ml021480131 - exigent steam generator technical specification changesan onofre nuclear generating...

7/31/2019 ML021480131 - Exigent Steam Generator Technical Specification ChangeSan Onofre Nuclear Generating Station U

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SSOUTHERN CALIFORNIASDwight E. Nunn

EO Vice PresidentAnEDISONINTERNATIONAL"' Company May 22, 2002

U. S. Nuclear Regulatory Commission

Attention: Document Control DeskWashington, D.C. 20555

Subject: Docket Nos. 50-361 and 50-362

Proposed Change Number NPF-10/15-543

Exigent Steam Generator Technical Specification Change

San Onofre Nuclear Generating Station

Units 2 and 3

Gentlemen:

In accordance with theprovisions of10 CFR 50.90, Southern California Edison (SCE) is

submitting an Exigent request for an amendment to SCE Licenses NPF-10 and NPF-15 to

change the Technical Specifications for San Onofre Units 2 and 3. The proposed change

specifically is to revise Technical Specification Steam Generator (SG) Tube Surveillance

Program requirement 5.5.2.11.f.1 .h to more clearly delineate the scope ofthe SG tube

inspection required in the tubesheet region. The basis for the proposed change is

WCAP-1 5894, Revision 0, "NDE Inspection Strategy For the Tubesheet Region In SONGSUnits 2 and 3," enclosed.

SCE believes that the existing San Onofre Units 2 and 3 Technical Specifications

adequately delineate the scope ofthe San Onofre SG tube inspections. Nevertheless,

becausethe NRC staffhas recently requested a clarifying Amendment, SCE is submitting

the enclosed exigent Amendment request. (This was discussed with the NRC staffin

teleconferences on May 14, 2002 and May 15, 2002.) An exigent Technical Specification

change is needed to prevent a delay in the resumption ofoperation ofUnit 2 following the

current refueling outage. Should the staff, however, conclude that no Amendment is

necessary, SCE will agree to withdraw this Amendment request.

SCE has determined that there are no significant hazards considerations associated with

the proposed change and that the change is exempt from environmental review pursuant

to the provisions of10 CFR 51.22 (c) (9).

Enclosure 1 to this letter provides a description and evaluation ofthe proposed change,

including copies ofthe appropriate Technical Specification pages from Units 2 and 3,

marked up to show the proposed change. This description and evaluation includes SCE's

determination that the proposed change does not involve a significant hazards

consideration and is exempt from environmental review. Enclosures 2 and 3 are

proprietary and non-proprietary versions, respectively, ofWestinghouse topical report

WCAP-1 5894, Revision 0, "NDE Inspection Strategy For the Tubesheet Region In SONGSUnits 2 and 3."

P.O. Box 128

San Clemente, CA 92674-0128

949-368-1480

Fax 949-368-1490


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Document Control Desk

Because Enclosure 2 contains information proprietary to Westinghouse, it is supported by

an Affidavit (Enclosure 4) signed by Westinghouse, the owner ofthe information. The

Affidavit sets forth the basis on which the information may be withheld from public

consideration by the Commission and addresses with specificity the consideration listed in

paragraph (b)(4) of10 CFR Section 2.790 ofthe Commission's regulations.

SCE requests exigent NRC review and approval as soon as possible but not later than

June 12, 2002 to support Unit 2 entry into Mode 4 from the current refueling outage. Mode

4 is currently scheduled for June 19, 2002. SCE is making no formal commitments that

would derive from NRC approval ofthe proposed amendment.

Ifyou have any questions regarding this request please contact me or Mr. Jack L. Rainsberry

at (949) 368-7420.

I declare under penalty ofperjury that the foregoing is true and correct.

Sincerely,

Executed on

Vice President

Enclosures:1.

2.

3.4.

Description and No Significant Hazards Analysis for Proposed

Change NPF-10/15-543AttachmentsA. Existing Technical Specification page, Unit 2

B. Existing Technical Specification page, Unit 3

C. Markup ofTechnical Specification page, Unit 2

D. Markup ofTechnical Specification page, Unit 3

E. Retyped Technical Specification page, Unit 2

F. Retyped Technical Specification page, Unit 3Westinghouse Topical Report WCAP-15894-P

Westinghouse Topical Report WCAP-15894-NPAffidavit for the Proprietary Westinghouse Topical Report

cc: E. W. Merschoff, Regional Administrator, NRC Region IV

A. B. Wang, NRC Project Manager, San Onofre Units 2, and 3

C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 & 3

S. Y. Hsu, Department ofHealth Services, Radiologic Health Branch

May 22, 2002-2-


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ENCLOSURE 1

Description and No Significant Hazards Analysis

for Proposed Change NPF-1 0/15-543San Onofre Nuclear Generating Station

Units 2 and 3


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DESCRIPTION AND NO SIGNIFICANT HAZARDS ANALYSIS

FOR PROPOSED CHANGE NPF-10/15-543

San Onofre Nuclear Generating Station Units 2 and 3

EXISTING TECHNICAL SPECIFICATIONS

Unit 2: See Attachment A

Unit 3: See Attachment B

PROPOSED TECHNICAL SPECIFICATIONS

(highlight for additions)

Unit 2: See Attachment C

Unit 3: See Attachment D

PROPOSED TECHNICAL SPECIFICATIONS(with changes)

Unit 2: See Attachment E

Unit 3: See Attachment F

DESCRIPTION OF CHANGE

1.0 Introduction

Southern California Edison (SCE) proposes a revision ofTechnicalSpecification Steam Generator (SG) Tube Surveillance Program requirement

5.5.2.11 .f.1 .h to clarify the extent ofthe SG tube inspections required in the SG

tubesheet (TS). The Surveillance Program requirement 5.5.2.11 .f.1 .h provides

a definition for tube inspection. The Surveillance Program requirement

currently reads as follows:

"Tube Inspection - An inspection ofthe SG tube from the point of entry (hot leg

side) completely around the U-bend to the top support ofthe cold leg; and"

The proposed change clarifies the scope ofthe tube inspection required for the

region within the SG TS. The proposed change addresses the portion ofthe

tube within the TS below the tube engagement area (TEA) length, as follows:

"Tube Inspection - An inspection ofthe SG tube from the point of entry (hot legside) completely around the U-bend to the top support ofthe cold leg excluding

the portion ofthe tube within the tubesheet (TS) below 5 inches from the

secondary face ofthe TS."

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2.0 Reason for the Proposed Change

SCE performs San Onofre Unit 2 and 3 SG rotating coil eddy current tests in

areas defined by the San Onofre Nuclear Generating Station (SONGS)

Degradation Assessment. The extent within the TS of recent past inspections

and ofthe upcoming, planned inspectionsis 5 inches into the hot leg TS.

Recent conference calls were held with NRC staffmembers to discuss the

planned San Onofre Units 2 and 3 SG tube inspections. During the

teleconferences, the staffasked questions on the extent ofthe tube inspections

that were being planned with a rotating probe within the TS region. The extent

ofSCE's rotating plus point probe inspections in the TS region covers 5 inches

(as a minimum) below the top ofthe hot leg TS. SCE will repair or plug on

detection any tubes with indications ofcracking. The NRC requested that SCE

clarify tube inspection criteria within the TS for this region of the tube.

Consequently, SCE is proposing the enclosed change as an exigent Technical

Specification change to clarify the current San Onofre Units 2 and 3 Technical

Specification tube inspection extent.

3.0 Safety Analysis

The SGs at San Onofre Units 2 and 3 were manufactured by Combustion

Engineering with a U-tube configuration. Each tube is secured in the TS above

the lower plenum ofthe SG by an explosive expansion process (explansion).

