L-PI-10-094, Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures from the Licensing Basis Based Upon Application of Leak-Before-Break Methodology - Response to RAI

Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures from the Licensing Basis Based Upon Application of Leak-Before-Break Methodology - Response to RAI

ML102810518
Person / Time
Site:	Prairie Island
Issue date:	10/08/2010
From:	Schimmel M Northern States Power Co, Xcel Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-PI-10-094, TAC ME2976, TAC ME2977
Download: ML102810518 (16)

Text

L-PI-10-094 40 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units Iand 2 Dockets 50-282 and 50-306 License Nos. DPR-42 and DPR-60 Supplement to License Amendment Reauest to Exclude the Dvnamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensina Basis Based Upon Application of Leak-Before-Break Methodologv - Response to Request for Additional lnformation (TAC Nos. ME2976 and ME29771

References:

1. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, "License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology," L-PI-09-134, dated December 22, 2009, ADAMS Accession Number MLI 00200129.

2. Letter from T. Wengert (NRC) to M. Schimmel (NSPM), "Prairie Island Nuclear Generating Plant, Units 1 and 2 - Request for Additional lnformation Related to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology (TAC Nos.

ME2976 and ME2977),11dated June 10,2010, ADAMS Accession Number MLI 01550668.

3. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, "Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology - Response to Request for Additional lnformation (TAC Nos. ME2976 and ME2977)," L-PI-10-077, dated July 23, 2010, ADAMS Accession Number MLI 02040612.

1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1121

Document Control Desk Page 2 In Reference 1, Northern States Power Company, a Minnesota corporation (NSPM),

doing business as Xcel Energy, submitted a License Amendment Request (LAB) to apply leak-before-break (LBB) methodology to cerfain piping systems at the Prairie Island Nuclear Generating Plant (PINGP), To support review of this LBB LAB, the U.S.

Nuclear Regulatory Commission (NRC) Stae requested additional information in Reference 2.

In Reference 3, NSPM submitted responses to the NRC requests with the exception of two questions regarding Reactor Coolant System leakage detedion. These two outstanding questions are addressed in Enclosure 1. NSPM submits this supplement in accordance with the provisions of 10 GFR 50.90.

Enclosure 2 contains a discussion concerning leak detection statements in the original LBB LAR (Reference 1). Based on this discussion, Reference 1 is supplemented with corrections and changes to the leak detection capabilities described in Enclosure 2.

The supplemental information provided in this letter does not impact the conclusions of the Determination of No Significant Hazards Consideration or Environmental Assessment presented in the Reference 1 submittal.

In accordance with 10 CFR 50.91, NSPM is notifying the State of Minnesota of this LAR supplement by transmitting a copy of this letter to the designated State Official.

If there are any questions or if additional information is needed, please contact Jennie Eckholt at 612-330-5788.

Summary of Commitments This letter contains no new commitments and no revisions to existing commitments.

I declare under penalty of perjury that the foregoing is true and correct.

Mark A. Schimmel Site Vice President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosures (2) cc: Administrator, Region Ill, USNRC Project Manager, PINGP, USNRC Resident Inspector, PINGP, USNRC State of Minnesota

ENCLOSURE I Response to NRC Reauest for Additional lnformation Dated June 10, 2010, Related to License Amendment Request to Exclude the Dynamic Effects Associated at the Prairie lsland Nuclear Generatina Plant This enclosure includes responses from the Northern States Power Company, a Minnesota corporation (NSPM), to Requests for Additional Information (MI)regarding Reactor Coolant System (RCS) leakage detection capabilities at the Prairie Island Nuclear Generating Plant (PINGP).

I I These RAls are associated with NSPM's License Amendment Request (LAR) submitted December 22, 2009 (Reference I ) regarding the use of Leak-Before-Break (LBB) methodology. The RAls were included in a letter from the Nuclear Regulatory Commission (NRC), dated June 10, 2010 (Reference 2). NSPM responded to other questions not related to RCS leakage detection in a letter dated July 23, 2010 (Reference 3).

This Enclosure quotes each RAI question in italics and each question is followed by the NSPM response. Referenced documents are identified at the end of this Enclosure.

