ML19248D568

Responds to IE Bulletin 79-02,Revision 1.Final Rept Will Be Issued When Testing & Insp Program Is Completed. Completion Date Is 791231

ML19248D568
Person / Time
Site:	Peach Bottom
Issue date:	07/06/1979
From:	Daltroff S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
NUDOCS 7908160565
Download: ML19248D568 (7)

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PHILADELPHIA ELECTRIC COMPANY 2301 M AF<KET STREET P.O. BOX 8699 P:llLADELPHI A. PA.19101 SHIELDS L. DALTROFF ELEctmic pm o c son July 6, 1979 Docket Nos.: 50-277 50-278 Re: IE Bulletin 79-02 Mr. Boyce H. Grier, Director Office of Inspection & Enforcement Region I United States Nuclear lagulatory Commission 631 Park Avenue King of Prussia, PA 19406

Dear Mr. Grier:

This la in response to your letter of June 21, 1979, which forwarded IE Bullctin 79-02 (Revision 1) and included by reference IE Bulletin 79-02, forwarded by your letter of March 8, 1979. The actions requested, and our responses as they pertain to the Peach Botton Atomic Power Station, Units 2 and 3, are listed sequentially below.

Action to be Taken by Licensee:

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 'f rigidity, the base plates should be ccnsidered flexible if the unstiffened distance between the member welded to the plate and the edge of the base plate is greater than twice the t h f.e k n e s s of the plate. It is recognized that *his criterion is conservative. Less conservative acceptance criteria must be justified and the justification subnitted as part of the response to the Bulletin. If the base plate is determined to be flexible, then recalculate the bolt loads using an appropriate analysis. If possible, this is to be done prior to testing of anchor bolts. These calculated bolt loads are referred to hereafter as the bolt design loads. A bbdCI 1908160 % {

Mr. Boyce H. Grier Page 2 nes crip ti on of the analytical model used to verify that pipe support base plate flexibility is accounted for in the calculation of anchor bolt loads is to be submitted with yotr response to the Bulletin.

Resoonse The flexibility of the base plate was not considered in the design of the Seismic Category I pipe supports.

All pipe anchor and support base plates using expansion anchor / bolts were (re) analyzed to a c c o u r. t for plate flexibility, bolt stiffness, shear-tension interaction, minimum edge distance and proper bolt spacing. Depending on the complexity of the individual base plate configuration one of the following methods of re-analysis was used to determine the bolt forces:

(1) A quasi analytical method, developed by Bechtel Power Corporation was used for base plates with eight bolts or less. A review of the typical base plates used in supporting the subject piping systems indicate that the majority of them were anchored either by 4, 6 or 8 bolts. The plate thicknesses vary from 1/2" to 2" and are not generally stiffened. For these types of base plates an analytical f ormula tion has been developed which treate the plates as a beam on multiple spring supports subjected to coments and forces in three orthogonal directions. Based on analytical considerations as well as the results of a number of representative finite elenent analyses of base plates (using the "ANSYS" Code), certain empirical factors were introduced in the simplified beam model to account for (a) the affect of concrete foundation (b) the two way action of load transfer in a plate. These tactors essentially provided a way for introducing the interaction effect of such parametric variables as plate dimensions, attachment sizes, bolt spacings and stiffness on the distribution of e ::t e r n a l loads to the bolts.

The results of a number of case studies indicated excellent correlation between the results of the present formulation and th os e by the Finite Element 'f e th od (using the "ANSYS" Code). The quasi analytical method generally gives the bolt loads greater than the Finite Element Method.

A computer pr gram for the analytical technique described above has been implemented for determining the bolt loads for routine applications. The program requires plate dimensions, number of bolts, bolt size, bolt spacing, bolt stiffness, the applied forces and the t>YOU

Mr. Boyce H. Grier Page 3 allowable bolt shear and tension loads as inputs, The allowable loeds for a given bolt are determined based on the concrete edge distance, bolt spacing, embedment length, shear cone overlapping, manufacturer's ultimate capacity, and a design safety factor. The program computes the bolt forces and calculates a shear-tension interaction value based on the allowable loads.

(2) For special cases where the design of the support did not lend itself to the foregoing method, the finite element method using the "ANSYS" code and/or other standard engineering analytical techniques with conservative assumption were employed in the re-analysis.

(3) Otuer cases uere solved using an approach based on the strength design metnod gi'en in the ACI 318-77 code.

2. Verify that the concrete expansion anchor bolts have the f ollowin g mininum factor of ,afety between the bolt design load and the bolt ultinate capacity determined from static load tests (e.g., anchoc bcit manufacturer's) which simulate the actual conditions of installation (i.e., type of ccncrete and its strength properties):

a. Four - for vedge a n et 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 can not be shown then justification must be provided.

Response

The calculated bolt design loads are being compared to the manufacturer's published ultimate capacities adjusted to the conditions existing at Peach 3ottoa to verify the adequacy of the existing factors of safety. Of the 1217 suppo-ts re-analyzed for the operating and seisnic loading (Design 3 asis Earthquake), 1125 have factors of safety exceeding 5 in the maximun stressed bolt, and 92 have factors of safety less than 5. The pipe support drawings indicate that self-drilling shell type anchors were generally used.

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Mr. Boyce H. Grier Page 4 The following summarizes the distribution of these 92 supports previously reported it LER 2-79-32/1T and the factors of safety:

Factor of No. of Safety Sunoorts 4 to 5 20 3 to 4 27 2 to 3 24 1 to 2 13 Less than 1 8 Modifications are being made to the 21 supports having a bolt safety factor less than 2, and are expected to be conpleted by July 31, 1979. In the cases when extreme environmental loads are included, a facter of safety of at least three is used for acceptance in accordance with Section B.7.2 of the Proposed Addition to Code Requirements for Nuclear Safety Related Concrete Structures (ACI 349 August, 1978. In cases where the factor of safety exc s two (but is less than three), a program of 100% verification of acceptable anch or bolts will be implemented.

