ML19242B196

Responds to NRC 790621 Ltr Re IE Bulletin 79-02,Revision 1. Discusses Reanalysis of Generic Base Plate Stresses & Anchor Bolts Applied Loads,Insp of Concrete Expansion Anchor Bolts & Base Plate Flexibility Computer Analysis

ML19242B196
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	07/06/1979
From:	Grace R VERMONT YANKEE NUCLEAR POWER CORP.
To:	Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
NUDOCS 7908070653
Download: ML19242B196 (4)

Text

o VERMONT Y AN KEE NUCLEAR POV 2R CORPORATION SEVENT Y SEV EN GROVE STP EET B.4.2.1 RUTL AND, YEIDIONT 05701 H EPLY TO:

ENGINEERING OFFICE TURNPlKE RO AD WEsTDORO. M ASS ACHUSETTS 01581 T E LEPH O N E 6 s 7 3 6 6-9 011 WY 79-76 July 6, 1979 United States Nuclear Regulatory Commission Office of Inspection and Enforcement Region i King of Prussia, Pennsylvania Attention: Mr. Boyce H. Grier, Director

References:

(a) License No. DPR-28 (Docket No. 50-271)

(b) USNRC Letter to VYNPC dated March 8, 1979; Ir Bulletin 79-02 (c) U b.- J Letter to VYNPC dated June 21, 1979; I&E Bulletin 79-02, Revision No. 1

Subject:

Response to I&E Bulletin No. 79-02, Revision 1 Upon receipt of the subject ISC Bulletin a three part ef fort was initiated by Vermont Yankee which addresses your concerns as follows:

a. A program was initiated to develop a generic base plate flexibility computer analysis.

b. Planning for re-analysis of base plate stresses and anchor bolt aoplied loads was initiated.

c. A program of inspection of concrete expansion anchor bolts at Vermont Yankee was initiated.

The following presents an item by item explanation of r or actions to meet your concerns. These are presented in the same sequence as your bulletin:

1. Since base plate flexibility was not considered in Vermont Yankee design, we have initiated a program to develop a finite element computer program which accounts for flexibility in the 7 9 08070 o b '?' (p'

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United States Nuclear Regulatory Conmission July 6, 1979 titention: Mr. Boyce H. Grier, Director Page Two existing base plates. This program will produce anchor bolt loads, base plate stresses and deflections which result from applied loads, shears, moments and the effect or' the stiffness of the bass plate and attached structure.

The analytical model used in this analysis employs a finite element, three dimensional cesh assuming linear elastic steel to model the base plate. Tension only, one dimensional axial, non-linear elements are used to represent the bolts; and compression only, non-linear axial elements are used to model the concrete behind the base plate.

The process of reanalyzing Vermont Yankee base plates is ongoing. The following sequence of events is being followed:

- Identify affected base plates and verify with drawings.

- Compile loads, shears and moments from piping analysis.

- Transfer loads, shears and moments to base plates.

- Reanalyze base plates.

- Review resulting anchor bolt loads to verify they are less than bolt design loads.

2. Original design loads for seismic piping su) port anchor bolts at Vermont Yankee were predicated en the recommendations of the anchor bolt manufacturer. These values are supported by his test program. Properly installed anchor bolts will develop the ultimate loads originally published. The factor of safety recommended by the manufacturers of all concrete expansion anchor bolts in use at Vermont Yankee is four. In other words the ultimate load, verified by the manufacturers test program is four ti=es the design load. If testing justifies a change in the ultimate load our design load will change by the four to one factor of safety but the factor itself is an arbitrary value equally applicable to all equipment. We, therefore, see no way te justify the use of two f actors of safety for one type of equ.pment. We will, for these reasons, continue to use the manufacturers recommended factor of safety of four for all concrete expansion anchor bolts.

The ultL= ate capacity of the bolts will include the effects of shear and tension interaction, proper edge distance and spacing.

3. To prevent the application of high cyr.lic 1 ceding on concrete 6/I

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United States Nuclear Regulatory Commission July 6, 1979 Attention: Mr. Boyce H. Grier, Director Page Three expansion anchor bolts at Ver=ont Yankee our test program is designed to verify that a pre-tension equal to the bolt design load exists in each anchor bolt. Manufacturers test data indicates that this procedure develops the full tension and shear capability and assures little to no cycling of anchor bolt loads.

4. Sufficient QC documentation cannot be found at Vermont Yankee to assure correct installation. A testing program has been initiated to accomplish this. Testing consists of, first identifying the number, size (diameter), plate hole size, thread engagement, type, location and length (em'.edment depth) of the bolts. The bolts are then torqued or loaded in tension to an equivalent tensile value equal to the bolt design load (the relationship of torque to tension de being verified by test) . The test assures that anchor b, hells sleeves and leveling nuts are not in contact with sack side of the base plate. An initial visual inspect revealed less than 5% of the concrete expansion ancnor bolts were loose. These were retorqued above design load. The testing program has shown thus far no failures of any anchor bolts. Furthermore, since anchor bolts are used for dead-weight anchors as well as seismic restraints and have not shown a history or failures even though they have been under censtant load since their installation, we feel that initial correct installation has been amply demonstrated. Ocr program will continue, however, until we are confident the sample population assures that correct installation has been achieved for all Seismic Catcaory I piping systems at Vermont Yankee.

It is possible that verification of correct installation of anchor bolts at Vernout Yankee will be completed before the analytical program. In the event a review of the applied loads from tha results of the re-analisis indicates any value in excess of the design load for any bolt, a design adjustment will be made and modifications to the ctructure accomplished to rectify any inadequacies.

A large majority of the 2h inch diameter and smallar pipes at Vermont Yankee were analyzed by the chart method which can be shown to be very conservative. Visual inspection of the supports for these pipes will be conducted any failure to meet our inspection requirements will require the failed piping supports to be included into our sampling and testing program.

They would then be required to meet the requirements of that program.

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United States Nuclear Regulatory Commission July 6, 1979 Attention: Mr. Boyce H. Grier, Director Page Four If no failures or incorrect installation of 'he concrete expansion anchor bolts for these pipes is noted, no further effort will be under aken.

5. Anchor bolt testing at Vermont Yankee is now being conducted in accessible areas. This testing program consists of the following tasks:

- Develop testing and inspection procedure.

- Develop and execute test program to correlate torque versus bolt tension.

- Identify seismic supports and verify with drawing.

- Test all applicable anchor bolts per procedure.

All areas inaccessable during power operation will be tested prior to return to power after our next scheduled refueling outage.

It should be noted that Vermont Yankee pipe analyses were conducted by highly conservative static methods. Included in these analyses was the " Robinson Fix". This anr.lytical method account;d for possible resonances between structura and piping and imposed multipliers tc all piping to include further conservatism. It has been showv in '.ater analyses that most piping does not fall in the resonance regime thus, these systems are over designed by factors ranging from approximately 7 to 13 due to design analysis conservatisms.

In conclusion we feel that cecause of the vary low f ailure rate identified in our initial inspection program already accomplished, because of the complete lack of noted failures of dead load supports and due to the known conservatisms in design, Vermont Yankee has demonstrated initial adequacy in the design and installation of seismic piping restraints and their anchor bolts.

Our program of continued testing and analysis will v-this adequacy.

We feel certain the above answers your concerns on this s .,

however, if you require further information, please contact us u. your convenience.

Sincerely, VERMONT YANKEE NUCLEAR POWER CORPORATION kb Robert H. Groce, Licensing Engineer RHG/scw C /, 'L/

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