Enclosure 7 to the December 22,2009 Submittal E7-2. Page 7:

The licensee stated that when LBB was applied to the RCS loop piping in an LBB evaluation in 1986, a criterion of 1 gallon per minute (gprn) in one hour for RCS leakage was used for the leak detection system capability. However, for the current submittal, the licensee used a leakage detection limit of 0.2 gpm. The use of 0.2 gpm in the proposed LBB evaluation is an improvement in the leakage detection capability from the original licensing basis of 1 gpm. However, discuss whether the design basis for the RCS leak detection system needs to be changed in the Updated Final Safety Analysis Report and plant technical specifications via a license amendment process. If not, provide justification.

NSPM Response:

The PINGP Updated Safety Analysis Report (USAR) will be revised to reflect the change in the RCS leak detection capabilities. The PINGP Technical Specifications do not require revision.

USAR The licensing and design basis for PINGP's current approved LBB analyses is described in USAR Section 4.6.2.3, Elimination of Large Primary Loop Pipe Rupture as the Structural Design Basis, and USAR Section 4.6.2.4, Elimination of Pressurizer Surge Line Rupture as the Structural Design Basis for Prairie lsland Unit 7. PINGP is Page 1 of 12

Enclosure 1 NSPM LBB - Responses to RAis Regarding RCS Leakage Detection not changing the design and licensing requirements listed in USAR Section 4.8.2.3 or USAR Section 4.6.2.4. The 1 gprn detection limit continues to apply, Upon approval by the NRC of the LBB LAR (Reference I), NSPM will add another section to the PlNGP IJSAR, as required by 10 CFR 50.71(8), to address the application of LBB methodology to the RCS branch lines included in the LBB M R . It will include a discussion of the requirement that the PlNEP leakage detection system be capable of detecting a minimum leakage of 0.2 gprn in order to support the analysis for these lines.

Technical Specifications No changes to the PlNGP Technical Specifications (TS) are required to implement the analysis assumptions or any other considerations associated with the LBB LAR as justified below.

GDC The PlNGP TS leakage limits and instrumentation requirements are based on Atomic Energy Commission (AEC) General Design Criterion (GDC) 16 (insofar as AEC GDC 16 is equivalent to 10 CFR 50, Appendix A, GDC 30). The LBB LAR was submitted in conformance to 10 CFR 50, Appendix A, GDC 4, and does not affect the AEC GDC 16 compliance basis. Therefore, conformance with AEC GDC 16 has not changed, and the TS do not require change.

Technical Specifications According to the Bases, TS 3.4.16 RCS Leakage Detection Instrumentation relies on the ability to detect a 1 gprn RCS leak. No response time is identified in either the TS or Bases. This capability is assured by the 0.2 gprn acceptance criterion for LBB (Reference 1). TS 3.4.14 RCS Operational Leakage continues to rely on the daily inventory balance as the primary source for meeting the LCO.

PlNGP TS 3.4.14 currently permits no pressure boundary leakage (leakage through a non-isolable flaw in the RCS pressure boundary). The LBB analysis uses 0.2 gprn as an acceptance limit for leakage from Reactor Coolant Pressure Boundary (RCPB) piping. Therefore, the zero leakage limit in the TS is quantitatively more restrictive than the LBB analyzed flaws. Further, the 1 gprn unidentified leakage and 10 gprn identified leakage limits are also addressed in the TS. These criteria are based on implementation of AEC GDC 16, and are not changed by the LBB LAR. The LBB methodology is applied to exclude dynamic effects associated with postulated piping ruptures from the design basis in accordance with GDC 4.

Generic Letter (GL) 84-04, "Safety Evaluation of Westinghouse Topical Reports Dealing with Elimination of postulated Pipe Breaks in PWR Primary Main Loops," states that:

"To comply with the NRC criteria specified in Section 4.1 for defining postulated flaw size, calculations were performed to define the relationship between leak rate and crack opening area. The leak rate calculations were performed to show that a postulated throughwall crack was large enough to produce leaks that could be detected at normal Page 2 of 12

Enclosure I NSPM LBB Responses to RAls Regarding RCS Leakage Detection operating conditions by leakage detection devices normally uged to detect primary system leakage." The GL did not require any tetechniml specification changes. The leak rate calculations performed for PINGP LBB showed that the calculated leak could be detected at normal operating conditions by the leakage detsctian deviws normally used to detect primary system leakage at PINGP; therefore, no technical specification changes are required.

