ML14071A378

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Requests for Additional Information for the Review of License Renewal Application
ML14071A378
Person / Time
Site: Limerick  Constellation icon.png
Issue date: 03/12/2014
From: Gallagher M
Exelon Generation Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME6555, TAC ME6556
Download: ML14071A378 (17)
v • d • e


Text

March 12,2014 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Units 1 and 2 Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353

Subject:

Requests for Additional Information for the review of the Limerick Generating Station, Units 1 and 2, License Renewal Application (TAC Nos. ME6555 and ME6556)

References:

1. Exelon Generation Company, LLC letter from Michael P. Gallagher to NRC Document Control Desk, "Application for Renewed Operating Licenses", dated June 22, 2011
2. Letter from Leslie Perkins (NRC) to Michael P. Gallagher (Exelon), "Requests for Additional Information for the Review of the Limerick Generating Station License Renewal Application," dated February 12, 2014 In the reference 1 letter, Exelon Generation Company, LLC (Exelon) submitted the License Renewal Application (LRA) for the Limerick Generating Station, Units 1 and 2 (LGS). In the reference 2 letter the NRC requested additional information to support the staff's review of the LRA.

The Enclosure contains the response to this request for additional information.

U.S. Nuclear Regulatory Commission March 12, 2014 Page 2 If you have any questions, please contact Mr. AI Fulvio, Manager, Exelon License Renewal, at 610-765-5936.

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

Executed on 3-12 -laf Respectfully,

Enclosure:

Response to Request for Additional Information cc: Regional Administrator - NRC Region I NRC Project Manager (Environmental Review), NRR-DLR NRC Project Manager (Safety Review), NRR-DLR NRC Project Manager, NRR- DORL Limerick Generating Station NRC Senior Resident Inspector, Limerick Generating Station R. R. Janati, Commonwealth of Pennsylvania

Enclosure Page 1 of 15 Enclosure Response to Request for Additional Information Introduction Presented below are Exelon Generations responses to each of the Requests for Additional Information (RAIs) set forth in a letter from Leslie Perkins (NRC) to Michael P. Gallagher (Exelon), Requests for Additional Information for the Review of the Limerick Generating Station License Renewal Application, dated February 12, 2014. For each RAI, the NRCs question is repeated in its entirety, followed by Exelon Generations response.

RAI #1 The following table provides a list of Potentially Cost Beneficial SAMAs that have been identified at other Mark II boiling water reactors (BWRs) that have completed license renewal. Additional information regarding these Potentially Cost Beneficial SAMAs is provided in the NRCs final supplemental EIS and the applicants environmental reports. See References below.

Enclosure Page 2 of 15 Potential Cost Beneficial SAMAs at other Mark II BWRs Nine Mile Point 2

  • Enhance Station Blackout procedures.
  • Use of a portable charger for the batteries.
  • Reduce unit cooler contribution to EDG unavailability by providing redundant means of cooling.
  • Improve procedure for loss of instrument air.
  • Improve control building flooding scenarios.

Susquehanna

  • SAMA 2a - Install minimal hardware changes and modify procedures to provide cross-tie capability between the 4 kilovolt (kV) alternating current (AC) emergency buses.
  • SAMA 2b - Improve the cross-tie capability between 4 kV AC emergency buses, i.e., between A or D emergency buses and B or C emergency buses (a more flexible cross-tie option than SAMA 2a).
  • SAMA 3 - Modify procedures to stagger RPV depressurization when fire protection system injection is the only available make-up source.
  • SAMA 5 - Modify portable station diesel generator to automatically align to 125 V direct current (DC) battery chargers.
  • SAMA 6 - Procure an additional portable 480 V AC station diesel generator to power battery chargers in scenarios where AC power is unavailable.

