ML111650746
| ML111650746 | |
| Person / Time | |
|---|---|
| Site: | Kewaunee  |
| Issue date: | 12/27/1991 |
| From: | Steinhardt C Wisconsin Public Service Corp |
| To: | NRC/IRM |
| Shared Package | |
| ML111650747 | List: |
| References | |
| NUDOCS 9201070168 | |
| Download: ML111650746 (32) | |
Text
AC'CELERATED DITRIBUTION DEMONSTDATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSION NBR:9201070168 DOC.DATE: 91/12/27 NOTARIZED: YES DOCKET #
FACIL:50-305 Kewaunee Nuclear Power Plant, Wisconsin Public Servic 05000305 AUTH.NAME AUTHOR AFFILIATION STEINHARDT,C.R. Wisconsin Public Service Corp.
RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
SUBJECT:
Application for amend to License DPR-43,consisting of Proposed Amend 105,changing TS 3.1.d & 4.2.b re SG tu support plate alternate plugging criteria.
?
"Kewaunee SG Tube Plugging Criteria...." encl & withheld.
D DISTRIBUTION CODE: A001D COPIES RECEIVED:LTR 4 ENCL TITLE: OR Submittal: General Distribution NOTES:
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aNSIC NOTE TO ALL "RIDS" RECIPIENTS:
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WPSC (414) 433-1598 TELECOPIER (414) 433-5544 EASYLINK 62891993 WISCONSIN PUBLIC SERVICE CORPORATION 600 North Adams
- P.O. Box 19002
- Green Bay, WI 54307-9002 December 27, 1991 10 CFR 50.90 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:
Docket 50-305 Operating License DPR-43 Kewaunee Nuclear Power Plant Proposed Amendment 105 to the Kewaunee Nuclear Power Plant Technical Speciications, Steam Generator Tube Support Plate Alternate Plugging Criteria In order to preclude unnecessarily plugging tubes in the Kewaunee steam generators (SG) during future refueling outages an alternate plugging criteria (APC) has been developed. The proposed APC is based on the bobbin coil inspection voltage amplitude which is correlated to the tube integrity issues including tube burst margins and leakage potential under accident conditions.
The scope of the proposed APC will be limited to those indications contained within the thickness of the tube support plates for which outside diameter stress corrosion cracking (ODSCC) is the dominant degradation mechanism. Indications in the other regions of the SG tube, indications not attributable to ODSCC, and circumferential indications, will be dispositioned by the current depth based Technical Specification (TS) limit.
The APC was developed to ensure structural margin against tube burst in accordance with NRC Regulatory Guide 1. 121 and to minimize leakage at normal operating conditions. The APC will also ensure that the radiological consequences of a steam line break do not exceed a small fraction of the 10 CFR part 100 limits. The technical basis and regulatory analysis are contained in WCAP-12985 (proprietary) and WCAP-12986 (non-proprietary) "Kewaunee Steam Generator Tube Plugging Criteria for ODSCC at Tube Support Plates."
In support of this amendment request the following information is provided in attachment 1:
o Description of the Proposed Change o Safety Evaluation o Significant Hazards Determination o Environmental Considerations FOIJR AD OC:K 0!50003059/V111/l/V6(/4/(
/
1V PDR NIP/
Document Control Desk December 27, 1991 Page 2 The proposed changes to Kewaunee TSs 3. 1.d and 4.2.b are provided in attachment 2. Please note that section 3.1 has previously been submitted to the NRC as a part of proposed amendment (PA) 101 and PA 103. The formatting and administrative changes being submitted at this time are identical to those previously submitted. The technical changes proposed by PA 101 and PA 103 are not included as a part of this amendment request.
The technical justification to support the APC is provided as attachment 3. Also enclosed are a Westinghouse authorization letter, CAW-91-238, accompanying affidavit, Proprietary Information Notice, and Copyright Notice.
As WCAP-12985 contains information 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 information may be withheld from public disclosure by the Commission and addresses with specificity the considerations listed in paragraph (b)(4) of Section 2.790 of the Commission's regulations.
