ML20247H579

Requests Listed Info in Order to Make Final Determination That Potential Safety Issues Exists Re Ability of safety- Related above-ground Vertical Liquid Storage Tanks to Maintain Structural Integrity.Nrc Recommended Method Encl

ML20247H579
Person / Time
Site:	Callaway
Issue date:	05/23/1989
From:	Hannon J Office of Nuclear Reactor Regulation
To:	Schnell D UNION ELECTRIC CO.
References
TASK-A-40, TASK-A-46, TASK-OR NUDOCS 8905310267
Download: ML20247H579 (5)

Text

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. May 23,'1989 Docket No. :50-483 Distribution

. Mr. Donald F. Schnell C63 L NRC & Local PDRs TAlexion OGC

. Senior Vice President ' Nuclear .PDIII-3 r/f EJordan Union Electric Company GHolahan BGrimes Post Office Box ~149 MVirgilio. ACRS(10)

. St. Louis, Missouri 63166- PKreutzer- PDIII-3 Gray

SUBJECT:

SEISMIC DESIGN CONSIDERATION FOR CERTAIN SAFETY-RELATED

-VERTICAL STEEL TANKS (REQUEST FOR INFORMATION)

As a result of activities related to the technical resolution of Unresolved Safety Issue (USI) A-40, " Seismic Design Criteria," a preliminary determination

has been made that a potential safety issue exists with regard to the ability of certain safety-related above-ground vertical liquid storage tanks at your facility to maintain their structural and functional integrity during postulated earthquake events. To make a final determination as.to the safety significance of this. issue, the NRC staff requests the information identified below. The following.is a brief. description of the technical basis for the staff concern.

There'has been a significant evolution in the seismic. design practice for-tanks. :In the past, the method used for tank analysis (Ref.1 of the enclosure) did not account. for tank flexibility. As a result, some large tanks were designed.for significantly lower loads compared to_ current practice (Ref. 2.of

. the enclosure). .The Lawrence Livermore National- Laboratory (LLNL), an NRC contractor, has estimated this difference to a factor of 2 to 2.5. That is, the past design practice led to tanks being designed for loads that could be a factor of 2 t0.2.5 less than current practice. The source of this factor is the amplification of spectra at typical tank frequencies. Coupling the above-with the observation of tank failures at non-nuclear facilities during past earthquakes (uost recently, at Coa 11nga, California in May 1983, in Chile in 1984 and in Mexico in 1985), the staff considers this a potentially significant safety issue.

In order to make a. final determination on this issue, you are requested to provide within 120 days of receipt of this letter, the'information identified below.

1. If tant wall flexibility was considered in the seismic design of the Refueling Water Storage Tank ano the safety-related Condensate Storage Tank / Auxiliary Feedwater Storage Tank at your facility as outlined in 8905310267 890523 PFol DR ADOCK050g3

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the enclosure to this letter, provide a ssmmary of the analyses sufficient to show how steps a. through 1. of the enclosure were considered and the results of these analyses.

2. If tank wall flexibility was not considered as outlined in the enclosure to this letter for the alt:ye tanks, in view of the new information described above, provide the basis for continued confidence in the.

ability of the tanks to withstand the seismic event specified as a design basis for your facility. One option may be to use the procedures developed by the Seismic Qualification Utility Group (SQUG) under the resolution of USI A-46, " Seismic Qualification of Equipment in Operating Plants," to check the adequacy of the above-mentioned tanks for seismic events.

The reporting and/or recordkeeping requirements contained in this letter affect fewer than 10 respondents; therefore, OMB clearance is not required under Pub. L.96-511.

Sincerely,

/s/

John N. Hannon, Director Project Directorate III-3 Division of Reactor Projects - III, IV, V and Special Projects Office of Nuclear Reactor Regulation

Enclosure:

NRC Staff-Recomended Method for Seismic Analysis of Above-Ground Tanks cc w/ enclosure:

See next page

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[ Vertical Steel Tanks]

Office: LA/PDIll-3 PM/ -

l (LfSGBh*4[ PD/tDrII-3 Surname: PKr6 utter TAlexio e #

TGBagcni JHannon Date: .

5 '/ H /89 C/M/89 4/p/89 (/ 7)89

Mr. D. F.'Schnell Callaway Plant Union Electric Company Unit'No. 1 m cc:

Dr. J. 0. Cermack Mr. Bart D. Withers CFA Inc. President and Chief 4 Professional Dr., Suite 110 Executive Officer Gaithersburg, MD 20879 Wolf Creek Nuclear Operating Corporation Gerald Charnoff, Esq. P. O. Box 411 Thomas A. Baxter, Esq. Burlington, Kansas 66839 Shaw, Pittman, Potts & Trowbridge 2300 N Street, N. W. 'Mr. Dan I. Bolef, President Washington, D. C. 20037 Kay Drey, Representative Board'of. Directors Coalition

.Mr. T. P. Sharkey for the Environment

' Supervising Engineer, St. Louis Region i Site Licensing 6267 Delmar Boulevard Union Electric Company - University City, Missouri 63130 Post Office Box 620 Fulton, Missouri 65251 U. S. Nuclear Regulatory Connission Resident Inspectors Office RRf1 ,

