Text

Supplement 2 to Severe Accident Mitigation Alternatives Analysis, License Renewal Application
	ML12080A137
Person / Time
Site:	Seabrook
Issue date:	03/19/2012
From:	Freeman P; NextEra Energy Seabrook
To:	; Document Control Desk, Office of Nuclear Reactor Regulation
References
	SBK-L-12053
	Download: ML12080A137 (99)
	v • d • e

NEXTera March 19, 2012 SBK-L-12053 Docket No. 50-443 U.S. Nuclear Regulatory Commission Attention: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852 Seabrook Station Supplement 2 to Severe Accident Mitigation Alternatives Analysis NextEra Energy Seabrook License Renewal Application

References:

1. NextEra Energy Seabrook, LLC letter SBK-L-10077, "Seabrook Station Application for Renewed Operating License," May 25, 2010. (Accession Number ML101590099)

2. NextEra Energy Seabrook, LLC letter SBK-L-11001, "Seabrook Station Response to Request for Additional Information, NextEra Energy Seabrook License Renewal Application," January 13, 2011. (Accession Number ML110140810)

3. NextEra Energy Seabrook, LLC letter SBK-L-1 1067, "Seabrook Station Response to Request for Additional Information, NextEra Energy Seabrook License Renewal Application," April 18, 2011. (Accession Number ML1 122A075)

4. NextEra Energy Seabrook, LLC letter SBK-L- 11125, "Supplement to Response to Request for Additional Information - April 18, 2011, " June 10, 2011. (Accession Number MLI 1166A255)

In Reference 1, NextEra Energy Seabrook, LLC (NextEra) submitted an application for a renewed facility operating license for Seabrook Station Unit 1 in accordance with the Code of Federal Regulations, Title 10, Parts 50, 51, and 54. In Reference 2, 3 and 4, NextEra submitted responses to the NRC staffs RAIs.

NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874

United States Nuclear Regulatory Commission SBK-L-12053/ Page 2 The original SAMA was submitted in May 2010 (Reference 1) and was based on Seabrook's base case PRA model of record SSPSS-2006 (model SB2006). In NextEra Letter SBK-L-11001 (Reference 2), the next periodic update to the PRA model was discussed. NextEra has completed the PRA update (SSPSS-201 1) and is providing, in this letter, a supplemental SAMA analysis based on this PRA update.

The License Renewal Application, Appendix E, page F-6 contains a list of acronyms used in this supplement. If there are any questions or additional information is needed, please contact Mr.

Richard R. Cliche, License Renewal Project Manager, at (603) 773-7003.

If you have any questions regarding this correspondence, please contact Mr. Michael O'Keefe, Licensing Manager, at (603) 773-7745.

Sincerely Next ergy Seabrook, LLC.

Paul (YTFreeman Site Vice President Enclosure cc:

W.M. Dean, NRC Region I Administrator J. G. Lamb, NRC Project Manager, Project Directorate 1-2 W. J. Raymond, NRC Resident Inspector A.D. Cunanan, NRC Project Manager, License Renewal M. Wentzel, NRC Project Manager, License Renewal Mr. Christopher M. Pope Director Homeland. Security and Emergency Management New Hampshire Department of Safety Division of Homeland Security and Emergency Management Bureau of Emergency Management 33 Hazen Drive Concord, NH 03305 John Giarrusso, Jr., Nuclear Preparedness Manager The Commonwealth of Massachusetts Emergency Management Agency 400 Worcester Road Framingham, MA 01702-539

United States Nuclear Regulatory Commission SBK-L-12053/ Page 3 NEXTera ENERGY,.A SEABROK I, Thomas A. Vehec , Plant General Manager of NextEra Energy Seabrook, LLC hereby affirm that the information and statements contained within are based on facts and circumstances which are true and accurate to the best of my knowledge and belief.

Sworn and Subscribed Before me this Jq day of March, 2012 Thomas A. Vehec Plant General Manager Notary Pu ic

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Enclosure to SBK-L-12053 NextEra Energy Seabrook, LLC Supplement 2 to Severe Accident Mitigation Alternatives Analysis

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis

1.0 INTRODUCTION

This report provides an update to the original SAMA analysis for Seabrook Station. The original SAMA was submitted in December 2009 and was based on Seabrook's base case PRA model of record SSPSS-2006 (model SB2006). In NextEra Energy Seabrook Letter SBK-L-1 1001 (Reference 2), the next periodic update to the PRA model was discussed. NextEra Energy Seabrook has completed the PRA update (SSPSS-201 1) and is providing, in this letter, a supplemental SAMA analysis based on this PRA update.

Section 2.0 summarizes the method used to develop and evaluate SAMA candidate changes. Section 3.0 describes changes in the current PRA (SSPSS-201 1) from the PRA update used for the original SAMA submittal (SSPSS-2006). Section 4.0 provides the results of the supplemental SAMA and identifies several additional SAMA candidates as being potentially cost beneficial.

2.0 METHOD The SAMA supplement builds upon the original assessment provided in NextEra Energy Seabrook Letter SBK-L- 10077 (Reference 1) and subsequent RAI responses in NextEra Energy letters SBK-L-11001 (Reference 2), SBK-L- 11067 (Reference 3) and SBK-L- 11125 (Reference 4). The SAMA supplement follows the same industry guidance outlined in NEI 05-01, and uses the same technical process as the original SAMA. The general approach to the reassessment is summarized here:

a) Latest PRA models are used to determine the nominal and uncertainty public risk/consequences and associated maximum averted benefit (MAB).

b) The previous Phase 1 SAMA candidates, which were qualitatively screened from further detailed assessment based on the SAMA not being applicable to the plant design or the SAMA intent being met by the plant design, are not reviewed further in this supplement.

c) Previously-identified Phase II SAMA candidates are re-evaluated for possible changes to their cost-benefit worth. Phase II SAMA candidates identified as intent-met in RAI responses are not reviewed further in this supplement.

d) In addition to the previously-identified Phase II SAMA candidates, new potential SAMA candidates are identified based on a review of the latest PRA model results and risk ranking of the top-ranked initiating events and basic events that contribute to CDF and LERF. In addition, the top-ranked basic events associated with release categories that contribute to the top 90% of public risk are assessed. These top initiating events and basic events are evaluated by linking to an existing candidate Phase II SAMA evaluation or are specifically evaluated in Phase II as a possible new SAMA candidate.

e) The SAMA cost-benefit assessment is based on development of new PRA cases to conservatively (and in some cases, more realistically) estimate the potential cost-benefit worth based on the updated model. All SAMA cost-benefits are assessed for nominal (best estimate) and uncertainty (upper bound) with and without the seismic multiplier to account for the potential increase in seismic risk per GSI-199 information.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis f) The implementation cost of each SAMA is reassessed as necessary to ensure that the costs continue to be representative of the SAMA scope based on recent experience.

3.0 PRA MODEL The NextEra Energy Seabrook PRA model has been updated and is identified as SSPSS-201 1, Model SB201 1. The updated features of the SB2011 PRA model incorporated the following:

The Level I PRA model update includes a detailed assessment of internal flood initiating events, an update to latent human actions assessment, plant hardware changes and miscellaneous modeling changes.

" The Level 2 PRA model update includes a detailed assessment of release category source terms.

The Level 3 PRA model update includes the revised release category source terms and associated frequencies from the Level 2 PRA model.

The original Seabrook SAMA was based on PRA model SB2006, the model of record and in use at the time the Seabrook SAMA was performed in support of the License Renewal Application submitted on 05/27/2010, Letter SBK-L- 10077 (Reference 1). Subsequent to the SAMA submittal, the Seabrook PRA was updated in 2009 (Model SB2009) and most recently in 2011 (Model SB201 1).

The PRA model changes made in SB2009 were summarized in NextEra Energy's response to RAI 1a (Letter SBK-L- 11001, Reference 2). As stated in the RAI response, the updated SB2009 PRA model baseline core damage frequency decreased compared to the SB2006 PRA model by -19 percent, from 1.44E-05/yr (SB2006) to 1.17E-05/yr (SB2009). The LERF also decreased by -30 percent, from 1.1 5E-07/yr (SB2006) to 8.1 E-08/yr (SB2009). In addition, there was no significant shift in the relative importance of initiating events or components. Thus, as stated in the RAI 1a response (Reference 2), the plant changes incorporated into the SB2009 PRA model did not have a significant impact on the overall SAMA results.

Based on the PRA model changes made in SB201 1, as described below, the updated SB201I1 PRA model baseline core damage frequency increased compared to the SB2009 PRA model by -5 percent, from 1.17E-05/yr (SB2009) to 1.23E-05/yr (SB201 1). The LERF also increased by -14 percent, from 8.1E-08/yr (SB2009) to 9.2E-08/yr (SB201 1). In addition, there was no significant shift in the relative importance of initiating events or components except for the addition of new internal flood initiators.

3.1 LEVEL 1, LEVEL 2 and LEVEL 3 PRA CHANGES The specific plant changes and model changes made to the most recent PRA model SB2011 are summarized below.

PlantChanges Two significant plant changes were incorporated into the updated PRA model. These include the switchyard upgrade and PRA modeling of the fire protection system flow orifice.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Plant Change - Switchyard Upgrade - Breakers and Interconnections Switchyard breakers and interconnections were revised to reflect the Switchyard Project upgrade. The switchyard project improved the reliability and availability of the ring bus and enclosed a major portion of the switchyard/components for improved protection from weather and salt spray hazards. The PRA update included incorporation of new breakers and buses to reflect the completed, as-built configuration. The switchyard upgrade modification will have a positive influence on the reliability of offsite power. The loss-of-offsite-power (LOOP) initiator model is quantified based on overall generic and plant specific LOOP data, not the specific configuration of the switchyard. However, over the longer term, the switchyard improvements should result in a reduction to the frequency of the plant-specific plant-centered loss of offsite power events.

Plant Change - Flow Orifice in Fire ProtectionPiping in the Control Building Insights from the updated internal flood risk assessment identified that Control Building flood scenarios from postulated pipe breaks in the fire protection 6" and 4" diameter standpipe, while representing a low risk in an absolute sense, dominated the risk of internal flood. A modification was proposed to reduce the risk of Control Building flood by installing a flow limiting orifice upstream in the fire protection system. This orifice would effectively limit the maximum postulated break flow, yet not impact the design function of downstream hose stations during normal fire fighting activities. This flow limiting orifice modification was identified as SAMA #192 in NextEraEnergy's response to RAI la (Reference 2). This design change was recently installed and is undergoing final acceptance testing. It is included in the SB20 11 model update because of progress of the final design work and expected near-term acceptance. The reduction in CDF as a result of the flow orifice installation is approximately 4E-06/yr (-24 percent reduction in overall risk).

Model Changes A number of modeling and documentation changes were made to improve the PRA quality and completeness, The most significant model changes include upgrade to the internal flood risk assessment and revision to the Level 2 release category source terms. Incorporation of the revised latent human action assessment and other minor modeling changes did not have a significant impact to the modeling/results and are not discussed further. The significant modeling changes are summarized below.

Level I Model Change - Upgrade to the Internal Flood(IF) Risk Assessment The current SB2011 PRA model is based on a complete re-analysis of internal flood hazard.

The re-analysis was performed to: (1) incorporate plant design and operational changes since the previous studies, (2) include available EPRI data and guidance for performing internal flood probabilistic risk assessments, and (3) meet the requirements of the current PRA Standard. The updated internal flood model meets the requirements of Part 3 to ASME/ANS RA-Sa-2009, Standard for Level 1/Large Early Release Frequency ProbabilisticRisk Assessment for Nuclear Power PlantApplications, and Regulatory Guide 1.200 Rev 2, An Approachfor Determiningthe TechnicalAdequacy ofProbabilisticRisk Assessment Results 4 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis for Risk hiformed Activities. The internal flood analysis upgrade includes credit for the future plant modification (flow restricting orifice) as described above in plant changes. With this one exception, the internal flood analysis is based on the as-built and as-operated plant as of 2011.

The assessment of internal flood events produced 27 new flood initiating events for quantitative evaluation. This is compared to 3 internal flood events that were evaluated in the original study. The total core damage frequency from the 27 internal flood initiating events is approximately 2.6E-06/yr, compared to 5.4E-07/yr for the original 3 initiators.

There were no Level 2 containment isolation vulnerabilities identified in the internal flood study.

Level 2 and Level 3 Model Chan.ge - Revised Release Category and Source Terms Radiological source terms represent the fission product fractions and timings of releases to the environment, given a core damage accident with containment functional failure. The source terms are the input to the Level 3 analysis (Refer to Section 3.2) to allow calculation of offsite public impacts. The radiological source terms were significantly revised during the 2005 PRA model update based on the updated Level 2 analysis performed by Westinghouse Electric Company, LLC. The source terms were further revised during the SB201 1 PRA model update based on more detailed modeling using the Modular Accident Analysis Program (MAAP), Version 4.0.7. The revised Level 2 analysis includes modeling of the following 13 source term groups, with the related release categories.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Seabrook Source Term Release Categories Source Source Term Title : R

~Related Release.

Term Categories

Group .

LEI Large/Early Containment Bypass - SG Tube Rupture LEI la, LE12a, LE13a LE2 Large/Early Containment Bypass - ISLOCA LE21 a, LE2 I b, LE22a LE3 Large/Early Containment Penetration Failure to Isolate LE3aLE3b (Containment Online Purge valve failure)

LE4 Large Containment Basemat Failure with Delayed LE4a Evacuation SE1 Small/Early Containment Bypass - SG Tube Rupture SEllb,SE12b with Scrubbed Release SE2 Small/Early Containment Bypass - ISLOCA with SE2b Scrubbed Release SE3 Small/Early Containment Penetration Failure to Isolate SE3b LL3 Large/Late Containment Venting LL3b LL4 Large/Late Containment Overpressure Failure LL4b LL5 Large/Late Containment Basemat Failure LL5a SELL Small/Early Containment Penetration Failure to Isolate SELL3b, SELL4b, and Large/Late Containment Basemat Failure SELL5a INTACT1 Nominal Containment Leakage INTACT1 INTACT2 Excessive Containment Leakage INTACT2

(*) Release category IDs ending in "a" are "dry" scenarios while "b" release categories are "wet" scenarios.

As shown in the table, in some cases, there is a one to one relationship between source terms and release category. In other cases, a representative source term was selected to cover several release categories. The basis for this grouping is discussed below in the description of each source term. The source terms were evaluated using MAAP code Version 4.0.7 for a large set of accident sequences within each release category. The MAAP code accounts explicitly for source term release and depletion methods based on the current best estimate understanding of severe accident phenomenon. The MAAP code was used to generate source terms by running Seabrook-specific models.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis The release category source term definitions, based on specific representative MAAP cases, are summarized below and in the table of Seabrook Release Category Source Term Definitions. The information in the Release Category Source Term Definitions table is intended to provide a summary representation of the scenario/releases from associated MAAP cases.

Source Term LE1, Large/Early Containment Bypass - SGTR: Source term LEI is used for containment bypass releases through a ruptured steam generator tube, with no feedwater to the faulted steam generator so that the release is unscrubbed. This source term represents three sets of Level 2 release categories: LEI la, LE12a, and LEI3a.

One set (LE 11 a) includes core damage sequences where the steam generator tube rupture (SGTR) occurs as the accident sequence initiator. The second set (LE12a) includes core damage sequences where the SG tube rupture is pressure-induced as a result of anticipated transient without scram (ATWS) and steam line break (SLB) initiators. The third set (LEI 3a) includes Level 2 sequences with thermally-induced tube rupture resulting from the high pressure, high temperature conditions during the core melt progression.

The vast majority of LEl sequences are from release category LEl la, SGTR-initiated with failure of steam generator cooling or failure of operator to restore feed flow to the faulted steam generator before significant release.

The frequency of release category LEI2a is about a factor of 10 less than LEI la due to the low probability of these core melt sequences along with the conditional probability of a tube rupture.

The frequency for release category LE 13a is negligible (-I e-1 1/yr) based to the best-estimate severe accident phenomena in MAAP, specifically that the hot leg creep rupture (HLCR) is much more likely to occur than rupture of the steam generator tubes for the high pressure core melt sequences. In fact, MAAP sequences thermally induce steam generator tube rupture only when HLCR is turned off. This set of sequences could be screened out due to low frequency.

However, the frequency is preserved in LEI.

The release category LE Ila, LE12a, and LE13a sequences are similar with regard to the containment failure mode, through a ruptured steam generator direct to the environment with little opportunity for retention. As a result, they are subsumed into a single source term, LEI.

Because the LEI Ia sequences make up about 90% of the LEI frequency, the LE1Ia sequences are used to define the release category source term. MAAP code Case 103m is used as the representative scenario for LEI. For the 2011 update, a series of existing and new SGTR sequences were run in MAAP407.

Case 103m represents the situation where containment is bypassed via a failed steam generator tube, there is no feed to the steam generators, no emergency core cooling system injection, and the reactor coolant system remains at full pressure (i.e., not depressurized to containment). This results in an early core melt (-3 hrs), early reactor pressure vessel failure

(-7 hrs), and an initial fission product release (puff #1) based on CsI fraction released of 7 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis 1.4%. This is somewhat below the LERF threshold of 3%. In the long term, the containment fails due to over-pressure which is responsible for the puff #2 with significant particulate release. This is conservatively categorized as a LERF.

Source Term LE2, Large/Early Containment Bypass - ISLOCA: Source Term LE2 is used for release categories to represent Level 2 sequences involving an intersystem LOCA through the Residual Heat Removal (RHR) system, with large containment bypass from the reactor coolant system direct to the environment. The sequence is identified as the "V-sequence" based on WASH- 1400 terminology. This source term represents three sets of Level 2 release categories: LE21a, LE21b,and LE22a. The release path for LE2la and LE21b is a RHR pipe break in the RHR vaults as a result of failure of the RHR motor-operated isolation valves which pressurizes the low pressure RHR system to the reactor coolant system pressure.

The break elevation is assumed to be high in the RHR vaults, above the water level accumulated from discharge of the reactor coolant system and Reactor Water Storage Tank (RWST) inventories into the vault. The release will not be scrubbed by the accumulated water level in the RHR vault for this case; however, some retention does occur as a result of pathways and building surfaces. Release category LE21a includes the RHR pipe break scenario with no emergency core cooling system flow; LE2 1 b includes the RHR pipe break scenario with Charging pump flow. In addition, release category LE22a is similar to LE2 I a, with no emergency core cooling system flow, except the loss of coolant inventory is through the RHR pump seal - a smaller loss of coolant accident (LOCA) with release at the bottom of the RHR vault. Since LE22a has no emergency core cooling system flow, the release is unscrubbed (except for building pathways as mentioned earlier) and is subsumed into LE2. A similar sequence with RHR pump seal failure but with emergency core cooling system flow is modeled in SE2.

The frequency contribution to LE2 is dominated by release category LE2 lb (RHR pipe break with Charging pump flow). MAAP case # 104j is used as the representative scenario for LE2.

This case is a large LOCA (8" diameter) with release to the RHR vault and Charging pump flow until the RWST is emptied at about 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months .

Source Term LE3, Large/Early Containment Penetration Failure to Isolate: Source term LE3 is used for release categories containing core damage sequences with a large containment isolation failure. The result of the 8-inch diameter containment on-line purge valves (COP) failing to close is a direct release from the containment to the environment.

This source term represents two sets of Level 2 release categories: LE3a and LE3b. Release category LE3a includes "dry" containment sequences, i.e., with no RWST injection via Emergency Core Cooling (ECCS) or Containment Building Spray (CBS). Release category LE3b includes "wet" containment sequences, i.e., with RWST injection via ECCS or CBS.

The total frequency of LE3 sequences is very low (-1 e-9), with the dominant contribution from LE3b. Thus, the representative scenario is the "wet" containment case: MAAP Case

104k, medium LOCA with no ECCS injection, successful CBS injection, and failure of the COP valves.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Source Term LE4, Large Containment Basemat Failure with Delayed Evacuation: This is a new release category introduced as part of the source term revision. Source term LE4 is used for release categories which contain core damage sequences with a large containment structural failure due to basemat melt-through. This is a long term scenario, with the release beginning more than 20 hours2.314815e-4 days 0.00556 hours 3.306878e-5 weeks 7.61e-6 months after the sequence initiation. However, LE4 is used to represent extreme seismic events where it is assumed that evacuation would be delayed beyond 20 hours2.314815e-4 days 0.00556 hours 3.306878e-5 weeks 7.61e-6 months . Thus, this source term is identified with an "early" release category because of the potential for the release to occur before effective evacuation.

This source term represents a single Level 2 release category: LE4a, the "dry" containment scenario (MAAP case #104m). Extreme seismic event sequences would include a large LOCA with station blackout. Thus, the assumption of a dry containment (no RWST injection) is consistent with the scenario definition.

Source Term SE1, Small/Early Containment Bypass - SGTR with Scrubbed Release:

Source term SEI is used for containment bypass releases through a ruptured steam generator tube, with feedwater to the faulted steam generator so that the release is scrubbed.

Specifically, this includes steam generator tube rupture (SGTR) sequences with recovery of steam generator cooling to the ruptured generator prior to release. This source term represents two sets of Level 2 release categories: SEI lb and SE12b. One set (SEI Ib) includes core damage sequences where the steam generator tube rupture occurs as the accident sequence initiator. The second set (SE I2b) includes core damage sequences where the steam generator tube rupture is pressure-induced as a result of ATWS or SLB initiators. The vast majority of SE 1 sequences are from release category SE 11 b, SGTR-initiated with steam generator cooling and operator restoration of feed flow to the faulted steam generator before significant release.

The frequency of release category SE12b is about a factor of 100 less than SE 11 b due to the low probability of these core melt sequences along with the conditional probability of a tube rupture.

The release category SEI lb and SEl 2b sequences are similar with regard to the containment failure mode, through a ruptured steam generator with opportunity for fission product retention. As a result, they are subsumed into a single source term, SE 1. Because the SE 11 b sequences make up about 99% of the SEl frequency, the SE1 lb sequences are used to define the release category source term. MAAP Case #103k is used as representative scenario for SE1. This scenario was initiated by SGTR with restoration of feed flow to the faulted steam generator following core damage. The submerged release resulted in a significantly reduced particulate release in comparison with LEl.

Source Term SE2, Small/Early Containment Bypass - ISLOCA with Scrubbed Release:

Source Term SE2 is used for release categories representative of Level 2 sequences involving an intersystem LOCA (ISLOCA) through the RHR system, with containment bypass from the reactor coolant system to the bottom of the submerged RHR vault.

This source term represents one Level 2 release category, SE2b. SE2b is similar to release category LE21 b, with ECCS flow, except the inventory loss is through the RHR pump seal - a smaller LOCA with release at the bottom of the RHR vault. This is also similar to release 9 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis category LE22a, with the LOCA through the RHR pump seal, but with ECCS flow. Since this scenario has ECCS flow, the release is scrubbed and should be significantly reduced from LE2. MAAP case #1041 is used as the representative scenario for SE2. This case is a small LOCA with release near the bottom of the RHR vault and Charging pump flow until the RWST is emptied at about 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months .

Source Term SE3, Small/Early Containment Penetration Failure to Isolate: Source term SE3 is used for release categories containing core damage sequences with a small containment isolation failure but with long term containment cooling. The result of the Reactor Coolant Pump (RCP) seal return line isolation valves failing to close is a small release from the containment to the environment.

SE3 source term represents one Level 2 release category: SE3b. Release category SE3b includes "wet" containment sequences, i.e., with CBS injection and sump recirculation. The representative scenario for SE3 is the "wet" containment case: MAAP Case #105k, small LOCA and failure of ECCS injection and failure of small containment isolation valves, but success of CBS injection and recirculation.

Source Term LL3, Large/Late Containment Venting (Wet): Source term LL3 is used for release categories containing core damage sequences with RWST injection - wet containment but with loss of containment cooling - and operator action to intentionally vent the containment per SAMGs. LL3 results in a large, late release from the containment to the environment.

This source term represents one Level 2 release category: LL3b. Release category LL3b includes "wet" containment sequences, i.e., with ECCS injection and/or CBS injection, but with no sump recirculation.

The representative scenario for LL3b is the "wet" containment case: MAAP Case #107a, medium LOCA, CBS injection, and containment venting when containment pressure exceeds 130 psia. The release begins when the first venting occurs, at about 16 hours1.851852e-4 days 0.00444 hours 2.645503e-5 weeks 6.088e-6 months .

Source Term LL4, Large/Late Containment Overpressure Failure (Wet): Source term LL4 is used for release categories containing core damage sequences with RWST injection -

wet containment but with loss of containment cooling. This results in a large, late release from the containment to the environment.

This source term represents a single Level 2 release category, LL4b (wet containment). A dry containment could lead to a late overpressure failure, but it is much more likely to result in basemat melt-through. As a result, all long term containment failures with a dry containment are modeled through source term LL5. The representative scenario for LL4b is the "wet" containment case: MAAP Case #107d, medium LOCA with ECCS injection and CBS injection. The release begins when the containment reaches the overpressure failure pressure, at about 32 hours3.703704e-4 days 0.00889 hours 5.291005e-5 weeks 1.2176e-5 months .

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Source Term LL5, Large/Late Containment Basemat Failure (Dry): Source term LL5 is used for release categories containing core damage sequences with no RWST injection - dry containment. The containment fails by basement erosion from core-concrete interaction before long term over-pressure failure of the containment. This results in a large, late release from the containment to the environment.

The representative source term is MAAP Case #106f, a station blackout with Emergency Feedwater (EFW) success for 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months and with intact containment initially but with no power recovery. Thus, basemat melt through occurs at about 49 hours5.671296e-4 days 0.0136 hours 8.101852e-5 weeks 1.86445e-5 months .