Accordingly, it is respectfully requested that the information which is proprietary to Westinghouse be withheld from public disclosure in accordance with 10 CFR Section 2.790 of the Commission's regulations.
Correspondence with respect to the copyright or proprietary aspects of the items listed above or the supporting Westinghouse affidavit should reference CAW-91-238 and should be addressed to Mr. R. P. DiPiazza, Manager of Nuclear Safety Licensing, Westinghouse Electric Corporation, P.O. Box 355, Pittsburgh, Pennsylvania 15230-0355.
This PA has been reviewed and accepted by Wisconsin Public Service Corporation's Plant Operating Review Committee and the Kewaunee Plant Manager.
In accordance with the requirements of 10 CFR 50.30(b), this submittal has been signed and notarized. A copy of this submittal has been transmitted to the State of Wisconsin as required by 10 CFR 50.91(b)(1).
Sincerely, C. R. Steinhardt Senior Vice President - Nuclear Power
.Subscribed and Sworn to Meo e
This -1f'74Day SLB/jims of
. 1991 Attach.
PJ~r'yPulic SateofWisconsin cc - US NRC - Region III Mr. Patrick Castleman, US NRC My Commissin Expires:
Mr. R. S. Cullen, PSCW June 18: 1995 LIC\\NRC\\N531
50-305 WPSC PROPOSED AMDT 106 TO TECH SPECS RE STEAM GENERATOR TUBE SUPPORT PLATE ALTERN PLUGGING CRITERIA REC'D W/LTR DTD 12/27/91.... 9201070168 THE ATTACHED FILES ARE OFFICIAL RE-.
CORDS OF THE RECORDS & REPORTS MANAGEMENT BRANCH. THEY HAVE BEEN CHARGED TO YOU FOR A LIMITED TIME PERIOD AND MUST BE RETURNED TO THE RECORDS & ARCHIVES SERVICES SECTION P1-122 WHITE FLINT.
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ATTACHMENT 1 To Proposed Amendment No. 105 Letter from C. R. Steinhardt (WPSC)
To Document Control Desk (NRC)
Dated December 27, 1991 Description of the Proposed Change Safety Evaluation Significant Hazards Determination Environmental Considerations
Document Control Desk December 27, 1991, Page 1 Introduction A license amendment is being proposed to preclude unnecessarily plugging tubes due to the occurrence of outside diameter stress corrosion cracking (ODSCC) at the tube support plate (TSP) intersections in the Kewaunee steam generators (SGs).
The existing Technical Specification (TS) SG tube plugging limit based on tube wall depth penetration is very conservative considering current non-destructive examination (NDE) capabilities.
Continued application of this plugging criteria will result in the needless plugging or repair of SG tubes that have acceptable structural margin for continued operation.
An alternative plugging criteria (APC) has been developed for the TSP intersection ODSCC occurring in the Kewaunee SGs and is described in WCAP-12985, "Kewaunee Steam Generator Tube Plugging Criteria for ODSCC at Tube Support Plates". The APC involves a correlation between eddy current bobbin probe signal amplitude (voltage) and tube integrity issues including tube burst margins and the potential for tube leakage under postulated accident conditions.
The APC was developed from testing laboratory induced ODSCC specimens, extensive examination of pulled tubes from operating SGs and field data. The criteria being proposed by this license amendment is conservatively based upon Electric Power Research Institute (EPRI) and industry supported development programs that are continuing toward further refinement of tube plugging criteria.
Document Control Desk December 27, 1991, Page 2 NRC Regulatory Guide (RG) 1.121, "Bases for Plugging Degraded Steam Generator Tubes,"
issued for comment, was used as a basis for determining the acceptability of the proposed APC.
Application of the APC in the Kewaunee SGs may result in tubes with both partial and through wall cracks being returned to service. In the limiting case, the presence of a through-wall crack alone is not reason enough to remove a tube from service. The regulatory and technical basis for returning partial and through-wall cracks to service in the Kewaunee SGs is assessed in WCAP-12985. The APC was also developed to satisfy the Kewaunee Updated Safety Analysis Report (USAR) requirements for allowable leakage under accident conditions by demonstrating that the dose rate associated with potential leakage from tubes remaining in service is a small fraction of the 10 CFR 100 limits.