This process expands each tube over its entire length within the TS and forms

an interference fit between the tube and TS. This interference fit forms the

interface, which provides the structural and part ofthe leaktight boundary

between the primary and secondary systems at each end of a SG tube.Located near the top ofthe TS is a region where the tube transitions from theTS hole diameter to that ofthe original tube

An alternate tube repair criteria (referred to as W*) was developed by

Westinghouse Electric Company for Westinghouse plants to permit tubes with

predominantly axially oriented primary water stress corrosion cracking

(PWSCC) in the WEXTEX TS expansions to remain in service. The W*

analysis defines a W* length that would permit flaws to remain in service and

assure adequate strength is available to resist the axial pullout loads

experienced within the TS. The San Onofre Units 2 and 3 proposed change is

for the purpose ofdefining the inspection extent only and is not requesting an

alternate repair criteria as intended by W*.

This SONGS specific analysis (WCAP-1 5894, Revision 0) "NDE Inspection

Strategy For the Tubesheet Region In SONGS Units 2 and 3," is applicable to

the SONGS Unit 2 and 3 SGs and defines the maximum TEA length in section

8. For conservatism, and to provide assurance ofcomplete inspection ofthe

TEA length, SONGS is defining the area ofinterest to be 5.0 inches. The

presence ofthe surrounding TS prevents tube rupture and provides resistance

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against axial pullout loads during normal and accident conditions. In addition,

any primary-to-secondary leakage from tube degradation below the TEA length

is an inconsequential contribution to the total leakage assumed for a steam line

break (SLB) accident and may be considered negligible. Consequently, any

tube degradation that may go undetected below the TEA would not affectstructural or leakage margins.

Definitions:

TEA (tube engagement area) length - The length oftubing below the top

of-tubesheet ofthe explanded portion ofthe tube which must be

demonstrated to have no detectable degradation and is defined in WCAP

15894, Revision 0, section 8.

Inspection Extent Uncertainty - The uncertainty associated with the actual

probe location relative to the indicated location during data analysis ofthe

recorded eddy current data.

Inspection Extent - The minimum length oftubing below the hot leg top-of

tubesheet to be inspected to determine completely and unambiguously if

degradation is detected within the TEA length. The extent includes

inspection extent uncertainty to provide assurance that the TEA length is

completely inspected. The Inspection extent is 5 inches below the hot leg

top-of-tubesheet.

SONGS performs a Degradation Assessment to determine areas susceptible to

degradation, the areas ofthe tubing to be inspected, and the appropriate eddy

current techniques to detect and quantify degradation within each area. Inputdata needed for the subsequent Condition Monitoring and OperationalAssessment are considered in the Degradation Assessment.

The SONGS SG inspection fulfills Technical Specification 5.5.2.11 .f.1 .hrequirements for inspecting SG tubing by performing 100 percent full-length

inspection ofeach tube using a bobbin coil probe, with one exception. Thesmallest radius U-bends (rows 1, 2, and 3) are inspected with a rotating plus

point probe, rather than a bobbin probe. Inthese small U-bends, the rotating

plus point probe is a much better design for such changing geometry test

conditions. To reduce the probability and consequences ofSG tube rupture or

tube failure, the SONGS Degradation Assessment and critical area definition

process identify additional inspections. SONGS performs these additionalinspections in critical areas using the rotating plus point probe to identify crack

like indications that would not be easily identified with the bobbin coil probe.

For future inspections, ifprobe development results in new types ofprobes

which are equivalent or superior to the plus point rotating probe, SCE may

evaluate these for possible use in this application.

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The critical area ofthe tubes in the tube-to-tubesheet expansion in SONGS

steam generators includes the TEA length. The TEA length is defined for

SONGS Units 2 and 3 in WCAP-15894, Revision 0 considering the most

stringent loads associated with plant operation, including transients and

accident conditions, and with an additional margin provided by the use of3 X

Normal Operating Differential Pressure

The WCAP-15894, Revision 0 topical report does not entail an Alternate Repair

Criteria. The WCAP topical report is used to define the length oftubing within

the hot leg that should be inspected with a rotating plus point probe.

Tube burst is precluded for cracks within the TS by the constraint provided by

the TS. Thus, structural integrity is maintained by the TS constraint. However,

a 360-degree circumferential crackor many axially oriented cracks could permit

severing ofthe tube and tube pullout from the TS under the axial forces on the

tube from primary to secondary pressure differentials. Section 4 ofWCAP

15894, Revision 0 describes the testing that was performed to define the length

ofnon-degraded tubing that is sufficient to compensate for the axial forces on

the tube and thus prevent pullout. The operating conditions utilized in WCAP

15894, Revision 0 were specific to SONGS and are summarized in Section 3.

Operating experience has demonstrated negligible normal operating leakage

from primary water stress corrosion cracking (PWSCC) in expansion transitions.

PWSCC in explansions in the TS region would be even further leakage limited

by the tight tube-to-tubesheet crevice and the limited crackopening permitted

by the TS constraint. The SLB conditions provide the most stringent

radiological hazards for postulated accidents involving loss ofpressure or fluid

in the secondary system. WCAP-1 5894, Revision 0, Section 3.1.2 provides the

justification to neglect the total SLB leak rate contributed by cracks below the

TEA length. Therefore, rotating plus point probe inspection in the area below

the TEA length is not necessary to preclude normal operating or accidentinduced leakage.

In SONGS Operational Assessments, postulated cracking within the TEA length

is conservatively included in the allowable leakage calculations and no credit is

taken for the leak-limiting effect of the tubesheet.

4.0 No Significant Hazards Consideration

Southern California Edison (SCE) has concluded that operation ofSan OnofreUnits 2 and 3, in accordance with the proposed change to the TechnicalSpecifications, does not involve a significant hazards consideration. SCE's

conclusion is based on its evaluation, in accordance with 10 CFR 50.91 (a)(1),

ofthe three standards set forth in 10 CFR 50.92(c).

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SCE is proposing to modify the San Onofre Units 2 and 3 Technical

Specifications to revise the Technical Specification Steam Generator (SG)

Tube Surveillance Program requirement 5.5.2.11 .f.1 .h to clearly define SG tube

inspection scope. SCE's proposed change is to clarify the tube inspection to

exclude the portion ofthe tube within the tubesheet below the tube engagement

area(TEA) length. The analysis accounts for the reinforcing effect that the

tubesheet (TS) has on the external surface of the SG tube within the TS region.

The analysis shows that tube integrity and leakage below the TEA length

remain within the existing design limits.

1. Does the proposed change involve a significant increase in the

probability or consequences ofan accident previously evaluated?

Southern California Edison (SCE) proposes to modify the San Onofre

Units 2 and 3 Technical Specifications to define the SG tube inspection

scope. The San Onofre Nuclear Generating Station (SONGS)-specific

analysis takes into account the reinforcing effect the TS has on the

external surface of an expanded SG tube.

Tube-bundle integrity will not be adversely affected by the

implementation ofthe TEA tube inspection scope. SG tube burst or

collapse cannot occur within the confines ofthe TS; therefore, the tube

burst and collapse criteria ofdraft Regulatory Guide (RG) 1.121 are

inherently met. Any degradation below the TEA length is shown by

analyses and test results to be acceptable, thereby precluding an event

with consequences similar to a postulated tube rupture event.

Tube burst is precluded for cracks within the TS by the constraint

provided by the TS. Thus, structural integrity is maintained by the TS

constraint. However, a 360-degree circumferential crack or many axiallyoriented cracks could permit severing ofthe tube and tube pullout fromthe TS under the axial forces on the tube from primary to secondarypressure differentials. Testing was performed to define the length of

non-degraded tubing that is sufficient to compensate for the axial forces

on the tube and thus prevent pullout.

In conclusion, incorporation ofthe TEA inspection scope into San Onofre

Units 2 and 3 Technical Specifications maintains existing design limits

and does not involve a significant increase in the probability or

consequences ofan accident previously evaluated.

2. Does the proposed change create the possibility of a new or

different kind ofaccident from any accident previously evaluated?

Tube-bundle integrity is expected to be maintained during all plant

conditions upon implementation ofthe proposed tube inspection scope.

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Use of this scope does not induce a new mechanism that would result ina different kind ofaccident from those previously analyzed. Even withthe limiting circumstances of a complete circumferential separation ofatube occurring below the TEA length, SG tube pullout is precluded andleakage is predicted to be maintained within the Final Safety Analysis

Report limits during all plant conditions. Therefore, a possibility of a newor different kind ofaccident from any accident previously evaluated is notcreated.

