ML20009C612
| ML20009C612 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island, Fort Calhoun  |
| Issue date: | 07/14/1981 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | |
| Shared Package | |
| ML20009C611 | List: |
| References | |
| GL-81-14, NUDOCS 8107210264 | |
| Download: ML20009C612 (39) | |
Text
.. - _
i NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT UNITS 1 & 2 l
l SEISMIC QUALIFICATION OF AUXILIARY FEEDWATER SYSTEMS i
(NRC GENERIC LETTER NO. 81-14)
July 14, 1981 i
l l
8107210264 810714 PDR ADOCK 05000282 P
l l
I l
I UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY PRAIR1E ISLAND NUCLEAR GENERATING PLANT Docket No. 50-282 50-306 LETTER DATED JULY 14, 1981 RESPONDING TO NRC LETIER DATED FEBRUARY 10, 1981 (CENERIC LETTER 81-14) SEISMIC QU!.LIFICATION OF AUXILIARY FEEDWATER SYSTEMS Northern States Power Company, a Minnesota corporation, by this letter dated July 14,1981 hereby submits in response to NRC letter dated July 14, 1981, information concerning the seismic qualification of the Prairie Island Auxiliary Feedwater Systems as requested by NRC Generic Letter 81-14.
This submittal contains no restricted or other defense information.
NORTHERN STATES POWER COMPANY By d
e f_>Se
~ L 0 Maye[
Manager of Nuclear Support Services On this
/
day of 4M/
,//f/
, before me a r.otary public in and for said County, personallyfappfared L 0 Mayer, Manager of Nuclear Support Services, and being first duly sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof and that to the best of his knowledge, information and belief, the statements made in it are true and that it is not interposed for delay.
< "A.
Am DETTY J. DEAb Not Any pusuc. uis=Esot A 0 RAMSEY COUNTY
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Mr Commessen Eap.<es Dec to 1967
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TABLE OF CONTENTS TITLE PAGE 1.0 ABSTRACT 1
2.0 SEISMIC QUALIFICATION OF PIPING AND MECHANICAL COMPONENTS IN THE AFW SYSTEM 2
2.1 INTRODUCTION
2 2.2 SEISMIC DESIGN VERIFICATION 3
2.2.1 Auxiliary Feedwater System 4
2.2.2 Cooling Water System 5
2.2.3 Auxiliary Steam System 6
2.3 WALKDOWN OF THE AFW SYSTEMS 6
2.3.1 Auxiliary Feedwater, Cooling Water and Auxiliary Steam Systems 6
2.3.2 Primary Water Supply (Condensate) System 6
2.4 SEISMIC QUALIFICATION CRITERIA 7
5 2.4.1 Seismic Analysis Methods 7
2.4.1.1 Design Class I Piping 7
2.4.1.2 Design Class I Mechanical Components 8
2.4.2 Seismic Input 10 2.4.3 Load Combinations 10 2.4.4 Allowable Stresses 10 2.4.5 Qualification Testing 14 3.0 SEISMIC QUALIFICATION OF STRUCTURES SUPPORTING OR HOUSING AFW SYSTEMS 16 3.1.
SUMMARY
16
3.2 INTRODUCTION
16 3.3 STRUCTURE IDENTIFICATION AND CLASSIFICATION 18 3.4 SEISMIC QUALIFICATIONS 19 i
TABLE OF CONTENTS (CON'T) 4 TITLE PAGE 3.4.1 Methodologies 18 3.4.1.1 Gnield Building, Auxiliary building and Turbine Building 19 3.4.1.2 Cooling Water and Auxiliary Feedwater Piping Systems 24 3.4.1.3 Class I Areas of Screen House 24 3.4.1.4 Emergency Water Intake Crib 24 3.4.1.5 Emergency Cooling Water Intake 25 3.4.1.6 Buried Cooling Water Pipe Between Screenhouse and the Turbine Building 25 3.5 LOAD COMBINATIONS INCLUDING DBE 25 3.6 ALLOWABLE STRESSES 26 3.6.1 Reinforced Concrete Structures 26 3.6.2 Steel Structure 26 L
4.0 SEISMIC QUALIFICATION OF ELECTRICAL AND INSTRUMENTATION AND CONTROL COMPONENTS i
IN THE AFW SYSTEMS 27 4.1 POWER SUPPLIES 27 4.2 INITIATION AND CONTROL SYSTEMS 29 l
5.0 DEFICIENCIES 29 5.1 AUXILIARY FEEDWATER, COOLING WATER AND AUXILIARY STEAM SYSTEMS 29 i
5.2 PRIMARY WATER SUPPLY (CONDENSATE) SYSTEM 30 l
6.0
SUMMARY
OF OPERATING PROCEDURES 32 i
7.0 CONCLUSION
S 33
8.0 REFERENCES
- S APPENDIX A ii
1.0 ABSTRACT This report presents the results of the review performed to ensure the seismic qualifications of the Auxiliary Feedwater System.
Sections 1.0 through 3.0 contain discussion pertaining to the' seismic requirements, methodologies, and criteria required by the various disciplines for the seismic qualification of this system.