Columbia

  • AC/DC Reduce common cause failures (CCFs) between EDG-3 and EDG-1/2.
  • CC-03b - Raise RCIC backpressure trip set points.
  • FR-07a - Improve the fire resistance of critical cables for containment venting.
  • FR-07b - Improve the fire resistance of critical cables for transformer E-TR-S.
  • FR Improve the fire resistance of cables to RHR and standby SW.
  • HV Provide a redundant train or means of ventilation.
  • SR-05R - Improve seismic ruggedness of MCC-7F and MCC-8F.
  • FL-05R - Clamp on flow instruments to certain drain lines in the control building of the radwaste building and alarm in the control room.
  • FL-04R - Add one isolation valve in the SW, turbine SW, and fire protection lines in the control building area of the radwaste building.
  • FL-06R - Additional nondestructive evaluation (NDE) and inspections (in the control building).
  • CC-24R - Backfeed the HPCS system with SM-8 to provide a third power source for HPCS.
  • CC-25R - Enhance alternate injection reliability by including RHR, SW and fire water cross-tie in the maintenance program.
  • OT-07R - Increase operator training on systems and operator actions determined to be

Enclosure Page 3 of 15 Potential Cost Beneficial SAMAs at other Mark II BWRs important from the Probabilistic Safety Assessment.

  • OT-09R - For the non-Loss of Coolant Accident initiating events, credit the Z (power conversion system recovery) function.
  • FR-11R - Install early fire detection in the following analysis units: RC-02, RC-03, RC-04, RC-05, RC-07, RC-08, RC-11, RC-13, RC-14, and RC-1A Exelons ER does not specifically discuss whether these potentially cost beneficial SAMAs constitute new and significant information pertaining to the 1989 SAMDA analysis. Please provide a discussion of how, if at all, Exelon considered whether these potentially cost beneficial SAMAs impact the conclusions in the 1989 SAMDA regarding the risk and environmental impacts of severe accidents at LGS. Please indicate whether these SAMAs were discussed in Table A of Exelons December 14, 2012, Counter Affidavit (ADAMS Accession No. ML12349A328). If so, what is the basis for Exelons conclusions with respect to those SAMAs in Table A? If not, please provide the basis for why these SAMAs are not new and significant information with respect to the 1989 SAMDA.

Exelon Response In the License Renewal Environmental Report for Limerick [7], Exelon used a process for identifying new information that considered information related to plant functions (e.g., plant changes or new severe accident challenges) that contribute to the consequences of a severe accident. Five plant functions were identified and an assessment was performed of new information that has become known concerning these functions. The assessment was focused on Limerick-specific information and general industry experience rather than specific SAMAs from other plants. For completeness, all of the SAMAs from other plants that are listed in RAI #1 are evaluated in this response to determine if they represent new and significant information with respect to the 1989 Limerick SAMDAs.

Since the definition of significant is not well established in the context of SAMA analysis, a review of PRA standards and relevant guidance documents has been performed to develop a basis for what is significant in the SAMA context. For the reasons stated below, Exelon has selected a 50%

reduction in the maximum averted cost-risk (MACR) as the threshold for what may be significant.

There are a few notable documents that provide numerical criteria that may be applied to determine the threshold for significance. The first one is the American Society of Mechanical Engineers (ASME)/American Nuclear Society (ANS) PRA Standard [8] which includes the following definition of a significant basic event.

significant basic event: a basic event that contributes significantly to the computed risks for a specific hazard group. For internal events, this includes any basic event that has an FV [Fussell-Vesely] importance greater than 0.005 or a RAW [Risk Achievement Worth] importance greater than 2.

Enclosure Page 4 of 15 Similar numerical criteria also appear in NUMARC 93-01 [9], which includes the following guidance.

An SSC would probably be considered risk significant if its Risk Reduction Worth exceeds 0.5 percent of the overall Core Damage Frequency (Risk Reduction Worth >1.005).

[]

An SSC [structure, system or component] would probably be considered risk significant if its Risk Achievement Worth shows at least a doubling of the overall Core Damage Frequency and should be provided to the expert panel as an input in risk determination.