Therefore, for the reasons cited above, the PINEP TS do not require revision to incorporate the lower 0.2 gpm criterion for RCS leak detection,

Enclosure 1 NSPM LBB - Responses to RAls Regarding RCS bsakags Detection E2-2. Page 1-5:

Table 1-1 presents 12 leak detection systems at Praiffe Islmd with detectable leakage and response time. The licensee stated that Prair;ie Island has a very redundant leak detection system capable of detecting leakage as low as 0. I gpm, but it is being consetvative by using a leak detection capability of 0.2 gprn in the LBB analysis, The NRC staff questions the capability of the 12 detection systems and methods having the necessary redundancy and sensitivity to meet the specifications in Regulatory Guide (RG) 1.45, Revision I. First, of the 12 detection systems and methods listed in Table 1-I , only five monitoring methods can detect a minimum leakage of 0.2 gprn or lower, Of the five monitoring methods, the operator inspection method, the daily coolant inventory method, and the sump pump operating time method would not satisfy the RE 1.45 requirement of a response time of 1 gprn within I hour, The remaining two monitoring methods may be acceptable. The containment radioactive particulate monitor R- I I has an estimated response time of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> for a leakage rate of 0.5 gprn and it can detect a minimum of 0.1 gpm. The licensee may also take credit for the containment relative humidity monitoring which can detect a minimum leakage of 0.2 gprn with an estimated response time of 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for a 0.5 gprn leakage.

1 Of the 12 leak detection systems in Table I , confirm which leak detection systems satisfy RG 1.45.

2. On page 1-4, the licensee stated that Table 1-1 was taken from Reference 5, which is related to the PlNGP coolant leakage detection system performance and was submitted to the NRC on March 31, 1976. The information in Table 1-1 is more than 30 years old. Identify the leakage detection systems and methods at Units I and 2 that satisfy RG 1.45, Revision 1, in terms of redundancy, reliability, and sensitivity per Standard Review Plan (SRP) Section 3.6.3.111.4.

3. Provide the response time for the detectable leakage of 0.2 gprn because Table 1-1 presents response time based on the leakage of 0.5 gpm, 1.0 gprn and 5.0 gpm, and not 0.2 gpm.

NSPM Response:

The PINGP has sufficiently diverse, sensitive and reliable RCS leakage detection equipment that can detect coolant leakage prior to failure of the RCPB piping described in the LBB LAR (Reference I). The PINGP RCS leakage detection system is "consistent with the guidelines of Regulatory Guide (RG) 1.45 for detecting leakage of 1 gprn in one hour" (Reference 7). The PINGP is not consistent with other requirements of RG 1.45.

The design and licensing of PINGP preceded the publication of the Standard Review Plan (SRP) and RG 1.45, Revision I . Therefore, the leakage detection systems are not required to satisfy the SRP criteria in Section 3.6.3.111.4.

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Enclosure 1 NSPM LBB - Responses to RAls Regarding RCS L~akageDetection Consistent with RG I.45 Res~onseTime In the past, the PlNGP met the 1 gprn in one hour licensing requirement with the containment air particulate radiation monitor (hereafier referred to as R-1I ) , The R-I I monitor is listed in the 1976 report (Reference 4), which is summarized in Table 1-1 of Enclosure 2 to the Reference 1 LBB M R . R-I Iis the only method listed in this table with the capability to detect a Igprn leak in one hour, PlNGP has recently installed new containment particulate monitors, 1R-1I(Unit I ,

installed in July 2010) and 2R-1 I(Unit 2, installed in August 2010), which are beta scintillation detectors. The PlNGP beta detectors meet the 1E-9 pCi/cc sensitivity requirement described in the Bases for PlNGP Technical Specification 3.4.16, RCS Leakage Detection Instrumentation. However, the predicted response times for these detectors has increased in the past 30 years due to reduced RCS circulating activity levels, and differences in the detectors and analysis methodologies. Updated evaluations for the new and old R-I Imonitors indicate that the monitors are not capable of detecting a 1 gprn leak within one hour. The new R-I Imonitors are capable of detecting a 1 gprn leak in less than 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> using current RCS circulating activity, as recommended in RG 1.45, Revision 1 (Reference 15).

Based on the inability to meet the 1 gprn in one hour detection requirement, the RCS leakage detection system has been declared Operable But Nonconforming (OBN).

