ML11147A099

Response to Request for Additional Information Item Numbers 2, 3, 5 and 15 Regarding Severe Accident Management Design Alterative Review

ML11147A099
Person / Time
Site:	Watts Bar
Issue date:	05/25/2011
From:	Stinson D Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME8203
Download: ML11147A099 (44)

Text

Tennessee Valley Authority, Post Office Box 2000, Spring City, Tennessee 37381-2000 May 25, 2011 10 CFR 50.4 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Watts Bar Nuclear Plant, Unit 2 Docket No. 50-391

Subject:

WATTS BAR NUCLEAR PLANT (WBN) - UNIT 2 - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ITEM NUMBERS 2, 3, 5 AND 15 REGARDING SEVERE ACCIDENT MANAGEMENT DESIGN ALTERNATIVE REVIEW (TAC NO. MD8203)

References:

1. TVA to NRC letter dated May 13, 2011, "Watts Bar Nuclear Plant (WBN) - Unit 2 - Response to Request for Additional Information Regarding Severe Accident Management Design Alternative Review (TAC No. MD8203)"

2. NRC to TVA letter dated March 30, 2011, "Watts Bar Nuclear Plant, Unit 2 - Supplemental Request for Additional Information Regarding Severe Accident Management Design Alternatives Review (TAC No. MD8203)"

3. TVA to NRC letter dated January 31, 2011, "Watts Bar Nuclear Plant (WBN) Unit 2 - Response to Request for Additional Information Regarding Severe Accident Management Alternative Review (TAC No. MD8205)"

4. NRC to TVA letter dated January 11, 2011, "Watts Bar Nuclear Plant, Unit 2 - Request for Additional Information Regarding Severe Accident Management Alternative Review (TAC No. MD8203)"

The purpose of this letter is to provide a response to the NRC requests for additional information (RAI) Item Nos. 2, 3, 5 and 15 regarding the Severe Accident Management Design Alternatives (SAMDA) analysis discussed in Reference 2.

Reference 1 provided TVA's response to the majority of the requests for information

U.S. Nuclear Regulatory Commission Page 2 May 25, 2011 provides TVA's response to RAI item numbers 2, 3, 5 and 15. provides the list of commitments made in this letter.

If you have any questions, please contact Bill Crouch at (423) 365-2004.

I declare under the penalty of perjury that the foregoing is true and correct. Executed on the 25th day of May, 2011.

Respectfully, David Stinson Watts Bar Unit 2 Vice President

Enclosures:

1. Responses to NRC Request for Additional Information Item Numbers 2, 3, 5 and 15

2. List of Commitments cc (Enclosures):

U. S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257 NRC Resident Inspector Unit 2 Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, TN 37381

ENCLOSUREI RESPONSES TO NRC REQUEST FOR ADDITIONAL INFORMATION ITEM NUMBERS 2, 3, 5AND 15 By letter dated January 31, 2011, the Tennessee Valley Authority (TVA) provided a response to the Nuclear Regulatory Commission (NRC) staff regarding questions related to TVA's Updated Analysis of Severe Accident Mitigation Design Alternatives (SAMDAs) for Watts Bar Nuclear Plant (WBN), Unit 2. In its review of this information, the NRC staff requires further information and clarification on TVA's response. The information listed in the following request for additional information (RAI) refers to the RAI responses in the January 31, 2011, letter.

2. RAI I.f The response did not address the assumptions concerning the availability of WBN Unit I components/systems for both dual-unit and Unit 2 initiating events. Discuss how the availability of Unit 1 systems during Unit I outages is accounted for in evaluating WBN Unit 2 CDF and LERF.

TVA Response:

The WBN model is a dual-unit model which incorporates initiating event fault tree logic for a number of support-system initiators. The relevant fault tree logic is input into both unit-specific and dual-unit initiating events. Therefore, the impact of unavailability of Unit 1 components/systems with respect both to mitigation and to initiating events (unit-specific and dual-unit) is incorporated in the model for Unit 2, and the results are included in the calculations for CDF and LERF for Unit 2.

Primary systems for Unit 2 such as ECCS will not be impacted directly during Unit 1 outages, the impact will be seen in the unavailability of support systems such as service water and component cooling. Also, actual plant risk of the operating unit while the other unit is in a refueling outage will be monitored using the WBN EOOS (Equipment out of Service) model. WBN uses EPRI's EOOS program to monitor plant risk in accordance with 10 CFR 50.65a(4). As WBN has not yet completed a refueling outage on one unit while the other unit is operating, assumptions regarding these unavailabilities were made.

