ML20094C117

Submits Addl Analysis & Clarifications Re Spent Fuel Pool Rerack Structural Mods,In Response to Concerns Raised at 840725 Meeting

ML20094C117
Person / Time
Site:	Summer
Issue date:	07/31/1984
From:	Dixon O SOUTH CAROLINA ELECTRIC & GAS CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
NUDOCS 8408070373
Download: ML20094C117 (5)

Text

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Jc SOUTH CAROLINA ELECTRIC & GAS COMPANY

.05T OFFICE 764 CotuusiA. south CAROUNA 29218 O. W. DimCN. Jn, sve$n$.'"O,..IT[o;,

July 31, 1984 Mr. Harold R.

Denton, Director

' Office of' Nuclear Reactor Regulation U.S.. Nuclear Regulatory Commission Washington, D.C.

20555

Subject:

Virgil C.

Summer Nuclear Station Docket No. 50/395 Operating License No. NPF-12 Spent Fuel Pool Rerack Modification Structural Concerns

Dear Mr. Denton:

On January 28, 1984, South Carolina Electric and Gas Company (SCE&G) submitted a proposal to rerack the existing spent fuel pool at the Virgil C. Summer Nuclear Station.

A meeting was held on July 25, 1984-between SCE&G and several members of the Nuclear

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Regulatory Commission Staf f to address Staf f concerns.

As a result of this meeting, SCE&G was asked to supply the following additional analysis and clarifications.

The first question requested further clarification on the dropped

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fuel accident.(Dropped Fuel Accident II) referenced on page 6-25

-of the January 28, 1984 submittal.

One fuel assembly is dropped from an elevation of 36 inches above the rack and hits the top of

-the. storage location with a velocity of 114 inches per second.

This -impact produces a longitudinal stress wave of amplitude

'16,412 pounds per square inch.

An energy balance between the

. kinetic energy of the dropped assembly and the plastic strain energy ofzthe rack panel shows that 2.11 inches of the top of the panel will be plastically deformed.

The active fuel is located approximately 21 inches below the' top of the rack.

Therefore, over 18 inches of undeformed panel separates the dented zone from

'the active fuel zone.

This indicates that the subcriticality of the stored fuel will not ba compromised.

The second question requested'further justification and clarification on the hydrodynamic coupling mass assumption used

-in the structural analysis.

The fuel assembly is modelled as a blunt square' body inside a square cross section container.

The hydrodynamic coupling mass utilizes Fritz's well known correlations for infinitesimal motions.

Inclusion of finite amplitude motions (which is the case for a rattling fuel

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assembly) is known to significantly reduce the peak rack seimnic c

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iSpent:Fual; Pool Rsrcck-

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Pagel62 y,4'

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tresponsei(reference,. " Dynamic Coupling in a Closely Spaced Two

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Body;systemlVibrating in a Liquid-Medium," by'A. I.

Soler and K.

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PE Singh, Proc. of the' Third Intertational Conference on

Vibration:in Nuclear Plant, Keswick, U. K. 1982).. Therefore, 1Fritz's ' equations. used in the analysis lead to an upper bound on c

thefoolution.

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LThelthird ~questionirequested that further plant specific analysis

be performed to demonstrate the convergence of the structural-

analysis. IRack/A!(ll;x ll, Region 1 module) was run on the

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. fourteen degree-of-freedom (DOF) model of' the rack (coefficient Lof,frictionfd= 0.8,--all locations occupied).

The results, L tabulated 'in - Attachment' l for three discrete time steps, show Kj

convergence.. The 32 DOF solution presented in the Janaur-1 28,

'1984:submittalishows the' maximum x and y displacements to be 0.78 v'

, inches and'0.86 inches, respectively.

Therefore,-it can be noted that the 32'DOFLsolution~and 14.l>1F solution are in close agreement.

w-L.TheLequations of motion-in'both models follow identical

procedures, namely-(1). write the contributory terms of kinetic 3 energyL for the1 rack,L fuel-assemblies, and fluid coupling ef fects,

'(11) use: Lagrange's; equation of motion:to obtain dynamic equations of equilibrium, (iii) establish the coupling ratios of

.allfbeam,2stop and. friction springs,-(iv) promultiply the matrix equation byfthefinverted nass matrix to diagonalize the mass

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. matrix,Jand -(v)1 solve the resulting equation ' set using the Leentral difference scheme.

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The' chief distinguishing feature between the two models is the absen'e of rotary / inertia' degree-of-freedom equations in the 14 c

.DOF.; The~32.DOF model.has rotaryLinertia equations.which forces o

- th'e'use of very small time steps., This complicating attribute of x

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rotary rinertiafis fwell documented -in the -literature, ' for example.

"...In mary cases,1the rotational inertia contributes very little

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Eto the: total. kinetic energy.

