ML19208D727

Submits Second Supplementary Response to IE Bulletin 79-02, Revision 1, Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts. Anchor Bolts Have Been Insp &/Or Replaced to Achieve Required Design Loads

ML19208D727
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	08/29/1979
From:	Moody D VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
WVY-79-95, NUDOCS 7909290425
Download: ML19208D727 (4)

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VERMONT Y AN KEE NUCLEAR POWER CORPOR ATION SEVENTY SEVEN GROVE STREET B.4.1.1 RuTLAso, VEIO10NT 05701 WVY 79-95 REPLY TO ENGli T. RING OFFICE August 29, 1979 TURNPlKE RO AD WESTBORO. M ASS ACHUSETTS 01581 TELEPHONE 417-366-9011 United States Nuclear Regulatory Ccemission ag Office of Inspection and Enfercement D D Region I ga 631 Park Avenue ,

King of Prussia, PA 19406

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n ,D)I _h_1j' I Attention: Mr. Boyce H. Gr!'r, Director o J1 JJ _ _a

References:

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

(b) USNRC Letter to VYNPC dated March 8, 1979 (c) VYNPC Letter to USNRC dated July 6, 1979 (d) USNRC Letter to VYNPC dated July 26, 1979 (e) VYNPC Letter to USNRC dated July 31, 1979 (f) USNRC Letter to VYNPC dated August 3,1979

Dear Sir:

Sabject: Second Supplementary Response to I&E Bulletin 79-02, Revisien 1 As a result of several telephone conversations around August 2, 1979, a meeting between Vermont Yankee personnel and NRC staff members was held in Be.thesda, Maryland on August 8, 1979. This meeting covered in agenda included in Reference (f).

During the week of August 14, NRC staff members requested that certain work accomplished by Vermont Yankee before the meeting be redene using a more conser 7ative method. The following response documents the statements made at the original meeting and the resuits of the additional work requested:

At stated previously, Vermont Yankee concluded that Seismic Category I piping systers are capable of withstanding seismic design loads despite the low percentage of anchor bolt failures fcund during testing required by NRC. This is because of highly conservative seismic design loadings required during the original plant design. These conservatisms were incurred by the fcllowing design cycle.

1. Original design was acccmplished to loads derived from building response spectra from a ground motion of .07 g not amplified for equipment responses. Damping values used werc 5% for the concrete buildings and 1% for the steel dryt: Ll. The building response accelerations were increased by a factor of 4 to account for equipment responses.

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. IP United States Nuclear Regulatory Commission August 29, 1979 Attention: Mr. Boyce H. Grier, Director Page 2

2. Late in the construction cycle amplified response spectra were developed for Vermor.t Yankee and were found to give resonant peak accelerations much higher than those produced in the original estimate.

3 Pipe stresses and support loads were then divided by the original acceleratien factors and multiplied by the new ARS peak response accelerations times and a modal contribution factor of 1 3 The resulting loads en piping and seismic supports caused large scale redesign of supporting structures. All piping supports were designed to include a factor of safety of five for DBE.

This redesign cycle assumed that all piping systems were in resonance with the building structures and applied acceleration forces which would be present only if they were in resonance. Our resonance evaluation was conducted to show that most of our systems are not in resonanct and therefore, the new " Robinson Fix" accelerations are in reality factors of safety en these seismic supports.

This resonance evaluation was modified by an NRC staff request fer the use of a more conse" vat.'se method to determine piping runs which are in resonance. This method is taken from D. J. Gorman's " Free Vibration Analysis of Beats and Shafts," J. Wiley and Sons, 1975. The results of this modified resonance evaluation show the following runs to have natu al frequencies below ten cycles per second. Building peak response frequencies are at 5.5 cycles per second.

