ML20236T604

Proposed Tech Specs Incorporating Elevated F* SG Tube Repair Criteria

ML20236T604
Person / Time
Site:	Prairie Island
Issue date:	07/20/1998
From:	NORTHERN STATES POWER CO.
To:
Shared Package
ML20236T597	List: ML20236T595 ML20236T604
References
NUDOCS 9807280284
Download: ML20236T604 (10)

Text

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l I~ Attachment 1

. 4 Updated, Revised Technical Specification Pages Pages:

TS.4.12-2

! TS.4.12-3 TS.4.12-4 l TS.4.12-5 TS.4.12-6 TS.4.12-7 Table TS.4.12-1 B.4.12-2 B.4.12-3 1

l l

l new ta pages for EP star amendment. DOC 9907290294 990720 PDR ADOCK 05000282 P PM ,

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TS.4.12-2 REV l

2. The first sample of tubes selected for each in-service inspection (subsequent to the preservice inspection) of each steam generator j shall include:

i

! (a) All tubes that previously had detectable wall penetrations j (>20%) that have not been plugged or sleeve repaired in the i affected area.

l l (b) Tubes in those areas where experience has indicated potential problems.

l (c) A tube inspection-(pursuant to Specification 4.12.D.1.(h))

i shall be performed on each selected tube. If any selected l' tube does not permit the passage of the eddy current probe L for a tube inspection, this shall be recorded and an

! adjacent tube shall be selected and subjected to a tube

! inspection.

3. In addition to the sample required in Specification 4.12.B.2.a through c. all tubes which have had the F* or EF* criteria applied will be inspected in the F* and EF* regions of the roll expanded region. The region of these tubes below the F* and EF*

regions may be excluded from the requirements of 4.12.B.2.a.

4. The tubes selected as the second and third samples (if required by Tables TS.4.12-1 or TS.4.12-2) during each inservice i inspection may be subjected to a partial tube or sleeve inspection provided:

.(a) The tubes selected for these samples include the tubes from those areas of the tube sheet array where tubes with imperfections were previously found.

(b) The inspections include those portions of the tubes or sleeves where imperfections were previously found.

The results of each sample inspection shall be classified into one of the following three categories:  ;

Category Inspection Results C-1 Less than 5% of the total tubes inspected are degraded tubes and none of the inspected tubes are defective.

C-2 One or more tubes but not more than 1% of the total l

tubes inspected are defective, or between 5% and 10%

of the total tubes inspected are degraded tubes.

l- C-3 More than 10% of the total tubes inspected are degraded tubes or more than 1% of the inspected tubes  !

are defective.

Note: In all inspections, previously degraded tubes must exhibit significant (>10%) further wall penetrations to be included l

in the above percentage calculations.

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, TS.4.12-3 l REV l

l S. Indications left in service as a result of application of tube support plate voltage-based repair criteria shall be inspected by bobbin coil

' probe during all future refueling outages.

6. Implementation of the steam generator tube / tube support plate repair l criteria requires a 100 percent bobbin coil inspection for hot leg and cold leg tube support plate intersections down to the lowest cold leg {

tube support plate with known outside diameter stress corrosion cracking l (ODSCC) indications. The determination of the lowest cold leg tube support plate intersections having ODSCC indications shall be based on the performance of at least a 20 percent random sampling of tubes inspected over their full length.

C. Inspection Frequencies-The above required in service inspections of steam generator tubes shall be performed at the following frequencies:

1. In-service inspections shall be performed at intervals of not less than 12 nor more than 24 calendar months after the previous inspection. If two consecutive inspections following service under AVT conditions, not including the preservice inspection. result in all inspection results j falling into the C-1 category or if two consecutive inspections 1 demonstrate that previously observed degradation has not continued and no additional degradation has occurred, the inspection interval may be extended to a maximum of once per 40 months.

2. If the results of the inservice inspection of a steam generator conducted in accordance with Table TS.4.12-1 at 40 month intervals fall in Category C-3. the inspection frequency shall be increased to at least once per 20 months. The incresse in inspection frequency shall apply until the subsequent inspections satisfy the criteria of Specification 4.12.C.1: the interval may then be extended to a maximum of once per 40 months.

3. Additional unscheduled inservice inspections shall be performed on each steam generator in accordance with the first sample inspection specified in Table TS.4.12-1 during the shutdown subsequent to any of the following conditions.

(a) Primary-to-secondary tube leaks (not including leaks originating from tube-to-tube sheet welds) in excess of the limits of Specification 3.1.C.6.

(b) A seismic occurrence greater than the Operating Basis Earthquake.