Source Term SELL, Small/Early, Large/Late Containment Failure: This is a new release category introduced as part of the source term revision. Source term SELL is used for release categories containing core damage sequences with initial small containment isolation failure but with failure of long term containment cooling. The results of the RCP seal return line isolation valves failing to close is a small release from the containment to the environment. However, in the long term, the containment fails due to overpressure or basemat melt-through resulting in a large, late release from the containment to the environment.

This source term represents three Level 2 release categories, small early release (SE3) with one of the three large late release categories (LL3b, LL4b, and LL5a). The frequencies of these release categories are all small (SELL3b, 7e-9; SELL4b, 2e-8; SELL5a, 7e-8). Since SELL5a has the highest frequency and LL5a has the most significant source term of the large, late release categories, it is used to represent this source term. The SELL3b / 4b / 5a release categories are subsumed into SELL.

The representative scenario for SELL5a is the "dry" containment case: MAAP Case #106g, station blackout with EFW success for 12 hours1.388889e-4 days 0.00333 hours 1.984127e-5 weeks 4.566e-6 months and small containment isolation failure.

Note, this is the same case as for LL5 except for the addition of the small containment isolation failure.

Source Term INTACT1, Nominal Containment Leakage: Source term INTACTI represents Level 2 sequences with containment intact except for nominal leakage at the maximum Technical Specification allowable limits.

The representative source term is MAAP Case #102o, with containment spray injection and sump recirculation functional. This assures long term containment cooling as well as fission product scrubbing.

Source Term INTACT2, Excessive Containment Leakage: Source term INTACT2 represents Level 2 sequences with containment intact except for leakage that exceeds Technical Specification allowable limits by a factor of 10, consistent with previous modeling of the source term.

The representative source term is MAAP Case #102q, with containment spray injection and sump recirculation functional. This assures long term containment cooling as well as fission product scrubbing.

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NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Seabrook Release Category Source Term Definitions (Representative Summary)

(b) (c) Release Fraction (d)

Source Term "t:. .Reference Release a Rlae Wrig Release Warning ID" " . =,.

Description

Tim MAAP Case Start.e Duration Duration Xe, Kr CsA Te Sr Ru (hrs) (hrs) (hrs) Group Group Group: Group Group LEI Steam Generator Tube Rupture core melt #103m 3.2 1.0 0.3 0.15 0.014 0.008 1.4e-5 2.1e-4 with no feed flow to faulted steam generator (Puff #1)

(direct release without scrubbing) #103m 39.3 100.0 0.85 0.25 0.21 1.3e-3 2.5e-4 (Puff #2)

LE2 Interfacing system LOCA with RHR pipe #104j 11.7 2.0 0.1 1.00 0.42 0.43 0.021 0.051 rupture (direct release without scrubbing)

LE3 Medium LOCA with no ECCS and failure of #104k 1.1 5.0 0.1 1.00 0.31 0.23 1.9e-3 5.8e-3 large containment penetration (Containment Online Purge (COP) valves)

LE4 Seismic, large LOCA with no ECCS and #104m 20.8 2.0 20.1 1.00 0.33 0.12 2.7e-5 2.0e-5 containment basemat melt-through (delayed evacuation)

SE1 Steam generator tube rupture core melt with #103k 30.6 2.0 4.4 0.063 3.3e-4 6.2e-5 3.2e-7 7.2e-6 delayed feed flow to faulted steam generator (scrubbed release)

SE2 Interfacing system LOCA with RHR pump #1041 12.9 10.0 0.3 0.88 0.021 0.019 1.8e-3 4.7e-3 seal failure (scrubbed release) (Puff #1)

1041 81.0 20.0 0.12 0.073 0.014 --

(Puff #2)

SE3 Small LOCA without ECCS but with CBS #105k 1.4 1.0 0.2 0.19 2.4e-3 2.7e-3 2.4e-5 4.5e-4 injection and sump recirculation -- intact containment except for small penetration unisolated LL3 Medium LOCA without ECCS but with CBS #107a 16.4 30.0 15.4 1.00 9.4e-3 5.3e-3 2.7e-5 5.4e-4 injection (wet containment) and vented containment per SAMG 12 of 95

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis (b) (c): Release Fraction (d)

Source IDTerm Reference Release Release Duration Warning DecipinMAAP Case SStart

Time Duration rs) (hrs) Xe, GroupKr CsT Group Te Group Sr Group Ru Group

. , * ... (hrs)(h )G r u LL4 Medium LOCA without ECCS but with CBS #107d 31.9 2.0 30.9 1.00 0.092 0.068 2.6e-4 6. l e-5 injection (wet containment) and long term containment overpressure failure LL5 Station blackout with dry containment #106f 49.4 1.0 30.5 1.00 0.52 0.23 1.6e-5 1.6e-6 (RWST not injected) and long term containment basemat melt-through SELL Station blackout with small penetration #106g 19.5 10.0 0.7 0.46 0.022 0.022 5.5e-4 8.3e-4 unisolated and dry containment (RWST not (Puff #1) injected) and long term containment basemat #106g 49.8 10.0 -- 0.54 0.095 0.039 ....

melt-through (Puff #2)

106g 100.0 30.0 .... 0.377 0.085 ....

(Puff #3)

INTACT1 Loss of feedwater with feed and bleed failure #102o 2.3 2.0 n/a 0.0078 1.4e-6 9.9e-7 1.3e-7 8.7e-7 but with CBS injection and sump recirculation -- intact containment (TS allowed leakage only)

INTACT2 Loss of feedwater with feed and bleed failure #102q 2.3 2.0 n/a 0.074 1.4e-5 8.6e-6 1.9e-7 4.0e-6 but with CBS injection and sump recirculation -- intact containment (TS allowed leakage x 10)

TABLE NOTES:

(a) Release Start Time = "Time to Containment Failure" EXCEPT "Time to Core Exit TCs > 1800'F" for containment bypass or isolation failure.

(b) Release Duration = Time from -10% to -80% of Noble Gas release.

(c) Warning Duration = Time from core exit temperature exceeding 11 00°F to Release Start Time.

(d) Release Fractions = Five representative chemical groups from parameters FREL(1), FREL(20, FREL(3), FREL(4), FREL(5) in MAAP.

These five groups are presented as a summary representation of the release. MAAP also includes seven other isotope groups, CsOH, Ba, La, Ce, Sb, Te and U [FREL(6) to FREL(12)] (not presented).

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis 3.1.1 LEVEL 1 AND LEVEL 2 PRA MODEL RESULTS Level ] Results The updated SB201 I was quantified using a truncation level of E-14 consistent with previous PRA models. The baseline results are provided in the following table and compared with the SAMA-based PRA model SB2006. The mean core damage frequency (CDF) has decreased by approximately 14.5%, from 1.44E-05/yr (SB2006) to 1.23E-5/yr (SB20 11).

Level 1 Results SB2011 SB2006 Mean Core Damage Frequency (CDF) 1.23E-05/yr 1.44E-05/yr Uncertainty Lower Bound (5th percentile) CDF 3.29E-06/yr 7..37E-0 6/yr Uncertainty Upper Bound ( 9 5 th percentile) 286E05/ 275E-05/

CDF InitiatingEvent Contributionto CDF The following table lists the top 15 initiating events contributing to CDF.

The first four initiators are hazard-type events that fail offsite power and contribute 25% of the core damage risk:

Seismic events causing loss of offsite power initiator (E7T, E10T),

Severe weather causing loss of offsite power initiator (LOSPW), and

" Internal flood in the Turbine Bldg causing loss of offsite power initiator (F4TREL).

The top 10 initiators account for almost 50% of CDF and include seismic events (E7T, E 1OT, E 14T),

other losses of offsite power (LOSPW, LOSPG), internal flood events (F4TREL, Fl SWCY), LOCAs (SGTR, LOCI MD), and reactor trip (RXT l).

The internal flood initiating events (F4TREL and F 1SWCY) are new as a result of the internal flood upgrade. The change in the relative CDF contribution of initiating events between PRA models SB2011 and SB2006 is primarily due to the relative increase in the internal flood risk. In general, there is not a dramatic shift in the CDF contribution of the top initiating event groups compared to the previous SB2006 PRA model results.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Initiating Event Contribution to CDF (sorted by CDF) (SB2011)

Init. Event 1c[oIE Frequency CDF(IE) .Percent ofCDF SB2006 ID Description (per.yr) . (per yr) Total Contribution Seismic 0.7g 9.30E-06 9.33E-07 7.6% 6,3.%

Transient Event ...

Seismic 1.Og 1.77E-06 8.88E-07 7.2% 5.9%

Transient Event Loss of Off-Site 7.65E-03 6.82E-07 5.6% 10.0%'

LOSPW Power due to Weather Major Flood - 2.73E-04 5.89E-07 4.8% New F4TREL Rupture of HELB / (Internal Flood) impact Relay Rm SGTR Steam Generator Tube Rupture 4.09E-03 5.69E-07 4.6% 4'.40%

Reactor Trip - 7.3 8E-01 5.41 E-07 4.4% 6.4%

RXT1 Condenser Available Medium LOCA 1.88E-04 5.3 1E-07 4.3% 2.3%

LOC1MD Event Loss of Off-Site 1.15E-02 4.53E-07 3.7% 6.2%

LOSPG Power -Grid-Related Events Rupture of SW 1.27E-05 4.06E-07 3.3% New F1SWCY Common Return (Internal Flood)

Pipe in Yard Seismic 1.4g 6.OOE-07 3.64E-07 3.0% 2. 5% ..

Transient Event Fire in Control 4.5 1E-05 3.62E-07 3.0% 1.0%

FCRPL Room - PORV LOCA FSGBE6 Fire SWGR Room 1.00E-03 3.46E-07 2.8% 2.6%/

B-Loss of Bus E6 Loss of Train A 4.40E-03 3.19E-07 2.6% 2.4%..

LACPA Essential AC Power (4kV Bus E5)

Fire in SWGR 1.1OE-03 3.05E-07 2.5% 2.5%

Room A - Loss of _______.._

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Init. Event TE Frequency CDF(IE) Percent of CDF SB2006 ID .escripton (per yr) (per yr) JTotal . Contribution E5 Loss of Train B 9.90E-03 3.03E-07 2.5% 1.8%

LPCCBt* PCCW System'* ______-_-" _

HazardEvent Contributionto CDF The following table provides the contribution to CDF from a set of six hazard groups. Example initiating events are provided to help define each hazard group. With the exception of the revised internal flood hazards contribution, there is not a dramatic shift in the relative contribution of the hazards groups compared to previous SB2006 PRA model results.

CDF Contribution from External & Internal Event Initiators (SB201 _ _)

CDF Previous Hazard Group IE Examples' .(group)in Each Hazard Group (ru Percent jS...=!,CDF*SB 2 0 0 6 Internal Events RXT 1 (reactor trip), 6.7%.54'.4 5454E .--

LOCIMD (medium LOCA) 4.50E-06 36.7% .4%

External Flood EXFLSW (external flood impacting ocean 2.40E-08 0.2% 0.2%

SW pumps)

FCRPL (fire in control room opening Internal Fire PORV) 1.39E-06 11.3% 9.0%.

Internal Flood F4TREL (internal flood in turbine bldg 2.61E-06 21.3% 5.4%

failing offsite power)

Seismic Events E7T (0.7 g earthquake causing loss of 3.06E-06 24.9% 21.0%

offsite power)

Severe Weather LOSPW (loss of offsite power due to 6.82E-07 5.6% 10.0%

severe weather)

CDF Total 1.23E-05 100.0%

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Basic Event Contributionto CDF The following table lists the top 15 basic events contributing to CDF sorted by Risk Reduction Worth (RRW). The basic event RRW from the previous SB2006 PRA model is provided for comparison.

Top 15 Basic Events Contributing to CDF (SB2011)

Previous Basic Event ID Basic Event Description RRW SB2006

.S .FX Loss of offsite power subsequent to plant trip 1.06 1.04 initiator

[DGDGIA.FR3] DG-1A fails to run for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months 1.05 1.08.

Operator Action - Manual Alignment of 1.04 1.-002 Alternate Cooling to Charging Pumps

[DGDGIB.FR3] DG-lB fails to run for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months 1.04 1.07

[CCPllA.FS PCCW Pumps A, B, C, D Common Mode 1.04 1.01 -

CCP1 1B.FS Failure to Start CCPI IC.FS CCPI 1D.FS]

[EDESWG5.FX 4KV Emergency Buses 5 and 6 Fault (Common 1.03 1'04 in"*

EDESWG6.FX] mode failure)

[EDESWG1 1A.FX DC Power Panels A, B Common Mode Failure 1.03 1'-04 EDESWGI 1B.FX]

Operator Action- SI termination given 1.03 1:02'-

HH.OTSI3.FA successful cooldown and depressurization for SGTR Operator Action - Maintain stable plant 1.03 1'.02 P-conditions with SG cooling during transients Operator Action - Close SEPS breaker from 1.02 -1 02:

MCB, given seismic event with SI signal HH.OLPR2.FA Operator Action - Align ECCS for Low Pressure 1.02 402 1

Sump Recirculation for MLOCA Operator Action - Control SC level locally, with 1.02 1;00 (*)

EFW thru EFW Discharge Operator Action - Maintain stable plant 1.02 1 02 :i HH.OHSB6.FL conditions with SG cooling during transients, CR fire event SEPSDG2B.FR3 1-SEPS-DG-2-B fails to run within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months 1.02 1.03 SEPSDG2A.FR3 1-SEPS-DG-2-A fails to run within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months 1.02 ..1 03 17 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis

(*) Operator actions developed in SB2009; RRW reflects the SB2009 model.

Level 2 Results The large early release frequency (LERF) is 9.2E-08/yr. This is a decrease of approximately 20%

compared to the SB2006 model LERF result of 1.15E-07/yr.

Release Category Frequency The following table lists the release categories with their release frequency. These 13 release categories are based on total release magnitude (small, large) and release timing (early, late) as well as specific containment failure modes.

Containment Release Categories and Frequencies (SB2011)

Release ".Release Frequency IDescriptio Type Category (per year)

LARGE LEI 5.19E-08 Large/Early Containment Bypass - SG Tube EARLY Rupture Release LE2 1.81E-08 Large/Early Containment Bypass - ISLOCA LE3 8.61E-10 Large/Early Containment Penetration Failure to Isolate (Containment Online Purge valve failure)

LE4 2.11 E-08 Large Containment Basemat Failure with Delayed Evacuation SMALL SEl 5.08E-07 Small/Early Containment Bypass - SG Tube EARLY Rupture with Scrubbed Release Release Small/Early Containment Bypass - ISLOCA with Scrubbed Release SE3 9.97E-07 Small/Early Containment Penetration Failure to Isolate LARGE LL3 1.75E-07 Large/Late Containment Vent LATE LL4 5.79E-08 Large/Late Containment Overpressure Failure Release LL5 3.1 OE-06 Large/Late Containment Basemat Failure Small/Early Containment Penetration Failure to SELL 9.84E-08 Isolate and Large/Late Containment Basemat Failure INTACT INTACTI 7.07E-06 Nominal Containment Leakage (Leakage INTACT2 6.90E-08 Excessive Containment Leakage IRelease) I______

________________________________

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Basic Event Contributionto LERF The following table lists the top 15 basic events contributing to LERF sorted by RRW. The basic event RRW from the previous SB2006 PRA model is provided for comparison.

Top 15 Basic Events Contributing to LERF (SB2011)

": " "Previous Basic Event ID Basic Event Description RRW Preiou BasicEven IDSB2006 HH.XOEFW1.FA Operator establishes feed to faulted steam generator 1.36 1.19 prior to significant release ZZ.SY2.FX Loss of offsite power subsequent to LOCA initiator 1.24 1.18 HH.XOINE3.FA Operator H,, Fails O.N., to start containment FA injection early 1.20 1.00W-M without AC power (gravity drain of RWST)

Operator action for Safety Injection termination given 1.19 1.09 HH.OTSI3.FA successful cooldown and depressurization for steam generator tube rupture Operator action to minimize ECCS flow w/ sump 1.10 1.06 HH.ORWMZ1.FA recirculation failed during Small LOCA and Interfacing Systems LOCA (ISLOCA) sequences _ _______

FWP37A.FR Turbine Driven Pump FW-P-37A fails to run 1.09 1.42 RCV24.FTO RHR Train A suction relief valve failure to open 1.08 1100, RCV89.FTO RHR Train B suction relief valve failure to open 1.08 1.00 FWP37A.FSI Turbine Driven Pump FW-P-37A fails to start 1.05 1.08 Cooldown and depressurize RCS to minimize leak w/ 1.04 1.01 HH.ORWCD1.FA sump recirculation failed during Small LOCA and ISLOCA sequences HH.XOSMP1.FA Operator aligns containment sump recirculation after 1.04 1:00m" core melt Operator maintains stable primary and secondary 1.03 1006:

conditions for extended steam generator cooling (hot HH.ORWLT1 .FA standby) during LOCA or steam generator tube rupture (SGTR) _____-_

Initiate makeup to RWST, given Small LOCA with 1.02 1.7 recirculation failure (LOCA, SGTR)

RCPSY403A.FM PS403A pressure switch fails high (pressure permissive 1.02 1 00 to open RHR suction RC-V-23)

RCPSY405A.FM PS405A pressure switch fails high (pressure permissive 1.02 1.00 to open RHR suction RC-V-87) _____ _______

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis 3.2 LEVEL 3 MODEL CHANGES The Level 3 analysis was revised using the new accident release category definitions from the SB2011 PRA model. The probability of occurrence, timing (release times and duration) and rate/quantity of radionuclides released to the environment, and public warning times related to the release timing for each of the categories from the Level 2 analysis were also reflected in the Level 3 analysis. All other data used in the Level 3 calculation (e.g., meteorology, population distribution, agriculture and economy, rates of evacuation) were unchanged from the previous analysis.

The Release Tables provide the radionuclide release parameters for the revised model. The tables provide the MELCOR Accident Consequence Code System (MACCS2, version 1.13.1) parameters which simulate the release during the entire duration as provided by the plant-specific MAAP results used to characterize the Level 2 release categories. Note that, because of MACCS input requirements of a maximum of 4 plumes, each with a maximum duration of 1-day, the impact analysis compacts the entire 7-day MAAP calculated release in a compressed time period.

A total accident release/duration. of 7 days is assumed in the base case Level 3 runs. This is a conservative assumption that will overstate the public impact and the cost-benefit of candidate SAMAs because the model gives only modest credit for long-term release mitigation actions that are likely to be strategized and implemented via execution of the Severe Accident Mitigation Guidelines.