Implementation of the APC for the Kewaunee SGs is supplemented by a 100% bobbin coil inspection of the TSP intersections, a reduced operating leakage requirement, inspection guidelines to provide consistency in the voltage normalization and the requirement to perform a rotating pancake coil (RPC) inspection of bobbin coil indications > 1.5 volts at the TSP intersections in order to characterize the principle degradation mechanism as ODSCC.
In addition, a potential leakage rate for a steam line break (SLB) event will be calculated for tubes left in service to demonstrate that the cumulative leakage is less than the 260 gpm acceptance criteria for each SG.
Document Control Desk December 27, 1991, Page 3 Following is a description of the proposed TS changes, a safety evaluation, a 10 CFR 50.92 significant hazards determination, and an environmental considerations statement. Attachment 2 contains the affected TS pages and Attachment 3 contains the technical justification for the proposed APC.
Description of the Proposed TS Changes This proposed amendment modifies Kewaunee TS 3.1.d, "Leakage of Reactor Coolant,"
TS 4.2.b, "Steam Generator Tubes," and the associated basis to incorporate the reduced operational leakage requirements, tube inspection requirements and the acceptance criteria from WCAP-12985.
Specifically, the TSP plugging criteria for ODSCC in the Kewaunee SG is summarized as follows:
A plant shutdown will be initiated if normal operating leakage exceeds 150 gpd per SG.
A 100% bobbin coil inspection shall be performed of all hot leg and cold leg TSP intersections at each refueling outage.
Document Control Desk December 27, 1991, Page 4 A tube shall be plugged or repaired if the bobbin coil signal amplitude of the indication within the TSP intersection is > 3.5 volts.
All tubes with bobbin coil indications > 1.5 volts at TSP intersections shall be inspected using an RPC probe. The RPC results shall be evaluated to support ODSCC as the dominant degradation mechanism. Once an indication is characterized as ODSCC, RPC inspections at alternate refueling outages is acceptable.
Tubes with RPC indications not attributable to ODSCC, or with circumferential indications, shall be evaluated based on the 50% eddy current indicated depth limit.
The field eddy current inspection guidelines will require use of an ASME standard calibrated against a laboratory standard for consistent voltage normalization.
A predicted SLB leak rate due to ODSCC at TSPs for the tubes left in service shall be performed to verify a primary-to-secondary leak rate of <260 gpm in the faulted loop.
This assessment includes consideration for NDE uncertainties and ODSCC growth rates over the operating cycle.
A 30-day report shall be submitted to the NRC including a list of tubes to which the APC has been applied and location and voltage amplitude of the indications left in service.
Document Control Desk December 27, 1991, Page 5 In addition to the proposed changes associated with APC, the TS changes approved as Amendment No. 93 are being removed. TS Amendment No. 93 was approved by the NRC staff on May 3, 1991 to provide a method to disposition RPC indications in the SG hot leg crevice region during the 1991 refueling outage. The amendment was approved on an interim basis only for the 1991-1992 operating cycle, therefore, the provision of this amendment will not be applicable following the Kewaunee refueling outage scheduled for March 1992.
The TS changes being proposed to incorporate the APC for ODSCC at the TSP intersections are as follows:
- 1)
In TS 3.1.d.2, the reactor coolant-to-secondary leakage through the SG tubes is being reduced from 500 gpd to 150 gpd if the APC is applied,
- 2)
In TS 4.2.b, the definition of tube inspections is being expanded to include the inspection of all hot leg and cold leg TSP intersections, TS 4.2.b.2.a, is being expanded to state that if APC is applied, then the inspection requirements are for a 100% bobbin coil inspection of the TSP intersections and RPC of indications > 1.5 volts.
Document Control Desk December 27, 1991, Page 6 A note is being added to existing TS 4.2.b.4 to state that the depth based plugging limit does not apply to tubes experiencing ODSCC within the thickness of the TSPs.
New TS 4.2.b.5 contains the APC for indications in the TSP intersections.
TS 4.2.b.6.d is being added to include reporting the tubes for which APC has been applied.
