IR 05000260/1989062

Insp Rept 50-260/89-62 on 891109-1213.No Violations Noted. Major Areas Inspected:Design of CRD Housing Lateral Restraint,Design of Restraint Beam Assembly & Calculation of Equivalent Spring Constant K1 & K2

ML20011F502
Person / Time
Site:	Browns Ferry
Issue date:	02/13/1990
From:	Cheng T, Terao D Office of Nuclear Reactor Regulation
To:
Shared Package
ML20011F497	List: IR 05000260/1989062
References
50-260-89-62, NUDOCS 9003060145
Download: ML20011F502 (11)

Text

.._

_

-

_.

_

_

_

_._.

ll

,-

..-

~

'!( -

%,

UNITED STATES

+

-

NUCLEAR REGULATORY COMMISSION i-S WASHING TON, D. C. 20H6 j

y

%,,....+

.

>

UNITED STATES NUCLEAR REGULATORY COMISSION OFFICE OF NUCLEAR REACTOR REGULATION

!

TVA PROJECTS DIVISION

!

Report No.:

50-260/89-62 l

Docket No.:

50-260

i Licensee:

Tennessee Valley Authority

,

6N 38A Lookout Place

,

1101 Market Street

-

Chattanooga, Tennessee 37402-2801

_

Facility Name:

Browns Ferry Nuclear Plant, Unit 2

,

Inspection At:

1. Browns Ferry Nuclear Plant Site

!

Decatur Alabama

{

2. General Electric Company

'

San Jose, California

Inspection Conducted:

November 9 - December 13, 1989 Inspector:

ff I Y[/Mfo

Thomas P. Cheng, Team peader Date

'

i Consultant:

Tom Tsai Approved By:

/ O

'

David Terao, Chief Date Engineering Branch TVA Projects Division Office of Nuclear Reactor Regulation

-

f.Of0kOkib! 00 5g0

,

.0

-

- - - -

-

-4

--,,.,,,

4-

-..,------,

e

---m--..

,.-, - - --

.

..

-

-

-

-

--

.

. - -

.

y

,. :

[0

,.

,.

,

n

.

.

!

SPECIAL INSPECTION

'

"j !

RELATING TO BROWNS FERRY UNIT-2 SEISMIC DESIGN PROGRAM h

e

l

INTRODUCTION AND BACKGROUND As. documented in NRC: Inspection Report (IR) 50-260/88-38, dated April 19, 1989

]

(Reference 6.1), the staff conducted its first inspection of the Browns Ferry

-

Nuclear Plant Unit 2 (BFN-2) Seismic Design Program at BFN-2 site in i

.Decatur, Alabama..A total of 32 items were identified as summarized in

Enclosure 3 of IR 50-260/88-38.

One of these 32 items (CSG-9) concerned the potential impact of the newly generated amplified response spectra (ARS),

based.on the updated building model, on the existing evcluations of systems

"

and components, including the nuclear steam supply system (NSSS).

TVA committed to complete its evaluation of this item before the restart of BFN-2.

.

During the meeting held on January 5,1989 (Reference 6.2), TVA stated that the impact evaluation of the primary components of the NSSS (including the reactor pressure vessel (RPV), the reactor internals, and the RPV support) will be completed using time' history analysis with the El Centro 1940 earthquake

ground motion time history as input.

Furthermore, the evaluation would use damping ratios as described in the finsi safety analysis report (FSAR) and the

'

newly developed dynamic model of the primary system.

The staff found this approach acceptable.

TVA also explained that Bechtel Power Corporation (BPC),

L TVA contractor, would perform the seismic analysis using the updated detailed

,

primary system model provided by General Electric Company (GE), the other TVA contractor, coupled with the reactor building model to calculate the seismic s

loads (shears, axial' forces, and moments).

GE would then use these loads to-E complete its impact assessment of the NSSS components.

On April 24-25, 1989, during an inspection at GE offices, the NRC staff iden-

-

tified a modeling error in the NSSS seismic analysis which was performed as

,part of the licensee's restart activities.for BFN-2.

The error involved assuming the existence of seismic lateral restraints on the control rod drive (CRD) housing in the seismic analysis model when, in fact, none was installed

.

L I-

.at Browns Ferry.

The issue was identified as an unresolved item (URI 89-31-01)

L in NRC IR 50-260/89-31, dated July 17, 1989 (Reference 6.3).

