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TENNESSEE VALLEY AUTHORITY*

CH ATTANOOGA, TENNESSEE 37401

SN 157B Lookout Place

JUN 081989 .

U.S. Nuclear Regulatory Commission|ATTN: Document Control Desk

Washington, D.C. 20555

Gentlemen:

In the Matter of ) Docket Nos. 50-327Tennessee Valley Authority ) 50-328

.SEQUOYAH NUCLEAR PLANT (SQN) UNITS 1 AND 2 - NRC INSPECTION REPORT NOS.'50-327/88-12 AND 50-328/88-12 - RESPONSE TO UNRESOLVED ITEM (URI) 88-12-10 I

j

During the NRC's inspection in Knoxville, Tennessee, the week of IFebruary 15, 1988,~several miscellaneous issues were reviewed as follow-up jfrom previous NRC inspection items. The subject item, entitled " Seismic -!

'Analysis of the Steel Containment Vessel," resulted from deficiency D4.2-3from the SQN Integrated Design Inspection (IDI) 50-327, 328/87-48.

TVA's March 2, 1988, letter to NRC provided additional information on the )steel containment vessel vertical response spectra and time step effect that |was requested during the February 1988 inspection. The additional informationwas based on a TVA evaluation of ten piping systems. This additionalinformation showed that the design basis accident load dominates the total sumof. loads and that the time step effect issue does not change the total pipe.support loads by any significant amount. Based on NRC's review of thatletter, NRC issued URI 88-12-10, which was transmitted by S. D. Richardson'sJune 24, 1988, letter to S. A. White.

The enclosure provides TVA's response to URI 88-12-10. The informationprovided in this response is supplemental to TVA's response to IDI item D4.2-3that was transmitted by TVA's March 2, 1988, letter to NRC. TVA is availableto further discuss this item at your convenience.

If you have any questions, please telephone B. S. Schofleid at (615) 843-6172.

Very truly yours,

TENNESSEE VALLEY AUTHORITY

eq kManager, Nuclear Licensing

and Regulatory Affairs

L Enclosurecc: See page 2

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8906150028 890608PDR ADOCK 05000327 I (Q PDC

An Equal Opportunity Employer_ _ _ - _ _ -

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y; U.S. Nuclear Regulatory Commission g g ggL

-cc (Enclosure):Ms..S.-C.' Black, Assistant Director

for ProjectsTVA Projects DivisionU.S. Nuclear Regulatory CommissionOne White Flint, North11555 Rockville PikeRockville, Maryland 20852

1:| Mr. B. A. Wilson, Assistant Director

for Inspection Programs'-

1 TVA Projects Division-

| --U.S. Nuclear Regulatory Commission

- Region II -

b3a a, r a

Sequoyah Resident Inspector' Sequoyah Nuclear Plant

2600 Igou Ferry RoadSoddy Daisy, Tennessee 37379

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ENCLOSURE 1-

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URI 88-12-10'

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TITLE: SEISMIC ANALYSIS OF THE STEEL CONTAINMENT VESSEL

ITEM DESCRIPTION

' TVA's review of steel containment vessel vertical response spectra for the"

: time step. issue evaluated'the effects on a sample of piping systems attachedto the affected structures including the reactor coolant loop. These sampleswere considered adequate for restart. The staff considers that TVA shouldcomplete the evaluation of the remaining piping systems as a post-restartitem."

RESPONSE

TVA's response to Integrated Design Inspection (IDI) Item D4.2-3 on the steelcontainment vessel (SCV) vertical respon-se spectra was submitted to NRC onDecember 29, 1987. The response stated that, when the spectra were calculatedusing a smaller time step (0.005 second versus 0.01 second), the verticalspectra had shown increases over a limited frequency range at the verticalfundamental frequency of the SCV. The response also stated that TVA wouldaddress the significance of this issue on the total pipe support load.

In our March 2, 1988, supplemental response to NRC TVA documented the resultsof the delta-T study on ten piping analyses that were presented to NRC duringthe February 15-19, 1988, IDI closeout reviews. This evaluation is documentedin Calculation N2-TSTEP-MISC, revision 0 (B25 880226 816). The ten pipinganalyses reviewed included seven analyses previously evaluated for SCVvertical spectra changes in Calculation N2-PIR-8652-MISC, revision 1(B25 871201 801), and three additional analyses chosen based on worst-caseattributes in regard to the delta-T time step.

At the time that the concern was initially raised by NRC, it was agreedbetween TVA and NRC that the ten analyses evaluated for the SCV verticalspectra changes would be reevaluated for the delta-T time step issue.However, three of these analyses did not have spectra changes, and NRC wantedto review analyses that were included in the interior concrete structure (ICS)and auxiliary building structure (ABS) in addition to the SCV attached piping.

Worst-case attributes (low allowable stress margins, modal frequencies in theregion of spectra value increase, high contribution of seismic load andsupport qua11 fled to interim Criterion CEB-CI-21.89) were utilized in choosingthree additional analyses that were-located in the ICS or ABS. One of theanalyses evaluated in N2-PIR-8652-MISC, revision 1, was also noted to haveseveral of the above-listed, worst-case attributes. Table D4.2-3-1 of ourMarch 2, 1988, supplemental response listed these four analyses and theworst-case attributes associated with each.

The_ remaining six analyses evaluated were considered to have worst-caseattributes for the SCV vertical spectra change, which included low allowablestress margins, high elevation SCV rigid attachments, etc., as listed inEvaluation Package N2-PIR-8652-MISC, revision 1. For the purposes of thedelta-T time step evaluation, these six analyses were consideredrepresentative of the family of SCV attached piping analyses.

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The results of the ten piping analyses evaluation, as previously submitted byour March 2, 1988, supplemental response, showed that the delta-T time stepchange resulted in a general decrease in pipe stress for six of the analyses,

L with the remaining four exhibiting a negligible increase in stress. All tenanalyses showed a negligible increase in penetration loads, support loads, andvalve accelerations. There was no change in nozzle loads for six of theanalyses and a decrease in nozzle load for one analysis. The nozzle loads forthe remaining three analyses exhibited only a slight increase and met criteriarequirements. A copy of the summary of the evaluation results, as previouslysubmitted in our March 2, 1988, response, is attached.

This study has clearly demonstrated that the increase in pipe support loadsbecause of the delta-T time step change is insignificant. TVA has shown thatthe original design basis is adequate and that no safety issue exists.Therefore, it is TVA's position that no additional evaluation for delta-Teffects on the remaining piping systems is necessary.

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