ML20217F955

Application for Amends to Licenses DPR-77 & DPR-79,proposing Change to TS SRs & Bases to Incorporate ARC for Axial Primary Water Stress Corrosion Cracking at Dented Tube Support Plant Intersections

ML20217F955
Person / Time
Site:	Sequoyah
Issue date:	10/14/1999
From:	Salas P TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20217F959	List: ML20217F955 ML20217F970
References
TVA-SQN-TS-99-1, NUDOCS 9910210136
Download: ML20217F955 (14)

Text

"

.r e-j lhkOk l l

Tennessee VaHey Autrdty. Post Office Box 2000. Soddy-Daisy. Tennessee 37379 October 14, 1999 l

I TVA-SQN-TS-99-12 10 CFR 50.90 l L l

[ '

.U.S. Nuclear Regulatory Commission ATTN: Document-Control Desk Washington, D. C. 20555 Gentlemen:

In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority i 50-328 SEQUOYAH NUCLEAR PLANT (SQN) - UtL :) 1 AND 2 - TECHNICAL SPECIFICATION (TS) CHANGE No. 99-12, " ALTERNATE REPAIR CRITERIA (ARC) FOR STEAM GENERATORS (S/G) "

Reference:

TVA letter to NRC dated August 16, 1999, "Sequoyah Nuclear Plant (SQN) - Westinghouse Electric Company Topical Report" In accordance with the provisions of 10 CFR 50.4 do.90 TVA is submitting a request for an amendment to {

Licenses DPR-77 and 79.to change the TSs for Unit and 2. l The proposed. change revises TS surveillance requi: 1.ments and )

bases.to incorporate an ARC for axial primary water stress l corrosion cracking at dented tube support plate intersections. l l

TVA has determined that there are no significant hazards l considerations associated with the proposed change and that l the change is exempt frem environmental review pursuant to j the provisions of 10 CFF 51.22 (c) (9) . The SQN Plant j Operations ~ Review Committee and the SON Nuclear Safety Review ,

Board hatre reviewed this proposed change and determined that I operation of. SON Units 1 in accordance with the  !

g o a gp 2, 9910210136 991014-PDR 4 I ADOCK 05000327 I

,i. P- PDR ~

1 l

1

Y '

9 L U.S'.; Nuclear Regulatory Commission Page 2

' October-14, 1999.

. proposed: change,:will not. endanger the health'and safety of

'the public'. Additionally, in accordance with'10'CFR 50.91(b) (1), TVA is ' sending a copy of this letter to the Tennessee State' Department of Public. Health.

The' proposed TS changefis based on the methodology documented in Revision 1 t'o WCAP-15128,' dated 1 August 1999. Revision 0.

of this WCAP.was previously~ submitted to you by the referenced letter for1 advance-review.  ;

i 1

Enclosure 1 to this letter provides'the description and l

' evaluation-of the proposed TS change. .This includes TVA's

' determination-that the proposedLchange does not involve a Jsignificant hazards consideration, and'is' exempt from' i

environmental review. Enclosure 2 contains copies of the i appropriate TS:pages.from Unit's 1 and 2 marked up to show the {

. proposed' change. . Enclosure-3 forwards the. revised TS pages I for Units 1 and.2 which incorporate the proposed change.

TVA'is submitting this TS change'in advance of the Unit 1 Cycle >10 (U1C10) refueling outage. NRC approval of this TS change,is requested to support'the UIC10 refueling outage ,

currently scheduled to begin on February 22, 2000. l TVA requests that-the revised TS be made effective within i

-45.da'ys of NRC approval.. -If you have any questions.about.

this change, please telephone mesat (423) 843-7170 or J. D. .

Smith 'at' - (423) 841-6672'.

itnc s .

r ,-- ~

P Salas Lic,ensing and Ind'ustry Affairs Manager

, Y.

ecribed d sworn to b o e me on' . his' ^) day ' of A D ifA]'

lD I Y I A

l -. Notdff'Public F ' f My Commission 1 Expires October 9, 2002-

-Enclosures

,cc: .See pageL3 y r b

t g

5.

i: ,-

R U.S. Nuclear Regulatory, Commission Page-3

- October 14, 1999- ,

I i

l I

. cc (Enclosures).  ;

Mr. R. W. Hernan, Project Manager Nuclear Regulatory Commission l

One:,WhiteLFlint, North 11555 Rockville: Pike  !