Also, included in Section 2.0 is a discussion of the field inspec-tions performed to document non-safety related equipment in the area of the Auxiliary Feedwater Systems and to document by visual in-spection the requirements for seismic qualification of the primary supply.
Section 4.0 contains recommendations for improvements to the electrical and control components of the Auxiliary Feedwater Syrtem.
Section 5.0 contains a list of all mechanical deficiencies.
Section 6.0 contains a summary of operating procedures. Section 7.0 contains the conclusions which refer to Appendix A.
Appendix A contains completed Table I of NRC Generic Letter No. 81-14.
In general, the Auxiliary Feedwater System including the secondary water supply (cooling water system) is seismically qualified with exception of the deficiencies listed in Section 4.0 and 5.0.. _ _ _
~
4 2.0 SEISMIC QUALIFICATION OF PIPING AND MECHANICAL COMPONENTS IN THE ACW SYSTEMS
2.1 INTRODUCTION
This report verifies that the seismic qualification of Auxiliary Feedwater (AFW) Systems are in compliance with NRC Generic Letter No. 81-14.
The Auxiliary Feedwater System at Prairie Island Nuclear Generating Plant (Units 1 and 2) have been designed and maintained as seismically qualified systems.
The AFW systems are able to function following the occurrence of earthquakes up to and including a Design Basis Earthquake postulated for the plant.
4 The AFW systems design utilize Type I Components including piping in accordance with Design Class I criteria for the plant.
The Cooling Water System is the source of the water supply for the seismically qualified AFW Systems.
The portion of the Condensate System which is the primary source of the Auxiliary Feedwater supply is not seismically qualified.
I Procedures are incorporated in the operation of the plant to switch l
from primary source (the Condensate System) to the secondary source (the Cooling Water System) in the event of a loss of primary source I
of supply.
l The seismically qualified AFW System boundaries from suction to l
discharge include those portions of the system required to accomplish the AFW System function and connected branch piping including at least one valve in each branch piping which provides capability to i
isolate the AFW system.
The valve (s) in the branch piping are either normally closed or capable of automatic or manual closure
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2.1 INTRODUCTION
(CONT 'D) when the safety function is required.
This feature is further discussed in Section 2.2.
In addition, the AFW System boundary also includes any portion of the branch piping beyond the afore-mentioned valve (s) up to the first structural anchor or equipment connection.
Smaller branch piping originating beyond the boundary valve is not considered.
The AFW system within the above defined boundary includes portions of the Auxiliary Feedwater, Cooling Water, Auxiliary Steam, Main Steam and Feedwater Systems.
The AFW system is designed and con-structed to withstand a Design Basis Earthquake postulated for the plant utilizing the analytical, testing, evaluation methods and acceptable Class I Criteria consistent with other safety grade systems in the plant.
These systems are also included within the scope of seismic related NRC IE Bulletins 79-02, 79-04, 79-07, 79-14 and R0-11 and IE Information Notice 80-21.
A seismic evaluation of the primary supply piping was also per-fo rmed.
2.2 S;J IMIC DESIGN VERIFICATION All piping, in general, and components within the specified boundary of the AFW System are QA Type I, Design Class I as defined for the plant and are designed as such.
In order to confirm compliance to the seismic design criteria, pertinent documents have been reviewed.
Seismic analysis of the piping or component and its review and approval assured compliance.
2.2 SEISMIC DESIGN VERIFICATION (CONT ' D)
All piping within the boundaries have been verified for seismic qualification.
Valves within the boundaries were verified for seismic qualification.
AFW systems piping have been analyzed using Fluor Power Services (FPS) computer program PIPESTRSS and received an independent re-view and approval within the FPS organization.
The seismic qualification of the power supplies and initiation and control systems for the aux feedwater system was evaluated by Teledyne Engineering Services.
Data was gathered and evaluated, after which a team of engineers qualified in seismic analysis in-dividually inspected each electrical component covered under items 4 and 7 (Table 1) of NRC letter 81-14.
The evaluation was based more on experience and engineering judgement than on detailed analysis, although analysis was applied in cases where the structural adequacy of the anchorage was not obvious by inspection.
The evaluation resulted in the conclusio:: that the anchorage of most of the Auxil-I liary Feedwater System Electrical Components is adequate to with-stand a Safe Shutdown Earthquake.
The Auxiliary Feedwater, Cooling Water and Auxiliary Steam Systems are discussed in detail in the following sections.
2.2.1 Auxiliary Feedwater System The Auxiliary Feedwater (AF) System includes piping from the Auxiliary Feedwater pumps to the Steam Generators and branch pip-ing up to the second valve which is normally closed or a valve capable of automatic closure.
Portions of the main feedwater l
2.2 SEISMIC DESIGN VERIFICATION (CONT'D) 2.2.1 Auxiliary Feedwater System piping up to the first motor operated valve upsteam of the AF piping connection are also included.
These valves when closed will isolate the piping in the direct flow path of the auxiliary feeowater.