Finally, NEI 00-04 [10] provides detailed guidance on categorizing structures, systems and components for licensees that choose to adopt 10 CFR § 50.69, Risk-Informed Categorization and Treatment of Structures, Systems and Components for Nuclear Power Reactors. In the discussion of using risk analyses for SSC categorization, the following guidance is provided.

The risk importance process uses two standard PRA importance measures, risk achievement worth (RAW) and Fussell-Vesely (F-V), as screening tools to identify candidate safety-significant SSCs. The criteria chosen for safety significance using these importance measures are based on previously accepted values for similar applications.

[]

The importance measure criteria used to identify candidate safety significance are:

  • Sum of F-V for all basic events modeling the SSC of interest, including common cause events > 0.005
  • Maximum of component basic event RAW values > 2 In summary, an F-V value > 0.005 and a RAW value > 2 are well established indicators of PRA significance. This can be extended to apply to not just internal events core damage frequency (CDF) and large early release frequency (LERF), but to external events CDF and LERF, and other integrated key output figures of merit. In the context of license renewal, the accepted key output figure of merit for decision making is potential averted cost risk.

Enclosure Page 5 of 15 When averted cost risks are analyzed, the F-V importance measure would be highly dependent on the assumed reliability of the system once it is installed. This is illustrated in Figure 1 which shows an example of how the F-V value changes with assumed failure probability values given a case where a 50% reduction in the measured parameter is estimated assuming perfect reliability. In this example, a 0.005 F-V value would be obtained when the failure probability is ~0.005. This failure probability represents a system or component that is 99.5% reliable, which is fairly representative of many components modeled in typical PRA analyses.

0.10 0.09 0.08 0.07 0.06 FV Value 0.05 0.04 0.03 0.02 Better Reliability 0.01 0.00 1.00E+00 1.00E01 1.00E02 1.00E03 1.00E04 1.00E05 Failure Probability Figure 1 F-V AS A FUNCTION OF FAILURE PROBABILITY

Enclosure Page 6 of 15 On the other hand, as the reliability of the system increases (i.e., as the likelihood of system failure decreases), the RAW importance measure would asymptotically approach a RAW of 2 if 50% of the measured parameter can be averted. This is illustrated in Figure 2, which shows an example of how the RAW changes with assumed failure probability values when a 50% reduction in the measured parameter is estimated assuming perfect reliability. Therefore, a correlation to a RAW >

2 as the acceptance threshold for significance is established and a 50% reduction in the maximum averted cost-risk (MACR) is chosen for the significance threshold.

2.50 2.00 1.50 RAW Value 1.00 0.50 Better Reliability 0.00 1.00E+00 1.00E01 1.00E02 1.00E03 1.00E04 1.00E05 Failure Probability Figure 2 RAW AS A FUNCTION OF FAILURE PROBABILITY In other words, the 50% MACR threshold would be equivalent to a highly reliable system leading to doubling the cost risk when it is taken out of service for maintenance. This correlates to a well-established threshold for determining risk significance in the PRA applications discussed above.

In summary, a RAW value of 2 is selected as the key acceptance criterion for determining the significance of a potential plant enhancement in this context. This is consistent with a well-established threshold for determining risk significance in various PRA applications, and correlates well with a 50% reduction in the MACR for a SAMA that is implemented. Therefore, a 50%

reduction in the MACR is chosen for the significance threshold.

Enclosure Page 7 of 15 Table 1 summarizes Exelons evaluation of each potentially cost beneficial SAMA identified in RAI

  1. 1. The evaluation identifies and eliminates from further consideration SAMAs that have already been implemented at Limerick. Then, the percent change in the MACR from implementing each remaining SAMA at the plant for which it was potentially cost-beneficial is estimated using cost-benefit information from the ER from which the SAMA was taken and/or the GEIS. To determine whether the SAMA should be considered new and significant information with respect to the 1989 Limerick SAMDA analysis, the percent change in the MACR was compared with the definition above of significant. Changes at Limerick that are functionally equivalent but not identical to those named in a SAMA are also identified in Table 1. However, no SAMAs to which this situation applies were determined to be new and significant. Hence, further assessment of such information was not needed.