Seabrook Severe Accident Release Parameters for 7-Day Release RCLEI Plume-i Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 9328 Plume Duration, sec 3982 86400 73091 86400 Plume Start Time, sec from SCRAM 9328 13309 99709 172800 Radionuclide Group Release Fractions NOBLE (Xenon, Krypton) 1.48E-01 4.OOE-03 5.80E-02 7.89E-01 I (Iodine) 1.39E-02 2.OOE-04 1.71E-02 2.36E-01 CS (Cesium) 9.73E-03 8.08E-05 1.85E-02 2.55E-01 TE (Tellurium) 8.31E-03 1.60E-04 1.39E-02 1.92E-01 SR (Strontium) 9.73E-06 4.77E-06 8.65E-05 1.16E-03 MO (Molybdenum) 1.8 1E-04 2.30E-05 2.50E-05 2.28E-04 LA (Lanthanum) 1.13E-06 6.OOE-08 1.82E-06 2.47E-05 CE (Cerium) 3.72E-06 4.60E-07 4.62E-05 6.36E-04 BA (Barium) 1.36E-04 8.OOE-06 4.80E-05 6.02E-04 SB (Antimony) 3.47E-03 7.OOE-05 1.11E-02 1.52E-01 20 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis RCLE2 Plume- I Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 40162 Plume Duration, sec 7898 38340 86400 86400 Plume Start Time, sec from SCRAM 40162 48060 86400 172800 Radionuclide Group Release Fractions NOBLE 9.16E-01 4.60E-02 7.OOE-03 3.1OE-02 I 3.57E-01 1.90E-02 6.OOE-03 3.50E-02 CS 3.47E-01 1.81E-02 1.24E-02 6.25E-02 TE 3.48E-01 2.71E-02 1.02E-02 5.01E-02 SR 1.55E-02 4.40E-03 2.OOE-04 1.1OE-03 MO 1.21E-02 3.86E-02 0.OOE+00 0.OOE+00 LA 1.37E-04 7.1OE-05 2.40E-05 1.18E-04 CE 7.43E-04 2.87E-04 3.1OE-04 1.54E-03 BA 2.46E-02 8.40E-03 1.OOE-04 5.OOE-04 SB 1.45E-01 5.70E-02 4.80E-02 2.40E-01 RCLE3 Plume- I Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 2984 Plume Duration, sec 6113 76025 86400 86400 Plume Start Time, sec from SCRAM 4262 10375 86400 172800 Radionuclide Group Release Fractions NOBLE 3.35E-01 8.50E-02 9.70E-02 4.83E-01 I 1.14E-01 2.50E-02 2.80E-02 1.41E-01 CS 1.14E-01 2.32E-02 2.62E-02 1.30E-01 TE 1.04E-01 1.75E-02 1.96E-02 9.81E-02 SR 1.56E-03 5.OOE-05 5.OOE-05 2.60E-04 MO 3.49E-03 3.OOE-04 3.40E-04 1.69E-03 LA 3.15E-05 1.20E-06 1.40E-06 6.80E-06 CE 1.35E-04 4.OOE-06 5.OOE-06 2.30E-05 BA 3.43E-03 1.30E-04 1.50E-04 7.30E-04 SB 3.97E-02 3.02E-02 3.41E-02 1.72E-01 21 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis RCLE4 Plume- I Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 1984 Plume Duration, sec 71633 11642 86400 86400 Plume Start Time, sec from SCRAM 3125 74758 86400 172800 Radionuclide Group Release Fractions NOBLE 2.82E-03 2.19E-02 1.62E-01 8.13E-01 I 1.57E-04 7.29E-03 5.41E-02 2.70E-01 CS 7.37E-05 4.17E-03 3.1OE-02 1.55E-01 TE 4.87E-05 2.67E-03 1.98E-02 9.92E-02 SR 1.08E-06 5.60E-07 4.20E-06 2.1OE-05 MO 3.04E-06 3.60E-07 2.70E-06 1.35E-05 LA 8.50E-08 5.20E-08 3.85E-07 1.93E-06 CE 8.91E-07 6.29E-07 4.70E-06 2.35E-05 BA 1.04E-06 1.14E-06 8.42E-06 4.23E-05 SB 3.53E-05 8.69E-03 6.46E-02 3.23E-01 RCSEs Plume- I Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 75413 Plume Duration, sec 41393 742 55249 86400 Plume Start Time, sec from SCRAM 75416 116809 117551 172800 Radionuclide Group Release Fractions NOBLE 2.78E-02 2.65E-02 1.OOE-03 7.90E-03 I 1.54E-06 2.35E-04 1.1OE-05 8.60E-05 CS 1.14E-06 1.41E-04 6.42E-06 5.21E-05 TE 3.84E-07 2.80E-05 3.80E-06 2.99E-05 SR 6.OOE-09 1.67E-07 1.70E-08 1.31E-07 MO 1.06E-07 1.61E-06 6.20E-07 4.85E-06 LA 6.80E-12 1.13E-08 6.OOE-10 4.70E-09 CE 2.10E-13 4.36E-08 2.60E-09 2.01E-08 BA 1.97E-08 1.68E-06 1.20E-07 9.30E-07 SB 3.34E-06 7.96E-06 1.20E-06 9.1OE-06 22 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis RCSE2 Plume-i Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 42865 Plume Duration, sec 23638 19894 86400 86400 Plume Start Time, sec firom SCRAM 42869 66506 86400 172800 Radionuclide Group Release Fractions NOBLE 6.44E-01 2.1OE-02 5.60E-02 2.79E-01 I 1.33E-02 3.70E-03 1.29E-02 6.45E-02 CS 1.30E-02 2.78E-03 6.94E-03 3.48E-02 TE 1.08E-02 1.91E-03 3.49E-03 1.75E-02 SR 8.19E-05 8.71E-05 2.71E-04 1.35E-03 MO 1.64E-03 8.90E-04 3.70E-04 1.84E-03 LA 2.81E-06 1.35E-06 2.53E-06 1.26E-05 CE 1.37E-05 5.30E-06 1.37E-05 6.83E-05 BA 4.87E-04 2.31E-04 3.32E-04 1.65E-03 SB 2.82E-03 3.96E-03 1.91E-02 9.51E-02 RCSE3 Plume-i Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec firom SCRAM 3445 Plume Duration, sec 7024 74268 86400 86400 Plume Start Time, see from SCRAM 5108 12132 86400 172800 Radionuclide Group Release Fractions NOBLE 2.32E-02 2.05E-02 2.39E-02 1.19E-01 I 2.38E-03 1.OOE-05 0.OOE+00 4.OOE-05 CS 2.25E-03 8.34E-07 0.OOE+00 1.25E-05 TE 2.67E-03 1.20E-10 1.40E-10 1.00E-05 SR 2.40E-05 0.OOE+00 0.OOE+00 0.OOE+00 MO 4.45E-04 0.OOE+00 0.OOE+00 0.OOE+00 LA 1.08E-06 0.OOE+00 0.OOE+00 1.OOE-08 CE 8.40E-06 0.OOE+00 0.OOE+00 1.OOE-08 BA 8.05E-05 0.OOE+00 1.OOE-07 1.OOE-07 SB 6.35E-04 2.OOE-06 2.OOE-06 9.OOE-06 23 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis RCLL3 Plume-i Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 2988 Plume Duration, sec 5875 76244 86400 86400 Plume Start Time, sec from SCRAM 4280 10156 86400 172800 Radionuclide Group Release Fractions NOBLE 9.38E-05 1.28E-01 1.45E-01 7.26E-01 I 2.80E-05 1.20E-03 1.36E-03 6.82E-03 CS 2.80E-05 1.32E-03 1.49E-03 7.48E-03 TE 2.21E-05 7.29E-04 8.28E-04 4.13E-03 SR 4.08E-07 3.36E-06 3.80E-06 1.90E-05 MO 1.04E-06 6.93E-05 7.87E-05 3.92E-04 LA 7.74E-09 1.58E-07 1.79E-07 8.95E-07 CE 4.01E-08 3.21E-07 3.63E-07 1.82E-06 BA 8.06E-07 1.46E-05 1.66E-05 8.30E-05 SB 9.30E-06 1.11E-03 1.26E-03 6.29E-03 RC LL4 Plume- I Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 2988 Plume Duration, sec 5875 86400 76244 86400 Plume Start Time, sec from SCRAM 4280 10156 96556 172800 Radionuclide Group Release Fractions NOBLE 9.38E-05 2.95E-03 1.19E-01 8.78E-01 I 2.80E-05 1.41E-05 1.09E-02 8.09E-02 CS 2.80E-05 1.36E-05 1.08E-02 8.05E-02 TE 2.21E-05 1.53E-05 8.25E-03 6.14E-02 SR 4.08E-07 5.88E-07 3.03E-05 2.25E-04 MO 1.04E-06 1.17E-05 7.90E-06 4.OOE-05 LA 7.74E-09 2.62E-08 3.77E-07 2.77E-06 CE 4.01E-08 5.60E-08 1.41E-05 1.05E-04 BA 8.06E-07 2.37E-06 1.90E-05 1.38E-04 SB 9.30E-06 2.18E-05 2.50E-02 1.86E-01 24 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis RCLL5 Plume-I Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 63529 Plume Duration, sec 10249 10037 86400 81295 Plume Start Time, sec from SCRAM 71219 81468 91505 177905 Radionuclide Group Release Fractions NOBLE 1.60E-04 3.47E-04 2.98E-03 9.97E-01 I 3.83E-05 1.17E-05 1.01E-04 5.20E-01 CS 1.96E-05 4.83E-06 4.17E-05 4.76E-01 TE 3.82E-05 3.43E-06 2.96E-05 2.28E-01 SR 6.95E-08 1.16E-07 9.95E-07 1.43E-05 MO 2.42E-07 1.60E-08 1.38E-07 1.21E-06 LA 3.85E-09 1.01E-08 8.70E-08 1.24E-06 CE 1.96E-08 1.17E-07 1.01E-06 1.56E-05 BA 2.93E-07 7.1OE-08 6.13E-07 4.14E-05 SB 1.11E-05 3.1OE-06 2.70E-05 3.21E-01 RCSELL Plume- I Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 63378 Plume Duration, sec 10829 4536 86400 86400 Plume Start Time, sec from SCRAM 71035 81864 86400 172800 Radionuclide Group Release Fractions NOBLE 4.57E-02 8.30E-03 1.58E-01 7.88E-01 I 1.01E-02 4.20E-03 7.99E-02 4.OOE-01 CS 5.38E-03 2.98E-03 5.68E-02 2.84E-01 TE 1.47E-02 1.12E-03 2.20E-02 1.1OE-01 SR 1.60E-04 3.OOE-06 6.40E-05 3.18E-04 MO 5.94E-04 2.OOE-06 3.90E-05 1.95E-04 LA 3.03E-06 3.30E-07 6.24E-06 3.12E-05 CE 2.38E-05 3.80E-06 7.24E-05 3.64E-04 BA 2.31E-04 2.OOE-06 4.50E-05 2.24E-04 SB 3.05E-03 3.61E-03 6.87E-02 3.44E-01 25 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis RC INTACTI Plume-i Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 6527 Plume Duration, sec 11858 65585 86400 86400 Plume Start Time, sec from SCRAM 8957 20815 86400 172800 Radionuclide Group Release Fractions NOBLE 1.70E-04 8.50E-04 1.13E-03 5.61E-03 I 1.27E-06 2.OOE-08 2.OOE-08 1.00E-07 CS 4.44E-07 6.25E-09 8.08E-09 4.13E-08 TE 9.51E-07 4.OOE-09 6.OOE-09 2.80E-08 SR 2.62E-08 9.70E-09 1.29E-08 6.42E-08 MO 6.50E-07 2.50E-08 3.30E-08 1.64E-07 LA 9.80E-10 1.73E-09 2.29E-09 1.14E-08 CE 1.73E-09 2.06E-09 2.72E-09 1.36E-08 BA 1.30E-07 1.1OE-08 1.60E-08 7.50E-08 SB 9.14E-07 2.1OE-08 2.70E-08 1.38E-07 R C 1NTA CT2 Plume-i Plume-2 Plume-3 Plume-4 Category General Emergency Declaration, sec from SCRAM 6523 Plume Duration, sec 12035 65412 86400 86400 Plume Start Time, sec from SCRAM 8953 20988 86400 172800 Radionuclide Group Release Fractions NOBLE 1.70E-03 8.1OE-03 1.07E-02 5.35E-02 I 1.23E-05 2.OOE-07 2.OOE-07 1.OOE-06 CS 4.42E-06 5.33E-08 7.17E-08 3.49E-07 TE 8.25E-06 3.OOE-08 5.OOE-08 2.20E-07 SR 7.65E-08 1.22E-08 1.63E-08 8.OOE-08 MO 2.07E-06 2.20E-07 2.80E-07 1.42E-06 LA 2.48E-09 2.70E-10 3.60E-10 1.78E-09 CE 5.17E-09 5.50E-10 7.30E-10 3.65E-09 BA 3.42E-07 2.70E-08 3.50E-08 1.78E-07 SB 4.47E-06 1.80E-07 2.50E-07 1.21E-06 3.2.1 LEVEL 3 MODEL RESULTS The Level 3 base case release category offsite public dose and economic risk results are summarized in the following table.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Seabrook Station Release Category Public Dose and Economic Risk Results - Level 3 Model SEABRK LE-1 LE-21. I LE-3 LE-4 SE-I SE-2 SE-3 LL-3 LL-4 LL-5 SELL INTACTI INTACT2 INTACT 5.19E-08 1.81E-08 8.61E-10 2.11E-08 5.08E-07 2.79E-08 9.97E-07 1.75E-07 5.79E-08 3.10E-06 9.84E-08 7.07E-06 6.90E-08 7.14E-06 1.26E+07 4.27E+07 2.41E+07 1.1 IE+07 2.43E+05 8.60E+06 1.36E+06 3.63E+06 7.27E+06 1.03E+07 1.48E+07 2.62E+03 1.79E+04 2.77E+03 5.60E+10 7.14E+10 6.80E+10 4.91E+10 3.27E+08 3.09E+10 2.67E+09 9.05E+09 3.10E+I0 5.24E+10 6.53E+10 4.52E+01 2.21E+05 2.18E+03 6.54E-01 7.73E-01 2.08E-02 2.34E-01 1.23E-01 2.40E-01 1.36E+00 6.35E-01 4.21E-01 3.19E+01 1.46E+00 1.85E-02 1.24E-03 1.98E-02 1.73% 2.04% 0.05% 0.62% 0.33% 0.63% 3.58% 1.68% 1.11% 84.33% 3.85% .... 0.05%

2.91E+03 1.29E+03 5.85E+01 1.04E+03 1.66E+02 8.62E+02 2.66E+03 1.58E+03 1.79E+03 1.62E+05 6.43E+03 3.20E-04 1.52E-02 1.56E-02 1.60% 0.71% 0.03% 0.57% 0.09% 0.48% 1.47% 0.87% 0.99% 89.63% 3.55% .... 0.00%

Note:

(1) Table results are based on the Level 2 frequencies from model SB2011 (base case) and Level 3 SEABRK 7 day offsite release duration consequences.

(2) Consistent with the original SAMA evaluation and for simplification, release categories INTACT 1 and INTACT2 are combined into INTACT. The frequency of INTACT is simply the sum of the INTACT 1 and INTACT2 frequencies:

INTACT frequency = frequencyINTACT I + frequencyINTACT2 The consequence of INTACT is based on the sum of the probability-weighted INTACT1 and INTACT2 consequences:

INTACT consequence = (conseqINTACTI

freqINTACTI + conseqINTACT2

freqINTACT2) / (freqINTACTI + freqINTACT2) 27 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis 3.3 PRA MODEL CHANGE REVIEW Level 1 Model Review The upgraded internal flood risk assessment was peer reviewed in late 2009. The peer review resulted in 26 findings and observations that have been further categorized into significance levels as follows: 3 "B" level F&Os and 23 "C/D" level F&Os. There was no level "A" significance findings. All 26 internal flood peer review findings have been addressed in the SB2011 model update. The internal flood events PRA model meets the supporting requirements (SRs) identified in Part 3 to ASME/ANS RA-Sa-2009 (PRA Standard) and Regulatory Guide 1.200 Rev 2.

Level 2 Model Source Term Review The Seabrook source term analysis was performed by the Seabrook PRA group and was reviewed by industry experts at ERIN Engineering and Research, Inc. The scope of this review included an examination of the source term analyses and assessment of the representative sequences selected for each source term bin. In addition, all MAAP code results were reviewed to assure that the cases had been executed properly and that the results followed expected trends. Overall, the Seabrook source term analysis was found to represent a strong technical body of work and a solid basis for the License Renewal SAMA evaluation. The review concluded that the analysis addressed the major parameters impacting fission product release and the selection of representative sequences was appropriately made.

Level 3 Model Review The Level 3 model was performed by industry experts at Tetra Tech NUS and received independent review.

4.0 COST OF SEVERE ACCIDENT RISK / MAXIMUM BENEFIT 4.1 SCOPE OF COST BENEFIT EVALUATION The SAMA reassessment builds upon the original assessment and follows the same industry guidance outlined in NEI 05-01. The same technical process is used as in the original SAMA analysis. The approach to the reassessment is summarized here:

1. All originally-identified Phase II SAMA candidates are revaluated to identify if any of these SAMAs are now potentially cost beneficial (or "more" potentially cost beneficial).

2. The original Phase 1 SAMA candidates that were qualitatively screened from further detailed assessment based on the SAMA not being applicable to the plant design or the SAMA intent was met by the plant design, are not reviewed further in this supplement.

3. In addition to the originally-identified Phase II SAMA candidates, new potential SAMA candidates are identified based on a review of the latest SB20 11 PRA model results and risk ranking of the top-ranked initiating events and basic events that contribute to CDF and LERF.

4. The top-ranked basic events associated with release categories that contribute to the top 90% of public risk are assessed in Phase II. These top initiating events and basic events are evaluated by linking to an existing candidate SAMA Phase II evaluation or are specifically evaluated in Phase II as a possible new SAMA candidate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis

5. The SAMA cost-benefit assessment is based on development of new PRA cases to conservatively (and in some cases, more realistically) estimate the potential cost-benefit worth based on the updated PRA model. All SAMA cost-benefits are assessed for nominal (best estimate) and uncertainty (upper bound) with and without the seismic multiplier identified in response to RAI #4 (Reference 3) to account for the potential increase in seismic risk as suggested by NRC using GSI- 199 information.

6. The implementation cost of each previously evaluated SAMA is reassessed as necessary to ensure that the costs continue to be representative of the SAMA scope based on plant-specific and industry experience. The implementation cost of each new SAMA candidate is also estimated based on plant-specific and industry experience. The implementation costs and their bases are provided in Table 1 and Table 2.

Seismic Risk Multiplier The conservative seismic risk multiplier of 2.1 is used in the SAMA evaluation. Development of the Seismic multiplier was provided in NextEra Energy response to RAI #4 in Letter SBK-L-1 1067 (Reference 3). The multiplier is re-developed below based on the previous approach which credits the seismic benefit of the Supplemental Emergency Power Supply (SEPS):

The SB2011 PRA model seismic contribution (benefit) of the SEPS is approximately 26%

(same as previous). Thus, the estimated maximum seismic contribution from the NRC suggested GI-199 seismic risk of 2.2E-05/yr (which does not credit SEPS) can be reduced by 26%

2.2E-05/yr * (1.0 - 0.26) = 1.6E-05/yr

The baseline CDF from internal and external events is 1.23E-05/yr (SB201 1)

" The seismic contribution to baseline CDF is 3.06E-06/yr (SB201 1)

" Overall seismic increase factor is 2.05 and is rounded to 2.1 (1.23E-05/yr - 3.06E-06/yr + 1.6E-05/yr) / 1.23E-05/yr = 2.05 factor increase in CDF Dominant Basic Events SAMA candidates are evaluated for the top 15 basic events contributing to CDF, LERF and the dominant Level 2 release categories that cumulatively contribute to approximately 90% of the total public risk (dose and economic risks). The release categories that contribute to approximately 90% of the public risk include the following:

Dose Risk: LL-5 (84.3%), SELL (3.8%) and SE-3 (3.6%) = 91.7% of dose risk Economic Risk: LL-5 (89.6%), SELL (3.5%) = 93.1% of economic risk The top 15 basic events that contribute to each sequence group, CDF, LERF, LL-5, SE-3 and SELL are listed in the following table. This results in a total of 45 basic events, since some basic events contribute to multiple sequence groups.

CDFDominant InitiatingEvents SAMA candidates are evaluated for the top 15 initiating events (lEs) relative to CDF. The top 15 initiators to CDF are listed above in the Level 1 results.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Top 15 Basic Events Contributing to CDF, LERF, and RC Contributing to 90% of the Public Risk Description Contributing Metric Basic Event CDF, LERF, RC HH.OALT1.FL Operator Action - Manual Alignment of Alternate Cooling to Charging Pumps before CDF, LL-5, SELL RCP seal LOCA

[CCP1 1A.FS PCCW Pumps A, B, C, D Common Mode Failure to Start CDF, LL-5, SELL CCP11B.FS CCP11C.FS CCP 11D.FS]

[EDESWG11A.FX DC Power Panels A, B Common Mode Failure CDF, LL-5, SELL EDESWG11B.FX]

HH.XOEFW1 .FA Operator establishes feed to faulted SG prior to significant release LERF HH.OTSI3.FA Operator action for SI termination given successful cooldown and depressurization for CDF, LERF SGTR HH.OHSB 1.FA Operator action to maintain stable plant conditions with SG cooling during transients CDF, LL-5 HH.OLPR2.FA Operator Aligns ECCS for Low Pressure Sump Recirculation for MLOCA CDF HH.OSGLC3.FL Operator fails to control SG level locally, with EFW thru EFW Discharge CDF HH.OHSB6.FL Operator action to maintain stable plant conditions with SG cooling during transients, CDF CR fire events HH.XOINE3.FA Operator Fails to start containment injection early without AC power (gravity drain of LERF, LL-5, SELL RWST)

HH.ORWMZ1 .FA Operator action to minimize ECCS flow w/ sump recirculation failed during SLOCA and LERF ISLOCA sequences HH.ORWCD1 .FA Cooldown and depressurize RCS to minimize leak w/ sump recirculation failed during LERF SLOCA and ISLOCA sequences HH.ORWLT1 .FA Operator maintains stable primary & secondary conditions for extended SG cooling (hot LERF standby) during LOCA or SGTR HH.ORWIN1 .FA Initiate makeup to RWST, given SLOCA w/ sump recirculation failure (LOCA, SGTR) LERF 30 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Description Contributing Metric Basic Event.-

______________CDF, LERF, RC RCPSY403A.FM PS403A pressure switch fails high (press. permissive to open RHR suction RC-V-23) LERF RCPSY405A.FM PS405A pressure switch fails high (press. permissive to open RHR suction RC-V-87) LERF ZZ.SY1.FX Loss of offsite power subsequent to plant trip initiator CDF, LL-5, SE-3, SELL ZZ.SY2.FX Loss of offsite power subsequent to LOCA initiator LERF CCTE2171 .FZ PCC Train A Temperature Element CC-TE-2171 transmits false low LL-5 CCTE2271 .FZ PCC Train B Temperature Element CC-TE-2171 transmits false low LL-5 CCE17A.RT PCC Ht Ex 17A rupture/excessive leakage during operation LL-5 CCE17B.RT PCC Ht Ex 17B rupture/excessive leakage during operation LL-5 HH.ORHP12.FA Operator action to restore charging/HPI/RCS for long term makeup after recovery of LL-5 support systems during various trans/accidents

[SWAFN63.FS] CT SWGR Train B FAN SWA-FN-63 fails to start on demand LL-5

[SWAFN64.FS] CT SWGR Train A FAN SWA-FN-64 fails to start on demand LL-5

[SWFN51A.FS] SW Cooling Tower FAN SW-FN-51A fails to start on demand LL-5 HH.OSEP2Q.FA Operator fails to close SEPS breaker from MCB, given seismic event with SI signal CDF, SE-3, SELL

[DGDG1A.FR3] DG-1A fails to run for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months CDF, SE-3, SELL

[DGDG1B.FR3] DG-IB fails to run for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months SE-3, SELL ZZ.CIS.PRE.EXIST Small pre-existing unidentified containment leakage SE-3, SELL SEPSDG2A.FR3 1-SEPS-DG-2-A fails to run within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months SE-3, SELL SEPSDG2B.FR3 1-SEPS-DG-2-B fails to run within 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months SE-3, SELL HH.OSEP1Q.FA Operator fails to close SEPS breaker from MCB, given seismic event SE-3, SELL HH.OCI2Q.FL Operator fails to close CSV-167 manually/locally SE-3

[DGDG1A.FR3 DG 1A and DG1B common mode failure to run for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months SE-3, SELL 31 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis Description Contributing Metric.

Basic Event

_____________CD.F, LERF, RC DGDG1B.FR3]

[EDESWG5.FX 4KV Emergency Buses 5 and 6 Fault (Common mode failure) CDF, SE-3 EDESWG6.FX]

[CSV167.FTC] Penetration X-37 Isolation MOV CS-V-167 fails to close on demand SE-3 FWP37A.FR Turbine Driven Pump FW-P-37A fails to run LERF, SE-3 FWP37A.FS 1 Turbine Driven Pump FW-P-37A fails to start on demand LERF, SE-3 SEPSDG2A.FS 1-SEPS-DG-2-A fails to start on demand CDF, SE-3 SEPSDG2B.FS 1-SEPS-DG-2-B fails to start on demand CDF, SE-3 HH.XOSMP 1.FA Operator aligns containment sump recirculation after core melt LERF, SELL HH.XOINE1 .FA Operator fails to start containment injection early to prevent RPV failure SELL RCV24.FTO RHR Train A suction relief valve failure to open LERF RCV89.FTO RHR Train B suction relief valve failure to open LERF 32 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis 4.2 SUPPLEMENTAL SAMA RESULTS PRA Level ] and 2 QuantitativeResults The core damage frequency (CDF) has decreased from the 2006 results to the 2011 results by approximately 14.5%, from 1.44E-05/yr (SB2006) to 1.23E-5/yr (SB201 1). The large early release frequency (LERF) has decreased by approximately 20%, from 1.1 5E-07/yr (SB2006) to 9.2E-08/yr (SB201 1).

Maximum Averted Benefit The consequences of a severe accident have increased as a result of the revised Level 2 release source term modeling. This has resulted in an increase to the offsite dose/cost risk and offsite property/cost risk despite the reduction in annual core damage and large early release frequencies.

The nominal maximum attainable benefit (MAB) is $3,050,815 (SB201 1). This represents a factor increase of 3.7 over the previous MAB of $818,721 (SB2006). This increase in MAB is primarily the result of higher release category source terms. The original SAMA analysis was based on previous, historical source terms, which were developed from industry source term information and early versions of MAAP for various accident release fractions and accident timing. The new source term assessment provides a state of the art and consistent approach to analyzing accident source terms.

SAMA Sensitivity Assessments Annual Met Data Set The meteorological data sets used in the updated SAMA evaluation are the same as in the original SAMA evaluation and included years 2004 through 2008. Each data set was evaluated to ensure that the data year that provides the maximum dose risk and cost risk is used. Based on the assessment, the met data associated with year 2005 provides the maximum dose risk and cost risk (same as in original assessment) and was chosen as the baseline data set for the updated SAMA.

Meteorology Specification in last SpatialSegment Consistent with the original SAMA evaluation, the updated baseline SAMA evaluation assumes continuous rainfall imposed from 40 to 50 miles from release to force conservative population exposure for base case. The sensitivity case allows the 40-50 mile segment meteorology to follow the onsite meteorology. Elimination of the continuous rainfall assumption reduces the population dose risk to approximately 86% of the baseline and the cost risk to approximately 85% of the baseline. These results are consistent with the sensitivity results observed in the original SAMA study.

Sea-breeze Sensitivity The sea-breeze effect on population dose risk and economic cost risk was re-evaluated similar to the previous analysis described in NextEra Energy's response to RAI #4g ( Reference 2) to account for the new release category source terms. The results of the latest evaluation indicate that the population dose and offsite economic cost risks increase by 0.4% and 0.6% when applying a conservative sensitivity to account for sea breeze effects. The sensitivity of the thermal internal boundary layer (TIBL) lid height was also investigated by specifying a 110 meter height; a decrease 33 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis of 10 meters (from 110 to 100 meters) was found to change the dose and offsite cost risks by 0.8%

and 0.5%. Based on this evaluation and when considering other conservative SAMA assumptions (e.g., perpetual rainfall in the outer ring) the sea-breeze effects do not change the conclusions of the SAMA analysis.

Note - The previous sea-breeze assessment in RAI #4 (Reference 2) estimated sea-breeze effects could result in an increase to the population dose risk by 4%

and economic cost risk by 7%. These previous results were calculated in MACCS2 using the Monte Carlo random bin sampling technique. The revised evaluation summarized above used the MACCS2 sequential hour analysis technique, which provides a more accurate result compared to the Monte Carlo bin sampling technique. Thus, the latest results are shown to be less than previous results despite of the increase in release category source terms.

Release Category LE4 Sensitivity to No Evacuation As summarized in Section 3.1, Release Category LE4 is used to represent extreme seismic events where it is assumed that evacuation could be delayed beyond 20 hours2.314815e-4 days 0.00556 hours 3.306878e-5 weeks 7.61e-6 months and therefore, the release is assigned to LERF. The Level 3 base case population dose and economic cost consequences of LE4 are determined assuming normal evacuation occurring at the General Emergency declaration beginning at core uncovery. If no evacuation is assumed, the LE4 dose consequence increase is less than 1% (from a total base case dose of 1.11 E+07 person-rem to 1.12E+07 person-rem). The overall economic cost consequence does not change.

The LE4-specific dose consequence during the early phase of the release (exposure to the passing plume) for the no-evacuation scenario is 9% greater than the base case (with evacuation). However, the early phase dose is only 16% of the total LE4 dose consequence. The remaining 84% of the dose consequence occurs during the late phase and is a result of long-term exposure to the plume, independent of evacuation. Compounding the relatively small consequence of no-evacuation, with the relatively small portion of the total dose that can be affected by the action to evacuate results in a negligible affect (<1%) on the total LE4 dose consequence.

Sensitivity to Variation in Other Level 3 Parameters The sensitivity of the updated SAMA results to variations in other Level 3 parameters is expected to be consistent with previous sensitivity results. The previous Level 3 sensitivity cases included variations in release height, release heat, building wake effects, and evacuation speed, preparation, warning time and population fraction. Although the radionuclides released in the updated SAMA were different amounts compared to the original evaluation, the physical surroundings such as meteorology, population distribution and economy are unchanged. Therefore, the conclusions drawn from the original Level 3 sensitivity evaluation are representative of the updated SAMA evaluation.

Sensitivity to Variation in Discount Rate The nominal (baseline) cost-benefit assessment considers a "nominal" discount rate of 7%. Cost-benefit sensitivity to the discount rate is considered at 3% (conservative discount rate) and 8.5%

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis (best estimate discount rate). The nominal 7% rate and the conservative 3% rate are consistent with the NEI 05-01 industry guidance. The best estimate rate of 8.5% is specific to Seabrook Station and is consistent with the original Seabrook SAMA evaluation. The 3% conservative discount rate results in an increase the cost-benefit above the nominal, whereas the best estimate rate of 8.5%

provides a cost-benefit slightly lower than the nominal rate. No new potentially cost-beneficial SAMAs where identified as a result of the 3% and 8.5% sensitivity calculations. The cost-benefit worth of all SAMA candidates at the 3% conservative discount rate is shown to be less than the SAMA cost-benefit worth when considering the uncertainty (upper bound) benefit.

Sensitivit to Extended Period The nominal cost-benefit assessment considers a nominal benefit period of 20 years. The SAMA cost-benefit sensitivity to an extended period was explored to account for possible near term approval of the renewed license. Consistent with the original SAMA evaluation, an extended period of 41 years is used to represent the total period of the extended/renewed operating license. Based on this sensitivity study, the cost-benefit worth (MAB) during the extended period is a factor of -1.3 greater than the nominal MAB, but significantly less than the upper bound (95th percentile) MAB.

The cost-benefit worth of all SAMA candidates assuming the 41 year extended period is shown to be less than the SAMA cost-benefit worth when considering the uncertainty (upper bound) benefit.

