ML20211K784
| ML20211K784 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 04/25/1985 |
| From: | Wiesemann R WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19292F492 | List: |
| References | |
| CAW-85-035, CAW-85-35, TAC-61775, TAC-61776, NUDOCS 8606300259 | |
| Download: ML20211K784 (28) | |
Text
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> - %s Westinghouse Water Reactor Ba 355
"'its uren Pennsylvama 15230-0355 4
Electric Corporation Divisions 4
April 25,1985 CAW-85-035
! Mr. Harold R. Denton, Director Office of Nuclear Reactor Pegulation U.S. Nuclear Regulatory Comission Washington, D.C. 20555 APPLICATION FOR WITHHOLDING PROPRIETARY INFORMATION FROM PUBLIC DISCLOSURE
Subject:
McGuire Units 1 and 2 Tubesheet Region Plugging Criterion
Reference:
Duke Power Company Letter to NRC Dated April,1985
Dear Mr. Denton:
The proprietary material for which withholding is being requested in the referenced letter by Duke Power Company is further identified in an affidavit signed by the owner of the proprietary infonnation, Westinghouse Electric Corporation. De affidavit, which accompanies this letter, sets forth the basis on which the information may be withheld from public disclosure by the Comission and addresses with specificity the considerations listed in paragraph (b)(4) of 10CFR Section 2.790 of the Comission's regulations.
he proprietary material for which withholding is being required is of the same technical type as that proprietary material previously submitted with Application for Withholding CAW-81-79 Accordingly, this letter authorizes the utilization of the accompanying affidavit by Duke Power Company.
Correspondence with respect to the proprietary aspects of the application for withholding or the Westinghouse affidavit should reference this letter, j
CAW-85-035, and should be addressed to the undersigned.
l Very truly yours, sf b"
e6063%$$$I$o$369 DR PDR / + g/rt A. Wiesemann, Manager Regulatory & Legislative Affairs -
I
/pj Enclosures cc: E. C. Shomaker, Esq.
Office of the Executive Legal Director, NRC
$ ATTACHMENT
. (Insert to Duke Power Company Letter for Transmittal to the NRC)
Enclosed are:
- 1. copies of infomation titled "McGuire Units 1 and 2 Tubesheet Region Plugging Criterion" (Proprietary).
- 2. copies of infomation titled "McGuire Units 1 and 2 Tubesheet Region Plugging Criterion" (Non-Proprietary).
Also enclosed is a Westinghouse authorization letter (CAW-85-035), and accompanying affidavit.
THE FOLLOWING 1WO PARAGRAPHS SHOULD BE INCLUDED IN YOUR LEITER 10 THE NRC:
As item 1 contains infomation proprietary to Westinghouse Electric Corporation, it is supported by an affidavit signed by Westinghouse, the owner of the information. The affidavit sets forth the basis on which the infomation may be withheld from public disclosure by the Connission and addresses with specificity the considerations listed in paragraph (b)(4) of Section 2.790 of the Connission's regulations.
Accordir. gly, it is respectfbily requested that the infomation which is proprietary to Westinghouse be withheld from public disclosure in accordance with 10CFR Section 2.790 of the conmission's regulations. Correspondence with respect to the proprietary aspects of the Application for withholding or the supporting Westinghouse affidavit should reference CAW-85-035 and should be addressed to R. A. Wiesemann, Manager, Regulatory and Legislative Affairs, Westinghouse Electric Corporation, P. O. Box 355, Pittsburgh, Pennsylvania 15230.
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CAW-81-79 AFFIDAVIT COMMONWEALTH OF PENNSYLVANIA:
ss COUNTY OF ALLEGHENY:
Before me, the undersigned authority, personally appeared Robert A. Wiesemann, who, being by me duly sworn according to law, deposes and says that he is authorized to execute this Affidavit on behalf of Westinghouse Electric Corporation (" Westinghouse") and that the averments of fact set forth in this Affidavit are true and correct
- to the best of his knowledge, information, and belief
dA nn1A Robert A. Wiesemann, Manager Regulatory and Legislative Affairs l Sworn to and subscribed
[ before me this o day of D &u./u. 1981.
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f 'flfb o:- W / Wif rs UNotary[Publi@[
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CAW-81-79 (1) I am Manager, Regulatory and Legislative Affairs, in the Nuclear Technology Division, of Westinghouse Electric Corporation and as such, I have been specifically delegated the function of reviewing the proprietary information sought to be withheld from public dis-closure in connection with nuclear power plant licensing or rule-making proceedings, and am authorized to apply for its withholding on behalf of the Westinghouse Water Reactor Divisions.
(2) I am making this Affidavit in conformance with the provisions of 10CFR Section 2.790 of the Commission's regulations and in con-junction with the Westinghouse application for withholding ac-companying this Affidavit.
