ML20058E338

Forwards Response to NRC 931028 RAI Re Util Proposed Change 177 to License DPR-36 for Spent Fuel Pool Reracking.Summary of Synthetic Acceleration Generation Effort Calculation MYC-905 Encl

ML20058E338
Person / Time
Site:	Maine Yankee
Issue date:	11/23/1993
From:	Hebert J Maine Yankee
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20058E339	List: ML20058E338 ML20058E350
References
JRH-93-238, MN-93-106, NUDOCS 9312060267
Download: ML20058E338 (34)

Text

_

MaineYankee 61MbH3IGiWicay smcc dd EDISON DR!VE e AUGUSTA, t/ AINE 04330 + (207) 622-48C8 f

i i

P November 23, 1993 MN-93-106 JRH-93-238 UNITED STATES NUCLEAR REGULATORY COMMISSION Attention: Document Control Desk i

Washington, DC 20555 l

l

References:

(a) License No. DPR-36 (Docket No. 50-309)

'i (b)

Letter, MYAPCo to USNRC, " Proposed Technical Change No. 177:

Maine Yankee Spent Fuel Pool Reracking", MN-93-09, dated January 25, 1993.

(c) Letter, USNRC to MYAPCo, " Request for Additional Information--

l Maine Yankee Proposed Amendment to Rerack Spent Fuel Storage Pool", dated October 28, 1993.

Subject:

Response to USNRC Request for Additional Information: Proposed Change No.177 (Spent Fuel Pool Reracking).

l Gentlemen:

i Attached, please find the Maine Yankee response to the above referenced USNRC questions (Reference (c)), as related to the USNRC review of the proposed Maine l

Yankee spent fuel pool reracking (Reference (b)). This attachment contains the responses to the remaining questions received.to date'from the USNRC on this subject.

We trust that these responses are satisfactory. Please contact me should you l

have additional questions.

i I

Very truly yours, l

_ Ew ames R. Hebert, Manager Licensing & Engineering Support Department l

j Attachment I

c: Mr. Thomas T. Martin Mr. E. H. Trottier i

Mr. J. Yerokum

-l Mr. P. J. Dostie Mr. Thomas R. Dignan, Esq.

1 Mr. Paul Stern, Esq.

t L:\\93mn\\93106

~

l o n a, -.

\\

hpogg} %

9 i

i%

L

e i

i s

ATTACHMENT l

l 1.

NRC Ouestion 1: In constructing the acceleration and the displacement' time histories from the ground response spectra, demonstrate that the time history of the acceleration bound the design ground response spectra. Provide. the maximum ground response velocities in three orthogonal directions at SFP slab -

level (Page 3-3, Ref.I).

l Maine Yankee ResD0nse: The Maine Yankee 0.18g NUREG-0098 response spectra were created as part of the Maine Yankee " Seismic Margin Review" program in 1986. The i

synthetic time histories used to generate the amplified response spectra were created in accordance with the Maine Yankee specification MYPS-29 by CYGNA Energy Services. This effort was performed specifically to address the USNRC-Regulatory Guides 1.61, 1.92, 1.122 and Standard Review Plans 3.7.1 and 3.7.2.

l The CYGNA effort was independently reviewed by YNSD in calculation MYC-905 and l

was subsequently rereviewed as part of the " Margins" program. A summary ~ of the time history generation effort, excerpted from MYC-905, which demonstrates that j

the time histories bound the design ground response spectra, is provided as Attachment A to these questions and answers.

As discussed in our November 16, 1993, meeting, the free field response was l

input directly into the spent fuel pool floor slab without de-convolution.

j The peak ground response velocities at the spent fuel pool slab are 5.1 inches /second vertically, 9.60 inches /second in the N-S direction, and 9.48 inches /second in the E-W direction.

i L:\\93mn\\93106 1

l l

I l.

2.

NRC Ouestion 2: It is stated that local rack deformation under uplift or impact loads is considered permissible to the extent that subcriticality of the array is maintained and resultant damage to stored fuel is minimized.

Provide specific values for the local deformations allowed and discuss how these values are obtained and justify why such limits are adequate (Page 3-4).

Maine Yankee Response: Specific allowable levels of localized deformation were not developed for the high density fuel racks.

Ratiier, the deformation associated with the loading conditions that included uplift and impact on the rack modules was evaluated against the criteria of maintenance of subcriticality and minimized fuel damage.

The uplift and impact loads are defined as P, (Grapple Snag Loads) and Fo (Accidental Load Drop) in Section 3.1 of the Licensing Report.

General acceptance criteria for the load combinations defined in Table 3-1 (from SRP 3.8.4, Appendix DJ are ASME III Level B Service Limits for the combination including P,, and " functional capability" for the combination including Fa. The ASME III Service Limits, as discussed in Section 3.3, are defined as allowable levels of maximum normal (principal) stresses. The effects of highly localized stresses from impact loads are evaluated against the primary function of the spent fuel racks as stated in Section 3.2.

For the loading combination including uplift (P, is conservatively assumed to be 3000 lbs), the maximum stresses in the rack module are within Level B Service Limits, with no permanent localized deformation that affects the array of stored fuel. The magnitude of P, allowed for a dynamic impact factor on the 1,280 lb.

weight of a conventional fuel assembly, and also envelopes the weight of an assumed " double mass" consolidated bundle.

Maximum membrane stresses in the fuel storage cell are 4.4 ksi versus the Level B limit of 20.8 ksi.

Maximum weld shear is 5.3 ksi versus the Level B limit of 12.5 ksi.

Three separate cases of dropped objects impacting the rack modules were evaluated for the loading combination including impact (F,) : on an outside corner at the top of the module, on an interior edge at the top of the module, and on a fuel support surface at the bottom of a storage location. For the top impacts, maximum crushing (buckling) of the rack module was limited to the top 5.4" of the structure, with no rupture of cell-to-cell welds.

As the active fuel is 11" below the top surface of the rack and the pitch of adjacent storage cells is not disturbed, both the subtriticality and fuel damage criteria are met.

For the impact on the fuel support surface, failure of the base plate occurs due to penetration of the dropped object, but the failure does not propagate into adjacent cells.

As all damage is localized to one storage location, the subtriticality, cooling and fuel damage criteria are also met.

The cases of dropped objects leading to potential rack deformation are explicitly accounted for in both the thermal-hydraulic and criticality analyses (Reference, sections 5.3.6 and 6.2 of the Licensing Report).

l L:\\93mn\\93106 2

l

4 l

3.

NRC Ouestion 3: It is stated that the " nonlinear properties for impact springs and elemental damping values include local rack flexibility and fuel rod beam l

fl exi bil i ty... ". Provide a detailed discussion of the meaning of this sentence i

and also provide quantitative values together with corresponding analytical expressions for such nonlinear parameters and discuss how these values are obtained and why it is justifiable to use such values. (Page 3-5).

Maine Yankee Resoonse: The impact springs between the fuel bundle and rack cell was are represented by ANSYS$ STIF40 Combination elements as shown in Figure 3-l 1.

The portion of the element invoking i

the Fslide component was disabled - by setting K, to zero. The value of K was j

2 established using a detailed finite element model of the local impact region Fslide K 1 which included a single fuel bundle V

spacer grid bearing against the rack K2 Gap cell wall.

Unit loads were applied at the location of each fuel rod and the h

M i

resulting displacements were averaged i

C over all rods to obtain the stiffness

K.

The computed stiffness was 1.34x10 2lbs/in.

In addition, the fuel bundles have relatively stiff top and bottom plates. These were considered rigid and Fig. 3-1 STIF40 Element only the stiffness of the rack cell 5

l walls (5.2x10 lbs/in) was assigned to K I

2 at these locations. In the simplified models these stiffnesses were multiplied i

by the number of fuel bundles in the rack and, when appropriate, by the number of spacer grids " lumped" at a single elevation. The derivation of the damping l

term, C, is discussed in the response to Question 8.

i l

The stiffnesses were computed on a static basis. Maximum strain rates are on the order of 0.1 sec" and stresses are elastic.

Thus the effects of strain i

rate are negligible.

The fuel bundles are represented.by ANSYS$ STIF4 3-D Elastic Beam elements to P

reflect the beam stiffness of the bundles. A beam element extends from the base i

of the fuel bundle to the elevation of a first spacer grid (impact spring),

i another beam element spans the distance to the next spacer grid, etc., until the entire height of the fuel bundle is modeled.

The area, bending moments of inertia, etc., of the bundle are based on the integrated section properties of the fuel rod tubes and the guide rods. The tubes are considered " slip fit"'in-the spacer grids, thus the distance from the centerline of the bundle to each plane of tubes does not contribute to the bending inertia (i.e., there is no Ay 2

term). The values for a single bundle are:

Bending Ir rC, I = 0.234 in' Area, A = 10.9 in' L:\\93mn\\93106 3

(

Since the fuel rods do not attach to the top plate, only the properties of the guide rods are used for the top-most beam. Mass is distributed via the density l

of the beam 'lements and is also assigned locally, such as at the heavy top plate, using aJSYS* STIF21 General Mass elements.. The-density is selected to give the proper fuel bundle and consolidated bundle weights.

The bottom of the fuel bundles rest on the base plate of the rack.

