluation Work Sheets (SEWS).
2.2.3 Auxiliary Building The analytical model for seismic design of the auxiliary building consists of several lumped masses distributed as depicted in Figure F-3. Mass M1 represents the dome with the ring girder; masses M2 and M3 represent the cylindrical shell; mass M4 represents the auxiliary building; mass M5 represents the mat and the internal masses of the containment structure.
The analytical model of the five masses was assumed to have 13 degrees of freedom, namely; two horizontal translations in the principal directions of each mass, two rotations of the entire assumed rigid system, and uncoupled vertical motion of the entire mass of the system. The five translational movements of the masses and the rotational movement of the entire mass in the same plane are coupled. The uncoupling of the vertical motion and the motions in the two vertical planes was based on the fact that the center of gravity of the entire system reasonably coincides with the center of gravity of the elastic foundation.
The lateral stiffness coefficient of the foundation, kH, depends on the soil modulus and elastic properties of the piles and was determined from the field test of piles. Vertical and rotary stiffness coefficients, kv and ko respectively, were obtained on the basis of elastic properties of the piles and bedrock.
The stiffness matrix was formed on the basis of the lumped mass system with elastic properties in discrete parts which included bending and shear characteristics.
DSAR-Appendix F Information Use Page 19 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria The structure's viscous-friction was assumed to be 5 percent of the structure's critical damping for the maximum hypothetical earthquake and 2 percent for the design earthquake. For concrete structural components that would not crack under the maximum hypothetical earthquake, a damping factor of 2 percent was employed.
The choice of damping factors and their use in the seismic design of the containment structure was based on the following considerations. The containment structure and the auxiliary building are supported on a continuous mat, common to both structures. This mat is supported on 803 steel pipe piles driven to rock. During an earthquake, the response of this system would include horizontal and vertical translational movements of the whole structure, rocking motions of the containment and of the auxiliary building involving deformation of the piles, and an oscillatory motion of individual masses comprising the superstructure. The predominant damping effect during this motion would be in the soil-pile system and in the soil-mat system; for this damping effect, a value of damping coefficient of 0.02 was used for the design earthquake and 0.05 for the maximum hypothetical earthquake.
The following procedure was utilized for the seismic design of the containment and auxiliary building structure:
- a.
Determination of undamped modes and frequencies;
- b.
Determination of the response of all elements of the system using a damping coefficient of 0.02 for the design earthquake and maximum hypothetical earthquake;
- c.
Determination of the response of all the elements of the system using a damping coefficient of 0.05 for the maximum hypothetical earthquake.
- d.
For the design earthquake, the absolute accelerations obtained with a damping coefficient of 0.02 were applied to the containment and auxiliary building structures. For the maximum hypothetical earthquake, the absolute accelerations were obtained using both 0.02 and 0.05 damping factors, independently. The same damping factors were used in each mode. Then, the absolute accelerations resulting from a damping factor of 0.02 were applied to the containment shell only, and the absolute accelerations resulting from a damping factor of 0.05 were applied to the rest of the masses. This approach yields more conservative results in this case than would a method of analysis which uses different damping in different modes. For example, an approximate rule for determining the appropriate damping
DSAR-Appendix F Information Use Page 20 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria rn hn sn rn r
hn h
sn s
n E
E E
E D
E D
E D
D
+
+
+
+
=
for a mode is to weight the damping associated with the individual springs according to the stored energy in each spring:
Where Dn is the weighted average damping for the n-th mode; Ds, Dh and Dr are the damping factors for motion of the superstructure, for swaying due to soil-structure interaction and for rocking due to soil structure interaction, respectively, and Esn, Ehn, and Ern are the energies stored in the n-th mode in the superstructure and in the swaying and rocking springs, respectively. Since it is known that a large damping factor is associated with swaying and due to the fact that the principal contribution, in this particular case, is in the lowest frequency mode which is predominantly associated with swaying, one would expect that the accelerations obtained as described above, using relatively low damping factors, are conservative.
