DCL-87-115, Applicant Exhibit A-8,consisting of Responding to Questions Re Reracking Analyses Discussed in 870506 Reracking Meeting W/Nrc

Applicant Exhibit A-8,consisting of Responding to Questions Re Reracking Analyses Discussed in 870506 Reracking Meeting W/Nrc

ML20237J821
Person / Time
Site:	Diablo Canyon
Issue date:	06/17/1987
From:	Shiffer J PACIFIC GAS & ELECTRIC CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
DCL-87-115, OLA-A-008, OLA-A-8, NUDOCS 8709040084
Download: ML20237J821 (15)

Text

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(s//7 PGandE Exhibit No. 8 00LKEIII'

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.... U,'I* Hay 18, 1987 NWCLgaa . owes came.af tN PGandE Letter No.: DCL-87-115 U.S. Nuclear Regulatory Commission ATTW: Document Control Desk Washington D.C. 20555 Re: Docket No. 50-275, OL-DPR-80

, Docket No. 50-323, OL-DPR-82 Diablo Canyon Units I and 2 Additional Information on Reracking Analyses Gentlemen:

In the May 6, 1987, reracking meeting between the NRC Staff and PGandE. th'ree questions were identified which require a response from PGandE. PGandE responses to these questions are contained in the enclosure. ,

Kindly acknowledge receipt of this material on the enclosed copy of this letter and return it in the enclosed addressed envelope.

Sincerely, Enclosure cc: L. J. Chandler l

J. 8. Martin i M. M. Mendonca P. P. Narbut B. Norton C. M. Transnell CPUC Diablo Distribution Reracking Service List i 1438S/0050K/DH0/1998 l

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J PGandE Letter No.: DCL-87-115 ENCLOSURE RESPONSES TO NRC STAFF QUESTIONS RAISED AT THE MAY 6, 1987 RERACKING MEETING l

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O 1438S/0050K 1

4 NRC Ouestion No. I

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Provide documentation that the spent fuel pool liner is not safety-related.

PGandE ResDonse No. 1

FSAR Update Table 3.2-3 provides the seismic classification of structures, components, and systems. Sheet 3 of 58 (attached) indicates that the pool l liner is classified as Design Class II. A description of Design Class II applicability and requirements is provided in Table 3.2-1 (attached).

!!RC Ouestion No. 2 Discuss the rack baseplate spring constant which would appropriately represent the stiffness of the baseplate interaction with the pool wall.

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PGandE Resoonse No. 2

( STIFFNESS CALCULATION FOR BASEPLATE In order to evaluate the upper-bound stiffness of the fuel rack baseplate spring, the local spring constant of the baseplate was evaluated using classical linear elasticity theory. The basis of the spring constant calculation is the classical solution for a point load on the edge of a semi-infinits half-space. The configuration is shown in Figure 1.

The solution for the displacement, U(r,0) at 6 - 0, is shown to be given )

as (P has the units of lb/ inch of plate thickness):

U-- Inr+C vE where E is the modulus of elasticity and C is the constant of integration.

O 1438S/0050K l

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P Edge of Plate Load Point u .

s s O I e Nr N s, .

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,A, To compute the spring constant, we assume that the baseplate is held at d -

108 inch'es,. Then, relative to that point, the displacement in the direction of P, along the line 0 = 0 is:

d U

r" I"kj where r is the location under the load where the relative displacement is to be calculated. Since the total applied load on a plate of thickness t is Pt.

the s'tiffness of the baseplate is:

l Pt , g ,

wet U

r 2in(dj

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Taking note of the fact that immediately under the concentrated load, there will be plasticity effects that have not been included, a limiting value for r was selected equal to the thickness of the plate. Also, since the impact spring under evaluation is at the edge of the plate, the above solution is appropriately adjusted for the " quarter-plate" condition. This results in a reduction of the stiffness by 50 percent. Therefore, the stiffness, K, for a single baseplate is:

i K -

wet 4In(dj 6

For E = 27.9 x 10 psi, t = 0.625 in., and d = 108 in., we obtain:  !

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. i K = 2.658 x 106 lb/in.

For rack-to-rack impacts, two plates are involved. Therefore, the spring i

constant in the model can be set to be 50 percent of th above value for rack-to-rack 17 pact, resulting in K (rack / rack) = 1.33 x 106 lb/in.