In addition, it complicates a

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1 subsequent 1 dynamic analysis by' adding l rotational

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degree-of-f reedom1to,,the problemiand by ? adding high frequency terms-toithe' response computation.

The'latter are particularly tundesirablelif,the subsequent dynamic analysis is done using the

-step-by-step central 5 difference. approximations, since the time

... f steps used then-become very'small..." - (reference, " Component 1

f Element -Method 'in Dynamics," 4 Levy and Wilkinson, McGraw Hill,

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1976,cpage?l69.)-

JThe similarities'and differences between the 32 DOF and 14 DOF i olutions.are further' summarized in Attachment 2.

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y iMr.fHarold RS~Denton;

.'. ;g iSpentiFue10 Pool Rerack

) Structural Concerns

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JJulys31, 1984.

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iAs' discussed.'in the July-25, 1984 meeting, SCE&G is currently

'scheduledito begin the first refueling outage for the Virgil C.

t Summer. Nuclear Station-in September'1984 coincident with core

depletion.. To-prepare for this upcoming outage, SCE&G has farranged to begin ~ receipt of the 'new spent fuel pool storage racks;inlthe first week of August 1984.

After this initial shipment,.the. remaining racks are scheduled to arrive at weekly N

Jintervals through mid-September.

This schedule allows for full

.4 11nstallation'of all the racks-at the time refueling operations

. c o m m e n c e.L M As. stat'ed ^1n previous submittals on this issue, an expeditious

Staff resolution.to these. final concerns is required to support T'? '

iSCEEG's' proposed reracking modification schedule.

Also as

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discussed.previously,= performing'~this-modification before first refueling'.is extremely important because of the safety and reconomic benefitalderivable at--the.present_ time.

Because the Espent fuel pool:-is empty at' present, radiation doses are ALARA

.now-and will increase significantly after.first refueling.

Additionally,-commitments'have been formalized with the State of s

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.iSouth Carolina requiring SCE&G to make all reasonable efforts to-Tprovide-lifetime onsite-storage of our spent fuel.

Therefore we Lstill consider it'to be in the best interest of the general

• 4 fpublic a'nd-SCE&G.to rerack.the spent fuel pool before first a:

G-Trefueling.

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(i (Iti-is our. understanding that the' questions'and' responses n

contained herein resolve'thel final-Staff concerns on this issue.

Yourgexpeditiousireview and

cooperation'with our schedule on this LitemLis. appreciated.-

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Very truly yours,.

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Summer C. A.

Price

T. C.iNichols,.Jr./O. W. Dixon, Jr.-

C. L. Ligon (NSRC)

W E..yH.' Crews,.Jr.

K.~E. Nodland S

- E. ~ C.. Roberts -

_ R.-A.

Stough

W..A.-Williams, Jr.

G..Perciva1 iD JA.VNauman' C. W.

Heh1

,33 e J.1P. - O' Reilly.

J.

B.

Knotts, Jr.

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(Group Managers.

H.- G. Shealy

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O. S.-Bradham-NPCF

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d ATTACHMENT I

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14 DOF RESULTS-i, Time ' Step, Maximum' Maximum X-Displacemente Y-Displacement L(seconds)1 (inches).

(inches)

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' 0003 0.829 0.853 0002' 0.630 0.854 0001' O.829 0.854-

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c-7, ATDCHMENT 2 COMPARISON AND CONTRAST BE1 WEEN 32 DOF ANO 14 DOF MODELS Itan 32 DOF 14 DOF (i) ? Uses ccmputer code DYNAHIS Yes Yes

-(11).' Integration scheme is central Yes Yes difference (iii). Hydrodynamic coupling mass is ccuputed Yes Yes usirJ Fritz's equations (iv) %e analysis permits three dimensional Yes Yes

. motion of the structure (v) %e rack proper is modelled by 24 degrees-of-12 degrees-freedom (pg.

of-freedom 6-5 of Licensing (see reference 1)

Report)

.(vi) %e vibrating fuel asenbly group is Yes Yes permitted to have arbitrary x & y coordinates.

-(vii). %e fuel assembly group has 8 degrees-of 2 degrees-of-freedom freedom (viii) %e rack proper is modelled as a lunpal mass using a con-idealization sistent mass matrix (see Reference 1)

(ix) Structural Danping approximately approximately 2.5% of the 2.5% of the critical mass critical mass

-(x) credit for " form drag" No No (xi) credit for pinse lag between var'ious No' No rattling assembly groups

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'(xii) Credit for additional'danping in the No No

' fuel assembly (1) " Seismic Response of Free Standing Fuel Rack Construction to 3-D Floor Motion,"

. A.I. Soler and K. P. Singh, Nuclear Ehgineering and Design, (c.1984).

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