Sensitivity to Upper Bound Accident Costs The nominal cost-benefit assessment considers the mean (best estimate) core damage/accident release frequencies derived from the Seabrook SB20 11 PRA. To account for upper bound uncertainty in the PRA model results, the best estimate accident costs are multiplied by an uncertainty factor of 2.35 to represent the cost-benefit associated with the 95th percentile (upper bound) accident release impacts. The increase factor of 2.35 is based on the ratio of the best estimate CDF mean value of 1.23E-05/yr to the CDF upper bound (95th percentile) value of 2.86E-05/yr.

This approach is consistent with the NEI 05-01 industry guidance. The upper bound cost-benefit of each SAMA candidate is considered whenjudging the candidate as being potentially cost-beneficial.

Although this approach is consistent with NRC expectation for identification of potentially cost-beneficial SAMAs, it is noted that final determination of cost and benefit would include a more realistic assessment of both the cost of a specific modification and its associated value in risk reduction.

Sensitivity to IncreasedSeismic Risk The nominal and upper-bound cost-benefit values of each SAMA candidate are increased by a factor of 2.1 to account for possible higher seismic risk. The basis for the 2.1 multiplier is discussed in Section 4.1 of this report. This sensitivity approach is consistent with NRC expectations for identification of potentially cost-beneficial SAMAs.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis PotentialCost Beneficial SAMAs The four SAMA candidates that were identified as potentially cost-beneficial in the previous analysis remain as potentially cost-beneficial in the supplemental analysis. Three new potential cost-beneficial SAMAs are identified for further consideration within Seabrook's Long Range Plan (LRP) system. The potentially cost-beneficial severe accident mitigative alternatives identified do not involve aging management of passive, long-lived systems, structures, or components during the period of extended operation. All previous (p) and new (n) potentially cost beneficial SAMAs are identified in the following table.

Seabrook Station - Potential Cost-Benefit SAMAs SAMA # Description fPotential Benefit 157 Independent AC power source for battery Reduce the risk of core damage from long-(p) chargers (e.g., portable generator to facilitate term SBO sequences by extending battery timely charging of station batteries), life to allow more time to recover offsite/onsite power.

164 Method to refill the Condensate Storage Tank Reduce the risk of long term core damage (n) (CST) from alternate water sources (e.g., modify sequences that rely on long term SG makeup 10" condensate filter flange connection to via feedwater and CST suction source.

facilitate timely CST makeup from other sources such as firewater or alternate pump via hose connection).

165 Method to refill Reactor Water Storage Tank Reduce the risk of containment failure and (p) (RWST) from firewater during containment release during long term containment injection (e.g., modify 6" RWST flush flange injection sequences that would benefit from connection to facilitate timely firewater makeup additional makeup.

capability).

172 Replace existing RCP seal design with improved Reduce risk of core damage from transients (n) low leakage seal (e.g., evaluate installation of sequences with seal cooling hardware a "shutdown seal" developed by Westinghouse). failures, which result in RCP seal LOCA events.

192 Install flow limiting device in the fire protection Reduce the risk of core damage from internal piping located in the Control Building to limit flood sequences resulting from a postulated flood consequence of major pipe break (e.g., pipe break in Control Building fire protection install flow orifice), piping.

193 Replace outboard containment isolation valve Reduce the risk of release during SBO /

CS-V- 167 with a valve design that is independent seismic sequences that lead to core melt; of AC power (e.g., replace existing MOV with an improve reliability of containment isolation AOV). of RCP seal water return line.

195 Hardware changes to improve PCCW Reduce risk of core damage and release due (n) temperature control reliability - update of existing to sequences involving loss of PCCW equipment or provide additional redundancy in cooling function.

instrumentation / controls 36 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis 4.3 SUPPLEMENTAL SAMA EVALUATION RESULTS TABLES The cost-benefit assessment of each previous Phase II SAMA candidate is provided in Table 1. The cost-benefit assessment of each of the top 15 dominant BE-related SAMA candidates and IE-related SAMA candidates is provided in Table 2. The expected SAMA cost and bases are provided in Tables 1 and 2. SAMA candidates that were previously identified as "intent met" in the initial submittal or in subsequent RAI responses are not reviewed further in this supplement.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK - MAB & PHASE 2 SAMA REVIEW SBIK % Risk Total Benefit () Expecte Potential PR ae Reduction Baseline (with 2.1 d SAMA

.SAMVA Ipoe nt Description PR aemultiplier) ~ cost Evaluation Number Iirvmn

- -- CDF Pop Internal With

_______ ", .:"":.':i:: : . :,. Dose External Uncert. ________-_"_"_.______________"_*_: ________-_" ____

Not cost beneficial. The original PRA case NOSBO and recent PRA case NOSBO1 both conservatively assume elimination of all station blackout events by assuming Replace lead- Extended DC 224K 525K guaranteed success of both EDGs for all events and independent of all support systems 2acid batteries power capability NOSBO1 22 (470K) (11.M 1 .75M (control power, cooling, etc.)

with fuel cells during an SBO

Cost of physical plant modifications and analysis judged comparable in scope and I____Icomplexity to 'providing additional DC battery capacity" (Davis Besse AC/DC-01).

Not cost beneficial. The original and recent PRA case NOLOSP conservatively Install an Reduced assumed elimination of all LOSP events.

13 additional, buried probability of NOLOSP 18 17 531K 1.24M >3M Cost of physical plant modifications and analysis judged comparable in scope and off-site power loss of off-site (1.2M) (2.7M) complexity to "Burying off-site power lines" (Callaway 24). Cost of installing buried, source power alternate power source expected to significantly exceed benefit. Reduction in seismic risk would not be significant unless offsite power source is seismically rugged.

Not cost beneficial. The original PRA case NOSBO and recent PRA case NOSBO1 both conservatively assume elimination of all station blackout events by assuming Increased guaranteed success of both EDGs for all events and independent of all support systerr Install a gas availability of on- NOSBOs 22 224K 525K * (control power, cooling, etc.) Reduction in seismic risk would not be significant unless turbine generator siteaity AC power of on- (470K) (1.1 M) 2M gas turbine is seismically rugged.

Cost of physical plant modifications and analysis judged comparable to other plants that presently do not have these features (Davis Besse AC/DC-1 4). Some of the potential benefit of this SAMA would be realized with SAMA #172, RCP shutdown seal.

Not cost beneficial. The original PRA case NOSBO and recent PRA case NOSBO1 both conservatively assume elimination of all station blackout events by assuming Increased guaranteed success of both EDGs for all events and independent of all support systems Improve availability of 224K 525K (control power, cooling, etc.)

16 uninterruptible power supplies NOSBO1 22 6 (470K) (1.1 M) >2M Cost of engineering and implementing this upgrade is based on Seabrook engineering power supplies supporting front- estimate.

line equipment It is noted that due to the importance of improving reliability of uninterruptable power supplies, an action item has been entered into the Long Range Plan to assess future upgrade to the ELGAR inverters.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABRo6K - MAB & PHASE 2 SAMA REVIEW

%Tis otal Benefit($ Expecte SAMA Potential R1ucio iiaelinel(with 2.1 d sAMA Eauto NumbeA mrvmn Description PRA Case .multiplier) Costaio

-Number - ..-....

.- CD- PPop. internal n**Dose 'External& Uncert.

With ".

_____:_ ____:________________. .... ______

Not cost beneficial. The original PRA case NOSBO conservatively assumed eliminatior of all station blackout events by assuming guaranteed success of both DGs for all events and independent of all support systems (control power, cooling, etc.). The updated PRA case DGSW assumes success of SW components (valves) that are associated with DG cooling and alignment of the SW system (ocean and cooling Add a new Increased diesel tower). Guaranteed success of these components and the resulting increase in SW 20 backup source of generator DGSW <1 1 25K 53K 2M reliability is representative of the DG cooling water reliability gained from installing a diesel cooling availability (59K) (124K) backup source of cooling water. Insights from this analysis are that the existing arrangement of SW cooling to the DGs is of a reliable design; and making the DGs less dependent on SW does not provide a significant risk reduction because other train-specific components, such as ECCS pumps, also depend on SW cooling.

Cost of physical plant modifications and analysis judged comparable to other plants thai presently do not have these features (Grand Gulf 10).

Not cost beneficial. The original and recent PRA case NOLOSP conservatively Bury off-site Improved off-site power reliability NOOP1 7 531K 1.24M assumes elimination of all loss of offsite power events. Burying offsite power lines to 24 linesNOLOSP power 18 17 ( 1.2 4M >3M the station is judged not practical and cost is expected to significantly exceed benefit.

power lines during severe (1.2M) (2.7M) weather Cost of physical plant modifications and analysis judged comparable in scope and complexity to "Burying off-site power lines" (Callaway 24).

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE. 1 - SEABROOK - MAB:& PHASE12 SAMA REVIEW

... . Risk Total Benefit () Expecte SBK impKePe-ehto.:Baseline (wWh .2.1 dSAMA SAMA Iproteentia Description PRA Case Rdcin multiplier)" Cost Eauto Number Inera & it CDF Pp nenl Wt Dose External Uncert. *"

Not cost beneficial. The original PRA case LOCA02 conservatively assumed guaranteed success of all high head and intermediate head injection pumps (charging and SI pumps.) Therefore, the benefit of installing a single, independent, backup injection system was judged conservatively high. A more realistic PRA Case CSBX assumes that CS division B of high pressure injection (CSB) is independent and does not rely on support systems (independent of AC / DC power, cooling, etc.). This case is used to represent a "parallel" pump with same suction as CS-B. Installation of an independent, active or passive injection system is judged not practical and cost is expected to significantly exceed the conservative benefit. Given the seismic ruggedness of the existing injection system(s), any new/additional system would need Install an Improved to be equally rugged to significantly reduce plant risk. Including seismic ruggedness in independent prevention of 1.1M 2.5M the design would further increase cost.

25 active or passive high pressure core melt (2.3M) (5.3M) 8.8M Cost of physical plant modifications and analysis judged comparable to other plants thai injection system sequences presently do not have these features (Grand Gulf 20). This improvement was i spreviously estimated at greater than $2 million dollars in the Pilgrim License Renewal application. In the Duane Arnold License Renewal application, the Pilgrim estimate waE judged to be low and used a $20 million estimate based on similar modification experience. In addition, Grand Gulf SAMA #20 estimated the cost of a similar plant change at >$8.8M. Given these industry estimates and based on the Seabrook plant design, the cost for SAMA implementation would be expected to be in the range of $6 tc

$1OM or more. These estimates significantly exceed the upper bound sensitivity benefil and a more refined estimate is not warranted.

It is noted that some of the potential benefits of this SAMA would be realized with SAM

172, RCP shutdown seal.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK - MAB & PHASE 2 SAMA REVIEW Total Benefit (~Expecte SBK ,.% Risk Baseline (with 2.1 dSM SAMA._ I..mPotential provem ent . :: -. .. :

Description :: ..PRA Case: Reduction :m ultiplier) ° mutipier) SAMAt: :., .

"Cost.. :=° * : " .. :- !" va at n Evaluation = : .

Number ImprovementC Internal & With naCDF-Pop. C 7 Dose External Uncert.

Not cost beneficial. The original PRA case LOCA02 conservatively assumed guaranteed success of all high head and intermediate head injection pumps (charging and SI pumps.) Therefore, the benefit of installing a single, independent, backup injection system was judged conservatively high. A more realistic PRA Case CSBX assumes that CS division B of high pressure injection (CSB) is independent and does not rely on support systems (independent of AC / DC power, cooling, etc.). This case is used to represent a "parallel" pump with same suction as CS-B. Installation of an additional injection system is judged not practical and cost is expected to significantly exceed the conservative benefit. Given the seismic ruggedness of the existing injection Provide an system, any new/additional system would need to be equally rugged to significantly Providehanh Reduced reduce plant risk. Including seismic ruggedness in the design would further increase additional high frequency of cost.

26 pressure core melt from CSX22 3 i11M 2.5M 8.8M 26 injection pump small LOCA and CSBX 22 34 (2.3M) (5.3M) 8.8m Cost of physical plant modifications and analysis judged comparable in scope and with independent SBO sequences complexity to other plants that presently do not have these features (Grand Gulf 20).

diesel This modification was assumed to be the equivalent of adding one new high pressure injection pump powered by a diesel rather than an electric motor with a suitable injection path and suction source. In the Duane Arnold License Renewal application, the cost of this was one half the cost of replacing pumps discussed in SAMA 25 above, the cost would be $10 million. In addition, Grand Gulf SAMA #61 estimated the cost of a similar plant change at >$6.4M and >8.8M for Grand Gulf SAMA #20. Given these industry estimates and based on the Seabrook plant design, the cost for SAMA implementation would be expected to be in the range of $6M to $1 OM or more.

It is noted that some of the potential benefits of this SAMA would be realized with SAWA

172, RCP shutdown seal.

Not cost beneficial. The original PRA case LOCA03 conservatively assumed elimination all low pressure injection failures including injection pump trains, suction, accumulators and low pressure recirculation. A more realistic yet conservative PRA case for LOCA03 was performed to better address this SAMA, which is focused on Add diverse low adding diversity in for injection. The revised PRA case assumes guaranteed success o1 28 pressure Improve injection 68K 160K >11M the low head "injection" function provided by the pump trains when support systems are 2nepre system- capability LOCA03 2 2 (143K) (336K) available. Accumulators and containment recirculation are assumed to be subject to injection srandom failures.

Cost to engineer and Install an additional low pressure injection system is based on Seabrook previously reported estimate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TAL.1 ABLE -SEABROO KEA

- MA13MAREVIEW:

MABI&PHASE2 P SAM EViEW" i :* ~. . .. i .

SBKRsk Total Benefit Cs) Ex~pects A Potential Reduction n Baseline (with2.l<dSAMA "PRA Case SAMADescription multiplier) C . Evaluation Number Improvement "PCost NumCDF Pop. internal & With

__________.... "Dose External Uncert.

Not cost beneficial. The original and recent PRA case LOCA04 conservatively assume guaranteed success of the RWST volume as a continuous source of water for ECCS.

Therefore, the benefit of throttling low pressure injection to extend the time to RWST Throttle low depletion for medium or large break LOCA events is conservatively high. The current pressure system valves and controls do not allow throttling.

injection pumps earlier in medium Extended reactor 312K 731 K Cost to engineer and install is based on two trains, replacing manual valves with new 8" 35 or large-break water storage LOCA04 13 10 (655K) (1.53) >3M MOVs including control system design and associated hardware and cabling. Design LOCAs to tank capacity change to include a revised LOCA and Containment analysis. Additional analysis maintain reactor would be required to verify ECCS flow balance and NPSH for low, intermediate and water storage high head SI pumps. The implementing modification would need to address design anc tank inventory licensing basis changes as well as post mod testing to validate required flow balance is achieved.

Not cost beneficial. The original PRA case LOCA02 conservatively assume guaranteed success of all high head and intermediate head injection pumps (charging and Sl pumps.) Therefore, the benefit of replacing two electric motor pumps with diesel-driven Reduced pumps was conservatively high. Of the four SI pump trains, the intermediate head common cause pumps contribute slightly more to the CDF than the high head SI/charging pumps. A failure of the more realistic PRA Case DSIPP case assumes that the existing intermediate head SI Replace two of safety injection pump trains do not rely on AC power, but continue to rely on DC control power and the four electric system. The room cooling. This is judged representative of replacing the SI pump motors with diesel safety injection intent of this <1K <1K engines. The high head SI/charging pumps are assumed to remain dependent on AC 39 pumps with SAMA is to DSIPP <1 0 (<1 K) (<2K) >5M power. Installation of diesel-driven pumps in place of the existing motor-driven pumps diesel-powered provide diversity is judged not practical and cost is expected to significantly exceed the conservative pumps within the high- benefit. Given the seismic ruggedness of the existing injection system, any and low-pressure new/additional equipment would need to be equally rugged so as to not impact the safety systems injections current seismic design basis. Including seismic ruggedness in the design would further increase cost.

Cost to engineer and Install diverse pump drivers is based on Seabrook previously reported estimate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1 - SEABROOK - MAB & PHASE 2 SAMA REVIEW.

SK .Potential Description .dCase

% Risk. Total Benefit () Expecte

. Reduction: Baselie(t2 d SAMA Numbe Improe nt Decito PRACas multiplier) Cost Evaluation CDF Pop.- Internal With Dose :External Uncert.

__________.. _______._..-_.________________"___"_______..

Allows low pressure emergency core Not cost beneficial. The original and recent PRA cases LOCA01 conservatively Create a reactor cooling system 27K 64K assume elimination small LOCA events.

41 coolant depress injection in the LOCA01 2 1 >1M system event of small (57K) (134K) Cost to engineer and install an RCS depressurization system is based on Seabrook LOCA and high- previously reported estimate.

pressure safety injection failure Add redundant Not cost beneficial. The original and recent PRA cases SWO1 conservatively assume DC control Increased 11K 26K that the SW pumps are not dependent on DC power.

power for SW availability of SW (24K) (55K) Cost to engineer and install an independent DC power system for the SW pumps is pumps based on Seabrook previously reported estimate.

Not cost beneficial. The existing ECCS pump "motors" are air cooled motors, which relý on ventilation cooling for long term ambient room cooling. Ventilation cooling is provided by the Emergency Air Handling System (EAH) which cooled by CCW. The ECCS pump components also rely on CCW cooling (for example lube oil cooling, stuffing box cooling, etc.) The original and recent PRA case CCW01 conservatively assume guaranteed success of the component cooling water (CCW) systems to assess ReplaceElimination of the possible benefit of eliminating the ECCS pump dependence on CCW (room cooling pump motors ECCS 919K 2.15M and pump cooling). However, because CCW contributes is an important system that 44 with air-cooled dependency on CCW01 14 31 (1.93M) (4.6M) >6M contributes to the decay heat removal function, the benefit calculated with case CCW01 motorscomponent motorscooling system is highly conservative.

Cost to engineer and implement design modifications to replace the ECCS pumps with a design that does not depend on CCW (if even practical) is estimated greater than

$6M. This estimate is based on plant modifications judged to be of comparable yet less scope and complexity to SAMA #39, replacing ECCS pumps ($5M). It is also likely that modifications to room ventilation systems would still be needed at a cost of $1 M (similar to SAMA #80) to achieve full benefit.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK - MAB &-PHASE 2 SAMVA REVIEW B% %Risk >Total Benefit(S Expecte SAA mb Potential Improvemoent Decito D R aeemultiplier)Reduction Baeie(ih21 d Cost SAMA Evaluation NuDFe Pop. Internal & With Dose External Uncert.._"_________________-________-_..... .__________________________:_________

Not cost beneficial. The original PRA case RCPLOCA conservatively assumed that RCP seal LOCA events are eliminated. A more realistic PRA Case CSBX assumes tha CS division B of high pressure injection (CSB) is independent and does not rely on Install an Reduced support systems (independent of AC / DC power, cooling, etc.). This case is used to independent indepndent frequency core damageof represent a "parallel" pump with same suction as CS-B.

reactor coolant1.04M 2.45M >6.4M Cost to engineer and implement plant modifications and analysis judged comparable in 55 pump sealsystem, injection compont comont(2M) CSBX 28 34 5.) scope and complexity to "installing a backup water supply and pumping capability" injetio sytem coponet (.2M (52M)(Grand Gulf #61). Grand Gulf SAMA #61 estimated the cost of a similar plant change a with dedicated withdediated service cooling water, or >$6.4M. In addition, the Duane Arnold License Renewal application, the cost of this diesel service wat was one half the cost of replacing pumps discussed in SAMA 25 above, the cost would station blackoutbe$0mlin be $10 million.

It is noted that some of the potential benefits of this SAMA would be realized with SAMP

172, RCP shutdown seal.

Not cost beneficial. The original PRA case RCPLOCA conservatively assumed that RCP seal LOCA events are eliminated. A more realistic PRA Case CSBX assumes tha Reduced CS division B of high pressure injection (CSB) is independent and does not rely on Install an frequency of support systems (independent of AC / DC power, cooling, etc.). This case is used to independent core damage represent a "parallel" pump with same suction as CS-B.

reactor coolant from loss of 1.04M 2.45M >6.4M Cost to engineer and implement plant modifications judged comparable in scope and 56 pump seal component CSBX 28 34 (2.2M) (5.2M) complexity to "installing a backup water supply and pumping capability" (Grand Gulf without service water, #61). Grand Gulf SAMA #61 estimated the cost of a similar plant change at >$6.4M.

dedicated diesel but not a station The cost of installing an independent seal injection system with or without a dedicated blackout diesel is expected to significantly exceed benefit. Refer above to SAMA #55.

It is noted that some of the potential benefits of this SAMA would be realized with SAMA

172, RCP shutdown seal.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK:-.MAB &,PHASE 2zSAMA REVIEW

% Risk Total Benefit ($) Expecte S_.- Potential - - l Cs Reduction Baseline(t. 2.1 dS .".A Evaluation AnA .Im.provement : Description PRA""uaseý " multiplier) Cost Number CF Pop., internal & With Dose External Uncert.

Not cost beneficial. The original PRA case CCW01 conservatively assumed guaranteed success of the component cooling water (CCW) systems to provide heat removal. Thus, the benefit of installing an additional CCW pump was conservatively high. A more realistic PRA Case CCABCD assumes that all of the CCW pumps are Reduced guaranteed success when their AC and DC power support systems are available. This Install an likelihood of loss case is used to represent the benefit of an additional "parallel" CCW pump connected additional of component 335K 785K to the system. Seabrook has four CCW pumps. Adding an additional pump will not 59 component cooling water PCCABCD 4 11 >6.1M significantly reduce plant risk due to common-cause failure considerations and cooling water leading to a (704K) (1.7M) limitations in divisional power.

pump reactor coolant Cost to engineer and implement modifications for additional pump judged comparable in scope and complexity to "adding a service water pump" at other plants that presently do not have these features (Columbia SAMA CW-07 )

It is noted that some of the potential benefits of this SAMA would be realized with SAMW

172, RCP shutdown seal.

Reduced chance Install a digital of loss of main 3.05M 7.15M Not cost beneficial based on inspection of the MAB.

65 feed water feed water MAB (6.41M) (15.0M) 30M Cost to engineer and implement installation of the digital feedwater control upgrade is upgrade following a plant based on Seabrook previously reported estimate.

trip Provide a passive, Reduced Not cost beneficial based on inspection of the MAB. A passive heat removal system secondary-side potential for core 3.05M 7.15M using air as the ultimate heat sink would be extremely large.

77 heat-rejection damage due to MAB (6.41M) (15.OM) 15M

-

loop consisting loss-of-feedwater Cost to engineer and implement installation of large passive air cooling system is far in of a condenser events excess of the attainable benefit.

and heat sink Not cost beneficial. The original PRA case FW01 conservatively assumed elimination Replace existing of all loss of feedwater initiating events including all reactor trip events, whether or not pilot-operated the trip events were the result of a loss of feedwater. A more realistic PRA case PORV relief valves with Increased assumes guaranteed success of the PORVs. This case is used to represent a change larger ones, such probability of 1.7K 4.1K in PORV success criteria to reflect larger capacity valves. The cost of replacing the 79 that only one is successful feed PORV <1 0 (4K) (9K) >2.7M PORVs to increase capacity and improve feed and bleed performance is expected to required for and bleed significantly exceed benefit.

successful feed Cost to engineer and implement hardware design changes and replacement of PORVs and bleed judged comparable to other plants that presently do not have these features (Calvert Cliffs SAMA #77).

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SBK-L-12053 NextEra Energy Seabrook, LLC .

Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEAB.ROOK -" MAB &,PHASE 2 SAMAREVIEW

%

ik Total Benefit () Expecte SK Potential Reduction Baseline (with21 dSM SAMVA - ,cindSM mpro. ement : Description PRA Case ultiplier)

M.. Cost Evauaton Number Pop. Internal With 7 Dose External Uncert. _____________"_______________'__________...________"____________*

Increased Not cost beneficial. The original and updated PRA case HVAC2 conservatively assume Provide availability of no HVAC dependency for CS, SI, RHR and CBS pumps.

redundant train avaiabilty7o 80 or means of components HVAC2 3 5 (320K) (750K) >1M Cost to engineer and implement redundant ventilation design modification judged ventilation dependent on comparable to other plants that presently do not have these features (Callaway SAMA room cooling #80).

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1 - SEABROOK - MAB &PHASE2 SAMA REVIEW

% Risk Total Benefit () Expecte SIBIK dcto Baseline (with 2A1 dSM SAMA Ptnil Description> PRA Case rnlipir Cos Evlato Improvement Cos PoP. Internal With Number

_____Dose External Uncert.

Create ability to switch emergency Continued fan Not cost beneficial. The original and updated PRA case OEFWVS and OEFWV 84 fa oe room feedwater upy operationa in a OEFWVS <1 0 <1K

2) <$2K (4) >250K conservatively assume no HVAC dependency for EFW pumps.

fan power supply station blackout (2K) (4K) Cost to engineer and implement HVAC system design changes to allow for DC power to station supply is based on Seabrook previously reported estimate.

batteries in a station blackout Not cost beneficial. The original PRA case CONT01 conservatively assumed the containment does not fail due to overpressure. A revised PRA Case CONTX1 assumeE that one division of Containment Building Spray CBS (including spray injection, containment recirculation, and heat removal) does not depend on AC/DC power or Install a passive Improved 1.2M 2.7M PCCW support systems except for initiation signal. This case more realistically spra sytement rcntabiinmnty C(2.5M) (5.7M) 10M represents the potential risk reduction benefit that might be provided by installation of spray system spray capability an independent division of containment spray.