In addition, the staff identified two other open items (buckling evaluation of RPV support and redocumentation of Appendix J to the FSAR) that had to be resolved before the restart of BFN-2 (IR 50-260/89-31).

L The inspection conducted during the period August 14-16, 1989 (IR 50-260/89-39)

found that the three open items previously identified were still open.

"2 PURPOSE AND SCOPE

_

'The purpose of this inspection was to review TVA's responses to the three open items identified in IR 50-260/89-31 and IR 50-260/89-39 (Reference 6.4):

.(1) justification of the methods used for the evaluation of the NSSS components, including the evaluation results based on the new ARS; (2) redocumentation of Appendix J of the FSAR; and (3) the design adequacy of the new CRD housing support modification.

In addition, this inspection also covered the staff's concerns about the potential buckling of the RPV support skirt and_the effects

,

of the new CR0 housing support system on the existing ARS generated for the CRD piping analysis and design.

- -

.

-

-

,' ';;

q

$/

.

.

(

'3-REVIEW FINDINGS'

On November 9, 1989, the staff and its consultant conducted the third inspection-of the seismic design adequacy of the BFN-2 NSSS components at the plant site in Decatur, Alabama. The attendees of this meeting are listed in Enclosure 1.

,Because of the complexity of the issues, the staff review and discussions

>

-between the staff and TVA continued after November 9, 1389, and-the exit

.

meeting was not held until December 13, 1989.

The attendees of the exit meeting are listed in Enclosure 2.

The following paragraphs document the staff's inspection findings and conclusions,.

3.1 Design of the Control Rod Drive Housing Lateral Restraint

.

As stated in IR 50-260/89-39, the staff concluded that the conceptual design of the CRD housing lateral restraint is reasonable, and TVA agreed to provide the final design results, the feasibility study, and the impact evaluation of the new CRD housing restraint on the existing ARS to be used in the subsystem evaluation for the staff review.

During this inspection, the staff and its o.

consultant reviewed this information, and the subsequent findings and con-clusions are summarized below:

(1) Design of the Clamps Design loads included dead weight, safe shutdown earthquake (SSE) seismic load, normal operating thermal load, and loss-of-coolant accident (LOCA) thermal load.

Using an installation condition temperature equal to 80 degrees F as the reference temperature, the thermal loads were determined based on the following temperatures:

CRD Housings Restraint Beams Pedestal Wall Normal Operating Condition 150 degrees F 124 degrees F 124 degrees F LOCA Condition 250 degrees F 250 degrees F 124 degrees F The source for the 250-degree F LOCA temperature is GE Specification 257H346.

TVA Document B22 891227 201 shows that GE used this LOCA temperature in the design of 919D260 model CRD housings for 14 domestic licensed plants, in addition to BFN Units 1, 2 and 3.

The staff found the source acceptable.

The final design for the CRD housing clamps is documented in TVA Calculation B22 891202 129.

The calculation is based on the same stress limits specified in ASME Code Section III, 1965 edition, that were used in the design of the CRD housings.

The staff consultant found that the design used appropriate load combinations and allowable stress limits; the design calculations are therefore acceptable.

(2) Design of the Restraint Beam Assembly The design of the restraint beam assembly is based on the long-term criteria for miscellaneous steel as specified in TVA design criteria BFN-50-C-7100, Attachment G.

Design loads included dead weight, SSE seismir: load, normal operating thermal load, and LOCA thermal load.

To determine the load h

i

l

.

-.

-.

_

-

.n

.-

M

'

.;

.

.

.

distribution and stress in the restraint beams, a finite element analysis was-performed using the structure analysis computer code ANSYS.

In the finite element model, each individual unit of CRD housing flange and clamp is represented by an equivalent spring having a stiffness value of 2.5E6 lb/in.

The equivalent spring constant is based on GE test data.

Thermal loads were

. determined based on the same temperature data that were used in the design of the CRD housing clamps.

The staff consultant reviewed the design calcu-lations and results shown in TVA Calculation B22 891202 133 and found them acceptable.

(3) Calculation of Equivalent Spring Constant Kt and K2

!

The seismic model TVA used in the ARS generation includes-two lateral spring constants, K2 and K, to represent the effect of the CRD housing lateral

,

restraint system.

K1 is the equivalent sprfng constant representing the lateral stiffness of the restraint beam assembly.

K

,

2 is the equivalent spring constant representing the overall lateral stiffness of the CRD housing flange / clamp network.