The absolute modal accelerations were combined by the root-mean-square method, i.e., the square root of the sum of the squares of the modal accelerations was obtained.
- e.
The amplification due to the vertical ground excitation of the containment and auxiliary building with a common mat was carried out in the dynamic analysis. The entire structure was lumped into one mass for the vibration in the vertical direction. Furthermore, the vertical motion was assumed to be uncoupled from the rest of the motions of this system. The vertical rigidity constant of the foundation was obtained on the basis of elastic properties of the piles and bedrock.
Diagrams of the containment shell absolute accelerations as a function of height above the mat are shown in Figure F-4 for the design earthquake and maximum hypothetical earthquake.
Sufficiently wide joints are provided between the containment shell and adjacent structures to avoid any possible collision as the structures deflect independently under the seismic action.
DSAR-Appendix F Information Use Page 21 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria An additional dynamic analysis of the Containment and Auxiliary Building structures, as well as the Intake Structure and Turbine Building, was performed utilizing a more refined structural model and state-of-the-art methods of Soil Structure Interaction (SSI). These analyses utilize a time history methodology for deriving structural response to seismic input. The time histories used as input to these analyses were mathematically derived by generating artificial time histories having response spectra which conservatively envelope the ground spectra described in Section F.2.1.4. The results of these analyses were used to derive alternate floor response spectra and seismic anchor motions for use with damping values, criteria and methods (i.e., Alternate Seismic Criteria and Methodologies) more current than the original design basis. The details of the analyses performed and the resultant criteria and floor response spectra can be found in Reference 3.6. A review of these analyses and criteria was performed by the NRC, and Reference 3.5 documents NRC acceptance of them as the basis for an alternate (i.e., in lieu of the original design basis) seismic criteria and methodology for analyses of equipment and structures at Ft. Calhoun.
The use of the ASCM is optional (i.e., the original design basis may continue to be used) but it will become the design basis for those systems, equipment or portions thereof for which the criteria is used in analysis and design. This can apply to reanalysis of existing items or first-time analysis of new items and will be documented, therein, by reference to EA-FC-94-003 as design basis for those calculations. The caveats and requirements for use of the ASCM are set forth in Reference 3.6.
2.2.4 Fuel Handling Crane The fuel handling crane was analyzed considering that the supporting runway girders are subject to the accelerations obtained from the seismic analysis of the auxiliary building structure.
A structural analysis of all crane structural members was performed for the combination of seismic loads (horizontal and vertical) and dead load.
In order to avoid large forces on the crane structure the crane wheels must be permitted to move transversely across the rail. For this reason, the wheels are double flanged with sufficient clearance between the flanges to accommodate the maximum differential movement. For this reason also, rail clamps are not provided. However, stops are furnished to assure that the crane cannot be displaced from the rail during an earthquake.
DSAR-Appendix F Information Use Page 22 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria The stops are stiffened steel assemblies bolted to the crane girders and located so as to contact the sides of the runway girders should the wheel flange fail to stop the motion of the crane in the direction normal to the rail.
The striking surfaces of the stops provide flat contact with the runway girders.
A gap is provided between each stop and the runway girders to avoid contact during normal crane operation. The design function of the stops meets the requirements of ASME NOG-1-2004 and NUREG-0554.
The runway girders are designed for the applied crane loads from the wheels and the stops in accordance with Section 5.11.
Multi-mass modal analyses of the fuel handling crane have been performed utilizing the vertical floor responses spectrum applicable to the structure supporting the crane. The floor spectra have been developed by a modal analysis time-history method utilizing as input the ground motions of 1940 El Centro and 1952 Taft normalized to the ground acceleration of the maximum hypothetical earthquake. These analyses show that during the maximum hypothetical earthquake neither the main crane trucks nor the trolley will be subject to a net uplift.
Similar steel stops with vertical striking surfaces are provided on the trolleys to prevent the trolley wheels from being displaced from their rails.