Cost to engineer and implement passive containment heat removal system judged comparable in scope and complexity to plants that presently do not have these features (Callaway SAMA #91).

Not cost beneficial. The original PRA case CONT01 conservatively assumed the containment does not fail due to overpressure. It is noted that the Seabrook Station design includes the Containment On-line Purge (COP) and Combustible Gas Control Increased decay (CGC) systems, which can function to vent containment during an accident after all heat removal other means of containment decay heat removal have failed. Use of these systems to Install an capability for depressurize containment to the environment is included as a severe accident strategy 93 unfiltered, non-ATWS XOVNTS 39K 92K >$3M in the Seabrook Severe Accident Management Guideline SCG-2. Containment venting hardened events, without (82K) (193K) using the COP system is currently credited in the Level 2 PRA as a means of preventin, containment vent scrubbing over-pressure containment failure when support systems are available. The COP and released fission CGC systems discharge pathways are to the plant stack (located at the top of products containment) via a combination of pipe and rugged ductwork and fan/filter enclosures.

Cost to engineer and implement vent to allow decay heat removal capacity is based on Seabrook previously reported estimate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK -MAB & PHASE 2 SAMA REVIEW

% Risk Total Benefit () Expecte BK Potential Reduction Baeie(ih~ d SAMA Eauto NumbeA Number mrvmn Description PRA Case. u multiplier),-' Cost.Evlato PpI nternal& With

_____ __________ __________Dose 'External. -Uncert..

Not cost beneficial. The original conservative PRA case CONT01 assumed elimination of containment failure events due to overpressure. The context of this SAMA is to eliminate containment overpressure failure events by removing decay heat from Install a filtered Increased decay containment via a filtered vent which would retain fission products. A more realistic containment vent heat removal PRA Case CONTXl assumes that one division of Containment Building Spray CBS to remove decay capability for (including spray injection, containment recirculation, and heat removal) does not 94 heat. Option 1: non-ATWS CONTX0 40 1.2M 2.7M >7.8M depend on AC/DC power or PCCW support systems except for initiation signal. This Gravel Bed events, with (2.5M) (5.7M) case is used to represent the potential risk reduction benefit that might be provided by Filter; Option 2: scrubbing of installation of a filtered vent to prevent containment overpressure failure while retaining Multiple Venturi released fission some of the fission products.

Scrubber products Cost to engineer and implement decay heat capacity filtered vent judged comparable to other plants that presently do not have these features (Calvert Cliffs SAMA 12 provided an estimate of $5.7M in 1998, escalated to $7.8M in 2012).

Provide post- Reduced Not cost beneficial. The original and updated PRA case H2BURN conservatively accident likelihood of 18K 43K assume that hydrogen burns and detonations do not occur.

96 containment hydrogen and H2BURN 0 1 >100K inerting carbon monoxide (39K) (90K) Cost to engineer and implement a containment inerting system is based on Seabrook capability gas combustion previously reported estimate.

Not cost beneficial. The context of this SAMA is to eliminate or reduce containment overpressure failure events by adding reinforcement to containment. The original PRA case CONT01 conservatively assumed the containment does not fail due to overpressure. A more realistic, yet still conservative PRA Case CONTX1 is used to Strengthen estimate the risk benefit associated with strengthening containment. The new PRA primary/secondar Reduced case CONTX1 assumes one division of Containment Building Spray CBS (including y containment probability of 1.2M 2.7M spray injection, containment recirculation, and heat removal) does not depend on (e.g., add ribbing containment CONTX1 0 40 (2.5M) (5.7M) 11.5M AC/DC power or PCCW support systems except for initiation signal. This case more to containment over- realistically represents a reduction in the containment pressure challenge that might be shell) pressurization realized by further strengthening of the containment shell itself. It is noted that the installation of structural support members sufficient enough to gain further design pressure margin to the containment building is judged not practical at Seabrook Station.

Cost to engineer and implement installation of reinforcing steel to strengthen containment is estimated at >$11.5M for design, materials and installation.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1; - SEABROOK -~MAB & PHASE. 2 SAMA-REVIEW S" :" R isk Total Benefit ($) Expecte.

SAA 'Potential Reduction BaselineB(with 2.1.d.SAMA SAVADescription PRA Case m.rultiphier)- Cs Evaluation Number Improvement Wt CDoopsttral Dose External Uncert.

Not cost beneficial. The context of this SAMA is to eliminate or reduce containment release events by adding a system to maintain evacuation (negative pressure) in the containment. It is noted that Seabrook Station already has an enclosure building around the primary containment building, which is maintained in a negative pressure condition. The original PRA case CONT01 conservatively assumed the containment Construct a does not fail due to overpressure. A more realistic PRA Case CONTX1 is used to building to be Reduced estimate the risk benefit associated with improvements to the enclosure building to connected to probability of 1.2M 27M make it more robust relative to severe accident challenges, such as adding an 102 primary/sec. containment CONTX1 0 40 56.7M additional building with filtration system. The new PRA case CONTX1 assumes one containment and over- (2.5M) (5.7M) division of Containment Building Spray CBS (including spray injection, containment maintained at a pressurization recirculation, and heat removal) does not depend on AC/DC power or PCCW support vacuum systems except for initiation signal. This case more realistically represents the postulated reduction in the release challenge that might be realized by an evacuation building to capture releases.

Cost to engineer and construct a new building adjacent to containment with ventilation systems capable of maintaining a negative pressure is estimated at greater than $56M for design, materials and installation.

Not cost beneficial. The original and updated PRA Case OLPRS and OLPR Delay conservatively assume guaranteed success of the operator action to complete/ensure containment Extended reactor the RHRPLHSI transfer to long term recirculation during large LOCA events. The results 105 spray actuation water storage OLPR 3 0 11.7K 27.4K >100K of this case study show that the operator action does not contribute significantly to core after a large tank availability (25K) (58K) damage frequency.

LOCA Cost to engineer and implement control circuitry to delay containment spray actuation for large LOCA is based on Seabrook previously reported estimate.

Not cost beneficial. The original and updated PRA case LOCA04 conservatively assume guaranteed success of the RWST volume as a continuous source of water for ECCS. Therefore, the benefit of throttling containment spray flow to extend the time to Extended time RWST depletion is conservatively high. The cost of engineering analysis, installation of over which water the proper valves, control systems, etc. to accomplish this SAMA is expected to Install automatic remains in the significantly exceed the conservative benefit.

containment reactor water 106 spray pump storage tank, LOCA04 13 10 312K 731K >3M Cost to engineer and implement automatic flow throttling control system is estimated at header throttle when full (656K) (1.54M) greater than $3M. This assumes that both LOCA and Containment Mass Energy valves containment calculations need to be performed. Additional analysis would be required to verify spray flow is not ECCS flow balance and NPSH for low, intermediate and high head SI pumps. The needed implementing modification would address design and licensing basis changes as well as post mod testing to validate required flow balance is achieved. Pending review of the throttling capability of existing system valves, hardware changes may be necessary to achieve the desired results.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1.- SEABROOK - MAB & PHASE 2 SAMA REVIEW SBK SBK Potential

_ . .u..i ~~~%

Risk Ttlenft()

,:Baseline (With 2.1 Expecte d SAMA SAMA .mrvmn Description PRA Case Reduction mutiler) Cost Evaluation.

Not cost beneficial. The context of this SAMA is to eliminate containment overpressure failure events by adding a redundant containment spray system. The original conservative PRA case CONTX1 assumed that a division of containment building spray (CBS) was guaranteed successful. A more realistic PRA Case CONTX1 assumes that one division of Containment Building Spray CBS (including spray injection, containment Install a Increased recirculation, and heat removal) does not depend on AC/DC power or PCCW support 107 redundant containment heat CON-Xl 40 1.2M 2.7M >10M systems except for initiation signal. This case is used to represent the potential risk ccontainment removal ability (2.5M) (5.7M) reduction benefit that might be provided by installation of an additional redundant spray spray system system.

Cost to engineer and implement redundant spray system is estimated at greater than

$10M. This is based on the cost of physical plant modifications and analysis judged comparable in scope and complexity to "installing a passive containment spray system" at plants that presently do not have these features (Callaway SAMA #91).

Install an independent power supply to the hydrogen control system using either new batteries, a non- Not cost beneficial. The original and updated PRA case H2BURN conservatively safety grade Reduced assume that hydrogen burns and detonations do not occur.

108 portable hydrogeno2BURN 18.3K 43K >100K Cost to install an independent power supply to the H2 control system is based on generator, detonation (39K) (90K) Seabrook previous reported estimate.

existing station potential It is noted that SAMA #108 would benefit from SAMA #157, portable AC generator, batteries, or which was shown to be potentially cost beneficial.

existing AC/DC independent power supplies, such as the security system diesel Reduced Not cost beneficial. The original and updated PRA case H2BURN conservatively Install a passive hydrogen 18.3K 43K assume that hydrogen burns and detonations do not occur.

system detonationen0c1nt3oK)H(90K) detonation >100K (39K) (90K) Cost to install a passive hydrogen control system is based on Seabrook previous potential I IIIreported estimate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1- SEABROOK - MAB &:PHASE 2 SAMA REVIEW SB.K % Risk Total Benefit () Ex pecte.

Baseline (with 2.1 dSAMA SAA Potential Reduction Evaluatio

-. ^ . nt -poe Description PRA Case multiplier) Cost Evaluation Number Imrvmn

- CDF Pop. Internal & With

___________Dose- External Uncert. -

Erect a barrier that would provide Not cost beneficial. The original cost benefit was assessed based on MAB. The enhanced updated cost benefit assessment is based on PRA case HPMVE which assumes that protection of the Reduced high pressure melt ejection occurrences are completely eliminated. It is noted that high containment probability of <1K 1K pressure melt ejection phenomenon dose not represent a significant challenge to 110 walls (shell) from containment HPMVE 0 0 (<1 K) (2K) >10OM containment because of the current robust pressure design of the Seabrook ejected core failure containment.

debris following Cost to engineer and implement barrier modifications judged comparable in scope and a core melt complexity to plnsthat pentydo not have these features (Claa AMAA #110) scenario at high pat rsnl Claa )

pressure Not cost beneficial. The original and updated PRA case CONT02 conservatively assume guaranteed be success of all containment isolation valves. At Seabrook, containment isolation valves are already equipped with limit switches. The limit switch function is primarily for valve position indication/verification and judged not to contribute Add redundant Reduced significantly to the overall reliability of the containment isolation valves themselves.

and diverse limit frequency of Adding an additional limit switch would not provide significant improvement inthe 112 switches to each containment CONT02 0 6 115K 270K >1M reliability of the isolation function. For SAMA purposes, the limit switches are containment isolation failure (242K) (566K) conservatively assumed to contribute 50% to the containment isolation function. Thus, isolation valve and ISLOCAs the PRA case upper bound benefit is less than $566K

0.5 = $283K and is judged not cost beneficial.

Cost to engineer and implement diverse Cl valve limit switches judged comparable in scope and complexity to plants that presently do not have these features (Callaway SAMA #112).

Not cost beneficial. The original and updated PRA case LOCA06 conservatively assume complete elimination of all ISLOCA risk contribution. Performing increased testing of PIVs would not significantly reduce the ISLOCA event frequency. Nor is it practical to perform more frequent tests. This is because PIV testing cannot be safely performed during power operation and would require a plant shutdown. Plant transition to shutdown introduces risk and additional costs due to lost generation. For SAMA Increase leak Reduced 48K 114K purposes, increased PIV testing is conservatively assumed to reduce the ISLOCA 113 testing of valves ISLOCA LOCA06 <1 (11) (4K >1M frequency by 50%. Thus, the PRA case upper bound benefit is less than $240K *0.5=

in ISLOCA paths frequency 0 1Ks(4K 120K.

Cost to engineer and implement leak test system modifications judged comparable to other plants that presently do not have these features (Callaway 113). As stated, testing cannot be performed during power operation. The cost of lost generation as a result of even one plant shutdown and cooldown for several days needed to perform thE

____________________________________________________ ____________testing is expected to significantly exceed the benefit.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I -. SEABROOK -MAB & PHASE 2 SAMAREVIEW

" % Risk Total Benefit(S) Expecte SAMvIA Ptnil SBKBaseline Description PRA Case Redutn (with 2.1 multiplier) d Cost SAMVA Evaluation Number Improvement CDh Pop. Internal ,With Dose External Uncert. .. .. *"

Not cost beneficial. The original and updated PRA case CONT02 conservatively assume guaranteed success of all containment isolation valves. At Seabrook, isolation of containment penetrations is typically performed using motor operated valves (MOV),

air operated valves (AOV) and check valves (CV), and combinations of these valves, depending on the operational function and isolation requirements of the specific penetration. Check valves are considered to be self-actuated valves. MOVs and AOVs Install self- automatically close upon receipt of Engineered Safety Actuation Signals. Containment actuatingReduced 115K 270K penetrations are either closed (isolated) or if open, automatically close upon receipt of 114 containment frequencyiof CONT02 0 6 (242K) (566K) >2M reliable Engineered Safety Actuation Signals. Self-actuated valves are judged to not isolation valves failure significantly improve the reliability of the containment isolation function. For SAMA purposes, the benefit of a self-actuating valve(s) is assumed to contribute 50% to the containment isolation function. Thus, the PRA case upper bound benefit is less than

$566K

0.5 = $283K.

Cost to install self-actuating valves based assuming two trains of Cl valves requiring replacement of exiting containment valves with self actuating valves (assume AOVs).

Piping and support changes, controls and wiring also needed to support modifications.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK - MAB& PHASE 2 SAMA.REVIEW ..

Total Benei Expecte SB Risk eft()

.Baseline Potential Reductin (with 2.1 d SAMA SAMA Potential Description PRA Case - Reduction-...m..ltplir) Cost Evaluation Number mpoentCF Pop. Internal & With Dose External Uncert. ________________________________

Locate residual Reduced Not cost beneficial. The original and updated PRA case LOCA06 conservatively 115 heat removal frequency of LOCA06 <1 48K 114K >1M assume that ISLOCA events do not occur.

(RHR) inside ISLOCA outside (101 K) (240K) Cost to relocate the RHR system function to inside containment is based on Seabrook containment containment previous reported estimate.

Institute a maintenance practice to Not cost beneficial. The original and updated PRA case NOSGTR conservatively perform a 100% Reduced assume that SGTR events do not occur.

119 inspection of steam generator NOSGTR 5 2 (141K) (329K) >500K Cost to perform 100% inspection each refueling outage is based on previous Seabrook team generator s te rator reported estimate. Costs for this item were estimated to be >$3M in Kewaunee, Beaver tubes during tube ruptures Valley and Calvert Cliffs License Renewal submittals.

each refueling outage Increase the pressure Eliminates capacity of the release pathway Not cost beneficial. The original and updated PRA case NOSGTR conservatively secondary side to the 67K 157K assume that SGTR events do not occur.

121 so that a steam environment NOSGTR 5 2 >500K generator tube following a (141 K) (329K) Cost to engineer and analyze design to increase the SG secondary side pressure is rupture would steam generator based on Seabrook previously reported estimate.

not cause the tube rupture relief valves to lift Route the discharge from the main steam Not cost beneficial. The original and updated PRA case NOSGTR conservatively safety valves Reduced assume that SGTR events do not occur. It is noted that Severe Accident Management through a consequences of Guideline SAG-5, Reduce Fission Product Release, includes guidance and procedure 125 structure where a a steam NOSGTR 5 2 67K 157K >500K steps for use of external spraying sources for fission product plume reduction including water spray generator tube (141 K) (329K) possible reduction of SG releases.

would condense rute wouldsteamnde rupture Cost to install main steam safety valve spray system to reduce fission product release the steam and remove most of during SGTR is based on Seabrook previously reported estimate.

the fission products 53 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK - MAB & PHASE 2 SAMA REVIEW SBK % Risk Total Benefit ($) Expecte SAA Potential PR ae Reduction Baeie(ih21 d SAMA Eauto

. AMA S Im .-. r.veme

.. Description

Rl Case multiplier) Cost Evauaton NumberDF . Pop. Internal With ,s)

.___________"_ 1Dose External Uncert.

Install a highly reliable (closed loop) steam Not cost beneficial. The original and updated PRA case NOSGTR conservatively generator shell- Reduced assume that SGTR events do not occur.

side heat consequences of 67K 157K 126 removal system a steam NOSGTR 5 2 -15M Cost to install a passive, closed loop SG heat removal system is greater than $15M.

that relies on generator tube (141 K) (329K) This is based on the water cooled isolation condenser being extremely large and natural rupture expensive to install for a fully constructed plant. Conceptually this installation would be circulation and similar to SAMA 77.

stored water sources Reduced Not cost beneficial. The original and updated PRA case NOSGTR conservatively 129 Vent safetymain steam valves in consequences a steam of NOSGTR 5 assume that SGTR events do not occur.

2 67K 157K 12 sfeyale a tue ( ) (>500K Cost to engineer and analyze design to locate main steam safety valves in containment containment generator tubeor route existing Safety valve discharge to containment is based on Seabrook rupture previously reported estimate.

Add an Improved Not cost beneficial. The original and updated PRA case NOATWS conservatively 130 independent availability of NOATWS 2 60K 139K >500K assume that ATWS events do not occur.

boron injection boron injection (126K) (292K) Cost to install independent boron injection system is based on Seabrook previously system during ATWS reported estimate.

Add a system of relief valves to Improved Not cost beneficial. The original and updated PRA case NOATWNS conservatively prevent equipment 60K 139K assume that ATWS events do not occur.

damage from availability after (126K) (292K) Cost to install additional relief capacity is based on Seabrook previously reported dmgfrm an A1VVS estimate.

pressure spikes during an ATWS Install an ATWS Increased ability Not cost beneficial. The original and updated PRA case NOATWS conservatively sized filtered to remove 60K 139K assume that ATWS events do not occur.

133 containment vent ratrhtfom NOATWS 4 2>500K torme dea reactor heat from (126K) (292K) Cost to install filtered vent with capacity for ATWS heat removal is based on Seabrook to remove decay ATWS events heat previously reported estimate.

Install digital Reduced Not cost beneficial. The original and updated PRA case LOCA05 conservatively break slarge probability of a 77K 181K assume that LOCA events, as a result of pipe failures, do not occur.

LOCA protection 17LCprtcin LOCA (a leak large break LOCA05 9 2 (6K (162K) (30)Cost (380K) >500K to install a digital break detectionsystem is based on Seabrook previously system before break) reported estimate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK - MAB.& PHASE 2 SAMA REVIEW ""

SBK % Risk Total Benefit($) Expecte SAM P Reduction Baseline (with 2.1 d SAMA Evaluati.n NuSAMA IProvmentil Description PRA Case 1. ... o multiplier) Cost vauaton

.- CF Pop. Internal & With Dose External Uncert ________.__________._-_______.___..____________-___.________-__.___

Prevents secondary side depressurization should a steam line break occur upstream of the Insallseondry main steam side gu ard isolation valves. Not cost beneficial. The original and updated PRA case NOSLB conservatively assumE side guard pipes Also guards NOSLB <1 0 5K 11K that steam line break events do not occur.

steam isolation against or (01K) (24K) Cost to install secondary side pipe guards is based on Seabrook previously reported valves prevents estimate.

consequential multiple steam generator tube ruptures following a main steam line break event Modify SEPS Improve Not cost beneficial. The original PRA case OSEPALL and the updated PRA case design to reliability of OSEPS conservatively assume guaranteed success of all manual actions to align and accommodate onsite power; load the SEPS diesel generators. The current design requires the operator to manually automatic bus reduce SBO align SEPS to the desired bus and to manually load SEPS to ensure power is available 154 loading and CDF OSEPS 8 2 64K 151K >750K ainSP otedsrdbsadt aulyla ESt nuepwri vial automatic bus cDFtriEuSi8n2 (135K (318K) to needed components. The proposed SAMA is to install a control system to perform contribution; s these actions automatically.

alignment remove (Plant dependence on Cost to install automatic control system is based on Seabrook previously reported Personnel) operator action estimate.

Install alternate offsite power Improve offsite source that power reliability bypasses the and switchyard. For independence of Not cost beneficial. The original and updated PRA case NOLOSP conservatively 156 example, use switchyard and NOLOSP 18 17 531K 1.24M >7M assume elimination of all LOSP events.

campus power SF6 bus duct; (1.2M) (2.7M) Cost to install alternate offsite power source that bypasses the current switchyard powei source to allow restoration source is based on Seabrook previously reported estimate.

energize Bus E5 of offsite power or E6 within a few (IPE) hours I I I I IIII 55 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I1- SEABROOK - MAB & PHASE 2 SAMA REVIEW K : Potent ia -0 R-- Cas Reduction Total Benefit($) Expecte SBKtent.... Redutis Baseline (with 2.1 :d SAMA SAMA Improvement Description PRACase multiplier) Cost Evaluation CDFbe Pop.~ Internal& With Numer..Dose External Uncert.

Provide independent AC power source for Reduce CDF of Potential cost beneficial SAMA. SAMA #157 was shown to be potentially cost battery chargers. long term SBO beneficial in the previous study. The previous and updated PRA case INDEPAC For example, sequences; 34K 80K conservatively assume that station batteries have AC power available for battery 157 provide portable extend battery INDEPAC <2 1 (72K) 8K 30K charging guaranteed success of AC power recovery to represent the benefit of generator to life to allow extended battery life.

charge station additional time Cost to implement portable battery chargers is expected to be less than the potential battery for recovery benefit.

(IPE)

Reduce CDF of long term SBO Not cost beneficial. The previous and updated PRA case INDEPAC conservatively Install additional sequences; assume that station batteries have AC power available for battery charging by assuminc 159 batteries extend battery INDEPAC <2 1 34K 80K >1M guaranteed success of AC power recovery to represent the benefit of extended battery (IPE) life to allow (72K) (168K) life.

additional time Cost to install additional batteries is based on Seabrook previously reported estimate.

for recovery Alternate cooling Not cost beneficial. The original PRA case NOSBO conservatively assumed eliminatior Modify EDG to both EDGs of all station blackout events by assuming guaranteed success of both DGs for all jacket heat would reduce events and independent of all support systems (control power, cooling, etc.). The exchanger CDF long term updated PRA case DGSW assumes success of SW components (valves) that are service water sequences associated with DG cooling and alignment of the SW system (ocean and cooling supply and return involving LOOP tower). Guaranteed success of these components and the resulting increase in SW to allow timely and loss of SW 25K 53K reliability is representative of the DG cooling water reliability gained from installing a 161 alignment of /cooling tower. A DGSW <1 1 (59K) (124K) 2M backup source of cooling water. Insights from this analysis are that the existing alternate cooling loss of service arrangement of SW cooling to the DGs is of a reliable design; and making the DGs less water source water / cooling dependent on SW does not provide a significant risk reduction because other train-(supply & drain) tower with a specific components, such as ECCS pumps, also depend on SW cooling.

from firewater, LOOP could RMW, DW, etc. result in EDG Cost of physical plant modifications and analysis judged comparable to other plants thai (Expert Panel) failure and non- presently do not have these features (Grand Gulf 10). Backup diesel cooling water recovery system is also addressed in SAMA #20.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1- SEABROOK- MAB & PHASE 2 SAMA REVIEW SBK Potential % Risk Total Be~nef it.($ Expecte Reduction Baseline (with 2.1 d SANMtA SAA Improvement .DecitoPRCaemultiplier) Cost Evaluation Nube CF Pop. Internal & With C -.F. Dose :External Uncert. __________________.._._._.--_______..._._-__________. __._

Extend long term Not cost beneficial. The original and updated PRA case CST01 conservatively assume operation of a continuous, successful CST suction source for EFW.

EFW without operator action for CST makeup Cost of expanding capacity of the CST is based on project scope of Installing a new Increase the for sequences (larger) safety grade condensate storage tank, which is judged necessary to achieve ful capacity margin that do not go to 35K 81K benefit. Cost of physical plant modifications and analysis are comparable to other 162 of the CST cold shutdown. CST01 <2 1 (73K) (171K) >2.5M plants that presently do not have this feature (Callaway SAMA #71).

(Plant Enhance CST Personnel) margin for design-basis seismic event with cooldown via SG and transition to RHR Reduce CDF of SBO sequences by improving overall reliability of EFW system independent of Not cost beneficial. The original PRA case TDAFW conservatively assume guaranteed AC power. An success of the turbine-driven EFW pump. For simplification, the updated PRA case Install third EFW additional pump assumes guaranteed success of the motor-driven pump, i.e., the EFW pump function is pump (steam- might also have 356K 835K success and independent of AC power. Thus, the benefit of installing an additional 163 driven) a Level 2 benefit TDAFW 5 12 (748K) (1.8M) >2M turbine-driven pump is conservatively high.

by maintaining (Expert Panel) coverage of SG Cost of installing an additional steam-driven EFW pump is based on Seabrook tubes thus previously reported estimate.

reducing the release potential for induced SGTR given high pressure core melt sequence 57 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I - SEABROOK - MAB & PHASE 2 SAMA REVIEW Total Benefit ($)

SB %Risk Ep~ecte NSMbASAA Potential Improvement -:.> Description Reduction Baeie(ih21 mliPRArCase d cSAMA Eauto Evaluation CDF Pop. Internal & With Dose External Uncert.

Modify 10" Condensate Possible Filter Flange to enhancement of Potential cost beneficial SAMA. The original and updated PRA case CST01 have a 2hos-inch long term core 35K 81K conservatively assume a continuous, successful CST suction source for EFW.

164 female fire hose damage CST01 <2 1 71) >40K adapter with sequences that (73K) (171 K) Cost of modifying the condensate flange is expected to be less than the potential isolation valve credit CST benefit.