The piping within the AF system have been seismically qualified and meets the criteria for Design Class I piping.
A verification of seismic qualification for all valves was performed.
Some valves of size 2 inches and under were exempt from seismic qualification in accordance with the specifications.
All remaining valves were pur-chased with Dee4.gn Class I seismic qualification as a specified requirement.
Seismic analysis, review and approval documentation for certain VELAN valves were not found in the files.
It appears from pertinent documents that seismic calculations were performed for these valves.
Since the search for the documents was not exhaustive and since seismic analysis was required by the specifi-cation, it is felt that these valvcs were seismically qualified.
All other equipment in the system w s found to have the required seismic qualification.
2.2.2 Cooling Water System The Cooling Water System boundaries include piping from Design Class I pump discharge to Auxiliary Feedwater ptva suction and the ring header which provides a redundant path of cooling water supply to Units 1 and 2 and connecteo branch piping included at least one valve to isolate the system to provide its safety related function. -.
l 2.2 Sf,ISMIC DESIGN VERIFICATION (CONT 'D) 2.2.2 Cooling Water System The Ccolina Water System provides cooling water to a number of essential systems in addition to the Auxiliary Feedwater pump supply.
These systems will remain functional in the event of an accident.
Branch tons with a nominal pipe size of 4 inches and larger which supply coaling water to non-essential systems are provided with i
valves capable of automatic closure with the exception of a supply line to the sprinkler system with a nominal pipe size of 4 inches.
Branch runs with nominal pipe size smaller than 4 inches can be isolated by manual closure of the valves.
These valves are readily accessible for operatizin.
All piping within the defined boundaries, with the exception of four (4) branch runs with nominal pipe size of 2 inches which ar2 identi-fled in Section 5, have 5aen seismically qualified.
Valvcs 2 inches and smaller are exempted from seismic qualification in accordance with the specifications.
All revaining valves and equipment were found to be seismically qualified.
2.2.3 Auxiliary Steam System The Auxiliary Steam System boundaries include the 3 inches diameter steam piping from the main. steam header to the Auxiliary Feedwater Pump Turbine and portions of the Main Steam System from the steam generator up to the first isolation valve.
These main cc..
isola-tion valves which provide a boundary for the AFW system within the Auxiliary Steam System are capable of automatic closure.
The safety relief valves in the Main Steam System within the boundaries.
2.2 SEISMIC DESIGN VERIFICATION (CONT ' D) 2.2.3 Auxiliary Steam System are normally closed and the dump valves are designed to operate at the cet pressure.
All piping within the boundaries except drains to traps have been seismically qualified.
Equipment and valves with the exception of those smaller than 2 inches are also seismically qualified.
2.3 WALKDOWN OF THE AFW SYSTEMS A walkdown of the AFW system piping within the defined boundaries including the primary water supply piping was performed by personnel experienced in the design, analysis and evaluation of nuclear pip-ing systems.
2.3.1 Auxiliary Feedwater, Cooling Water and Auxiliary Steam Systems All piping and equipment within these systems (except as noted in Section 5) are seismically qualified.
The walkdown of tSess systems identified and located piping or components which were not designed in accordance with Class I design criteria or which could have poten-tial for damaging the AFW system piping.
2.3.2 Primary Water Supply (Condensate) System This system is not designed in accordance with Clcss 1 seismic de-sign criteria.
The purpose of the walkdown was to determine the extent of seismic resistance inherent in the p! ping system based on the present support system and to study the possibility of upgrading this system to the same grade as the rest of the AFW systems.
The majority of the piping in this system is in trenches.
Supports - _ _. -. _. _, - _ _
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2.3 WALKDOWN.OF THE AFW SYSTEMS (CONT 'D) 2.3.2 Primary Water Supply (Condensate) System in this system arc designed for dead weight load plus.5g seismic load.
The existing support system will provide adequate seismic resistance in the direction lateral to the header pipe (north-south).
Additional seismic restraints in the east-west direction would im-prove the seismic resistance of the primary system piping.
2.4 SEISMIC QUALIFICATION CRITERIA The fallowing Sections provide a description of seismit analysis i
methods employed, seismic input, load combinations which include the Design Basis Earthquake, allowable stresses and qualification testing.
Seismically qualified piping and-components satisfy these i
criteria.
i 2.4.1 Seismic Analysis Methods 2.4.1.1 Design Class I Piping AFW Tystems have been subjected to a multidegree-of-freedom dynamic l
l seismic analysis utilizing modal te'hniques and the response spec-trum method.
The piping system is modeled as a lumped mass system.
Valves and valve operators were considered as lumped masses in the pipe, applied at the center of gravity of the valve.
The stresses, deflections and accelerations at each point were determined by the square root of the sum of the squares method.
Seismic effects of piping systems due to the relativ9 displacement of structures and differential seismic movements at points of attach-ment to the structure have been considered.
These movements are imposed as the boundary conditions in a static displacement analysis. I l
l
2.4 SEISMIC QUALIFICATION CRITERIA 2.4.1.1 Design Class I Piping All movements are superimposed in such a manner as to yield the maximum relative displacements.