As can be seen in Table 1, given that all of the items identified in RAI #1 have either already been implemented at Limerick or were not considered to be significant in the plants for which they were determined to be potentially cost-beneficial, there is no evidence to suggest that the SAMAs would be new and significant for Limerick.

TABLE 1 EVALUATION OF POTENTIALLY NEW AND SIGNIFICANT INFORMATION FOR LIMERICK Item # Short Implemented Base Base Percent Evaluation Description at Limerick? Case Case Change MACR Averted Cost Risk Nine Mile Point 2 (NMP2) - Information obtained from References [1] and [4]

23a Provide redundant No $3.79M $210K 5.5% Not a significant SAMA for ventilation for NMP2.

residual heat removal (RHR) pump rooms 23b Provide redundant No $3.79M $264K 7.0% Limerick has HPCI not HPCS.

ventilation for high Not a significant SAMA for pressure core spray NMP2.

(HPCS) pump room 23c Provide redundant No $3.79M $77.5K 2.0% Not a significant SAMA for ventilation for NMP2.

reactor core isolation cooling (RCIC) pump room 213 Enhance loss of No $3.79M $264K 7.0% Station procedure S.10.7A service water (Abnormal Service Water procedure System Operation) directs appropriate actions for Limerick given a total loss of SW event. Not a significant SAMA for NMP2.

Enclosure Page 8 of 15 TABLE 1 EVALUATION OF POTENTIALLY NEW AND SIGNIFICANT INFORMATION FOR LIMERICK Item # Short Implemented Base Base Percent Evaluation Description at Limerick? Case Case Change MACR Averted Cost Risk 214 Enhance Station No $3.79M >$100K >2.6% Station procedure E1 (Loss of Blackout procedures all AC power (Station Blackout)) directs appropriate actions for Limerick given an SBO event.

Note that this SAMA was qualitatively assessed in NMP2 ER as providing greater than $100K of benefit.

However, a best estimate or upper bound estimate was not provided. The actual benefit should be no more than that provided by SAMA 215 below, which is also applicable to SBO scenarios. Therefore, this is not a significant SAMA for NMP2.

215 Use of a portable No $3.79M $507K 13.4% Not a significant SAMA for charger for the NMP2.

batteries 216 Hard pipe diesel fire No $3.79M $800K 21.1% Not a significant SAMA for pump to the reactor NMP2.

pressure vessel 221a Reduce unit cooler No $3.79M $342K 9.0% Not a significant SAMA for contribution to NMP2.

emergency diesel generator (EDG) unavailability by increasing the testing frequency 221b Reduce unit cooler No $3.79M $872K 23.0% Not a significant SAMA for contribution to EDG NMP2.

unavailability by providing redundant means of cooling (via procedure guidance to open EDG control panel room doors) 222 Improve procedure No $3.79M $273K 7.2% Station Procedure ON-119 for loss of (Loss of Instrument Air) directs instrument air appropriate actions for Limerick given an LOIA event.

Not a significant SAMA for NMP2.

Enclosure Page 9 of 15 TABLE 1 EVALUATION OF POTENTIALLY NEW AND SIGNIFICANT INFORMATION FOR LIMERICK Item # Short Implemented Base Base Percent Evaluation Description at Limerick? Case Case Change MACR Averted Cost Risk 223 Improve control No $3.79M $86.7K 2.3% Limerick has implemented a building flooding change to permanently throttle scenarios a valve supplying the fire header in the 4 kV corridor area to substantially reduce flooding risk in the control enclosure. Not a significant SAMA for NMP2.