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RCIC two runs D D HPCI one run g RER cne ~un -

SW one run 9 IM ~ fu T i G one run ] ))] ,,, j g( _,3 CST one run Of the systems in resonance the following approximate percentages apply to the affected portion of the total syotems:

RCIC 35 percent HPCI 8 percent RHR 8 percent SGT 70 percent CST 13 percent SW 5 percent To date, anchor bolts in the portions of the RCIC, HPCI, SW and RHR systems, initially identified to be in resonance have been inspected and/or replaced as necessary to achieve the required design load capability. The remaining runs, which were identified within the past week to be in resonance, will be addressed as follows:

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.. b United States Nuclear Regulatory Commission August 29, 1979 Attention: Mr. Boyce H. Grier, Director Page 3 b

1. RCIC (6" Suction from CST) - The accessible anchor bolts associated with the seismic restraints in question will be inspected and/or h

C repaired to achieve the required design load capability on or before September 4, 1979 In parallel, a more detailed engineering analysis, r~

b g versus the initial hand calculation, is being conducted to ascertain the degree of conservatism contained in the hand calculation method.

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, a If it can be shown by the detailed analysis that resonance is not a problem in the existing gecmetry, the schedule for completing the inspection and/or re' air will ne deferred until the end of the upcoming refueling outage {

2. CST (4" Suction to CRD Puas) - Visual examination of the subject line indicates that bolts sub .et to tensile stresses are the embedded type. The six expansion type anchor bolts installed in this system are subject to only shear stress.

3 RCIC (4" Test Line) - The portion of this line identified to be near resonance is isolable. It's configuration is such that propogation of failure to any other safety related system or loss of isolation capability is highly improbable.

4. SBGTS - The anchor bolts associated with the three seismic restraints in question will be inspected and/cr repaired to achieve the required design load capability en or before September 4, 1979.

Cross coupling due to the two direction earthquake for which Vermont Yankee piping systems were designed was considered to have inconsequential effects upcn the resonance estimates.

The amplified response spectra were developed by inputing time history accelerations into a multi-degree of freed:s dynamic model of the building. Time history accelerations were used to construct a maximum response spectrum of the piping systems located at the various building mass points. The ficor response spectra for piping systems used a damping ratio of .005. The time history input used the -N690W component of the Taft earthq d e normalized to .07 g for DBE. SSE values used are two times DBE.

Pre-tensien values for existing expansion anchor bolts at Verment Yankee are established by applied torques. To verify that tensile values are achieved by the torque =ethod, tests of several bolts of each size were conducted on existing bolts in the plant. These tests use belleville washers with known displacement versus load values and calibrated torque wrenches. Torque versus load curves were established which show our normally required torque values to be conservative. The following data are indicative of the results for Phillips Redheads:

fequired Required Tension at Standard Bolt Size Tension (lbs.) Torque (ft-lbs) Min. Tg. Value (lbs) Dev. (1bsl 1/2 2253 28-31 2271 135 3/4 4293 76-84 4646 80 7/8 4463 98-108 4648 125 1054 010

~ United States Nuclear Regulatory Commission August 29, 1979 Attention: Mr. Boyce H. Grier, Director Page 4 Safety priorities used on anchor bolt testing and replacement follow safety class boundaries where possible. In some cases it 4.s more convenient to repair or replace anchor bolts in a specific area, in which case some lower safety class systems will be replaced firrt. In cases where resonant system runs were identified these runs are being given priority over other runs and systems. Within these systems the higher safety class are receiving first attention.

The following are our estimates concerning number of base plates and types and number of bolts in the system runs identified to be in resonance which you requested. These are listed by system:

System No. Baseplates Type Baseplates No. Bolts /BP RCIC 6 wall 4 RBSW 7 wall 4 HPCI 13 wall, floor ceiling 2,2s 2,6s*

5,4s 2,5s 1,10 1,8 RHR 5 wall,1 floor 2,6s 1,4 1,8 & 1,10 SBGTS 4 wall 4,4s 52,2s means two, two bolt baseplatu etc.

Thic infor=ation for the two remaining systems has not yet been tabula ted. We estimate the numbers will be in about the same ratio as those presented above.

We are confident thnt this letter provides the information you require.

If, however, you need additional information, please contact > , at your convenience.

Very truly yours, VERMONT YANKEE NUCLEAR FCWER CORPORATIOh r .

(, o J D. E. $oody 7{

Manager of Operations dm, o 1054 011 i)Wgn r om oi)n@ g ,

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