ML18025A196

Letter Transmitting the Definitive Report of Deficiencies in Box Column Supports

ML18025A196
Person / Time
Site:	Susquehanna
Issue date:	08/29/1975
From:	Curtis N Pennsylvania Power & Light Co
To:	O'Reilly J NRC Region 1
References
Download: ML18025A196 (47)

Text

NR< DISTRIBUTION FOR PART 50 DOCw -T MATERIAL (TEMPORARY FORM)

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Pennsylvania Power 6 Lig Co., Allentown, Pa N W Curtis t DATE GF DOG A DATE REC'D

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0-38 and 388 DESCRIPTION:

Ltr notarized 9-3-75

~ ~, ~ trans the following Dist Per 1f; Rushbrook PLANT NAME:Susquehana 1 6 2 ENCLOSURES:

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Report On Deficiency In Box Column Supports for The Susquehanna Nuclear Plant

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0 August 29, 1975 Mr. Z. P. O'Reilly Director - Region I (fe U.S.'uelear Regulatory Commission 931 Park Avenue King of'russia, Pennsylvania 19406 TWO NORTH NINTH STREET, ALLENTOWN, PA.. 18101 PHONEf {215) 821-5151 CD ieger ti:j(8 ~YJ.

SUSQUEHANNA STEAM ELECTRIC STATION DEFINITIVE REPORT OF DEFICIENCIES IN BOX COLUMN SUPPORTS DOCKET NOSe1 50-387 and 50-388 LICENSE NOSe1 CPPR-101 and CPPR-102 ERs 100450/100508 FILE 840-4 PLA-82

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Dear Mr. O'Reilly:

This letter transmits the subject report which supplements PLA-74, dated. July 25, 1975 and is intended to complete PP&L's responsibility in reporting the deficiencies in fabricated. structural steel members (Box Column Supports) which had been located. in position fo" installa-tion in Susquehanna Unit 1 & 2 structures.

As indicated, in the attached report, the decision has been made to redesign the structures and. to replace all eight units, including.

those found. not to contain defects.

The replacement units employ material changes and weld )oint configurations which will facilitate fabric'ation and. should preclude the recurrence of the lamellar tearing phenomenon, experienced in original units.

In eddition to those corrective measures identified. in PLA-74 and. the attached Bechtel detailed report, PP&L has concurred in an increase in Bechtel surveillance activities at the vendor's fabrication facility (Bethlehem Steel Company's Pottstown, PA plant).

Additionally, receiving and. preinstallation activities at the SSES site will be aligned to perform a final visual examination before the new units are permanently committed to the plant structure.

We await your advice should you have any further questions or concerns on this matter.

Very truly yours lh,K N. W. Curtis Vice President - Engineering

& Construction s4oo ARS: b PENNSYLVANIA POWER 6 LIGHT COMPANY

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TWO NORTH NINTH STREET, ALLENTOWN, PA, 18101 PHONEME (215) 821 SISI Mr. J.

P. O'Reilly Pm-82 Pa e 2 Sworn to and. subscribed. before me this 1975.

Notary Public My commission expires:

cc:

Mr. Donald. F. Knuth Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, D.C.

20555 PENNSYLVANIA POWER S. LIGHT COMPANY

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REPORT ON DEFICIENCY IN BOX COLUHN SUPPORTS FOR THE SUSQUEHANNA NUCLEAR PLANT

~<<eivp AUG' 1975 US(UEIQ IAIDO t, Prepared by Checked by Approved by G.

Shah J.

N. Hulay H. J. Lidl BECHTEL POWER CORPORATION San Francisco California (B-2la)

TABLE OF CONTENTS 1.0 2.0 Introduction Description of Deficiency 2.1 Box Column Base Description 2.2 Description of First Crack 2.3 Visual and NDE Xnspection 3.0 investigation 3.1 NDE Shop 3.2 NDE Field 3.3 Analytical Xnvestigations 3.4 Lamellar Tearing 3.5 Conclusion 4.0 Remedial Measures Appendices:

A.

Design Criteria B.

/DE Reports C.

Design Considerations Figures 1

Original Column-Base Detail 2

Redesigned Column-Base Detail

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~ 'ntroduction This report is prepared in accordance with the requirements described in, Title 10, Code of Federal Regulations, Part 50, Section 50.55(e).