- 3)
In TS as TS 4.2.b, the following changes are being proposed to remove the conditions approved Amendment No. 93:
The definitions for distorted indication, tube sheet crevice region, and squirrel indication are being removed, In TS 4.2.b.4, footnote 2 referring to the hot leg crevice region criteria is being deleted, and TS 4.2.b.5, "Hot Leg Tubesheet Crevice Plugging Limit Criteria," and the accompanying footnote are being superseded by the "Tube Support Plate Alternate Plugging Criteria".
Document Control Desk December 27, 1991, Page 7
- 4)
In addition, an administrative change is being proposed to add the words "or repair" when referring to the plugging limit under the definition of defect and in the title of TS 4.2.b.4.
Concurrent with these changes, the basis is being revised and is submitted for your information.
Safety Evaluation WCAP-12985 provides the technical basis and regulatory analysis to support an APC for ODSCC at TSPs in the Kewaunee SGs. The APC involves a correlation between eddy current bobbin coil signal amplitude (voltage) and the tube integrity issues of tube burst margin and leakage potential under accident conditions.
The following safety evaluation includes a discussion on RG 1.121 which was used as a basis for determining adequate tube structural limits, a discussion on how the tube plugging limit was arrived at, and a review of normal operation and the Kewaunee USAR design basis events to demonstrate that application of the APC will not increase the probability of a previously evaluated accident or result in radiological consequences exceeding a small fraction of the 10 CFR 100 limits.
Document Control Desk December 27, 1991, Page 8 Tube Structural Limits (RG 1.121)
The proposed APC for the Kewaunee SGs is based upon the conservative assumptions that the tube to TSP crevices are open (negligible crevice deposits or TSP corrosion exists) and that the TSPs are displaced under accident condition loadings. The ODSCC is thus considered to be free span degradation under accident conditions, and the principal requirement for tube plugging or repair considerations is to provide margin against tube burst in accordance with RG 1.121. The open crevice assumption leads to maximum leak rates as compared to packed crevices and maximizes the potential for TSP displacements (which can uncover cracks) under accident condition loadings.
RG 1.121 and RG 1.83, "Inservice Inspection of PWR Steam Generator Tubes" provide the basis for determining that SG tube integrity considerations are maintained within acceptable limits. RG 1. 121 describes a method acceptable to the NRC staff for meeting General Design Criteria (GDCs) 2, 14, 15, 31 and 32 by reducing the probability and consequences of SG tube rupture through determining the limiting safe conditions of tube wall degradation beyond which tubes with unacceptable cracking, as established by inservice inspection, should be repaired or plugged. RG 1.83 describes a method acceptable to the NRC for implementing GDCs 14, 15, 31 and 32 through periodic inservice inspection for the detection of significant tube wall degradation.
Document Control Desk December 27, 1991, Page 9 RG 1. 121 applies safety factors for loads on tube burst and collapse that are consistent with Section III of the ASME Code.
In accordance with paragraph C.3.d(1) of RG 1.121, the applicable analytical and loading criteria in thinned or unthinned tubes with partial and through wall cracks can be summarized as:
- 1.
Through-wall cracks in minimum thickness tubes should not propagate and result in tube wall rupture under accident condition loadings.
- 2.
The maximum permissible crack length of the largest single crack should be such that the associated burst pressure is at least 3 times the normal operating pressure differential.
- 3.
The leak rate limit under normal operation set forth in the plant TSs should be less than the leakage limit determined for the longest permissible crack.
With regard to criterion 1 of RG 1.121, the postulated events considered were a Loss-of-Coolant Accident (LOCA) and a SLB in combination with the Safe Shutdown Earthquake (SSE). The potential effects of a postulated SLB in combination with a SSE event are enveloped by RG 1.121 criterion 2 which is discussed later.
In addressing the combined effects of the LOCA and SSE on the SG components there is the potential that tube collapse may occur. The tube support plates may become deformed as a
Document Control Desk December 27, 1991, Page 10 result of radial loads at the wedge support locations due to either the LOCA rarefaction wave or the SSE loadings. Deformation of the plates can result in subsequent tube deformation such that the post-LOCA secondary to primary pressure differential may cause some of the tubes to collapse.
