ML20244B139

From kanterella
Jump to navigation Jump to search
Containment Rock Overbreak/ Overexcavation Seismic Evaluation
ML20244B139
Person / Time
Site: Comanche Peak Luminant icon.png
Issue date: 09/30/1985
From: Hofmayer C, Philippacopoulo, Qingwu L
BROOKHAVEN NATIONAL LABORATORY
To:
Shared Package
ML20244B124 List:
References
FOIA-87-535 NUDOCS 8906120302
Download: ML20244B139 (20)
v • d • e


Text

. _ - _ _ _ _ _ _ _

Amom:- . ._

~ n 3

COMANCHE PEAK UNIT 1 CONT Altf1ENT ROCK OVERBREAK/0VEREXCAVATION SEISMIC EVALUATION By

- A J. PHILIPPACOPOULOS, C. HOFMAYER, L. OlNGWU C. J. COST ANiINO, C. A MILLER S. SHTEYNGART, M. REICH DEPARTMENT OF NUCLEAR ENERGY BROOKHAVEN NAT10NAL LABORATORY UPTON, NEW YORK,11973 SEPTEMBER 30,1985 e

e/a

  1. Sh kR hA B AUMAN /-535 - PDR p  ;

l . . -

- w. 2 T ABLE OF CONTENTS page Table of Contents... . . . . .. .. 2 1.ist of Figures... . .. . . .. . . . . . . 3 Abstrac t.. .... .. .. . . . . . . . .. . . . . 4

1. Introduction.. . . .. . . . . . . . S
2. Overbrake-Overexc.avation.. . . . ... 6
3. Model Description.. . .._.. . . . . . .. .. 7 3.1 Structural Model.. . . . . .. 8 3.2 Foundation Model.... . .. . . . . 9
4. Presentation of Results.. . . .. . .. 10
5. Conclusion... . .. . . . .. . ... 14

_ _ _ _ _ _ _ _ _ _ _ _ _ - . - - _ . _ _ _ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ - . a

_ . 3 LIST Of FIGURES Figure 1. Overexcavation Case Figure 2. Overbreak Case Figure 3. Schematic View of FLUSH T10 del Figure 4. Overbreak-Overexcavation Case Figure S. Floor Spectra Comparison. Containment internal Structure.

Figure 6. Floor Spectra Comp'tr$: 9n. Containment Building.

~ m 4 ,

l I

I ABSTRACT This report describes an investigation which was carried out for the Unit i Containment structure of the Comanhce Peak Nuclear Plant. The purpose of this investigation was to evaluate the potential effects of rock overbreak/overexcavation conditions on the seismic response of the containment structure. for this purpose, rock-structure interaction analyses were performed in which such conditions were assumed in the foundation. The report presents a description of the analytical procedures followed and the results obtained.

m n S 1.- INTRODUCTION Prior to the placement of the contair. ment building of the Comanche Peak Nuclear plant, some areas in the foundation were overexcavated and subsequently filled with dental concrete. Recently, it has been alleged that due to this overexcavation, the seismic response of the containment building may be effected. In response to this allegation the Nuclear Regulatorf Commission (NRC) requested Brookhaven National Laboatory (BNL) to perform an independent seismic evaluation with the objective of verifying by analysis the NRC Technical Review Team's conclusion that the excavation and repairs have had no safety impact upon the seismic response of the Unit 1 containment building.

The objective of this investigation was to evaluate the pctential l

effects of rock overbreak/overexcavation conditions on the seismic response of the unit I containment of the Comanche peak nuclear plant.

For this purpose, a rock-structure interaction analysis was performrd in which overbreak/overexcavation conditions were incorporated The analysis is based on the finite element method and utilizes the FLUSH computer code. A continuum type of analysis would be impractical for this l

particular problem since discontinuities in the foundation material must l

I

w _w _ . .. - u . - . s. - m e. w - m s

be accounted for, in order to simulate localized overbreak/overexcavation T.onditions.

A detailed mathematical model was developed and used to generate floor response spectra at several locations in the containment and internal structure, furthermore, response spectra were obtained at various locations in the foundation medium. The analysis was performed for a set of overbreak/overexcavation conditions. These cases were subsequently compared with a case in which no overbreak/overexcavation exist in the fWi)dation.