This interface is modeled with an ANSYS8 STIF52 Interface element..This element contains a gap, a normal stiffness and a lateral stiffness.' The lateral force i

l is limited to a value equal to the' coefficient of_ friction times the normal force. Slipping at the interface occurs to assure that this lateral force is 5

not exceeded. The vertical stiffness (7.9x10 lbs/in) is based on the stiffness of the fuel bundle foot in series with the flexural stiffness of the 1/4" thick i

8 plate which forms the base of each cell. The lateral stiffness (6.9x10 lbs/in) is based on the stiffness of the four feet on the fuel bundle.

These stiffnesses are derived using a finite element model of the region from the bottom plate of the fuel bundle to the perimeter of the baseplate at the vertical walls of a single cell.

In the simplified 'models these values are-i multiplied by the number of fuel bundles lumped together. The coefficient of friction is taken as identical to that used at the rack foot - to - pool floor interface (i.e., 0.2 to 0.8). Results indicate very little sliding and no lift-off at the base of the fuel.

l t

For the qualification of these elements and of the assembled analysis model, see i

l the response to Question 13.

l I

l 4

1

\\

L:\\93mn\\93106 4

0

4.

NRC Ouestion 4: It is stated that the buckling load of the cell is obtained by a large deflection theory.

Discuss the theory and demonstrate that the formulation of the theory and corresponding numerical method are such that a small change in input does not lead to a large change in result (Ref. 2, Page 367). Provide a verification of ANSYS code with experiments, if any, regarding the large deflection / buckling theory for plate and shell elements.

Also, discuss how the boundary conditions of the compressive member are treated in view of the fact that there are no positive lateral supports. Thus, for a case of a lateral load as in safe shutdown earthquake (SSE) load, an out of plane deformation is a possibility when the cross section of the rack is considered as a thin honeycomb cross section deforming in a diamond shape rather than rigid rectangular cross section. What are the margin from critical buckling loads for the cells as well as the rack under the worst load conditions (Page 3-7)?

Maine Yankee ResDonse: The large deflection method of the ANSYS* computer program involves an iterative solution in which the stiffness matrix is updated at every iteration to account for changing coordinates. It is favored over the eigenvalue method which is limited to geometries with no initial bending stress.

The validity of the method is demonstrated by comparing results of several methods: a finite element eigenvalue solution, a handbook solution and test.

The geometry used for the test was a 12 inch long section of rack cell from a preliminary design that had a 0.0625 inch wall thickness. This is thinner than the wall used in the final design. The cell width was 8.375 inches.

The results of the four methods are compared in Table 4-1.

The agreement between all solutions is very good.

l l

Table 4-1 Comparison of Critical Buckling Loads (Pounds) l Method Quarter Model 12" Long Cell FEM Large Displacement 3330 13320 FEM Eigenvalue 3340 13360 Handbook 3275 13100 Test

>l3300 A quarter symmetry model was used (Fig. 4-1) with both finite element analyses.

The eigenvalue analysis gave a buckling limit of 3340.4 lbs for the quarter model. Several analyses were performed by the large deflection method using different values of axial loading. The resulting maximum deflections normal to i

the surface are plotted in Figure 4-2.

It is clear that the solution converges l

quickly (by the third iteration) and is stable.

As anticipated, the normal l

deflection grows quickly as the buckling limit is reached; however the axial i

1 displacement increases only by a small amount (from 0.0022 to 0.0025 in. for the same load range).

At a slightly higher load (3350 lbs.) a solution was not i

achieved but, rather, an error notice " Buckling load has been exceeded" was l

printed.

The analysis method is well posed since it meets the three requirements specified in Ref. 4-1.

The solution is stable and properly reflects physical behavior which, at the buckling limit, produces large changes in lateral deflection for small changes in load.

L:\\93mn\\93106 5

4

.w-,

i i

The handbook solution is for a plate (one face of a cell) simply supported on j

four sides and uniformly loaded in compression on two opposing edges (Ref. 4-2, l

Table 35, Case la).

l The test showed a barely perceptible deviation from a linear force-deflection relation beginning at approximately 13300 poands. A more distinct transition occurred at 14500 pounds. For this geometry the buckling limit does not signal structural collapse.

Rather, the load shifts to the stiffer corners of the cell, one of which eventually exhibited localized plastic buckling. The test, terminated at a load of 25,700 pounds due to testing machine limitations, clearly demonstrates significant margin beyond the design allowable of 6660 l

pounds (0.5 x 13320).

I The boundary conditions are a function of the configuration being analyzed. For I

the axial cell loading described above, the boundaries at each end were simply supported with one end fixed axially. Any connectivity to adjacent cells was ignored. Symmetry boundary conditions were applied along the " cuts" defining i

the edges of the quarter-symmetry model.

A more limiting buckling condition occurs with transverse compression, that is with the load applied across the width of a cell, as if the tube were compressed in a vise.

For this model simple supports were modelled along the loaded edges of the cell and the ends of the cell were assumed free.

l The distortion of the cross-section of the array of cells from a square grid to a diamond shape is not buckling but rather one form of elastic deformation. In these rack designs there is sufficient rigidity to prevent this mode of deforma-tion at the base of the rack, but it is possible near the top of the rack. This is of no concern since the top is a region of negligible stress.

The allowable for buckling is taken as half the critical buckling load. Table l

3-5 of the Licensing Report shows that the most limiting compressive stresses are about 66% of this allowable, for a margin to buckling of 3.

References 4-1 Isaacson, E., and Keller, H.B., Analysis of Numerical Methods, John Wiley and Sons, 1967.

4-2 Roark, R.J, and Young, W.C., Formulas for Stress and Strain, Fifth Edition, McGraw-Hill Book Company, 1975.

l l

1:\\93mn\\93106 6

I

6 8

A 2

43*

L 6

2 9

P 2

8 7

2 49 S

0 I

0 289 911 15 2

1 0D 0

1 120 2001522' S5 1

Y15 l = = =

======='

S 5TTPR A

T V:OSEEX c

S 1

A02LOTTM SVVVIFF' 1

1PPSID DXYZDXY 1

1 m

/

//

l v/

'/.

/

' [' ' / /,

/

p y'8g ly do h

Y t

6,.

vl e

M tn e

mec

'o./

a lp l

s w

i D

le e

d g

o W

r M

a L

y r

l te

-(

.l j

l e

m C

m g

4 y l

1 n

o S

L l

Er Re 2

t 1

Ur Ga d

u I

FQ J

H

~

r

~

l i

kc u

b 1

FIGURE 4-2:

Maximum Deflection Normal to Cell Surface 0.0016 0.0014 ----------p'----------------------------------------

/

(n 0.0012 CD

.c

~

---

l------------------------------------------

l 0.001 C

O.0008

..O_

1. s O

o,999g (D

e l Q

e

'/---

C 0.0004 ------/

0.0002 0

0

.1 2

3 4

5 6

7 8

9 10 iteration 3000 3250 3300 3330

. 2 m

u m

l l'

?

l l

l 5.

NRC Ouestion 5: Provide a drawing of a rack base support assembly with dimensions as well as stress and displacement distribution.

Discuss how the allowable membrane and bending stresses of 23600 psi in Table 3-5 is justifiable since the presence of compressive stresses is most likely and beam column failure mode is a possibility (Page 3-7).

i Maine Yankee Response: Dimensioned details of the base are shown in Figure 5-1.

Stresses in psi and magnified displacements in inches near the base are shown in Figures 5-2 and 5-3.

These oblique views are from the bottom looking up.

The 23600 psi allowable for the OBE load combination is based on ASME III, Subsection NF, Class 3 requirements, as recommended for fuel rack design by Standard Review Plan section 3.8.4.

The suitability of this allowable may be l

judged by reviewing the most limiting case reported in Table 3-5 of the I

Licensing Report.

This maxima is in the cell base plate of a Region I rack, where a stress of 21670 psi is reported.

The stainless steel plate is 1/4" thick, is supported around the periphery of each cell, and serves to support the vertical weight and seismic loads from a single fuel bundle.

The reported stress occurs near each of the four locations where the fuel bundle feet rest on the plate and is the result of local plate bending. The analysis model of this local region is similar to that depicted in Figure 3-7 of the submittal, differing only by having a more refined mesh.

The same effect with a coarser analysis mesh is visible in Figures 5-2 and 5-3.

As shown in Table 3-5 of the submittal, compressive stresses are conservatively singled-out for comparison to the buckling allowable which is much lower, i

particularly for horizontal compressive loads in the cell walls in regions away l

from the reinforcing of the base.

i l

I L:\\93mn\\93106 7

l

.r t

t' 26 1/7 (Tw) 7 15/1tf

(*)

F1 f1

'll l

ll

\\\\

ll I

l I l l

l l

l

{

j L

j l,

-+

-c+-______

3 sgf 1

.-rtow mc i

c RQn-.-f)/'

1 (!

')

l~

l I f I

I I f I

l ll ll ili i

ill

}

U t

1 1. -

i PLAN - CENTER SUPPORT FOOT CASTNG

[

I i

i i

I

\\

\\

i 5 3 "NH i

d i

1 61/7 Dm.

m - Ct. sue,ont rwr C,s1.o

[ SPENT FUCL STORACE CELLS (TYP) l wwwwww I

k 4

q c

}

7--

Nl

/

\\

1 51/7 THREAD FIGURE 5-1:

Rack Base Support

- Ct. $_,,, _,

l' II

' 'i

/C 3 : _.,___ _,,!!'

ANSYS 4.4A 5

1 l

\\I i!

/

il

,f f '

f NOV 18 1993

/,,

'1 / -

\\

'I 16:30:39 j\\C IN N

PLOT NO.