The acceleration of the crane runway during the maximum hypothetical earthquake has been considered in the design of the stops. End bumpers were also provided on the trolley and runway.
2.3 Plant Seismic Instrumentation Seismic instrumentation is provided to determine the response of the containment and auxiliary building structure in the event of an earthquake so that such response can be compared with that used as the basis of design.
Two strong motion triaxial accelerographs are provided, one at the top of the foundation mat in the basement of the containment building and one directly above it on the operating deck at elevation 1045'-0". Since the foundation mat is common to both the containment and the auxiliary buildings and the dynamic analysis utilizes a model which includes the auxiliary building, the containment and their common foundation; the measured response at these two points will permit an evaluation of the actual response versus the seismic design values.
The upper accelerograph is located directly above the lower accelerograph and the horizontal axes of both instruments coincide. Each accelerograph is connected to a magnetic tape recording system located in the control room. The magnetic tape playback system can be connected to a strip chart recorder, thus providing a permanent record of the acceleration time history in both the vertical and the two orthogonal, horizontal directions. Operation of both accelerographs is initiated
DSAR-Appendix F Information Use Page 23 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria simultaneously by a single seismic trigger which responds to vertical or horizontal acceleration at a preset low level. Switch closure is maintained for a minimum duration after the vibrational level drops below the preset value. The seismic trigger also automatically resets itself after each actuation so that any aftershocks are also monitored.
The instruments are operated by batteries which are automatically recharged and are enclosed in sealed metal containers rigidly bolted to the supporting structure. The accelerographs are accessible for periodic maintenance which consists of calibration runs of the instrumentation and replacement of batteries as required.
Should a seismic disturbance occur in the neighborhood of the plant or such that the seismic instrumentation is triggered, the accelerations recorded within the plant will be the basis for a decision as to required equipment evaluation. The recorded maximum acceleration will be compared to 1.0 times the acceleration predicted during the operating basis earthquake (see Figure F-28) for the structure at the point where the seismic instrumentation is located to help evaluate actions required to address potential damage. After the danger of aftershocks is considered to have become negligible, testing will be performed to ensure that required equipment is undamaged and in proper working order. A visual inspection of the plant will also be carried out to verify that no structural damage has occurred.
Maintenance of the seismic instrumentation consists of periodic checks to ensure continuous Functionality. Exact maintenance procedures and intervals are in accordance with the manufacturer's recommendations.
2.4 Seismic Class II Criteria Seismic design for all Class II structures was governed by the requirements of the National Building Code, 1967 edition. The National Building Code is the governing code for Washington County, Nebraska, in which the plant is located. This code is identical with the Uniform Building Code for earthquake design requirements. The numerical coefficient representing seismic intensity is equal to 0.25 and is the value of "Z" as established by this code for locations in zone 1, the zone designated for the area in which the plant site is located on the map of seismic probability included as a part of the code.
Seismic Class II equipment and components conform to the applicable design codes and standards..
The Turbine Building, which is seismic Class II, was dynamically analyzed, in Reference 3.6, to determine values of Seismic Anchor Motion (SAM) and Floor Response Spectra (FRS) for use in analyzing the Main Steam and Main Feedwater piping which pass between these structures. The Turbine Building was not structurally evaluated for the associated moments and forces from this analysis.
DSAR-Appendix F Information Use Page 24 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria 2.5 Seismic Design of Equipment and Piping For the Fort Calhoun plant, the criterion is that if the lowest dominant natural frequency of the equipment or piping is 6 Hz or above horizontally or 18 Hz or above vertically, the ground motion response spectra, normalized to the acceleration at the elevation of the equipment support, may be used as an input for the analysis to determine the equipment response.
The basis for this criterion is that the lowest dominant natural frequency of both the reactor building and the auxiliary building is approximately 3 Hz horizontally and 9 Hz vertically and that higher modes of vibration of the building will not contribute significantly to the response of equipment attached to the building. The latter statement is made specifically for this particular plant and follows from the fact that the combined mat which supports both buildings is founded on long end-bearing steel piles. This type of foundation with its high vertical rigidity and relatively low horizontal rigidity, responds to horizontal seismic excitation primarily in horizontal translation and only very slightly in rocking. Thus the principal contribution to the total response of the internal structure of the reactor building and the auxiliary building is in the lowest frequency mode due primarily to horizontal translation arising from the soil-pile interaction.