There are two issues associated with SG tube collapse. First, collapse of the SG tubing reduces the reactor coolant flow area through the tubes. The reduction in flow area decreases the heat removal capability of the SG, which, in turn may potentially increase Peak Clad Temperature (PCT). Second, there is the potential that tubes with partial through-wall cracks could progress to through-wall cracks during tube deformation.
These issues are addressed for the Kewaunee SGs by application of leak-before-break principles to the primary loop piping. Calculations for the SG inlet line break combined with SSE shows that no tubes will undergo permanent deformation of greater than 0.025 inch (basis is discussed more fully in section 11.2 of the WCAP). Although specific leakage data is not available, it is judged that deformations of this magnitude will not lead to significant tube leakage.
On this basis, no tubes in the Kewaunee SG need to be excluded from the APC for reasons of tube collapse and deformation resulting from combined LOCA and SSE loadings. Therefore, it is reasonable to expect that through-wall cracks will not propagate and result in tube wall rupture under accident condition loadings.
Document Control Desk December 27, 1991, Page 11 With regard to RG 1. 121, criterion 2, a factor of 3 times normal operating pressure differential on tube burst is inherently satisfied during normal operating conditions by the presence of the TSP. The presence of the TSP enhances the integrity of the degraded tubes in that region by precluding tube deformation beyond the diameter of the drilled hole. It is not certain whether the TSP would function to provide a similar constraining effect during accident condition loadings at Kewaunee. Therefore, no credit is taken in the development of the plugging criterion for the presence of the TSP during accident condition loadings.
Testing of model boiler specimens for free standing tubes at room temperature conditions show burst pressures as high as 5000 psi for ODSCC with voltage measurements as high as 30 volts.
Burst testing performed on pulled tubes with up to 10 volts indication show burst pressures exceeding 3 times normal operating pressure differential. Smaller voltage signals, in the range of 0.2 volts to 2.3 volts, with 34% and 60% through-wall cracking respectively, were demonstrated to have burst pressures in excess of 7800 psi at room temperature.
Based on the existing data base for free span tubing, this criterion is satisfied with bobbin coil voltage indications of less than 5.6 volts, regardless of the indicated depth measurement. This structural limit is based on a lower bound limit of the data.
With regard to RG 1. 121 criterion 3, a leakage rate limit of 150 gpd will be implemented to provide for leakage detection and plant shutdown in the event of an unexpected single crack
Document Control Desk December 27, 1991, Page 12 resulting in leakage that is associated with the longest permissible crack length. The acceptance criteria for establishing operating leakage limits are based on leak-before-break considerations such that a plant shutdown is initiated if the leakage associated with the longest permissible crack is exceeded. The longest permissible crack length is the length that provides a factor of safety of 3 against bursting at normal operating pressure differential. As previously stated, a voltage amplitude of 5.6 volts for typical ODSCC corresponds to meeting this tube burst requirement at the lower 95 % confidence level on the burst correlation curves.
The single through-wall crack lengths that result in tube burst at 3 times normal operating pressure differential and SLB conditions are approximately 0.39 inch and 0.84 inch, respectively. Nominal leakage for these crack lengths range from 0.1 gpm to 4.5 gpm while lower 95% confidence level rates range from about 0.02 gpm to 0.6 gpm.
A maximum operating leak rate of 150 gpd will provide for the detection of 0.4 inch long cracks at nominal leak rates and 0.6 inch long cracks at the 95% confidence level leak rates. Therefore, the 150 gpd limit provides for plant shutdown prior to reaching critical crack lengths for SLB conditions at leak rates less than a lower 95 % confidence level and for three times normal operating pressure differential at less than nominal leak rates.
Document Control Desk December 27, 1991, Page 13 Tube Plugging Limit The APC limit provides margin to tube burst in accordance with RG 1.121. The burst pressure versus voltage correlation defines a voltage of 5.6 volts for the structural requirement for a free span tube to have a burst capability equivalent to 3 times normal operating pressure differential.