(Plant makeup Personnel)

RWST fill from firewater during containment Could enhance injection - Modify long term Potential cost beneficial SAMA. SAMA #165 was shown to be potentially cost 6" RWST Flush containment beneficial in the previous study. The previous and updated PRA case NORMW 165 Flange to have a injection NORMW 5 2 57K 134K 50K conservatively assume guaranteed success of RWST makeup.

2%/-inch female sequences that (121 K) (283K) Cost of modifying the RWST flange is expected to be less than the potential benefit.

fire hose adapter would benefit with isolation from RWST valve makeup (Plant Personnel) 58 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I.- SEABROOK - MAB &'PHASE 2 SAMA REVIEW

% Risk Total Benefit () Expecte SK Potential Reduction Baeie(ih21 d SAMA SAMA Improv

°e:ment Description PRA Case multiplier) Cost Evaluation Numer- CF Pop. Internal & With Dose External. Uncert.

Not cost beneficial. The original PRA case RCPLOCA conservatively assumed that RCP seal LOCA events are eliminated. A more realistic PRA Case CSBX assumes tha CS division B of high pressure injection (CSB) is independent and does not rely on support systems (independent of AC / DC power, cooling, etc.). This case is used to represent a "parallel" pump with same suction as CS-B, credited for seal injection. The Install new PRA case is judged conservative in that it benefits not only seal injection but also independent seal Reduce CDF high pressure injection.

injection pump contribution from 167 (low volume RCP seal LOCA CSBX 22 34 1.1M 2.5M 6.4M Cost of this modification is estimated at greater than $6.4M. This modification was pump) with events driven by (2.3M) (5.3M) assumed to be the equivalent of adding one new high pressure injection pump powered automatic start seal cooling by a diesel rather than an electric motor with a suitable injection path and suction hardware failures source. In the Duane Arnold License Renewal application, the cost of this was one half (IPE) the cost of replacing pumps discussed in SAMA 25 above, the cost would be $10 million. In addition, Grand Gulf SAMA #61 estimated the cost of a similar plant change at >$6.4M.

It is noted that some of the potential benefits of this SAMA would be realized with SAMA

172, RCP shutdown seal.

Not cost beneficial. The original PRA case RCPLOCA conservatively assumed that RCP seal LOCA events are eliminated. A more realistic PRA Case CSBX assumes tha' Install CS division B of high pressure injection (CSB) is independent and does not rely on independent seal Reduce CDF support systems (independent of AC / DC power, cooling, etc.). This case is used to 168 (low volume RCP seal LOCA 11 M 2.5M represent a "parallel" pump with same suction as CS-B, credited for seal injection. The p(llump) wh 168 e tsdreal b CSBX 22 34 (2.3M) 25.3M) 6.4M new PRA case is judged conservative in that it benefits not only seal injection but also pump) with events driven by CSX2 4 (2.3M) (5.3M) high pressure injection.

manual start seal cooling hardware failures Refer above to SAMA#167 for approximate cost estimate.

(IPE)

It is noted that some of the potential benefits of this SAMA would be realized with SAMP

172, RCP shutdown seal.

Reduce CDF Not cost beneficial. The original PRA case RCPLOCA conservatively assumed that Install contribution from RCP seal LOCA events are eliminated. A more realistic PRA Case CSBX assumes tha' independent RCP seal LOCA CS division B of high pressure injection (CSB) is independent and does not rely on charging pump events driven by support systems (independent of AC / DC power, cooling, etc.). This case is used to (high volume seal cooling 1.1M 2.5M represent a "parallel" pump with same suction as CS-B, credited for seal injection. The 169 pump) with hardware CSBX 22 34 (2.3M) (5.3M) 6.4M new PRA case is judged conservative in that it benefits not only seal injection but also failures; improve high pressure injection.

manual start decay heat Refer above to SAMA#167 for cost basis.

(IPE) removal using It is noted that some of the potential benefits of this SAMA would be realized with SAMW feed & bleed #172, RCP shutdown seal.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1 - SEABROOK - MAB & PHASE 2 SAMAREVIEW Total Benefit ($) Expecte

% Risk.!

SBK Baseline (with 2.1 d SAMA Potential Reduction SAMA Description .PRA Case multiplier) Cost Evaluation Improvement Number Pop., IInternal 8 With CDF Dose. External Uncert. Ms I. .4-----------------------------------------.4 Replace the Not cost beneficial. The original PRA case RCPLOCA conservatively assumed that Positive RCP seal LOCA events are eliminated. A more realistic PRA Case CSBX assumes tha Displacement CS division B of high pressure injection (CSB) is independent and does not rely on Pump (PDP) with Reduce CDF support systems (independent of AC / DC power, cooling, etc.). This case is used to a 3rd centrifugal contribution from 1.1M represent a "parallel" pump with same suction as CS-B, credited for seal injection. The charging pump. RCP seal LOCA 2.5M 170 CSBX 22 34 6.4M new PRA case is judged conservative in that it benefits not only seal injection but also Consider low events driven by (2.3M) (5.3M) high pressure injection.

volume and seal cooling cooling water hardware failures Refer above to SAMA#167 for cost basis.

independence It is noted that some of the potential benefits of this SAMA would be realized with SAMP (Expert Panel) #172, RCP shutdown seal.

Potential cost beneficial SAMA. The original and updated PRA cases RCPLOCA and Evaluate Reduce CDF RCPL conservatively assume elimination of the loss of RCP seal cooling initiating event installation of contribution from (LRCPCS) and also assumes guaranteed success of seal cooling for transients, thus a "shutdown seal" transients with avoiding RCP seal LOCA events subsequent to a plant transient.

172 in the RCPs being seal cooling RCPL 34 49 1.5M 3.5M 2M Cost of installing the RCP shutdown seals is expected to be less than the potential developed by hardware failures (3.2M) (7.4M) benefit.

Westinghouse resulting in RCP seal LOCA It is noted that installation of the RCP low leakage shutdown seals will benefit SAMAs (Expert Panel) events #14, #25, #26, #55, #56, #59, #167, #168, #169, #170 (Table 1) and BE#1, and BE#2 (Table 2).

Improve reliability of reactor scram by Provide alternate providing Not cost beneficial. The original and updated PRA case NOATWS conservatively scram button to remote-manual assume elimination of all ATWS risk.

remove power capability to NOATWS 4 2 59.5K 139K >500K Cost of modifying the scram system to provide an alternate scram button is based on 174 from MG sets to remove rod drive (125K) (292K) >eabrook pously reporte estimate.

CR drives power should the Seabrook previously reported estimate.

(IPE) reactor trip breakers fail; reduce ATWS contribution 60 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1 - SEABROOI- MAB & PHASE 2 SAMA- REVIEW, BSB % R is k Be n e fit C Tot ali2", s) E x pe cte -" -.. . . .

SAMA Potential Decito ae Reduction Baseline (w~ith 2.1 d SAMA Eauto SAMAD Impo n - Descrption po .P PRA Case.

C multiplier) Cost Evaluation NumCrd Pop. Internal With :

Dose External Uncert.

Not cost beneficial. The original PRA case FIRE1 conservatively assumed complete elimination of the control room fire initiating event that results in a PORV challenge. A Fire induced refined PRA Case FIRE1A assumes guaranteed success of the operator action to close LOCA response Possible the PORV block valve during the postulated control room fire event (thus the CR fire procedure from reduction in CDF <1K <1K event is assumed to occur at its current frequency). The proposed SAMA is to improve 179 Alternate if mitigating fire- FIRE1A 0 0 (<1 K) (<2K) >20K operator procedures for coping with a small LOCA due to fire and opening of a PORV.

Shutdown Panel induced LOCA The procedure change would not eliminate, but potentially reduce the significance of (IPEEE) this event. Therefore, the estimated benefit is conservative for this SAMA.

Cost of modifying the operator response procedures and controls is based on Seabrook previously reported estimate.

Not cost beneficial. The original and updated PRA case SEISMIC01 conservatively assume complete elimination of relay chatter. As stated in the ER SAMA report, there Improve relay Reduce CDF is significant uncertainty in relay fragility and this is not necessarily addressed by 181 chatter fragility contribution from SEISMIC01 12 3 87K 204K >600K component replacement and is beyond state-of-the-art.

(IPEEE) relay chatter 0Cost of modifying/replacing existing relays is based on Seabrook previously reported estimate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I- SEABROOK - MAB & PHASE 2 SAMA REVIEW

-% Risk Total Benefit () Expecte SBK Potential Reduction Baseline (With 2.1 d SAMA SAMA Improvement Description PRA Case ___multiplier) Cost Evaluation Nube OE Pop. Internall. With

-> ____ Dose External Uncert.

Improve seismic Improve capacity of EDGs component Not cost beneficial. The original and updated PRA case SEISMIC02 conservatively 182 and steam-driven EFW fragility and reduce seismic SEISMIC02 <1 0 2.4K (6K) 5.6K (12K) >500K assume no seismic failures of the EDGs and turbine-driven EFW pump occur.

182 event Cost of upgrading the EDGs or the TD-EFW pump is based on Seabrook previously contribution to reported estimate.

(IPEEE) CDF Purge path is large opening.

Control/reduce Reduce time that the exposure time of Not cost beneficial. The original PRA case PURGE and the updated PRA case COP containment open path, <1K <1K conservatively assume that the containment purge valves are continuously in the closed 184 purge valves are improve COP 0 0 (<1 K) (<2K) >20K position and are not opened periodically.

lity of Cl, reduce Cost of procedural changes is based on Seabrook previously reported estimate.

(IPE) Cl failure contribution to large release Improve Install containment containment reliability by Not cost beneficial. The original and updated PRA case CISPRE conservatively 186 leakage reducing the CISPRE 0 0 4.4K 10.4K >500K assume complete elimination of pre-existing containment leakage.

monitoring potential for pre- (12K) (27K) Cost of installing leakage monitoring system is based on Seabrook previously reported system existing estimate.

(IPE) containment leakage 62 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE I1- SEABROOK - MAB & PHASE 2 SAMA REVIEW ik

% Total Benefit () Expecte SBK Risk Baseline (with 2.1 dSAMA Potential Evaluationn SAMA Descripton PRA Case Reduction multiplier) Cottion Cost Number Improvement N.CDF" Pop. 'Internal & With

______Dose External Uncert.

Not cost beneficial. The original and updated PRA case LOCA06 conservatively assume complete elimination of all ISLOCA risk contribution. However, improved leak Install RHR detection will eliminate some but not all ISLOCA events. For SAMA purposes, installing Reduce ISLOCA a leak detection system is assumed to reduce the ISLOCA frequency by 80%. Thus, isolation valve challenge to the PRA case upper bound benefit is estimated at $238K

0.8 = $190K.

leakage RHR by LOCA06 <1 48K 113K >500K 187 monitoring identification of (101 K) (238K) Cost to install a leakage monitoring system at the RHR isolation valves is judged system upstream valve comparable to other plants that presently do not have these features (Callaway SAMA (IPE) failure #111). This modification will require pressure and/or temperature transmitters installed in containment between isolation valves, the use of additional containment electrical penetrations to allow remote readouts/alarms in the control room to alert the operator that lower pressure piping is being challenged by RCS leakage.

Modify or analyze SEPS Allow all capability; 1 of 2 equipment to be Not cost beneficial. The original PRA case assumed a change to the SEPS success SEPS for LOSP run following criteria in that one of two SEPS DGS was capable of handling AC loads without a SI 189 non-SI loads, 2 LOSP with EDG SEPS 63K 148K >2M (LOCA) signal present, with no change to the manual alignment scheme. For of 2 for LOSP SI failure but (133K) (311 K) simplification, the updated PRA case conservatively assumes guaranteed success of al loads successful start SEPS hardware and no change to the current scheme of manual alignment.

and load of Cost to modify SEPS is based on Seabrook engineering estimate.

(Plant SEPS Personnel)

Add Eliminate current Not cost beneficial. The original PRA case NOSBO and recent PRA case NOSBO1 synchronization requirement for both conservatively assume elimination of all station blackout events by assuming capability to dead bus 224K 525K guaranteed success of both EDGs for all events and independent of all support systems 190 SEPS Diesel transfer from NOSBO1 22 6 (470K) (1.1 M) >6.4M (control power, cooling, etc.)

(Plant SEPS to normal The cost to install synchronization capability to the SEPS diesel is based on Seabrook Personnel) power engineering estimate.

Remove the Potential for Not cost beneficial. The original and updated PRA Case PCTES assume elimination of 135F some the inadvertent failure of the redundant temperature element/logic as a failure mode of temperature trip improvement in <1K <1K the associated PCC division for both loss of PCCW (A/B) initiating events (during the 191p teliminaiity of (<1 K) (<2K) >100K year) and loss of PCCW (A/B) mitigative function (mission time).

pumps by eliminating (Plant consideration of Cost and scope of modifying the temperature trip is based on Seabrook previously Personnel) spurious trip reported estimate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1 - SEABROOK - MAB.& PHASE'2 SAMA REVIEW ux

% Risk Total Benefit $) Expecte

-SBK Potential Reduction* Baseline (With 2.1 d SAMA SAMA Description PRA Case multiplier)CotEauin Numer mpoveen - DF Pop. InternalA With

____________Dose External Uncert.

Potential cost beneficial SAMA. SAMA #192 was shown to be potentially cost beneficial in the previous study. The updated benefit of the SAMA was estimated from the ratios of the previous flood model MAB result to the updated model MAB. A new specific SAMA model case was not performed.

Cost to install proposed flow reducing orifice is expected to be less than the potential Install flow orifice Reduce CDF benefit.

in fire protection contribution of Based on the previously estimated benefit of $161 K (nominal) and $307K (UB), the 192 system CB flooding due NOCBFLD 24 11 470K l.M 370K proposed SAMA to install a flow reducing orifice in the Control Building fire protection (New - Plant to fire protection (987K) (2.3M) system pipe continues to be potentially cost beneficial.

Personnel) pipe break Previous Flood model MAB: $1,042,683 (nominal), $1,982,048 (upper bound)

Revised SEABRK model MAB: $3,050,815 (nominal), $7,154,678 (upper bound)

Ratio increase: 2.92 (nominal), 3.61 (upper bound)

Nominal = 2.92 * $161K = $470K ($978K)

Upper bound = 3.61 * $307K = $1.1M ($2.3M)

Eliminate CSV167 AC Reduce Potential cost beneficial SAMA. SAMA #193 was shown to be potentially cost power containment 86K 201K beneficial in the previous study. PRA case CSV167 assumes guaranteed success of 193 dependence isolation failure CSV167 0 5 80K) (423K) 300K the operator action to close containment isolation valve CS-V-167 locally.

contribution of Cost to implement a change to the design of CS-V-1 67 is expected to be less than the (New- Plant CSV167 potential benefit.

Personnel)

Purchase or Not cost beneficial. The original and updated PRA cases MSSVRS assume success of manufacture of a the MSSVs to reseat.

"gagging device" that could be Improve release Cost to implement a safety valve gagging device is based on Seabrook previously used to close a mitigation for a <1K <1K reported estimate.

194 stuck-open SGTR event MSSVRS 0 0 (<1 K) (<2K) >30K steam generator prior to core safety valve damage (New - NRC RAI) 64 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 1 - SEABROOK - MAB & PHASE 2 SAMA REVIEW SBK Total Benefit () Expecte Potetia Risk - Baseline (with 2.1 dSM SAMA improent Description PRA Case Reduion multipier) Cost Evaluation Number - CDF Pop. Internal- With Dose External Uncert. ____________...._,_____________

Potential cost beneficial SAMA. NextEra has entered into the long range plan for a modification to improve the reliability of CC-TV-2171/2271 -1 & 2. Refer to BE #9 (Table 2)

New SAMA The SAMA concept is to install hardware changes to improve the reliability of the CCW systems and reduce the loss of CCW initiating event frequency. Based on inspection of the CCW PRA model, the component failures that contribute the most to Make PCC Train B the loss of CCW initiator are components associated with temperature 195 improvements to Temperature 144K 337K control/modulation. In the PRA, these components are modeled as temperature New PCCW Element CC-TE- CCTE1 3 (302K) (709K) 300K elements (TE) causing failure of the temperature control scheme. PRA case CCTE1 is SAMA temperature 2271 transmits used to represent the potential risk reduction benefit. This case conservatively control reliability false low assumes guaranteed success of the TE function for PCC Trains A and B that could fail PCCW during the year (as an initiator) and during the mission time (support system model). Hardware changes to improve temperature control reliability - update of existing equipment or provide additional redundancy in instrumentation / controls.

Cost to engineer and install improvements to CCW temperature control are expected to be less than the potential benefit.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 - SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic (BE*) Evn or*

(BE). or...._

RC RC I

E.I(;

vent Event

eatdSM

" SAMAWs

::

-and Proposed

. TReated : '.

PRA Case

% Risk

R::

Ieduction Rui Total

' Baseline . (with.($)%

Benefit multiplier) 2.1' .. Expected

-

-SAMA Cost

- :*.

Evaluation Initiating Event (1E)

I Group

_-______

Description SAMA(s)l

"___ I___ CD.

"__

Pop.

Dose Internal &

External With Uncert. __,

($)

-

______ ______________"__________________

Basic Event (BE) Related SAMAs Not cost beneficial. The SAMA concept is to enhance the operator's ability to align alternate cooling to the standby charging pump oil cooler in time to allow the standby pump to restart and restore RCP seal cooling before heatup of RCP seals. Success of the action avoids an RCP seal LOCA event. The PRA case conservatively assumes guaranteed success of the operator action to align alternate cooling. The cost of hardware changes to automate the alignment of alternate cooling will exceed the conservative Operator Action - Related SAMA #172. benefit.

BE #1 CDF Manual Alignment Provide automatic 340K 797K > 2.4 M HH.OALT1.FL LL5 of Alternate alignment of alternate OALTO 4 11 (714K 797K C pl o SELL Cooling to cooling based on (714K) (17M) Cost of physical plant modifications and Charging Pumps applicable signals analysis judged comparable in scope and complexity to STP SAMA #17, automation needed to protect RCP seals of 2.4M.

This SAMA is related to SAMA #172 (RCP shutdown seal). The importance of this SAMA would be reduced or eliminated with the installation of the RCP shutdown seal, which has been shown to be potentially cost beneficial.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 -SEABROOK BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event. '"-: -Total Benefit ($)'

(BE) or R Event:: : :.Related SAMA # : Reduction Baseline (with 2.1. ,Expected Event

-nitiati-...-- Group Descriptiand Proposed PRA Case multiplier) - SAMA Cost Evaluation SA(1E)* CD Pop. Internal & With1$

(IE).Dose ~Externa[ ýUncert.

Not cost beneficial. The SAMA concept is to improve CCW pump reliability (eliminate common cause pump failures) by installing an additional diverse CCW pump. PRA case PCCABCD conservatively assumes guaranteed success of the four existing component cooling water pumps provided the pumps have the necessary AC and DC power support systems. Based on this case, adding an additional pump will not significantly reduce Related SAMA #59. plant risk. Installation of an additional pump Install a diverse and would still rely on the same power supplies as BE #2 CDF PCCW Pumps A, independent CCW 335K 785K the existing pumps. An independent diesel-CCP11AIBIClD LL5 B, C, D Common pump, reduce (704K) (1.65M) driven CCW pump is judged not practical. The SELL Mode Failure to potential for common cost of installing an additional CCW pump is mode failure expected to significantly exceed the conservative benefit.

Cost to engineer and implement plant modifications and analysis judged comparable in scope and complexity to Columbia SAMA CW-07 estimated at $6.1M, which added a SW Pump to provide cooling to vital loads.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event Related SAM ". % Risk TotalI Be nef it(s)

ReatddtA' Baseline (with 2.1 Expected (BE) or RC Event anRrpsd R ae eduction mlile) SM otEauto Initiating Event Group Description adPooe R aemlile) SM otEauto (I) -- SAMA(s) CF Pop., Internal & With

____________

_________________________Dose External Uncert. ______ _________________

Not cost beneficial. The SAMA concept isto improve DC bus reliability (eliminate common cause bus failures) by installing an additional diverse DC bus. The PRA case conservatively assumes elimination of bus failures that could cause failure of the associated power division during mission time (support system model) by assuming guaranteed success of both buses.

It is noted that due to their relatively passive design, DC buses are relatively reliable and have a low failure rate. A hardware change that would significantly improve bus reliability, Related SAMA #16. for example adding a redundant bus within a BE #3 ODE DC Power Panels Improve Bus 11AIB 289K 678K > 1.8 M dvsoi ugdipatcl EDSG1B LL5 A, B Common reliability, reduce SWG11lAB 3 10 (608K) (1.42M) Cs oegne n mlmn ln DEW1AB SELL Mode Failure potential for common Cs oegne n mlmn ln mode failure modifications and analysis judged comparable in scope and complexity to Columbia SAMA AC/DC-01 estimated at $1.8M, which would provide additional DC Battery Capability.

This BE SAMA is considered similar to Seabrook Table 1, SAMA #16 (improve uninterruptible power supplies). An action has been entered into the Long Range Plan to assess future upgrade to the ELGAR inverters.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 -SEABROOK - BASIC EVENT& INITIATING EVENT SAMAIRE=VIEW.

Total Benefit($)

(BasEe RC Related SAMA #'s %Risk Baseline (with 2.1 Expected Initiatin.Event Group Description and Proposed PRA Case Redtion . multiplier) SAMA Cost EvaluationI (IE) AMs)CF Pop. Internal & :With($

_____________ ________Dose External. Undbrt.

Not cost beneficial. The SAMA concept is to install hardware changes to improve early containment injection reliability during various scenarios when AC power is available, recovered, and not available (SBO) to prevent RPV failure. PRA case XOINE0 assumes Related SAMAs #90, guaranteed success of "all" of the operator

100, #101 and #188, actions to perform early injection during these all of which are "intent AC power scenarios (actions XOINE1, Operator fails to met". XOINE2 and XOINE3. Procedures directing BE #4 start containment 291K 683K this action are sufficiently detailed and HH.XOINE1 .FA SELL injection early to Hardware change to XOINE0 <1 10 > 1.5 M thi in aresufficien detailean prevent RPV improve the reliability failre o cotainentanalysis. (612K) (1.43M) evaluated Any in the PRA human changes reliability are to procedures injection for judged not to have a significant beneficial sequences where impact on release risk.

cont'mt press is low.

Cost to engineer and implement plant modifications and analysis judged comparable in scope and complexity to Davis Besse SAMA CC-19 to automate controls for injection switch over is similar in magnitude and complexity was estimated at $1.5M.

Not cost beneficial. The SAMA concept is to incorporate hardware change to improve operator's ability to control/maintain stable hot standby conditions following transient/accident events. Operator must monitor and control Hardware change to primary and secondary conditions including Operator action to improve ability to PZR level and pressure, RCS temperature and BE #5 CDF maintain stable maintain stable 143K 335K SG levels to maintain stable hot standby HH.OHSBI.FA CDF plant conditions primary and OHSBa (301 K) (705K) >1M conditions for extended cooling using the SG.

with SG cooling secondary conditions PRA case OHSB0 assumes guaranteed during transients with plant in hot success of "all" actions OHSB1 (trans),

standby. OHSB2 (SBO), OHSB3 (SLOCA/SLB) and OHSB4 (SGTR) for maintaining stable hot standby conditions. Procedures directing these actions are sufficiently detailed and evaluated in the PRA human reliability analysis. Any changes to procedures are judged not to have a significant beneficial 69 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 -SEABROOK -. BASIC EVENT &INITIATING EVENT SAMA REVIEW Basic.:,

E tR (BE)iot

.: - . " a d A * -- Risk

- ..Total Benefit($)

En Related SAMA#R's %di*n Baseline (with 2.1 Expected (BE) or RC Evn and Proposed PRA Case Rdci ..... multiplier) SAMA Cost Evaluation Initiating Event Group Description SAA/s) CD"Dose xterna Uncer. ____"_____".___________"__"____

(IE)

. : ; t' ;:/ :. I~ii*i;;* :t : M.,s-

!i* " ]: .i ii i~ ur Pop.

Dose Internal With Extern'al& Uncert.: (,) - :*; * . ;

impact on release risk.

Cost to engineer and implement plant modifications and analysis judged comparable in scope and complexity to Davis Besse SAMA CC-1 9 to automate controls for injection switch over is similar in magnitude and complexity was estimated at $1.5 M.

Related SAMAs #90,

100, #101 and #188, Operator Fails to all of which are "intent BE #6 start containment met". Not cost beneficial.

HH.XOINE3.FA LL5 SELL injectionAC without early 291K 683K > 1.5 M power Hardware change for XOINE0 <1 10 (612K) (1.43M)

(gravity drain of automatic initiation of Evaluated under SAMA BE #4.

RWST) containment injection gravity drain, eliminate operator action Not cost beneficial. SAMA concept is to install hardware changes to reduce the likelihood of consequential loss of offsite power. PRA case ZZSY12 conservatively assumes complete elimination of all loss of offsite power events BE #7 CDF Loss of offsite #13, #156, #160 that occur subsequent to a plant trip ZZ.SY1 .FX LL5 power subsequent Eliminate ZZSY12 144K 337K >2M (consequential loss of offsite power).

SELL to plant trip consequential loss of (302K) (709K)

SE3 initiator offsite power events Cost of power system upgrades that would significantly reduce or eliminate the potential for consequential loss of offsite power is based on Seabrook previously reported estimate.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE,2- SEABROOK- BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event % Risk" -Total Benefit($)

(BE) or (BE)soriRC - RC..-

.... Event. ....... , . -Related... SAMA#s . . . . Redu tonu Reduction . : Baseline

- (with= 2.1 ,* *......