Rockville, Maryland'20852-2739L {

Mr. Michael H. Mobley,' Director (w/o Enclosures)

Division of Radiological Health.

]j Third Floor L&C Annex  !

401 Church: Street Nashville, Tennessee-37243-1532 NRC Resident-

.Sequoyah-Nuclear Plant 2600'Igou Ferry Road Soddy-Daisy, Tennessee 37384-2000 q l

Regional Administrator U.S. Nuclear Regulatory Commission Region II' l Atlanta Federal Center i 61 Forsyth St., SW,. Suite 23T85 l

~ Atlanta, Georgia 30303-3415 1

l

- I f

f

$k -

pp '+y, ,

i : x:

t I I T

re -

't ENCLOSURE 1 TENNESSEE VALLEY AUTHORITY SEQUOYAH NUCLEAR PLANT (SQN)

UNITS 1 AND 2 t DOCKET NOS. 327 AND 328 PROPOSED TECHNICAL SPECIFICATION (TS) CHANGE DESCRIPTION AND EVALUATION OF THE PROPOSED CHANGE I. DESCRIPTION OF THE PROPOSED CHANGE TVA proposes to modify the SON Units 1 and 2 TSs to incorporate new surveillance and reporting requirements associated with steam generator (S/G) tube inspection and repair. The new requirements establish alternate repair criteria (ARC) at dented tube support plate (TSP) intersections. The proposed changes are as follows:

1. Add Surveillance Requirement (SR) 4.4.5.2.e that reads:

"e. Inspection of dented tube support plate inte:: sections will be performed in accordance with WChP 15128, Revision 1, dated August 1999."

2. Add language to the plugging limit acceptance criteria of SR 4.4.5.4.a.6. that reads:

"This definition does not apply for greater than or equal to 40 percent deep indications of axial PWSCC located within the tube support plate, PWSCC indications located within and extending outside the tube support plate, or PWSCC indication located at the edge of the tube support plate. Refer to 4.4.5.4.a.11 for the repair limits applicable to these intersections."

3. Add Item 11 to Acceptance Criteria of SR 4.4.5.4.a that reads:

Primary Water Stress' Corrosion Cracking (PWSCC)

~

"11.

Tube Support Plate Plugging Limit is used for the disposition of.an Alloy 600 steam generator tube for continued service that is experiencing predominantly axially oriented PWSCC at dented tube support plate intersections as described in WCAP 15128, Revision 1, dated August 1999."

El-1

. .w-

'P

.7

4. Add Reporting Requirement (Item e) to SR 4.4.5.5 that reads:

"e. For implementation of the depth-based repair criteria for axial PWSCC at dented TSPs, the results of the condition monitoring and

< operational assessments will be reported to the NRC within 120 days following completion of the inspection. The report will include tabulations of indications found in the inspection, tabulations of tubes repaired and left in service under the ARC, and growth rato distributions for .

indications found in the inspection as well as the growth distributions used to establish the tube repair limits. Any corrective actions found necessary in the' event that condition monitoring requirements are not met will be identified in the report."

5. Add language to Bases Section 3/4.4.5 Steam Generators that reads:

"The steam generator tube repair limits for primary water stress corrosion cracking (PWSCC) of SR 4.4.5 represents a steam generator tube alternate repair criteria for greater than or equal to 40 percent deep PWSCC indications within the tube support plate, PWSCC indications located within and extending outside the tube support plate, or PWSCC. indications located at the edge of the tube support plate. The repair bases for PWSCC are not applicable to other types of localized tube wall degradation-located at the tube-to-tube support plate intersections.

The. ARC includes completion of a condition monitoring assessment to determine the end-of-life (EOC) condition of the tube bundle. Next, an operational assessment is completed to determine the need for tube repair on a forward-fit basis. The ARC is based on the use of crack depth profiles obtained from Plus Point analyses.

Burst pressures are calculated from depth profiles by searching the total crack length for the partial length '

that results in the lowest burst pressure. The repair bases for PWSCC at dented TSP intersections are obtained by projecting the crack profile to the end of the next operating cycle and determining if the projected profile meets the burst margin requirements of WCAP-15128, Revision 1, dated August 1999. The following provides the limits and bases for repair established in the WCAP analyses:

El-2 i

__a

.c '

Maximum Depth Repair Limit The repair. limit for maximum depth is established to obtain a low likelihood of SLB leakage for the operational assessment. The repair limit is based on ensuring against through-wall degradation at 95 percent confidence. The repair limit for maximum depth is obtained by reducing through-wall penetration by 2 percent for breakthrough, by NDE uncertainties on maximum depth at 95 percent confidence and by growth of maximum depth at 95 percent cumulative' probability. j Note: The maximum depth repair. limit is dependent upon growth rate and cycle length. Repair limits are i updated when new growth data is obtained and when cycle i lengths and/or operating temperatures are changed. i Crack Length Limits The crack length limit is defined as 0.60 inches from the centerline of the TSP.