Susquehanna (SSES) - Information obtained from References [2] and [5]

2a Install minimal Yes N/A N/A N/A Limerick already has full 4 kV hardware changes emergency bus cross-tie and modify capabilities from the main procedures to control room.

provide cross-tie capability between the 4 kilovolt (kV) alternating current (AC) emergency buses 2b Improve cross-tie Yes N/A N/A N/A Limerick already has full 4 kV capability between 4 emergency bus cross-tie kV AC emergency capabilities from the main buses, i.e. between control room.

A or D emergency buses and B or C emergency buses (a more flexible cross-tie option than SAMA 2a) 3 Modify procedures No $1.09M $138K 12.7% Not a significant SAMA for to stagger RPV SSES.

depressurization when fire protection system injection is the only available make-up source 5 Modify portable No $1.09M $368K 33.9% Not a significant SAMA for station diesel SSES.

generator to automatically align to 125 V direct current (DC) battery chargers 6 Procure an No $1.09M $267K 24.5% Not a significant SAMA for additional portable SSES.

480 V AC station diesel generator to power battery chargers in scenarios where AC power is unavailable

Enclosure Page 10 of 15 TABLE 1 EVALUATION OF POTENTIALLY NEW AND SIGNIFICANT INFORMATION FOR LIMERICK Item # Short Implemented Base Base Percent Evaluation Description at Limerick? Case Case Change MACR Averted Cost Risk Columbia (CGS) - Information obtained from References [3] and [6] (1)

AC/DC- Reduce common No $1.89M $73K 3.9% Not a significant SAMA for 28 cause failures CGS.

(CCFs) between EDG-3 and EDG-1/2 CC-03b Raise RCIC No $1.89M $54K 2.9% Not a significant SAMA for backpressure trip CGS.

set points FR-07a Improve the fire No $1.89M $330K 17.5% Not a significant SAMA for resistance of critical CGS.

cables for containment venting FR-07b Improve the fire No $1.89M $75K 4.0% Not a significant SAMA for resistance of critical CGS.

cables for transformer E-TR-S FR-08 Improve the fire No $1.89M $520K 27.6% Not a significant SAMA for resistance of cables CGS.

to RHR and standby SW HV-02 Provide redundant No $1.89M $210K 11.1% Not a significant SAMA for train or means of CGS.

ventilation SR-05R Improve seismic No $1.89M $57K 3.0% Not a significant SAMA for ruggedness of MCC- CGS.

7F and MCC-8F FL-05R Clamp on flow No $1.89M $250K 13.3% Not a significant SAMA for instruments to CGS.

certain drain lines in the control building of the radwaste building and alarm in the control room FL-04R Add one isolation No $1.89M $260K 13.8% Not a significant SAMA for valve in the SW, CGS.

turbine SW, and fire protection lines in the control building area of the radwaste building FL-06R Additional No $1.89M $130K 6.9% Not a significant SAMA for nondestructive CGS.

evaluation (NDE) and inspections (in the control building)

Enclosure Page 11 of 15 TABLE 1 EVALUATION OF POTENTIALLY NEW AND SIGNIFICANT INFORMATION FOR LIMERICK Item # Short Implemented Base Base Percent Evaluation Description at Limerick? Case Case Change MACR Averted Cost Risk CC-24R Backfeed the HPCS No $1.89M $170K 9.0% Limerick has HPCI, not HPCS.

system with SM-8 to Not a significant SAMA for provide a third CGS.

power source for HPCS CC-25R Enhance alternate No $1.89M $12K 0.6% Not a significant SAMA for injection reliability by CGS.

including RHR, SW and fire water cross-tie in the maintenance program OT-07R Increase operator No $1.89M $200K 10.6% Not a significant SAMA for training on systems CGS.

and operator actions determined to be important from the Probabilistic Safety Assessment FW-05R Examine the No $1.89M $72K 3.8% Not a significant SAMA for potential for CGS.

operators to control reactor feedwater (RFW) and avoid a reactor Trip OT-09R For the non-Loss of No $1.89M $130K 6.9% Not a significant SAMA for Coolant Accident CGS.

initiating events, credit the Z (power This SAMA appears to conversion system represent a PRA modeling recovery) function change rather than a plant enhancement that would reduce plant risk.