3. Does the proposed change involve a significant reduction in amargin ofsafety?

Upon implementation of the TEA inspection scope, operation withpotential cracking below the TEA length in the explansion region of theSG tubing meets the margin of safety as defined by RG 1.121 and RG

1.83 and the requirements ofGeneral Design Criteria 14, 15, 31, and 32.Accordingly, the proposed change does not involve a significantreduction in a margin ofsafety.

4.0 Environmental Impact Consideration

The proposed change does not involve a significant hazards consideration,a significant change in the types ofor significant increase in the amountsof any effluents that may be released offsite, or a significant increase inindividual or cumulative occupational radiation exposure. Therefore, theproposed change meets the eligibility criteria for categorical exclusion setforth in 10 CFR 51.22(c)(9). Therefore, pursuant to 10 CFR 51.22(b), anenvironmental assessment ofthe proposed change is not required.

PCN543c

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Attachment A

(Existing Pages)

SONGS Unit 2


11/92

Procedures, Programs, and Manuals5.5

5.5 Procedures, Programs, and Manuals (continued)

5.5.2.11 Steam Generator (SG) Tube Surveillance Program (continued)

e) Imperfection - An exception to the dimensions,finish, or contour of a tube from that required by

fabricationdrawings or specifications. Eddy

current testing indications below 20% of thenominal tube wall thickness, if detectable, may beconsidered as imperfections;

f) Repair Limit - The imperfection depth at or beyondwhich the tube shall be removed from service orrepaired and is equal to 44% of the nominal tubewall thickness; Sleeves shall be removed fromservice upon detection of service-induceddegradation of the sleeve material or any portionof the sleeve-to-tube weld.

g) Preservice Inspection - An inspection of the fulllength of each tube in each SG performed by eddycurrent techniques prior to service to establish abaseline condition of the tubing. This inspectionshall be performed prior to initial MODE Ioperating using the equipment and techniquesexpected to be used during subsequent inserviceinspections. These examinations may be performedprior to steam generator installation. Similarly,for tube repair by sleeving, an inspection of thefull length of the pressure boundary portion ofthe sleeved area shall be performed by eddycurrent techniques prior to service. This

includes pressure retaining portions of the parenttube in contact with the sleeve, the sleeve-totube weld, and the pressure retaining portion ofthe sleeve.

h) Tube Inspection - An inspection of the SG tubefrom the point of entry (hot leg side) completelyaround the U-bend to the top support of the coldleg; and

i) Unserviceable - The condition of a tube if itleaks or contains a defect large enough to affectits structural integrity in the event of an

Operational Basis Earthquake, a loss-of-coolantaccident, or a steam line of feedwater line breakaccident as specified in Specification 5.5.2.11.e.

(continued)

Amendment No. 4-2-7, 140SAN ONOFRE--UNIT 2 5.0-18


12/92

Attachment B

(Existing Pages)

SONGS Unit 3


13/92





fabrication drawings or specifications. Eddycurrent testing indications below 20% of thenominal tube wall thickness, if detectable, may beconsidered as imperfections;


g) Preservice Inspection - An inspection of the fulllength of each tube in each SG performed by eddycurrent techniques prior to service to establish abaseline condition of the tubing. This inspectionshall be performed prior to initial MODE Ioperating using the equipment and techniquesexpected to be used during subsequent inserviceinspections. These examinations may be performedprior to steam generator installation. Similarly,for tube repair by sleeving, an inspection of thefull length of the pressure boundary portion ofthe sleeved area shall be performed by eddycurrent techniques prior to service. This


h) Tube Inspection - An inspection of the SG tubefrom the point of entry (hot leg side) completelyaround the U-bend to the top support of the coldleg; and

i) Unserviceable - The condition of a tube if itleaks or contains a defect large enough to affectits structural integrity in the event of anOperational Basis Earthquake, a loss-of-coolantaccident, or a steam line of feedwater line breakaccident as specified in Specification 5.5.2.11.e.

(continued)

Amendment No. ++& 132SAN ONOFRE--UNIT 3 5.0-18


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Attachment C

(Proposed Pages)

(Redline and Strikeout)

SONGS Unit 2


15/92

Procedures, Programs, and Manuals

5.55.5 Procedures, Programs, and Manuals (continued)


e) Imperfection - An exception to the dimensions,finish, or contour of a tube from that required byfabrication drawings or specifications. Eddycurrent testing indications below 20% of thenominal tube wall thickness, if detectable, may beconsidered as imperfections;


g) Preservice Inspection - An inspection of the full

length of each tube in each SG performed by eddycurrent techniques prior to service to establish abaseline condition of the tubing. This inspectionshall be performed prior to initial MODE 1operating using the equipment and techniquesexpected to be used during subsequent inserviceinspections. These examinations may be performedprior to steam generator installation. Similarly,for tube repair by sleeving, an inspection of thefull length of the pressure boundary portion ofthe sleeved area shall be performed by eddycurrent techniques prior to service. Thisincludes pressure retaining portions of the parent

tube in contact with the sleeve, the sleeve-totube weld, and the pressure retaining portion ofthe sleeve.

h) Tube Inspection - An inspection of the SG tubefrom the point of entry (hot leg side) completelyaround the U-bend to the top support of the coldleq excludinq the Dortion of the tube within thetubesheet (TS) below 5 inches from the secondaryface of the TSi n


(continued)

Amendment No. 127, 140SAN ONOFRE--UNIT 2 5.0-18


16/92

Attachment D

(Proposed Pages)

(Redline and Strikeout)

SONGS Unit 3


17/92







g) Preservice Inspection - An inspection of the fulllength of each tube in each SG performed by eddycurrent techniques prior to service to establish abaseline condition of the tubing. This inspectionshall be performed prior to initial MODE 1operating using the equipment and techniquesexpected to be used during subsequent inserviceinspections. These examinations may be performedprior to steam generator installation. Similarly,for tube repair by sleeving, an inspection of thefull length of the pressure boundary portion ofthe sleeved area shall be performed by eddycurrent techniques prior to service. This


h) Tube Inspection - An inspection of the SG tubefrom the point of entry (hot leg side) completelyaround the U-bend to the top support of the coldleq excluding the portion of the tube within thetubesheet (TS) below 5 inches from the secondaryface of the TS.;-aned

i) Unserviceable - The condition of a tube if it

leaks or contains a defect large enough to affectits structural integrity in the event of anOperational Basis Earthquake, a loss-of-coolantaccident, or a steam line of feedwater line breakaccident as specified in Specification 5.5.2.11.e.

(continued)

Amendment No. 11-6 -132SAN ONOFRE--UNIT 3 5.0-18


18/92

Attachment E

(Proposed Pages)

SONGS Unit 2


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e) Imperfection - An exception to the dimensions,finish, or contour of a tube from that required byfabrication drawings or specifications. Eddycurrent testing indications below 20% of thenominal tube wall thickness, if detectable, may beconsidered as imperfections;


g) Preservice Inspection - An inspection of the full

length of each tube in each SG performed by eddycurrent techniques prior to service to establish abaseline condition of the tubing. This inspectionshall be performed prior to initial MODE 1operating using the equipment and techniquesexpected to be used during subsequent inserviceinspections. These examinations may be performedprior to steam generator installation. Similarly,for tube repair by sleeving, an inspection of thefull length of the pressure boundary portion ofthe sleeved area shall be performed by eddycurrent techniques prior to service. Thisincludes pressure retaining portions of the parent

tube in contact with the sleeve, the sleeve-totube weld, and the pressure retaining portion ofthe sleeve.

h) Tube Inspection - An inspection of the SG tubefrom the point of entry (hot leg side) completelyaround the U-bend to the top support of the coldleg excluding the portion of the tube within thetubesheet (TS) below 5 inches from the secondaryface of the TS.


