ML080710160

RAIs for Vogtle Interim SG Tube ARC LAR

ML080710160
Person / Time
Site:	Vogtle
Issue date:	03/10/2008
From:	Siva Lingam NRC/NRR/ADRO/DORL/LPLII-1
To:	Graham R, Stringfellow N Southern Nuclear Operating Co
Lingam, Siva NRR/DORL 415-1564
References
TAC MD7450, TAC MD7451
Download: ML080710160 (7)

Text

From: Siva Lingam To: dorgraha@southernco.com; njstring@southernco.com Date: 3/10/2008 5:38:46 PM

Subject:

RAIs for Vogtle Interim SG Tube ARC LAR Attached please find the RAIs for the Vogtle interim ARC license amendment

request. These RAIs are similar to those sent to Wolf Creek (e.g., the same

technical issues), with the addition of four new questions (RAIs 14 to 17).

Please note that RAIs 14, 16 and 17 were discussed with Wolf Creek and

Westinghouse last week. RAI 15 is an additional issue with the same equation

discussed in RAI 14.

If necessary, we can support a phone call to ensure mutual understanding of

the RAIs.

Please provide your responses as early as possible.

Siva P. Lingam

Project Manager (NRR/DORL/LPL2-1)

Surry and Vogtle Nuclear Stations

Location: O8-D5

Mail Stop: O8-G9

Telephone: 301-415-1564

Fax: 301-415-1222

E-mail address: spl@nrc.gov

CC: Allen Hiser; Andrew Johnson; Emmett Murphy; John Lubinski; Melanie Wong

REQUEST FOR ADDITIONAL INFORMATION RELATING TO STEAM GENERATOR TUBESHEET AMENDMENT ON INTERIM ALTERNATE REPAIR CRITERIA VOGTLE ELECTRIC GENERATING STATION

The NRC staff has the following requests for additional information related to

your submittal:

1. Technical specification (TS) 5.5.9.d.3 states that if crack indications are found in any steam generator (SG) tube, then the next inspection for

each SG for the degradation mechanism that caused the crack indication

shall not exceed 24 effective full power months (EFPM) or one refueling

outage (whichever is less). The proposed amendment would change TS 5.5.9 d to exclude cracks in the lower 4 inches of the tubesheet from

application of TS 5.5.9.d.3. The staff notes that TS 5.5.9 d.3 reflects

the uniquely high detection thresholds, high measurement uncertainties, and high growth rate uncertainties that cracking generally exhibits and, therefore, is intended to ensure timely detection of cracks before tube

integrity is impaired. In addition, no significant crack growth rate

data exists for circumferential cracking in the tubesheet expansion. As a result, discuss your plans to modify your amendment request to remove

your proposal from TS 5.5.9.d.

2. For the same reasons as cited above, discuss your plans to modify TS 5.5.9.c.3 to eliminate the proposed alternate repair criteria (ARC)

applicable to a 36-month eddy current inspection interval. In addition, discuss your plans to modify the following clauses: "and subsequent 18-

month eddy current inspection interval," "and subsequent 36-month eddy

current inspection interval," and, "and subsequent 18-month and 36-month

eddy current inspection intervals." with the following, "and the

subsequent operating cycle." Similarly, discuss your plans for

modifying the parenthetical expressions, "(and any inspections performed

in the subsequent 18-month inspection interval or 36-month inspection

interval)," in proposed new reporting requirements in TS 5.6.10.h, i, and j with the following: "and any inspections performed in the

subsequent operating cycle." 3. Given that the ability of eddy current to size cracks in the weld has not been demonstrated, justify the position in the amendment request

that visual inspection of the weld will not be performed unless the eddy

current results indicate that a weld flaw is greater than the weld crack

acceptance criteria.

4. Please discuss your plans to modify the proposed application of the ARC from circumferential, service induced, crack-like flaws to the

circumferential component of flaws in general. An example of an

acceptable approach is to replace the proposed words, "tubes with less

than or equal to a 214 degree circumferential service-induced crack-like

flaw-," with the words, "tubes with service induced flaws having a

circumferential component less than or equal to 214 degrees-"

5. Visual examinations of the weld will be performed on a best effort basis with inspection systems capable of achieving a resolution similar to the

Maximum Procedure Demonstration Lower Case Character Height as discussed

in ASME Section XI. Please provide the code edition and addenda that

describe this proposed inspection resolution. For visual detection of

stress corrosion cracks in other components, a resolution sensitivity

sufficient to detect a 1 mil wide wire or crack (as a substitute for a

visual examination) has been accepted by the NRC, as described in Title

10 of the Code of Federal Regulations, Part 50.55a(b)(2)(xxi). For the

inspection approach to be implemented under this license amendment, provide a description of the performance demonstration process and

results that demonstrate the ability to reliably detect flaws with

characteristics similar to those that might be expected to be found in

these welds.