The resulting stresses were com-bined with stresses due to other loading conditions as given in Table 1 (see following page).
All Class I piping is isolated by structural anchors from piping for which Class I analysis is not required.
Class II or Class III pipe which is connected to Class I pipe is analyzed as Class I up to a structural or equipment anchor which provides a means for isolating the Class I piping from the Class II or III piping.
2.4.1.2 Class I Mechanical Components Class I Mechanical components are designed tc be capable of con-tinued safe operation within normal design limits when subjected to the combination of normal operating loads and the Operating Basis Earthquake loads.
For the Design Basis Earthquake the mech-anical components are designed so that deflections or distortionc resulting from the combination of normal operating loads and twice the OBE loads shall not prevent their proper functioning, shall not endanger adjacent or attached equipment, and shall not cause the equipment to operate in an uncontrolled manner.
In general, mechanical components and its supports are designed to be sufficiently rigid so that its natural frequency or frequen-i cies will be out of the tenge of reasonance with the building structure where it is located.
A proper mathematical model is used to determine the natural frequency or frequencies of the !
1 I
TABLE 1 LOAD COMBINATION FOR CLASS 1 COMPONENTS 1.
Normal Dead + Live 2.
Normal & Optrational Dead + Live + OBE Basis Earthquake (OBE) 3.
Normal & Design Basis Dead + Live + DBE Earthquake (DBE) 4.
Normal & Pipe Rupture Dead + Live + DBA (or other pipe rupture loads if greater) 5.
Normal & Design Basis Dead + Live + DBE + DBA Earthquake & Pipe Rupture (or other pipe rupture loads if greater)
DBA - Design Basis Accident as defined for the plant Extracted from the F.S.A.R., Table B.7-1. _ _.
2.4 SEISMIC QUALIFICATION CRITERIA 2.4.1.2 Class I Mechanical Components component.
For a single-degree-of-freedom model, a static analysis is performed by applying the accelerations at the mass center corre-sponding to the natural frequency of the component.
In the case of a multidegree-of-freedom model, the model superposition is used to determine the responses of the dynamic system.
For those components for which the natural 'requency cannot be determined the peak values of the floor response accelerations multiplied by the maximum Lor-sional acceleration factor is applied at the mass center of the component to determine the seismic responses.
2.4.2 Seismic Ingut Seismic analysis is accomplished by the response spectrum method utilzing the applicable floor response spectra.
The floor response spectra were obtained by the dynamic multidegree-of-freedom modal analysis of the structures.
2.4.3 Load Combinations Load combinations for piping and components are listed in Table 1.
Two type of seismic loading are considered, Operational Basis Earthquake (OBE) and Design Basis Earthquake (DBE).
2.4.4 Allowable Stressas The plant operating condition categories are Normal, Upset, Emer-gency and Faulted conditions as defined in Section B.7 of the FSAR.
The deaign stress limits for piping are given in Tables 2 and 3 (see following pages).
The design stress limits for components.
l TABLE 2 LOADIN3 CONDITIONS AND STRESS LIMITS:
PRESSURE PIPING IN ACCORDANCE'WITH ANSI B31.i Loading Condition Stress Limits 1.
Normal Condition P f, S 2.
Upset Condition P 1 1.25 3.
Emargency Condition P 1 1.5 (1.2S) 4.
Faulted Cenditien For 9tainless Steel Design Limit Curves as defined in Figure B.7-3 in Reference 1.
For Carbon Steel y or 1.8S whichever P f,igher**.
is h Where:
P = Stress S = Allowable stress from ANET B31.1, code for Power Piping, 1967 S
= Minimum specified yield strength (ASME B&PV Code,Section III, Y
Table N-421 or equivalent).
- At some points of high local stress, intensification P may exceed this limit.
For such pointr local piping deflection will be limited to twice the calculated OBE deflection to insure no loss of function in the " Faulted Condition".
(Extracted from the F.S.A.R., Table B.7-3) _.
TABLE 3 LOAD COMBINATION AND STRESS LIMITS FOR Class I Components i
LOAD COMBINATION STRESS LIMIT 1.
Normal (Desdweight, thermal Normal Conditions and pressure 2.
Normal & Operational Upset Condition Basis Earthquake 3.
Normal & Design Basis Faulted Condition Earthquake 4.
Normal & Pipe Rupture Faulted Condition 5.
Normal & Design Basis Faulted Condition Earthquake & Pipe Rupture I
(Extracted from the F.S.A.R., Table B.7-5) i l
2.4 SEISMIC QUALIFICATION CRITERIA 2.4.4 Allowable Stresses other than pressure vessels and piping are the allowable stress of the materir.1 as given in the applicable codes and 90% of the yield strength of the material for the upset and faulted conditions, respectively.
For the Operetional Basis Earthquake, the nuclear cteam supply system is designed to be capable of continued safe operation or return te power operation.
In case of Design Easis Earthquake it is ensured that the AFW system does not lose its capability to perform the required safety function.
This capability is ensured by maintaining the stress limits discussed above.