(3) I have personal knowledge of the criteria and procedures utilized by Westinghouse Nuclear Energy Systems in designating information as a trade secret, privileged or as confidential commercial or financial information.
(4) Pursuant to the provisions of paragraph (b)(4) of Section 2.790 of the Commission's regulations, the following is furnished for consideration by the Commission in determining whether the in-formation sought to be withheld from public disclosure should be withheld.
l (1) The information sought to be withheld from public disclosure l is owned and has been held in confidence by Westinghouse.
I
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CAW-81 -79 (ii) The information is of a type customarily held in confidence I
by Westinghouse and not customarily disclosed to the public.
Westinghouse has a rational basis for determining the types of information customarily held in confidence by it and, in that connection, utilizes a system to determine when and whether to hold certain types of information in confidence.
The application of that system and the substance of that system constitutes Westinghouse policy and provides the rational basis required.
Under that system, information is held in confidence if it falls in one or more of several types, the release of which might result in the loss of an existing or potential com-petitive advantage, as follows:
(a) The information reveals the distinguishing aspects of 1 a process (or component, structure, tool, method, etc.)
where prevention of its use by any of Westinghouse's competitors without license from Westinghouse consti-tutes a competitive economic advantage over other companies.
l (b) It consists of supporting data, including test data, relative to a process (or component, structure, tool, i method,etc.),theapplicationofwhichdatasecuresa l competitive economic advantage, e.g., by optimization l or improved marketability.
~. .
- CAW-81 -79 (c) Its use by a competitor would reduce his expenditure of resources or improve his competitive position in the design, manufacture, shipment, installation, assurance of quality, or licensing a similar product.
(d) It reveals cost or price information, production cap-acities, budget levels, or commercial strategies of Westinghouse, its customers or suppliers.
(e) It reveals aspects of past, present, or future West-inghouse or customer funded development plans and pro-grams of potential commercial value to Westinghouse.
(f) It contains patentable ideas, for which patent pro-tection may be desirable.
(g) It is not the property of Westinghouse, but must be treated as proprietary by Westinghouse according to agreements with the owner.
There are sound policy reasons behind the Westinghouse system which include the following:
i (a) The use of such information by Westinghouse gives Westinghouse a competitive advantage over its com-petitors. It is, therefore, withheld from disclosure to protect the Westinghouse competitive position.
CAW-81-79 (b) It is information which is marketable in many ways.
The extent to which such information is available to competitors diminishes the Westinghouse ability to sell products and services involving the use of the information.
(c) Use by our competitor would put Westinghouse at a competitive disadvantage by reducing his expenditure of resources at our expense.
(d) Each component of proprietary information pertinent to a particular competitive advantage is potentially i as valuable as the total competitive advantage. If competitors acquire components of proprietary infor-l mation, any one component may be the key to the entire puzzle, thereby depriving Westinghouse of a competitive advantage.
(e) Unrestricted disclosure would jeopardize the position of prominence of Westinghouse in the world market, and thereby give a market advantage to the competition in those countries.
- (f) The Westinghouse capacity to invest corporate assets in research and development depends upon the success in obtaining and maintaining a competitive advantage.
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CAW-81-79 (iii) The information is being transmitted to the Commission in confidence and, under the provisions of 10CFR Section 2.790, it is to be received in confidence by the Commission.
(iv) The information sought to be protected is not available in public sources or available information has not been pre-viously employed in the same ori.ginal manner or method to the best of our knowledge and belief.
(v) The proprietary information sought to be withheld in this submittal is that which is appropriately marked in " Steam Generator Tube Plugging Margin Analysis" for the Virgil C.
Summer Nuclear Power Plant Unit No.1 WCAP-9912, Revi-sion 2 (Proprietary) being transmitted by South Carolina Electric and Gas Company letter Application for Withholding Proprietary Information from Public Disclosure, Nichols to Denton, November 1981. The proprietary information as sub-mitted for South Carolina . Electric and Gas Company, Virgil C.
Summer Nuclear Station use is expected to be applicable in other licensee and applicant submittals in response to cer-tain NRC requirements for justification of the steam generator tube plugging margin.
This information is part of that which will enable Westing-house to:
(a) Provide documentation of the analyses, method and test-ing for determining plugging margin.
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CAW-81-79 (b) Establish the minimum wall thickness in compliance with Regulatory Guide 1.121.
(c) Establish the stress limits versus thinning of the remaining tube wall.
(d) Establish the maximum allowable leakage in support of the leak-before-break criteria.
(e) Assist the customer to obtain NRC approval.
Further this information has substantial commercial value as follows:
l (a) Westinghouse plans to sell similar information to its customers for purposes of meeting NRC requirements for licensing documentation.