1

/

\\ li

/)9, y

l POST 1 STRESS STEP =9999

\\-

ll

'o

\\

ITER =1

('

\\

a C

/'

N S

(AVG)

~"C' /

YI l

DMX =0.338926

,/

A E

SMN =567.268 D

,^

f

[-

g - ;,

r SMX =18438

\\C g

vi j\\

XV

=0.5 (J', O'

'i M[

~

(' 4 YV

=-1 g

p/

g -p]

ZV

=-1.5 y

',.:a 7

h

$[

p~

il

• DIST=33.38

/ ;-

, _f

• XF

=5.013

-f [

g) x)i

• YF

=48.666 1

l f+3~

g h '. j

'Is

• ZF

=52.292

_j

'I VUP =Z j,

PRECISE HIDDEN Q es ks

y. 'g

,2 y

k_,W

,i A

=1560

\\t

[j N.

if i

'T

%.f '

q)

B

=3546

- 1 'l'

.p C

=5531 e

<.' ((f.

y D

=7517 f

,ug 2

.+

E

=9503 g

1

-- h, n}

F

=11489 s

G

=13474 cp

~ gg l

+,

H

=15460 I

=17446 p

M n },

%W FIGURE 5-2:

Stress Near Base--Isometric 1/4 Symmetry 6x8 Rack W/ Fuel - D+L+ E' Combination

ANSYS 4.4A 1

gN.,y[7 3 __

l rg NOV 18 1993 7

gh-

- 1

- p 16:37:01 lf

'~

5

'~ "

/

PLOT NO.

1 4

. $ ~'y g-Y

~gs, tgt)

POSTl STRESS STEP =9999

_____3

.___a "3

j iB

' :13 ITER =1 l

_.... j SI (AVG)