(continued)

SAN ONOFRE--UNIT 2 Amendment No.5.0-18


20/92

Attachment F

(Proposed Pages)

SONGS Unit 3


21/92







g) Preservice Inspection - An inspection of the fulllength of each tube in each SG performed by eddycurrent techniques prior to service to establish abaseline condition of the tubing. This inspectionshall be performed prior to initial MODE 1operating using the equipment and techniquesexpected to be used during subsequent inserviceinspections. These examinations may be performedprior to steam generator installation. Similarly,for tube repair by sleeving, an inspection of thefull length of the pressure boundary portion ofthe sleeved area shall be performed by eddycurrent techniques prior to service. This


h) Tube Inspection - An inspection of the SG tubefrom the point of entry (hot leg side) completelyaround the U-bend to the top support of the coldleg excluding the portion of the tube within thetubesheet (TS) below 5 inches from the secondaryface of the TS.


(continued)

SAN ONOFRE--UNIT 3 5.0-18 Amendment No.


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ENCLOSURE 3

Westinghouse Topical Report WCAP-1 5894-NP,

Revision 0: "NDE Inspection Strategy For the

Tubesheet Region In SONGS Units 2 and 3"

(Non-Proprietary)


23/92

Westinghouse Non-Proprietary Class 3

NDE Inspection StrategyFor the Tubesheet RegionIn SONGS Units 2 and 3

Copyright 2002

Westinghouse Electric Company LLC


24/92

Westinghouse Non-Proprietary Class 3WCAP 15894-NP Page 2 of67

NDE Inspection StrategyFor the Tubesheet Region

In SONGS Units 2 and 3

May 2002

P.R. Nelson

This document contains information proprietary to Westinghouse Electric Company LLC and Nuclear

Services Business Unit; it is submitted in confidence and is to be used solely for the purpose for which it

is furnished, then returned upon request. This document and such information is not to be reproduced,

transmitted, disclosed or used otherwise in whole or in part without prior written authorization of

Westinghouse Electric Company LLC and the Nuclear Services Business Unit.

Westinghouse Electric Company LLC

P.O. Box 355

Pittsburgh, PA 15230-0355

05/21/02


25/92


EXECUTIVE SUMMARY

Based on evaluation oftesting results, analysis, and supporting references, a conservative NDEinspection extent below the secondary face ofthe tubesheet (TTS) has been determined to be five

inches for the San Onofre Nuclear Generating Station (SONGS) Units 2 and 3.

An engineeringjustification for limiting the required inspection area to the upper region ofthe

tubesheet on the hot leg side has been developed. This engineeringjustification was developed

for two reasons:

", Flaws below five inches in this region are unlikely to be a safety concern (which was

confirmed by the work performed for this report) and,

"* Existing NDE methods necessitate optimized inspection within the area ofmost need and

relevance.

This report provides the SONGS specific information from a project conducted for the

Combustion Engineering (CE) Owners Group (Reference 1).

The inspection extent value offive inches has been derived based on a conservative assumption

that a maximum number oftubes equal to [](c) Primary Water Stress Corrosion Cracking (PWSCC)

susceptibility increases markedly with increasing temperature and may be assumed to only be

prevalent in steam generator tubing on the hot leg side ofthe tube bundle. A review ofPWSCC

history in CE designed units demonstrates that the assumption that less than [

](c) is a reasonable basis for specifyingthe inspection extent value. The inspection extent must be inspected by an adequate NDE

inspection method to ensure that less than [

](c) within five inches ofthe TTS. The inspection extent assumes that all indications

oftube degradation within the inspection extent will be repaired or plugged on detection.

CE explanded and WEXTEX joints compare favorably. The W* ARC (for WEXTEX) values

used as a figure ofmerit for benchmarking the results ofthis effort are inspection lengths of[ ](b). The [ ](b) value are differentiated by

tubesheet flexure, which has been considered for the SONGS units.

05/21/02


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Westinghouse Non-Proprietary Class 3WCAP 15894-NP Page 4 of 67

TABLE OF CONTENTS

1.0 INTRODUCTION ............................................................................................. 8

1.1 Purpose .................................................................................................. . . 8

1.2 CE Design "Explansion" Joint ............................................................... 91.3 WEXTEX Joint and W* .......................................................................... 9

1.4 SONGS Plant Design ............................................................................. 10

1.5 Testing Acceptance Criteria .................................................................. 10

1.6 Overview ofApproach ........................................................................ 11

1.7 Conservatisms in Results ...................................................................... 13

1.8 Quality Assurance ................................................................................. 14

1.9 Other Considerations ............................................................................. 14

2.0 DEFIN ITIONS ................................................................................................. 18

3.0 TECHNICAL APPROACH SUMMARY .................................................... 20

3.1 Test Methods and Acceptance Criteria ................................................. 20

3.1.1 Pullout Load Tests Methods and Criteria ................................. 20

3.1.2 LeakRate Tests Methods and Criteria ...................................... 22

3.1.3 In Situ Pressure Testing for Supplementary Pullout

and Leak Rate ........................................................................... 26

3.1.4 Tubesheet Deflection Analysis Method .................................... 26

3.2 Elevated Temperature Tests .................................................................. 27

3.2.1 Pullout Tests - Single Tube Mockups ..................................... 27

3.2.2 LeakRate Tests - Single Tube Mockups ................................. 27

3.3 Test Specimens ..................................................................................... 28

3.3.1 Boston Edison Steam Generator ............................................... 283.3.2 Single Tube Mockups .............................................................. 29

3.3.2.1 Tubesheet and Tubing Specifications ........................ 29

3.3.2.2 Drilled Tubesheet Hole ............................................... 29

3.3.2.3 Test Matrix Overview ............................................... 29

4.0 PULL-OUT LOAD TESTS AND RESULTS ............................................... 44

4.1 Boston Edison Steam Generator .......................................................... 44

4.2 Single Tube Mockups .......................................................................... 45

5.0 LEAK RATE TESTS AND RESULTS ........................................................ 51

5.1 Surface Leak Rate Results ................................................................... 505.1.1 Boston Edison Steam Generator LeakRate Results ................. 51

5.1.2 Single Tube Mockups LeakRate Results ................................. 52

05/21/02


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TABLE OF CONTENTS (Cont'd.)

6.0 TUBESHEET DEFLECTION ANALYSIS ................................................... 56

7.0 OTHER FACTORS ........................................................................................ 58

7.1 MDM Cutting Effects .......................................................................... 587.2 Explansion Taper ................................................................................. 58

7.3 NDE Axial Position Uncertainty ........................................................... 58

8.0 RESULTS EVALUATION ............................................................................ 59

8.1 Tube Engagement Area Length Based on Burst Criteria ...................... 59

8.2 Tube Engagement Area Length Based on Leakage Criteria ................. 59

8.3 Tubesheet Dilation Correction Factor.................................................. 60

8.4 Threshold Length for NDE Inspection ................................................. 60

9.0 REFERENCES ............................................................................................... 61

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Westinghouse Non-Proprietary Class 3Page 6 of67

LIST OF FIGURES

Figure 1.1Figure 1.2

Figure 1.3

Figure 3.1

Figure 3.2

Figure 3.3

Figure 3.4

Figure 3.5

Figure 3.6

Figure 3.7

Figure 3.8

Figure 3.9

Figure 3.10

Figure 3.11

Figure 3.12

Figure 3.13

Figure 4.1

Figure 4.2

Figure 4.3

Figure 4.4

Figure 4.5

Figure 5.1

Figure 5.2

Figure 5.3

Explansion Process Schematic ............................................................. 15

Charge Assembly Shop Drawing ........................................................... 15

Depiction OfExplansion During SG Manufacturing ........................... 16

Load Cell Test Rig Schematic .............................................................. 33

Windsor Load Cell Test Rig ................................................................. 34

Windsor Load Cell Controls and Data Plotter ...................................... 35

LeakRate Test Rig Schematic ............................................................. 36

LeakR ate Test ...................................................................................... 37

W indsor ISPT Test Rig ........................................................................ 38

Elevated Temperature Test Single Tube Prior to Inserting into

the BEMCO Test Chamber .................................................................... 39

