ML19291B044
| ML19291B044 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 07/06/1979 |
| From: | Short T OMAHA PUBLIC POWER DISTRICT |
| To: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| Shared Package | |
| ML19291B045 | List: |
| References | |
| NUDOCS 7908290244 | |
| Download: ML19291B044 (27) | |
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Omaha Public Power District 1623 HARNEY a OMAHA, NEDRASKA 68102 s TELEPHONE D36 4000 AREA CODE 402 July 6,1979 Mr. K. V. Seyfrit, Director U. S. iluelear Regulatory Commission Office of Inspection and Enforcement Region IV 611 Lyan Plaza Drive Suite 1000 Arlington, Texas 76011 9
Reference:
Docket No. 50-285
Dear Mr. Seyfrit:
The Omaha Public Power District received IE Bulletin 79-02 (Revision
- 1) dated June 21, 1979 requesting information regarding pipe support base plate designs using concrete expansion anchor bolts.
Accordingly, please find enclosed a response to that request.
C.
Sincerely, S
j
- T. E. ' Nt Assistant General Manager s
TES/KJM/3Jil:cb Enclosure
.'O U. S. Huclear Reguldtory Cctimission cc:
Office of Inspection and Enforce:r.ent Division of Reactor Operations Inspection Washington, D. C. 20555 LeBoeuf, Lamb, Leiby & MacRae 1333 Hew liampshire Avenue, H.W.
Washington, D. C. 20036
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7908290 f
ENCLOSURE i
Introduction Omaha Public Power District is part of the Owner's Group who, in con-junction with Teledyne Engineering Services is addressing the generic aspects of Bulletin 79-02 (Revision I).
On A 26, 1979 the Owner's Group and Teledyne Engineering Services (TES)pril met with representatives from IE and NRR of NRC to discuss a generic approach to Bulletin 79-02 (reference I).
The basic elements of the Teledyne Engineering Services (TES) Utility Committee program were presented and discussed.
The following is a brief description of the program:
1.
TES has developed a computer program specifically for analyz-ing base plate / anchor bolt installations.
The character of the program is described as follows:
a.
ANSYS program.
b.
Quadrilateral element representation of the base plate.
c.
Spring element for bolt.
d.
Non-linear element representation of plate / concrete in terface.
. Tension or moment (multi-directional) load input capa-e.
bility.
TES's development work includes a pre-processor for generating the model and a post-processor which gives plate deflections and stresses with bolt loads.
These additions to the ANSYS-problem specific program simplify the applications for the large number of cases involved.
2.
The computer program is being used to develop a family of curves for solving bolt design loads for various edge dis-tances and plate sizes.
3.
TES is conducting tests for the purposes of:
a.
Verifying the analytical program.
The tests will include tension and bending loading situations.
b.
Verifying that preload is not the only measure of cyclic capability.
3 Hz (representing seismic) and 20 Hz (representing flow induced vibration) loads will be applied along with a constant shear load as suggested by Dr. J. Fair of the NRC.
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Developing a table of spring constants (stiffness values for the anchor bolts to be used in the computer program).
d.
Developing shear-tension interaction curves.
TES and the Owners' Group advised the NRC that the exper! mental phase of the program would be completed by July 15.
NRR's respor e to the tech-nical aspects of the generic program presented has t-
. favorable.
The general conclusion was that the proposed program will address the concerns in a fashion that is acceptable to NRC (reference I).
The District's response to Items 1 through 5 of NRC Bulletin 79-02 Revision I is as follows:
Request:
1.
Verify that pipe support base plate flexibility was accounted for in 'the calculation of anchor bolt loads.
In lieu of supporting analysis justifying the assumption of rigidity, the base plates should be considered flexible if the unstiffened distance between the member welded to the plate and the edge of the base plate is greater than twice the thickness of the plate.
It is recognized that this criterion is conservative.
Less conservative acceptance criteria must be justified and the justification submitted as part of the response to the Bulletin.
If the base plate is determined to be flexible, then recalculate the bolt loads using an appro-priate analysis.
If possible, this is to be done prior to testing of anchor bolts.
These calculated bolt loads are referred to here-after as the bolt design loads.
A description of the analytical model used to verify that pipe support base plate flexibility is accounted for in the calculation of the anchor bolt loads is to be submitted with your response to the Bulletin.
Response
Those systems which are classified as Seismic Category I in the Fort Calhoun Station FSAR, are as follows.