(c) A loss-of-coolant accident requiring actuation of the engineered safeguards.

(d) A main steam line or feedwater line break.

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,' TS.4.12-4 REV D. Agneptance Criteria

1. As used in this Specification:

'(a) Imperfection means an exception to the dimensions. finish or contour of a tube from that required by fabrication drawings or specifications. Eddy-current testing indications below 20% of the nominal tube wall thickness, if detectable, may be l considered as imperfections.

L (b) Degradation means a service-induced cracking wastage, wear or general corrosion occurring on either inside or outside of a j . tube.

(c) . Degraded Tube means a tube containing imperfections 220% of the nominal wall thickness caused by degradation.

(d)  % Degradation means the percentage of the tube wall thickness affected or removed by degradation.

l (e) Defect means an imperfection of such severity that it exceeds

[ the repair limit. A tube containing a defect is defective.

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.( f) Repair Limit means the imperfection depth at or beyond which l the tube shall be removed from service by plugging or repaired by sleeving because it may become unserviceable prior to the

! next inspection and is equal to 50% of the nominal tube wall thickness. If significant general tube thinning occurs. this criteria will be reduced to 40% vall penetration. This definition does not apply to the portion of the tube in the tubesheet below the F*'or EF* distance provided the tube is not i l degraded (i.e.. no indications of cracks) within the F* or EF* 1 distance for F* or EF* tubes. The repair limit for the I pressure boundary region of any sleeve is 31% of the nominal sleeve wall thickness. This definition does not apply to tube L support plate intersections for which the voltage-based repair _

l criteria are being applied. Refer to Specification 4.12.D.4 l for the. repair limit applicable to these intersections.

! (g) Unserviceable describes the condition of a tube if it leaks or l contains.a defect large enough to affect its structural  ;

integrity in the event of an Operating Basis Earthquake, a J loss-of-coolant accident. or a steam line or feedwater line break.

'(h) Tube Incoectinn means an inspection of the steam generator tube '

from the point of entry (hot leg side) completely around the U-bend to the top support of the cold leg. j (i) Sleeving is the repair of. degraded tube regions using a new Alloy 690 tubing sleeve inserted inside the parent tube and l sealed at each end by velding or by replacing the lower veld in a full depth tubesheet sleeve with a hard rolled joint. The new sleeve becomes the pressure boundary spanning the original degraded tube region.

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, TS.4.12-5 REV F=

l (j) F* Distance is the distance from the bottom of the hardroll L

transition toward the bottom of the tubesheet that has been l conservatively determined to be 1.07 inches (not including eddy j- current uncertainty). The F* distance applies to roll expanded regions below the midplane of the tubesheet.

(k) F* Tube is a tube with degradation, below the F* distance, equal to or greater than 40%, and not degraded (i.e., no indications of cracking) within the F* distance.

(1) EF* Distance is the distance from the bottom of the upper hardroll transition toward the bottom of the tubesheet that has l- been conservatively determined to be 1.62 inches (not including i eddy current uncertainty). EF* diatence applies to roll

expanded regions when the top of the additional roll expansion

! is 2.0 inches or greater down from the top of the tubesheet.

(m) EF* Tube is a tube with degradation, below the EF* distance.

equal to or greater than 40%, and not degraded (i.e., no 1 indications of cracking) within the EF* distance.  !

2. The steam generator shall be determined OPERABLE after completing the

corresponding actions (plug or repair by sleeving all tubes exceeding the repair limit and all tubes containing through-wall cracks or classify as F* or EF* tubes) required by Tables TS.4.12-1 and l TS.4.12-2.  !

3. Tube repair, after October 1, 1997, using Combustion Engineering welded sleeves shall be in accordance with the methods described in the following:

CEN-629-P, Revision 2. " Repair of Westinghouse Series 44 and 51 Steam Generator Tubes Using Leak Tight Sleeves":

CEN-629-P, Addendum 1, Revision 1. " Repair of Westinghouse Series 44 and 51 Steam Generator Tubes Using Leak Tight Sleeves"

4. Tube Support Plate Renair Limit is used for the disposition of a steam generator tube for continued service that is experiencing predominantly axially oriented outside diameter stress corrosion l cracking confined within the thickness of the tube support plates.

At tube support plate intersections, the repair limit is based on maintaining steam generator serviceability as described below:

a. Steam generator tubes, whose degradation is attributed to outside diameter stress corrosion cracking within the bounds of the tube  ;

support plate with bobbin voltages less than or equal to 2.0 volts will be allowed to remain in service.

b. Steam generator tubes, whose degradation is attriauted to outside diameter stress corrosion cracking within the bounds of the tube support plate with a bobbin voltage greater than 2.0 volts, will be repaired or plugged, except as noted in Specification 4.12.D.4.c below.