The response of the five lumped masses of the reactor and auxiliary buildings model for six modes of vibration in a vertical plane have been obtained from the seismic analysis of the structure. These values are tabulated in Table F-3 and F-4 together with the total response of each mass calculated as the square root of the sum of the squares of the modal responses. On Figures F-5 thru F-11, the mode shapes of the system are shown for each of the modes. It can be readily seen that the principal contribution to the response of the internal structure is in the lowest frequency mode and that the rocking associated with this mode is insignificant. In the second frequency mode of about 6 Hz, there is some distortion arising from flexural and shearing effects of the containment dome and the upper and lower portions of the containment shell but the principal contribution to the total response of these masses is in the lowest frequency mode.
It should be noted that the seismic analysis of the structure is based on a somewhat conservative assumption that the sum of the mass moments of inertia of the individual masses, which assumes no vertical distortion between the masses, can be replaced by the moment of inertia of the assumed rigid entire mass. This assumption results in higher values associated with the rotary inertia effect. Moreover, the modal analysis of the structure is based on flexible rocking springs calculated on the conservative assumption that the axial rigidity of the piles alone, without the effect of the surrounding soil, contributes to the stiffness of the rocking springs. These two assumptions increase the calculated rocking effect.
The masses for the containment, shell, and internal structure are kept in the DSAR to maintain the model and are no longer required to be a seismic Class I structure.
DSAR-Appendix F Information Use Page 25 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Table F Seismic Responses of Reactor and Auxiliary Buildings Obtained by Modal Analysis Using Response Spectrum Concept Operating Basis Earthquake Direction of Ground Excitation N-S VERT E-W Modal Natural Frequencies -Hz Mass 3.02 6.23 8.85 20.30 24.40 29 COMB RMS 9.12 3.03 6.37 8.78 19 23.3 30.7 COMB RMS Location Absolute Accelerations - g's and g-rad/ft Dome 1
0.258
-0.076 0.005
-0.001 0.002 0.0 0.269 0.090 0.250
-0.067 0.005
-0.002 0.002 0.0 0.260 Upper Containment Cylindrical Shell 2
0.227
-0.044 0.003 0.002
-0.003 0.001 0.231 0.090 0.224
-0.039
.004
.002
-0.003 0.001
.227 Lower Containment Cylindrical Shell 3
0.182 0.001 0.001 0.002
-0.001 -0.001 0.182 0.090 0.183
-0.001 0.001 0.003
-0.001 0.001 0.183 Auxiliary Building 4
0.175 0.013
-0.001
-0.001
-0.001 0.0 0.177 0.090 0.177 0.12
-0.002
-0.001
-0.001 0.0 0.178 Internal Structure Within Containment and Mat 5
0.161 0.016 0.0 0.001 0.001 0.0 0.163 0.090 0.163 0.013 0.0 0.001
.001 0.0 0.164 Entire Structure Rotary Interia 0.0263 x10-2
-0.0214 x10-2
-0.0037 x10-2 0.0032 x10-2 0.0016 x10-2 0.0 0.0344 x10-2 0.0 0.0208 x10-2
-0.0147 x10-2
-0.0045 x10-2 0.0003 x10-2 0.0002 x10-2 0.0 0.0258 X10-2 NOTE: RMS = Square root of the sum of the squares of modal responses.