L3 TOP N

N{3 DMX =0.338926 3, --~ ' ~K

~~~ ~

SMN =567.268 A

B SMX =18438 iA

-V

^

3 YV

=-1 DIST=95.769 1

A XF

=20.631 r- _ _

YF

=15.381 A

ZF

=79.688 A

A VUP =Z PRECISE HIDDEN k

A

=1560 1h B

=3546 C

=5531 g

D

=7517 E

=9503 at

/t F

=11489 G

=13474 B

B 11

=15460 g

I

=17446

-:-R B

,B h q 3

B g

E-Q \\

u g

\\

f

\\Q

\\

\\

C C

C D..

hM;j _ _..

._ g j

FIGURE 5-3:

g DiSplacenlents Near Base--Elevation

)

4 Syn ne t1 t y 6x8 Rack W/ Fuel

._ _D+ L +

E' Combination t

1

_ _ _ _._a

... m-.

.a

m. m

m. a.

r

_m_-,w

--v-u

-+w-

+- -,-

w--y---w ae-

+-d w-.w

--rT-

6.

NRC Ouestion 6: In page 3-11, a static analysis is discussed.

Please provide numerical values for the loadings considered with a discussion as to how the load relates to corresponding parameters of the SSE analysis.

Provide the results of the static analysis and associated margins from the allowable values.

Also provide the same information for deadweight alone when the gravity load is applied in the horizontal direction assuming a static problem for 1.0 g horizontal acceleration (Page 3-11).

Maine Yankee Response: Table 3-3 of the submittal provides numerical values for the peak loads developed in the simplified models for the load combinations D+L+E D+L+E' where D - dead load, L = live load (fuel),

E - OBE, and E' - DBE.

The peak loads and moments in each coordinate direction are taken to act simultaneously in stress analyses by manual or finite element methods.

For example, the gusseted foot assembly is evaluated for the peak foot loads by conventional manual stress analyses, whereas the juncture of the rack cell assembly to the base is evaluated by finite element analysis.

The results of the static analysis and the applicable allowables are provided in Table 3-5 of the submittal.

i The stresses in psi for a 9x10 Region 11 rack with a 1 g static load applied in the vertical and horizontal directions, are shown in Figures 6-1 and 6-2 respectively. The stress in a quadrant of a 6x8 Region I rack, for these two static loading conditions, are shown in Figures 6-3 and 6-4.

These plots also show the distortions highly magnified. These unit-load results must be factored by the actual equivalent static loads in each direction (>1x vertical, <lx horizontal).

L :\\93ra\\93106 8

_k l

I 8

E I

9 "

5 D

43 S

4 1

D 9,

E 6y 5

5 I

)

49 R

G 0ggl 5

2 O

00112233 I

T V

0g7l 5

g581a,s420 n

7036 15 5oS A

,40

.l 9

209 11(

0gi71 0 - j 6 122s4s67 o

J S5 I

Y16 I = =

= ;

= =

==

=

i S

4TTPR B

T C

g V:OSEE pXligX e

l l

A O 3 L O T T y o M M,a s o yM VyV[j, R

I

- P P S I n" T D XyZU

[

fD -

FGHI l

y x

9 1 -

-6l a

gt c

p' q

- ) h' Ei f

\\

,\\ g

,\\'

g

'e Rt

\\

N p'. AT*;,.

k

]

\\'

,\\,

\\

\\

\\

s-

\\

gN

\\

r

~

Ue z

\\

\\.

\\

is \\

h

/

w6 G V

\\

,\\

n(, g x

~

gS g

i l

7

\\

\\'

s

\\

I 8 4.

+.,

\\,'\\

\\

F1

'3 i

\\

3 i

i

\\

/

\\s R

\\ q'.~

s

\\

.\\

Af

. [9

>t

\\' Y \\\\' K Q\\

J c1 f ['/j.I. C s

I l

lj, E

y c.

g\\.

~

,m g

lf' p

\\

d

- gg G

\\

3

('

,3 I

,\\

l g'

\\ @,,<.

]

3 U

a 3

p

~

c 7

,\\3 i

j ca f

/

..Q ~

h [j, p/

e c~

t r

%g

) g.

e

~

/

V y

,/Y} d

[

y g

. p,-

~-

9 5

g c f.

7.

C

,?.\\.

.d.

y

'C

.s

,I f

N c

'd'.

[,? 3 ~

p

^

~

b-

.,4 y

y

/ y,, f.,j/ D,/f,#O(A ' q, j.

y,C"- '

iy

\\.

r y

\\

k

?

r d

2,-

. \\

(f K % '

4. \\, s

, s_

i l

a 9

/.

yLw /

yA [.S y

J a

A g\\py-F 3

y

\\

, \\'

a~

~

A

~

~-

p, \\1 (f@

i u

s

\\

y~

g s-(lQh l-

'c g

u~

,(f 2 g~ Q@)/

/

p k

.'n j

\\

= [i n-a~-

i l

,l U

I 3

E I

^

1S 18 D

4 S

25 824 D

n E

0757 3991 I 51627 o

)

d R

G 7

56 5

7021 H384977665 i

.T V

1450 5.

.0 988784062 g

3OS A

936 1

661.E406214792 e

M 11(

0123 0 - 17259S146911112 R

= = =

=I

= = = = = = =

1 = =

= =

=

1 TTPR B

T C

OSEE PXNXX S

E 0

A LOTTIOMMMM vVyI FFFB 1

1 PPSISTDSSS xYzDXYZPABCDEFGHI x

9

l 2 a t

6 no Ezi Rr UIo

'6 GI y'\\

N\\

N 4

t, I g

\\

x FI

\\

\\y\\<

\\i

,\\

N 4-N'

,\\

N\\' /

j, -,

\\

g

\\\\

N'

\\

-\\

\\

(

M g'

\\

s

\\(

\\

\\

\\\\

/

N

~

\\

~

\\

/

4 k

f

['

,,/

.j

~

.\\, Cs,,..

, v'

/g, / -

1,. -

g

< 's 3

'./,

,/

\\,

., /

I 6

~

s

/

t

\\

p.

/,

74 y,

7

~-

k

'\\

j

?b

,' /

(.

N

\\

,,' / /

'q g, -

4 ],

3 y

\\,'

4 -s g

\\)

,(. N,

/

h N

47

. [..

\\

..~

y 7/

5 p'

~, ' /

~

m 1

I N

7 3

E n

A 1S 4

4 D1 o

43 S

25 910 D3 i

02 3187 I2 g

9 E

1. 0 187*

5 58236 H

1615 5

e 49 R

R 6

67788 0

5' 12

.T 395 0

1305.

E56789 4

3OS 0191

- 2210ZS51234 9

S8 N

41 8

=

======I

====="

=

Y19 l==

gXNX*

x T

C S

3TTPR S

PE 6

NV:OSEE AO4LOTThMMM" VIFFFUR 3

N1 PPSI 7 DSS" X

ZDXYZVPABCDE I

-6l a

ggM'

/

Ei l

c

~

~'

y' O

Rt

/

r y

Ue

)

.. N G V p\\ k' jI x

FI I g l

~

E

, [ilf l

,'j ll [

}

s

~

~

y x/Q s~iy4(q N(g..fw;:

/

/

q N.

q N

c-l j

a i;

4i N

I

'G

. v,V c

A E

y.

i Q

i N

L t

N lg r

e MsD,"(x-'

V

-x j~,, p s'g',,'

fy F

g

, l!i f

....g_g

, /:!

g l

I,

, l!'

w g f:

g ]-

l

$' p -

g'{; x'f x' {N

/

l f

y' k

e

- g2'-

N%$x' $

- x'.

/

e i

u F

fk 4 v

$(x>7 N

t,

/

W N'

s k.

s k

Q N

//,$ $

c y

a

, [ 4 )/g Q [ _

J7;7' W'7p R

j

" jr> 4,/ u 8

j t

),'

6 x

h s N }-

x l

~.

I A_

w hy4 sd

?

6 y

f g

r t

3f?

y e

}.,

'f c

m g 9;, y(( [p-.

e g

qj4jl T

3'3 m

,\\

y

,i sx&

?

S 7:

}

q 4

y

)

/

J i

j" 1

,,/

'.. 5 j'e, j

s 4

i j K:

j

,/

jj(

s

!if.

- ' /?

A

'\\

y

/

N,. Y

/

l r

/

/.', $ /, g

/ /.

a c-

'g

/

n A

j

/

f c

'e

/

j!

\\![.

1,:i" i

q j!:[::i{'

,l

[,

t

/

i:,i a

j t

/

1 f

/i}

d' S

7

m I

n N

o 4

E i

3 1S 3

D g

43 S

5 241 D

e m

,9 E

8 8

638 I

382716 R

)

49 R

G 2

7 5473 H949544332 1

T V

4 32 5

665432109 E765036924 8

0M1905 65 S

A

- 221 S147111122 x

g8 11(

0 25 7

=

==

I = = = = = = ===

6 y1 1 = =

=

=

g TPR B

T C

gV hSEE PX X

S PE XWZDXY V

VIFF R

gO OTTIOM M

l g

PABCDEFGHI 4 a N

ppSI STD SS t

6 n o

Ez Rr i

Uo 4

G H 1

\\

)

y h

I g

\\

,3g@i t

1 FI

_s

\\

,s, E 4

\\ \\'

\\

\\x

'm., /[(-

\\D s

s

I' i

T' d y

\\

\\ N

\\'

'\\

\\

N

,. 3

\\

\\

y@)s e

i

'x g4 t

\\

l s:

a pI r

S l

t d

\\

l e

h$Vg' cj.

N '

\\

t T

,K

\\

a t

AIC/3' -

)

L s Y /~ A ;;;

{.

3

[i v

3 s

(

m[3 g \\k~'

g C-p [jL! '-

1

~

~

'1 p1

/

g/

h', h'. < / V -

N C

j

/

t l

4; J

k 7

c. '

e

['$'

E u

/f s

l F

i' k@k.

)

(\\

p

/

7, 5

W x,,'

C

- q'[' p B-

,g#

. h

['-

k

'f f['c d'

c

~c, T

a

,w.

R j Yj 1Qr8;g,j.'-~

j/

h g-.

8 n E ['1A.,-

.~

yx%

6 s

g x

t b'f y

I ij

. A C' '

f

' 1 y

h b ji s

M,# '

.~

y Y

7.,r'Of:

r

(

j

'?

t_

e_

'1 rb 3

s ::.

/, #..

m

\\

m

\\. x' G

g j j{e {D

' 31

- L

- - 'K y

N

~

S A[ ';'- kl p g' }B,.,

i j

4 N

r 'N ~

D 7,

\\!!k

/,~.1

/

fr(p~'.-(',

i f

1 9

f,f

\\

\\.r -

\\

_ 7; j

's s

.?

d'

.{

f s

3 y

/

. ::d \\

j l

3A U

g

\\

t -

n

\\,

Ifo

~

f A

C\\

s' 1:

7 c

'j [J i

r fili t

a t

1 S

[

i 1

l 7.

NRC Ouestion 7: It is stated that "a value of 4% in the range 18 to 33 Hz is assigned to the models for the DBE and 2% for the OBE." Provide a basis for the i

damping values and discuss how the frequency dependent dampings are treated in the calculational scheme. (Page 3-19).

Maine Yankee Response: "In practice it is difficult, if not impossible, to determine for general finite element assemblages the element damping parameters, in particular because the damping properties are frequency dependent. For this reason the matrix [C] is in general not assembled from element damping matrices, but is constructed using the mass matrix and stiffness matrix of the complete element assemblage... " (Ref. 7-1). This approach is used by the ANSYSS program.

The damping matrix is expressed as:

l

[C] = a[M) + #[K]

1 l

where:

[M] is the mass matrix,

[K] is the stiffness matrix, and i

a and B are constants.

l The effective damping ratio, f, at a given frequency, w, is:

y=

+

Using this equ W on, the damping ratio at any two frequencies can be assigned and the ratio at other frequencies derives from the equation. The a term gives higher damping at lower frequencies whereas the B term gives higher damping at l

higher frequencies.

In these analyses a was conservatively set to zero and B l

was set to give 2% or 4% damping at 33 Hz for the OBE and DBE, respectively.

These are the Regulatory Guide 1.61 (Ref. 7-2) damping values for welded steel structures.

The consequence of this approach is that the effective damping ratio is proportional to frequency and is less than the prescribed values at any frequency below 33 Hz. At the frequencies of interest the effective damping is very low and consequently the dynamic response is conservatively over-predicted.

For example, for the DBE case, the damping is only 0.12% at 1 Hz and 1.2% at 10 Hz.

References 7-1 Bathe, K.J., Finite-Element Procedures in Engineering Analysis, Prentice-Hall, 1982.

7-2 Regulatory Guide 1.61, Damping Values for Seismic Design of Nuclear Power Plants.

1 l

L:\\93mn\\93106 9

8.

NRL Ouestion 8: Discuss and justify 10% damping for fuel to cell interaction analysis 1 context of governing equation. Phase discuss impact analysis: (1) between fuel and cell, and (2) between rack feet and concrete slab (Page 3-19).

Maine Yankee Response: The fuel-to-cell impact is implemented via the ANSYS*

STIF40 Combination Element (see response to Question 3). This element includes the gap, impact stiffness, and damping. The governing equation for damping is the classical expression which sets the damping force proportional to relative velocity.

This damping force contributes to the loads on the cell walls and fuel.

It acts only during the brief periods of contact and thus has little effect on the over-all damping.

It is set to 10% at the natural frequency of the impact, based on the stiffness of the impact spring and the local mass of the fuel bundle.

The value of 10% is justified since:

The loads are locally high at the point of impact, Fuel bundles have inherently high damping since fuel is not an integral mass but rather an assembly of multiple rods with slip fits through spacer grids.

(These grids define the impact points with the rack cell walls.)

The damping is associated only with the impact element not tne whole model.

By analogy, the 7% SSE damping permitted for bolted structures by Regulatory Guide 1.61 (Ref. 8-1) is actually a weighted average of a damping higher than 7% in the joints (analogous to the impact element) and lower than 7% in the structural members (analogous to the rack).