2.- OVERBREAK/0VEREXCAVATION The terms overbreak and overexcavation are used throughout this report for reasons of convenience. In particular, the term overexcavation is used to refer to the case of rock removal from below the containment mat and it is associated with the base-interaction between structure and foundattort This case is shown in Fig.1. On the other hand, the term overbreak is used to denote the case of rock removal from the sides of the containment. fig 2 shows the overbreak condition.

In the study reported herein, three types of configurations were considered. These are:

A a

a) Overexcavation case b) Overbreak case c) Combination of a & b cases l

As will be discussed in the following sections of this report, l-variations in assumed conditions in cases (a), (b) and (c) were considered in the rock-structure interaction evaluations.

1 3.- MODEL DESCRIPTION The general characteristics of the rock-structure interaction model used in this study are schematically shown in Fig. 3. The modeling procedures followed are of the FLUSH type, i.e., the structure and the rock y

foundation are directly coupled in a single linite element mesh. As shown in Fig. 3, the containment / internals are represented by a lumped mass

' stick" model. According to standard modeling techniques, _ a . pair of transmitting boundaries were placed at both sides of the mesh. In addition, viscous boundarles were used in order to account for radiation in the third dimension (i.e., out of plane). Finally, the size of the mesh in the vertical direction was kept small as compared with the wavelength of the S-waves at the frequency of interest (33 Hz). H' her frequencies such as 1

7 50 Hz may also be transmitted by the finite element mesh. The above are i

_ _ _ _ ___m.-_ _ ,____.-___mm__-- _ _ - - - . . - _ _ _ _ _ . _ _ ___._m-m__ ______m A

F

. )

Standard modeling procedures used over the last decade for FLUSH type 4

evaluations of building-foundation interaction.

-1 3,1- Structural Model in modeling the containment and internal structures of Unit 1 of the plant, the objective was to generate models similiar to those described in the CpSES Final Safety Analysis Report (FSAR). Based on this, the containment / internals were represented by a two-stick dynamic model similiar to that shown in Fig. 3.78-34 of the FSAR. The elevations of the lumped masses' were obtained from Table 3.78-9 of the FSAR.

Furthermore, the relative mass distribution which was assigned to the stick models of the containment and internals was obtained from Table 3.78-14 of the FSAR.

Thus, the type, geometry and mass distribution of the 1

containment / Internals model used in the rock-structure evaluations reported herein are based on information from the FSAR. Since the section properties for the beam elements of the containment / Internals model l

were not reported in the FSAR, they were obtained as follows. a) the internal structure was assumed to be rigid and b) the containment section properties were chosen so that a predominant frequency of approximately

{ .

1 3.4 Hz was obtained by the overall rock-structure model. The latter frequency is the first-mode frequency of the untracked model given ta the FSAR(see Table 3.78-31, sheet 1 of 2, FSAR). These assumptions are not considered critical for the purpose of this evaluation since we are only interested in observing changes in the building response as result of variations in the foundation conditions.

3.2- Foundation Model The finite element mesh used to represent the foundation medium extents.147 ft laterally from each side of the centerline of the containment and 173.5 ft below the ground surface. Since transmitting boundaries were placed at the sides of the mesh, the lateral dimension is more than enough for the purpose of the analysis. The vertical dimension of 173.5ft is more than two times the foundation radius and it is sufficient for the rock-structure model under consideration.

As shown in Fig. 3, a finer mesh is used near the containment mat so that overoreak/overexcavation conditions can be modeled. Horizontal layering was used which is associated with the profile properties given in Table 3.7B-3 of the FSAR. The shear modulus, Poisson's ratto and rass density for the Glen Rose 1.imestone above elevation 770 f t are:

. ---i 17' ,

u n m

- G 1.15x105 Kst, V =0.3 and q=150 pcf respectively. The corresponding 5

properties for the limestone below elevetion 770 ft are G=1.73x10 Ksf, V=0.27 and(=155 pcf respectIvely.