(b) Westinghouse can sell support and defense of the tech-nology to its customers in the licensing process.
Public disclosure of this information is likely to cause l_ substantial harm to the competitive position of Westinghouse i because it would enhance the ability of competitors to pro-( vide similar analytical documentation and licensing defense j
services for commercial power reactors without commensurate expenses. Also, public disclosure of the information would enable others to use the information to meet NRC require-ments for licensing documentation without purchasing the right to use the information.
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CAW-81-79 The development of the technology described in part by the information is the result of applying the results of many years of experience in an intensive Westinghouse effort and the expenditure of a considerable sum of money.
In order for competitors of Westinghouse to duplicate this information, similar technical programs would have to be performed and a significant manpower effort, having the requisite talent and experience, would have to be expended for system design software development.
Further the deponent sayeth not.
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PROPRIETARY INFORMATION NOTICE TRANSMITTED HEREWITH ARE PROPRIETARY AND/OR NON-PROPRIETARY VERSIONS OF DOCUMENTS RJRNISHED TO EE NRC IN CONNECTION WITH REQUESTS FOR GENERIC AND/OR PLANT SPECIFIC REVIEW AND APPROVAL.
IN ORDER 10, CONFORM 10 EE REQUIREMENTS OF 10CFR2.790 0F THE COMMISSION'S REGULATIONS CONCERNING THE PROTECTION OF PROPRIETARY INFORMATION SO SUBMITIED TO THE NRC, EE INFORMATION WHICH IS PROPRIETARY IN EE PROPRIETARY VERSIONS IS CONTAINED WITHIN BRACKETS AND WHERE THE PROPRIETARY INFORMATION HAS BEEN DELETED IN THE NON-PROPRIETARY VERSIONS ONLY THE BRACKETS REMAIN, EE INFORMATION THAT WAS CONTAINED WITHIN WE BRACKETS IN EE PROPRIETARY VERSIONS HAVING BEEN DELETED. THE JUSTIFICATION FOR CLAIMING THE INFORMATION SO DESIGNATED AS PROPRIETARY IS INDICATED IN BOTH VERSIONS BY MEANS OF LOWER CASE LETTERS (a) THROUGH (g) CONTAINED WITHIN PARENTHESES LOCATED AS A SUPERSCRIPT IMMEDIATELY FOLLOWING 1HE BRACKETS ENCLOSING EACH ITEM OF INFORMATION BEING IDENTIFIED AS PROPRIETARY OR IN THE MARGIN OPPOSITE SUCH INFORMATION. THESE LOWER CASE LETTERS REFER 1D THE TYPES OF INFORMATION WESTINGHOUSE CUS10MARILY HOLDS IN CONFIDENCE IDENTIFIED IN SECTIONS (4)(ii)(a) through (4)(ii)(g) 0F THE AFFIDAVIT ACCOMPANYING THIS 1RANSMITTAL PURSUANT 1010CFR2.790(b)(1).
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CustomerReferenceNo(s).
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Westinghouse Reference No(s).
] (Change Control or RFQ As Applicable)
NS-RCSCL-C/L- 85-156, Rev.1 f -
) WESTINGHOUSE i
NUCLEAR SAFETY EVALUATION CHECK LIST j 1) NUCLEARPLANT(S) McGuire Units 1 and 2 I 2) CHECK LIST APPLICABLE TO: Tubesheet Plugging Criteria
} (SubjectofChange)
U
- 3) The written safety evaluation of the revised procedure, design change or modification i
required by 10CFR50.59 has been prepared to the extent required and is attached. If a safety evaluation is not required or is incomplete for any reason, explain on Page 2.
Parts A and B of this Safety Evaluation Check List are to be completed only on the
, basis of the safety evaluation performed.
CHECK LIST - PART A t
(3.1) Yes No X A change to the piant as described in the FSAR?
j (3.2) Yes No X A change to procedures as dese,ribed in the FSAR?
i (3.3) Yes No X A test or experiment not described in the FSAR?
l (3.4) Yes jL No A change to the plant technical specifications (Appendix A Ag to the Operating License)?
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- 4) CHECK LIST - PART B (Justification for Part B answers must' be included on Page 2.) ,
j (4.1) Yes No X Will the probability of an accident previously evaluated in i
the FSAR be increased?
(4.2) Yes No X Will the consequences of an accident previously evaluated in i
the FSAR be increased?
j' (4.3) Yes No X May the possibility of an accident which is different than any j already evaluated in the FSAR be created?
) (4.4) Yes No X Will the probability of a malfunction of equipment important to i
safety previously evaluatedin the FSAR be increased?