FR-11R lnstall early fire No $1.89M $510K 27.0% Not a significant SAMA for detection in the CGS.

following analysis units: RC-02, RC-03, RC-04, RC-05, RC-07, RC-08, RC-11, RC-13, RC-14, and RC-1A (1)

The information from the Columbia ER [3] was superseded in the GEIS [6]. The GEIS shows two sets of PRA results for the first six SAMAs. In those cases, the higher averted cost risk is shown in this table. In all cases for Columbia, the lower base case MACR value is shown in this table. These two choices ensure that the maximum percent change is conservatively reported for this assessment.

Enclosure Page 12 of 15 RAI #2 On page 5-6 of the ER, Exelon provides a history of the reductions in core damage frequency (CDF). Exelon further states that the reduction in CDF reflects improvements in reliability data, improvements in procedural guidance and plant capabilities, and a reduction in the number of reactor trips. Furthermore Exelon states, Reductions in CDF reflect implementation of the IPE, IPEEE, and CPI program.

What is the status of these improvements and mitigation measures? Please indicate which have been implemented and when. Describe other mitigation activities that have been implemented at LGS to substantially reduce the CDF or Large Early Release Frequency since the 1989 SAMDA.

Exelon Response Table 6.2-2 of the Limerick IPE [11] listed four improvement items that were planned as part of the IPE and which were implemented prior to or shortly after the 1992 IPE submittal. These are listed below along with their current status.

  • Relax restrictions in Drywell Spray Initiation Curve (Capability maintained in the drywell spray initiation limit curve in the site emergency operating procedures.)
  • Create procedure to crosstie 4 kV electrical buses (Capability maintained in current site response procedures which allow for alignment of alternate power supply for any 4kV Safeguard Bus using any diesel generator.)
  • Create procedure to power C & D ESW Pumps from Unit 1, Division 3 & 4 respectively.

(Capability maintained in a current station procedure.)

  • Create cross connection between diesel driven Fire Pump and Fire Water System and RHR.

(Capability maintained in a current station procedure.)

Section 7 of the Limerick IPEEE [12] listed the following plant improvement items. All of the items were addressed shortly after the 1995 IPEEE submittal.

  • Address housekeeping concerns identified from the seismic walkdowns. This included items such as unrestrained lifting devices, open S-hooks, and free standing equipment and maintenance concerns such as rusting support bolts and loose battery rack spacer pads. (A maintenance housekeeping procedure and a guidance procedure for storage and housekeeping are both active to ensure good housekeeping practices at the site.)
  • Designate fire compartments 1, 7, 22, and 23 as transient combustible free zones.

(Transient combustible free zones are currently controlled via an operations procedure.)

  • Replace all wood scaffolding with metal scaffolding and revise procedures to prevent further use of wood scaffolding. (Scaffolding installation, inspection, and removal is controlled via a maintenance procedure. The original commitment was subsequently slightly altered to minimize use of wood scaffolding in the RCA. This change was reported to the NRC.)
  • Revise the combustible control procedure to provide more conservative combustible control guidelines in safety related areas within the reactor enclosures. (Combustible controls are currently maintained via an operations procedure.)

Enclosure Page 13 of 15

  • Administratively control additional doors as fire doors to limit the amount of air available for combustion. The existing doors are fire rated. (Fire barriers are currently controlled via a station procedure.)
  • Increase the fire brigade drill activities and awareness of fixed combustible risk in fire compartments 2, 20, and 26. (Fire brigade activities are currently controlled via an operations procedure. The original commitment was subsequently slightly altered to indicate that fire drill scenarios should focus on realistic fire situations based on plant operating experience and that challenge plant operations in risk significant areas.)