4- PRESENTATION OF RESULTS The model described above was employed to investigate the potentf al magnitude of the effect of overbreak/overexcavation conditions on the response of the Unit I containment structure. The variation of these assumed conditions was treated in a parametric fashion. Variations of the overexcavation depth in the range of 6 to 12 f t below the bottom of the containment mat were considered. Variations of the extent of the overbreak from 0 f t up to 40 f t starting from the sides of the containment mat were also considered.

The earthquake time history used at the surface of the foundation is the time history used in the FSAR (page 3.78-4, FSAR). It has approximately a 10 second duration with a time step equal to 10 msec.

L for simplicity, the acceleration time history was normalized to 1.0 g.

1' Using deconvolution the input motion at the base of the rock-structure interaction model was obtained. The deconvolution was performed also using the Ft.USH code. Finally, a hysteretic rock damping equal to 5 E was

  1. _ -2. .__ _ _ _ . _ _ , , . . _ . . _ . _ , . , . _ _ _ _ . ___

1 used in the response evaluations. The assumption of the hysteretic rock damping value is considered reasonable for these rock types and is not considered to be critical since it was kept the same in all computations  ;

with the FLUSH code. Computer runs with 2% hysteretic damping for the rock were also made. As expected, no change on the floor spectra was noted.

Preliminary computer runs were made by assuming the superstructure to behave as a rigid body. In these runs, large values for the section properettes of the stick models were assigned in order to numerically simulate nonflexible behavior. This was done in order to evaluate the ability of the model to reproduce the interaction frequencies.

Subsequently, the section properties discussed in section 3 were used for the superstructure model and the following computations were made using the FLUSH code a). Response computation without overbreak/overexcavation condition in the foundation (basic case).

b). Response computation by assumino different overbreak/overexcavation conditions in the foundation (perturbation cases).

Response spectra were generated at various location in the model. In l all FLUSH computations, F ourter transf ormattons were periormed ior a p

l

n n 15 total of 2048 points. In the computations of the structural response for the overbreak/overexcavation conditions considered, the elements in the FLUSH model associated with t.hese conditions had a Young's modulus equal to 0.txiO5 psi. The later value was decided in order to represent a granular material. The corresponding Young's modulus of the dental concrete is much higher.

The following perturbation cases were considered.

CBSft Condition A overexcavation B overbreak in one side of containment C overbreak in both sides of containment D overexcavation plus overbreak in one side of containment E overexcavation plus overiveak in both sides of containment Floor spectra comparison between the basic and the overbreak cases indicated that the overbreak condition has no effect on the response of the containment building. This result was confirmed by means of approximate calculations which provided a bounding estimate to the effects of rock l

overbreak on the frequency of the containment-foundation system.

Floor spectra comparison between the basic case and a " worst

  • type of
3

=.' .

combined overbreak/overexcavation case are shown in Figs. 5,6. The later case is schematically shown in Fig. 4 The floor spectra comparison shown in Figs. 5 and 6 are for the nodes 111 and 117 respectively. These nodes represent the following locations in the FLUSH model.

Node Location i11 top of internal structure 117 top of containment structure in Figs. 5 and 6, the solid line represents the result from the basic case whereas the symbol + represents the corresponding result for the overbreak/overexcavation case shown in Fig. 4 Similiar floor spectra comparisons at other locations in the model were obtained. Based on such comparisons for the overbreak/overexcavation conditions considered in this study, it was concluded that the later conditions had no safety impact upon the seismic response of the containment building.

l l l 4

)

l - - _ _ -_-_-____-_ _ -

5.- CONCLUSION A series of computer evaluations using the FLUSH code were used to evaluate the potential effects of rock overbreak/overexcavation on the seismic response of the Unit 1 Containment building. These results were in part also conittmed by means of approximate analytical procedures. The conclusion is that for the overbreak/overexcavation conditions analysed, no effect on the building response was noted.