BEMCO Temperature Test Chamber ................................................... 39

Boston Edison Scrapped Steam Generator .......................................... 40

Boston Edison Steam Generator, Flow Distribution Plate Cut Out ..... 40

Load Cell Test Rig Tube Pull Fixture ................................................... 41

Single Tube Mockups .......................................................................... 42

Single Tube Mockup Explansion Setup ............................................... 43

Boston Edison SG Pull Data ................................................................. 49

Single Tube Mockup 4, 2.5" Crevice, Ambient Pull ............................ 49

Single Tube Mockup 6, 2.5" Crevice, Ambient Pull ............................ 50

Single Tube Mockup 8, 3" Crevice, High Pressure Pull ....................... 49

Rough Surface Finish Pullout Force vs. Joint Length ........................... 51

Boston Edison Steam Generator Leak Data ........................................... 54

Boston Edison SG and Single Tube Mockup Leak Data ...................... 55

Rough Single tube mockups Leak Tests at RT and NOT ..................... 55

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LIST OF TABLES

Table 3-1 Tube Measurements Before And After Testing .................................... 30

Table 3-2 Boston Edison SG Test Matrix ............................................................. 31Table 3-3 Single Tube Test Matrix ........................................................................ 32

Table 4-1 Boston Edison SG Pull Test Data ........................................................ 47

Table 4-2 Single Tube Mockup: Pull Test Data .................................................... 47

Table 5-1 Single Tube Mockup: LeakTest Data @ Room Temperature ............. 53

Table 5-2 Single Tube Mockup: LeakTest Data @ NOT ................................... 53

Table 6-1 Single Tube Mockup Pull Test Data .................................................... 57

APPENDICES

A) Test Plan MatrixB) Boston Edison Steam Generator Test Data

C) Single Tube - Tubesheet Mockup Tests Data

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WCAP 15894-NP Page 8 of67

Section 1

Introduction

1.0 INTRODUCTION

A testing program was conducted to provide a recommended NDE inspection extent for

detecting potential cracking in the tubesheet region in the San Onofre Nuclear Generating Station(SONGS) Units 2 and 3 steam generators (SGs). The evaluation provided in this report utilizes

the SONGS applicable information from a CE owners Group project recorded in Reference 1.

SONGS Units 2 and 3 have the Combustion Engineering designed explosively expanded

(referred to as explanded) tube-to-tubesheetjoints. A conclusion ofthis work is that CE

designed explanded and Westinghouse designed WEXTEXjoints are quite similar. The

Westinghouse explosive tube expansion (WEXTEX) alternate repair criteria (ARC) values are

used as a figure ofmerit for benchmarking the results ofthis effort. Based on an evaluation of

testing and analysis results, a conservative distance for nondestructive examination (NDE)

inspection ofthe tubes in the SONGS SGs below the secondary face ofthe tubesheet, also

referred to as the top ofthe tubesheet (TTS), has been determined to be five inches.

Testing was performed using tubesheet mockups and the SG from a cancelled plant steam

generator to determine the leakand burst limiting tube to tubesheetjoint length needed to assure

operation within generic licensing and industry developed limits.

1.1 Purpose

An engineeringjustification for limiting the required inspection area to the upper region ofthe

tubesheet has been developed. This engineeringjustification was developed for two reasons:

"* Flaws deep in this region are not a burst or significant leakage concern.

"* Existing NDE methods necessitate optimized inspection within the area ofmost need andrelevance.

"* Based on testing ofrepresentative samples a defined inspection extent distance below the

TTS is established. The threshold distance offive inches is based on the number oftubes

in the steam generator.

Babcock& Wilcox (B&W) designed plants have discovered tube cracks within the tubesheet

region leading the NRC to issue Information Notice (IN 98-27) alerting the PWR industry to the

events. The B&W tube-to-tubesheet joint design is a rolledjoint that has limited applicability to

the CE design but highlighted the need to review inspection practices in this region.

Some Westinghouse design plants have implemented alternate repair criteria, W*, to addresstube cracks in the tubesheet region. W* provides for leaving axial cracks in-service ifthey meet

W* criteria. The inspection extent defined in this report is not intended tojustify leaving stress

corrosion cracks in the inspection extent in-service.

References 2 and 1 provide industry consensus requirements for inspection. Rotating probes

such as the +Point probe have traditionally been used in the range oftwo inches above and below

the TTS to inspect the explansion transition region. Several MRPC probes are qualified for

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WCAP 15894-NP Page 9 of67Section 1Introduction

detection ofcracks in the tubesheet region but would add significant cost and time to outage

schedules to inspect the remaining twenty plus inches oftubesheet region. In general, industry

practice is to assume undetected flaws are present only ifthe particular flaw mechanism is

detected. The case presented in this report is that the presence ofundetected flaws in the

tubesheet region below the threshold distance criteria are inconsequential from a tube burst andleakage standpoint. Reasonable assurance ofdetection offlaws in the region above a threshold

distance will be provided using a qualified detection technique (e.g. +Point).

1.2 CE Design "Explansion" Joint

Beginning in 1961, Combustion Engineering pioneered the use ofexplosive expansion for steam

generator tubesheetjoints, termed "explansion". The desired design features were to provide a

cost-efficient method for closing the tube to tubesheet gap over the full length with sufficient

pullout strength, leak tightness and without excessive residual stress in the tube.

Figure 1.1 is a conceptual schematic ofthe explansion process. Figure1.2 is a shop drawing of

the charge assembly used in the explansion process and Figure 1.3 depicts a typical explosive

expansion setup in the manufacturing plant. The installation processes for expansionjoints were

reviewed in detail to support this effort. Combustion Engineering explansion process

development/review reports and qualification reports (3, 4, 5, 6) demonstrate that process

controls support the position that CE explansionjoints are ofconsistent high quality and radial

force in all installedjoints is within a reasonable variance. This was verified by the results from

the Boston Edison (BE) SG tube pull tests. Incomplete explansions have been detected in

operating units, but are a fraction ofa percent ofall tubejoints in-service and are detected and

application ofthe criterion would not be applied to those tubes.

A gun drill process was used for drilling the SONGS units tubesheet holes. Reaming ofthe

tubesheet hole, as had been the industry practice for rolledjoints, was considered unnecessary

and undesirable for the explansion process. The surface finish ofthe tubesheet hole was required

to not exceed 250 micro-inches (AA) ofroughness.

W* was developed based on two radial zones to credit less tubesheet flexure for the radial zone

nearest the steam generator shell. Only one radial zone was considered for tle CE designed SG

tube threshold distance. This is because the tubesheets in the SONGS units experience less

flexure near the stay cylinder and the shell due to the support provided by these parts ofthe

steam generator.

1.3 WEXTEX Jointand W*

The WEXTEXjoint is a full depth explosively expandedjoint used in some operating

Westinghouse design plants. The process for installing the WEXTEXjoint is similar to that used

for the CE designedjoints. After the tube is placed in the tubesheet, the tube end is rolled and

welded in-place. The tube is then expanded into the tubesheet hole by an explosive cord over the

full length ofthe tubesheet.

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Section 1Introduction

Although the CE and WEXTEX processes are similar, there are some differences in the resulting

joint. All CEjoints were installed in a controlled manufacturing shop. Some Westinghouse units

had WEXTEXjoints installed in the field where processes can be harder to control than in a

manufacturing shop. WEXTEX units were constructed utilizing low temperature mill annealed

A600 tubing rather than the high temperature mill annealed tubing used in CE designed units.The WEXTEX units have experienced more PWSCC indications than the CE designed SGs.

Also, it has been shown that the WEXTEX expansion may leave a small tapered region at the top

ofthe tubesheet (refer to Figure 1.4), while there has been no evidence ofany such effect in the

CE explansionjoints.

The NRC has reviewed and approved the use ofthe W* ARC for leaving cracked tubes in

service that meet the W* criteria. The W* criteria implemented by some units utilizes two

threshold distances dependent on tube radial position. These values were a useful reference for

comparison to the values derived in this work.