(4.5) Yes No X Will the consequences of a malfunction of equipment important to safety previously evaluated in the FSAR be increased?
(4.6) Yes No X May the possibility of a malfunction of equipment important to '
- safety different than any already evaluated in the FSAR be
! created?
! (4.7) Yes No X Will the margin of safety as defined in the bases to any
) technical specification be reduced?
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- Page 1 of 2
i
. If the answers to any of the above questions are unknown, indicate under 5) REMARKS and explain below.
If the answer to any of the above questions in 4) cannot be answered in the negative, based on written safety evaluation, the change cannot be approved without an applica-tion for license amendment submitted to NRC pursuant to 10CFR50.90.
- 5) REMARKS:
The following sumarizes the justification upon the written safety evaluation.(I) for answers given in Part B of the Safety Evaluation Check List:
Please refer to the attached Safety Evaluation.
II) Reference to document (s) containing written safety evaluation:
FOR FSAR UPDATE 3 Section: Page(s): Table (s): Figure (s):
Reason for/ Description of Change:
, Preparedby(NuclearSafety): I p/ Y &- Date: -/ 2 CoordinatedwithEngineer(s): M s, .DobkAL Date: .
Coordinating Group Manager (s): M , Date: I l
Nuclear Safety Group Manager:
,n-AM -
Date:
8I Page 2 of 2
WESTINGHOUSE NON-PROPRIETARY CLASS 3 Ref. MS-RCSCL C/L-85-156, Rev.1 MCGUIRE UNITS 1 AND 2 :
1 TUBESHEET REGION PLUGGING CRITERION INTRODUCTION The purpose of this document is to address the issue of repairing or plugging steam generator tubes when degradation has been detected in the full depth hard roll expanded portion of the tube which is within the tubesheet. For McGuire Units 1 and 2, existing tube repairing / plugging criteria, i.e.,
current applications of USNRC Regulatory Guide 1.121, apply throughout the tube length and do not take into account the reinforcing effect of the tubesheet on the external surface or the tube. The presence of the tubesheet will constrain the tube and will complement its integrity in that region by essentially precluding tube deformation beyond its initial outside diameter.
The resistance to both tube rupture and tube collapse behavior is strengthened by the tubesheet, and the use of an alternate criterion for establishing plugging margin is justified.
The evaluation forms the basis for the development of a criterion for obviating the need to repair a tube (by sleeving) or to remove a tube from service (by plugging) due to eddy current (ECT) indications for most of the l
1ength of tubing within the tubesheet. This evaluation assesses the integrity of the tube bundle with ECT indications on tubes within the tubesheet under normal operating and postulated accident conditions. Three aspects cf bundle integrity are addressed: 1) maintenance of a fixed tube end condition in the tubesheet with the limiting case of a circumferential indication near the top of the tubesheet, 2) limitation of primary-to secondary leakage consistent with accident analysis assumptions, and 3) maintenance of tube integrity under postulated limiting conditions of primary-to-secondary and secondary-to-primary differential pressure.
The result of the evaluation is the identification of a distance of 1.282 inches, designated P*, below the top of the tubesheet for the McGuire Units 1 and 2 steam generators for which tube degradation of any extent does not .
8658Q:10/043085 Page 1 of 8
WEST!NGHOUSE NON-PROPRIETARY CLASS 3 necessitate remedial action except as dictated for compliance with tube
' leakage limits as set forth in the plant technical specification. Limitations on the usage of the P* criterion are discussed in the evaluation section of this report.
EVALUATION
- 1. MAINTENANCE OF A FIXED TUBE END CONDITION The criterion for maintaining a fixed tube end condition in the tubesheet is determined by evaluating the minimum distance, P*, below the top of the tubesheet that will provide margin against pullout of the tube for a postulated "circumferential" separation of the tube. This evaluation conservatively considers limiting loading conditions associated with both normal operation and postulated design basis accidents.
In the development of the P* criterion, the separated tube is conservatively postulated to travel upwards to a position where the extrados surface of the U-bend apex is in contact with the tube directly above it (one row higher in the same column). The vertical displacement of the separated tube is limited to the actual manufacturing clearance between the separated tube and the intact tube above it in the U-bend. Studies have shown that the as i manufactured clearance'between adjacent U-tubes may exceed the nominal drawing value; therefore, the geometric clearance has been based on the nominal U-bend gap [ ] plus manufacturing tolerance considerations [
)* * ' # . On this basis, the manufacturing clearance is
[ )***** for a Model D2/03 steam generator.