The voltage structural limit is reduced by a conservative allowance of 20% (0.7 volts) for NDE uncertainties and 40% (1.4 volts) for crack growth over an operating cycle to obtain a tube plugging limit of 3.5 volts.
Normal Operations and USAR Analysis With application of the APC for the Kewaunee SGs, no leakage is expected during normal operating conditions and limited leakage is expected under accident conditions even with the presence of through-wall cracks. This is because the stress corrosion cracking occurring in the Kewaunee SGs appears as short, tight, axially oriented microcracks separated by ligaments of material and contained within the thickness of the TSPs. No leakage during normal operating conditions has been observed in the field for crack indications of this nature with signal amplitudes less than 7.7 volts. Relative to expected leakage during accident condition loadings, laboratory data for pulled tubes and model boiler specimens show limited leakage for indications between 3 and 10.0 volts during SLB conditions, with no leakage below about 2.8 volts regardless of the indicated depth of through-wall penetration.
Document Control Desk December 27, 1991, Page 14 The accidents that are affected by primary-to-secondary leakage are those that include modeling of leakage and secondary steam release to the environment in the activity release and offsite dose calculations. The accidents in the Kewaunee USAR that result in a secondary steam release are:
Loss of Reactor Coolant Flow (locked rotor), USAR 14.1.8 Loss of External Electrical Load, USAR 14.1.9 Loss of AC Power, USAR 14.1.12 Steam Generator Tube Rupture, USAR 14.2.4 Rupture of a Steam Pipe, USAR 14.2.5.
The most limiting accident is the postulated SLB event. The SLB is limiting because of the assumption that leakage to the faulted SG is released directly to the environment, i.e., it is assumed that the affected SG boils dry, therefore, no credit is taken for mixing with the secondary coolant or partitioning of the activity.
For other accidents in which there is a secondary side steam release, there is justification for mixing and iodine partitioning in the SG following potential uncovery of the top of the tube bundle after the reactor trip. These factors, along with a smaller primary to secondary pressure differential, significantly reduces the release of iodine to the environment for accidents other than the SLB.
For the Kewaunee SGs, a limiting SLB accident condition leak rate of 260 gpm in the faulted SG and 150 gpd in the intact loop is consistent with the assumptions of the USAR and will limit off-site doses to a small fraction of the 10 CFR 100 limits. With application of the APC, a projected potential SLB leak
Document Control Desk December 27, 1991, Page 15 will be determined for tubes left in service to demonstrate satisfaction of the 260 gpm leakage limit during each refueling outage.
Although the guidelines of RG 1.121 are used to establish tube plugging limits, the potential for tube burst at SLB conditions is shown to be negligible based on both deterministic crack length considerations and probability estimates.
The burst pressure versus crack length correlation utilizing the Belgian burst data (EPRI NP-6864-L) developed under prototypic flow conditions shows that a through wall crack length of 0.84 inch is required for tube burst at SLB pressure differentials. This crack length exceeds the 0.75 inch TSP thickness which bounds the potential crack lengths for ODSCC at TSPs.
Consequently, tube burst for ODSCC is essentially precluded by the crack length limit.
Moreover, an alternate assessment was performed by considering the probabilities associated with a limiting end of cycle (EOC) voltage including growth and comparing with the probability of tube burst at the limiting EOC voltage amplitudes.
This analysis shows that an indication left in service at the tube plugging limit would have a probability of burst at SLB conditions of approximately 5 x 10 per cycle. This value does not include the probability of an SLB event occurring; hence the actual burst probability (combined probability of SLB and burst) would be further reduced. Thus tube burst is not a significant concern for application of the plugging limits for ODSCC at TSPs. The use of free span burst pressure criteria to establish tube plugging limits therefore leads to very conservative plugging limits.
Document Control Desk December 27, 1991, Page 16 Significant Hazards Determination The proposed change was reviewed in accordance with the provision of 10 CFR 50.92 to show no significant hazards exist. The proposed change will not:
- 1) involve a significant increase in the probability or consequences of an accident previously evaluated.