GE performed a finite element anlaysis of the restraint system using.the ANSYS code in order to derive the equivalent spring constant.

The derivation included the effect with and without the thermal preloads.

In order to develop a-set of spring constants (K3 and K ), various-theories and

-

methods were used.

For derivation of Kt the mid-span theory wastused in addition to the finite element analysis.

For derivation of K, four different

equivalence bases were used, namely, global strain energy, local strain energy, global frequency, and local frequency.

Each individual housing flange / clamp unit in the analysis model was represented by a spring having an equivalent stiffness equal to 2.5E6 lb/in, which is based on GE test data.

Because various theories, assumptions, and methods were applied, a range of spring constant values were calculated.

The staff consultant reviewed the theories, assumptions, methods and calculation results for Kt and K2 as shown in TVA

-

Document B22 891202 133, Appendix E, and found them reasonable.

These Kg and K2 results were compared to the-spring constants used in the existing seismic model which TVA used in the ARS generation for the primary system, as follows:

Ki (1b/in)

K (lb/in)

-

Calculated Results 2.38E6 to 4.94E6 0.63E7 to 1.55E7 e

Existing. Seismic Model 2.37E6 1.51E7 The spring constants in the existing seismic model represent the lower bound-for K1 and the upper bound for K.

The staff expressed a concern about the

y possibility that the ARS of the primary system could be sensitive to the variation of Kg and K.

To resolve the staff concern, GE performed a

sensitivity study.

The staff finding on the effects of these new spring constants to the existing ARS is discussed in Section (5) below.

,

_ ___ _ __________

--

--

__

.

.

,

.

(4) Feasibility Study TVA Document 822 891206 910 evaluates the safety impact of the permanent installation of the CRD housing lateral restraint clamps and beam assembly and

concludes that the installation will not impact the safety function of the

CRDs.

Further, installation of this assembly will limit the lateral vibration of the CRD housings and insert / withdrawal piping, resulting in improvement of the structural integrity margin.

The staff and consultant reviewed TVA's u

safety impact study and concur with the TVA conclusion regarding the accept-ability of the lateral restraint system as a permanent installation.

(5) Adequacy of Existing Amplified Response Spectra

-

According to Section (3) above, the calculated values of K1 and K2 vary by a factor of more than 2.0 from the lower to the upper bound, while the spring constants in the existing seismic model is near the lower bound for K 1 and near the upper bound for K.

The staff was concerned that the ARS generated

from the existing seismic model could be sensitive to the variation of the spring constants.

To address this staff concern, GE performed a sensitivity h

study for the ARS at the lower ends of the CRD housings (represented by Nodes 17 and 63 in the existing seismic model).

The input motion is the North-South

<

component of the response motion at the RPV bottom head (Node 98) calculated on the existing seismic model.

Three different combinations of K1 and K2 were taken into account:

Case (1) - lower bound Ki and upper bound K2 (existing seismic model); Case (2)

upper bound K

-

1 and lower bound Kg; Case (3) - lower bound K and lower bound Kg.

The results presented in TVA Document B22 891227 202 indicate that Cases (2) and (3) produced the lowest and the highest ARS

-

peak, respectively, at the CRD housing frequency around 13 to 15 Hz.

However, the amount exceeded in the ARS peak of Case (3) over Case (1), which represents the existing seismic model, is less than 10 percent.

Based on this result, the staff concludes that the ARS that TVA previously generated for the primary system is reasonable for the analysis of CRD piping, and the concern about the sensitivity of the primary system ARS to the variation of K and K2 is

therefore resolved.

3.2 Reactor Pressure Vessel (RPV) Support Bucklina Evaluation In IR 50-260/89-31, the staff expressed a concern about the potential of buckling of the RPV skirt support.

During the first inspection, GE stated that there is only one 18-inch diameter opening on the RPV skirt.

The center of the opening is about 17 inches above the bottom of the skirt.

The skirt is 230 feet in diameter, 60 inches in height and 1-1/4 inches in thickness.

GE confirmed the stability of the skirt against buckling using two different methods.

The first method is based on the classical theory of cylinder

-

buckling.

A stress concentration factor of 3 was used to account for the effect of the opening.

The second method is based on ASME Code Case N-284.

The results are documented in GE Calculation DRF B11-00457, Index B10 (dated August 11,1989) and Index B14 (dated August 14,1989).

The results from both methods showed that the skirt is adequate against buckling because the resulting stresses are within the ASME Code Case N-284 limit.