The evaluation of the currently installed racks used a damping value of 10%

for the fuel (Reference 8-2).

Values of 15% damping have been approved in other licensing submittals for rerackings (Ref. 8-3).

The impact analysis between the fuel and rack used a nominal gap of 0.393 inches for the Region I racks and 0.305 inches for the Region 11 racks. This is based on the difference between the inside dimensions of the rack cell and the outside dimensions of the fuel bundle. The impact stiffness is derived considering the local flexural stiffness of the rack cell wall in series with the stiffness of the fuel bundle grid spacers (see response to Question 3). The impact damping is described above.

l The rack-to-pool floor impact used the ANSYS* STIF52 Three-Dimensional Interface element.

For a description of this element, see the response to Question 3.

There is no damping for rack-to-floor impact. The gaps are initially closed to represent the racks resting on the pool floor before the seismic event.

The normal stiffness is based on the stiffness of the rack foot in series with the stiffness of the concrete approximated as an infinite half-space. The lateral stiffness is based on the foot stiffness alone.

L:\\93mn\\93106 10

i I

i References i

8-1 Regulatory Guide 1.61, Damping Values for Seismic Design of Nuclear Power l

Plants.

8-2 "Model Description, Formulation, and Assumptions for the Seismic Analysis of the PWR Spent Fuel Storage Racks for Maine Yankee," GCA Corporation par Systems Report DD-9016-1, dated September 1981.

i 8-3 Crystal River Unit No. 3, Reracking License Amendment No. 134, 1990.

l j

i l

l l

l

(

l t

I l

l L:\\93mn\\93106 1I l

l

i i

9.

NRC Ouestion 9: Discuss what is meant by effective stiffness and mass properties of a beam element and provide numerical examples and how these values are used in the rack analysis (Page 3-11).

Maine Yankee Resoonse: The nonlinear time-history analysis uses a simplified model as shown in Figure 3-6 of the Licensing Report. The statement refers to the portion of the model connecting nodes 27 through 36. This series of beam elements has the same metal area, dimensions, bending stiffnesses, torsional stiffness and shear stiffnesses as the composite rack honeycomb structure. The weight is also identical to that of the honeycomb.

Using the above beam properties, in conjunction with other beams representing the base and support feet, the simplified model closely approximates the dynamic characteristics of the detailed shell element model of Figure 3-13, as seen from the following comparison of natural frequencies:

Shell Model Stick Model Bending about softer axis 42.6 Hz 42.2 Hz Bending about stiffer axis 46.4 Hz 45.4 Hz Torsion about vertical axis 80.5 Hz 85.3 Hz I

l I

t i

l i

L:\\93mn\\93106 12 l

I I.

i

10. NRC Question 10: Discuss difference between single rack and multirack analyses in it ras of resulting displacements and reactions.

Also, discuss the key procedures and assumptions for developing three dimensional multi-rack model and provide a basis for considering it as the bounding case. Discuss sensitivity of the modeling in terms of difference in responses between, for example, two rack and three rack multi-rack analyses (Page 3-14).

Maine Yankee Response:

l Displacements The racks behave almost as rigid bodies.

The deflections due to flexure are small compared to the motions of sliding and tipping.

The following maximum displacements were computed:

i Fully Loaded Racks: Peak Displacements (Inches)

Coefficient Motion Single Rack Analysis Multiple of Friction Rack l

Region I Region II Analysis 0.2 Uplift 0.010 0.008 0.019 Slip 0.090 0.046 0.139 0.8 Uplif t 0.044 0.013 0.030 Slip 0.123 0.049 0.083 Empty Racks: Peak Displacements (Inches)

Coefficient Motion Single Rack Analysis Multiple of Friction Rack Region I Region II Analysis 0.2 Uplift 0.005 0.001 0.010 Slip 0.039 0.001 0.080 0.8 Uplift 0.012 0.001 0.008 i

Slip 0.014 0.001 0.051 These displacements demonstrate that, for full racks, there is no statistically significant difference between the results of single and multiple rack analyses (i.e., two of four maxima occur in single rack analyses and the other two occur in the multiple rack analyses). For empty racks, there is a difference. These racks are light and move more readily. In a single rack analysis they move in unison with the pool, whereas in multiple rack analyses, their motion tends to average the motions of the pool and the adjacent racks.

i L:\\93mn\\93106 13

i Somewhat larger displacements occur in partially full racks which have artificially adverse fuel loading (full along one edge or to one side of a diagonal.

These eccentrically loaded racks have a greater tendency to tip (uplift) and also rotate about their vertical axis.

Reactions In the following comparison, Region I racks are excluded since they do not contain consolidated fuel. Thus they are lighter than the Region Il racks and it is meaningless to compare their reactions to Region II rack results.

Fully Loaded Racks: Peak Reactions (Kips)

Coefficient Foot Single Multiple of Friction Reaction Rack Rack Analysis Analysis 0.2 Vertical 61.3 128' Shear 11.2 21.6' 0.8 Vertical 92.6 134' Shear 18.7 52.0' i

1) Simplified model has only four feet. Actual 10x7 rack has 8 feet. Therefore the reported loads are conservatively approximately twice actual.

)

Empty Racks: Peak Reactions (Kips)

Coefficient Foot Single Multiple of Friction Reaction Rack Rack Analysis Analysis 2

0.2 Vertical 2.2 5.7 l

Shear 0.3 1.I' 0.8 Vertical 2.7 6.7

)

2 Shear 0.6 3.5*

2) Simplified model has only fotr fc-et. Actual 9x6 rack has 6 feet. Therefore the reported loads are conservatively approximately 1.5 times actual.

i L:\\93mn\\93106 14

l 4

While the multiple rack analysis gives higher foot reactions, the analysis model was simplified and contained only 4 feet whereas the actual racks have more.

1 When this difference.

., considered, the results are comparable. Once again it is clear that the empty racks are jostled more in the multiple rack analysis but, being unloaded, the reactions are small.

Procedures for Model Development The key procedures in developing the multiple rack model are:

A section through the pool having widely disparate rack spacings is selected to bound the range of fluid gaps.

Simplified stick models are develoaed for each of the racks.

A range of fuel distributions (ful' rack, empty rack, rack with all fuel at l

one end, rack with all fuel to one side of a diagonal) is modelled by locating the fuel at the centroid appropriate for each case.

For eccentrically load racks, stiff artificial members are used to connect the stick figure of the rack to the centroid location where the fuel bundle model, fuel-to-cell fluid coupling and fuel-to-cell impact gaps are located.

l Another set of artificial members extends to the centroid of the unoccupied cells where a water mass is located.

The water mass in the occupied cells appears in the fuel-to-cell fluid couplin; elements.

A sliding / gap element is located at the base of each fuel bundle.

The coefficient of friction is assumed the same as between the rack and pool liner.

(No lift-off and very little sliding is observed.)

Rack-to-rack and rack-to-pool fluid coupling elements are added in all three directions.

The model is checked statically by applying a 19 acceleration sequentially in each of the three directions (sliding / gap elements are fixed in these analyses). This is done: (1) with racks only, (2) with racks and fuel, and (3) with a complete model.

Reaction loads are reviewed and shown to equal (1) the weight of the racks, (2) the weight of the racks and fuel, and (3) the submerged weight (considering buoyancy), res3ectively.

All three stages of model building are also chec(ed by modal analysis.

Nonlinear time-history analysis is performed with the verified model.

The results are reviewed.

Analytical and Modelino Assumptions The analytical and modeling assumptions in the multiple rack model are:

The shell structures of the rack are modeled as simplified stick figures.

Diagonal shear modes of the shell structure are ignored.

The models contain only four feet per rack although the actual racks contain l

more.

l All fuel bundles in a rack are conservatively assumed to move in unison and i

are represented by a single massive bundle.

l Lateral impacts between the fuel and rack are assumed to occur.

l Fluid coupling coefficients are conservatively computed at the nominal rack l

separations.

l Fluid coupling members are conservatively aligned with the rack centerline i

and offer no resistance to rack rotation.

Fluid damping is conservatively ignored.

J

\\

L:\\93mn\\93106 15

i Boundina Case For rack design, the differences between the single rack and multiple rack loads i

and displacements are small. However the multiple rack analysis provides the more limiting pressures on the pool wall for the reasons discussed in the response to Question 11 and is bounding for this application. The more detailed single rack analyses, having the proper number of feet and many more im)act elevations are more accurate for determing loads & displacements and have aeen analyzed for many more scenarios.

Sensitivity 1

As shown above, the rack displacements and reactions are not particularly different in the single and multiple rack analyses. The only factor sensitive to this modelling difference is the pressure at the pool wall where the more limiting values were used (See Question 11).

f i

l i

l l

L:\\93mn\\93106 16

11. NRC Ouestion 11: Discuss the difference in location and distribution of peak fluid pressure on the rack during the fluid and rack interaction between the 3-D single and multi-rack analyses cases.

Also, provide results of any existing experimental study that verifies the simulation of the fluid coupling utilized in the numerical analy.es (Page 3-19).

c Maine Yankee Response: There is no fundamental difference in the location or distribution of peak fluid pressures in the single and multiple rack analyses.

However in the multiple rack analysis, the magnitudes of the pressures are higher around the perimeter of the pool.

In a single rack analysis, the l

pressure need only accelerate a single rack whereas in a multiple rack analysis the pressure at the pool walls must accelerate several racks which, at high frequencies, are caused to move essentially in unison with the pool walls.

Although the absolute pressures differ, the differential pressure across a l

single rack is similar for these two types of analysis. Thus the loads and slip displacements obtained in these two analysis types are comparable.