The following describes the current modeling approach used in the CAFTA model.

The WBN Unit I maintenance rule database was the primary data source used to develop estimates of system train unavailability due to testing and maintenance of modeled components; i.e., TI-119, "Maintenance Rule Performance Indicator Monitoring, Trending, and Reporting", 10 CFR 50.65. This database includes component failure and unavailability for periods when a system is required. For systems such as ERCW, Component Cooling and Compressed Air, the systems are required during power operation (Mode 1) and for some periods of time when the unit is in Modes 2-6. For dual unit operation, excessive unavailability from outage downtime would adversely impact the maintenance rule metrics. In addition, dual unit operation with controlling technical specifications from each unit will limit the outage time for common systems compared to single unit operation. As an example, E1-1

two trains of ERCW must be operable during modes 1, 2, 3, and 4 (per LCO 3.7.8),

or within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> the unit must begin the transfer to mode 5. This LCO does not apply to single unit operation when in mode 5 or 6 already. However, when dual unit operation begins, if one unit is in an outage (i.e., Mode 5 or 6), the LCO will apply to the unit that is in Modes 1, 2, 3, or 4. Therefore, the duration of such maintenance events while one unit is in an outage will be limited by the TS requirements on the non-outage unit. This train maintenance is included in the model Maintenance Rule data is collected on a train basis for most systems. The data for each train was used to calculate the probability of the train being unavailable due to maintenance. Each of the calculated probabilities was given a variable name which was added to the type code table in the WBN PRA CAFTA database. These variables are assigned to the applicable maintenance basic events for each train during fault tree construction.

Where maintenance rule data were not available, generic information from NUREG/CR-6928 was generally used. However, since NUREG/CR-6928 data for unavailability consider only events during critical hours from the Mitigative System Performance Index (MSPI) data, the generic experience data from plant outages are not considered. Also, unavailability was calculated or estimated in some instances where neither appropriate maintenance rule data nor NUREG/CR-6928 data were available. However, based on the maintenance rule unavailability limitations and the technical specification limits, we believe the unavailability times used in the CAFTA model are sufficient for proper decisionmaking with respect to proposed SAMA measures.

3. RAI I.h

a. The response to the RAI states "The following peer cert findings remain open and are considered documentation related (i.e., are judged to not have the potential for significant change to model results or risk ranking):..." Among the findings listed, the following, from the description in the IPE, do not appear to be limited to just documentation:

(1) 1-4 (DG [diesel generator] load sequencer) - states certain failures are missing from the logic model, (2) 2-11 (T-H [thermal-hydraulic] timing for HRA [human reliability analysis] cues, no simulator runs) - does this mean the runs were not performed, or that they were performed but not documented, and (3) 5-1 (Optimistic room heat-up times used).

Provide further justification that each of these items is only a documentation issue and that final resolution is unlikely to impact the SAMA evaluation.

TVA Response:

a. (1) This relates to standard Supporting Requirement SY-B10. The peer reviewer's comment about this element is as follows: "Assessment: Cat 2-3 E11-2

is MET. Basis: Appropriate actuation signals from RPS and ESFAS are modeled. However, the actuation signals from the DG load sequencers are not modeled for each load. This is expected to have minimal impact on the results because the sequencer dependency is modeled for the ERCW system which is required for diesel generator support."

ERCW is the only load with an individual sequencer modeled. The sequencer is modeled with the diesel generator and fails the diesel generator if failed. The supporting requirement is judged as 'met' with respect to this element; therefore, the significance of the issue is believed to be relatively minor. The peer reviewer also specifically indicated that a minimal impact on results was expected. Therefore, any final resolution is unlikely to impact the SAMA evaluation.

(2) This relates to standard Supporting Requirement HR-E4. The requirements for that element are as follows:

Category I No requirement for using simulator observations or talk-throughs with operators to confirm response models.

Category 1/11 USE simulator observations or talk-throughs with operators to confirm the response models for scenarios modeled.

The peer reviewer's comment about this element is as follows: "Assessment:

Cat 1 is MET. Basis: The Process for Post initiator actions provided in MDN-000-999-2008-0144 Section 7 does not discuss use of simulators. However, timing data for post initiator actions are provided in MDN-000-999-2008-0153 section 8.0 based only on judgment of the operators, which includes some very optimistic times. Also, the operator interviews should produce some insights related to the risk model, use of procedures, etc. CAT I met for this element."