Note: The 0.60 inch length limit allows a crack to begin the cycle with a length of 0.225 inch outside the TSP (TSP is 0.375 inch + 0.225 inch = 0.60 inch) . The 0.225 inch allows a margin of 0.275 inch for potential

. growth to 0.5 inch outside the TSP which bounds ,

expected growth at 95 percent confidence. This maximum i length limit is provided to limit potential freespan lengths and provide significant margins against leakage and burst. The crack left in service must also satisfy the following operational assessment repair bases.

Operational Assessment Repair Bases j If the indication' satisfies the above maximum depth and total length requirements, the repair bases is then obtained by projecting the crack profile to the end of the next operating cycle and determining the burst i pressure for the projected profile. The burst pressure is compared to the burst. margin requirements in WCAP-15128, Revision 1, dated August 1999. Separate burst analyses are required for the total crack length and the length outside the TSP due to differences in burst margin-requirements. If the. projected EOC burst margin l requirements are satisfied, the indications will be l left in service;  ;

The results of the condition monitoring and operational assessments will be reported to the NRC within 120 days

- following completion of the inspection."

i El-3 M _ _

't-3.

II. -REASON FOR THE PROPOSED CHANGE TVA'is proposing to change. SON Unit 1 and 2 TSs to avoid the need.for repairing or plugging.S/G tubes'having-indications with greater.than or equal to 40 percent deep axial PWSCC at dented TSP intersections. . The proposed change would preserve reactor coolant-flow margins through the S/Gs that are; assumed in the loss of coolant accident (LOCA) analysis.

In. addition, the proposed change reduces the radiation exposureLincurred by personnel involved in tube pluggingLand repair operations (approximately 0.060 ' man-rem per tube of exposure'would be-saved for a plugging operation). Other benefits of'not plugging TSP indications that meet the ARC would-be a' reduction in man-hours and potential impact to critical path time during refueling outages.

III. SAFETY ANALYSIS The purpose of S/G tube repair limits is-to provide reasonable assurance that tubes accepted for continued service without plugging and repair will exhibit adequate structural and leakage integrity with appropriate allowance )

for error or variability and for defect growth prior to the next inservice inspection.

TVA's proposed TS amendment implements ARC for axially oriented PWSCC indications at dented tube TSP l intersections. The analysis for this ARC (as documented in WCAP.15128,. Revision 1, dated August 1999) is based on the

. computational assessment that is to be completed for each tube indication.to ensure that each indication meets j specific performance criteria for tube integrity and leak tightness until the next scheduled inspection. The ARC is based on the use of. crack profiles obtained from Plus. Point ,

analyses. Tube burst pressures are calculated from the  !

depth profiles by searching the total-crack length for the l partial length that results in the lowest burst pressure. ,

-The' length'and average depth repair bases is obtained by projecting the crack profile to the end of the next operating cycle and. determining if the burst pressure for l

El-4 w e

t 6 :

t the' projected profile meets.the burst pressure margin requirements.~ If the projected EOC burst margin is satisfied, the' indication is left in service. Thus, the repair, bases relative to length and average depth assures that the' operational assessment requirements are satisfied.

Crack length' limits.are defined to assure that crack extensioncand' growth'outside of the TSP provide adequate

margin against burst for the free span crack in addition to

.the total: crack length. A-repair limit is-also established on. maximum depth-to provide a high confidence that the

indication will not progress through the wall at the end of an_ operating-cycle.

A. description of some'of the criteria for the proposed ARC is described below:

LFreespan Indications Freespan is defined'as an indication originating from the dented intersection, but located entirely outside the-TSP, with one or_both' crack tips' greater than 0.25 inch from the TSP edge. Freespan-indications are repaired if the maximum depth is greater than or equal to 40 percent. This criteria applies the current TS repair limit when using a qualified sizing technique.

Indications With the Crack Tip Less Than 0.6 Inch From the Center of the TSP The current tube plugging limit is changed to permit an assessment-for each indication.