The Maine Yankee analysis utilized the peak fluid pressures to determine rack-to-rack and rack-to-wall impacts. There were no calculated impacts.

The following general observations provide some insights to the character of fluid coupling:

The fluid forces experienced in a single rack analysis are representative of those around a rack near the middle of the pool.

Higher fluid forces result if a rack is heavy (full of fuel) than if it is light.

Closely spaced racks tend to move in unison at higher frequencies but the I

motion is not as strongly correlated at low frequencies.

The magnitude of the peak fluid forces experienced at the lower and upper fluid coupling members (See Figs. 3-6 and 3-16 of the Licensing Report) are about equal and often occur at nearly the same time.

In any given analysis the peak pressure may occur in either the upper or lower coupling member. There is no systematic tendency for the force at one elevation to dominate.

The simulation of fluid coupling used in the analysis is based on the method of Fritz (Ref. 11-1).

In addition to developing an analytical method, this reference also compares the results of analysis to those obtained by test.

References 11-1 Fritz, R.J., The Effect of Liquids on the Dynamic Motions of Immersed Solids, Journal of Engineering for Industry, February, 1972, American Society of Mechanical Engineers, pp. 167-173.

L:\\93mn\\93106 17 i

12. NRC Ouestion 12: It is stated that the rack evaluations bound the sliding friction by using the minimum and maximum value of the static frictions of 0.2 and 0.8.

Provide a technical basis for the statement (Page 3-22).

Maine Yankee Response: Since a precise value for the coefficient cannot be guaranteed, the rack response must be computed for a range of potential values.

The lower and higher friction coefficients used in the analysis conservatively bound the plus and minus two standard deviation limits of tests by Rabinowicz performed for Boston Edison and are the values most frequently cited in licensing submittals (Ref.12-1). The tests showed that the static coefficient of friction was similar to the dynamic coefficient at low velocities (0.04 in/sec) and decreased moderately (-35%) at higher velocities (4 in/sec). The range 0.2 to 0.8 bounds both the static and dynamic cases.

In addition to enveloping the results of friction tests, this range in friction coefficient is considered adequate since the results are not overly sensitive to this variable (see the results provided in response to Question 10).

The only exception, as would be expected, is the shear load at the feet. However, this load does not increase if the coefficient of friction were higher since, even with the current analysis, slippage of the feet does not occut at the times of highest shear load.

References 12-1 DeGrassi, G., NUREG/CR-5912, Review of Technical Basis and Verification of Current Analysis Methods Used to Predict Seismic Response of Spent Fuel Storage Racks, Brookhaven National Laboratory, October,1992.

L:\\93mn\\93106 18 l

l

13. NRC Ouestion 13: It is stated that all computer programs utilized in performing the rerack analysis were verified.

Provide the code verification documents (both experimental and analytical) which apply to the current usage for rack responses (e.g. nonlinear dynamic analysis and large deformation buckling analysis).

Also, provide information with reference to the code quality assurance (QA) program and discuss whether the QA was reviewed and approved by l

the NRC staff. Also, indicate whether or not the QA documentation is available I

for a staff audit. The report also stated that the ANSYS code was reviewed and approved by the NRC.

Please provide the reference for the approval.

Discuss the extent to which the current rack application is consistent with the capability and limitation of the ANSYS code (Page 3-24).

Maine Yankee Response: The ANSYSS version 4.4A program was used for all computer l

aided mechanical analyses.

This program is purchased from Swanson Analysis l

Systems, Inc. (Swanson) by Stone & Webster. Swanson is an approved QA Category I vendor based on reviews and audits of Swanson's QA program, as conducted in accordance with Stone & Webster's QA program. The Stone & Webster QA program, the Standard Nuclear Quality Assurance Program, SWSQAP l-74, has been reviewed and accepted by the NRC as in compliance with Appendix B of 10CFR50.

l i

Swanson's ANSYS$ QA Program is consistent with the requirements of Appendix B l

of 10CFR50 and is established and implemented by Swanson's Quality Assurance l

Department.

This QA Program applies to all software and its related documentation that is identified as the ANSYS program. The AA Program applies j

to all persons involved in the development, documentation, support, verification and testing, and release of the ANSYS$ program. The Swanson QA Program has been reviewed and approved by Stone & Webster in accordance with its NRC-approved QA l

Program and is periodically audited by Stone & Webster.

Verification of ANSYS$ was conducted by Swanson in accordance with their QA l

Program. Many test cases were run by Swanson that compare ANSYS* solutions to theoretical solutions, experimental results, or other independently-calculated results. A list of recent comparisons is in Appendix A of the Licensing Report.

The documentation of this verification is held by Swanson. Stone & Webster has qualified ANSYS$ for its use in accordance with its QA Program by demonstrating that results obtained from test pioblems are consistent with the results published by Swanson.

Swanson and Stone & Webster QA documentation of ANSYS$ verifications is available for a staff audit.

l The ANSYS$ computer code has been used in numerous structural dynamic applications in NRC licensed facilities.

Some examples are:

l Qualification of the spent fuel storage racks in the previous Maine Yankee Spent Fuel Storage Modification.

Comanche Peak Steam Electric Station, Units 1 and 2:

I Seismic Category I structures Feedwater Line Break dynamic piping response ASME III piping Integral Welded Attachments Containment polar crane dynamic response L:\\93mn\\93106 19 l

l

i I

Millstone Nuclear Power Station, Unit 2 Reactor coolant system dynamic analyses Millstone Nuclear Power Station, Unit 3 ASME III component supports analyses Seismic Category I structures analyses Shoreham Nuclear Power Station, Unit 1 Reactor building polar crane dynamic response Trojan Nuclear Plant Main Steam stress and fatigue analyses Oyster Creek Drywell vessel evaluation Palo Verde Reactor internals dynamic analysis Arkansas Nuclear One Spent fuel racks The application of ANSYS* to the Maine Yankee sSent fuel racks is fully consistent with the proven capabilities of ANSYS.

Only ANSYSS elements released for use in the ANSYS Users' Manual were used.

These elements were qualified for use at Stone & Webster as described above.

A select sample of ANSYSS solutions which verify the functionality of the elements used in these analyses is attached to this response.

In addition, numerous checks were performed to verify that the models developed as an assemblage of these elements functioned in a reasonable manner. The following is an example of one of these checks based on the multiple rack model.

(1) Application of a la vertical acceleration. This analysis was performed for three cases and the results are summarized in Table 13-1.

Case A is the empty racks in air.

The weight of the fuel is added in Case B.

The difference from Case A accurately reflects the weight of the fuel.

Case C adds the hydrodynamic coupling elements.

The difference from Case B accurately reflects the buoyant force (weight of water displaced by each l

rack and its contained fuel bundles).

In addition, thir analysis gives a load on the 2001 floor due to the weight of the water in the pool. For the racks with tie skewed distribution of fuel, the reactions of the individual rack feet vary smoothly from one side (or corner) of the rack to the other.

)

l L:\\93mn\\93106 20

Table 13-1 Summed Foot Reactions from Ig Vertical Load (lbs)

Case Rack A (9x7)

Rack B (10x7)

Rack C (10x6)

Rack D (9x6) 10 Fuel Full (70 Fuel 12 Fuel Empty i

Bundles Bundles)

Bundles (diagonal (side loading) i loading)

A 8608 9664 8266 7538 B

34598 191670 39467 7538 C

30694 172941 35120 6248 (2) Apolication of la horizontal accelerations. The fluid mass terms in each horizontal direction appear in hydrodynamic elements oriented to produce no mass in the vertical or other horizontal direction. Static 19 analyses were again performed in each of the horizontal directions for Cases A through C and the results of Table 13-1 were reproduced for each horizontal direction.

(3) Modal Analyses.

Modal analyses were also For a description of how ANSYS$ performed for each of the above 3 cases.

treats nonlinear elements in a modal (or static) analysis, see the response to Question 16.

For Case A, the results are shown in Table 13-2.

These results reflect the proper trend when comparing one rack to another. Also the results are consistent with the values provided in the response to Question 9.

For example, in the direction 9 cells wide, the results for Racks A (39.4 Hz) and D (41.4 Hz) are consistent with the 9x10 rack results (42.2 Hz). In the direction 10 cells wide, the results for Rack B (44.4 Hz) and Rack C (43.7 Hz) are also consistent with the 9x10 rack results (45.4 Hz).

Table 13-2 Natural Frequencies, Case A (Hz)

)

Mode Rack A Rack B Rack C Rack D l

Bending 31.5 33.2 28.4 29.6 Soft axis Bending 39.4 44.4 43.7 41.4 Stiff axis Torsion 61.5 64.5 54.7 63.0 Case B adds the fuel which has a very low natural frequency: 0.95 Hz (First i

mode bending) and 3.2 Hz (second mode bending).

f l

L:\\93mn\\93106 21

j Case C adds fluid coupling elements to the analysis model. The water drops the natural frequencies and couples the fuel to the racks and the racks to each other and to the pool. For example, the first mode frequency for the fuel becomes 0.75 Hz in bending.

The differential from Case B is consistent with the anticipated result.

The presence of the water decreases the natural frequency only slightly since the water can flow through the open array of fuel rods. The next modes of vibration involve l

rack motion.

Racks C and D flex out-of-phase at 1.7 Hz and, similarly, l

Racks A and B flex out-of-phase at 1.9 Hz. Since sliding is precluded in l

modal analyses (see response to Question 16), out of phase flexural motion produces the highest lateral fluid velocity out of the gaps between racks and hence the greatest apparent coupled mass.

This effect is most pronounced if the racks are closely spaced.