Once the separated tube is assumed to have moved into contact with the intact tube directly above it, itt further vertical displacement is both coincident with and limited by any vertical displacement of the intact tube. The superimposed effect of thermal and differential displacement of the intact tube on the vertical displacement of the separated tube are considered in the following paragraphs:
8658Q:10/043085 Page 2 of 8
WESTINGHOUSE NON-PROPREETARY CLASS 3
. 1.. ) Thermal growth of the tube bundle during plant heatup to operating temperatures (hot and cold leg) results in a vertical U-bend displacement of the intact tube. This vertical extension of the .
i intact tube U-bend permits a corresponding vertical displacement of the separated tube U-bend. The effect of this U-bend displacemant at the separated tube and in the tubesheet is limiting at the assumed cold leg separation. Although the vertical displacement of the U-bend is offset partially at the tubesheet by the downward ;
axial thermal growth of the separated cold leg tube end, the net upward displaccment of the separated cold leg tube end at the tubesheet is determined to be [0.044 inches]*****.
2.) Axial displacement due to the primary-to-secondary differential pressure will result in axial stretching of the intact tube one row j
above the separated tube. The limiting condition of primary-to-secondary differential pressure occurs during a postulated feedline break (FLB) accident and has been conservatively determined to be 2650 psi. Under this loading, the intact tube would stretch, allowing a presumed equivalent vertical displacement of the separated tube end of [ ]"'C.
The effects of limiting bending loads and tube rocking on vertical displacement of the tube end in the tubesheet have also been considered. For this case, the loading condition with the limiting effect at the tubesheet is safe shutdown earthquake (SSE). For a tube with a maximum span length between supports, tube uplift effects due to SSE loading have been determined to be negligible.
Dented tube conditions are bounded by the criterion evaluation in that the constriction (s) at the tube support plate (s) would act to limit the axial movement of the individual tube to a value determined by the axial movement of the total bLndle. Thus, the initial relative motion between the separated tube and the next adjacent higher tube would not be expected for a steam generator with dented tubes. The resultant axial movement of the separated tube would be that associated with accident condition loading only, and is less than the P* criterion. No credit was taken, however, for restricted vertical displacement due to possible denting of the tube.
8658Q:1D/043085 Page 3 of 8
UESTINGHOUSE NON-PROPRIETARY CLASS 3 Combining the various components of possible vertical displacement of a tube results in a limiting value of 1.032 inches. This value is the P* criterion for minimum acceptable depth below the top of the tubesheet of a presumed tube separation. If the depth of the tube degradation is greater than the above criterion, remedial action such as plugging of sleeving need not be taken.
The P* criterion for repairing or removing tubes from service is considered to be conservative. The basis for the analysis is the assumption that the degradation is oriented circumferential1y; however, circumferential cracking has never been observed in the tubesheet region of domestic steam generators.
One occurrence in the French Dampierre plant steam generators was due to incorrect application of a hardrolling technique known as " kiss-rolling."
Thus, the criterion is addressing an extremely low probability phenomenon.
The usefulness of the criterion stems from the elimination of any applicable structural integrity criteria and of the need to determine the orientation on of indications located within the tubesbeet. Relative to the assumptions explicit in the development of the criterion, in addition to the postulated tube gap geometry and conservative loading conditions considered, additional margin is provided by the resistance to vertical displacement of a separated tube that develops due to interference between the tube and the tubesheet, the tube support plates and the anti-vibration bars. However, no credit was taken for this in the development aalysis for the P* criterion.
In using the P* criterion for determining whether or not remedial actions need to be taken for tubes with indications in the tubesheet region, the following considerations must be taken into account.
l a.) As discussed in the description of the development of the criterion, maintenance of a fixed tube end condition at the tubesheet is an issue only for a postulated separated tube condition. If an i indication on a tube within the tubesheet has been determined to be axial, pullout from the tubesheet is not an issue. The disposition of tubes with axial or circumferential indications located above 8658Q:1D/043085 Page 4 of 8
l, WESTINGHOUSE NON-PROPRIETARY CLASS 3 the P* criterion would be made according to plant technical specification requirements and the USNRC Regulatory Guide 1.121,
" Basis for Plugging Degraded PWR Steam Generator Tubes." .
b.) A second consideration in the application of the P* criterion i relates to the assumption in the development that the tube one row above the postulated separated tube is structurally intact , i.e.,
it does not contain indications which would result in its inability to resist in the load imposed by the separated tube. The case of
- two adjacent tubes in the same column with significant circumferential indications has not be considered in the development of the criterion due to the low probability of the simultaneous occurrence of the postulated limiting conditions, i.e., the maximum tube gap between adjacent U-bends, "circumferential" degradation on adjacent tubes, postulated separation on of adjacent tubes, zero f rictional restraint of separated tube ends.
c.) A third consideration relates to the uncertainty in the ECT determination on of the location of an axial or circumferential indication below the top of the tubesheet. To maintain conservatism in the criterion, it must be applied to a reported location, of a presuned 'circumferential" indication, below the top of the tubesheet which conservatively accounts of ECT signal interpretation uncertainty as determined to apply at the time of the inspection.