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,' TS.4.12-6 REV I

c. Steam generator tubes, with indications of potential degradation l attributed to outside diameter stress corrosion cracking within l the bounds of the tube support plate with a bobbin voltage greater '

than 2.0 volts but less than or equal to the upper voltage repair l limit, may remain in service if a rotating pancake coil (or comparable examination technique) inspection does not detect degradation. Steam generator tubes, with indications of outside diameter stress corrosion cracking degradation with a bobbin voltage greater than the upper voltage repair limit will be plugged or repaired.

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d. If an unscheduled mid-cycle inspection is performed, the following mid-cycle repair limits apply instead of the limits in Specifications 4.12.D.4.a. b and c. The mid-cycle repair limits are determined from the following equations:

ymu - - SL

< CL - A t '

1.0 + NLR5 + Gr

< CL >

l

Vntat =Y nuat - (Vust - 2.0) f CL - At'

< CL ,

vhere:

Vnt - upper voltage repair limit Vuz = lower voltage repair limit

! Vmmt - mid-cycle upper voltage repair limit based on time into cycle l Vmat mid-cycle lower voltage repair limit based on Vmmt and j time into cycle l

at= length of time since last scheduled inspection during which Vnt and Vua were implemented CL = cycle length (time between two scheduled steam generator l inspections) l I

Vst = structural limit voltage Gr = average growth rate per cycle length NDE = 95 percent cumulative probability allowance for nondestructive examination uncertainty (i.e., a value of 20 percent has been approved by the NRC)

Implementation of these mid-cycle repair limits should follow the same approach as described in Specifications 6.12.D.4.a b and c.

Note: The upper voltage repair limit is calculated according to l the methodology in Generic Letter 95-05 as supplemented.

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TS.4.12-7 REV j E. Reports i

1. Following each in-service inspection of steam generator tubes, if there

'are any tubes requiring plugging or sleeving, the number of tubes {

I plugged or sleeved in each steam generator shall be reported to the Commission within 15 days.

2. The results of steam generator tube inservice inspections shall be included with the summary reports of ASME Code Section XI inspections submitted within 90 days of the end of each refueling outage. Results of steam generator tube inservice inspections not associated with a refueling outage shall be submitted within 90 days of the completion of the inspection. These reports shall include: (1) number and extent of tubes inspected, (2) location and percent of wall-thickness penetration for each indication of an imperfection and (3) identification of tubes plugged or sleeved. l

3. Results of steam generator tube inspections which fall into Category  ;

C-3 require notification to the Commission prior to resumption of plant l operation, and reporting as a special report to the Commission within 1 30 days. This special report shall provide a description of l

investigations conducted to determine cause of the tube degradation and '

corrective measures taken to prevent recurrence.

4. The results of inspections performed under Specification 4.12.3 for all tubes that have defects below the F* or EF* distance, and were not l plugged, shall be reported to the Commission within 15 days following l the inspection. The report shall include:

a. Identification of F* and EF* tubes. and l

b. Location and extent of degradation.

5. For implementation of the voltage-based repair criteria to tube support plate intersections, notify the NRC staff prior to returning the steam generators to service should any of the following conditions arise:

a. If estimated leakage based on the projected end-of-cycle (or if not practical, using the actual measured end-of cycle) voltage distribution exceeds the leak limit (determined from the licensing basis dose calculation for the postulated main steamline break) for the next operating cycle.

l b. If circumferential crack-like indications are detected at the tube support plate intersections.

c. If indications are identified that extend beyond the confines of l the tube support plate.

d. If indications are identified at the tube support plate elevations that are attributable to primary water stress corrosion cracking.

e. If the calculated conditional burst probability based on the projected end-of-cycle (or if not practical, using the actual measured end-of cycle) voltage distribution exceeds 1 x 10".

notify the NRC and provide an ansessment of the safety significance of the occurrence.

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, B.4.12-2 REV l 4.12 STEAM GENERATOR TUBE SURVEILLAblC2 l Hasta continued l

l 0.025 Mehes will have adequate margins of safety against failure due to loads' imposed by normal plant operation and design basis accidents (Reference 1). Steam generator tube inspections of operating plants have

! demonstrated.the capability to reliably detect wastage type defects that j

have penetrated 20% of the original 0.050-inch wall thickness (Peference 2).

(' Flugging or sleeving is nat required for tubes meeting the F* or EF* criteiria.