The stresses induced in the AFW system by the DBE are limited so that they do not cause a rupture in the system.
The AFW system is adequately protected such that damage from pipe rupture of adjacent high energy piping will not result in a loss of the system safeguard function.
2.4.5 Qualification Testing 1.
Continuous Test:
The test was executed at frequencies incremented within the range of significant structural response.
The test consisted of the application of a continuous sinusoidal motion corre-sponding to the maximum structural acceleration for which the equipment was to be qualified and for an appropriate length l
of time.
The equipment was properly mounted during testing so as to reflect the field installed condition and energized if required. I
2.4 SEISMIC QUALIFICATION CRITERIA 2.4.5 Qualification Testing 2.
Sine Beat Test:
Natural or resonant frequencies were detected by scanning from the lowest practical frequency to 25 Hz.
The test at resonant frequencies consisted of the application of sine beats of peak acceleration values corresponding to that for which the equipment was to be qualified.
The duration of the beat for each particu-lar test frequency was chosen to most nearly produce a magnitude of equipment responae equivalent to that ptoduced by the particu-lar floor acceleration with proper damping ratio.
The equipment was properly mounted daring testing so as to reflect the field installed condition and energized if required.
Seismic input values used for analysis or testing purposes to verify the adequacy of Class I components were cbtained from Reference 3.
I
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3.0 SEISMIC QUALIFICATION OF STRUCTURES SUPPORTING OR HOUSING AFW SYSTEMS 3.1
SUMMARY
A review Of engineering design calculations, the FSAR, structural drawings and other pertinent reports was done to establish seismic design criteria and their implementations as they apply to NRC's Generic Letter 81-14 for the Auxiliary Feedwater Piping System.
8 The seismic design criteria, seismic input, and methodology for their implementations are briefly described in subsequent sections.
Our review indicates that all structural components were properly de-signed for the seismic criteria at the time of its original design.
3.2 INTRODUCTION
A review was conducted to identify the structures and ares which directly house or support the Auxiliary Feedwater (AFW) System and to review their design criteria and design implementation.
A brief description of the AFW system is provided in order to clearly define the scope of the work.
l The primary source of supply for the AFW System is from the conden-sate makeup storage tank and through a piping system to the suction of the Auxiliary Feedwater Pumps.
The AFW Systems ' safeguard source of supply is the Cooling Water System.
This area was also reviewed from the source of supply to the area where the AFW system connects.
The water supply for the Cooling Water System is obtained from Sturgeon Lake, which in reality is the backwaters of tue Mississipp3 River. _
~.
3.2 INTRODUCTION
(CONT'D)
Normally, water enters the system through the Circulating Water in-take canal and flows to the screenhouse.
A redundant system provides water in an emergency situation.
This Emergency Cooling Water System consists of an intake crib and a 36" diameter intake pipe.
This pipe le routed below the bottom of the intake canal and enters the emergency pump bay of the screenhouse.
Cooling water is pumped'and then conveyed through the screenhouse via a series of pipes to an underground piping systea located between the Screenhouse and the Turbine Room.
Recently an addition to the Adminis-tration Building was constructed in this area.
Upon entering the Turbine Room area the piping turns upwards, from below grade, and con-tinues southward under the mezzecine ficor to the Auxiliary Feedwater Pump area.
The Auxiliary Feedwatcr system's water supply is withdrewn from the Cooling Water System at this point and is fed to either the motor driven or the turbine driven Auxiliary Feedwater pumps.
I The Cooling Water piping continues into the Auxiliary Building at this point and serves numerous functions in this building.
The Auxil-iary Feedwater piping originates at the discharge of the Auxiliary l
Feedwater pumps and is routed through the Auxiliary Building to the Shield Building.
It traverses the annulus space and penetrates the reactor containment and continues to the steam generator.
l Another piping system directly related to the AFW System is the steam l l L
3.2 INTRODUCTION
(CONT'D) supply used to drive the turbine driven AFW pumps.
This system ori-ginates at the Main Steam header located outside the shield building and runs in a northerly direction through the Auxiliary Bu!.lding to the inlet of the turbine drives for the AFW pumps located in the Turbine Building.
3.3 STRUCTURE IDENTIFICATION AND CLASSIFICATION Reference 6 lists the various structures or areas and provides the design classification as given in the FSAR (Reference 1) and as de-signed by Fluor Power Services.
Equipment attachments to structural members were criginally designed considering all loads including seismic as supplied by the equipment supplier.
The methodologies, load combinations and allowable stresses are discussed in Section 3.4, seismic Qualifications.
3.4 SEISMIC QUALIFICATIONS 3.4.1 Methodologies 3.4.1.1 Shield Building, Auxiliary Building and Turbine Building The design of the Shield Building, Auxiliary Building and the Turbine Building was based on a dynamic analysis performed by John A.
Blume and Associates, Engineers (Reference 2).
The results of the analysis were prepared for the Operating Basis Earthquake (0.06g).
Values for the Design Basis Earthquake (0.129) were obtained by doubling the results for the Operating Basis Earthquake.
A mathematical cantilever model with lumped mass points was prepared.