The WBN Model used walk-throughs rather than simulator runs. The peer review comment indicates that the supporting requirement was judged to be met at least at capability category I, and it is also noted that talk-throughs with operators were in fact performed. The talk-throughs were performed and were well-documented, which would appear to meet the requirements of capability category Il/111. Documentation demonstrates that the talk-throughs with members of the operations staff at WBN were conducted over a significant number of hours and with several highly experienced individuals having diverse operations backgrounds. Therefore, the results are believed to be generally reasonable and appropriate. There is no information to indicate that any significant changes might result should simulator runs be performed.

(3) The peer review comment reads as follows:

The mission time used for room heat-up calculations (MDN-000-999-2008-0143, Appendix B, WBNOSG4-242, 200, and 197) was optimistically justified.

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(This F&O originated from SR SC-A5.)

Basis for Significance. According to WBNOSG4-197, 200 and 242, the mission time for mitigation was verified based on simplified calculations and optimistic engineering judgment. Because the component cooling relies on HVAC, the results of room heat-up calculation affect the ability of components to function without room cooling.

The resolution of this item will be that based on room heat-up calculation results, judge whether the safe and stable condition is met and the basis of the judgment should be presented explicitly.

TVA calculation MDN-000-999-2008-0143 summarized results and identified a number of areas as requiring room cooler/ HVAC support including residual heat removal pump rooms, safety injection pump rooms, containment spray pump rooms, charging pump rooms, the turbine-driven auxiliary feedwater pump room, and the emergency diesel generator rooms. Mission times of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> were generally assumed. No information was identified in MDN-000-999-2008-0143 to indicate that these results are optimistic with respect to those for other Westinghouse PWR sites. The peer review report indicates that all supporting requirements for Success Criteria were met at Category II (or Il/111) or above, therefore success criteria elements are indicated to be adequately met. The proposed resolution indicates that additional review, judgment, and documentation of this process may be sufficient to resolve the question. There is therefore no indication that any changes will be developed which could substantially impact the SAMA evaluation.

b.

TVA stated (p. EI-13), with reference to internal flooding, that "the current model is judged to be adequately bounding for this application," which is based on conservatisms in the flooding model described in the response. While this may be true, there are a large number of open internal flood findings from the peer review and an updated flooding analysis is to be included in the next model update. Section 3.7 (p. 70) of the WBN Unit 2 IPE submittal states that two sets of sensitivity studies were performed on the internal flooding analysis, with one set focused on evaluating alternative design/procedural changes that would significantly impact (i.e., reduce) the flood related CDF and LERF while the other was designed to address epistemic uncertainties identified in the WBN internal flooding probabilistic risk assessment (PRA). Provide a description of these studies, their results and conclusions, and how the results and conclusions support the conclusion that the current flooding model is bounding for the SAMA application.

TVA Response:

b. A sensitivity study was performed to evaluate re-routing or sheathing with guard pipes certain raw cooling water piping segments in flood areas 772.0-A8, 772.0-A9, 757.0-A9 and 757.0-A17. A reduction in CDF of approximately 7.32%

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and a reduction in LERF of approximately 12.98% were estimated for this configuration.

A sensitivity study was performed to examine the flooding risk contributions associated with raw cooling water and high pressure fire protection piping failures in areas 757.0-A2, -A5, -A9, -A17, -A21, and -A24, 772.0-A7, -A8, -A9 and -A10, comparing the risk associated with carbon steel piping vs. stainless steel piping.

The study compared a baseline configuration of stainless steel piping with carbon steel piping. The carbon steel piping configuration CDF was approximately 45.43% greater and LERF was approximately 81.30% greater.

A sensitivity study was performed to evaluate the significance of operator actions to mitigate certain flooding scenarios. A case was run setting the failure probability of all the subject mitigating actions to 0 (certain to succeed) and then another case was run setting the failure probability to 1.0 (certain to fail). Setting the actions to 0 resulted in a reduction in CDF of approximately 2% and a reduction in LERF of approximately 1%. Setting the actions to 1.0 resulted in an increase in CDF of approximately 44% and an increase in LERF of approximately 23%.

A sensitivity study was performed to evaluate the contributions due to maintenance and human-induced flooding events. Suppressing contributions from these causes resulted in a decrease in CDF of approximately 0.3% and a decrease in LERF of approximately 0.4%.