As noted in NEI 91-04 [13], the CPI program issues applicable to Limerick were effectively subsumed into the IPE process in Supplement 1 and 3 to Generic Letter 88-20. Additionally the Emergency Procedure Guidelines (EPG) and Severe Accident Guidelines (SAG) developed by the BWROG and implemented at Limerick incorporate the accident management strategies identified in the CPI program and elsewhere [14]. Therefore, other than EPG/SAG implementation, there are no additional specific items to list related to the CPI program.

Note that in addition to the items noted above, other plant enhancements have been made over the years at Limerick since the 1989 SAMDA. Examples of changes that have been implemented at the site to substantially reduce CDF and LERF since the 1989 SAMDA include the following items.

  • Isolation valves were installed in the ESW loop piping to limit the affected portions of ESW during maintenance to one unit at a time.
  • Technical Support Guidelines were developed to refill the CST from the existing fire system.

Enclosure Page 14 of 15 References

[1] U.S. Nuclear Regulatory Commission (NRC). May 2006. Generic Environmental Impact Statement for License Renewal of Nuclear Plants: Regarding Nine Mile Point Nuclear Station, Units 1 and 2 - Final Report (NUREG-1437, Supplement 24), Washington, D.C.

(ADAMS Accession No. ML061290310).

[2] U.S. Nuclear Regulatory Commission (NRC). March 2009. Generic Environmental Impact Statement for License Renewal of Nuclear Plants: Regarding Susquehanna Steam Electric Station, Units 1 and 2 (NUREG-1437, Supplement 35), Washington, D.C. (ADAMS Accession No. ML090700454).

[3] U.S. Nuclear Regulatory Commission (NRC). 2012. Generic Environmental Impact Statement for License Renewal of Nuclear Plants: Regarding Columbia Generating Station Final Report, Main Report, Volume 1 and Appendices, Volume 2 (NUREG-1437, Supplement 47, Vol. 1), Washington, D.C. (ADAMS Accession Nos. ML12096A334 and ML12097A271).

[4] Constellation Energy. May 2004. Nine Mile Point Nuclear Station. License Renewal Application, Environmental Information, Appendix F. Severe Accident Mitigation Alternatives (SAMAs) (ADAMS Accession No. ML041490222).

[5] PPL Susquehanna, LLC (PPL). September 2006. Susquehanna Steam Electric Station Units 1 and 2 Application for License Renewal, Appendix E: Applicants Environmental Report - Operating License Renewal Stage. Allentown, Pennsylvania. (ADAMS Accession No. ML062630235).

[6] Energy Northwest. January 2010. Appendix E, Applicants Environmental Report, Operating License Renewal Stage, Columbia Generating Station, Docket No. 50-397 License No.

NPF-21. (ADAMS Accession No. ML100250666).

[7] Exelon Generation Company, LLC. June 2011. Applicants Environmental Report -

Operating License Renewal Stage, Limerick Generating Station, Units 1 and 2. (ADAMS Accession No. ML11179A104).

[8] ASME/ANS RA-Sa-2009, February 2009. Addenda to RA-S-2008, Standard for Level 1/Large Early Release Frequency Probabilistic Risk Assessment for Nuclear Power Plant Applications.

[9] NUMARC 93-01. April 1996. Industry Guideline for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants, Revision 2.

[10] NEI 00-04. July 2005. 10 CFR 50.69 SSC Categorization Guideline.

[11] Philadelphia Electric Company. July 1992. Individual Plant Examination Limerick Generating Station Units 1 & 2.

[12] PECO Energy. June 1995. Limerick Generating Station Units 1 & 2 Individual Plant Examination for External Events (IPEEE).

Enclosure Page 15 of 15

[13] NEI 91-04 (Formerly NUMARC 91-04). December 1994. Severe Accident Issue Closure Guidelines, Revision 1.

[14] BWR Owners Group. March 2001. Emergency Procedure and Severe Accident Guidelines, Revision 2.

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