The probability of an accident previously evaluated will not be significantly increased by this proposed TS change to incorporate an APC. The APC will be limited to ODSCC occurring within the thickness of the TSPs. A tube integrity assessment performed in accordance with the criteria of RG 1.121 demonstrated that the tubes in the Kewaunee SGs maintain a safety factor of three times normal operating pressure differential for crack indications with voltages up to 5.6 volts with no credit taken for potential constraint of the TSP under normal and postulated accident condition loadings.
The potential for a tube rupture event has been shown to be negligible upon implementation of the APC.
The consequences of an accident previously evaluated will not be significantly increased by application of an APC.
Although tubes are not expected to burst under accident conditions, it cannot be assured that the cracks will not leak during postulated accident
Document Control Desk December 27, 1991, Page 17 condition loadings as discussed in the USAR.
Of the accidents that are affected by primary-to-secondary leakage and steam release to the environment, SLB is most limiting relative to the potential for off-site doses. Upon implementation of the APC, it will be verified that the predicted leak rate from ODSCC at TSPs for the tubes left in service would be less than 260 gpm for the faulted loop during a postulated SLB event. This level of tube leakage results in radiological consequences that are within a small fraction of the 10 CFR 100 limit at the site boundary.
- 2) create the possibility of a new or different kind of accident from any accident previously evaluated.
Implementation of an APC for ODSCC in the SG at the support plates is not expected to reduce the overall safety and functional requirements of the SG tube bundles. The SG tube bundles will continue to sustain, within the guidelines of RG 1.121, the loads during normal operation and the various postulated accident conditions without loss of safety function. There are no tubes that need to be excluded from application of the APC for reasons of tube collapse and deformation resulting from combined LOCA and SSE loadings. Therefore, the proposed change does not create the possibility of a new or different kind of accident.
Document Control Desk December 27, 1991, Page 18
- 3) involve a significant reduction in the margin of safety.
Application of the APC for the Kewaunee SGs has been demonstrated to maintain tube integrity commensurate with the RG 1.121 criteria and hence, meets GDCs 14, 15, 31 and 32.
Also, GDC 2 is met in that the SGs will continue to perform their intended safety function upon implementation of the APC. Even under the worst case conditions, the occurrence of ODSCC at the TSPs is not expected to lead to a SG tube rupture event during normal or faulted plant conditions. The most limiting effect would be a possible increase in leakage during a SLB event.
Excessive leakage during a SLB event is precluded by verifying that the expected distribution of crack indications would result in less than 260 gpm primary-to-secondary leakage.
With this level of leakage, the radiological consequences from tubes remaining in service is a small fraction of the 10 CFR 100 limits.
In conjunction with the APC, requirements will be incorporated into the TSs to limit operating leakage to 150 gpd per SG and to perform a predicted SLB leak rate due to ODSCC at TSPs for the tubes left in service. The operating leakage limit of 150 gpd per SG will be established to provide for detection of a rogue crack which could leak at much higher SLB leak rates than used in the criteria limits. The requirement to perform a predicted SLB leakage assessment is to ensure that the tubes left in service result in a combined leakage less than 260 gpm for each SG including considerations for NDE
Document Control Desk December 27, 1991, Page 19 uncertainties and ODSCC growth rates over an operating cycle. If it is found that the potential SLB leakage for degraded intersections planned to be left in service exceeds 260 gpm, then additional tubes will be plugged to reduce SLB leakage potential to below 260 gpm.
Additionally, the combined effects of the LOCA and SSE loadings on the SG components was assessed. Based on this analysis, no tubes need to be excluded from the APC for reasons of deformation resulting from the combined LOCA and SSE loadings.
Therefore, the proposed change will not result in a significant reduction in the margin of safety.
Document Control Desk December 27, 1991, Page 20 Environmental Considerations This proposed amendment involves a change to an inspection requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20.
Wisconsin Public Service Corporation has determined that the proposed amendment involves no significant hazards considerations and no significant change in the types of any effluent that may be released off site and that there is no significant increase in individual or cumulative occupational radiation exposure. Accordingly, this proposed amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). This proposed amendment also involves changes in record keeping, reporting or administrative procedures or requirements.
Accordingly, with respect to these items, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(10).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with this proposed amendment.