The model is a discrete mass system with masses lumped at each floor 3.4 SEISMIC QUALIFICATIONS 3.4.1.1 Shield Building, Auxiliary Building and Turbine Building and roof level, at points of intersection of diagonal bracing in the steel structures, and at intermediate points in the shield and con-tainment structures.
The structure has been idealized as a three-dimensional model with 190 degrees of freedom that include north-south and east-west translation for symmetrical elements and both translation and torsional rotation for unsymmetrical and irregular elements.
Each mass point represents the mass of the concrete and i
steel structural elements at a particular level plus the tributary mass of the equipment and walls between adjacent levels.
Soil-structure interaction was represented by translational and rotational springs in the model.
In general, the moments of inertia and effective shear areas of the vertical elements between the mass points were determined for the concrete structures by cutting a horizontal section through the building between the mass points and computing the moments of inertia and shear areas of the wall thus intersected.
The stiffness of the braced steel structures were com-puted by considering the axial deformation of the bracing members.
Centers of mass and rigidity were calculated by conventional methods of structural analysis.
The spectral methods was used for the dynamic analysis of the Reactor-Auxiliary-Turbine Building.
The response spectra used for this analysis are shown on Figures 1 and 2 (see following pages).
The maximum response for each mass point for each mode were computed and were combined, to determine the total response, by adding the.
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3 TABLE 4 DAMPING VALUES Percent of Item Critical Damping Containment Vessel 1.0 Shield Building 2.0 Steel Structures 2.0 Reinforced Concrete Construction 2.0 Foundation 5.0 I
i f
l l
3.4 SEISMIC QUALIFICATIONS 3.4.1.1 Shield Building, Auxiliary Building and Turbine Building square root of the sum of the squares of the maximum response of each mode.
The structure was analyzed for earthquake motion in both the north-south and east-west directions acting non-concurrently.
Individual modes of vibration were identified as being due primarily to the deformation of specific structural elements (or a combination of such elements) and were assigned appropriate damping values.
The damping values used for various structural systems are listed in Table 4.
Curves showing the maximum translational accelerations, displacements, shears, and moments and torsional accelerations, moments and rotation were prepared for the Shield Building, Contair. ment Vessels, Auxiliary Building, Fuel Tank Area. and Turbine Building.
The structures were designed to resist the seismic shears and moments including torsional effects plus a vertical acceleration of 0.04g acting simultaneously I
l with'the horizontal acceleration.
The allowable stresses in this case were not increased above the code allowables.
l Tbc structures were then reviewed to ensure that it could resist twice the seismic shears and moments described above without hindering the l
ability of the plant to safely snut down.
A vertical acceleration of 0.08g acting simultaneously with twice the horizontal accelerations was used for design as criteria for safe shutdown of the plant.
The l
allowable stresses for this case are indicated in Section 3.6.
Changes in soil properties and structural conditions were made after 1. _,
3.4 SEISMIC QUALIFICATIONS 3.4.1.1 Shield Building, Auxiliary Building and Turbine Building the initial analysis was completed and a review of the calculations was undertaken that indicated all previous results should be in-creased by ten percent.
This was done.
Detailed discussions are presented in Reference 2.
3.4.1.2 Cooling Watec and Auxiliary Feedwater Piping Systems The Cooling Water and the Auxiliary Feedwater piping systems in the buildings were analyzed using the Response Acceleration Spectra obtained from the building analysis as given in Reference 3.
The pipes and their supports were designed based on the dynamic analysis.
The -upport loads were imposed on the various structural elements.
t Hanger loads consisting of dead plus thermal plus DBE were routed to the structural department.
Upon receipt of these loads the original calculations were reviewed to ensure adequate structural support.
3.4.1.3 Class I Areas of Screen House The Class I areas of the Screenhouse were statically designed by applying the seismic factors listed below:
Operati0nal Basis Earthquake:
0.09 horizontal 1
l 0.05 vertical l
l Design Basis Earthquake:
0.18 horizontal l
0.10 vertical Class I Equipment supports, piping and pipe hanger were designed using the Response Acceleration Spectra obtained from the building analysis as given in Reference 3.
3.4.1.4 Emergency Water Intake Crib f
The emergency water intake cribe was statically designed by applying the seismic factors listed below: --
3.4 SEISMIC QUALIFICATIONS 3.4.1.4 Emergency Water Intake Crib Operational Basis Earthquake:
0.09 horizontal 0.05 vertical Design Basis Earthquake:
0.18 horizontal 0.10 vertical 3.4.1.5 Emergency Cooling Wate. Intake Crib The design of the buried emergency cooling water intake pipe was governed by possible liquefaction consideration.
Therefore settle-ments due to possible liquefaction were accounted for by providing gimbal joints to allow for movement of the pipe.
In addition the pipe was bedded in a non-liquefiable backfill and covered with com-pacted or uncompacted non-liquefiable backfill mr :erial.
A further evaluation of the buried emergency cooling water intake pipe was completed in a report entitled " Evaluation of Emergency Cooling Water Intake Pipeline Under the Proposed Dike" (Reference 4).
