ML19309A928

Responds to Questions Raised in Telcons W/Nrc Re Util 751219 & s Requesting Increased Fuel Storage at Facility

ML19309A928
Person / Time
Site:	Rancho Seco
Issue date:	03/30/1976
From:	Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	Reid R Office of Nuclear Reactor Regulation
References
NUDOCS 8004010682
Download: ML19309A928 (4)

Text

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NRC DISTRIBUTION POR PART 50 DOCKET MATERIAL TO:

FROM: SMUD DATE OF DOCUMENT MR R V REID SACRAMENTO, CALIF e 3-00-76 DATE RECEIVED J J MATTIMOE 4-1-76 RLETrEn ONOTORIZE D PROP INPUT PORM NUMBER OF COPIES RECEIVED hCRIGINAL UNCLASSIFIE D 1 SIGNED LICOPY DESCRIPTION ENCLOSU RE LTR FURN RESPONSES TO QUESTIONS FOR INCREASE FUEL STORAGE AT THE RANCHO SECO NUCLEAR GENERATING STATION, LHIT NO 1.....

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SACRAMENTO MUNICIPAL UTILITY DISTRICT O 6201 S Street, Box 15830, Sacramento, California 95813; (916) 452-3211 March 30, 1976

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Director of Nuclear Reactor Regulation M

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Mr. Robert W. Reid, Chief i

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Rancho Seco Nuclear Generating Station, Unit No. 1 V

Dear Mr. Reid:

This letter is in response to questions which have been raised during telephone conversations between the NRC staff and District personnel regarding the District's submittals of December 19, 1975 and March 5,1976 for increased fuel storage at the Rancho Seco Nuclear Generating Station, Unit No. 1.

1.

Question:

s A system analysis should be performed to evaluate stresses g

in interconnecting members between rack models.

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The seismic analysis performed by EDS Nuclear was modeled b

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by one rack with appropriate boundary conditions to account u.f Q

for the effects of adjacent racks, the pool wall and pool p

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/h floor.

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Seismic and stress analyses were performed for all load carrying members including the plates which interconnect

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adjacent rack modules. These analyses show that all member

~g and weld stresses are within allowable values.

The loads calculated in the rack interties by the computerized nadal analysis method are predominately vertical, placing bending loads on the interties. The interties were stress analyzed at the computed load level. The analysis treats the intertie as a beam fixed at both ends at the centers of gravity of the weld patterns.

In this particular case tlie OBE loading was found to be the most limiting loading condition, producing a stress level equal to 67% of the allowable stress.

2.

Question:

Represent the springs by actual stiffness and establish conservatism of seismic loads used for design.

YA AN ELECTRIC SYSTEM S E RVIN G MORE THAN 600,000 IN THE HEART OF C All F 0 R N B A

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~' o Mr. Robert W. Reid March 30, 1976 Answer:

The springs were represented by their actual stiffnesses.

The stiffness of each structural element was obtained from the cross section properties of the element.

Beam equations, including shear deflection terms, were used to calculate element stiffness.

The side adjusting screws were represented by their axial stiffness only, and therefore, they do not con-strain motion in the plane perpendicular to their axes. Since the analyses which were performed conform to the NRC request, reestablishment of the conservatism of seismic loads required for design is not necessary.

3. ' Question:

Discuss the effects of small gaps on the seismic response of the racks.

~ Answer:

Small gaps (typically 3/16") between rack lateral adjustment screw assemblies and pool walls, which are required for thennal growth clearances, may result in short duration impulsive loads being imposed on the fuel rack structure during a seismic event.

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During a seismic occurrence, the pool structure will move essentially at ground acceleration and velocity and the racks will slide across the pool floor.

(Friction forces associated with this slidi.ng will dissipate a portion of the seismic energy.)

This sliding comes to a halt rapidly when lateral adjustment assemblies contact the pool wall and the rack experiences a short duration impulsive load. The maximum distance that the rack group can move is small (twice the initial lateral clearance) and maximum structural and fuel guide tube deformations will be small compared to seismic deformations associated with the support arrancment assumed for design evaluation.

Although design calculations have assumed that the racks are restrained against sliding, actual support arrangements allow a limited movement. The boundary support assumptions are as follows:

A.

No lateral support with racks permitted to slide without contact with pool walls.

B.

Complete lateral support without sliding of the racks.

In the first assumption, the only seismic induced forces are friction forces associated with the relative sliding between racks and pool.

Design calculations include these frictional l

forces.

In the second assumption, that used in the design l

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Mr. Robert W. Reid March 30, 1976 evaluation, full lateral vibratory motion is transmitted to the rack assemblies. The analytical assumption used in the analysis, which include both frictional forces and full transmittal of lateral seismic excitation, is bounding and therefore. conservative.

Impulsive loading due to rack bumping are not in phase with maximum forced vibration and the deforma-tions are small compared to the design seismic deformations.

Therefore, these loads are not limiting.

Jf we can provide any further infonnation regarding our request for additional fuel storage, please advise.

Sincerely yours,

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J. J. Mattimoe Assistant General Manager and Chief Engineer e

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