Auxiliary Coolant Chemical Volume and Control Safety Injection feedwater Main Steam Auxiliary Feedwater Reactor Coolant Raw Water Waste Disposal Fire Protection 2013 162 4 5-3 ' 3 4 3 3
t There are approximately 750 pipe support base plates in the above systems which require further analysis as specified by NRC IE Bulletin 79-02 Revision 1.
The original design calculations have not accounted for base plate flexibility.
A finite element program has been used in lieu of the "2t" criteria to examine baseplate flexibility.
The finite element models used by the TES/0wners' Group computer program utilize ANSYS which is a verified finite element code.
Further justi-fication for the finite element program is being provided by conducting actual tests on base plate anchor bolt configurations.
The results of these tests will be compared to the finite element model and are anti-cipated to be supplied to the District on or about July 15.
The loads at the base plate were calculated since these were not avail-able from the original design documents of the architect-engineering firm who originally designed the plates.
The loads at the base plates has been calculated by limit load analysis method i.e. using the con-servative assumptions of full moment, shear or pull out load.
Any loads which could not be determined because of the support geometry conditions were calculated by finite element models using STRUDL, an industry accepted program developed at MIT.
The District verified the accuracy of the support drawings by selecting a number of supports that provides a representative sample of all Seismic Category I systems.
The representative systems that were chosen are as follows:
feedwater, raw water, safety injection, and auxiliary coolant. The in plant testing program focuses on these same systems.
Base plate flexibility was determined using the TES pre and post pro-cessor computer program and preliminary hand calculations based on a conservative model.
The computer model characteristics and the prelimi-nary hand calculations are shown in Attachment I.
General base plate curves furnished by TES were utilized to verify flexibility analysis for selected base plates.
Any base plate configuration which when analyzed by the conservative method and resulted in anchor bolt loads exceeding the factor of safety criteria, were then analyzed using the pre and post processor for the AilSYS program as furnished by TES.
At present, approximately 95% of all base plates have been analyzed using the TES pre arid post processor techniques.
Approximately 5% of the base plates remain to be analyzed. This remaining work involves the supports for which seismic loads are not available at present and those with difficult configurations to model.
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Request:
2.
Verify that the concrete expansion anchor bolts have the following minimum factor of safety between the bolt design load and the bolt ultimate capacity determined from static load tests (e.g. anchor bolt manufacturer's) which simulate the actual conditions of installation (i.e., type of concrete and its strength properties):
(a)
Four - For wedge and sleeve type anchor bolts, (b)
Five - For shell type anchor bolts.
The bolt ultimate capacity should account for the effects of shear-tension interaction, minimum edge distance and proper bolt spacing.
If the minimum factor of safety of four for wedge type anchor bolts and five for shell type anchors cannot be shown then justification must be provided.
_ Response:
Anchor bolts in use at the Fort Calhoun Station are the Phillips Redhead shell type embedded in the required 4000 psi strength concrete.
Shear-tension interaction analysis are being performed to correlate the effects of shear and tension acting in conjunction on the anchor bolt.
The procedure that is being used is shown in Attachment II.
This type of analysis is conservative since it models the shear-tension interaction mechanism as a straight line. The TES/0wners' group is conducting tests
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that will provide more realistic data for shear-tension interaction calculations.
The conservative calculations indicate approximately 15% of the total number of anchors do not meet safety factor criteria specified by the NRC.
The anchors which do not meet the NRC factor of safety criteria will be reevaluated when tho final shear-tension interaction data is available.
The anchors niiidi do not have an adequate factor of safety will be either:
- 1. ) Tension tested to the new calculated design inad.
2.) The anchor bolt and/or base plate configuration will be modi fied.
- 3. ) The anchors will be replaced.
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Request:
3.
Describe the design requirements, if applicable, for anchor bolts to withstand cyclic loads (e.g., seismic loads and high cycle operating loads).
Response
Attachment III from the Phillips Redhead Company concludes that a safety factor of five is sufficient for working loads under dynamic conditions such as those associated with a seismic experience.
Because of the absence of extensive cata on the cyclic capabilities for shell type anchor bolts, the TES/0wners' Group is conducting tests to determine an appropriate safety factor for design requirements of shell type anchor bolts for both seismic (low cycle high amplitude) and operating loads (high cycle low amplitude).
It should be noted that this data will be available on or about July 15.
Attachment III does indicate a safety factor of five on shell types is adequate to withstand dynamic working conditions, s
Request:
4.
Verify from existing QC documentation that design requirements have been met for each anchor bolt in the following areas:
(a)
Cyclic loads have been considered (e.g., anchor bolt preload is equal to or greater than bolt design load).
In the case of the shell type, assure that it is not in contact with the back of the support plate prior to preload ' testing.