3.4.1.6 Buried Cooling Water Pipe Between The Screenhouse and the Turbine Building The seismic effect on the buried emergency cooling water pipe located between the screenhouse and the turbine room was expected to be insig-nificant.
For a further discussion see Volume 5, Appendix B, pages B.7-4a and B.7-4b of the FSAR (Reference 1).
A further evaluation of this piping was completed in a report entitled " Administrative Build-ing Addition - Safety Evaluation of Class I Cooling Water Piping" (Reference 5).
l l
3.5 LOAD COMBINATIONS INCLUDING DBE l
l For Class I structures the conditions of loading for the Design Basis
3.5 LOAD COMBINATIONS INCLUDING DBE (CONT'D)
Earthquake included:
Dead Load + Live Load + Snow Load + Design Basis Accident +
Design Basis Earthquake 3.6 ALLOWABLE STRESSES 3.6.1 Reinforced Concrete Structures For Design Basis Earthquake loading combinations, Class I Structures, the allowable stress for reinforced concrete are 1-1/2 times ACI-318-63 allowable values.
Listed below are the actual allowable stress used in the design of Units 1 and 2 of the Prairie Island Nuclear Generating Plant.
Reinforcing Steel Stresses A 615 Grade 40 A 615 Grade 60 Concrete Allowable Percent of Allowable Percent Stresses Working Min Spec Working Min Spec Criteria Stress-psi Yield (1)
Stress-psi Yield (1) 1-1/2 times ACI 318-63 allowable values 0.675 30,000 75 36,000 60 Minimum specified yield points of steel reinforcement are as follows:
A 615 Grade 40 40,000 psi A 615 Grade 60 60,000 psi 3.6.2 Steel Structures For Design Basis Earthquake loading combinations, Class I Structures, the allowable stresses for Structural Steel were 1-1/2 times the AISC Allowable values. - _.
4.0 SEISMIC QUALIFICATION OF ELECTRICAL AND INSTRUMENTATION AND CONTROL COMPONENTS IN THE AFW SYSTEMS 4.1 Power Supplies The anchorage of power supplies and related equipment used by the Aux Feedwater System is designed, constructed and maintained to with-stand a Safe Shutdown Earthquake consistent with other safety-grade systems at Prairie Island.
Several items were noted by Teledyne Engineering Services, which need further evaluation:
1.
Provide anchor bolts 'co unload plug wells on one 4160 V switchgear cabinet.
2.
Replace a bolt missing in each of several 480V switchgear cabi-nets.
3.
Modify the anchorage of motor control centers.
4.
Modify battery rack design, and protect the batteries from ancillary equipment.
5.
Test the frequency of fundamental modes of vibration and associated damping magnitudes for selected panels, racks, and cabinets.
Redesign and stiffen the support for components for which the fundamental response is less than 6 Hz.
4.2 Initiation and Control Systems The anchorages of initiation and control system components associated with the Aux Feedwater System are designed, constructed, and main-tained to withstand a Safe Shutdown Earthquake consistent with other safety-grade systems at Prairie Island.
Several items were noted by Teledyne Engineering Services, which need further evaluation: -
4.2 Initiation and Control System (Cent'd) 1.
Improve the mounting of selected pressure indicators and conduits.
1 2.
Protect control room panels from ancillary equipment.
3.
Test the frequency of fundamental modes of vibration and associated i
damping magnitudes for selected cabinets, racks, and panels, and the local control switch for s motor operated valve. Redesign and stiffen the support for components for whf eh the fundamental response is leas than 6 Et.
j.
l 1
i l
c.
5.0 DEFICIENCIES 5.1 Auxiliary Feedwater, Cooling Water and Auxiliary Steam Systems 1.
As discussed in Section 2.2 four (4) Cooling Water branch runs within the AFW system boundaries have not been analyzed.
These lines are identified below with the isolation valve tag number at the 30 inch diameter cooling water header and the unit coolers served by these branches.
CL-99L-2 Auxiliary Feedwater pump unit coolers 2CL-99B-2 CL-99B-3 Charging pump motor unit coolers 2CL-99B-3 Based on the present support system provided and based on engi-neering judgement, these branch piping possess some inherent seismic resistance.
2.
The modeling of the wall sleeve where the 30 inches diameter cooling water header pipes penetrate the Screenhouse at Column Row By, may not be conservative.
These portions of the pip-ing are contained in Parts IV and V of the Cooling Water system.
3.
A reanalysis,r initial analysis of some portions of the Auxil-iary Feedwater, Cooling Water, and Auxiliary Steam systems have l
been performed as a result of the NRC IE Bulletin 79-14.
Review I
of stress analysis is complete.
Any remaining work is being handled in accordance with the procedures establiched for the implementation of IE Bulletin 79-14.
l 4.
Certain concerns identified during the walkdown regarding non-l
5.0 DEFICIENCIES (CONT ' D) 5.1 Auxiliary Feedwater, Cooling Water and Auxiliary Steam Systems seismic components with potential for damaging AFW systems have not been resolved.