Resolution of this condition is being performed in accordance with the PlNGP Corrective Action Program (CAP), and compensatory measures include logging Containment Sump Pump "A" run times on an increased frequency. The Containment Sump Pump "A" run times are recorded twice a shift.

In addition, NSPM has re-evaluated the relative humidity monitoring capabilities based on the NRC1squestions. NSPM identified that Table 1-1 and the USAR Section 6.5, Leakage Detection Systems, contain conflicting information. Table 1-1 indicates that the humidity monitor is capable of detecting leakage levels as low as 0.2 gpm, while the USAR indicates that the containment relative humidity monitor is only capable of detecting a 2 to 10 gprn leak. The discrepancy between the two source documents has been entered into the CAP system. The PlNGP USAR identifies that the sensitivity of this method (humidity monitoring) depends on cooling water temperature, containment air temperature variation, and containment air recirculation rate. While the containment relative humidity monitor is not capable of detecting a 1 gprn leak in containment, unexpected changes in humidity levels provide a diverse means of detecting unidentified RCS pressure boundary leakage. Therefore, the containment relative humidity monitor is no longer being described as a stand-alone method of detecting a

<I gprn leak rate. For further details please see Enclosure 2, item 2.

Detection Methods PlNGP meets the intent of SRP 3.6.3, Section 111.4, in that the leakage detection system is "suficiently reliable, redundant, and sensitive so that a margin on the detection of unidentified leakage exists for through-wall flaws to support the deterministic fracture Page 5 of 12

Enclosure 1 LBB - Responses to RAls Regarding RCS Leakage Detadisn mechanics evaluation" (Reference 14). The detection methods listed in the 1976 report (Table 1-1, Enclosure 2) are credited in the plant's USAR as valid leakage detection instrumentation. USAR Section 6.5, Leaaksgrr Detection Systems, states that "the detection of abnormal reactor coolant leakage at the Prairie Islend Nuclear Generating Plant is accomplished by a wide vats"8tyof methods." The leakage detection system is made up of several diverse instruments which are responsive to different categories of unidentified RCPB leakage. The following methods are listed in USAR Section 6.5 and TS Bases 3.4.16 as means for detecting RCS leakage:

Operator inspection RCS inventory balance Volume Control Tank (VCT) level trending Charging rate monitoring Sump pump run time trending (two separate pumps, each with its own run time meter, with different actuation levels)

Containment pressure, temperature, and humidity trending Containment radioactive particulate and radioactive gas monitoring Fan coil unit condensate flow alarms Together these methods serve as diverse means of detecting RCPB leaks. Based on historical experience, the containment particulate radiation monitor and the RCS inventory balance provide the first indication of very small leaks. For somewhat larger leaks, the containment pressure, temperature, and humidity indication trends would be looked at in aggregate. Since several factors influence the humidity, temperature, and pressure levels, a quantitative evaluation of an indicated leakage rate may not be practical. Therefore, the many instruments that comprise the leak detection system each may not have the ability to detect a small leak on a stand-alone basis, but when taken collectively demonstrate sufficient sensitivity.

This has been demonstrated by plant historical operating experience. On January 24, 1998 the PlNGP Unit 1 was taken off-line following the detection of a leak, later found to be through-wall, on the G-9 part-length Control Rod Drive Mechanism (CRDM) housing.

Detection was initially by the R-I Imonitor, and confirmed by visual inspection during a containment entry. The unidentified leakage via inventory balance on the day the leak was detected was 0.19 gpm, and increased to 0.256 gpm the following day prior to the forced shutdown. On August 5, 1994, the PlNGP Unit 2 was taken off-line to repair a CRDM canopy seal weld leak. The leak was identified by the R-I Imonitor. The average unidentified leak rate from inventory balance in the week prior to the forced shutdown was 0.196 gpm. The PlNGP operating experience highlights the effectiveness of its diverse leakage detection system in identifying small RCPB leaks.

Detection Sensitivitv As mentioned above, PlNGP has demonstrated in the past that the RCS leakage detection system is capable of detecting small RCS leaks of 0.2 gpm. The RCS inventory balance and R-I Iparticulate radiation monitor are capable of detecting a 0.2 Page 6 of 12 NSPM LBB - Responses to RAls Regarding RCS Leakage Detection gpm leak in the RCPB. In addition to these methods, PINGP utilizes an RCS Leakage Detection Program to trigger a leakage inspection when leakage exceeds 0 2 gpm. The response time and deteaion capability for each of these methods are described below.