DSAR-Appendix F Information Use Page 26 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Table F Seismic Responses of Reactor and Auxiliary Buildings Obtained by Modal Analysis Using Response Spectrum Concept Design Basis Earthquake Direction of Ground Excitation N-S VERT E-W Modal Natural Frequencies -Hz Mass 3.02 6.23 8.85 20.30 24.40 29 COMB RMS 9.12 3.03 6.37 8.78 19 23.3 30.7 COMB RMS Location Absolute Accelerations - g's and g-rad/ft Dome 1
0.538
-0.143 0.009
-0.003 0.004
-0.0007 0.555 0.130 0.525 -0.130 0.011
-0.004 0.004
-0.0006 0.540 Upper Containment Cylindrical Shell 2
0.474
-0.083 0.006 0.003
-0.006 0.0018 0.482 0.130 0.465 -0.077 0.008 0.004
-0.007 0.0016 0.472 Lower Containment Cylindrical Shell 3
0.380 0.001 0.002 0.005
-0.002
-0.0028 0.381 0.130 0.380 -0.002 0.002 0.007
-0.003
-0.0023 0.381 Auxiliary Building 4
0.254 0.017
-0.002
-0.002
-0.002 0.0 0.255 0.130 0.257 0.016
-0.002
-0.003
-0.001 0.0 0.258 Internal Structure Within Containment and Mat 5
0.234 0.021 0.0 0.001 0.002 0.0 0.236 0.130 0.236 0.017 0.0 0.002 0.002 0.0003 0.238 Entire Structure Rotary Interia 0.0380 x10-2
-0.0273 x10-2
-0.0052 x10-2 0.0006 x10-2 0.0005 x10-2 0.0 0.0416 x10-2 0.0 0.0300 x10-2
-0.019 x10-2
-0.0064 x10-2 0.0008 x10-2 0.0003 x10-2 0.0 x10-2 0.0362 x10-2 NOTE: RMS = Square root of the sum of the squares of modal responses.
DSAR-Appendix F Information Use Page 27 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria In order to substantiate the statement that the lowest frequency mode of the structure governs the response of equipment, a time-history analysis has been performed for a piece of equipment of a single-degree-of-freedom representation with a natural frequency in resonance with the lowest frequency mode of the structure. The analysis has been performed using six modes of vibration of the structure in a vertical plane and also using only the lowest dominant frequency mode of the structure. The time-history is the 1940 El Centro N-S ground motion record. Damping is assumed to be one percent of critical for the equipment and two percent for the structure corresponding to the Operating Basis Earthquake. The equipment supports are assumed to be located at an elevation of 995'-0", (i.e., at the center of gravity of the mass of the analytical model representing the internal structure of the containment and the mat). The maximum acceleration obtained using six structure modes 2.33 of gravity as compared to 2.19 of gravity using the lowest frequency mode of the structure. These results also indicate that the rocking motion due to soil-pile-structure interaction is negligible.
Floor response spectra have been developed for masses No. 2, No. 4 and No. 5, by a modal analysis time-history method using as input the normalized El Centro ground motion. For this purpose the recorded El Centro N-S horizontal time-history has been scaled to 0.08g and 0.17g which correspond to the Fort Calhoun OBE and DBE ground accelerations respectively. The analytical model used for the construction of the horizontal floor response spectra (as shown in Figure F-5 Part A) consists of five masses, namely mass No. 1 representing the concrete dome, masses No. 2 and No. 3 simulating the upper and lower portion of the containment shell respectively, mass No. 4 representing the auxiliary building and mass No. 5 representing the containment internal structure and mat. Each mass was assumed to have two translational degrees of freedom in the two principal directions. The two additional degrees of freedom are due to rotary inertias of the entire structure about the two horizontal principal axes. All six structure modes of vibration were used in the development of the horizontal response spectra. Equipment damping is taken as 0.5% of critical. The procedure used to generate the floor response spectra is described below:
Having established the normal modes, the equation of structure motion in matrix form can be written:
°° ° °°
{qn} + [2wns] {qn} + wn 2 {qn} = -R S(t) {n} (1)
°° ° where {qn}, {qn} and {qn} are the column matrices of model relative accelerations, velocities and displacements of the structure in normal coordinates, wn is the circular natural frequency of the structure of mode n, s is the fraction of critical damping of the structure in mode n, [n] is the column matrix of the modal participation factors, S(t) is the time varying acceleration of a recorded ground motion and R is the scaling factor by which the maximum acceleration of an actually recorded accelerogram is scaled to the maximum acceleration predicted for the site of the structure involved.