1.4 SONGS Design Considerations

Westinghouse designed tubesheets react to a postulated main steam line break(MSLB) event in a

similar way to the CE designed tubesheets despite a significant design difference in the thickness

oftubesheets. Early in the design ofCE plants, it was decided to add a stay cylinder central to

the tubesheet to stiffen the tubesheet and allow the use ofa less thickplate. Westinghouse

designed SGs do not use stay cylinders to add out ofplane stiffness to the tubesheet. A

difference in the tubesheet response to MSLB event between CE and Westinghouse designed

units is that the maximum flexure occurs at different radial positions (i.e., circular zones).

A flexure and concomitant tubesheet hole dilation effect onjoint contact was determined for the

SONGS units and is reported in Section 6 ofthis document.

Both SONGS units have Alloy 600 high temperature mill annealed (HTMA) tubes with the same

material property specifications and a wall thickness of48 mils.

1.5 Testing Acceptance Criteria

Testing in the course ofthe determination ofa sufficient tube engagement length in the tube to

tubesheetjoint satisfied two primary concerns: pullout force and leak rate. The acceptance

criteria applicable to the CE design used as a basis for these test parameters are the structural

integrity burst pressure for pullout load and the MSLB accident induced leak rate.

A 100% throughwall 3600 extent circumferential PWSCC flaw condition was conservatively

mocked up for testing by cutting tested tubes in the tubesheet specimens. These manufactured

flaws are recognized to be substantially less leak tight than either axial or circumferentially

oriented flaws at the same locations. Operating experience ofplants with identified PWSCC

flaws has shown that leakage is not a concern (21).

Pullout force as a function ofjoint length is determined to demonstrate that a tube severed some

distance into the tubesheet (i.e. ofa specificjoint length) will not pullout ofthe tubesheet and

therefore will not present a burst tube condition. Pullout force is used synonymously with

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WCAP 15894-NP Page 11 of 67

Section 1

Introduction

blowout force as referred to in the historical records. Structural integrity per historical approach

and discussion between industry and NRC leaders is defined as the ability ofa tube to withstand

pressure ofthree times the normal operating primary to secondary differential pressure

(3NODP). A 3NODP value of4410 psid was used in this work. The pullout load value of2000

lbfused in testing was derived from the 3NODP value of4410 psid acting on the area oftheinside diameter ofthe tubesheet hole [

](b). The threshold value for pullout is less than the

threshold length for leaks so the threshold length for leaks determines the threshold length for

inspection Details ofthe pullout load testing and criteria are provided in Section 3.1.1.

Leakrate as a function ofjoint length was determined in order to demonstrate that an assumed

number of100% throughwall tube flaws would not exceed the leakrate criterion The leak rate

criterion was derived from an MSLB accident induced leakrate limit of0.5 gpm per steam

generator, which is bounding based on the traditional limiting condition for operation (LCO)

limit for event initiation. The Standard Review Plan (22) specifies that the LCO leakage limit

would result in one-fifth ofthe 1OCFR100 dose limit.

[ ](c).

No tubes have been pulled to confirm PWSCC but the explansion is a full depthjoint that makes

ODSCC unlikely. [

](c).

To provide allowance for leakage from other defect types, particularly in operational assessment

calculations, the contribution ofleakage from tubesheet region flaws was conservatively limited

to [ ](c). Operational assessment calculations include

assumptions for undetected flaw populations and determine acceptable plant run-time based in

part on acceptable EOC leakage. Thejoint length leak rate (determined by testing) multiplied by

the number oftubes assumed to be defective that results in a leak rate less than or equal to the

leakrate criteria of[ ](c) is the threshold length for leaks. Details ofthe leakrate test

methods and criteria are provided in Section 3.1.2.

1.6 Overview ofApproach

A parametric approach was used for testing the pressure, temperature, and explansion contact

force effects to consider the key contributions tojoint integrity. Two types oftests were

conducted: pullout load and leak rate. Both test types were conducted on two test beds applicable

to the SONGS units:

"* The Boston Edison canceled plant as-built steam generator

"* Single tube to tubesheetjoint mockups (collars)

The test beds are described in the Section 3.3 ofthis report.

This workhad several major steps:

1. Develop a preliminary test plan for pullout and leak rate testing.

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2. Develop acceptance criteria for pullout and leak rate.

3. Pull and Leaktest Boston Edison SG tubejoints as a benchmark to as-built plants.

4. Pull and Leak test single tube to tubesheetjoint mockups (collars) at various pressures

and temperatures.

5. Verify that mockup collars are representativeofBE SG (i.e., as operating SGs).

6. Determine the effect oftubesheet hole dilation under MSLB conditions.

7. Calculate inspection lengths (threshold length for inspection) from the test results.

Other considerations that factored into the uncertainties in the development ofthreshold length

were:

"* Joint contact force at the explansion transition

"* Joint contact force changes during a MSLB

"* NDE axial position uncertainty

NDE probe axial position uncertainty is not explicitly considered in this report. The uncertaintyisjudged to be a minor effect and may be handled in the same way that utilities consider position

uncertainty in the current tubesheet region inspection scope. Uncertainty in axial flaw position as

measured by NDE probe is considered to be covered within the conservatisms applied in the

results reported in this report.

A reduction injoint contact force at the expansion transition is addressed in the W* topical report(1_0). [

].(b)

Visual inspection ofseveral sectioned specimens indicates that a taper is not present in the CE

explansionjoint. A taper ofseveral tenths ofan inch wouldbe visually observable but no taper

was observed in single tube mockup specimens examined by microscope. This supports the

information provided in Reference 4 indicating that CE explansionjoints do not have a taper

effect.

The metal disintegration machining (MDM) process ofcutting the artificial flaws usedin the pull

and leaktesting provides conservatism in that the tube material pulled away from the tubesheet

wall such that all measuredjoint lengths are considered conservative by several tenths ofan inch.

Under MSLB conditions, the differential pressure across the tubesheet causes tubesheet flexure

and dilation ofthe tubesheet hole. Dilation ofthe hole reduces the contact force in the region of

dilation. The other side ofthe tubesheet actually compresses, but it is not in the range ofinterest.

Reduced contact in thejoint may increase existing leakage and reduces the resistance to pullout.

I](b) A compensating effect occurs as primary to secondary

pressure increases. Increasing differential pressure induces axial and hoop stresses on the tube

ID. The hoop stress due to internal pressure is nominally twice the axial stress in magnitude

resulting in a diametric expansion ofthe tube approximately one mil at MSLB differential

pressure. This tends to mitigate the effect ofthe tubesheet hole opening at and near the tubesheet

surface.

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WCAP 15894-NP Page 13 of67Section 1Introduction

Tubesheet hole surface roughness was addressed in the fabrication oftubesheet mockups and

visual inspection ofthe roughness in the Boston Edison steam generator and several single tube

mockups. Tubesheet mockup holes were fabricated by drilling to represent the CE design

applicable to SONGS. The drilledholes are referred to as rough bore holes in some parts ofthis

report representing the gun drill process. Smoothness beyond the roughness specification criteria

of250 micro-inches was identified in early process development reports (3, 4, f) as not desirable

for explandedjoints. There is expected to be variability in tubesheet hole roughness in

operating steam generators. The variability is best characterized by the Boston Edison steam

generator results and appears to be a small factor. NDE measurements for each test were

recorded for comparison.

Leakrate testing was conducted using a very small capacity positive displacement pump, high

accuracy pressure gauge, recording equipment, and associated tubing. Pump strokes were

counted measuring nominally 0.6 milliliters per pump stroke, over a defined test period of

approximately forty minutes, providing a minimum detectable leak rate ofapproximately 5x10-6

gpm per tube. Ifno strokes were recorded, one stroke was assumed. In most cases, the test logs

indicate that seepage was observable at the tube - tubesheet interface even though no pump

stroke occurred. Leakage from the manufactured flaws in tests would not experience as large a

pressure drop across the flaw as would be expected in any SCC flaw in the tubesheet region. The

test leakrate reported accounts only for thejoint length pressure drop and not the pressure drop

across the flaw. This can be a significant conservatism depending on the flaw size and location.