RCS Inventory Balance The RCS inventory balance is conducted onw per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, consistent with the surveillance interval for TS SR 3.4.14. I,RCS Op@rationalLeakage. This surveillance requirement is not required to be performed until 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> after establishment of steady state operation, "Therefore, the response time for a 0.2 gpm leak is nominally 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, assuming steady state operation.

As allowed by procedure, an RCS inventory balance can be performed at any time an operator suspects unidentified leakage. When unusual or unexpected indications occur, operators will check any redundant or backup indications that may be available to validate the instrument response. Operators will respond to instrument readings and indications in a timely, conservative and deliberate manner as required by operating procedures.

Containment Particulate Radioactivity Monitor (R-I I)

As described above, the response times given in the 1976 report are no longer representative of current expected performance for the R-1Imonitors. The response time for these monitors has increased due to reduced RCS circulating activity and differences in the detector and analysis methodologies. The response times to various RCS leakage rates for the new R-11 monitors are as follows:

Table 1 - Response Time (Hours) of R-11 Particulate Monitor RCS Leakage Rate (GPM)

RCS Source Term 1 0.2 1 0.5 1 1.0 1 5.0 1 I 1 1 1 1 I

Recent Unit 1 RCS Activity 53.0 13.5 / 6.3 0.9 I Recent Unit 2 RCS Activity / 280.7 1 25.4 1 6.9 1 0.5 1

• Note: response time is shown in hours The response times are best estimates of current plant conditions, and will vary depending on plant conditions (i.e., RCS activity and baseline readings). These response times were calculated using the standard ISA-67.03-1982, which is referenced in RG 1.45, Revision 1. This standard conservatively assumes a 0.999 plateout factor and results in longer response times than those indicated by PINGP operational experience. Changes in the detector technology have also altered the response time. With current circulating activity levels, R-I 1 will require greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to detect a 0.2 gpm leak, and therefore, this size leak will be detected first by the daily RCS inventory balance assuming steady state operation.

Page 7 of 12

Enclosure 1 NSPM LBB - Responses to RAIs Regarding RCS Leakage Detection RCS Leakage Monitoring Program In addition to the detection methods listed above, Prairie Island has adopted NRC approved WCAP-16465, PWR Owners Gmup RCS Leakage Action Levels and Response Guidelines (Reference 1O), which implements statistical process control methods to detect very small leaks, In accordance with the recommendations of WCAP-I 6645 and WCAP-16423, Stand@&Process and Methods for Calculating RCS leak Rats in PWRs (Reference 12), the PINGP implemented a program designed to supplement existing GDC 30 controls. The PINGP's RCS Leakage Monitoring Program has an administrative limit of 0.2 gpm unidentified leakage for each PINGP unit. By procedure, any leakage value exceeding this limit requires the plant to begin an immediate leakage investigation.

A leakage investigation requires the following actions (among others):

confirmatory checks of the inventory balance inputs, trending of the other diverse leakage detection instrument readings, a review of plant manipulations and recent maintenance activity that may have inadvertently created a leak path or diversion path, system walk downs outside containment, immediate planning for a containment entry and inspection, sump water sampling for radiochemical analysis, and a containment atmosphere grab sample.

Reliability The instruments that comprise the leakage detection system are highly reliable.

Typically each instrument, including Containment Pressure, Temperature, Humidity, VCT Level, and the Sump Run Time Monitor, experiences little to no unavailability each year. Each is subject to periodic calibration checks.

The containment particulate monitors, IR-11 and 2R-11, are new monitor installations.

These new monitors were installed in Unit 1 in July 2010 and in Unit 2 in August 2010.

Although in-plant reliability data for these monitors is not yet available, the new monitors incorporate many features to enhance their reliability, such as an improved paper drive system.

LBB Response Time The piping lines credited in the Reference 1 LBB analysis exhibit slow crack growth and afford sufficient time for a safe and orderly shutdown after detection of a leak. NUREG-1061, Volume 3 indicates that application of the LBB methodology is only applicable when the known fracture mechanics provides a sound basis for predicting the conditions under which cracks in the primary pressure boundary will be stable. In particular, the ACRS noted that this NUREG has provided confidence in predicting the range of crack sizes that will be stable and grow slowly (Reference 13).

