View source for SBK-L-12053, Supplement 2 to Severe Accident Mitigation Alternatives Analysis, License Renewal Application

{{Adams
| number = ML12080A137
| issue date = 03/19/2012
| title = Supplement 2 to Severe Accident Mitigation Alternatives Analysis, License Renewal Application
| author name = Freeman P
| author affiliation = NextEra Energy Seabrook, LLC
| addressee name = 
| addressee affiliation = NRC/Document Control Desk, NRC/NRR
| docket = 05000443
| license number = 
| contact person = 
| case reference number = SBK-L-12053
| document type = Letter type:SBK
| page count = 99
| project = 
| stage = Supplement
}}

=Text=
{{#Wiki_filter: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 hours.
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 hours after the sequence initiation. However, LE4 is used to represent extreme seismic events where it is assumed that evacuation would be delayed beyond 20 hours. 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 hours.
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 hours.
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 hours.
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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 hours and with intact containment initially but with no power recovery. Thus, basemat melt through occurs at about 49 hours.
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 hours 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&deg;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 hours                  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 hours                  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 hours       1.02          1.03 SEPSDG2A.FR3             1-SEPS-DG-2-A fails to run within 24 hours       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 hours                                                    CDF, SE-3, SELL
[DGDG1B.FR3]     DG-IB fails to run for 24 hours                                                    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 hours                                         SE-3, SELL SEPSDG2B.FR3     1-SEPS-DG-2-B fails to run within 24 hours                                         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 hours                             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 hours 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) &deg; mutipier)           SAMAt: :., .
: "Cost..            :=&deg;   * : " ..      :-    !"     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 rel&#xfd; 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""uase&#xfd;                 "      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).
45 of 96

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.
50 of 96

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.
54 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 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.
56 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         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
                 &deg;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.
65 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 (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.
66 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.   '"-:                                                               -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[     &#xfd;Uncert.
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.
67 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                                   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.
68 of 96

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.
70 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"   -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)&deg;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.
72 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                                    -                                               /   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 hours        #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 hours           #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 hours             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 hours             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 hours 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.
79 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                 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.
83 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 BasicBEvent                                      Related SAMA #'s                  '            Risk   -    Total Benefit($)
(BE) or.      RC W                       ReductionA     Baseline (with 2.1        Expected Event             and Proposed          PRA Case     -:&#xfd;. 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&& &#xfd;&#xfd; 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.
85 of 96

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.&#xfd;  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.
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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 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 hour 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 $3M.
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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2- SEABROOK - BASIC EVENTA&INITIATIN' EVENT SAMA REVIEW Basic Event                                                                                             Total Benefit($)
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.
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SBK-L-12053 NextEra Energy Seabrook, LLC Supplement to Severe Accident Mitigation Alternatives Analysis TABLE 2 - SEABROOK,'- BASIC &#xfd;EVENT & 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).
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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
                                                                                                                                                                                           -- *Totali
_.   .  * =:::::::: :.,Related       Related SAMA AA #s*::                 ',....,&#xa3;
                                                                                                      % 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.
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