The items requiring further evaluation include:
a.
Evaluate adequacy of attachments of electrical boxes 1185 and 1768.
b.
Re-evaluation of adequacy of turbine building HVAC ductwork.
c.
Re-support small conduits resting on cooling water supply piping.
d.
Evaluate and resupport unit coolers in AFW pump room.
e.
Evaluate adequacy of HVAC ductwork in Auxiliary Building which is routed above the Auxiliary Steamline supplying the turbine driven AFW pump.
(
5.
The floor anchor plates supporting cooling water strainers 11, 12, 21, and 22 must be reviewed for the increased loading conditions i
documented in the revised report for cooling water screenhouse Part I.
6.
Drain piping to traps in the Auxiliary Steam System are not analyzed.
l 5.2 Primary Water Supply (Condensate) System This system is Design Class III and is not analyzed for earthquake and, therefore, not considered as part of the safety related AFW systems.
However, based on the walkdown of the system it is felt that minor modification could enhance the seismic resistance of the l !
1
s 1
5.0 DEFICIENCIES (COMT 'D) 5.2 Primary Water Supply (Condensate)
"f, stem system substantially.
Structural anchors may be required to isolate the water supply path from the condensate make-up storage tank to the auxiliary feedwater pumps from the remaining portions of the con-densate system.
The block supports outside the turbine building up to the condensate make-up storage tank may not adequately resist a Design Basis Earthquake.
The condensate make-up storage tank and the foundation for the condensate maka-up storage tank should be reviewed with respect to a Design Basis Earthquake.
4 i
1 i
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l l t
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6.0 SUMMAR'.' OF OPERATING PROCEDURES Prairie Island requires immediate shutdown of an AFW pump if suction is lost for any reason.
Additionally as condensate storage tank level decreases actions are prescribed to afford additional water sources to the Condensate Storage Tanks.
However, as a last redort instructions are provided for valving in the safety grade Cooling Water Supply to the AFW pump suction.
The switch is simply made by opening one motor operated valve in each AFW pump suction pipfng.
s 7.0 CCSCLUSIONS Excapt for the deficiencies discussed in Section 4.0 and 5.0, and excluding the primary water supply, the AFW system is seismically qualified.
Appendix A contains the completed Table I from NRC Generic Letter 81-14. Note that the table refers to sections within this report which include the documented deficier cies.
Recommendations regarding improvements to several components have been made.
In some cases specific modification can be made without further analysis.
However, in most cases more testing, analysis and design work will be required before modification is possible.
The evaluation of seismic qualification of aux feedwater electrical equipment is included within the scope of IE Information Notice 80-21 and its addenda (or subsequent bulletin).
The analysis, testing, and improvement of a broad range of electrical devices could potentially result from completion of the work relating to 80-21.
In order to avoid duplication of effort and allow a consistent design approach, it is preferable to defer further testing and l
redesign until the requirements relating to 80-21 are more clearly l
defined.
Therefore, it is impossible to provide a firm schedule as i
to when these modifications can be accomplished.
However, we will l
keep you informed as to the progress being made and submit a schedule when one becomes apparent.
r i
8.0 REFERENCES
(1)
Facility Description and Final Safety Analysis Report, Prairie Island Naclear Generating Plant, Northern States Power Company, Minneapolis, Minnesota.
(2)
Earthquake Analysis:
Reactor - Auxiliarv - Turbine Building, Prairie Island Nuclear Generating Plant, JAB-PS-02, amendment 9.
Repcrt prepared by John A. Blume and Associates, Engineers, dated January 22, 1971.
(3)
Earthquake Analysis:
Reactor - Auxiliary - Turbine Building, Response Acceleration Spectra, Prairie Island Nuclear Generating Plant, JAB-PS-04, Amendment 9.
Report prepared by John A. Blume and Associates, Engineers dated February 16, 1971.
(4)
Evaluatio'. of Emergency Cooling water Intake Pipeline Under the Proposed Dike dated February 26, 1981, Activity 000246, FN-3763.
(5)
Administrative Building Addition - Safety Evaluation of Class I Cooling Water Piping dated May 30, 1979, Activity 000252, FN-3094.
(6)
Verification of Seismic Qualification for Structures Supporting or Housing AFW System, Prepared by Fluor Power Services, dated June 16, 1981.
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4 APPENDIX A TABLE I OF NRC GENERIC LETTER 81-14 l
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TABLE 1 AUXILIARY FEEDWATER SEISMIC QUALIFICATION (1)
Pumps / Motors (2)
Piping (See Section 5.0 for Deficiencies)
(3)
Valves / Actuators (4)
Power Supplies (See Section 4.1 for Discussion)
(5)
Primary Water and Supply Path (See Section 5.2 for Discussion)
(6)
Secondary Water and Supply Path *
(See Section 5.1 for Deficiencies)
(7)
Initiation and Control System (See Section 4.2 for Discussion)
(8)
Structures Supporting or Housing these AFW System Items
- Applicable only to those plants where the primary watery supply or path is not provided, however, a seismically qualified alternate path exists.
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