The staff found the results reasonable.

Therefore, this item is closed.

_

-

!

L

--

..

.

..

.

.

_

,0'-

j

.

.-

,

l 3.3 LRedocumentation of Appendix J to the FSAR l

-

Through the letter from M. Ray, TVA, to NRC dated June 23, 1989, TVA resubmitted Appendix J to the FSAR to NRC.

Therefore, this item is considered closed.

-4'

CONCLUSION Based on the review findings discussed in Section 3 above, the staff reaches the following conclusions:

(1) The methods used for the evaluation of the NSSS components and the

,

evaluation results are reasonable and accepteble.

(2) Appendix J to the FSAR has been adequately redocumented.

(3) The results of the RPV support buckling evaluation are acceptable.

-

(4) The ARS generated based on the original'CRD housing restraint model_are reasonable and suitable for the evaluation of the attach 9d piping and components.

(5) The final design of the CRD housing restraint is considered acceptable.

(6) The feasibility study performed by GE/TVA for the housing restraint appears reasonable.

TVA DOCUMENTS AND CALCULATIONS REVIEWED 5.1 CRD Housing Lateral Restraint Evaluation (1) TVA Calculation for " Stress Analysis for the CRD Housing Lateral Restraint Clamps" (B22 89122022 129).

(2) TVA Calculation for "CRD Housing Lateral Seismic Restraint Beam Structural Analysis"_(B22 8912022 133).

(3) GE Calculation DRF-A00-03429, " Browns Ferry Nuclear Plant Unit 2 CRD Housing Response Spectra Comparison Study, December 20, 1989 (B22 891227.202).

(4) TVA Design Change Notice (DCN) No. W7792B (B22 891206 910).

(5) Letter from B. H. Keopke (GE) to J. Rochelle (TVA), dated December 17, 1989 (B22 891227 201).

5.2~ RPV Support Bucklina Evaluation

'(1) GE Calculation DRF B11-00457, Index B10, August 11, 1989.

-

-(2) GE Calculation DRF B11-00457, Index B14, August 14, 1989.

!

.

.-

.

...

.-

-

-

'

• :8

.

.

i'

..

.

.

.

"

"

6 REFIRENCES

,

6.1 Letter from B. D. Liaw, NRC, to 0. D. Kingsley, Jr., TVA, "NRC. Inspection Report No. 50-260/88-38," dated April 19, 1989.

6.2 G.E. Gears, NRC, " Summary of Meeting with Tennessee Valley Authority"(TVA)

Held on January 5, 1989 to Discuss Civil /Seismi'c Issues (TAC 00016),

dated March 22, 1989.

6. 3 Letter fror 9. D. Liaw, NRC, to 0. D. Kingsley, Jr., TVA, "NRC _ Inspection i

Report No. 30-260/89-31," dated July 17, 1989.

'

6.4 Letter from B. D. Liaw, NRC, to 0. D. Kingsley, Jr., TVA, "NRC Inspection-Report No. 50-260/89-39," dated Septemb.er 13, 1989.

..

F s

-

-

-

-

-

..

-.

.'

j

'

,

p

..

..

]{

a

,

-1i ENCLOSURE 1-BFN CRD HOUSING LATERAL RESTRAINT

!$

u

,

ENTRANCE MEETING ATTENDEES - NOVEMBER 9, 1989 i

' W. R'. Jackson-GE

'

J. A. Steininger GE

J. E.' Olin GE D.

K.- Henrie GE/ San Jose G. A. Deaver GE/ San Jose

'

Kenneth Ivey.

NRC/ Resident Inspector Ed Hartwig TVA/ProjectManagement J..K..Rochelle TVA-Civil -

Krys Gromek TVA-Civil-Thomas Cheng NRC Tom N. C. Tsai NRC Consultant Wayne Massie TVA BFN Site Licensing

.Jen R. Rupert TVA BFN/ Civil Ruoen 0. Hemcndez NE-Civil

,

L

l l

l l

l l

'

i

f

.,, -

,

..

...

.

.,.

ENCLOSURE 2-

.

>

BFN CRD HOUSING LATERAL RESTRAINT EXIT MEETING ATTENDEES - DECEMBER 13, 1989~

r

,

s Wayne A. Massie BFN Site Licensing t

,

Tom N. C. Tsai

~ NRC Consultant Thomas Cheng NRC-

.