Because the faces of the Region II racks are solid and have a large surface area, the escape.of fluids from the gap is difficult and the effective mass is large. Thus the observed behavior is appropriate.

(4) Dynamic Nonlinear Time History Analysis.

The results of the dynamic analysis were reviewed to' assure:

No force is transmitted when gaps are open.

The shear force at frictional interfaces does not exceed the product of the coefficient of friction times the normal force.

There is no slipping when the lateral force is less than the product of the coefficient of friction times the normal force.

The force and displacement in the impact springs are consistent with the prescribed stiffnesses.

l The above comparisons indicate that the model formed by combining these various elements produces results that are physically meaningful.

l l

I l

L:\\93mn\\93106 22

J ATTACHMENT TO RESPONSE 13 VERIFICATION OF ANSYS ELEMENTS The following elements were used in the analyses.

The test case numbers of each applicable problem provided in the ANSYS Verification Manual are listed after each element.

l RTIF4 3-D Elastic Beam Element 21,36,57,59,179

$TIF21 General Mass Element 45,46,47,48,49,52,57,65,68,77,80,89 i

90,91,131,156,197 i

STIF38 Dynamic Fluid Coupling Element 154 STIF40 Combination Element 9,36,68,69,71,72,73,74,75,79,81,83 86,87,88,182,183 STIF52 3-D Interface Element 27 STIF63 Elastic Quadrilateral Shell Element 23,34,39,54,62,66,139,177,03,C4,D2 Sample test cases are summarized below:

l l

STIF4 Test Case 21. Tie Rod with lateral Loadina l

l This test case examines a 200 in. long simply supported beam with a 2.5 inch square cross section subject tg a uniformly distributed load of 1.79253 lb/in. The elastic i

modulus is 30x10 lb/in.

The STIF4 Elastic Beam element is used.

The result is l

compared to a closed form solution in Timoshenko, Strength of Materials (Ref.13-1).

Parameter Target ANSYS l

Maximum Deflection, in

-0.382406

-0.382407 l

End Rotation, rad 0.0061185 0.0061185 Maximum Moment, in-lb

-8962.65

-8962.65 STIF21 Test Case 45. Natural Frecuency of a Sprina-Mass System i

The natural frequency of a spring-mass oscillator with k=48 lb/in, W-2.5 lbs and 2

g=386 in/sec is computed as 13.701 Hz by ANSYS$ using a model in which the weight is represented by a STIF21 General Mass element.

This result agrees with the classical expression STIF36 Test Case 154. Vibration of a Fluid Couclina This analysis considers a massless, 7-inch diameter cylinder, saring-supported within a fixed 8-inch diameter cylindrical hole filled with water. Tie spping stiffness is 10 lb/in and the density of the fluid is taken as 0.0000934 lb-sec /in. The result is compared to a closed form solution based on the method of Fritz (Ref.13-2). Both methods give the same result, 1.5293 Hz.

L:\\93mn\\93106 23

STIF40 Test Case 83. Impact of a Block on a Sprina Scale The solution of this complex problem requires only two STIF40 elements (Fig.

ay 13-1).

A 50 pound block (W,) is dropped l

through a 71.75 inch height (the initial Wb gap of a STIF40 element) onto a 25 lb pan (W

of a spring scale having a stiffness "h

W C2 K2 K,=,)00 l b/in. The accelpration of gravity

,SDF40 1

D l_

is taken as 386 in/sec.

The impact of the two masses is assumed critically k

damped so the impacting mass does not K 1

,SUF40 rebound. The impact spring is assumed to have a stiffness K -10000 lb/in. Critical 2

damping requires that C be 50.90 lb-l 2

sec/in.

A comparison to the solution

,9 (Ref.13-3) for a perfectly plastic impact is shown below.

Figure 13-1 Mass Dropped onto Spring Scale Time = 0.6865 sec Target ANSYS t

6, in

-7.7000

-7.6792 y, in

-79.450

-79.480 l

STIF52 Test Case 27. Thermal Expansion to Close a Gap This problem (Ref.13-4) uses a STIF52 Interface element with an initial 0.0q2 in.

gap and ag arbitrarily high stiffness. A 3 inch long aluminum bar (E-10.5x10 psi, a-12.5x10 in/in-F), fixed at one end, is heated from 70 F to 170 F, closing the gap and introducing a thermal stress. The bar and interface element are placed at a skew angle to demonstrate the 3-D character of the interface element. The axial thermal stress is computed as -6125 psi, in perfect agreement with theory.

STIF63 Test Case 23. Thermal Stresses in a Plate A 1/2 in. thick by 5 in. square plate with clamped edges is subjected to a non-uniform temperature distribution (Ref. 13-5).

The temperature varies linearly through the thickness and,is 0 F on one fa,ce and 100 F on the other. The properties of the plate are E-30x10 lbs/in, a-7x10 in/in-F and v-0.3.

The edge moment and maximum bending stress comparisons are shown below.

Parameter Target ANSYS M, in-lb/in

-625

-625

%, psi

-15,000

-15,000 l

L:\\93mn\\93106 24

References 13-1 Timoshenko, S., Strength of Materials, Part 2, Advanced Theory and Problems, Third Edition, D Van Nostrand Co., Inc., New York,1956, p. 42, Article 6.

13-2 Fritz, R.J., The Effect of Liquids on the Dynamic Motions of Immersed Solids, Journal of Engineering for Industry, February, 1972, American Society of Mechanical Engineers, pp. 167-173.

13-3 Beer, F.P., ar.d Johnston, Jr., E.R., Vector Mechanics for Engineers, Statics and Dynamics, McGraw Hill Book Co, New York,1962, p. 531, Problem 14.6.

13-4 Harris, C.O., Introduction to Stress Analysis, The Macmillan Co, New York, First Printing,1959, p. 58, Problem 8.

13-5 Timoshenko, S., Strength of Materials, Part 2, Advanced Theory and Problems, Third Edition, D Van Nostrand Co., Inc., New York, 1956, p. 91, Eqn. 87.

i I

i l

i i

l L:\\93mn\\93106 25

I i

14. NRC Ouestion 14: It is stated that "due to the large number of iterations required, several iterations of the first second of response are performed with varying time steps to establish the longest time step producing a valid result".

Please explain the statement particularly regarding how one determines a " valid result" (Page 3-23).

t Maine Yankee Response: The ANSYS* program uses computational routines for time history analysis which are inherently stable and which progress through time in discrete intervals (time steps). At each time step, in nonlinear analysis, one or more iterations may occur until the solution is in force equiliorium. As the duration of the time step is decreased, it becomes possible to resolve phenomena at higher response frequencies.

Figure 14-1 shows the reaction force on the i

foot of Rack A in the multi-rack analysis computed in five separate analyses l

using time steps of 0.0005 sec., 0.001 sec., 0.0167 sec., 0.0025 sec. and 0.005 l

sec.

In all cases the responses are very similar and, for the three shortest l

time steps, the results are identical to within the width of the plotted line.

l The 0.0167 second time step was used since it provides results essentially identical to those obtained using shorter time steps.

L:\\93mn\\93106 26

~

ve c

3 97 CCCD

-m mc t,-

.Oc mOCOO

-x N

n a n a a t*:

o" b

b

, ~..,.

m v-

.~<<-OC

>~A11

- r, c SOX >N M @

C O

~ O P

• O p

...,...u

.. ~

J-O

,__,,__.a~-~~.

w

' '^*-

.nn..m.,

• %...s.;.,

.~~-gga.nW c

6-m M M&'g,

% m *%.%"%

-O m

.... w. ~. ~ ~ "

g

w..

~..

o. --a-~m~~.-~..

O

-.*x-

.-~.

-....... ~.... _ _..

b

...... -- ~ ' -

• O A

. ~ ~ ~,.

Eesem%,,,,,g,

1. ,g.

-o A

n b

p e

e

,sn*

f,.a.,

% '"' ".a...u.

I o

- - -.. ~ ~ ~. =~'_,

...A g

O j

m l

"**%=m.

e

{

5.

O l

m

..-,,,2,.-

se u k*

O a,-- %,

pq N

c.

_ O 11 O

=

O 1

.A a

s '"*hrg g

g

+-

m Ch O

C O

w w

_ Q

(

O rj)

+

em o

u n

D

".3 Q

p, O

a ma l

W X

l W

eo m

i O

O O

O 9

o o

O O

O O

O O

O O

.2 W

f r2 O

c O

O O

O O

c:

a O

N O

D N

2 m

~.

m m

m a

w N

D m

N

~

M i

Do W e.se 8.e W **

i l

I I

I j

e e

I i

15. NRC Ouestion 15: Provide any verification of the ANSYS code with physical experiments simulating rack responses to an earthquake. The experiment should

(

include a substantial variation of the parameters and input forcing function to see corresponding changes in rack responses.

The experiment should address overall response of a rack as well as addressing each component of parameters such as damping, stiffness, gap sizes and hydrodynamic mass etc. and different i

forcing functions (Page 3-23).

Maine Yankee Response: ANSYS is a multi-purpose analysis tool for - varied engineering disciplines that is well suited for application to high density spent fuel storage racks. As such, verification of the code does not explicitly address the behavior of spent fuel storage racks under earthquake conditions.

Appendix A of the Licensing Report lists the test cases comparing ANSYS-calculated solutions with well known theoretical solutions, experimental i

results, or other independently-calculated solutions as verification of the analysis types and element designations in the code.

The verification activities are conducted in accordance with established procedures under an overall Quality Assurance program at Swanson Analysis Systems, Inc.

Also included in the Appendix to the Licensing Report is a partial list of other publications verifying the ANSYS program.

l I

i L:\\93mn\\93106 27

t

16. NRC Ouestion 16: Discuss how a modal analysis was performed in view of the many nonlinear elements in the model (Page 3-23).

t Maine Yankee Response: Modal analyses were not performed on nonlinear models.

The complete models consist of linear structures (the racks and fuel) coupled by nonlinear phenomena (gaps, friction, hydrodynamic coupling). Modal analysis was meant solely as one means of verifying that the manual analysis process used to derive the simplified model produced a reasonable model. See the responses to Questions 3 and 9 for examples. For these modal analyses, the ANSYS$ program treats these nonlinear elements as follows:

Gap elements maintain their initial status.

That is, initially open gap elements (fuel bundle spacer grids - to - rack cell walls) remain open; initially closed and non-sliding gap elements (fuel bundle baseplate - to -

rack base plate and rack feet - to -fuel pool floor) remain closed, non-sliding and load bearing (even if in tension).

The effective masses of the hydrodynamic coupling elements are imposed on the model.

The modal analysis was intended to verify that the manual analysis process used to derive the simplified model produced a reasonable model. See the responses to Questions 3 and 9 for examples.

l L:\\93ms\\93106 28

17. NRC Ouestion 17: It is stated that " MYAPCO is performing confirmatory analysis of the spent fuel pool walls to address all design basis loads--- ". Please provide a summary of the analysis results and indicate any change in safety margin of the pool structure (Page 4-4).