The studies were not performed to demonstrate that the current model is bounding but rather to compare various possible plant changes or to examine the importance of certain inputs to the analysis. However they do demonstrate that the model responds as expected, showing reductions in flood risk associated with improvements, thereby providing additional confidence in its results.

TVA has previously committed to installing flood detection in WBN areas 772.0-A8 and 772.0-A9. Please see commitment 9 of Enclosure 2 of the January 31, 2011 letter from Marie Gillman (TVA) to the USNRC, "WATTS BAR NUCLEAR PLANT (WBN) - UNIT 2 - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING SEVERE ACCIDENT MANAGEMENT ALTERNATIVE REVIEW (TAC NO. MD8203)" (T02 110131 001).

TVA now numbers this as a new SAMA, 340, to install flood detection in areas 772.0-A8 and 772.0-A9.

5. RAI 2.a.iv

a. The discussion of the determination of release category characteristics (i.e.

source terms) indicates that the SEQSOR methodology was used. This methodology does not calculate release fractions from first principles but uses input from other calculations and has been used in the past for Sequoyah. The WBN Unit 2 IPE submittal discusses the use of Modular Accident Analysis Program (MAAP) 4.0.7 for the LERF analysis. Clarify the origin of the source terms used for the SAMDA analysis. Note that in the July 23, 2010, TVA response to RAI 2. f, TVA took the position that results from MAAP analysis were E1-5

more valid than those from SEQSOR. Clarify this apparent change in TVA's position.

TVA Response:

The WBN Unit 2 IPE submittal did use the Modular Accident Analysis Program (MAAP) 4.0.7 for the LERF analysis. The use of this code, however, was specifically for the thermal hydraulic analyses needed to justify sequence success criteria, not for source term calculations. TVA has not taken the position that release fractions computed by MAAP are more or less valid than the SEQSOR approach for WBN.

In the original IPE for WBN Unit 1 (published in 1992), release fraction results from MAAP 3B were used to satisfy IPE requirements. The latest WBN Unit 2 CAFTA model, used for the SAMA analyses, results in different dominant scenarios for each Release Category than those previously assessed. Since the SEQSOR approach makes use of release fractions computed for WBN Unit 2's sister plant, Sequoyah, it was deemed prudent to use these same inputs for the SAMA evaluation.

The SEQSOR methodology itself uses release fractions originally calculated from first principles for the Sequoyah plant. The origin of the source terms used for the revised SAMA analysis is described in the previously submitted response to RAI 2.a.iv. The approach is to identify dominant scenarios for each release category specific to WBN Unit 2, note their specific release characteristics in terms of accident progression, and then follow the SEQSOR methodology to arrive at mean release fractions for each Release Category.

The SEQSOR emulator developed for use in this analysis is described in the following paragraphs.

The SEQSOR program used to calculate the source terms for Sequoyah in NUREG-1 150 was not available for this analysis. SEQSOR is explained in NUREG/CR-4551 Volume 5, Chapter 3 and Appendix B of that volume. Instead, for this analysis, a spreadsheet based SEQSOR Emulator was developed and used to emulate the basic calculation of the SEQSOR program used during the NUREG-1 150 analyses.

The SEQSOR code was developed because of the large number of possible sequences a plant could undergo during an accident. The complexity and time of running a phenomenological code, such as MAAP, for each of these sequences would have been impossible. Instead, the SEQSOR code was developed as a relatively simple parametric code to select from a representative set of results of detailed phenomenological codes as probability distributions. This approach allows one to estimate a large number of cases in a short time.

SEQSOR uses blocks of data containing probability distributions, by release class (the nine release classes are groups of elements with similar chemical E1-6

behavior) for a variety of terms in the basic SEQSOR equations, given in equations 3.1 and 3.2 of NUREG/CR-4551, Volume 5. Equation 3.1 gives the behavior in the early phase, before the reactor vessel breach (if any). Equation 3.2 gives the behavior in the late phase, which considers the core-concrete interaction. Each of the data blocks represents a term in one or both of these equations and the data in each is a function of a probability level between 0%

and 100%, and in most cases is also a function of the radionuclide group. During the Monte-Carlo process, a random variable between 0 and I is used to select a value (or a set of values for each radioisotope group) for the calculation. The same data blocks were used in the SEQSOR emulator, except where processes or equipment that needed to be considered for this analysis were not included in the NUREG-1 150 analyses. The blocks considered in both SEQSOR and the SEQSOR emulator are shown below:

Early releases from fuel to RCS (two oxidation states)

Fraction of core released from RCS before vessel breach (six conditions)

Fraction of containment contents released in the early and late phase (nine containment failure modes)

Containment state (wet or dry)

" Sprays during early phase (three conditions)

Number of holes in the RCS if vessel failure (one or two)

DCH release (two conditions)

" Core-concrete interaction pool scrubbing (two conditions)

SGTR scrubbing (three conditions).