I i

e

.g ? 63f) o )

ev ~[.4 9*

  • ,o"#

g y_ IMAGE EVALUATION b, t /

pJ.9gjf /f4 j/ / 9.[ kgfs#

//o TEST TARGET (MT-3) p,,,,\'W/'

{+,,,, f'

[ fj;f ll!!!$$

l,1

[ ' UM l18 I.25 I.4 i.6 4 150mm >

4 6" >

Y A,,,?y%///// ,/

/so,,m////p 4 y .

o ,:(f5j'

,p

~

r .. ------_m

o) 6 41 W@9 )h 9 IMAGE EVALUATION .&%

t b l $f// TEST TARGET (MT-3)

///// / f).jf /g, N \/,// '

sy,,, %f> lfs f9

+  %

l.0 lt S W t Lt

.. w

!U M E

j!J1 1.25 1.4 l ig 4 150mm >

4 -

6" >

w/s >,s.  ?%y, <$ 4

~

.ea,e

,p ,qe 0

,(p

~ .

^~- ___ ___

q;/h E O o

W(), ' d ' IMAGE EVAL.UATION dh

////

4p TEST TARGET WT@

pppp

/

_ b [;!i lllllM m ~

1.8 sais 1.25 1.4 1.6 4 150mm >

d 6" >

&~  %

A g;g? *4,, 4 ?4 sp3////p y//

v O #p2 V'

,y

c. ,
. ;,, .e
w. . h. m l

l

'Vxd FIG.1 Overexcevetion Case 1

1

_z ._ . _ _ . _ _ ,_

_j, ;i s ,) l . . . . . .

6

[ ..

A. n 4

i:-1 4 I

l i

h

( ~.'

i.

f e e FIG. 2 Overbreak Cese

e, n II B

4>

containment internels

(>

transmitting boundery 4>gg (both sides) gp n n MF Ya finer mesh rock discretization FIG. 3 Schematic View of FLUSH Model i

1 i

l l

IE O m B

i f I I bb#A $

i  :

C A= 12 FT 8:40 FT C=23 FT FIG. 4 Overbreek/Overexcavetion Case

- - . _ _ - _ _ _ . . - . _ _ - _ _ _ - _ _ __ - _ . - _ _ _ _ _ - _ _ _ _ _.___-__.__m-_-.._-.--__m___ .m_____-_____ . _ _ _ ____.__----__.._--__m._- - _ _ - _._____ -

n 6 29 j 1

i l

NO OVERBREAK OVERENCAVATION WITil OV ERHRE A K OVI'RENCAV..\ TION c D A M Pl NG: 5~i N OD C .\ 0.: 111

. - . +. -.. ------ s. -- e . s_..., ,

.------.._..n...._..

o .o s

- 4 i

z

  • 4 O

E.3 ,

.._...._1_..___..-.d,..-.-..._.-......._........_.

k ,. .

= I t .-

% N 1 .

k r .. ,

C.

U i 4 1

5 Uc + . --,--.-.1.-.. .__

7.-_.__._.._______.-. . _ ,

4

=

i ,

lli I

,,'f 1( 10 t

1(f TREQl'ENCY (CPS) l l

FIG. 5 Floor Spectra Comparison. Containment Internal Structure L-__ __--- - -- --, - _ -

- - =  % - .. . , _ . . . . .. . . _ _ . . . . . .,

t

- ^ 20 1

4 SO OVERBREAK OVI:RENCAATION

-- WITil OVERBREAK OVERl:NCAVATION 117 -

D AhiPl SG: 5~ NODI: NO.: ....._. . _ . .

=.,.

Cl._I f

d

+ -

n g _,. _

C x

C- . - - . . . - . ..

pg. . _ _ - -

~

1 h'

h: i N

Y

. -. ._ .. f.

- . _...\ . _ . - . . . _

f., _ - - - _ .

s

'n~~.-. a

?

+

w

=_ - _ , . ,

10' Kf 10" 1Cf T' REQ 1 ENCY (CPS)

FIG. 6 Floor Spectra Comparison. Containment Building-

- - _- _ _ _ _ - _ _ - " ' _ - - ------_%, _ _ _ . _ _ _ , , _ _ _ _ _ _ - - - - - " ^ ' - - - - - - _ . - - _ _ _ _ _ . , _ _ ___,

Retrieved from "https://kanterella.com/w/index.php?title=ML20244B139&oldid=3107816"