Steedman, Missouri 65077 Mr. Alan C', Passwater, Mt, nager

. Licensing and Fuels Union Electric Compan;,'

Post Office Box 149 St. Louis, Missouri 63166 Manager'- Electric Department Missouri Public Service Commission 301 W.'High ~

Post Office Box 360

. Jefferson City, Missouri 65102 Regional Administrator U. S. NRC, Region III 799 Roosevelt Road Glen Ellyn, Illinois 60137 Mr. Ronald A. Kucera, Deputy Director Department of Natural Resources P. O. Box 176 Jefferson City, Missouri 65102 i

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Enclosure l

NRC Staff-Recommended Method for Seismic. Analysis of Above-Ground. Tanks Most above-ground fluid-containing vertical tanks do not warrant sophisticated, finite element, fluid-structure interaction analyses for seismic loading.

However, the commonl assumption (Ref.1) may y used alternative in be inadequate ofsome analyzing cases.such The tanks with rigidiswall major problem l that direct application of this method is consistent with the assumption that the combined fluid-tank system in the horizontal impulsive mode is sufficiently rigid to justify the assumption of a rigid tank. For the case of the flat-bottorned tanks mounted directly on their bases, or tanks with very stiff skirt supports, the assumption leads to the usage of a spectral acceleration equal to the zero-period base acceleration. Recent evaluation techniques (Ref. 3 and 4) have shown that for typical tank designs the frequency for this fundamental horizontal impulsive mode of the tank shell and contained fluid is generally between 2 and 20 Hz. Within this regirne, the spectral acceleration is typically far greater than zero-acceleration. Thus, the assumption of a rigid tank could lead to inadequate design loadings.

The acceptance criteria below are based upon the information contained in References 1-4 These references also contain acceptable calculational techniques for the implementation of these criteria.

a. A minimum acceptable analysis should incorporate at least two horizontal modes of combined fluid-tank vibration and at least one vertical mode of fluid vibration. The horizontal response analysis should include at least one impulsive mode in which the response of the tank shell and roof are coupled together with the portion of the fluid contents that moves in unistn with the shell. Furthermore, at least the fundamental

- sloshing (convective) mode of the fluid should be included in the horizontal analysis,

b. The frequency of fundamental horizontal impulse mode of the tank and the fluid system should be estimated. It is unacceptable to assume a rigid tank unless the assumption can be justified. The horizontal impulsive-mode spectral acceleration is then determined using this frequency of fundamental horizontal impulsive mode and tank-shell damping. The maximum horizontal spectral acceleration associated with the tank support at the tank-shell damping level may be used instead of determining frequency of fundamental horizontal impulsive mode,

c. Damping values used to determine the spectral acceleration in the impulsive mode should be based upon the values for tank shell material as specified in the current SRP Section 3.7.1.

d. In determining the spectral acceleration in the horizonts1 convective mode the fluid damping ratio should be 0.5% of critical damping unless a higher value can be substantiated by experimental results.

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e. The maximum overturning momentn M at the base of the tank should be obtained by the modal and spatial combination methods discussed in the SRP Section 3.7.2.II. The uplift tension resulting from M should be resisted either by tying the tank to the foundation with a$chor bolts, etc., or by mobilizing enough fluid weight on a thickened base skirt plate. The latter method of resisting M must g be shown to be conservative

f. The~ seismically-induced hydrodynamic pressures on the tank shell at any level can be determined by the modal and spatial combination methods in the SRP Section 3.7.2. The hydrodynamic pressure at any level should be added to the hydrostatic pressure at the level to determine the hoop tension in the tank shell.

g. Either the tank top head shoulo be located at an elevation higher than the slosh height above the top of the fluid or else should be designed for pressures resulting from fluid sloshing against this head. The method in current design codes for calculating slosh height is not necessarily conservative. Formulas given in Ref. 1 can be used to calculate slosh height,

h. The tank foundation (see also SRP Section 3.8.5) should be designed to accommodate the seismic forces imposed by the base of the tank. These forces include the hydrodynamic fluid pressures imposed on the base of the tank as well as the tank shell longitudinal compressive and tensile forces resulting from Mg .

i. In addition to the above, consideration should be given to prevention of buckling of tank walls and roof, failure of connecting piping, and e

sliding of the tank.

References:

1. " Nuclear Reactors and Earthquakes," TID-7024, prepared by Lockheed Aircraft Corporation anc Holmes & Narver, Inc.,

for the Division of Reactor Development, U.S. Atomic Energy Commission, Washington, D.C., August 1963.

2. D. W. Coats, " Recommended Revisions to Nuclear Regulatory Commission Seismic Design Criteria," prepared by Lawrence Livermore National Laboratory for the U.S. Nuclear Regulatory Commission, NUREG/CR-1161, May 1980.

3. A. S. Veletsos and J. Y. Yang, " Dynamics of Fixed-Base Liquid-Storage Tanks," U.S.-Japan Seminar for Earthquake Engineering Research with Emphasis on Lifeline Systems, Tokyo, Japan, November,1976.

4. A. S. Veletos, " Seismic Effects in Flexible Liquid Storage i Tanks," Proceedings of Fifth World Conference on Earthquake Engineering, Rome,1974.

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