.Afcondition monitoring assessment is completed for each

~ indication.to determine EOC compliance with the' guidelines of_ draft _NRC Regulatory _ Guide (RG) 1.121 and Revision 1 to RG 1.83.

Next, an. operational assessment is performed to determine the need;for< repair for each indication. A beginning-of-

. cycle (BOC) crack. profile (length and average depth) for each_ indication is analyzed for growth and compared with acceptaisce limits' (i.e. ,.a length / average depth acceptance curve). The acceptance curve combines uncertainties for the burst correlation, material propertier and

.Non-destructive Examination (NDE) length and NDE average depth sizing. .The need to repair a tube is determined from these~ curves by. adding growth in length and average depth to the mea ~sured indication of the crack parameters and comparing the resultant crack profile with the acceptance i' El-5 L

{

i curve. A calculated burst pressure for each projected EOC crack profile can be used as an equivalent alternative to the depth / length curves.

Based on the analysis of crack profiles and the accuracy that can be demonstrated for PWSCC indications in the TSP region, the proposed change will preserve structural and leakage integrity of SG tubes.

IV. NO SIGNIFICANT HAZARDS CONSIDERATION DETERMINATION TVA has concluded that operation of SQN Units 1 and 2, in accordance with the proposed change to the technical specifications (TSs) does not involve a significant hazards consideration. TVA's conclusion is based on its evaluation, in accordance with 10 CFR 50. 91 (a) (1) , of the three standards set forth in 10 CFR 50.92 (c) .

A. The proposed amendment does not involve a significant increase in the probability or consequences of an accident previously evaluated.

Operation of Sequoyah Units 1 and 2, in accordance with the proposed license amendment, does not involve a significant increase in the probability or consequences of an accident previously evaluated.

Examination of crack morphology for primary water stress corrosion cracking (PWSCC) at dented intersections has been found to show one or two microcracks well aligned with only a few uncorroded ligaments and little or no other inside diameter axial cracking at the intersection. This relatively simple morphology is conducive to obtaining good accuracy in Non-destructive Examination (NDE) sizing of these indications. Accordingly, alternate repair criteria is-established based on crack length and average and maximum depth within the thickness of the tube support plate (TSP) or limited extension outside the thickness of the TSP.

The application of the alternate repair criteria (ARC) requires a condition monitoring assessment. If all indications satisfy the structural limits with regard to bounding lengths and average depths, the ,

condition monitoring burst pressure requirements are satisfied.

In addition, an operational assessment is performed to determine the length / depth repair bases. The crack profiles are projected to the end of the operating cycle for comparison with acceptance limits El-6

r (i.e., length Jimit and average depth limit). Burst pressures are calculated from the depth profiles by searching the total crack length for the partial length that results in the lowest burst pressure.

Because the burst pressure can be lower than that for the longest acceptable crack length at its average depth, a-fixed repair limit is not established. The repair bases is obtained by projecting the crack profile to the end of the next operating cycle and determining if the burst pressure for the projected profile meets the burst pressure margin requirements defined by WCAP-15128, Revision 1, dated August 1999.

If the projected end-of-cycle (EOC) burst margin requirements are satisfied, the indication is left in service. Thus,.the repair limit relative to length and average depth assures that the operational assessment requirements are satisfied.

Crack length limits are established in the WCAP to assure that crack extension and growth outside of the TSP provides adequate margin against burst for the free-span crack (i.e., 3APno burst capability is maintained) in addition to the total crack length. A repair limit is also established in the WCAP for maximum depth to provide a high confidence that the indication will not progress through the wall at the end of an operating cycle.

Based on.the above, the proposed amendment does not result in any increase in the probability or consequences of an accident previously evaluated within the Sequoyah FSAR.

.B. The proposed amendment does not create the possibility ,

of a new or different kind of accident from any accident previously evaluated.

Implementation of the proposed S/G tube ARC does not introduce any significant changes to the plant design basis. A single or multiple tube rupture event would not be expected in a S/G in which the plugging criteria has been applied. Both condition monitoring and operational assessments are completed as part of the implementation of ARC to determine that structural and leakage margin exists prior to returning S/Gs to service following inspections. If  !

the. condition monitoring requirements are not )

satisfied for burst or leakage, the causal factors El-7

L for EOC indications exceeding the expected values will be evaluated. ~rhe methodology and application of this ARC will continue to ensure that tube integrity is maintained during all plant conditions consistent with the requirements of draft RG 1.121 and Revision 1 of RG 1.83.