RIS 2009-02, Revision I , "Use of Containment Atmosphere Gaseous Radioactivity Monitors as Reactor Coolant System Leakage Detection Equipment at Nuclear Power Page 8 of 12

Enclosure I LBB - Responses to M l s Regarding RCS Leakage Detection Reactors," (Reference 5) states the following concerning the RCS leakage detection response time:

"The NRC considers the longer response times of the containment atmosphere gaseous radioactivity monitors to be of very low safety significance. The monitom would still be able to detect degradation in the RCPB long before components fail in a manner that would aflect plant safety, Additionally, plants also have multipl@

diverse and redundant methods available to detect RCS I~akageand to provide licensees with a means to detect significant RCPB degmdation and to take appropriate action to ensure the continued protection of public health and safety.

Finally, nuclear power plants are designed to provide adequate corn cooling following postulated loss-of-coolant accidents up to and including a break equivalent in size to the double-ended rupture of the largest pipe in the RCS. This design feature, coupled with the extremely low likelihood of unstable crack gmwth msulting in a loss-of-coolant accident, leads the NRC to conclude that the risk significance of this issue is very low."

These statements from the RIS place the importance of detecting a leak on the diversity of monitoring equipment, and detecting RCPB degradation long before it "would affect plant safety" (Reference 5). The PlNGP leak detection methods are able to detect degradation in the piping lines credited in the LBB LAR (Reference 1) long before the components would fail, as described below.

Crack Growth PlNGP is capable of detecting a 0.2 gprn leak from the limiting 8" Residual Heat Removal (RHR) Line in the LBB LAR (Reference 1) long before the pipe would fail.

Structural Integrity Associates (SI) has recently performed an analysis of crack growth rates. Node 246 of Unit 2 Loop B 8-inch Residual Heat Removal (RHR) Line, with a leakage of 2.12 gprn [Table 5-24 of Reference I], was chosen for the analysis due to its limiting leakage. The analysis determined that it would take 95 days for a crack with a 2.0 gprn leak rate (corresponding to the 0.2 gprn detection capability) to grow to a 2.12 gprn leak (the leakage flaw identified in Enclosure 3 to the LBB LAR). Furthermore, the SI analysis determined that it would take another 5 years for the 2.12 gprn leakage flaw to grow to critical size at which point the crack would become unstable. Based on the above, the ability to detect a 0.2 gprn leak within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> ensures that a leak would be detected well before it would grow to the half-critical flaw size determined by the LBB analysis, and long before it could grow to the point of failure.

The detection capabilities for the leakage monitoring system are allowed to deviate from the guidance in RG 1.45, Revision Iin regard to application of the leak-before-break methodology. The RG 1.45, Revision 1 states the following on response times required to support LBB analyses:

"Plants should use multiple, diverse, and redundant detectors at various locations in the containment, as necessary, to ensure that the transport delay time of the Page 9 of 12

Enclosure 1 NSPM LBB - Responses ta RAIs Regarding RCS Leakage Detection leakage from its source to the detector (instrumant location) will yield an acceptabb overall response time. If leak-behm-bmak (LBB) analysis is appmved far the plant, the overall response time of the lsakagta monitor^ingsystem should be sufficient to support the LBB analysis pmcsdures. " (Reference 15)

Assuming steady state operations, a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> response time to a 0.2 gprn leak sufficiently supports the fracture mechanics analysis completed for the LBB M R (Reference I). Therefore, the PINGP meets the intent of RG 1.45, Revision 1 in that the leakage detection system is capable of detecting a 0.2 gpm leakage flaw long before it could propagate to failure.

Conclusion Many diverse leakage detection systems are provided in the PlNGP containment to monitor for RCPB leakage. Past operating experience at the PINGP has also demonstrated that these systems have sufficient reliability and sensitivity to detect small leaks in the RCPB. This satisfies the intent of SRP 3.6.3.111.4 and RG 1.45, Revision 1 for diversity, reliability, and sensitivity. The quickest response time to a 0.2 gprn leak in the piping lines credited in the LBB LAR (Reference 1) is 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> assuming steady state operations. Based on the time calculated for a 2.12 gprn half-critical flaw to propagate to failure, PlNGP will detect and mitigate a crack in the LBB LAR piping long before failure.