Jerry Deaver GE-Engineering-Allen R. Smith GE-Licensing Barry Koepke GE-Engineering James K. Rochelle TVA-ME-Civil

,

-

- -....

.

,

.

c

February 16,-1990

.

Docket No.~50-260

,

Mr. Oliver D. 'Kingsley, Jr.

' Senior Vice President,. Nuclear Power-Tennessee Valley. Authority.

'6N'38A Lookout Place 1101 Market Street.

Chattanooga, Tennessee 37402-2801

Dear Mr.- Kingsley:

SUBJECT:' NRC INSPECTION REPORT NO. 50-260/89-62 Th_is letter forwards a' report on the results' of a _ special inspection of the Browns Ferry Nuclear Plant Unit 2-(BFN-2) NSSS component (reactor pressure vessel, internals, CRD housings, and support) seismic reevaluation program conducted at BFN-2 site in Decatur, Alabama on November 9, 1989,1and at General Electric Company's-(GE's) office in San Jose, California on December 11-13, 1989.- As a result of this-inspection, all the open items identified during the previous inspection were closed. Therefore, no further inspection on this program will be conducted by the. staff before restart of BFN-2.:

In accordance with Section 2.790 of the NRC's " Rules of Practice," Part 2, Title 10, Code 'of Federal Regulations, a copy of this letter and its enclosure

will be placed in the NRC Public Document Room.-

"

Should you have any questions concerning this inspection, please contact us, n

'

Sincerely, B. D. Liaw, Director

,

TVA Projects Division

,

Office of Nuclear Reactor Regulation

_ Enclosure:

_ Inspection Report 50-260/89-62 cc w/ enclosure:

'See'next page

• See Previous Sheet for Concurrence 70FC :TVA:EB"

TVA:EB/BC* :TVA:AD/TP" :TVA:AD/P"

TVA.

NAME ~ :Tcheng: kj

DTerao

RPierson

SBlack

BDLia

_____:____________.____________.____________:__________...____________.____________._________

E

' DATE :2/9/90

2/13/90

2/13/90

2/15/90

2A /90

0FFICIAL RECORD COPY

,

Document Name:

INSPECTION REPORT 50260/8962 e

_ _ _ _ _ _ _

_--_-_____.___-____-_---_--__-_-_._-______-_-_-.-__w

,

-

- -.

.

-%

.;

>

.

.

,

j i

Docket-No. 50-260:

.

'

Mr. Oliver DJ Kingsley, Jr.

.m

' Senior Vice President, Nuclear Power Tennessee Valley Authority;

'

6N 38A: Lookout _ Place

.

-

1101' Market Street

'

Chattanooga, Tennessee 37402-2801

.

.

DearMr.iKingsley:

SUBJECT:~ NRC INSPECTION REPORT NO. 50-260/89-62

,

This letter forwards a report on the results of a special inspectionf of: the Browns Ferry Nuclear Plant Unit 2 (BFN-2) NSSS Component- (reactor pressure

',

vessel, internals, CRD housings, and support) seismic reevaluation program

- conducted at BFN-2 site in Decatur, Alabama on. November. 9.1989, and at v

L-Genera 1' Electric Company's (GE's) office in Sen Jose, California on. December s

11-13,,1989. As a result of this inspection, all the open items identified

.

during the previous inspection were closed.

Therefore, no future: inspection

'on this program will be planned by the staff before restart of BFN-2.

In accordance with Section 2.790 of the NRC's " Rules of Practice," Part 2 Title 10, Code of/ Federal Regulations, a copy of this letter _ and its enclosure

.will be placed in the NRC Public Document Room.

,

Should you have-any questions concerning this inspection, please contact us.

,

Sincerely,

\\

B. D. _ Liaw, Director.

TVA Projects Division Office of Nuclear Reactor Regulation

,;

!

Enclosure:

Inspection Report 50-260/89-32 cc w/ enclosure:

See next page-OFC_ :TVA:E

TVA:EB/BC

TVA:A TP

TVA:

TVA:D

..___:....

__..:-__....

..:..

...__:__.

...:____________:... ________:_______ _

=NAME':TCh

DTerao

RP n

SBla

BDLiaw

.... :....... ___.:......______:...

.....:.____._____:....._______:.__________.:_________

DATEj2/f/90

2/f)/90

2/\\y90

2//6/90

2/ /90

OFFICIAL RECORD C0FY Document Name:

INSPECTION REPORT 50260/8962