6. Figure 3-7 (LTR-CDME-08-11 P) needs to provide all geometry details assumed in the weld analysis on pages 7, 9 and 10. (The staff does not

understand the assumed weld geometry based on the discussion on pages 7, 9 and 10.) With respect to the equation for S.A. near the top of page

10, what is the parameter whose value is 0.020 and what is the solution

for "y"? 7. On page 10, the assumed flaw is said to extend a distance "d" into this "surface." Does "surface" refer to the outer ellipse or inner ellipse

in Figure 3-5? Figure 3-5 suggests it is from the inner ellipse.

8. What was the assumed flow stress for the weld material? What was the basis for selecting this value?

9. LTR-CDME-05-P states that the tube to tubesheet welds were designed and analyzed as primary pressure boundary in accordance with the

requirements of Section III of the ASME Code. Please provide a summary of the Code analysis, including the calculated maximum stress and

applicable Code stress limit.

10.Regarding the weld repair criterion:

A detailed stress analysis (e.g., finite element) would be expected to

reveal a much more complex stress state than that assumed in the

licensee's analysis, which may impact the likely locations for crack

initiation and direction of crack propagation. In addition, the

dominant stresses for crack initiation and crack growth may involve

residual stresses in addition to operational stresses. Thus, the 35-

degree conical "plane" is not the only plane within which cracks may

initiate and grow.

One hypothetical crack plane, which appears more limiting than the one

assumed by the licensee, is the cylindrical "plane" defined by the

expanded tube outer diameter where the weld is in a state of shear.

The staff estimates that the required circumferential ligament to

resist an end cap load of 1863 lb is greater than 180 degrees (without

allowances). Please address these concerns and provide a detailed

justification for why the submitted analysis is conservative.

11.The proposed tube and weld repair criteria do not address interaction effects of multiple circumferential flaws that may be in close proximity (e.g., axial separation of one or two tube diameters). Please address

this concern and identify any revisions which may be needed to the

alternate tube repair criteria and the maximum acceptable weld flaw

size. 12.The technical support document for the interim ARC amendment does not make it clear how licensees will ensure they satisfy the accident

induced leakage performance criteria. Please describe the methodology

to be used to ensure the accident induced leakage performance criteria

is met. Include in this response (a) how leakage from sources other

than the lower 4-inches of the tube will be addressed (in the context of

ensuring the performance criteria is met), and (b) how leakage from

flaws (if any) in the lower 4-inches of the tube will be determined (e.g., determining the leakage from each flaw; multiplying the normal

operating leak rate by a specific factor).

[The staff makes two observations here in response to possible industry

concerns regarding Item 12.

First, the staff acknowledges that the ratio of the allowed accident

leakage and the operational leakage is 2.5 for Wolf Creek, which is

equal to the factor of 2.5 above, while the ratio is 3.5 for Vogtle and

5 for Byron/Braidwood). This is not an atypical situation as is

discussed in NRC RIS 2007-20. The operational leakage limit in the

technical specifications can never be assumed to ensure that accident

leakage will be within what is assumed in the accident analysis, even if

the technical specification limit is zero. For example, part through

wall flaws in the free span which are not leaking under normal operating

conditions may pop through wall and leak under accident conditions. For

cracks in the free span which are leaking under normal operating

conditions, the ratio of SLB leakage to normal operating leakage can be

substantially greater than 2.5 depending on the length of the crack. It

is the licensee's responsibility to ensure that the accident leakage

limits are met through implementation of an effective SG program, including an engineering assessment of any operational leakage that may

occur in terms of its implications for leakage under accident conditions (based on considerations such as past inspection results and operational

assessments, experience at similar plants, etc.).

Second, the staff is not aware of any operational leakage to date from

the tubesheet region for the subject class of plants, and there seems

little reason to expect that this situation will change significantly in

the next 18 months. Thus, the NRC staff's approach discussed above is

not expected to have any significant impact for the licensees requesting

relief from the tube repair criteria in the lower 4-inches of the tube.]

13.The proposed "modified B*" approach relies to some extent on an assumed, constant value of loss coefficient, based on a lower bound of the data.

This contrasts with the "nominal B*" approach which, in its latest form (as we understand it) is not directly impacted by the assumed value of

loss coefficient since this value is assumed to be constant with

increasing contact pressure between the tube and tubesheet. Given the

amount of time for the staff to review the interim ARC, the staff will

not be able to make a conclusion as to whether the assumed value of loss

coefficient in the "modified B*" approach is conservative. However, the

staff has performed some evaluations regarding the potential for the

normal operating leak rate to increase under steam line break conditions

using various values of (l NOP/ l SLB) determined from the "nominal B*"

approach (which does not rely on an assumed value of loss coefficient).

With these analyses and recognizing the issues associated with some of

these previous H*/B* analyses, it would appear that a factor of 2.5

reasonably bounds the potential increase in leakage that would be

realized in going from normal operating to steam line break conditions.

Please discuss your plans to modify your proposal to indicate that the

leak rate during normal operation (for flaws in the lower 4-inches of

tube) will increase by a factor of 2.5 under steam line break

conditions.