In summary, NSPM has established the following for each Subpart of Question E2-2:

Subpart (1) Of the 12 leak detection systems listed in Table 1-1 in Enclosure 2, none of the leakage detection methods are currently capable of detecting 1 gprn in one hour. As a result, the RCS leakage detection system is currently OBN. PlNGP is resolving this OBN condition in accordance with the PlNGP Corrective Action Program.

Subpart (2) The PlNGP has leakage detection systems that meet the intent of RG 1.45, Revision 1 in terms of redundancy, reliability and sensitivity.

Subpart (3) The RCS inventory balance and R-I Iparticulate radiation monitor are capable of detecting a 0.2 gprn leak in the RCPB. The RCS inventory balance will detect a 0.2 gprn leak in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> under steady state operation, which is much less than the 95 days that SI calculated it would take for a 2.0 gprn flaw in the 8" RHR line to grow to a 2.12 gprn half-critical size flaw. Additionally, if the unidentified leakage rate exceeds 0.2 gprn PlNGP initiates a leakage investigation.

Page 10 of 12

= .".

Enclosure 1 NSPM LBB - Responses to Mls Regarding RGS Leekage Detection References 1 Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, '"License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology," L-PI-09-134, dated December 22,2009, ADAMS Accession Number MLI 00200129.

2. Letter from T. Wengert (NRC) to M. Schimmel (NSPM), "Prairie Island Nuclear Generating Plant, Units Iand 2 Request for Additional Information Related to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology (TAC Nos. ME2976 and ME2977)," dated June 10,2010, ADAMS Accession Number ML101550668.

3. Letter from Northern States Power Company, a Minnesota corporation, to the Nuclear Regulatory Commission, "Supplement to License Amendment Request to Exclude the Dynamic Effects Associated with Certain Postulated Pipe Ruptures From the Licensing Basis Based Upon Application of Leak-Before-Break Methodology - Response to Request for Additional lnformation (TAC Nos.

ME2976 and ME2977)," L-PI-10-077, dated July 23, 2010, ADAMS Accession Number MLI 02040612.

4. Report to NRC from Northern States Power (NSP), "Coolant Leakage Detection System Performance at the Prairie Island Nuclear Generating Plant," submitted to the NRC March 31, 1976.

5. Regulatory Issue Summary (RIS) 2009-02, "Use of Containment Atmosphere Gaseous Radioactivity Monitors as Reactor Coolant System Leakage Detection Equipment at Nuclear Power Reactors," Revision 1, NRC, May 8, 2009.

6. Not Used

7. Letter, D M Musolf (NSP) to Director NRR (NRC), "Request for Exemption from the Requirements of 10 CFR Part 50, Appendix A, GDC-4", October 21, 1985.

8. Not Used

9. Not Used 10.WCAP-16465-NP, "Standard RCS Leakage Action Levels and Response Guidelines for Pressurized Water Reactors," Revision 0, September 2006.

11. PINGP Procedure H60, "RCS Leakage Monitoring Program," Revision 0.

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Enclosure 1 NSPM LBB - Responses to Mfs Regarding RCS Leakage Deteclion

12. WCAP-16423-NP, "Standard Process land Methods for Calculating RCS Leak Rate for Pressurized Water Reacton," Revision 0, September 2008.

13. NUREG 1061, Volume 3, "Evaluation of Potential for Pipe BreaksIJ'dated November 1984.

14. Standard Review Procedure 3.8.3, Revision 1, "Leak Before Break Evaluation Procedures," dated March 2007, I 15. Regulatory Guide 1.45, Revision 1, "Guidance on Monitoring and Responding to Reactor Coolant System Leakage," dated May 2008.

16. Letter from Patrick D. Milano (NRC) to Mary G,Korsnick (Ginna),

Subject:

"R.E.

Ginna Nuclear Power Plant - Amendment RE: Application of Leak-Before-Break Methodology for Pressurizer Surge Line And Accumulator Lines (TAC No. MC4929),

dated September 22,2005 (ADAMS Accession No. ML052430343).

17. Letter from John G. Lamb (NRC) to Thomas Coutu (Kewaunee),

Subject:

Kewaunee Nuclear Power Plant - Review of Leak-Before-Break Evaluation for the Residual Heat Removal, Accumulator lnjection Line, And Safety Injection System (TAC No. MB1301), dated September 5,2002 (ADAMS Accession No. ML022400097).

18. R. E. Ginna Nuclear Power Plant. LLC, Docket No. 50-244, Renewed Facility Operating License No. DPR-I8 Technical Specifications (ADAMS Accession No. ML052720231).