Details ofthe results are provided in Section 4.0 ofthis report. Evaluation ofthe results is

provided in Section 8.

1.7 Conservatisms in Results

A number ofconservatisms have been employed which ensure that the results reported are

reasonable for safe operation. The conservatisms are also addressed in more detail in the other

sections ofthis report but are listed here to highlight the combined effect on results.

Conservatisms used in this work are:

"* A 360', 100% throughwall circumferential cut represents a limiting flaw form for pullout

and leaktesting.

" Use ofan MDM tool to cut the flaw results in a large width flaw providing little or no

flow resistance compared to SCC.

"* Tube draw-back due to MDM cutting heat up and contraction ofthe tube is not credited

in the measuredjoint length. There was no evidence that MDM cutting resulted in

solidification at the tube-tubesheet interface.

"* Only partial credit is taken for the increase in tube-to-tubesheet contact force due

differential thermal expansion between the tube and tubesheet.

"* Only partial credit is taken for the increase in tube-to-tubesheet contact force due to from

the internal pressure in the tube during NOP.

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WC


AP 15894-NP Page 14 of67Section 1Introduction

"* Tubes used in single tube mockup tests have material properties at the upper end ofthe

yield specification at 54 ksi per CMTR (18). The higher yield strength tubing would

result in a lower tube-tubesheet contact from the explansion process. This can have a

significant effect on pullout force and leakrate (8).

"* No credit is taken for corrosion ofthe tubesheet in the tubesheetjoint."* Choked flow effects under MSLB conditions are not considered.9 1

](C)

1.8 Quality Assurance

This workwas completed under the requirements ofthe Westinghouse Quality Assurance

Program M(_. QA documentation for the Boston Edison steam generator was not retrieved from

Westinghouse information archives, but is reasonably assumed to meet all requirements

regarding tube material specifications and the tubejoint installation process.

1.9 Other Considerations

Corrosion ofthe carbon steel tubesheet probably occurs even with the minute amount ofair and

moisture trapped in the tubesheetjoint after explansion. Corrosion would tend to increase the

friction between the tube and tubesheet impeding both pullout and leakage. Operating steam

generators would have more corrosion in thejoint than the mockups fabricated for this work. No

explicit credit is taken for corrosion in the tubesheetjoint. However, corrosion ofthejoint may

explain some ofthe variability in results in the single tube mockup leak rate tests. In particular,

leak rates tended to decrease as more tests were done on a given mockup indicating an increasing

flow resistance over time after the initial test. Red rust (iron oxide) was observed at the top ofthesingle tube mockup in some tests that were run later in the testing program.

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WCAP 15894-NP Page 15 of 67Section 1

Introduction

Figure 1.1

Explansion Process Schematic

Figure 1.2Charge Assembly Shop Drawing

&PLud~Ifi MAW ASSEflLY

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WCAP 1589.Westinghouse Non-Proprietary Class 3

4,-N Page 16 of67

Section 1

Introduction

Figure 1.3Depiction ofExplansion During SG Manufacturing

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WCAP 15894-NP

Westinghouse Non-Proprietary Class 3Page 17 of 67


Figure 1.4

WEXTEX Joint Expansion Taper Concept

STaper

WEXTEX

S: Transition

i " "F"- .

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Westinghouse Non-Proprietary Class 3WCAP15894 -NP Page 18 of 67

Section 2Definitions

2.0 DEFINITIONS

ARC - Alternate repair criteria are approvals by NRC to utilize specific criteria for repairdecisions based on detection offlaws.

Single tube mockup - Tubesheet mockups were fabricated from tubesheet bar stockmaterial

SA-508, Class 3. The machined bar stockin which a tube was explosively expanded was referred

to in this project as a collar.

EOC - End ofthe operating cycle

Joint - The tube and tubesheet contact surface area created by the explansion process.

Leakage criteria [

](c)

LCO - Technical specifications limiting condition for operation.

MSLB - The design basis event known as main steam line break.

NODP - Normal operating differential pressure. RCS pressure minus SG pressure at normal fullpower operating conditions.

3NODP = 4410 psid. Three times the NODP is the governing performance criterion for tube

integrity for the SONGS SGs for this evaluation.

Pullout force - The force required to overcome thejoint static and sliding friction such that tube

movement within the tubesheet may occur.

Pullout force criterion - The load value of2000 lbfderived from a 3NODP value of4410 psid

acting on the area ofthe inside diameter ofthe tubesheet hole [](a)

POD - Probability ofdetection based on the ability ofan NDE technique to indicate the presence

ofa flaw.

Rough Bore - The machined surface on the inside diameter ofeach rough bore single tube

mockup was drilled on a lathe to a surface roughness not greater than 250 micro- inches (AA) to

mockup the gun-drilled tubesheet hole surface.

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WCAP15894 -NP

Westinghouse Non-Proprietary Class 3Page 19 of 67

Section 2Definitions

Taper- The theoretically incomplete contact near the top ofthejointjust below the explansion

transition. [

](b)

Tube Engagement length- The tube to tubesheetjoint length below the TTS that provides a

sufficient contact force to preclude pull out at 3NODP and leakage at MSLB pressures.

TTS - Top ofthe tubesheet

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Section 3

Technical Approach Summary

3.0 TECHNICAL APPROACH SUMMARY

This is a summary ofthe approach used for collecting and evaluatingthe data orom which the

recommendations are derived. Detailed test apparatus, test procedures, technique description,

and data tables are provided in the references.

As part ofthe test design, it was decided that a parametric approach would be used to identify the

contributions ofthe three components ofjoint force due to explansion, temperature and pressure.

All materials were procured and methods/procedures were executed under Combustion

Engineering Nuclear Power (CENP) quality requirements.

All Alloy 600 tubing used for the mockups was selected to be in the upper range ofthe 35 to 55

ksi yield strength to bound tubing installedin operating steam generators. All tubes were from

the same heat ofmaterial and had yield strength of54 ksi. Use oftubing at the upper end ofthe

yield strength ranges provides conservatism injoint contact force (.8). As the Boston Edison

tubing information was not available for review it was assumed to be nominally in the mid-range

and attendant larger variability in properties, i.e., throughout the range ofthe CE procurement

specification.

3.1 Test Methods and Acceptance Criteria

Acceptablejoint length was determined by testing for two categories ofconcern: pullout load

and leakrate. Pullout load and leak rate testing data were compared to industry accepted criteria

Q(1).

The tube - tubesheetjoint length needed to ensure that both pullout (burst) and leakage criteria

are met are provided in this report. The length needed to ensure both criteria are met is

dominated in all cases by the threshold length defined by the leakage criterion.

3.1.1 Pullout Load Tests Methods and Criteria

Pullout testing was conducted in laboratory facilities in Chattanooga, Tennessee and in Windsor,

Connecticut using calibrated load cells (16, 17). Pullout testing is reported in Section 4 as the

force required to move the tube in the tubesheet hole against the sliding friction. Data is reported

in units ofpounds- force (lbf.).

Figure 3.1 is a schematic representation ofthe load cell used for the pull tests. Figure 3.2 is a

photograph ofthe load cell apparatus used in the tests conducted in Windsor. Figure 3.3

illustrates the data logging and process control equipment used in the Windsor tests. Chattanooga

load cell equipment was essentially the same.

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Section 3


The pull test results were directed toward establishing the threshold length below which a

completely severed tube would not be ejected from the tubesheet. Mockups with varying

engaged lengths oftubing were tested in accordance with Procedure 00-TP-FSW-001, Rev. 01.

The engaged lengths for rough hole mockups were 2, 2.5, 3, 3.5 and 4 inches.