Hairline cracks were found in major weldments at the base of box columns.

The significance of these linear indications,has been evaluated and it is concluded that the box column bases which were found to be defective, represents a deficiency in construction (fabrication) which will require extensive repair or rede-sign and replacement, and which, were the defi-ciencies to have remained uncorrecrted, could have an adverse effect on the structure in the performance of the intended safety function.

2.0 Description of Deficiency 2.1 Box Column Base Description Four (4) box colums are provided in the Reactor Building of each unit.

These box columns support the con-crete girders which form the walls of the spent fuel pool and dryer and separator pool.

They also support the intermediate floors.

Figure 1

shows the details of the box column and its base.

4 As shown in Figure 1 the column is 3'-0" square and made. of four steel; plates welded together with partial penetration welds.

Top.of the column

-is rigidly connected to the steel box girder which is provided below the con-crete fuel pool girders.

At the bottom, stifieners and base plates are welded to the column to transmit the design loads.

As shown in Figure 1, the base plate stiffeners are welded to the column with full penetration butt welds, while fillet weld is used to con-nect them with the base plate.

Nominal fillet weld is provided between the-base plate and the column.

In order to re-,

. duce the base plate thickness, a system (B-21a)

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of main and secondary stiffener is provided.

The design criteria for box column base is discussed in Appendix A of this report.

2.2 Description of First Crack During the course of random visual inspec-tion of installed structures of Unit 1, PL's Quality Assurance engineers noted the appearance of welds on four (4) box column bases and questioned their compliance with AHS Dl.l. PL Deficiency Report No. 0022 was issued to document the condition.

Subsequently, closer inspection revealed the existence of a visible hairline crack at the toe of a full penetration weld between a stif-fener and the box column S-27.5. Bechtel NCR

{Nonconformance Report) 376 was issued request-ing further non-destructive examination. It was decided to carry out the ultrasonic exami-nation (UT) to establish the extent of the crack+

The UT examination was carried out by Bechtel's NDE Subcontractor, Peabody Testing Company.

The results of UT examination revealed that the crack extended into the base metal.

The crack was ap-proximately 37" long and located at approximately 1-3/8" from the face of the column.

Appendix B

shows the details of UT examination.

2.3 Visual and NDE Inspection Further visual examinations of welds revealed a

similar subject condition on box column Support Q-36.

The UT examination revealed a crack varied from surface to l-l/4" depth and was approximately 27" long.

NCR 377 documented the defective condi-tion of column base Q-36.

Since identical design details were used on all box columns, it was decided to perform UT examina-tion on all remaining seven columns.

Bethlehem Steel Corporation, Pottstown Plant, carried out the task.

The UT examination was carried out on all the columns in the field.

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page 3

0 Four additional column bases Q-22, Q-36, S-30.5 and S-36 were found to have additional indica-tions (interpreted subsequently as lamellar tear-ing) in the base material of the box column.

Two additional NCRs 401 and 402 were issued to do-cument these defects.

Appendix B describes the details of UT.

NDE of the columns indicated that three (3) columns did not show any defects.

Before these defects were

observed, small cranes had been installed on top of erected columns for lifting reinforcing bars.

The loads applied to these columns through the cranes are considerably smaller than the inservice column loads.

3.0 Investigations 3.l NDE Shop The full penetration butt welds joining the stiffeners to the box, columns were 100% UT, examined in the shop of Bethlehem Steel Corporation prior to shipment.

All fillet-welds were 100% examined by Magnetic Particle Testing (MT). The column bases were also post weld heat treated as specified, after fabrica-tion in the shop.

3.2 NDE Field 4

3.3 The UT exami:nation that was performed'in the field has been described in detail under Sec-tion 2.3 of this report.

The limited amount of magnetic particle (MT)

~ testing was also performed for fillet welds joining the stiffeners to the base plates.

MT examination was performed since analytical investigations described in Section 3.3 below indicated if one of the two welds (; tiffener to box column or stiffener to base j.late) is

adequate, the load can be transferred satis-factorily.

Analytical Investigations I

'nalytical investigation was made to check if the design loads could be adequately transfer-red to the foundation from the column even

page 4

with the observed linear indications in the base metal.