Ice condenser decontamination factor for early phase (three conditions)

Ice condenser decontamination factor for late phase (four conditions)

Fraction of core mass ejected from high pressure mass ejection (four conditions)

Early phase ice condenser bypass (three conditions)

Late phase ice condenser bypass (three conditions)

All of these data blocks with the exception of the SGTR scrubbing were used in the original SEQSOR analysis. Three additional containment failure modes were considered: intact containment, failure to isolate, and late unfiltered vent.

The SEQSOR Emulator was developed to use the same SEQSOR logic but in a spreadsheet format. The SEQSOR Emulator was independently reviewed prior to use for SAMA analysis. For each Release Category, the fraction of each condition for each set of data blocks is determined from the scenarios included.

Then, a set of 4096 Monte-Carlo samples from the resulting probability space was selected and the resulting release fractions calculated according to the computational rules in equations 3.1 and 3.2 from the SEQSOR approach. This distribution of release fractions was used to determine the mean and other statistical measures for each radionuclide group. Finally, these release fractions and other sequence attributes (e.g., for timing and release points) were used in MACCS2 to determine the consequences for each sequence sub-category.

b. The discussion of the source terms states that the, "The source terms for each set of accident characteristics are weighted in accordance with the % contribution for each release type in Table 2. a. iv-3." This process is valid only if the consequences of the releases are linear with respect to the source terms. This is E1-7

not necessarily true. Provide support that this process provides a valid estimate of consequences.

TVA Response:

The quoted statement could have been more clearly worded. The actual approach taken is as stated in the final sentence of the same paragraph describing Table 2.a.iv-3; "Each release characteristic type in Table 2.a.iv-3 are calculated separately with MACCS and then weighted by frequency to determine the averaged dose and economic consequences shown in Table 2.a.iv-6." TVA agrees that the doses and consequences used for SAMA evaluations cannot be assumed linear and must instead be calculated separately and then frequency weighted. This is what was done.

In addition to the average weighted dose and economic consequences applied to the SAMA evaluations, as sensitivity, we have here instead applied the worst accident sequence dose and consequences of the sub-categories from each release category to the SAMAs to see if any of the Phase 2 SAMA results would then become cost beneficial. After applying the worst accident doses and consequences, we then reviewed the SAMAs for cost benefit using the CDF 9 5 th percentile sensitivity. The SAMAs remain well below the cost benefit threshold except for one, SAMA 93.

This new sensitivity of cost and benefits was evaluated using the 2.70 multiplying factor for the CDF 95th percentile. Applying the 2.78 multiplying factor for the CDF 951h percentile, as suggested in NRC item 12, would not change these results developed using the worst accident doses and consequences. Again, the one exception is for SAMA 93 which is discussed further below.

SAMA 93 proposes to install an unfiltered hardened containment vent for the prevention of containment failure in late release sequences. SAMA 93 has a cost benefit of 0.96 at the CDF 9 5th percentile when using the average late release category dose and economic consequences for the baseline. If the worst case doses and consequences were instead used, the cost benefit ratio would exceed 1.0 for the CDF 95th percentile sensitivity. However, if implemented SAMA 93 would reduce the Level 2 release consequences of the late Release Category but would not change the core damage frequency. The mix of sequences contributing to the late release category would also not be changed by implementing SAMA 93. Therefore, we maintain that the baseline risk should use the weighted average accident dose and consequences in the baseline risk evaluation so that the cost benefit of the CDF 9 5 th percentile would remain at 0.96 for SAMA 93. Further, using the 2.78 multiplying factor for the CDF 9 5th percentile for SAMA 93 and average accident doses and consequences for the baseline would result in a cost benefit of 0.99 which remains below the cost benefit threshold.

Examination of the contributors to the frequency of the Late Release Category, which would be mitigated by implementation of SAMA 93, reveals that 40% of the frequency is attributed to RCP seal LOCAs with leakages of 182 gpm per pump.

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TVA's response to Item 16 (Reference 1) commits to follow the progress of the seal package design defined in SAMA 58 and to install it if proven reliable.

Implementation of SAMA 58 would greatly reduce the benefits of SAMA 93.