Expected - ::: :..

'InInititing it ia t in g :Evvent e nt G ro up "

Grou De scu~

r ip t io n Description .

and Proposed . . . . .. :.

PRA Case Po multiphier) - SAMA

. . . Cost. Evaluation (IE) CF p Internal &

PSAMA(s) With ($)

Dose External Uncert."

Not cost beneficial. PRA case ZZSY1 2 conservatively assumes complete elimination of all loss of offsite power events that occur subsequent to a plant trip (consequential loss BE #8 Loss of offsite #13, #156, #160 of offsite power).

ZZ.SY2.FX LERF power subsequent clmnt ZY2 4K 37 2 to LOCA initiator consequential loss of ZZSY12 (302K) (709K) >2M offsite power events Cost of power system upgrades that would significantly reduce or eliminate the potential for consequential loss of offsite power is based on Seabrook previously reported estimate.

Potential cost beneficial SAMA. NextEra has entered into the long range plan a modification to improve the reliability of CC-TV-2171/2271-1 & 2. Refer to new SAMA Case #195.

The SAMA concept is to install hardware changes to improve the reliability of the CCW systems and reduce the loss of CCW initiating event frequency. Based on inspection of the PCC Train A CCW PRA model, the component failures that BE #9 Temperature Make improvements 144K 337K contribute the most to the loss of CCW initiator CCTE2171 .FZ LL5 Element CC-TE- to PCCW temperature CCTE1 3 170K) 300K are components associated with temperature 2171 transmits control reliability (302K) (709K) control/modulation. In the PRA, these false low components are modeled as temperature elements (TE) causing failure of the temperature control scheme. PRA case CCTE1 is used to represent the potential risk reduction benefit. This case conservatively assumes guaranteed success of the TE function for PCCW Trains A and B that could fail PCCW during the year (as an initiator) and during the mission time (support system model). Hardware changes to improve temperature control reliability - update of existing equipment or provide additional 71 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis

-TABLE 2.- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event RltdSM %RikTotal Benefit Epce (BE)°oren. RC DEVron ad PRela opsed PRA Case# R Baseline (with 2.1 Expeed (B)o vntadPrpsd R R as eucinmultiplier) SAMA Cost: Evaluation Initiating Event Group Description SM~)CF Pp nenl& Wt $

(I)Dose External Uncert.

redundancy in instrumentation / controls.

Cost to engineer and install improvements to CCW temperature control are expected to be less than the potential benefit.

PCC Train B BE #9A Temperature Make improvements 144K 337K Potential cost beneficial SAMA.

CCTE2271 .FZ LL5 Element CC-TE- to PCCW temperature CCTE1 3 (302K) (709K 300K 2271 transmits control reliability Evaluated under SAMA BE #9.

false low BE #10 PCC Ht Ex 17A Improve PCC Ht Ex SAMA Intent Met. PCCW Heat Exchanger CCE17A.RT LL5 rupture/excessive reliability, eliminate CCE17 116K 273K Intent Met tubes have been replaced with titanium.

leakage during potential for heat (245K) (574K) Experience to date has found this to be the operation exchanger leakage best available technology.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2.- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic.Event - / ikTotal. Benefit ()

RCEvnt' Related SAMA#'s -Baseline. (With 2.1 Expected (BE) or R vn euto and Proposed PRA Case Rdcin -- Multiplier) SAMA Cost Evaluation Initiating Event .Group Description SM~)Pp nenl& Wt $

(I) DF Dose External Uncert.

Not cost beneficial. The SAMA concept is to provide hardware change for automatic restoration of high pressure injection sources following recovery of needed support systems.

PRA case ORHPI2 conservatively assumes that all actions to restore high pressure Operator action to injection long term are success; this includes restore IpoeteORHPI1, ORHPI2, ORHP13 and ORHPI4.

B#1charging/HPI/RCS the Imroeliblt/aat Current procedural guidance is judged BE #11for long term reiblt/aait fadequate Procedures directing these actions HH.ORHPI2.FA LL15 makeup after the operator to restore ORHPIO 3 4 111K 260K > 5M are sufficiently detailed and evaluated in the recovery of RCS makeup after (233K) (546K) PRA human reliability analysis. Any changes support systems support systems are to procedures are judged not to have a during various made available. significant beneficial impact on release risk.

trans/accidents Cost to engineer and implement plant modifications and analysis judged comparable in scope and complexity to Columbia; SAMAs CC-01 and CC-02 to diversify HPI that will reduce the probability of Human error at a cost of $5.2M.

BE #12 PCC Ht Ex 17B Improve PCC Ht Ex SAMA Intent Met.

CC17B.RT LL15 rupture/excessive leakage during reliability, potential foreliminate heat CCE17 2 4 116K 273K Intent Met (245K) (574K) operation exchanger leakage Evaluated under SAMA BE #10.

Not cost beneficial. The SAMA concept is to provide hardware changes to add redundant SWCT SWGR room fan or control equipment in the divisional SW SWGR room to improve Impoerlaiiyo reliability. PRA case SWAFN assumes that BE #13 CT SWGR Train proe reiailty ofG the ventilation fan and associated damper and SWF6.S 115 A FAN SWA-FN- thm e ntlto SWCT, SWGR 1 91 K 213K 480K temperature switch associated with Fan FN-64 SWFN4.S L5 64 fails to start on Roomint v oentltion fans 1(91 0WFK) (445K) are successful when support systems are deadfan failure available.

Cost to engineer and implement plant modifications and analysis judged comparable in scope and complexity to Columbia SAMA 73 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2-- SEABROOK -BASIC EVENT& INITIATING EVENT SAMA REVIEW

% Risk Total. Benefit ()

Basic

(BE)Event or:: (B)o...-RC:*; : ;=: Event CEetRelated :: .. **::

SAMA #'Reucio. [ :: = * =: ::*Reduction : Baseline (with 2.1 Expected; Initiating Event Group Descrito and Proposed PRA Case multiplier) SAMA Cost Evaluation

( E SAMA(s). Pop. Internal & With (-)

__________________Dose External Uncert: ______

or means of ventilation and estimated at 480K.

Also, Callaway SAMA 80 is similar and is estimated at > $1M.

Not cost beneficial. The SAMA concept is to provide a hardware change to improve the reliability of the SW Cooling Tower Fan 1-SW-FN-51A, by adding an additional or redundant cooling tower fan. PRA case SWFN assumes that the cooling tower cooling fan SW-FN-51A is completely successful when support systems are available. Benefit is overstated BE #14 SW Cooling Improve reliability of because model assumes that CT fans are Tower FAN SW- the SW cooling tower SWFN 74K 174K >1M needed 100% of the time and recovery of a SWFN51A.FS LL5 FN-51A fails to fans, eliminate (156K) (366K) failed fan (for which there is time) is not start on demand potential for fan failure credited.

Cost to engineer and install modifications is based on Seabrook estimate to utilize the abandoned unit 2 FN-51A. Large piping and MOV modifications to block U1 CT cell and align U2 CT cell when needed. Complete installation of U2 spray header and fan in addition to interfacing control changes.

Not cost beneficial. The SAMA concept is to provide hardware changes to add redundant SWCT SWGR room fan or control equipment Improve reliability of in the divisional SW SWGR room to improve BE #15 CT SWGR Train the SWCT SWGR reliability. PRA case SWAFN is representative SWAFN63.FS LL5 B FAN 63 fails SWA-FN-to start on Room ventilation fans, eliminate potential for SWAFN 91K (191 K) 213K (445K) 480K of SW-B Fan FN-63. This case assumes that the ventilation fan and associated damper and demand fan failure temperature switch are successful when support systems are available.

Cost to engineer and implement plant modifications and analysis is same as SAMA 74 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 - SEABROOK- BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event R ela te d S AMA Ws Ris Risk Reduction* BTOtal e (w ith ($)%

aselinBenefit 2. Ex pe cte d Evaluation (BE) or; Ev enti , .

Initiatin Evt Gu Dand Proposed - PRA Case mutiper) SAMACost..Evaluato (IE) IPI SAMIVA(s) CDF Pop. Internal & With .$)

IitiatingEvent

!-Group Descr-Dose External Uncert.

BE #13.

Not cost beneficial. The SAMA concept is to install hardware changes to improve reliability of sump alignment. PRA case XOSMPO conservatively assumes guaranteed success of the operator action to align containment sump recirculation "late" after core melt, given recovery of Containment Building Spray (CBS).

Provide a hardware BE #16 Operator aligns modification for auto- Procedures directing this action are sufficiently HH.XOSMP1.FA SELL containment sump control, eliminate XOSMP0 <1 61K 142K > 1.5 M detailed and evaluated in the PRA human recirculation after operator action to (128K) (299K) reliability analysis. Any changes to procedures core melt align sump after core melt. are judged not to have a significant beneficial impact on release risk.

Cost to engineer and implement plant modifications and analysis judged comparable in scope and complexity to Davis Besse SAMA CC-1 9 to automate controls for injection switch is similar in magnitude and complexity was estimated at $1.5 M.

75 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW

~

Reiatd SAM .Total Benefit (s)

Event easic RsSK Baseline (with 2.1:. Expected (BE) or r.RC Event Reduction multiplier) SAMA Cost. Evaluation (1E) SAMA(s) CDF Pop. .Internal'& With.. $

__________Dose External Unceirt.

Not cost beneficial. The SAMA concept is to install a leakage detection system having the proper sensitivity to detect leakage. Thus, upon detection of a leak, actions would be taken to identify the leakage source and take actions to reduce leakage. PRA case CISPRE conservatively assumes complete elimination Related SAMA #186. of the probability of all pre-existing containment leakage; small leakage BE #17 Small pre-existing Hardware or (CIS.PRE) and large (CILPRE). Procedures ZZ.CIS.PRE.EXI SELL unidentified eliminate or reduce CISPRE <1 4K 10K 50K to 1OOK directing this action are sufficiently detailed ST SE3 containment elimiat or reduce (12K) (27K) and evaluated in the PRA human reliability leakage likelihood of small pre-existing unidentified analysis. Any changes to procedures are leakage judged not to have a significant beneficial impact on release risk.

Cost to engineer and install hardware system for leakage detection system is based on Seabrook previously reported estimate.

Not cost beneficial. SAMA concept is to install additional DG to improve overall reliability of onsite emergency power. PRA case NOSBO1 conservatively assumes elimination of all station blackout events by assuming guaranteed success of onsite emergency diesel generators. This assumes complete independence of DG support systems (DC BE#18 CDF DG-1A fails to run Related SAMA #9, 224K 525K power, SW). Thus, the benefit of modifying DGDG1A.FR3 SELL for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months #10,#14,#155. NOSBO1 22 (470K) (1.1M) 2M. the onsite electrical power system to add or SE3 modify a DG to substantially improve reliability and reduce/eliminate DG start and run failures, is conservatively high.

Cost to engineer and install additional DG needed to significantly improve reliability of onsite power based on Seabrook cost to install the SEPS DGs exceeding $5M. Also Davis-Besse SAMA AC/DC-1 4 to install a Gas 76 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 - SEABROOK - BASIC EVENT & INITIATING- EVENT SAMA REVIEW Basic Event - % Risk ~ oa eei s (BE) r R. Event ... Related SAMA WRduction Baseline (with 2.1 Expected and Proposed _PRA Case '.__

multiplier) SAMA Cost>. Evaluation Initiating Event 'Group~

Description:

.SM()Pp nenl& Wt $

lI) DF Dose External Uncert.

turbine is estimated to be at least 2M.

BE #19 Not cost beneficial.

DGDG1B.FR3 CDF DG-1B fails to run Related SAMA #9, NOSBO1 22 6 224K 525K 2M SELL for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months #10, #14, #155. (470K) (1.1M)

SE3 Evaluated under SAMA BE #18.

Not cost beneficial. The SAMA concept is to install a control system to automatically close the SEPS DG breaker to the desired bus. The PRA case OSEPS conservatively assumes guaranteed success of all manual actions to Operator fails to Related SAMA #154. align and load the SEPS diesel generators.

BE #20 CDF breaker from Hardware change for 64K 151K The current design requires the operator to HH.OSEP2Q.FA SELL MCB, given auto closure of SEPS OSEPS 8 2 (135K) (318K) >750K manually align SEPS to the desired bus and to SE3 seismic SI signalevent with breaker operator toaction eliminate manually load SEPS to ensure power is available to needed components.

Cost to install automatic control system is based on Seabrook previously reported estimate 77 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2.- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event RelaTeAT A.#s A i %Risk Total Bnfit (BE) ore Event-Reduction Baseline (with"I) 2.1 Expected and Proposed PRA Case . multiplier). . >SAMA Cost Evaluation It(IE)v Group Description SAMA(s) CDF Pop. Internal & With ($)

Dose External Uncert.

Not cost beneficial. SAMA concept is to modify the SEPS electrical power system by installing or modifying a DG to substantially improve reliability and reduce /eliminate DG start and run failures. PRA case SEPS Related SAMA #9, conservatively assumes elimination of all BE #21 CDF 1-SEPS-DG-2-A #14, #189. SEPS DG hardware failures (assumes SEPSDG2A.FR3 SELL fails to run within Elimination of all SEPS 6 2 63K 148K >2M guaranteed success of SEPS DG A and B).

SE3 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months potential for SEPS (133k) (312K) failure Cost to engineer and install additional DG needed to significantly improve reliability of onsite power based on Seabrook cost to install the SEPS DGs exceeding $5M. Also Davis-Besse SAMA AC/DC-14 to install a Gas turbine is estimated to be at least 2M.

Related SAMA #9, BE #22 CDF 1-SEPS-DG-2-B #14, #189. 63K 148K Not cost beneficial.

SEPSDG2B.FR3 SELL fails to run within Elimination of all SEPS 6 2 (133k) (312K) 2M SE3 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months potential for SEPS Evaluated under SAMA BE #21.

failure Not cost beneficial.

BE #23 DG1A and DG1B DGDG1A/1B. SELL common mode Related SAMA #9, NOSBO1 22 6 224K 525K 2M Evaluated under SAMA BE #18.

FR3 SE3 failure to run for #10, #14, #155. (470K) (1.1 M) 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months Operator fails to Related SAMA #154.

BE #24 SELL close SEPS Hardware change for 64K 151K Not cost beneficial.

HH.OSEP1Q.FA SE3 breaker MCB, givenfrom auto closure breaker of SEPS to eliminate OSEPS 8 2 (135K) (318K) >750K Evaluated under SAMA BE #20.

seismic event operator action BE #25 Operator fails to Related SAMA #193.

HH.OC12Q.FL SE3 close CSV-167 Provide a hardware OC12 This SAMA basic event candidate is related to manually/locally modification basic event CSV1 67.FTC and SAMA #193, 78 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- .SEABROOK- BASIC, EVENT & INITIATING EVENT SAMA REVIEW - . .

Basic Event " o, Rs - Total BenefitR($)

(BE) or.. RC ... Ev.e.nt-.

Related SAMA #Ws Reduction.,

. Baseline (with 2.1 Expected Evaluation and Proposed PRA Case multiplier) SAMA Cost Evaluation (IEDecritin' AMAs)

Initiating.Event Group DF Pop.

Dose Internal External

& With($

Uncert. ________________-___________________

(additional signals or which has been shown to be potentially cost remote capability) to beneficial based on assumed replacement of allow closure of V-167 MOV with FC AOV. Refer to SAMA #193.

Potential cost beneficial SAMA. This BE SAMA is related to SAMA #193, which was shown to be potentially cost beneficial in the previous study. PRA case CSV1 67 assumes BE #26 Penetration X-37 Related SAMA #193. guaranteed success of the operator action to CSV167.FTC SE3 Isolation MOV Hardware MOVchange CS-V-167 fails to eliminate AC to CSV167 86KK)

(181 201K (422K) guaa close conteed locally. t isolation valve CS-V-167 close on demand power dependence Cost to implement a change to the design of CS-V-1 67 is expected to be less than the potential benefit.

Not cost beneficial. This BE SAMA is related to SAMA #163 to install an additional steam-driven EFW pump. The original PRA case TDAFW conservatively assume guaranteed success of the turbine-driven EFW pump. For simplification, the updated PRA case assumes BE #27 Turbine Driven Related SAMA #163. guaranteed success of the motor-driven pump, FWP37A.FR SE3 Pump FW-P-37A Install additional EFW TDAFW 5.3 12 356K 835K >2M i.e., the EFW pump function is success and fails to run pump (steam driven) (748K) (1.75M) independent of AC power. Thus, the benefit of installing an additional turbine-driven pump is conservatively high.

Cost of installing an additional steam-driven EFW pump is based on Seabrook previously reported estimate.

BE #27A Turbine Driven Related SAMA #163. TDAFWNot cost beneficial.

FWP37A.FS1 SE3 Pump FW-P-37A Install additional EFW 5.3 12 (748K) (1.75M) >2M fails to start pump (steam driven) Evaluated under SAMA BE #27.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic vent -Total Benefit($

(BE) or.Related SAMA #'s % Ri Baseline (with 2.1

Expected tandProposed PRACase multiplier) SAMA Cost Evaluation Initiating Event~ ~Group Description Sandropsed PACae Rduto

IE) 1 S AD Pop. Internal & -With Dose External Uncert. __________________

Related SAMA #9, Not cost beneficial.

BE #28 1-SEPS-DG-2-A #14, #189. 63K 148K SE3 fails to start on Elimination of all SEPS 6 2 2M Evaluated under SAMA BE #21.

SEPSDG2A.FS demand potential for SEPS (133k) (312K) hardware failure Related SAMA #9, Not cost beneficial.

BE #29 1-SEPS-DG-2-B #14, #189.

SEPSDG2B.FS SE3 fails to start on Elimination of all SEPS 663K 148K 2M Evaluated under SAMA BE #21.

demand potential for SEPS (133k) (312K) hardware failure Operator action Implement hardware Not cost beneficial. SAMA concept is to install BE #30 for SI termination change to improve hardware to significantly improve reliability of HH.OTSO3.FA CDF given successful reliability of SGTR OTSI0 3 1 26K 61K >300K operator termination of SI for SGTR mitigation.

LERF cooldown and control, eliminate or (55K) (128K) Cost to install automatic control system is depressurization reduce operator failure based on Seabrook previously reported for SGTR to terminate SI estimate.

Not cost beneficial. SAMA concept is to install Operator Aligns Related SAMA #105. hardware modifications to improve reliability of

31 ECCS for Low Hardware change to 12K 27K ECCS transfer to long term recirculation. PRA HH.OLPR2.FA CDF Pressure Sump improve reliability of OLPR 3(25K) (58K) >100K case OLPR conservatively assumes Recirculation for ECCS transfer to long guaranteed success of the operator action to MLOCA term recirculation complete/ensure the RHR/LHSI transfer to long term recirculation during large LOCA events. The results of this case study show 80 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 -SEABROOK --BASIC EVENT & INITIATING EVENT SAMVA REVIEW Basic Event Reae AA~% Risk ...a Bnfi $

(BE) or RC Event Reduction Baseline (with2 Expected InitiatingEvent:

Initiating Ee Group G Descri....ption .*

Description .

and Proposedl PRA Case " " .. multiplier) SAMA , Cost: ,.. Evaluation "

(IE) - SAMA(s) CDF Pop. Internal & With ($)

_*"__-_.._ .. :- .*- Dose External Uncert.

that the operator action does not contribute significantly to core damage frequency.

Cost to engineer and implement control circuitry to delay containment spray actuation for large LOCA is based on Seabrook previously reported estimate.

Not cost beneficial. The SAMA concept is to provide hardware changes to improve operator ability to control/maintain stable hot standby conditions following transient/accident events Hardware change to due to CR fire. PRA case OHSB670 Operator action to improve ability to assumes success of operator actions OHSB6 BE #32 maintain stable maintain stable (transient) and OHSB7 (w/seal LOCA)

BElaintaconditionstabl maintaind stae 6occurring during a control room fire with HH.OHSB6.FL CDF plant SG with conditions cooling primary andconditions secondary OHSB670 3 1 29K (61 K) 68K (143K) >420K evacuation the benefit isand control at the RSSP. Thus, conservative.

during transients, with plant in hot CR fire events standby during CR fire Cost to engineer and implement plant events modifications and analysis judged comparable in scope and complexity to Grand Gulf SAMA 39 and 55, which provide proposals to improve ability to maintain stable primary and secondary conditions with plant in hot standby during CR fire events; estimates are >$420K.

Not cost beneficial. The SAMA concept is to provide a hardware change that would significantly improve the operator action reliability and capability to control EFW flow Hardware change to and SG level during various transients Operator fails to improve operator including SBO. PRA case OSGLC0 assumes BE #33 control SG level reliability or provide 29K 68K success of actions OSGLC1 (via EFW/SUFP HH.OSGLC3.FL CDF locally, with EFW automatic feature to OSGLCO 2 1 (62K) (144K) >500K through EFW discharge), OSGLC2 (via thru EFW control SG levels via EFW/SUFP through EFW discharge), and Discharge EFW discharge OSGLC3 (locally via EFW thru EFW pathway discharge), and OSGLC4 (control via SUFP through MFW Disch).

Cost to engineer and implement plant modifications and analysis judged comparable 81 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2.- SEABROOK -:BASIC EVENT & INITIATING EVENT SAMA REVIEW BasccEvent % R.is Total Benefit($)

BaicEvntRelated SAMA W~s Baseline.(with 2.1. Expected (BE)itio*rvent Roup Eves int : and Proposed PRA Case Reduction multiplier) SAMA Cost"- Evaluation

.Initiating Event Group ~Description SAAv)alpuItenationh $

. (IE) - :A - . .' D Pop. Internal& With Dose External Uncert.

in scope and complexity to Callaway SAMA 163,which estimates a hardware change to increase reliability to feed steam generator secondary side at $500K.

Not cost beneficial. The SAMA concept is to provide a hardware change that would significantly improve the reliability of the 4kV electrical switchgear, Buses 5 and 6 and thus reduce or eliminate bus failures, including assumed common mode failures. PRA case SWGE561 conservatively assumes elimination of Bus E5 and E6 random failures that could cause an initiating event (IE model) and/or fail BE #34 4KV Emergency Ithe associated power division during mission ECDF Buses 5 and 6 Im104K 244K >1.2M time (support system model) by assuming EDESWG56.FX C u reliability, eliminate SWGE561 3 2K) guaranteed success. It is noted that due to SE3 Fault (Common potential for bus fault (219K) (513K) their relatively passive design, 4kV buses are relatively reliable and have a low failure rate.

Cost to engineer and install modifications is based on Seabrook estimate to design additional bus to achieve improvement in bus reliability with a cost of >$1 M. Bus reliability improvements is also similar in scope to SAMA #16 (improved uninterruptible power supplies), at a cost of $2M.

Not cost beneficial. The SAMA concept is to provide a hardware change that would significantly improve the reliability of feeding Operator Hardware change to the faulted SG during SGTR sequences to BE #35 establishes feed improve operator 21K 50K scrub/reduce release to the secondary plant.

HH.XOEFW1.FA LERF to faulted SG prior reliability to feed a XOEFW 0(44K) (104K) > 500K PRA case XOEFW assumes success of the to significant faulted SG during operator action HH.XOEFW1.FA.

release SGTR Cost to engineer and implement plant modifications and analysis judged comparable in scope, complexity and cost to hardware 82 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE2 - SEABROOK - BASIC EVENTA&INITIATING EVENT SAMA REVIEW Basic Event Related .AA#sisk Total Benefit(($)

(BE) or- RC Event Reduction Baseline (with 2.1 Expected Initiating Event Group De"criptlon and Proposed IPRA Case . multiplier) SAMA Cost - Evaluation (iE) - . SMA(s) CDF Pop. Internal & With ($)

C. Dose External Uncert...

changes estimated for Basic event #33, which estimates a hardware change to increase reliability to feed steam generator secondary side at $500K.

Not cost beneficial. The SAMA concept is to provide hardware changes to improve operator ability to control/throttle ECCS flow for only certain scenarios when the containment sump is not available (during SLOCA and ISLOCA).

PRA case ORWMZ assumes guaranteed success of the operator action. Thus, the benefit is conservative.

Operator action to BE #36 minimize ECCS Hardware change to The cost of hardware changes needed to HH.ORWMZ1.F flow w/ sump improve operator 15K 35K realize the benefit are expected to significantly A LERF recirc. failed reliability or provide ORWMZ 2 0 (32) (74K) exceed the upper bound benefit and no further during SLOCA automatic feature to refinement of the benefit or cost estimate is and ISLOCA throttle ECCS warranted.

sequences Cost to engineer and implement plant modifications and analysis judged comparable in scope, complexity and cost to hardware changes estimated for Basic event #33, which estimates a hardware change to increase reliability to feed steam generator secondary side at $500K.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW BasicBEvent Related SAMA #'s ' Risk - Total Benefit($)

(BE) or. RC W ReductionA Baseline (with 2.1 Expected Event and Proposed PRA Case -:ý. Rdt .. multiplier) SAMA Cost Evaluation, Initiating Event Group Description - SAMA(s) Pop . ' & With (IE) CDF Pp nenl& Wt $

_______ _ . - . "-Dose External Uncert .

Not cost beneficial. The SAMA concept is to provide hardware changes to improve operator ability to control RCS cooldown and depressurization for only certain scenarios where the containment sump is not available Cooldown and (during SLOCA and ISLOCA). PRA case depressurize RCS Hardware change to ORWCD1 assumes guaranteed success of BE #37 to minimize leak improve operator the operator action. Thus, the benefit is HH.ORWCD1 .F LERF w/ sump recirc. reliability or provide ORWCD1 <1 0 5.3K 12K > 500K conservative.