Maine Yankee Response: The Maine Yankee spent fuel pool walls were analyzed for the load increase due to rack-to-wall hydrodynamic 3ressure effects caused by l

the movement of the racks during a seismic event. T11s analysis was performed using manual calculatiens based on the ultimate strength concept, in accordance with the requirements of ACI 318-63 and the load combinations of SRP 3.8.4. The loads due to the rack-to-wall hydrodynamic oressure effects were combined with other applicable design loads. The applica)le design code for the spent fuel pool reinforced concrete structure is ACI 318-63 (Ref. 17-1), including increases allowed for other stresses produced by earthquake loads in combination with other appropriate loads (ref. 17-2, Section 5.4.2.1). ACI 318-63 is the design code originally used for the design of the spent fuel pool and other l

safety related, Seismic Category I reinforced concrete structures at Maine Yankee. The allowable stresses for s?.chr and flexure are defined by the criteria in Sections 1700 and 1600 of ACI 313-63.

The increased wall loads produced by the rack-to-wall hydrodynamic pressure effects are within their load carrying capacity. Maine Yankee con ludes that there is no significant change to tne safety margin of the pool stratae from this effect.

t References 17-1 Building Code Requirements for Reinforced Concrete, American Concrete Institute, Standard ACI 318-63.

17-2 Maine Yankee Final Safety Analysis Report, Revision 10.

i I

i L:\\93mn\\93106 29

I

18. NRC Ouestion 18: It is stated that the new rack configuration does not affect existing SFP bundle drop structural considerations. Describe briefly what the previous bundle drop analysis consisted of. Discuss Maine Yankee's fuel handling experiences including adverse incidents such as dropping and damaging the fuel assembly, if any (Page 4-4).

Maine Yankee Response: In support of the 1982 design change which installed the existing spent fuel storage racks, an analysis of an accidental fuel assembly l

drop was performed. This analysis assumed that a consolidated fuel assembly was dropped from a height of 198 inches above the spent fuel pool liner (18 inches i

above the top of the existing spent fuel storage racks). The analysis additionally assumed that: (a) the assembly was infinitely rigid, (b) that the assembly drops at such an angle that the lower end fitting contacts the liner, and (c) that the liner is penetrated. The depth of penetration into the spent t

fuel pool concrete mat was conservatively calculated as 2.43 inches by using the modified conservative NDRC Formula for penetration of concrete by a missile.

This depth of penetration, and its consequences, were concluded to be bounded by Maine Yankee's original licensing evaluation of a 100 ton spent fuel shipping l

cask (18 inch penetration, 2 to 5 gpm leakage; reference, Maine Yankee FSAR).

i lt is therefore concluded that, since the fuel design parameters influencing the results of the assembly drop have not changed, the results of the fuel assembly dro) analysis remain valid for the installation and operation of the proposed rac(s. It is additionally concluded that since Maine Yankee has only one fuily consolidated assembly in the spent fuel pool, with no further plans for consolidation of additional assemblies, the use of a consolidated assembly in this analysis adds significant conservatism to the results.

j Maine Yankee's spent fuel pool fuel handling experiences have been excellent.

Within the past 10 years, there have been only two incidences of fuel damage l

attributable to handling problems. Both incidences are characterized as interactions between the fuel assembly and an operating piece of equiptment (eg; l

l either the new fuel elevator or the upender). Neither incident resulted in the release of radioactivity or the breach of the fuel cladding.

Maine Yankee has never dropped a fuel assembly.

The use of the proposed racks is not expected to change the manner in which Maine Yankee handles fuel in the spent fuel pool. The proposed racks will utilize the same procedures, tooling, equiptment, and processes as are currently in use.

i i

l I

I L:\\93mn\\93106 30 l

19. NRC Ouestion 19: No detailed quantitative information were provided in the submittal for the pool liner analysis.

Provide the following:

a)

Analytical approaches or methodologies, b)

Loading conditions, c)

Failure (tear and rupture) criteria, d) Material properties used including concrete bearing strength and friction between the pedestal and liner, and e)

A summary of the findings.

Maine Yankee Resoonse: Maintenance of the leaktight integrity of the '// thick austenitic stainless steel spent fuel pool liner was verified based on maximum horizontal and vertical support foot loadings generated by the detailed single rack time-history analyses.

(he governing case was for a 9x10 Region 11 rack for the (D + L + f + E') loading combination as defined in Table 3-1 of the licensing report. iherackmodulewastakenasfullyloadedwiththeassumed

• double-weight" consolidated fuel, with horizontal loading determined by the maximum friction coefficient case (

= 0.8) between the liner and the support feet.

The loadings imposed on the liner floor were conservatively taken as acting simultaneously at an individual support foot, without regard for the duration or time phasing of the loads, or for the specific foot location on the rack module. Thus, the governing case consists of the maximum vertical load at any support foot combined with the maximum horizontal loads at any support foot on the same rack module, treated as steady state loads on the liner. The liner was checked for vertical shear due to support foot compression, and tearing due to the scrubbing action of the horizontal load.

Per the discussion in Section 4.2.2 of the Licensing Report, no new evaluation of the liner is required for cask drop, spent fuel bundle drop, or drop of other items handled over the spent fuel pool, as the proposed reracking does not affect any of the parameters for the existing licensing basis regarding these topics.

Basic sizing of the rack module support foot was determined by consideration of the bearing strength of the reinforced concrete supporting the liner as defined in ACI 318. The concrete bearing strength was based on a conservative value of f) 3,000 psi, and p = 0.7 for direct bearing, ensuring that the concrete does not crush under the rack foot and that the liner remains supported.

Final layout of the fuel rack modules in the pool accounted for the location of support feet with respect to liner seams and other discontinuities in the pool floor Figure 19-1).

Support feet located within one diameter of a liner seam were provided with bridging plates to distribute the load over a larger area on either side of the seam and not bear directly on the weld. The bridging plates also preclude any potential for shearing through the liner over leak chase channel locations.

The leak chase channels, shown in Figure 19-2, provide a l

redundant watertight boundary at liner seams, and provide attachment to floor anchors embedded in the concrete structure.

Maximum compressive stress on the liner is 1,843 psi; maximum shear stress in the liner is 7,450 psi; and the maximum stress intensity in the liner due to the governing load case is 15,000 psi. Based on a specified minimum yield point of 30,003 psi for Type 304 stainless steel, it is concluded that the leaktight integ-ity of the fuel pool liner is maintained.

L : \\93mn\\93'.0E.

31 1

t I

I r

FIGURE 19-1:

l Fuel Pool Floor Liner Seams I

i

\\

1

~

,c,tc i

r I

=-

==

=.

,s,cn

,o,o

,o,o

.c ei j

1 i

H i

~.

O Uu a

t I'

i t

f 1

1 1

?--

t l

I t

i 3

3 s

1 1

1

.I i

l I

i.

5

[

.o I

u; 1r

-T 9

,o,o

,o,e 0,9 l

.e,4 0

N

..'b l

l u

h 1

h 9

~

( f f

1 V

l I

. L l

g 6

}

/

j g

4 l

_J su

~)

• T k

",O,.

6--

U 1.-

q z

.y I

y t/)

r s

h h

}

l k

i i

I

'I

/

\\

i h

i l

1 1

I i

i i.

<=

,9,

-o ane

- ogse se i>

Dd e

}

f 4

i i

~i)

(d i

n I

1

\\

)

l l

am -

Ig.oA-

!O w-sex cme mocasoc A PENELD FOR RAL.

i

~~

/ v u,, n. n m._...

..I-

.y w w

r

\\

c J, f.

E.:.1 J[

E. -'id '** "f"'

,, s L

N f

i gy

- v Ex w

g yi. 3 3 LJ x 4 3 N;.,. :..

.'g T... -

i..;,rr

[

wp 8.l tl l

!!*io x l{*co x j'Tu K --

k"

'b'O kAIN WA5WER HEX 500 tt0 SCR 1, =,= =

1

).10 Aj.00 X k.THK cocaTt uw LEAD WASWER in sNacs TYP GTAIL G RCCR ANCMCQ i

1 l

l FIGURE 19-2:

Leak Chase Channel & Floor Anchorage

~. _ _ _ _ - _

1 i

20. NRC Ouestion 20: Describe a plan, specifications, and procedures for the post l

operating basis earthquake inspection of fuel rack gap configurations. Provide a justification as to why such specifications including tolerance are adequate.

t Maine Yankee Response: Maine Yankee currently has in place an Abnormal Operating l

Procedure (A0P 2-41) which is designed to identify and define the steps necessary to place the plant in a safe condition in the event of an earthquake.

This A0P also provides for the post-earthquake walkdown initial reviews and inspections of key areas of the plant by the plant operators and the onsite nuclear safety engineers. Additional detailed inspections by at least two Senior

'i Titled mechanical / structural engineers, per the Yankee Atomic Electric Company procedure MYPTP-12, are directed by A0P 7-41 under specific circumstances as j

defined by either the magnitude of the earthquake or the indication of seismic i

damage as defined in Reference 20-1.

j i

While neither AOP 2-41 nor MYPTP-12 specifically include the post-earthquake measurement of rack-to-rack or rack-to-wall gaps, both procedures require inspections of the Fuel Building and Spent Fuel Pool areas for seismic damage l

indicators in equiptment, structures, piping, supports, etc.

In order to ensure that the spent fuel pool rack ' a-rack and rack-to-wall gaps are maintained in a post-earthquake situation, Maine Yankee commits to modifying l

the detailed inspection procedure, MYPTP-12 (Engineering Evaluations Following i

an Earthquake at Maine Yankee), to include examination of these gaps.

This procedural modification will be com)1eted prior to the installation of the proposed racks in the spent fuel pool.

Reference 20-1 Electric Power Research Institute Report NP-6695, " Guidelines for Nuclear Plant Response to an Earthquake".

l l

l i

l 1

l L:\\93mn\\93306 32 l

l l

1 l

l l

l ATTACHMENT A

SUMMARY

OF SYNTHETIC ACCELERATION GENERATION EFFORT Calculation NYC-905 (Pages 243-277) l l

l l

NOTE:

This Attachment is being provided in support of the answer to the NRC Question 1.

L:\\93mn\\93106 33 i

l