14.The mathematical constant has been omitted from the first term of the equation near the top of page 8 and the equation at the bottom of page

8. It is not clear if this is a typographical error, or if has been purposely omitted. If the omission is intentional, please explain.

15.The last term of the equation at the bottom of page 8 includes the parenthetical (r o 2 + r i 2). The staff believes this should be (r o 2 - r i 2). It is not clear if this is a typographical error, or if the radii are

intentionally being summed. If intentional, please explain why the

squared radii should be summed and not subtracted.

16.Explain why it is necessary to subtract A f (area of the flaw) from S.A. (surface area of the frustum) in the first term of the force balance equation on page 10. (The staff believes this term should be deleted.)

17.Explain the use of the mathematical constant P i (internal pressure) rather than P (3P or 4800 psi) in the equations on pages 8 and 10.

The explanation on page 11 is not sufficient and appears to the staff to

be incorrect.

The NRC staff has the following observations related to your submittal:

A. Your current proposal for modifying the TS is in terms of calendar months. This is inconsistent with the remainder of the steam generator

TS inspection requirements which are in terms of effective full power

months. In the past, having inspection requirements tied to calendar

months has necessitated the need for subsequent amendments in the event

of an extended shut-down period.

B. In Section 5.1(1) of Enclosure I to your February 13, 2008 letter, there is a discussion concerning the relationship of normal operating leakage and accident induced leakage. In this discussion, you indicate that

assuming all normal operating leakage to be from indications below 17

inches from the top of the tubesheet that the accident induced leakage

would be less than your accident-induced leakage limit of 0.35 gpm. The

NRC staff agrees that it is appropriate to assume all normal operating

leakage is from flaws within the tubesheet region (since the source of

normal operating leakage will not be known); however, the previous

statement is only true when the other sources of accident induced

leakage do not contribute more than 0.15 gpm of accident induced leakage (assuming that the normal operating leak rate doubles going from normal

operating to accident conditions as is discussed in your submittal).

This issue is discussed further under "Issue 5" in Regulatory Issue

Summary 2007-20, "Implementation of Primary-to-Secondary Leakage

Performance Criteria."

C. In Section 2.0 of Enclosure 6 to your February 13, 2008 letter, there is a statement following the structural integrity performance criterion

that this criterion is based on ensuring that there is reasonable

assurance that a steam generator tube will not burst during normal

operation of postulated accident conditions. Although this statement is

true, it is not complete since the criterion is also intended to ensure

the tube will not collapse.

D. In the last paragraph of Section 4.1 of Enclosure 6 to your February 13, 2008 letter, there is a statement that: "This means that the leakage

during accident conditions can increase by no more than 2 to 6 times the

leak rate during normal operating conditions for the plants under

consideration." This statement is confusing since it implies that the

leakage observed during accidents may be six times higher than that

during normal operation. We believe the intent of this statement is

that the accident induced leakage limit is a factor of 2 to 6 times

higher than the normal operating leakage limit for the plants under

consideration. With respect to the plants under consideration, the

staff notes that the report does not always address Model 51F steam

generators (top of page 2 of Enclosure 6) although Surry (which has

Model 51F steam generators) is referenced in the report. In addition, the report does not reference Indian Point 2 (which has thermally

treated Alloy 600 tubing with hydraulic tube expansions).

E. Although arguments were provided regarding the sizing of the circumferential extent of circumferential cracks, it is not clear that

this is always the case. If cracks are found and there is more than one

operating cycle between inspections, this issue may become important

since the depth of flaws deep in the tubesheet may not follow the trends

of flaws at other tube locations (i.e., they could be deep over most of

their measured circumferential extent).

F. If cracks are found in a steam generator, these locations should be required to be re-inspected during all subsequent inspections (and an

assessment of the growth rates (in the circumferential direction) should

be provided).

Mail Envelope Properties (47D5AA66.CAA : 13 : 35786)

Subject:

RAIs for Vogtle Interim SG Tube ARC LAR Creation Date 3/10/2008 5:38:46 PM From: Siva Lingam Created By: SPL@nrc.gov Recipients Action Date & Time nrc.gov EBGWPO01.HQGWDO01 Delivered 3/10/2008 5:38:50

PM MCW CC (Melanie Wong) Opened 3/10/2008 5:41:39

PM

nrc.gov OWGWPO04.HQGWDO01 Delivered 3/10/2008 5:38:50

PM ABJ1 CC (Andrew Johnson) Opened 3/11/2008 8:30:17

AM ALH1 CC (Allen Hiser) Opened 3/11/2008 6:06:44

AM

nrc.gov TWGWPO01.HQGWDO01 Delivered 3/10/2008 5:38:46

PM ELM CC (Emmett Murphy) Opened 3/10/2008 6:06:44

PM JWL CC (John Lubinski) Opened 3/10/2008 5:55:26

PM

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PM dorgraha (dorgraha@southernco.com)

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