Further, in the Reference 1 response to item 16, TVA further committed to re-evaluate the benefits of SAMAs 215, 226, 50, 55, and 56 for mitigation of RCP seal LOCA scenarios if SAMA 58 is not proven reliable. TVA further commits to add SAMA 93 to this list for re-evaluation should SAMA 58 not prove reliable.

Note also that scenarios in which there is a loss of control air (e.g., during a station blackout) and failure of the operators to locally control the AFW LCVs to allow the turbine-driven AFW pump to continue steam generator cooling contribute 10% to the Late Release Category frequency. TVA has committed to implement SAMA 339 (in place of the new air accumulators called for in SAMA

70) to provide a new capability to allow the operators to transfer from the normal compressed air supply to the station nitrogen system for control of the AFW LCVs for these sequences. See the response to item 11 a for RAI 5.b.

Implementation of SAMA 339 will further decrease the evaluated benefit of SAMA 93, further affirming that it is not cost beneficial even for the CDF at 9 5 th%

sensitivity assessment.

c. The discussion of release category definitions and contributors in response to RAI 2.a.ii and iii indicates that early steam generator tube ruptures (SG TRs) are assigned to the BYPASS release category under the contributor LERF-SG TR (SLERF) corresponding to the SLERF CET end state. The WBN Unit 2 IPE indicates that thermally induced SGTRs make up 32 percent of the WBN Unit 2 LERF. The SLERF end state is not included in the RAI revised model dominant CET end states listed in Table 2.a.iv-2. It is noted that plant damage state (PDS) bin 4B1, which, according to Table 2.a.i-2, is made up of large SGTR sequences, is not represented in the dominant CET end states. Clarify the reason for this and describe the SGTR contribution to WBN Unit 2 consequences.

TVA Response:

There are 2 types of SGTR sequences that contribute to LERF releases in the Containment Event Tree (CET):

1) SLERF Sequences - SGTR Initiating Events that lead to Core Damage (PDS Bin 481 or 4B2) and release.

2) BLERF Sequences - Non-SGTR Initiating Events that lead to Core Damage (PDS Bin 2) and Thermal-Induced SGTR (TI-SGTR) or Pressure-Induced SGTR (PI-SGTR) in the CET.

In the WBN Unit 2 IPE model, both BLERF and SLERF sequences contributed to LERF frequency. In the WBN Unit 2 SAMA model, the SGTR IE sequences are separated from the Non-SGTR IE sequences; however, both types of sequences still contribute to LERF frequency.

The sequences that contribute to LERF are shown in Table 5c-1 below. The SGTR sequences contribute negligibly. In the WBN Unit 2 SAMA Model, the Non-SGTR IE (BLERF) sequences that lead to TI-SGTR contribute 3.41 E-07 El1-9

(22%) of the overall LERF frequency of 1.61 E-06. The difference from the WBN Unit 2 IPE Model is due to the changes made in the WBN Unit 2 SAMA model as documented in Attachment B.4 of the October 2010 SAMA submittal.

Table 5c-1 (LERF)

CET Sequences that Lead to large Early Release Frequency CET End PDS SBO CET Sequence Sate Bin Non-SBO CET Sequence Events Frequency BLERF-01 2

Non-SBO Not PI-SGTR, Not RCS Depressurization, TI-SGTR 3.97E-1 1 BLERF-02 2

Non-SBO PI-SGTR 6.32E-09 BLERF-04 2

SBO Not PI-SGTR, Not RCS Depressurization, TI-SGTR 2.84E-07 BLERF-05 2

SBO PI-SGTR 5.1 OE-08 (Non-SGTR Sequences) BLERF Subtotal 3.41 E-07 SLERF-01 4B1 Non-SBO (Containment Bypassed - No CET Events) 4.95E-10 SLERF-02 4B2 Non-SBO (Containment Bypassed - No CET Events) 5.13E-10 SLERF-03 4B1 SBO (Containment Bypassed - No CET Events)

<1E-14 SLERF-04 4B2 SBO (Containment Bypassed - No CET Events) 7.69E-13 (SGTR Sequences) SLERF Subtotal 1.01E-09 BLERF and SLERF Total 3.42E-07

d. The development of the RAI revised source term characteristics given in Table 2.a.iv-3 includes four contributors to the late release category, whereas Table 2.a.iv-2 identifies six dominant CET end states from three different PDS bins. Explain the development of the four late release category contributors and their weighting.