For example, for a standard bobbin coil probe a conservative eddy current uncertainty would be [ ]****'.
A potential limitation to the use of the P* criterion could be postulated to occur in the case of adjacent tubes in the same column. The assumption of circumferential cracking in each of the tubes leads to the consideration that, for the inboard tube, the neighbor affords no restriction to vertical travel.
This is not, however, considered to be a credible assumption. Reiterating the discussion on the conservativeness of the criterion, operating experience has revealed no circumferential cracking in mill annealed Inconel 600 full depth rolled tubes. In developing the criterion, it has been considered prudent to 8658Q:10/043085 Page 5 of 8
WESTINGHOUSE NON-PROPRIETARY CLASS 3 postulate the existence of circumferential cracking for a single tube under consideration. At the same time, it is not considered credible to postulate circumferential cracking of two adjacent tubes. Any cracking that has been .
observed in operating units has generally been located in the non-e:panded to expanded transition of the tube hard roll and/or or skip roll locations in the tubesheet. The observed cracking has always been typified as short and axially oriented. On this basis, also, an intact tube can be defined as a tube which has not been degraded beyond its structural limit over an azimuthal extent of 360 degrees in the free span, i.e., outside of the tubesheet region.
- 2. LIMITATION OF PRIMARY-TO-SECONDARY LEAKAGE Primary-to-secondary leakage during nornal plant operation is limited by the McGuire Units 1 and 2 technical specifications to 0.35 gpm in a steam generator. This limit, based on plant radiological releases and implicitly enveloping the leak-before-break consideration for a through wall crack in the free span of a tube, is also applicable to a leak source within the tubesheet. In evaluating the primary-to-secondary leakage aspect of the P*
criterion, the relationship between the tubesheet region leak rate at postulated FLB or steamline break (SLB) conditions is assessed relative to that a normal plant operating conditions. The analysis was performed by assuming a leak path to exist, however, not actual leak path would be expected due to the hardrolling of the tubes into the tubesheet.
For the postulated leak source within the tubesheet, increasing the tube differential pressure increases the driving head for the leak. It also decreases the length of the leak path annulus, due to the pullout oof a postulated separated tube and, increases the tube tubesheet loading. Of these effects, only the last two are significant to a leakage source within the tubesheet. For an initial location of a leak source below the top of the tubesheet equal to P*, this effect results in approximately a 10 percent increase in the leak rate relative to that which could be associated with normal plant operation. This small effect is reduced by the increased tube-to-tubesheet loading associated with the ir. creased differential 8658Q:10/043085 Page 6 of 8
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WEST 2NGHOUSE NON-PROPRIETARY CLASS 3 I
pressure. Thus, for a circumferential indication within the tubesheet region l s ich is left in service in accordance with the pullout criterion (P*), the
, existing technical specification primary-to-secondary leakage criterion is sufficient to maintain conditions consistent with accident analysis assumptions.
For axial indications in the tubesheet region, the tube end remains i structurally intact, minimizing any amount of pullout due to the previously identified mechanisms. For this case, the leak rate due to feedline break dif ferential pressure would be bounded by the leak rate for a free span leak source, with the same crack length. This is the basis for the accident analysis assumptions.
- 3. TUBE INTEGRITY UNDER POSTULATED LIMITING CONDITIONS The final aspect of the evaluation is to demonstrate tube integrity under the postulated LOCA condition of secondary-to-primary differential pressure. A review of tube collapse strength characteristics indicates that the constraint provided to the tube by the tubesheet gives a significant margin between tube collapse strength and the limiting secondary-to-primary differential pressure condition, even in the presence of circumferential or axial indications.
- 4. EXCLUSIONS The analysis for the development of P* is based on consideration of the restraint afforded by a neighboring tube. The peripheral tubes in the bundle do not have outboard neighbors; however, restraint is afforded generally by the presence of the anti-vibration bars retaining rings. Even so, there may be several tubes in the bundle where such restraint does not exist. These may be considered as follows:
a.) Peripheral Tubes - Since the tube bundle in the U-bend region does not form a smooth, uniform surface not all tubes on the periphery are contacted by the anti-vibration bars retaining rings. Also, the tubes in the first and last two columns may be beyond the extent of 86580:10/043085 Page 7 of 8
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WESTINGHOUSE NON-PROPRIETARY CLASS 3 p.