DSAR-Appendix F Information Use Page 28 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria In order to obtain response of any one-degree system mounted within the structure, the following equation of motion can be used:
°° ° N °° °° qm + 2wme qm + w2 qm = -( in qn + R S (t)) (2) n=1
°° ° where qm,qm and qm are the equipment relative acceleration, velocity and displacement, respectively, wm is the circular frequency of the equipment, e is the critical damping ration of the equipment, and in is the modal shape of the structure of mass i in mode n.
Equations (1) and (2) are solved by numerical integration utilizing the computer program presented in Reference 3.1 for IBM 1130 computer. The output consists of the following accelerations:
°° R S(t)
=
scaled predicted ground motion
°° N °° °° Wi = inqm + R S(t)
= absolute acceleration for any mass n=1 (i) of the structure
°° qm
=
relative acceleration of the equipment
°° °° Wi + qm
=
absolute acceleration of the equipment Suitable time intervals t for a step-by-step numerical integration were selected.
It should be noted that a system of equations of motion, consisting of several masses and spring constants of a structure subjected to a time-history support motion, may also be solved by numerical integration. In this case, the numerical integration technique must be performed simultaneously for all of the coupled equations. This procedure is cumbersome, requiring a large amount of computations, and is susceptible to computational difficulties. For example, it is difficult to know how small the time intervals should be to avoid mathematical instability. Furthermore, there is no really satisfactory way to determine all of the damping coefficients in these equations.
Because of these difficulties, the modal method of analysis was used as described above.
The resulting spectra for masses No. 2, No. 4, and No. 5 for DBE and OBE are shown on Figure F-12 thru F-17. The normalized ground response spectra for frequencies exceeding 3 Hz are also shown on these figures.
DSAR-Appendix F Information Use Page 29 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria For the modal analysis of the reactor coolant system, horizontal response spectra have been developed by the procedure described above, but using the computed responses to actual time-history inputs of two ground motion records: 1940 El Centro N-S component and 1952 Taft N-21E component. Also, the San Francisco Golden Gate recorded accelerogram was used in some instances in order to check the conservatism of the response. The responses obtained from Taft and El Centro accelerograms govern the peaks in all cases. The envelope of maximum peaks was used for the construction of the spectra for equipment frequencies in the horizontal direction between approximately 6 Hz and 1 Hz and in the vertical direction between approximately 15 Hz and 5 Hz. As for the spectra discussed above, all six structure modes of vibration were used. Uncertainties associated primarily with the evaluation of the foundation rigidities were taken into account by parametric studies which resulted in shifting of the resonance peaks of the floor spectra. Normalized ground motion response spectra were used for equipment frequencies of about 6 Hz and above for the construction of horizontal spectra and for equipment frequencies of about 18 Hz and above for the vertical spectra. The resulting horizontal floor response spectra of the containment internal structure and mat (mass No. 5), shown in Figures F-18 and F-19, have been developed at an elevation of 995'-0", the center of gravity of mass No. 5. Figures F-20 and F-21 show these spectra normalized to an elevation of 1006'-4 1/2" which is the elevation of the reactor vessel inlet and outlet nozzles. Normalizing of these spectra is in accordance with the variation in structure acceleration shown on Figure F-28 and F-29. These spectra (Figures F-18, F-19, F-20 and F-21) are only applicable to the reactor coolant system which is no longer in service. The internal structure within the containment consists of box type heavy concrete shear wall assemblies, especially the reactor support walls whose heavy thicknesses are provided for radiation shielding purposes. It has been found that the lowest natural frequency of this internal structure, based on conservative assumptions, is approximately 18 Hz. This indicates that the internal structure is relatively rigid and, therefore, validates the assumption made in the analytical model for the dynamic analysis of the reactor and auxiliary buildings that the internal structure within the containment can be considered as an integral part of the mat. The vertical response spectra shown in Figures F-22 thru F-27 were constructed for all elevations of the reactor and auxiliary buildings since the analytical model of these buildings was assumed as a single-degree-of-freedom system, that is the entire mass of these buildings was considered to be lumped into one.