A.S/G tube rupture event is one of a number of design basis accidents that are analyzed as part of a plant's licensing basis. In the analysis of a S/G tube rupture event, a bounding primary-to-secondary

' leakage rate equal to the operational leakage limits in the TSs, plus the leak rate associated with the double ended rupture of a single tube, is assumed.

For other design basis accidents such as a main steam ,

line break and loss of alternating current power, the tubes are assumed to retain their structural i integrity and exhibit primary-to-secondary leakage j within the limits assumed in Final Safety Analysis )

Report (FSAR) accident analyses. The proposed ARC  !

does not result in an accident leakage rate in excess of that assumed or calculated in SON's current accident analyses.

Even under severe accident conditions, the potential for significant leakage would be expected to be small l and not significantly different than for other l degradation mechanisms repaired to 40 percent depth I limits. It is concluded that application of the proposed ARC for PWSCC at dented TSP locations results in a negligible difference from current 40 percent repair limits. l TVA continues to implement a maximum operating condition leak rate limit of 150 gallons per day (0.1 gallons per minute) per S/G to preclude the potential for excessive leakage during all plant l conditions.

The possibility of a new or different kind of accident from any previously evaluated is not created because S/G tube integrity is maintained by inservice inspection and effective primary-to-secondary leakage monitoring. l El-8

+.

C. The~ proposed amendment does not involve a significant reduction in a margin of safety.

Tube. repair limits provide reasonable assurance that tubes accepted for continued service without plugging or repair.will exhibit adequate tube structural and leakage integrity during subsequent plant operation.

..The implementation of the proposed ARC is demonstrated to maintain S/G tube integrity consistent with the criteria of draft NRC Regulatory Guide 1.121 . The guidelines of RG 1.121 describe a method acceptable to the NRC staff'for meeting

' General Design Criteria (GDC) 2, 4, 14, 15, 31, and 32 by ensuring the probability or the consequences of -

S/G tube rupture remain within acceptable limits.

This is accomplished by determining the limiting 3 conditions of degradation of S/G tubing, for which tubes.with unacceptable cracking should be removed from service. l Upon implementation of the proposed ARC, even under j the worst-case conditions, the occurrence of PWSCC at the '..ube support plate elevations is not expected to lead to a S/G tube rupture event during normal or faulted plant conditions. All tubes are shown to retain the margins of safety against burst consistent with the safety factor margins implicit in the stress limit criteria of Section III of the American Society of Mechanical Engineers Code, for all service loading conditions. In addition, all tubes have been shown to retain a margin of. safety against gross failure or burst consistent with the stress limits of NB-3225 of Section III crf the ASME Code under postulated accident conditions concurrent with a safe shutdown earthquake.

-In addressing the combined effects of loss-of-coolant accident plus safe shutdown earthquake on the's/G component (as required by GDC 2), it has been  ;

determined that tube collapse will not occur in the  !

Sequoyah S/Gs. This analysis is discussed'in WCAP j 13990, dated May 1994. No tubes are excluded from l the application of the proposed ARC. l l

Based on the above, it is concluded that the proposed license amendment request does not result in a

=significant reduction in margin with respect to the  !

plant safety analyses'as defined in the FSAR or TSs. l l

1 El-9 4

o V. ENVIRONMENTAL IMPACT CONSIDERATION The proposed change does not involve a significant hazards consideration, a significant change in the types of or significant increase in the amounts of any effluents that may be released offsite, or a significant increase in individual or cumulative occupational radiation exposure. Therefore, the proposed change meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22 (c) (9) .

Therefore, pursuant to 10 CFR 51.22 (b), an environmental assessment of the proposed change is not required.

El-10

3 ENCLOSURE 2 TENNESSEE VALLEY AUTHORITY SEQUOYAH PLANT (SQN)

UNITS 1 AND 2 PROPOSED TECHNICAL SPECIFICATION (TS) CHANGE MARKED PAGES I. AFFECTED PAGE LIST Unit 1 3/4 4-7 3/4 4-9 l 3/4 4-9b 3/4 4-10 B'3/4 4-4 Unit 2 1

3/4 4-11 3/4 4-13 >

3/4 4-14a 3/4 4-14b B 3/4 4-3a i l

II. MARKED PAGES-See attached.

1 i

l