I.
the retaining rings. Since peripheral tubes may be bridged by the retaining rings such that a full tube pitch exists between the tube and the retaining ring, it is therefore considered prudent to exclude all peripheral tubes from the P* criterion.
b.) Interior Tubes - Neighbor restraint will not be afforded within the tube bundle for the interior tubes adjacent to and on the tube lane side of the tube support plate stayrods. The specific tubes may be identified by referring to a tube sheet map for the Model D2/03 steam generator of interest. For these tubes, the P* criterion also does not apply.
SUMMARY
On the basis of this evaluation, it is determined that tubes with eddy current indications in the tubesheet region below the P* pullout criterion of 1.032 inches can be left in service. Tubes with eddy current indications of pluggable magnitude and located less than P* below the top of the tubesheet
' should be removed from service by plugging or by sleeving in accord with the plant technical specification and USNRC RG 1.121.
The uncertainty in position of the eddy current indication must be added to the criteria for the final calculation of P*. For example, for a standard ~T a,c,e bobbin coil probe a conservative eddy current uncertainty would beg ,
therefore, P* for the McGuire Units 1 and 2 steam generators is 1.282 inch.
On the basis of this evaluation of the criteria developed herein does not represent an unreviewed safety question as defined in 10CFR5059.
8658Q:10/043085 Page 8 of 8
b i
Significant Hazards Consideration for the Proposed McGuire Units 1 and 2 Tech Spec Change As required by 10CFR50.91, the following assessment substantiates that the proposed changes to the McGuire Units 1 and 2 technical specifications incorporating the tubesheet plugging criterion do not involve any Significant Hazards Consideration as defined by 10CFR50.92.
The attached evaluation addresses the issue of plugging or repairing detected steam generator tubes when degradation has been in the full depth hard roll expanded portion of the tube which is within the tubesheet. Existing tube repairing / plugging criteria, i.e.
current applications of USNRC Regulatory Guide 1.121, apply throughout the tube length and do not take into account the reinforcing effect of the tubesheet on the external surface of the tube. The presence of the tubesheet will complement tube integrity in that region by essentially precluding tube deformation beyond its initial outside diameter.
The resistance to both tube rupture and tube collapse behavior is strengthened by the tubesheet, and the use of an alternate criterion for plugging margin is justified. The result of the evaluation P*,
designated is the identification of a distance of 1.282 inches, degradation of below the top of the tubesheet for which tube any extent at or below that distance does not necessitate remedial action except as dictated for compliance with tube leakage limits as set forth in the McGuire Units 1 and 2 technical specifications. Details of the above are provided in the attached safety evaluation.
Duke Power Company has evaluated the impact of the proposed technical specification change with respect to the requirements of 10CFR50.92 with the following results:
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' The proposed amendment to the tube plugging criteria in the tubesheet region of the McGuire Units 1 and 2 steam generators will not involve a significant increase in the probability or consequences of an accident previously evaluated. The resistance to both tube rupture and tube collapse behavior is strengthened by the tubesheet, and the use of an justified.
margin is alternate criterion for establishing plugging I 2.
The proposed amendment does not create the possibility of new a or different kind of accident from any accident previously evaluated. The proposed change revises the existing acceptance criteria for degraded steam generator l tubes by redefining the t
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)* acceptable plugging limit of a degraded tube in the tubesheet region. The tubesheet plugging criterion fully meets the intent of R.G. 1.121, " Bases for Plugging Degraded PWR Steam Generator Tubes".
- 3. The proposed amendment does not involve a significant reduction in a margin to safety. The tubesheet plugging criterion has been demonstrated to maintain the integrity of the tube bundle with eddy current indications within the tubesheet under normal operating and postulated accident conditions loadings.
Based on the preceeding analysis Duke Power Company Company concludes that the proposed amendments do not involve a Significant Hazards Consideration.
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ATTACHMENT 4 a
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J Analysis of Significant Hazards Consideration l
As required by 10 CFR 50.91, this analysis is provided concerning whether the
- proposed amendments involve significant hazards considerations, as defined by 10 CFR 50.92. Standards for determination that a proposed amendment involves no significant hazards considerations are if operation of the facility in cccordance with the proposed amendment would not
- 1) involve a significant increase in the probability or consequences of an accident previously evalu- .
ated; or 2) create the possibility of a new or different kind of accident from any accident previously evaluated; or 3) involve a significant reduction in a margin of safety.
The proposed change addresses the issue of plugging steam generator tubes when degradation has been detected in the full depth hard roll expanded portion of the tube which is within the tubesheet. Existing tube repair-ing/ plugging criteria, i.e. current applications of USNRC Regulatory Guide 1.121, apply throughout the tube length and do not take into account the i reinforcing effect of the tubesheet on the external surface of the tube. The presence of the tubesheet will complement tube integrity in that region by essentially precluding tube deformation beyond its initial outside diameter.