Absolute accelerations of masses No. 2, No. 4 and No. 5 as obtained by the modal analysis time-history using the scaled El Centro ground motion are shown in Tables F-5 and F-6. Comparison of Tables F-3 thru F-6 verifies that the specified ground response spectrum is compatible with the scaled El Centro ground motion, as has been stated in Reference 3.2.
It can be seen from Figures F-12, F-13, F-15 and F-16 that for equipment or piping supported on mass No. 4 or No. 5 and which is in resonance with the second frequency mode of the structure (6.23 Hz) the acceleration given by the normalized ground response spectrum for this frequency exceeds the acceleration obtained by a time-history analysis using the El Centro ground motion. These results in conjunction
DSAR-Appendix F Information Use Page 30 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria with the demonstrated fact that for the Fort Calhoun plant the higher structure modes of vibration have an insignificant contribution to the response of the structure justify the proposed approach to the seismic design of piping and equipment supported within the reactor internal concrete or auxiliary building.
This approach was that if equipment or piping within the containment internal structure or auxiliary building has a lowest dominant natural frequency of 6 Hz or more horizontally or 18 Hz or more vertically, the acceleration of the equipment or piping was taken directly from the normalized ground response spectrum. In the case of piping, restraints were spaced to limit the natural frequency of the piping to this criterion.
The following criteria have been applied:
- a.
The greater of the responses shown in Figure F-12 through F-17 was used for the appropriate frequency of the system analyzed.
- b.
Items which cannot be removed from resonance were designated to 1.3 times the peak of the appropriate floor response spectra (to account for participation of the higher modes in the system or equipment); allowable stresses calculated on an elastic basis were limited in these analyses to those corresponding to the emergency condition limit of the B31.7 (1968) piping code.
- c.
Items which cannot meet the criteria (b) above were analyzed by the response spectrum modal method using the appropriate floor response spectra.
Where piping is connected to equipment whose lowest dominant natural frequency is less than 6 Hz horizontally and 18 Hz vertically, restraints were spaced to limit the lowest dominant natural frequency of the piping to 25 Hz up to the first point of full fixity. If this was not feasible, a modal analysis was performed on an analytical model of a lumped mass system which included the piping and the equipment to which it is attached. The appropriate floor response spectrum was used. Stops or damping devices were provided to limit stress to acceptable values.
An alternative procedure to that described in the preceding paragraph was to space the piping restraints to limit the lowest natural frequency of the piping to 6 Hz and assume a response equal to the peak of the appropriate floor response spectrum. The piping was then designed in accordance with code requirements for the Emergency Condition. As noted in Section F.2.2.3, alternative structural dynamic analyses, criteria and methods, to those described above, were developed and the results may be used as an alternative design basis (i.e., in lieu of the original design basis described above) for analysis and design of piping.
DSAR-Appendix F Information Use Page 31 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria As noted in Section F.2.2.2, an alternative method of evaluating the seismic adequacy of equipment was developed and the results may be used as an alternative design basis method (i.e., in lieu of the original design basis described above) for analysis and design of mechanical and electrical equipment.
Table F Seismic Response of Auxiliary Buildings Obtained by Modal Analysis Using Time-History Concept Operating Basis Earthquake El Centro - May 18, 1940 Taft - July 21, 1952 Input Earthquake Scaled N-S Component Scaled N21°E Component Direction of Ground Excitation N - S VERT.
N - S VERT.
Time - Sec.