1438S/0050K ____-____ ____-_

( For rack-to-Wall impacts, the preceding value would be reduced further, since the spring constant for the concrete wall is less than that for the baseplate. ' Assuming concrete properties of E - 3 x 100 psi and u - 0.15, the solution for a half-space under a concentrated load gives the maximum displacement as:

2 g""* , 2(1-u ) P waE l

where P is the load applied over a circular area of radius a. To simulate baseplate impact on the wall, let a - t/2, where t is the baseplate thickness. Then:

K c* 2

" 1 P$' '

4(1-u )

The effective spring constant for baseplate-to-wall impact is:

I 1 1 1 K K K e plate e or 1 / 1 1 3 -6 -6

+ )

_.- =1 1x 10 = x 10 K, (2.658 1.507 ) 0.962 0

Therefore, for baseplate-to-wall impacts, K, = 0.962 x 10 psi i

The inclusion of local flexibility of the gridwork above the baseplate would reduce the calculated spring constant even further. Therefore, the value calculated above should be considered to be an upper-bound.

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1438S/0050K It can be seen that the K, calculated above is approximately equal to the value'used*in the design basis analysis. It should be noted that the analyses of the racks'have shown that the ratio of the girdle bar impact force to the baseplate impaci: force is insensitive to the ratio of the girdle bar spring constant to the baseplate spring constant. .Thus, significant changes in the design basis predictions for impact loads are not expected if the baseplate impact spring constant used in the design basis model is revised to the values calculated above.

NRC Ouestion No. 3 l

Provide weld capacities based on a suggested alternate interpretation by an NRC consultant at the May 6, 1987 meeting, and compare the result with PGandE's calculations presented at that meeting.

PGandE Response No. 3 -

The capacity of the weldments joining the support feet to the rack baseplate was calculated using allowables established by Section III, Subsection NF of the ASME Code. The allowables PGandE used are as follows:

• Level A Service Limit

Fillet Held

The direct tension stress limit is 18 ksi for the 304L material baseplate l

l Groove Held: The direct tension stress limit is 21 kst for the 304L material baseplate

• Level 0 Service Limit The allowable stresses are increased by a factor of 2.0 for Level D service (Hosgri) conditions. (Appendix F, Paragraph F-1334, j

Summer 83 Addendum) l 1438S/0050K _

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The maximum Naction !oads on the support baseplate weldment are:

i Lateral shear: 226 kips Axial thrust: 290 kips BeNing moment: 1294 kip-inches Although these loads are applied for an extremely short duration, ne' credit is taken for their dynamic nature.

l Based on the above, a support foot conservative weld calculation for, cast ACORN 10 was provided to the NRC Staff in the meeting of May 6,1987. This calculation indicated that for support foot No. 3, the maximum compression and bending stress results in a stress ratio of 1.5, and the maximus shear stress results in a stress ratio of 1.26; the allowable stress ratio is 2.0 for Level 0 service conditions. This corresponds to a minimum factor of safety of 1.33. -

Ouring the meetiny of May 6,1987, an alternate interpretation of the ASME Code was suggested (by an NRC consultant) to PGandE for the Level D Service Limit, which wu as follows: m

-E The allowable stresses for groove welds can be increased by a factor of 2.0 over the Level A Service Limit; this corresponds to the allowable i value of 42 ksi.

The allowable stresses for fillet welds can be increased such that the value does not exceed 0.42uS , where S is the ultimate tensile u

stress of the base metal; this corresponds to the allowable value of 28.6 ksi.

Thealiowableshearstressforallweldsisalsotakenas28.6ksi.

O 1438S/0050K 3- y ._

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Table 1 gives the weld data on the support foot. Referring to Table 1 and the foregoing data on the allowable shear stress, the factor of safety against i

weld shear failure is:' ,

4-(34.24)(28.6) r 3

= _ , _ = 4.33 226 The factor of safety against direct stress is computed by considering the combined effect of the axial thrust and bending moment. Figure 2 shows the interaction curve. This curve is generated by assuming a rectangular stress profile for each weld line (perfectly plastic response; no credit for strain-rate effect). Referring to Figure 2, the factor of safety is defined as:

rd =

= = 1.92 O

The above values result in a higher factor of safety than the values reported in the May 6, 1987, meeting, thereby confirming the conservatism in PGandE's methodology.

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Table 1

'. Held Data Effective Shear Area Weld Line Throat (.in.) radius (in.) (in.2)

1. Interior groeve 0.442 3.33 9.25

2. Exterior groove 0.442 4.29 11.91 3.

Exterior fillet 0.442 4.71 13.08 TOTAL 34.24 in.2 O .

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