ML20247P853

Responds to Request for Addl Info Re Seismic Design Considerations for safety-related Vertical Steel Tanks Transmitted by from Fj Hebdon to Bd Withers

ML20247P853
Person / Time
Site:	Wolf Creek
Issue date:	09/22/1989
From:	Rhodes F WOLF CREEK NUCLEAR OPERATING CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ET-89-0076, ET-89-76, NUDOCS 8909280024
Download: ML20247P853 (5)

Text

% W

-~

~

y

~

4 W@NUCLEAROPERATING CO LF CREEK Forrest T. Rhodes vie, Premderv.

Engineering & Dichn6 cal Servlose September 22. 1989 ET 89-0076 U. S. Nuclear ReEulatory Co:maission-ATTN: Document Control Desk

~ Mail 3tation P1-137-Washington, D.

C.,

20S55

Reference:

Letter dated May 25, 1989 from F. J. Hebdon, NRC to B. D. Withers, WCNOC

Subject:

Docket No. 50-482:

Response to Request for Additional Information Concerning Seismic Design Considerations for Certain Safety-Related Vertical Steel Tanks Gentlemen:

The purpose of this letter is to respond to the~ request for additional information concerning seismic design considerations for certain safety-related vertical steel tanks transmitted by the Reference.

The attachment to this letter provides the results.of a reanalysis of the Refueling Water Storage Tank (RWST) structure including its foundation, performed in accordance with the guidance of Draft Revision 2 of Standard Review Plan Section 3.7.3.

This reanalysis meets the intent of the acceptance criteria (items'n through 1) of the Enclosure to'the Reference.

Results of this reanalysis confirm that the RWST structure continues to meet the Wolf Creek Generating Station (WCGS) Updated Safety Analysis Report requirements for both the OEE and SSE seismic design ground response spectrum inputs.

The Reference requested that Volf Creek Nuclear Operating Corporation (WCNOC) ensure that tank wall flexibility be considered in the seismic design of the RWST and the safety-related Condensate Storage Tank / Auxiliary Feedwater Storage Tank at WCGS.

However, since the WCGS design does not utilize either a safety-related Condensate Storage' Tank or safety..related Auxiliary Feedwater Storage Tank only the RWST is addressed in response to the Reference.

As described in Updated Safety Analysis Report Section 10.4.9, the Essential Service Water System provides WCGS's safety-related source for the Auxiliary Feedwater System.

p in w} M 9..w;y.

0f eggg800:4 3

g t i P.O. Box 411/ Burlington, KS 66639 / Phone: (316) 364-8831 An Equel oppoqunity Ernployer MOHcVET

.. 7 I

i ET 89-0076 i

Page 2 of 2 September 1989 j

i 1

If you have any question concerning this matter, please contact me or Mr. O. L. Maynard of my staff, i

Very truly yours, i

h e

I h

/\\ s A

Ws/

l Y' Forrest 7. Rhodes Vice President Engineering & Technical Servicee FTR/aem j

i Attachment l

i i

cc:

B. L. Bartlett (NRC), w/a D. V. Pickett (NRC), w/a 1

F. J. Hebdon (NRC), v/a E. J. Holler (NRC), w/a i

1 i

I 1

i l

l 1

1 1

Attachm:nt to ET 89-0076

.Pcg3 1 cf 3 INTRODUCTION The original vendor analysis of the subject structure was-based on the "Housner Method *,

discussed in Reference 2,

and a rigid tank wall

.essumption.

Recent analytical techniques (Reference 3),

however, have indicated that the previous design methods may not be appropriate and/or conservative for the majority of tank structures. Specifically, the'recent technical developments have shown that for typical tank designs the fundamental frequency associated with the combined fluid-tank shell system, in the horizontal. impulsive mode, is not sufficiently high (>33Hz) to justify the assumption of a rigid tank wall.

The NRC subsequently issued Draft Revisien 2 of Standard Review Plan (SRP),

Section 3.7.3 (Reference 4), identifying this concern cnd adopting these new analytical techniques.

In addition, Reference 4 also identified the need to l

consider soil-structure interaction (SSI) effects when evaluating such structures.

In order to address these concerns, a complete reanalysis of the Refueling Water Storage Tank (RWST) structure including foundations was completed incorporating these newly adopted analytical techniques.

Additionally, in accordance with the acceptance criteria of Reference 4,

Subsection II.14, the effects of this analysis on the connecting piping were also evaluated.

This report provides a summary of the design approaches and corresponding results.

REANALYSIS METHODOLOGY The RWST structure was evaluated using a lumped mass stick model depicting the seismic system.

Response Spectrum Analyses (ESA) were performed for both the design OBE and SSE earthquakes, using the BSAP (CE800) and BSAP Dynam (CE207) computer programs.

The analyses were conducted for all three orthogonal directions using ground acceleration of 0.20g SSE and 0.12g OBE.