A failed during automatic feature to (11 K) (26K)

SLOCA cool & depress RCS Cost to engineer and implement plant sequences modifications and analysis judged comparable in scope, complexity and cost to hardware changes estimated for Basic event #33, which estimates a hardware change to increase reliability to feed steam generator secondary side at $500K.

Not cost beneficial. The SAMA concept is to provide hardware changes to improve operator ability to maintain stable primary and secondary conditions to extend SG cooling Operator (during SLOCA and ISLOCA). PRA case maintains stable Hardware change to ORWLT1 assumes guaranteed success of the BE #38 primary &improve operator operator action. Thus, the benefit is HH.ORWLT1 .FA LERF conditions for reliability or provide 5.3K 11K conservative.

extend SG automatic feature to ORWLT1 <1 0 (11 K) (24K) cooling (hot maintain stable plant standby) during conditions. Cost to engineer and implement plant modifications and analysis judged comparable LOCA or SGTR in scope, complexity and cost to hardware changes estimated for Basic event #33, which estimates a hardware change to increase reliability to feed steam generator secondary side at $500K.

Initiate makeup to Hardware change to Not cost beneficial. The SAMA concept is to BE #39 RWST, given improve operator provide hardware changes to improve operator HH.ORWIN1 .FA LERF SLOCA w/Recirc reliability or provide ORWIN <1 4K 9.3K > 500K ability to initiate makeup to the RWST to Failure (LOCA, automatic feature to (8.4K) (20K) extend ECCS injection (during SLOCA and SGTR) initiate makeup.RWST ISLOCA) with recirculation failed. PRA case ORWIN1 assumes guaranteed success of the 84 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE2 - SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event Related SAMA% Rk Total Benefit : Expected..

..(BE),or ~ RC EventReuto and Proposed PRA Case Reductio multipiier), SAMA Cost Evaluation Initiating Event (IE)* ,, [ Gop ,,,! Description

,: : : SM~)Pp

'* ' : : nenl&& ýý CDF : Pop.: Internal* Wt Vl .

i With: $ : ::-: ':* *. ,,: ,

Gru CF Dose External Uncert.

operator action. Thus, the benefit is conservative.

Cost to engineer and implement plant modifications and analysis judged comparable in scope, complexity and cost to hardware changes estimated for Basic event #33, which estimates a hardware change to increase reliability to feed steam generator secondary side at $500K.

Not cost beneficial. The SAMA concept is to provide hardware changes to improve the reliability of the low pressure permissive signal needed to align the RHR suction. PRA case PS40XA assumes guaranteed success of PS403A pressure HPSY403A (Train A) and PSY405A (Train B).

BE #40 switch fails high

40XAs2witch.-fails..hi50h ardwarethechange to Thus, the benefit is conservative.

RCPSY403A.FM LERF (press. permissive improve the reliability PS40XA 9K 21K to open RHR permissivessure Cost to engineer and implement plant suction RC-V-23) permissive signal. modifications and analysis judged comparable in scope, complexity and cost to hardware changes estimated for Basic event #33, which estimates a hardware change to increase reliability to feed steam generator secondary side at $500K.

Not cost beneficial.

PS405A pressure Hardware change to BE #41 switch fails high improve th bit RCPSY405A.FM LERF (press. permissive ofproelow reiaiiy PS40XA 2 0 9K 21K > 500K Evaluated under SAMA BE #40.

to open RHR f the low pressure suction RC-V-87) permissive signal.

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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis

.TABLE2 - SEABROOK - BASIC EVENT U&INITIATING EVENT SAMA REVIEW Basic Event . . % Risk TotaloBenefith($) E (BE) o..r (E.r RCEetRelated RC.- - SAMA #5s -

and Proposed, PRA Case Redutio eu.... Baseline (with. 2.1 multiplier) Expected SAMA Cost Evaluation initiating Event ,Group. Description SAAvalupaItrnltiWthon$

(I) DF Dose External Uncert.

Not cost beneficial. The SAMA concept is to provide hardware modifications to improve the relief valve reliability to open when demanded for ISLOCA sequences. PRA case RCVR RHR Train A Hardware change to gaate ucs fbt eifvle BE #42 LEF Suction Relief improve the reliability RCVR <1 2 23.5K 55K > 500K guRCV4antee suCcess tof bothnanrecleovles RCV24.FTO LEE Valve failure to of relief valve opening (50K) (116K) open on demand Cost to engineer and implement plant modifications (redundant relief valve at each RHR suction location) is to significantly exceed the benefit.

Not cost beneficial.

RHR Train B Hardware change to BE #43 LEF Suction Relief improve the reliability RCVR <1 2 23.5K 55K > 500K Evaluated under SAMA BE #42.

RCV89.FTO LEE Valve failure to of relief valve opening (50K) (116K) open on demand 86 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 - SEABROOK"' BASIC EVENT & INITIATING EVENTSAMA REVIEW Basic Event

!:*

I Basc~~~~~~~vent~~~~

.--.

*. .*.;--*

-. * * .;*;:

.*i*: ---

. SAMA Related

-I..Related SAMA #s .

,*.

'

. ""

-- . ..-

" "

-

isk oRisk . ..

" * .:. _

Total Benefit ($)

.:. -*...

,*Baseline (with 2.11**

' -.

Expected:

..

...

i-

-.

"--

...

-.-

"*

IGroup

...

Initiating. vn

,

ru (lE)~ I

"

(!E!*::

-SAPop..

,and DescriptionSAA)Doe i *

i*:

Proposed

'....

PRA Case

CDF.:I Dose Etra multiplier)

.Internal Unet

& Uncert.

External;'I Rth~

SAMA Cost

______

. . .: I -.

___________________

__________________

. .

Evaluation

-

Initiating Event (IE) Related SAMAs Not cost beneficial. SAMA concept is to install hardware changes to improve the seismic response of the plant. PRA case E7T Related SAMA #181, assumes complete elimination of the 0.7g

182. seismic initiating event and therefore provides IE #1 CDF Seismic 0.7g Hardware changes to E7T 8 2 77K 181K >500K a conservative benefit.

E7T Transient Event reduce or eliminate (162K) (380K) impact of 0.7g seismic events.

Cost to engineer and install upgrades is based on Seabrook previously reported estimate.

Not cost beneficial.

IE #2 CDF Seismic 1.0g Transient Event Refer to initiator E7T.

ElOT Evaluated under SAMA IE #1 Not cost beneficial. LOSPW initiating event is covered by existing SAMAs. The NOLOSP case conservatively maximizes the benefit by assuming that all LOSP initiating events are completely eliminated.

Related SAMA #2, #9, Cost of physical plant modifications and

10, #13, #14, #16, analysis, particularly to protect the plant from Loss of offsite #20, #24, #154, #155, loss of offsite power due to weather-related IE #3 CDF power due to #156, #160, #161, NOLOSP 18 17 531K 1.24M >3M events is judged comparable to burying power LOSPW weather-related #190 - all are (1.2M) (2.7M) lines to protect the lines from possible weather events hardware changes to impacts (refer to SAMA # 24).

reduce the risk of LOSP.

It is noted that Seabrook Station has recently completed a multi-phase, multi-million dollar, comprehensive project to improve the reliability of the electrical switchyard. These switchyard upgrades will enhance the reliability of offsite power including weather-related events and should result in an overall 87 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2.. SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW-Basic*,Event..- : ,I .-*: :. .%'is

= Baseline iwIt -h 2.1 ,:: Expected:.: :::

Basic Event - .. .%- *:: ,. - .:: :; :," ': . / Risk Total: Bene t...($) :*-" - *:: :

(BE) or RC_ EventR Reduction Baseline (wt 2 Expected Evaluation Initiating Event Initiating.-vent: -Grou G.roup. Descriptionand

.:*: Description : :* Proposed

, , , :: PRA Case: _ _. multiplier)

. . SAMA, ,Cost

. * : : i:. - -- :::: Evaluation

. *

(IE); AAs D Pop. Internal & With($

,. . _-. .. :. _ *]. D External E n .Uncert.

uc 1"Dose reduction in loss of offsite power initiating event frequency.

Not cost beneficial. Initiator F4TREL models a major rupture of a high energy pipe (condensate, steam, etc.) located in the vicinity of the Relay Room. Baseline modeling of this initiator conservatively assumes that the high energy break can impact the relay room structure resulting in damage to relay TB flood due to Provide analysis and equipment and loss of offsite power. The PRA rupture of HELB hardware changes to case F4TREL conservatively assumes IE #4 piping in TB with protect Relay Room 46K 107KK complete elimination of this initiator. The Sfrom CiFcF4TREL 5 1 (97K) (225K) >300K proposed SAMA concept is to perform a Relay Room & postulated HELB detailed structural analysis and add structural offsite power. impact. support and/or guards to the relay room structure and adjacent high energy piping to limit or prevent the assumed pipe break impact on the relay room.

Cost to engineer and implement plant modifications and analysis based on scope comparison to other Seabrook modifications.

88 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2.- SEABROOK - BASIC7EVENT & INITIATING EVENT SAMA REVIEW Basic Event ...:::*.:. .. ....

"::*!:. : ::... .Related Related SAMAS #s ". ,. .Risk..

. - 1=Baselfne T Benefit (')

(with2.1* Expected . .... .. - * :i :

(BE).or. RC Event~ Reduction Baeie(th21H Epcd Initiating Event Group Description and Proposed PRA Case ____ multiplier) SAMA Cost Evaluation (IE) ~, AAs D: Pop.ý Internal & With. s

(!E__________

.=Dose External Uncert.

Not cost beneficial. The SGTR initiating event is covered by existing SAMAs that have been shown to be not cost beneficial. PRA case SGTR conservatively assumes complete elimination of the SGTR initiating event in IE #5 ODE Steam Generator elated SAMA #119, 67K 157K >500K addition to pressure and thermal-induced tube SGTR LERF tube rupture #129. # 41K) (329K) rupture.

Cost to engineer and install upgrades aimed at eliminating SGTR based on Seabrook previously reported estimate.

Not cost beneficial. Initiating event is covered by existing SAMAs. Modifications to significantly reduce/eliminate reactor trip risk are judged not cost beneficial based on assumed complete elimination of initiator RXT1.

Related SAMA - all Cost of physical plant modifications judged BE SAMAs are related comparable in scope and complexity to other to plant trip. plants that do not have these features, for IE #6 Reactor trip with Improve overall 205K 481K example Callaway SAMA 65 and Seabrook RXT1 CDF condenser Seabrook Station RXT1 4(431 K) (1.01 M) 19M SAMA 65 ($30M) for digital controls feedwater available reliability; reduce upgrades.

potential for plant trip initiating event Seabrook Station is engaged in an ongoing a frequency. multi-phase, multi-million dollar project to install a digital feedwater control system and digital electro-hydraulic control system. These upgrades replaced obsolete components and enhance the reliability of the existing control systems and should result in an overall reduction in reactor trip initiating event frequency 89 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE2 - SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event % ikTotal Benefit()

(B~e)or RC

Ev-.t Related SAMA #'s % Risk Baseline (with* 2 Expected Initiating Event Group

.. Description and Proposed PRA Case Reduction multipler)' SAMA Cost - . Evaluation (1V -IE - . AMFs Pop;. Internal With($

"Dose CDF External Uncert.-

Not cost beneficial. Initiating event is covered by existing SAMA. The LOCA05 case conservatively maximizes the benefit by assuming that all pipe break-type LOCA events, including small, medium and large Related SAMA #147. break events, are eliminated. SAMAs are not IE #7 CDF Medium LOCA Hardware changes to LOCA05 77K 181K >500K practical to achieve the conservative benefit.

LMC1MD Event reduce/eliminate pipe (162K) (380K) break LOCA events. Cost of physical plant modifications based on installation of leakage detection system, Seabrook SAMA #147.

Loss f ofsiteNot cost beneficial.

Loss of offsite Refer to initiator IE #8 LOSPG CDF power due to grid- LOSPW.

related events Evaluated under SAMA IE #3.

Loss f ofsiteNot cost beneficial.

Loss of offsite Refer to initiator IE #9 LOSPG CDF power due to grid- LOSPW.

related events Evaluated under SAMA IE #3.

Not cost beneficial. Initiator F1SWCY models a major rupture of the SW ocean return pipe common to both SW trains. The common return pipe is located underground in the yard Hardware changes to and in the vicinity of SW Cooling Tower supply Major flood due to reduce risk of SW and return piping. The initiator baseline IE 10 CDF rupture of SW common return line F1SWCY 263K 616K >5M modeling is judged conservative. The base F1SWCY common return major rupture event in (552K) (1.3M) line model assumes that continued break flow piping in Yard yard. for more than 60 minutes from the ruptured common ocean return pipe will eventually undermine the structural support for the SW CT pipes, thus causing failure of the SW CT divisions. The PRA case F1WCY assumes complete elimination of this initiator.

90 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 - SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic EventR Si Total Benefit ( ..

(BE) or. RC Event Relaned Pe dctn .. Baseline (with 2.1 Expected ntt Eroposed RACase - multiplier) SAMA Cost: Evaluation (IE) -SAMA(s) CDF Pop. Internal & With($

Dose External Uncert.".-.: -

Cost to engineer replacement options for the buried SW piping is currently under review and is included in the station long range plan.

Approximately 70% of the SW system piping is

-buried at approximately 25 feet below grade. It is estimated that >$5M per refueling outage will be necessary to support the plan.

Not cost beneficial.

IE#11 CDF Seismic 1.4g Refer to initiator E7T. E7T E14T transient event Evaluated under SAMA IE #1.

Not cost beneficial. The SAMA concept is to provide hardware modifications to reduce the potential for the fire initiating event or spurious actuation of a PORV. PRA case FIRE1 conservatively assumes complete elimination of the initiating event FCRPL.

l Related SAMA #179 Thus, the benefit is conservative.

IE#12 ~~~~~~Fire in Control RltdSM#7 4 4 IE#12 CDF Room - PORV Possible reduction in FIRE1 3 0 14K 34K >100K FCRPL LOCA Event CDF if mitigating fire- (31 K) (71 K) SAMA induced LOCA. and was#179 is related shown to this to be not costIEbeneficial.

SAMA #12 Cost to engineer and install hardware changes needed to realize the benefit are judged to exceed the lower bound cost estimate for hardware changes.

Not cost beneficial. The SAMA concept is to provide hardware modifications that will reduce or eliminate fire initiating events in Improve or reduce the Switchgear Room B. PRA case FSGBE6 IE #13 Fire Switchgear B CDF contribution of 28K 65K assumes elimination of fire initiator FSGBE6, FSGBE6 CF - Loss of Bus E6 Switchgear Room B FSGBE6 3 1 (58K) (136K) >500K fire in Switchgear B resulting in loss of fire events. electrical bus E6, to conservatively assess the benefit of possible SAMAs to reduce the fire frequency and core damage consequence.

FSGBE6 is not a significant contributor to CDF. The fire ignition frequency for scenario 91 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 - SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic Event (BE) RCo Eent ~ Related SAMA #'s T R~% Riskc~n TtlBnft$

Baseline (with 2.1 Expected (B)o CEetand Proposed PRA Case Reduction_ multiplier) SAMA Cost Evaluation

ntaigEvent ~Group Description SAMA~s D Pop. Internal & -: >With>: $

___________ __________________

_____________ _________ ___ .ose Dose____ Extrna .JUncrt ___________________________

FSGBE6 is based on the total ignition frequency for Bus E6 (21 cubicles) and other electrical cabinets (86 cabinets) located in the "B" switchgear room. Bus E6 cabinets are a fixed combustible and fire within the bus is assumed to fail the bus. Other electrical cabinets located in the switchgear room are also a fixed combustible. Fire in these other cabinets has a potential to raise the room temperature and jeopardize operation of the various electrical components within the room.

Switchgear Room B is separated from Switchgear Room A with a 3 hour3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months fire barrier.

Given the safety system electrical separation, it is concluded that there are no practical, cost-beneficial SAMAs that would significantly reduce the fire risk contribution of FSGBE6.

Initiator FSGAE5 (Swithgear Room A) is similar.

Cost to engineer and implement plant modifications and analysis based on scope comparison to STP SAMA 8 to enhance fire barriers in CRE Panel, estimated at $1.1M.

t t 1 1- t t Not cost beneficial. The SAMA concept is to provide hardware modifications to reduce or eliminate the potential for random loss of emergency bus as an initiating event. PRA case LACPA conservatively assumes Improve Bus E5 complete elimination of the initiating event Loss of Train A reliability and LACPA (Division A). Thus, the benefit is IE #14 essential AC 44K 103K CDF eliminate or reduce LACPA 3 1 >3M conservative.

LACPA power (4kV Bus (92K) (216K) bus faults contributing E5) to initiating events.

Cost to engineer and implement plant modifications and analysis based on scope comparison to STP SAMA 5, estimated hardware change to provide alternate feed to Bus at greater than $3M.

92 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- SEABROOK - BASIC EVENTA&INITIATIN' EVENT SAMA REVIEW Basic Event Total Benefit($)

Event % Risk Bsi(wh. Expected Related SAMA #'s t in Baseline(with21 Expected (BE) orRC E and ProposedR PR :Case mutiper)- SAMA Cost Evaluation Initiating Event Group: Description adPooe- PACs utpir AACs:Eauto (IE) ".AMI-A(s) C Pop. Internal & With "-.

Dose External Uncert. _____;__________ -._

Improve or reduce the Not cost beneficial.

IE #15 CDF Fire Switchgear A CDF contribution of FSGBE6 3 1 28K 65K >500K FSGAE5 StLoss of Bus E5 Switchgear Room A (58K) (136K) fire events. Evaluated under SAMA IE # 13.

Related SAMA #59, BE #2 and BE #9. This IE SAMA is related to SAMA #59, SAMA IE #16 Loss of PCCW Install hardware to 144K 337K BE #2 and SAMA BE #9. SAMA #59 and LPCCB CDF Train B improve the reliability of the CCW, CCTE1 3 5 (302K) (709K) 300K SAMA BE #2 are not cost beneficial. Refer to thus SAMA BE #9 for evaluation of potential cost reduce potential for beneficial SAMA.

loss of CCW initiators.

IE #17 LERF ISLOCA - V- Related SAMA #113, LOCA06 <1 3 48K 4(101K) 113K (238K) >500K Not cost beneficial. The SAMA concept is to 93 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW Basic EventE) or RC v SAMA # " % Risk Total Benefit 15)

BacRelated SAMA Ws %R Baseline (with 2.1 Expected and) Prpoe PRC Caset PRA Case.o Rdandutoposed mutilir)uctAMiCsoEalato multplien SAMAnCost Evaluation Initiating Event Group Description (IE) . . SAMA(s) C*F Pop. Internal & With ($)

___________-___Dose External Uncert.

LOC1VI sequence LOCA #115, #187. provide hardware changes aimed at reducing in RHR injection Hardware changes to the ISLOCA risk. PRA case LOCA06 path reduce / eliminate conservatively assumes that ISLOCA events ISLOCA risk. do not occur.

Related SAMAs #113, #115 and #187 have all been shown not cost beneficial.

Related SAMA #113, ISLOCA - V- #115, #187. Not cost beneficial.

IE#18 LERF sequence LOCA Hardware changes to LOCA06 <1 3 48K 113K >500K LC1VS L in RHR suction (101 K) (238K) path reduce / eliminate Evaluated under SAMA IE #17.

ISLOCA risk.

Related SAMA #147.

LERF Seismic 2.5g Hardware changes to 77K 181K Not cost beneficial.

IE#19 E25L LE LOCA event reduce or eliminate LOCA05 9 2 (162K) (380K) >500K impact of 2.5g seismic Evaluated under SAMA #147.

events / LOCA.

Not cost beneficial.

IE #20 LERF Seismic 1.8g Refer to initiator E25L. LOCA05 No cs benfical El 8L LOCA event Evaluated under SAMA IE #19.

Not cost beneficial. . The SAMA concept is to provide hardware changes to increase the seismic response of the plant and reduce Related SAMA #181, seismic-induced transient risk. PRA case

182. El 8T conservatively assumes complete IE #21 LERF Seismic 1.8g Hardware changes to El 8T <1 0 5.6K 13K >500K elimination of transient event E18T.

E18T Transient event reduce or eliminate (12K) (28K) impact of 1.8g seismic events / Transient. Cost to engineer and install seismic upgrades to significantly reduce the risk of seismic-induced transient risk is expected to significantly exceed the benefit.

Not cost beneficial.

IE #22 LERF Seismic 2.5g Refer to initiator El 8T E18T E25T Transient event Evaluated under SAMA IE #21.

94 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 - SEABROOK,'- BASIC ýEVENT & INITIATING EVENT SAMA REVIEW.

SBasic Event " Related SAMA #'s :::Rdcin

-0/0 Ri*

ik " Total Benefit Baselinie ($)- ,!

(with.2.1 Expected "::i:!::: ::::*:

(BE) or RC . Event and Proposed PRA Case Reduction Baslne (uwithr 2 SAMACosted Evaluation Initiating

." (IE):Event

Group, ;

DescriptionP

-'i*..i: " - A A s D Pop. Internal &

With :$ i! : : : : : i:

(lE)~CDIF Dose External Uncert.

Not cost beneficial. PRA case NOATWS conservatively assume that ATWS events do not occur (including seismically initiated IE#23 LERF Seismic 1.4g Related SAMA #130, NOA'WS 4 2 60K 139K >500K AT'IWS).

E14A AT]WS event #131, #132, #174 (126K) (292K)

Cost of installing seismic upgrades to significantly reduce the risk of ATWS is expected to significantly exceed the benefit.

Not cost beneficial.

IE #24 LERF Seismic 1.8g Refer to initiator E14A NOATWS .cost No benefic E18A LF ATWS event Evaluated under SAMA IE #23.

Not Not cost cost beneficial.

bene.

IE #25 LERF Seismic 2.5g Refer to initiator E14A NOATWS E25A ATWS event Evaluated under SAMA IE #23.

Not cost beneficial.

IE #26 LERF Seismic l.g Refer to initiator E14A NOATWS Not cost bene.

E10A ATWS event Evaluated under SAMA IE #23.

Not cost beneficial.

IE #27 LERF Seismic 0.7g Refer to initiator E14A NOATWS Not cost bene.

E7A A'WS event Evaluated under SAMA IE#23.

Not cost beneficial. Related SAMAs are #130, ATWS with Loss #131, #132, #174. PRA case NOATWS IE LERF of Main #131, SAMA#174 NOATWS 4 2 6K (29K >500K conservatively assume that ATWS events do AMFW Feedwater #131, #132, #174 (126K) (292K) not occur (including seismically initiated ATWS).

95 of 96

SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- SEABROOK - BASIC EVENT & INITIATING EVENT SAMA REVIEW

-- *Totali

_. . * =:::::::: :.,Related Related SAMA AA #s*:: ',....,£

% Risk : :: Baseline (with .2.1 " .Expected Tota Benefit.($) . .:

Basic Event (BE) or :: RC Event Case*- Reduction Baselin ( 2.1 Expected and Proposed PRA Case multiplier) -SAMA Cost. Evaluation Initiating Event. Group DescriptionDoe Etra Unrt (IE) (IE) . -*": -'::!i.,::i:

.ii:::SAMA(s)

: :: : ' . CDF DF iDose Internal & Uncert.

Pop. ::External With ' ($) . = .*i: .'- . -

Cost of installing upgrades to significantly reduce the risk of ATWS is based on related SAMA costs.

Not cost beneficial. Related SAMA is #153 -

install secondary side guard pipe protection.

PRA case NOSLB conservatively assume that IE #29 Main Steam Line 5K 11K steam line break events do not occur.

MSLBO MSLBO LERF ~~~Containment Break Outside Related SAMA #153 NOSLB <1 0 (ilK)

(1K (24K) 2K >500K Cost of installing hardware changes to reduce or eliminate the risk of SLB events is based on SAMA #153.

Not cost beneficial. Related SAMA is #194.

PRA case MSSVO assumes complete IE #30 Main Steam <1K 2K success of the safety valves to close.

MSSVO LERF Safety Valve Stuck Open Related SAMA #194 MSSVO <1 0 (2K) (4.5K) >30K Cost to engineer and install hardware is based on SAMA #194.

96 of 96

v t e Letter Sequence Supplement
TAC:ME3959, (Approved, Closed)
Initiation Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request, Request Acceptance, Acceptance Supplement Administration Meeting, Meeting, Meeting Questions 31 July 2012 29 October 2010 21 December 2010 16 November 2010 3 January 2011 28 February 2011 4 March 2011 7 April 2011 20 March 2012 16 July 2012 1 November 2012 Answers 23 November 2010 23 November 2010 23 November 2010 23 November 2010 23 November 2010 23 November 2010 23 November 2010 23 November 2010 23 November 2010 23 November 2010 23 November 2010 22 January 2014 22 January 2014 22 January 2014 23 November 2010 23 November 2010 13 January 2011 16 March 2011 18 April 2011 10 June 2011 13 September 2012 22 January 2014 6 September 2016 Results Approval, Approval, Approval, Approval, Approval, Approval, Approval Other: ML103070056, ML103360209, ML103360212, ML11126A365, ML11343A025, ML12352A141, ML13352A511, ML13353A536, ML18127A116
MONTHYEAR2010-08-10 [Table View]

SBK-L-12053, Supplement 2 to Severe Accident Mitigation Alternatives Analysis, License Renewal Application

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SBK-L-12053, Supplement 2 to Severe Accident Mitigation Alternatives Analysis, License Renewal Application

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