2.6674 2.6464 2.6704 2.4814 9.8314 9.8344 9.9965 9.1385 Location Mass Absolute Accelerations - g's Auxiliary Building 4 0.1942 0.1791 0.1947* 0.1369* -0.2956 -0.2962* 0.2453 0.1161*
Aux Bldg Mat 5 0.1837* 0.1663 0.1834 0.1369* -0.2819* -0.2816 0.2193 0.1161*
- Maximum Response
DSAR-Appendix F Information Use Page 32 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria Table F Seismic Response of Auxiliary Buildings Obtained by Modal Analysis Using Time-History Concept Maximum Hypothetical Earthquake El Centro - May 18, 1940 Taft - July 21, 1952 Input Earthquake Scaled N-S Component Scaled N21°E Component Direction of Ground Excitation N - S VERT.
N - S VERT.
Time - Sec.
2.6614 2.6644 2.6464 2.4824 9.6504 9.8435 9.8465 9.1364 Location Absolute Accelerations - g's Mass Auxiliary Building 4 0.3289 0.3289* 0.3167 0.2338* 0.4313 -0.4418 -0.4429* 0.1803*
Aux Bldg Mat 5
0.3127*
0.3120 0.2981 0.2338* 0.4010 -0.418* -0.4165 0.1803*
- Maximum Response
DSAR-Appendix F Information Use Page 33 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria 3.0 APPENDIX F REFERENCES 3.1 Nuclear Reactors and Earthquakes, TID-7024, Division of Licensing and Regulation, AEC, Washington, D.C., August, 1963 3.2 Design Criteria for Nuclear Reactors Subjected to Earthquake Hazards, Newmark, N. M., Department of Civil Engineering, University of Illinois, (paper presented in Tokyo, 1968) 3.3 IBM Application Program, H20-0282-1 1130 Continuous System Modeling Program, (1130-CX-13X), Program Reference Manual 3.4 Report to AEC Regulatory Staff, Adequacy of the Structural Criteria for Fort Calhoun Station - Unit No. 1, Omaha Public Power District (Docket No. 50-285), by N. M. Newmark, W. J. Hall and A. J. Hendron, January 12, 1968 3.5 USNRC Safety Evaluation Report of Alternate Seismic Criteria and Methodologies-Fort Calhoun Station, April 16, 1993, TAC No. M71408 (NRC-93-0150) 3.6 EA-FC-94-003, Alternate Seismic Criteria and Methodologies, Rev. 0 3.7 Generic Implementation Procedure (GIP) for Seismic Verification of Nuclear Power Plant Equipment, Revision 2, Corrected 02/14/98, Seismic Qualification Utility Group (SQUG), February 1992 3.8 NRC letter to SQUG Members dated May 22, 1992, Supplemental No. 1 to Generic Letter 87-02 transmitting Supplemental Safety Evaluation Report No. 2 (SSER No. 2) on SQUG Generic Implementation Procedure, Revision 2, Corrected February 14, 1992 (GIP-2) 3.9 SQUG Letter to NRC dated August 21, 1992, SQUG Response to Generic Letter 87-02, Supplement 1 and Supplementary Safety Evaluation Report No. 2 on the SQUG GIP 3.10 EA-FC-93-085, NRC USQ A-46 and Seismic IPEEE Resolution 3.11 NRC Letter to OPPD dated July 30, 1998, Fort Calhoun Station, Unit No. 1 - Closeout of Unresolved Safety Issue A-46 (TAC No. M69447), OPPD Tracking No. NRC-98-129
DSAR-Appendix F Information Use Page 34 of 34 Classification of Structures and Rev. 2 Equipment and Seismic Criteria 3.12 Generic Implementation Procedure for Seismic Verification of Nuclear Power Plant Equipment, Revision 3, Updated 05/16/97 (GIP-3), Seismic Qualification Utility Group (SQUG), May 1997 3.13 NRC Letter for SQUG dated December 4, 1997, Supplemental Safety Evaluation Report No. 3 (SSER No. 3) on the Review of Revision 3 to the Generic Implementation Procedure for Seismic Verification of Nuclear Power Plant Equipment, Updated May 16, 1997 (GIP-3)