Fluid Parameters The design fluid parameters were dr.veloped in accordance with the procedures outlined in Reference S.

Specifically, the fluid was modeled considering the appropriate breakdown between the rigid (impulsive) and oce111ating (sloshing / convective) portions associated with this mass.

Soil-Structure Interaction Effects In order to include the effects of soil-structure interaction, the tank stick model was coupled with the foundation medium (s) using a lumped parameter, elastic half-space representation.

The soil parameters (Springs & Dampers) were computed in accordance with the procedures outlined in Reference 1.

In order to account for the sensitivity associated with these parameters pertaining to the resulting responses, the soil shear modulus value(s) was varied by i 50 percent in the analysis.

As such, this resulted in three cases (i.e. lower bound, average & upper bound) being investigated.

i

[A:

- Att chment to ET 89-0076

'P;g2 2 of 3

-o 1;p

,s

-The lumped parameter, elastic half-space representation. was selected, in lieu of a finite element representation..baseo on the p

=results.of previous SNUPPS studies and/or the shallow embedment L+

(i. e.-

only'.'4.5 feet base-slab which is less than 10 percent) of L

.this: structure as compared to its overall height of'53 feet.-

Nozzle Loads The nozzle loads used in tank / foundation reanalysis were taken directly from Reference 6.

Although'it was anticipated that these design loads would change due to the assumption.of a flexible tank, which would result in larger nozzle displacements,- this-approach.

was deemed' acceptable considering the insignificanticontribution of:

the nozzle to-the overall moments and forces. on~ the tank / foundation.

RESULTS Seismic Responses of Tank / Foundation System General Per. Reference 3, a minimum of two horizontal modes (one impulsive and one convective) and one vertical mode of response must be considered. The subject reanalysis, however, was performed considering all modes below 50 Hz.

Horizontal Impulsive Modefs)

The dominant horizontal impulsive mode occurred between frequencies of 5.92 and 6.16 Hz and represented approximately 70 percent of the total system horizontal mass.

The horizuntal convective / sloshing mode occurred at 'a frequency of 0.22 Ez and represented approximately 15 percent of the total system horizontal mass.

Note that only 1 convective mode is applicable.

Vertical Mode In the vertical direction, the dominant mode occurred between 12.23 and 13.07 Hz and represented approximately 93 percent of the total system vertical mass.

Design Forces and Moments For Tank / Foundation Reanalysis Revised seismic forces and moments for tank / foundation were computed for both the design OBE and SSE earthquakes.

The umrimum values of these revised seismic loads were then combined with the appropriate nozzle forces and moments from Reference 6 and utilized to reanalyze the various structural components per the applicable requirements of References 7-9.

Attcchm;nt to ET 89-0076

• '~]

,. Pcg3 3 of 3 Connected Pipine Evaluation The effects of the new RWST analysis on the connected piping and associated supports were also evaluated and all items found to be structurally adequate.

CONCLUSIONS The results of the tank / foundation reanalysis confirm that the WCGS RWST structures meet the licensed Updated Safety Analysis Report requirements.

Specifically, the structures and their foundations are acceptable without modifications, based on References 3 and 4 design methodology, for both the licensed 0.12g OBE and 0.20g SSE seismic design ground response spectrum inputs.

Additionally the existing piping and support analyses, including tank nozzles, have also been reviewed and reanalysis performed as necessary and all components found adequate for the effects of the new analysis.

The new nozzle loads resulting from the revised piping analyses were visually compared with the old nozzle loads and the effects on the tank / foundation reanalysis were found to be insignificant.

REFERENCES 1)

Topical Report BC-TOP-4-A,

" Seismic Analyses of Structures and Equipment for Nuclear Power Plants", Revision 3, November 1974.

2)

TID-7024, ' Nuclear Reactors and Earthquakes *,

Prepared by Lockheed Aircraft Corporation and Holmes & Narver, Inc.

for the Division of Reactor Development, U.

S.

Atomic Energy Commission, Washington, D. C. 8/63.

3)

D. W. Coats,

' Recommended Revisions to Nuclear Regulatory Commission Seismic Design Criteria."

4)

Standard Review Plan (SRP) Section 3.7.3, Draft Revision 2.

5)

Specification No. 10466-M-109(Q), Revision 9 Design Specification for Contract for Furnishing, Erecting and Testing of Steel Field Erected Tanks for the Standardized Nuclear Unit Power Plant System (SNUPPS).

6)

Bechtel Vendor Document No. 10466-M-109-026, Submittal No. 01.

7)

SNUPPS Civil and Structural Design Criteria, 10466-C-0(Q), Revision 7.

8)

Wolf Creek Generating Station Updated Safety Analysis Report.

9)

ASME Boiler and Pressure Vessel Code, 1974 Edition-Up to end including Winter 1975 Addenda.

1

_ _ _ __ _ _ _ _. _ _ _ _ _. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _. _ _. _ _