Due to the variable effect of tubesheet bow with elevation the F* criterion

!- applies only below the tubesheet centerline and the EF* criterion is applied no higher than two inches down from the top of the tubecheet.

The F.* and EF* distances will be con:crolled by a combination of eddy current l

inspection and/or process control. For a new additional roll expansion, the requirement will be at least 1.2 (1.8 inches for EF*) inches of new hard roll.

This is controlled by the 1.25 inch (two inches for EF*) effective length of the rollers. The distance from the original roll transition zone is also.

controlled by the process in that the lower end of the new roll expansion is located one inch or greater above the original roll expansion. In the case'of l the new roll, eddy current examination will confirm there are no indications in the new roll region and that there is a new roll region with well defined i- ' upper and-lower expansion transitions.

When eddy current examination, alone, must determine the F* or EF* distance. l such as in the existing hard roll region, or when multiple lengths of additional hard rolls have been added, the eddy current uncertainty is qualified by testing against known standards. That value is expected to be 0.18 inches. Therefore, the F* distance measured by eddy current (sum of 1.07 and 0.18) will be conservatively set at 1.3 inches. The EF* distance measured by eddy current (sum of 1.62 and 0.18) will be conservatively set at 1.9 inches.

When more than one Alternate Repair Criteria are used, the summation of leakage from all tubes left in service by all repair criteria must be less than the allowable leakage for the most limiting of those Alternate Repade Criteria.

l Whenever the results of any steam generator tubing in-service inspection fall

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into Category C-3. these results will be promptly reported to the Commission prior to resumption of plant operation. Such cases will be considered by the Commission on a case-by-case basis and may result in a requirement for I analysis laboratory examinations, tests. additional addy-current inspect $on, and revision of the Technical Specifications.if nseessary.

Degraded steam generator tubes may be repaired by the installation of l sleevas which span the section of degraded utesm generator tubing. A L steam generator tube with a sleeve installed meets the structural i requirements of tubes which are not degraded.

I l- The following sleeve designs have been found acceptable by the NRC Staff: ,

a. Westinghouse Mechanical Sleeves (WCAF 10757)

b. Westinghouse Brazed Sleeves (WCAP 10820)

L c. Combustion Engineering Leak Tight Sleeves (CEN 294-F. for sleeves

' installed prior to October 1. 1997) l.

[i

o.

B.4.12-3 REV 4.12 STEAM GENERATOR TMLSURVEILLAEE Banga continued 9

• L d. Combustion Engineering Leak Tight Sleeves (CEN-629-P. for sleeves installed after October 1. 1997)

Descriptions of other future sleeve designs shall be submitted to the NRC for review and approval prior to their use in the repair of degraded steam generator tubes. The submittals related to other sleeve designs shall be made at least 90 days prior to use.

Tube Sugggrt Pla.te Repair Limit The voltage-based repair limits of Specification 4.12.D.4 implement the guidance in Generic Letter 95-05 and are applicable only to Westinghouse-designed steam generators with outside diameter stress corrosion cracking (ODSCC) located at the tube-to-tube support plate intersections. The voltage-based repair limits are not applicable to other forms of steam generator tube degradation nor are they applicable to ODSCC that occurs at i

other locations within the steam generator. Additionally, the repeir criteria apply caly to indications where the degradation mechanism is dominantly axial ODSCC with no significant cracks extending outside the l thickness of the support plate. Refer to Generic Letter 95-05 for l additional description of the degradation morphology.

I Implementation of Specification 4.12.D.4 requires a derivation of the voltage structural limit from the burst versus voltage empirical correlation and then the subsequent derivation of the voltage repair limit from the structural limit (which is then implemented by this surveillance). 1 The voltage structural limit is the voltage from the burst pressure / bobbin voltage correlation. at the 95 percent prediction interval curve reduced to account for the lower 95/95 percent tolerance bound for tubing material properties at 650'F (i .e . . the 95 percent LTL curve). The voltage structural limit must be adjusted downward to account for potential flaw i

growth during an operating interval and to account for NDE uncertainty.

The upper voltage repair limit: Vat . is determined from the structural voltage limit by applying the following equation:

Vat = Vst - Vor - %s where Var represents the allowance for flaw growth between inspections and Vn represents the allowance for potential sources of error in the measurement of the bobbin coil voltage. Further discussion of the assumptions necessary to determine the voltage repair limit are discussed l

in Generic Letter 95-05.

The mid-cycle equation in Specification 4.12.D.4 should only be used during unplanned inspections in which eddy current data is acquired for indications at the tube support plates.

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