TVA Response There are actually 12 CET sequences rather than the 6 CET sequences listed in Table 2.a.iv-2 that contribute to the release characteristics in Table 2.a.iv-3.

All 12 sequences are shown in Table 5d-1 below. The 12 CET sequences were combined into 6 for development of the source terms. Each sequence characteristic contributes a percentage to the release characteristics as shown in the table. The percentages are rounded off to the values shown in Table 2.a.iv-3.

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Table 5d-1 CET Sequences that Contribute to the Late Release Category PDS CET Sequence Frequency Level I Core Damage Sequence Release Characteristics Bin RCS Pressure (Hi or LO)

Hi Lo Hi Lo ARFS Success or Failed F

F S

S (S or F)

Level 2 Release Sequence 6.5%

28.8%

2.4%

60.6 1

10%

LATECA-05 1.35E-06 Steam Break Outside RCS Depressurization, ARFS 8.9%

Containment, SG isolated, SI available, No containment terminated, PORV fails to failure early, No CHR reclose, SI restarted, HPR fails 1

LATECA-01 3.62E-07 Steam Break Outside No RCS Depressurization, 2.4%

Containment, SG isolated, SI ARFS available, No DCH, No terminated, PORV fails to containment failure early, No reclose, SI restarted, HPR fails CHR 2

60%

LATECNA-28 3.64E-06 Flood IEs leading to SBO and RCS Depressurization, LPME, 24.0%

CD Not Bypassed, High RCS ARFS failed, No containment Pressure and SG Dry failure early, No CHR 2

LATECNA-09 2.71E-06 Loss of ERCW or CCS leading RCS Depressurization, ARFS 17.8 to CD Not Bypassed Low RCS available, No containment Pressure and SG Dry failure early, No CHR 2

LATECNA-24 2.95E-07 LOSP leading to SBO and CD RCS Depressurization, ARFS 1.9%

Not Bypassed, High RCS failed, No containment failure Pressure and SG Dry early, No CHR 2

LATECNA-20 9.15E-07 Flood Es leading to SBO and No RCS Depressurization, 6.0%

CD Not Bypassed, High RCS HPME, ARFS failed, No Pressure and SG Dry containment failure early, No CHR 2

LATECNA-1 1 1.41 E-07 LOSP or Loss of ERCW or CCS RCS Depressurization, ARFS 0.9%

leading to CD Not Bypassed failed, No containment failure Low RCS Pressure and SG Dry early, No CHR 2

LATECNA-12 1.06E-07 LOSP or Loss of ERCW or CCS RCS Depressurization, ARFS 0.7%

leading to CD Not Bypassed failed, No containment failure Low RCS Pressure and SG Dry early, No CHR 2

LATECNA-16 8.34E-08 LOSP leading to SBO and CD No RCS Depressurization, 0.5%

Not Bypassed, High RCS ARFS failed, No containment Pressure and SG Dry failure early, No CHR 3A, 30%

LATE_CA-09 4.92E-06 Loss of ERCW or CCS leading ARFS available, No 32.4 3B to CD Not Bypassed Low RCS containment failure early, No Pressure and SG Wet (3A) or CHR Dry (3B) 3A, LATECA-36 1.98E-07 Flood lEs leading to SBO and LPME, ARFS failed, No 1.3%

3B CD Not Bypassed, High RCS containment failure early, No Pressure and SG Dry CHR 3A, LATECA-10 2.22E-07 Loss of ERCW or CCS leading ARFS available, No 1.5%

3B to CD Not Bypassed Low RCS containment failure early, No Pressure and SG Wet (3A) or CHR Dry (3B)

e. Table 2.a.iv-6 gives the October 2010 RAI offsite population dose for release category Ill as 8.19E06 person-rem. This is a significant increase over the original October 2010 result of 1. 13E06 person-rem, and when multiplied by the release category frequency of 1. 3E-05 per year gives an annual population dose of 107 person-rem. This is a factor of 10 higher than that given in Table 5.c-1.

Confirm that the value in Table 2.a.iv-6 should be 8. 19E05 person-rem.

TVA Response The value should be 8.19E+05 person-rem.

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f Provide the revised Off-Site Exposure Cost and Off-Site Economic Cost used to develop the maximum averted cost risk (MA CR) as given in Section 5.1 and 5.2 of the October 14, 2010, RAI response submittal (and On-Site Exposure Cost in Section 5.3 and On-Site Cleanup and Decontamination Cost and Replacement Power Cost in Section 5.4 if these have changed for any reason) of the October 14, 2010, submittal.