The resistance to both tube rupture and tube collapse behavior is strength-
- sned by the tubesheet, and the use of an alternate criterion for plugging cargin is justified. The result of the evaluation is the identification of a below the top of the tubesheet for distance of 1.282 inches, designated P*,
which tube degradation of any extent at or below that distance does not necessitate remedial action except as dictated for compliance with tube leakage limits as set forth in the McGuire Units 1 and 2 technical speci-fications. As an additional margin, Duke Power is proposing two inches as the P* distance.
- 1) The supporting P* evaluation (Attachment 3) demonstrates that the presence of the tubesheet will complement tube integrity in that region by precluding tube deformation beyond its initial outside diameter. The resistance to both tube rupture and tube collapse behavior is strength-ened by the presence of the tubesheet in that region. Furthermore, the i existing Technical Specificat' ion leakage rate requirements remain in l place in the unlikely event leakage from this region does occur.
' Therefore the proposed amendment does not involve a significant increase ,
in the probability or consequences of an accident previously evaluated.
- 2) The supporting evaluation demonstrates that implementation of the P*
criterion minimizes the potential for any possible tube indications that
- may exist from creating any type of accident.
In order to obtain a meaningful quantitative value for the P* criterion,
- the hypothetical case of the circumferential separation of both ends of a steam generator U-tube, subsequent vertical displacement and contact with the tube directly above it (one row higher, same column) was assumed as described in the supporting evaluation. Generally, cracking that has been observed in operating units has been located in the non-expanded to expanded transition of the tube hardroll and/or skip roll locations in the tubenheet, and has been typified as short and axially oriented. For axial indications in'the tubesheet region, the l
tube end remains structurally intact, minimizing any potential for tube
! pullout ;ue to mechanisms defined in the development of the P* criter-ion.
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J The proposed change is fully bounded by the steam generator tube rupture analysis though this could only happen through tube pullout, which is precluded as tubes with indications of degradation above P* will be plugged; therefore the proposed amendment does not create the possibility of a new on different kind of accident from any accident previously evaluated.
- 3) The tubesheet plugging criterion has been demonstrated to maintain the integrity of the tube bundle with eddy current indications within the I tubesheet under normal operating and postulated accident conditions l loadings; and the unnecessary plugging of tubes would reduce the RCS flow margin, thus this change would help maintain the margin on flow.
Thus, the proposed amendment does not involve a significant reduction in a margin to safety.
Based on the preceding analysis Duke Power Company concludes that the i proposed amendments do not involve a Significant Hazards Consideration.
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d ATTACMfENT 5 I
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Following is an identification of the 7 criteria required for the processing of a Technical Specification on an emergency basis (this request is for processing on an exigent basis), in accordance with NRC Staff procedure.
- 1. A safety evaluation with a No Significant Hazards Determination.
See Attachments 2, 3, and 4.
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- 2. Revised Technical Specification page(s).
See Attachment 1.
- 3. A discussion of proposed interim compensatory measures to be imposed.
The unit is shutdown for a refueling outage and can go no higher t.han Mode 5 (Cold Shutdown, T-ave less than 200 degrees F) until this proposed amendment is processed.
- 4. A discussion of the circumstances involved and a determination af why the need for prompt action could not be avoided.
The use of the P* criteria for Westinghouse plants has been a matter of discussion between the NRC staff and affected members of the nuclear industry for over a year. While it was known that McGuire was not immune to the problem, it had not been observed at McGuire. It was only this refueling outage that a problem was identified at McGuire, and the P* Criteria would prevent the unnecessary plugging of 106 steam generator tubes this outage. The NRC staff has been reviewing the issue of a generic basis as the result of a January 16, 1986 submittal by South Carolina Electric and Gas for their VC Summer plant which is in the final stages of review. A couple of issues have not been fully resolved at this time such that waiting for the resolution of these issues would delay unit restart following this outage. It is on these i issues (definition of " intact tube" and inspections of " intact tubes")
i that Duke is proposing a very conservative position to expedite the i
review of the proposal. If less conservative values may be justified, Duke may pursue this change at a later date on a normal (non-emergency) basis.
r 5. The scheduled date for returning inoperable components to an operable condition, or for accomplishing required surveillance.
The outage schedule calls for Mode 4 on July 24, 1986 at which time the Steam Generators must be operable, either by issuance of the amendment or plugging of the tubes.
l l 6. A statement that a best effort has been made to notify State personnel.
The State is being notified by copy of this letter.
- 7. Information for the NRC to prepare an Environmental Assessment.
This proposal does not involve any environmental impact. The steam generator plugging criteria does not affect any offsite releases as the only possibility is primary to secondary le'akage which is limited by 1 Technical Specifications and has been considered in establishing the Technical Specification limits.
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