19. Dominion Energy Kewaunee. Inc., Docket No. 50-305, Kewaunee Power Station, Facility Operating License As Amended, License No. DPR-43 Technical Specifications (ADAMS Accession No. ML053040352).

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ENCLOSURE 2 The purpose of this Enclosure is to correct and make changes to certain documents contained within the Leak-Before-Break (LBB) License Amendment Request (LAR).

Updates to the LBB LAR The following changes to the documents submitted with the December 22,2009 LBB LAR are being made:

1) Enclosure 1: page 7, Northern States Power Company, a Minnesota corporation (NSPM), states in the Leakage Acceptance Criferia section that "In this analysis NSPM used a criterion of 1 gpm in one hour for an acceptance criterion for RCS leakage as this was compliant with RG 1.45." This statement should be corrected to state that this criterion of 1 gpm in one hour was used for acceptance criterion "as this was consistent with RG 1.45" to match the statements made in previous LBB analyses (References 1 and 2). NSPM did not intend to imply that Prairie Island Nuclear Generating Plant (PINGP) complies with RG 1.45. RG 1.45 has been cited for comparison purposes but PINGP is not committed to RG 1.45, either Revision 0 or Revision I.

2) Enclosure 2 - Structural Integrity Associates (SI) Report, page 1-4, section 1.3 states that Table 1-1 taken from Reference 3 lists all the leak detection methods at the PINGP, the minimum detectable leakage and the estimated response time for various leak rates. Further statements are made in this section utilizing information from Table 1-1. NSPM is hereby withdrawing statements and conclusions made in section I.3 based on the use of Table 1-1, as discussed below.

SI indicated to NSPM that this information was not a significant element of their analyses, and that they did not use the response time as an input. Therefore, references to the response time can be changed without any detrimental impact to their report.

In the Request for Additional Information (RAI) questions in Enclosure I , the NRC questioned the use of the 1976 Report, "Coolant Leakage Detection System Performance at the Prairie Island Nuclear Generating Plant" (Reference 3), and specifically Table 1-1 of that report. Based on this question, NSPM performed a review and determined that this report no longer reflects the rigor and assumptions that are required to support the LBB LAR.

The review of the 1976 Report (Reference 3) identified deficiencies in the following areas:

Page 1 of 2 NSPM Corrections and Changes to taok-Before-Break Analyses o Coolant Activity levels - The coolant activity source term used in the 1976 report are not representative of current coolant activities.

o Sump Pump Response Time - The response time for "Sump Pump Operating Time" instrumentation is calculated based on the volume between the pump start and pump stop limit switches. The actual current limit switch settings have been reviewed and found to be inconsistent with the inputs to the 1976 report.

o Leakage Sensitivity The leakage sensitivity of the Containment Pressure instrumentation, Containment Temperature instrumentation and Containment Relative Humidity instrumentation was calculated in the 1976 report as the leak rate that would result in any finite measurable change in the indication at the limits of the instrument's readability. This does not represent the way in which these containment instruments are used as an element of the overall leakage detection system.

Based on these findings it is concluded that the 1976 report no longer reflects the rigor and assumptions that are required to support the LBB LAR. The findings associated with Reference 3 described above have been entered into the PlNGP Corrective Action Program (CAP).

3) Enclosure 4: page 5-3, Westinghouse states in Section 5.2.3 on Leak Rate Calculations that the "Prairie Island Plants RCS pressure boundary leak detection system has capability of detecting smaller than 0.2 gpm in one hour for the Unit 2 Pressurizer Surge Line." This statement should be corrected to delete the "in one hourJ'to reflect the current leak detection system capabilities. Westinghouse indicated to NSPM that the one hour duration did not factor in to the analysis.

References

1. Letter, D M Musolf (NSP) to Director NRR (NRC), "Request for Exemption from the Requirements of 10 CFR Part 50, Appendix A, GDC-4", October 21, 1985.

2. Letter, T M Parker (NSP) to NRC, "Response to NRC Bulletin No. 88-11 Pressurizer Surge Line Thermal Stratification," June 17, 1991.

3. Report to NRC from Northern States Power (NSP), "Coolant Leakage Detection System Performance at the Prairie Island Nuclear Generating Plant," submitted to the NRC March 31, 1976.

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