(b) Specified design size and type is correctly installed (e.g.,
proper embedment depth).
If sutiicient document does not exist, then initiate a testing program that will assure that minimum design requirements have been met with respect to sub-items (a) and (b) above.
A sampling technique is acceptable.
One acceptable technique is to randomly select and test one anchor bolt in each base plate (i.e., some supports may have more than one base plate).
The test should provide verification of sub-items (a) and (b) above.
If the test fails, all other bolts on that base plate should be similarly tested.
In cnv event, the test program should assure that each Seismic Category I system will perform its intended functbn.
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2013 165 The pieferred test method to demonstrate that bo'.? preload has been T
accomplished is using a direct pull (tensile test) equal to or greater than design load.
Recognizing this method may be difficult due to accessibility in some areas, an alternative test method such as torque testing may be used.
If torque testing is used, it must be shown and substantiated that a correlation between torque and tension exists.
If manufacturer's data for the specific bolt used is not available, or is not used, then site specific data must be devloped by qualification tests.
Bolt test values of one-fourth (wedge type) or one-fifth (shell type) of bolt ultimate capacity may be used in lieu of individually calculated bolt design loads where the test value can be shown to be conser rative.
Response
A testing program consisting of pull tests on Red head shell anchors has been initiated by the District. The test procedure verifies that anchor bolt preload is equal to or greater than bolt design load and provides assurance that the specified design size and type have been correctly installed.
The hydraulic tensioners are used under the supervision of NPS-Crouse, the architect-engineering fire hired to assist in the test-ing and have been checked and calibrated for the District in order to assure their reliability. The testing is proceeding on those base plates initially surveyed in the verification study.
The suggested procedure of Bulletin 79-02 of pulling on one bolt per plate to 1/5 the ultimate pull out load as specified by the bulletin for shell type anchor bolts is being followed.
In addition, if the bolt fails the pull test all anchors in that plate will be tested.
Through July 6,1979 201 anchors have been tested on 190_ baseplates with a failure rate of 3.48 %.
Request 4 Paragraphs 6-9:
Appendix A describes two sampling methods for testing that can be used.
Other sampling methods may be used but must be justified.
Those options may be selected on a system by system basis.
Justification for omitting certain bolts from sample testing which are in high radiation areas during an outage must be based on other testing or analysis which substantiates operability of the affected system.
-851 107 x 2013 166 9
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Bolts which are found during the testing program not be be preloaded to a load equal to or greater than bolt design load must be properly tre-loaded or it must be shown that the lack of preloading is not detri-mental to cyclic loading capability.
If it can be established that a tension load on any of the bolts does not exist for all loading cases, then no preload or testing of the bolts is required.
If anchor bolt testing is done prior to completion of the analytical work on base plate flexibility, then the bolt testing must be performed to at least the original calculated bolt load.
For testing purposes, factors may be used to conservatively estimate the potential increase in the calculated bolt load due to base plate flexibility.
After com-pletion of the analytical work on the base plates the conservatism of these factors may be verified.
Response Paragraphs 6-9:
The District has previously described our sampling method on page 6 as part of the response to Item 4.
Since the Fort Calhoun Nuclear Station is not currently in an outage, paragraph 7 does not apply at the present time.
In addition, the TES/0wners' Group is conducting tests to determine the cyclic load capability for anchor bolts.
This program is acceptable to the NRC as discussed in the TES/0wners' Group meeting with NRC on April 26,1979 (Refereace I).
The District is not testing those bolts which have only a shear load or take only compressive dead weight loads.
It was ne med earlier on Page 6 in response to subitems a) and b) of Item 4 that ti9 District is testing bolts to Pu/5 as recommended by the bulletin.
The original design load indicated on page 2 of Attachment 4 utilized an approximately 6 to 1 safety factor. After completion of analytic M.. ark, the conservatism of the test load (Pu/5) will be checked and verified for those plates tested.
Request 4, Paragraph 10:
For base plate supports using expansion anchors, but raised from the supporting surface with grout placed under the base plate, for testing purposes, it must be verified that leveling nuts were not used.
If leveling nuts were used, then they must be backed off such that they are not in contact with the base plate before applying tension or torque tes ting.
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Response
Thir, aspect of 79-02 Revision I has been incorporated into the testing precedure. Where leveling nuts are used, the grout is chipped away and the leveling nut backed off at least 1/8 anch.
After testing the support is repaired.
Request 4, Paragraph 11:
Bt.lletin No. 79-02 requires verification by inspaction that bolts are properly installed and are of the specified size and type.
