ML080710160: Difference between revisions
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| issue date = 03/10/2008 | | issue date = 03/10/2008 | ||
| title = RAIs for Vogtle Interim SG Tube ARC LAR | | title = RAIs for Vogtle Interim SG Tube ARC LAR | ||
| author name = Lingam S | | author name = Lingam S | ||
| author affiliation = NRC/NRR/ADRO/DORL/LPLII-1 | | author affiliation = NRC/NRR/ADRO/DORL/LPLII-1 | ||
| addressee name = Graham R | | addressee name = Graham R, Stringfellow N | ||
| addressee affiliation = Southern Nuclear Operating Co, Inc | | addressee affiliation = Southern Nuclear Operating Co, Inc | ||
| docket = 05000424, 05000425 | | docket = 05000424, 05000425 | ||
Line 14: | Line 14: | ||
| page count = 7 | | page count = 7 | ||
| project = TAC:MD7450, TAC:MD7451 | | project = TAC:MD7450, TAC:MD7451 | ||
| stage = | | stage = RAI | ||
}} | }} | ||
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The NRC staff has the following requests for additional information related to | The NRC staff has the following requests for additional information related to | ||
your submittal: | 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 | : 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 | ||
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data exists for circumferential cracking in the tubesheet expansion. As a result, discuss your plans to modify your amendment request to remove | 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. | 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) | : 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) | ||
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current results indicate that a weld flaw is greater than the weld crack | current results indicate that a weld flaw is greater than the weld crack | ||
acceptance criteria. | acceptance criteria. | ||
: 4. Please discuss your plans to modify the proposed application of the ARC from circumferential, service induced, crack-like flaws to the | : 4. Please discuss your plans to modify the proposed application of the ARC from circumferential, service induced, crack-like flaws to the | ||
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flaw-," with the words, "tubes with service induced flaws having a | flaw-," with the words, "tubes with service induced flaws having a | ||
circumferential component less than or equal to 214 degrees-" | 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 | : 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 | ||
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characteristics similar to those that might be expected to be found in | characteristics similar to those that might be expected to be found in | ||
these welds. | 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 | : 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 | ||
Line 148: | Line 148: | ||
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 | 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. | 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? | : 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 | : 9. LTR-CDME-05-P states that the tube to tubesheet welds were designed and analyzed as primary pressure boundary in accordance with the | ||
Line 205: | Line 205: | ||
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 | 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). | operating leak rate by a specific factor). | ||
[The staff makes two observations here in response to possible industry | |||
concerns regarding Item 12. | concerns regarding Item 12. | ||
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conditions. | 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 | 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. | : 8. It is not clear if this is a typographical error, or if has been purposely omitted. If the omission is intentional, please explain. | ||
Revision as of 14:54, 12 July 2019
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
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
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
southernco.com Transferred 3/10/2008 5:39:21
PM dorgraha (dorgraha@southernco.com)
NJSTRING (njstring@southernco.com)
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