The equipment for the pull tests in the Chattanooga and Windsor laboratories were similar and

both were calibrated to accepted standards. For the tests performed in Chattanooga, a mechanical

gripper secured the upper end ofthe tube to the load cell. A tight fitting mandrel inside the tube

prevented the gripper from deforming the tube at the gripper location and a bracket secured the

mockups to the piston that applied the load. For the tests performed in Windsor, a retention plate

with a threaded hole was used to secure the upper end ofthe tube to the load cell and a similar

plate was used to secure the single tube mockup to the crosshead. Threaded plugs that had a

means ofallowing water to enter and exit the tube were welded to the upper end ofthe tube and

to the lower end ofthe single tube mockup. The threaded portion ofthe plugs were screwed into

the threaded hole ofthe two retention plates. Whena

pressurizedtest was conducted, the tube

was filled and pressurized with water through holes that were drilled in the plug. X-Y plotters

were used to record load versus crosshead displacement.

After the specimen was secure in the test machine, loads were applied at a fixed crosshead

displacement rate in the Windsor tests and at a manually adjusted load in the Chattanooga tests

until the severed tube was pulled from the tubesheet. The load at which first slippage ofthe tube

in the tubesheet occurred and the maximum load during the test were noted and recorded. A plot

ofload versus crosshead displacement was also obtained for each mockup tested. In the

Chattanooga tests, the slope ofthe ascending load vs. time curve varied as the rate at which the

hydraulic pump pressure regulator screw was adjusted. This was done manually and intentionally

slowly so as not to miss the data readings. Once the tube began to move, the pressure regulatorwas not adjusted any more, unless the tube stopped moving. In most cases, the maximum force

was achieved after the tubes had moved some distance.

The pressurized specimens had welded plugs ofthe same type as the high temperature leak rate

specimens. During the pull tests, these specimens had an internal pressure of2575 psi + 100 -0

psi to determine ifinternal pressure would affect the loads required to displace the specimens

from the tubesheets.

An accumulator with a 3000 psig rating and a three gallon capacity or a positive displacement

pump were used to maintain pressure during tests.

For the hydrostatic test approach, a nitrogen gas bottle was used to apply pressure to the

accumulator. A system to collect the leakage from the mockup was used to insure that the

amount ofspillage onto the test machine was minimized. The mockups were pressurized to the

specified pressure before starting the test and the pressure was maintained until approximately

one-halfinch oftubing remained in the mockup, at which time pressure was reduced to 0 psig.

The data acquisition system monitored mockup pressure throughout the test.

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Section 3Technical Approach Summary

The pullout load criterion is based on 3NODP. The 3NODP value is 4410 psid based on SONGS

data:

NODP 1470 psid3NODP 4410 psid

Pullout is based on the tube burst criteria of3NODP because it was conservatively assumed for

this work (consistent with W*) that the tube is completely severed and can move axially up

under a pressure load. Ifthe severed tube can exit the tubesheet, system effects and off-site dose

consequences would be the same as a postulated guillotine tube burst. The 3NODP criterion is

consistent with NEI 97-06 requirements (11) and is conservative relative to the criterion of1.4

times the MSLB differential pressure (including accounting for the larger dilation ofthe

tubesheet holes). Because the MSLB is the most probable event that would cause a tube to be at

risk for pullout and because the MSLB criterion is a fixed value whereas 3NODP increases

margin as steam generator pressure degrades over the operating life ofthe plant due to plugging,etc., the 3NODP criterion is considered as very conservative for use in this test program.

The pull force is dependent upon the contact force, contact area, coefficient offriction, and in

general, the tribology. Pullout at 3NODP for these tests is recorded as a function ofjoint length

and tube surface roughness. The force (F) required on a 0.75" nominal diameter tube equivalent

to 4410 psid is:

Tube area = 7r 0.758" / 2)2 = 0.451 in.2

F = 4410 lbf/in * 0.451 in. =- 2000 lbf. (1989 lbfrounded up)

Pullout force was applied using two different load cell processes. The Chattanooga load cellapplied a manually adjustable constant load process. The Windsor load cell was applied in a

constant displacement rate process. The test plan called for two single tube mockup specimens to

be tested in Chattanooga as a cross-reference between the Chattanooga and Windsor load cell

tests to show that the test setups would provide comparable results. The difference in processes

results in some variability in the results as indicated by the two rough bore single tube mockup

specimens (specimens 20 and 21) tested in Chattanooga and the remainder ofthe rough bore

single tube mockup specimens tested in Windsor.

Pullout testing was conducted after leak rate testing on the majority ofthe specimens. A few

specimens had pull tests without leak tests. Measurements were taken on the Boston Edison SG

before and after leaktesting from a fixed reference point to determine tube movement. Table 3-1illustrates that thejoint was not measurably disturbed at the leak test pressure (i.e. MSLB

pressure).

3.1.2 LeakRate Tests Methods and Criteria

Leak rate is a function ofdifferential pressure. Empirical data is necessary for understanding the

leakrate as a function ofjoint length but the Poiseuille equation (L2) provides an expression that

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Section 3


approximates the fundamental relationship between the length ofthe tubesheetjoint and leak

rate:

dP= 64 L p v

2

Re D 2g,

Where:

Re = Reynolds number

D in this case, the diameter difference between the tube and tubesheet

p = fluid density

g= gravitational constant

L - joint length

v = fluid velocity or flow rate

dP = differential pressure at MSLB

For the leak rate tests conducted in this project, all ofthe terms in the equation are essentially

constant except thejoint length and flow rate. Therefore, it can be stated that the flow rate varies

inversely as the square root ofthejoint length. This relationship indicates that flow rate should

reduce quickly over a very sltortjoint length and then flatten out over longerjoint lengths. This

set oftests did not attempt to establish experimentally or analytically the knee ofthe curve or a

usable formulation to cover alljoint lengths. This relationship is conservative with respect to

expected flow conditions in the event ofa MSLB. During a MSLB event the maximum

differential pressure (the flow forcing function) will occur when the steam generator pressure is

approaching atmospheric pressure. Any primary coolant leaking from tubesheetjoints into

atmospheric pressure will undoubtedly flash to steam and create a choked flow condition. Thechoked flow condition is not considered in this project but is an additional conservatism in the

development ofthe thresholdjoint length. The purpose ofthese tests was to determine a

sufficient joint length that satisfied the criteria and provided a cost-effective NDE inspection

length.

The leak rate criterion is based on the generic allowable leakage technical specification limiting

condition for operation of0.5 gpm per steam generator. Operational assessment calculations

include assumptions for undetected flaw populations and determine acceptable plant run-time

based in part on acceptable EOC leakage. [

](c)

Each tube has twojoints - the hot leg and the cold leg sides. PWSCC is a temperature driven

cracking mechanism and hot-legjoints will be the predominate number oftubejoints affected

over time. On this basis, only the hot- legjoints are considered in the development ofthreshold

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Section 3


length for inspection. Leakrate is considered cumulatively for all tubejoint leaks in the steam

generator. Therefore, the test results provided on a singlejoint basis are multiplicative ofthe

number oftubes assumed to be leaking. [

](c) This approach is very conservative as explained in Section 1.5.

Leakrate testing was used to determine thejoint length (i.e. the threshold length for leakage) for

acceptable leakage at MSLB conditions from through-wall defects located within the tubesheet

region. This phase ofthe program used the tube-tubesheet joint mockups and cut tubes in the

scrapped Boston Edison steam generator. A test procedure U(3), was developed and used for

both types oftests.

Figure 3.4 is a schematic diagram ofthe leak rate test system. The testing system consisted of:

"* An air operated positive displacement pump (Haskel model MS 110),"* A calibrated pressure gauge (0 to 10,000 psi),

"* A calibrated pressure transducer (0 to 7,500 psi range),

"* Data acquisition system (including DATAQ signal conditioner/processor and a

computer),"* A reservoir ofdemineralized water, a high pressure hose with a mechanical plug/seal,

and

* Ancillary tubing and valves

It was not necessary to adjust leakrates for accident conditions. Appendix D ofthe EPRI Steam

Generator In Situ Guidelines (26) calls for a correction to account for the difference in materialproperties at room and operating temperature. The factors tha

ml021480131 - exigent steam generator technical specification changesan onofre nuclear generating...

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