Parame ters which should be included are embedment depth, thread engagement, plate bolt hole size, bolt spacing, edge distance to the side of a concrete member and full expansion of the shell for shell type anchor bolts.
Response
As indicated earlier, a verification inspection of 221 base plates was made in four systems and the results indicate that the drawings are accurately depicted.
At present the data on embedment depth and thread engagement are being reviewed to note any discrepancies.
In conjunction with this review the same anchors that were inspected during the veri-fication studies are baing tested.
Any discrepancias or installation errors are being noted and corrected.
Request 4, Paragraph 12:
If piping systems 21/2 inch in diameter or less were computer analyzed then they must be treated tne same as the larger piping.
If a chart analysis method ms ised and this method can be show'1 to be highly conservative, then tie proper installation of the base plate and anchor bolts should be verified by a sampling inpsectiun.
The parameters inspected should includ thuse described in the preceding paragraph.
If small diameter piping is not inspected, then justification of system operability must be p ci.ded.
Response
A chart method was used by the District and the following actions are being taken:
1.
OPPD has contacted the responsitle A & E to determine the con-servatism of their nomograph which was used for spacing pipe supports.
2.
The majority of 24" and smaller piping is in containment an6 n
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} (30 unavailable for inspection during operat' ion.
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The design criteria used for small piping limited loads to less than 3000 psi stress levels in 2h" diameter and smaller piping for a seismic even t.
Based on the field verification Mne on other piping systems as des-cribed in the District's response
'0 la.a 1, it is the District's opinion that the pipe supports have been installed according to the design requirements.
The spacing of supports is such that all frequencies for 21" diameter 3
and smaller piping are high enough to avoid any amplification of seismic loads.
Request:
5.
All holders of operating licenses for power reactor facilities are requested to complete items 1 through 4 within 120 days of date of issuance of the Bulletin.
No extension of time to complete action requested in Bulletin 79-02 is granted by issuance of this revision of the Bulletin.
(Due Date - July 6,1979).
A reactor shutdown is not required to be initiated solely for purposes of this inspection aSove.
However, it is expected that testing of othenvise inacces-sible supports will be performed during the earliest extended outage following Bulletin issuence.
It is also expected that test-ing of anchor bolts in accessible areas in operating plants will be performed within the reporting intereal.
In the event the required testing is not completed at the time of the initial report, on or about July 6,1979, the licensee should justify system operability and therefore continued plant operation based upon the results. of testing completed.
Response
Although the District has not completed testing, continued operation is clearly justified because of the testing completed to date.
As of July 6, 1979, 201 anchor bolts on 190 baseplates have been tested, resulting in a very low failure rate of 3.48%. The failures have occurred under a conservative testing load of Pu/5 (ultimate pullout load /5). These bolt failures have not occured on adjacent supports and multiple bolt failures have not been found on a single base plate.
All failed anchors are being replaced and retested in order to assure their operability.
Replacement is performed according to plant technical specifications.
The bolts tested to date represent a sample which is indican c mc3c of the bolt, base plate configurations at the station.
I, ee eved that these sample results are applicable to untested supp.. cs.,
baseplates.
2013 169 h5 In light of the foregoing inform ~. lor, and considering the low seismic activities expected at the site (1.e. low probability of an earthquake enhancing support / base plate failure), continued operation is justified and would not present any increased hazard to the health and safety of the public.
Summary:
After the additional data is received from TES on tests conducted in relation to Items 2, 3, and 4 of the bulletin, the District will evaluate the efforts of this information on the work accomplished to date.
By August 15, 1979, the District will submit a report to the Commission which will detail final field testing results and provide a schedule for performing additional analysis and testing as required.
2013 170 Oh f'
References I.
U.S. NRC Memorandum Dated May 15, 1979 Attachments I.
Analytical Model for Flexibility Analysis II.
Shear-Tension Interaction Model III.
Phillips Red Head Dynamic Testing IV.
Bergen-Patterson Design Letter 2013 171 E t r3*2s
WTELEDYNE ENGINEERING SERVICES Cr 3
,i 303 DE AH H't L f10AD WALTHA% MAOSACHUSETTS 02 54 (M7)890-3350 TWX(7iC)324 7508 ATTACHMENT I June 29, 1979 3501-33 To:
Distribution
Subject:
Status Report - Generic Program Baseplate / Expansion Anchor Studies As the generic program nears completion, TES is taking this opportunity to summarize the essentials of the program and give a brief status report.
BACKGROUf!D In April of this year several utilities joined together to sponsor an analytical and experimental investigation of pipe support baseplates for Seismic Category I piping.