3. Describe the design requirements if applicable for anchor bolts to withstand cyclic loads (e.g., seismic loads and high cycle operating loads).

Resoonse In the original design of the piping systems Bechtel Power Corporation considered deadweight, thermal stresses, seismic loads, and dynamic loads in the generation of the pipe support design loads. To the extent that these loads include cyclic considerations, these effects are included in the design of the hangers, base plates and a n ch o ra g e s .

The safety factors used for concrete expansion anchors, installed on supports for safety related piping systems, were not increased for loads which are cyclic in nature. The use of the same safety factar for cyclic and static loads is based on the Fast Flux Test Facility Tests. (Drilled - In Expansion 3cits Under Static and Alternate Loads. Report '! o .

BR 5853-C-4 by Bechtel Power Corp., January, 1975). The test results indicate:

1) The expansion anchors successfully withstocd two aillion cycles of long term fatigue loading at a maximum intensity of 0.20 of the static ultimate capacity. FThen the maximun load intensity was steadily increased beyond b32OCE

Mr. Boyce ii . Grier Page 5 the aforementioned value and cycled for 2,000 times at each load step, the observed failure load was about the same as the static ultimate capacity.

2) The dynamic load capacity of the expansion anch ors ,

under simulated seismic loading, was about the same as their corresponding static ultimate capacities.

4. Verify froc axisting QC documentation that design requirements have been met for each anch or bolt in the following areas:

(a) Cyclic loads have been considered (e.g. a n ch or 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 sufficient documentation does not exist, then initiate a 2 sting program that will assure that minimum design equirements have been met with respect to sub-items (a) and ib) 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 ve rif f.ca t i on of sub-items (a) and (b) above. If the test fails, all other bolts on that base plate should be similarly tested. In any event, the test program should assure that each Seismic Category I system will perform its intended function.

Resoonse Philadelphia Electric Company has initiated a testing and inspect'an program.

. This program is currently under way at the Peach Bottom Atomic Power Station. Testing and inspection will be done on all Seismic Category I piping systems, with the exception of small piping (2 1/2" diameter or less) which was chart analyzed. Based on the conservativeness of this analysis, system operability is not compromised, and small piping supports have not been included in the testing program.

Also excluded from the testing and inspection program are th os e supports which re-analysis indicates that under design bNOC

Mr. Boyce H. Grier Page 6 loading conditions, none of the bolts are subject to tensile loads.

The testing ano inspection program will verify that:

a) The installed anchor is the proper diameter and an acceptable type, b) Preload in the anchor bolt is verified by the application of the a specified torque to the bolt.

Attainment of specified torque will verify that the bolt preload is in excess of the bolt design load. Testing is being done on one bolt in each base plate. Should the specified test torque not exist in the bolt tested, that bolt shall be torqued to the specified value, and the remaining bolts tested in a sinilar manner. To assure validity of the torque test on shell type anchors, it shall be verified that shell to base plate contact does not exist. The specified test torque values have been developed by Bechtel Power Corporation and represent a bolt preload not less than 25% of the manufacturer's published ultimate load. Site specific torque-tension relationships are being developed based on testing performed at the site.

c) 3cits are of sufficient length to assure adequate thread engagenent for shell type anchors, and proper embedment of wedge type anchors in the concrete.

It has been determined that there are no Seismic Class I supports requiring anchor bolt testing in areas which are not accessible during unit operation. The balance of the Seismic Class I systems are normally accessible for inspection during operation.

Up to June 29, 1979, testing has been c onp le t e d on 5* of the supports requirias testing. Of a total of 15: concrete expansion bolts tested to date, 7 have failed t nee t the specified torque requirements, and necessary correctiva action has been taken. Bechtel Pouer Corporation will review for structural adequacy any support in which an expansion bolt fails to meet test criteria. Corrective actions required as a result of testing are bein; done in an expeditious manner. In cases where insufficient threid engagement is found, a bolt of sufficient length is being installed to provide adequate thread engagement. "here expansion bolts fail to develop the specified torque, or fail by pull-out, these balts will be renoved and replaced with new expansion bolts. As other problems arfse, these are being revieued on a case-by-case basis, an- todifications made as required.

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Mr. Boyce . Grier Page 7 The testing and inspection of Seismic Class I piping system supports an ch o red with expansion bolts in being done to assure adequacy of support and operability of each Seismic Category I piping system. During the testing and inspection progran, system operability is maintained by limiting removal of one bolt at a time from any base plate. This restriction als o applies when it may beconc neces ary to replace an expansion bolt.

The safety and operability of the Seismic CateL)ry I piping systems will not be compromised during the testing and inspection program now being implemented. Upon completion of the program, it will have been verified that expansion anchor ,

bolts installed at Peach Bottom have pre-load exceeding bolt design loads. Improperly installed bolts will have been replaced where necessary, or by engineering analysis, the remaining acceptable bolts in a support plate shall have been demonstrated to be adequate to sustain design loads. Where necessary, modifications vill have been made to supports to assure safety and operability of the Seismic C l a s s. I piping systems.

A final report will be issued when the testing and inspaction program is completed as required by the Bulletin. The entire testing and inspection program, including any modifications required, is expected to be completed by December 31 1979 Should you have any questions or require additional information, please do not hesitate to contact us.

Very truly yours, i

~,7ff f: I ccr United States Nuclear Regulatory Commission Office of Inspection and Enforcement Division of Reactor Operations Inspection Nashington, DC 20555 C"2OI