The following are the analytical considerations:

(a)

Column base will be subjected to axial loads only.

(b)

The column stiffeners where linear indications were found, would be subjected to compressive and shear stresses from the base plate loading.

(c)

Compressive stresses can be ade-'uately transferred through the cracks.

(d)

It is questionable if shear stres-ses can be adequately transferred from stiffener to the column un-der the existing condition.

However,

-the base plate along with stiffeners would be able to transfer shear forces.

From the above mentioned analytical considera-tions, it was concluded that the box column base would adequately transfer the load with the existing linear indications provided these indications would not propagate.

3.4 Lamellar Tearing.

Bechtel's metallurgical staff was further'consulted to identify the observed linear indications and to determine if these indications would propagate through the application of external design loads.

~ Metallurgical staff indicated that the observed de-fects were classical examples of lamellar tearings.

These are caused by the shrinkage of we. 3 metal which induced stresses in the base meta, in a direc-tion transverse to the material "grain"." Lamellar tearing phenomenon has received attention in the industry fairly recently, and therefore, several as-pects of this phenomenon are not yet fully defined and understood.

Further evaluation by metallurgists from Bechtel and Bethlehem Steel Corporation indicated that (B-21a)

page 5

most probably the lamellar tears would not pro-further'ince the stress due to weld pagate any ur e'llar tears.

This shrinkage is relieved due to lame d

conclusion is again augmented y

b the fact that rect tensile load will not be applied to the a-fected area.

3.5 Conclusion t

ossible to establish conclusively Since it is no possi ro a ate under that the lamellar tears will not propaga e un 1

ds we have to conclude that the observe service loa s, we av ar tears 'would d fects are reportable.

If lamellar have propagated extensively, then th' ec this deficiency might have adversely affected the structural'integ-rity of the plant.

4.0 Remedial Measures Even though on a purely theoretical baasis it could be demonstrate a

d th t the column bases would function ade-uatel

, it was considered prudent to repair j

or re'ect 1

b s.

Because of the indeterminate the existing column ases.

nd the in-nature of the lamellar tearing phenomenon and t e in-replace all eight (8) column support bases wi new ports'having a different design detail.

column base considerably reduces the C of hi o t-possxbility of lamellar tears.

Appendix o

of the base connection.

Figure 2

lines the details of redesign o

shows the revised column base details.

The rationale of redesigned base can be summarized as follows:

{a) e we

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Th ld detail for the revised detail i.", such that the possibility of lamellar tears ha s have been greatly reduced.

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b)

N 'th r base plate nor box column is subjected to thorough thickness loading during pp a

lication of design loads.

(c)

.The redesxgne ase d b se of box column will adequately

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transfer the design loads during service life o the plant.

(B-21a)

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APPENDIX A DESIGN CRITERIA'

1.0 Loaves Box columns are designed to support following loads:

(a)

During construction Box column supports the crane load, load of intermediate foaming and of the wet concrete

'f the fuel pool concrete girders.

(b)

During plant operation.

Box column is designed to transfer loads of intermediate floors and fuel pool concrete girders.

2.0 Loading Combinations and Allowable Stresses:

The detailed design criteria is outlined in Appendix "C" "Structural Design and Loading Criteria" of Preliminary Safety Analysis Report

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APPENDIX C DESIGN CONSIDERATIONS

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Original Column Base Following assumptions were made in the design:

(a)

The box column was assumed to be a

'ontinuous member, with a pinned base and supported laterally at intermediate levels.

Therefore, the column base was designed mainly for'axial loads.

(b)

Because of the rigid connection with box girders at the top, moments are transmit-ted to the column top depending on the re-lative stiffenesses of the column and the girder.

(c)

Column load is.distributed uniformly ove'r the entire area of the base plate.

(d)

Stiffeners and base plate act as a composite section for transmitting design loads.

2.0 Redesigned Column Base The major change made in the redesign of box column base'is elimination of stiffeners for the base plate.

The',.base plate utilizes the original erection bolts as shown in Figure l.

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FIGURE 1 ORIGINAL COLUMN BASE DETAIL

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REDESIGNED COLUMN BASE DETAILS

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