This became known as the " generic program" and its function is to provide supportive data and an analytical tool to the utilities to assist them in their responses to NRC IE Bulletin 79-02.
Since all of the utilities were affected by the bulletin in a similar way, it was felt that generic studies would benefit the utilities in their plant speci.fic investigations.
Many of the plants involved use similar anchor bolts and baseplate configurations.
The utilities required anchor bolt test data for shear-tension inter-action and cyclic loadings which are not currently available or which are only partially available.
Also, an efficient procedure for analyzing baseplates accounting for plate flexibiity was also required.
The generic program addresses both of these requirements.
ANALYTICAL WORK
- c. q.;
It is recognized that the finite element method is the m'ost versatile method of analyzing baseplates accounting for plate flexibiity in addition to nonlinearities such as gapping and variable bolt stiffness.
- 11ence, TES has developed a pre-and postprocessor to the commercially available ANSYS computer code.
A complete finite element model of a baseplate, concrete subgrade, anchor bolts, and attachment consisting of any rolled shape may be input in only five punched cards.
The postprocessor reduces the output and summarizes bolt loads and plate stresses.
Revision B of the program has been issued and i't includes geometry plot capability, averaging of plate bending stresses and the option to add or delete bolts and concrete spring elements in addition to several other enhancements.
The pre-and postprocessor has been verified analytically using stan-Also, four-bolt and eight' bolt experimental baseplates dard ANSYS analyses.
have been constructed and instrumented to compare results with the pre-
-MIN 3 2013 172 ENGINEEllS AND fAETAI l.URGisTS
"vPTELEDYNE ENGINEERING SERVICES s
Distribution June 27, 1979 Page Two and postprocessor.
The four-bolt' plate experiment has been completed and the results compare favorably with the computer program.
Utilities are now using Revision B of the pre-and postprocessor program.
Curves of bolt load versus plate thickness have been generated for typical baseplates and bolts.
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June 11,1'79 3501-21 T0:
DISTRIBUTION FR0!!:
TES
SUBJECT:
BASEPLATE STRUCTURAL ANALYSIS SYSTEM, USER DOCUMENTATION - REVISION B 1.
The enclosed document defines Revision B of the user documentation the BASEPLATE pre-and post-processors.
modification and includes the following enhancements: Revision B represents a major s
Calculate k using Timoshenko Equation.
c Plot capability.
Add / delete anchor bolts.
Wave front minimization.
Average bendi19 stress.
Capability to eliminate concrete springs.
Optional moment resisting bolt / plate connection.
Capability to move the attachment within the bolt lines.
Capability to apply a six degree of freedom loading at the centroid of the attachment.
The bi-linear tension no compression bolt material property he-havior option (described in the manual) is not functional at the present time.
incorporated into the pre-and post-processor. Notification will be sent wh 2.
Revision A, dated May 16, 1979, will be retained for use as an alternate back-up capability until all users have achieved a high level of con-fidence with the utilization of Revision B.
3.
Software access code names have been incorporated into the preprocessor as a security measure, in order to execute the preprocessor, the user code name is required as an input parameter on card type B (the 2nd input data card) columns 16-20.
It has been omitted from the user documenta tion for security reasons.
Utility is The code name assigned to your B, columns 16-20) each time the program is executed.and must be defi perly define the code name will result in job termination. Failure to -pro-p345
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2013 174
"RTELEDYNE ENGINEERING SERVICES June 11, 1979 3501-21 Page 2 4.
An additional password has been included in the job control language for the version maintained by TES on the CDC CYBERNET SYSTEM (CYBER 76 SCOPE 2.1 and CYBER 75 SCOPE 3.4 SYSTEli ECZ The password is defined on the ATTACH card for the preprocessor).
and postprocessor, and is necessary for control permission to gain access to the per-manent files.
The password is defined as PW= BEAVER on the ATTACH cards.
The ATTACH cards should read as follows for the preprocessor and postprocessor respectively; ATTACH ( PRE, B AS E PL ATE P R ER EVB, I D= G9, MR=1, PW= BEAVER )
ATTACH (POST,BASEPLATEPOSTREVB,ID=G9,MR=1,PW= BEAVER) 5.
Questions relative to the application and utilization of the pre-and postprocessors should be directed to the following TES personnel; Alan Beardsley, Ken Lanham, or Jack Diluna at 617-890-3350.
Sincerely, TELEDYt1E ENGIllEERING SERVICES
'l
' Alan Beardsley, Senior Project Engineer AB/bsl 2013 175