TVA Response Below are the revised costs for the SAMA MACR. The table shows the October 2010 costs as compared to the Revised RAI MACR costs.

October 2010, Revised (RAI)

Cost Category SAMA Report SAMA Results Off-Site Exposure Cost $

$514,379

$369,019 Off-Site Economic Cost $

$466,032

$718,959 On-Site Exposure Cost $

$8,153

$8,153 On-Site Economic Cost $

$666,023

$666,023 Total Base Cost $

$1,654,587

$1,762,154 Base Cost with External Event Multiplier 2.0

$3,309,174

$3,524,309 Base Cost with External Event Multiplier 2.28

$3,772,461

$4,017,712

15. RAI 6 This RAI requested an assessment of the impact of uncertainty on the Phase I screening of SAMDAs due to either excessive cost or very low benefit similar to that given in response to the original RAI 7.a. The response to this new RAI does not provide this assessment. While Table 19 of the October 14, 2010, SAMDA submittal is cited, this table addresses the impact of uncertainty on the Phase II cost benefit analysis not the Phase I screening. The current marginal MACR is a factor of 2.6 times that on which the original screening was performed, while the risk profile of the current PRA is considerably different from that used in the original screening. These changes could impact the judgments made in the Phase I screening without requiring a Phase II cost evaluation. Provide the requested assessment.

TVA Response:

This response provides an assessment of the impact of uncertainty on the Phase I screening of SAMAs due to either excessive cost or very low benefit. A comparison of the Maximum Averted Cost of Risk (MACR) for the Revised RAI SAMA results are shown in Table 15-1. The Revised RAI sensitivity results show the 95% uncertainty (multiplier of 2.7) MACR for an External Event multiplier of 2.28 is $10,847,822. This $10,847,822 MACR value can be used to screen the Phase I SAMAs for either Excessive Cost or Very Low Benefit.

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Table 15 Revised RAI SAMA Maximum Averted Cost of Risk (MACR) Results Cost Description Revised (RAI) SAMA Results MACR Onsite Costs MACR Offsite Costs (Function of Core (Function of Core Total Damage without Damage and Release MACR Release Costs)

Costs)

Base Cost with External

$3,524,309

$1,348,352 38%

$2,175,957 62%

Event Multiplier 2.0 Base Cost with External

$4,017,712

$1,526,731 38%

$2,490,981 62%

Event Multiplier 2.28 95% Cost with External

$9,515,634

$3,615,941 38%

$5,899,693 62%

Multiplier 2.0 (95%

Multiplier 2.70) 95% Costwith External

$10,847,822

$4,122,173 38%

$6,725,650 62%

Multiplier 2.28 (95%

Multiplier 2.70)

If we assume 100% Core Damage Frequency (CDF) reduction is worth

$10,847,822, we can estimate the potential change in MACR of various impacts from proposed SAMAs. Table 15-2 shows the potential change of MACR of 7 cases of risk reduction according to what aspects of the CDF and Release category frequencies the proposed change impacts.

Table 15-2. 95% MACR Risk Reduction Case Types LERF Potential SAMA (Early &

Contribution Change in Case CDF Bypass)

LATE SERF to MACR MACR 1

Changed Linear Linear Linear 100.0% $10,847,823 2

Fixed Changed Fixed Fixed 10.6%

$1,150,720 3

Fixed Fixed Changed Fixed 47.9%

$5,201,087 4

Fixed Fixed Fixed Changed 3.2%

$345,785 5

Changed Changed Fixed Fixed 14.2%

$1,538,656 6

Changed Fixed Changed Fixed 77.0%

$8,348,905 7

Changed Fixed Fixed Changed 11.7%

$1,272,159 Case 1 is calculated as a linear function of the total MACR based on the fractional change in CDF. For Cases 2 through 4, the values are calculated by zeroing the release category frequency contribution and subtracting the result from the total MACR. For Cases 5 through 7, the values are calculated by zeroing the release category frequency contribution, subtracting the release frequency from the CDF, and then subtracting the changes from the total MACR.

For SAMA Case 1 in Table 15-2, if the risk reduction changed the CDF and the LERF, LATE and SERF Release categories are changed linearly, the MACR available for reduction would be the full $10,847,823. A 1% reduction in CDF would be worth $108,478, a 10% reduction in CDF would be worth $1,084,782 and so forth.

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For SAMA Cases 2 through 7, if the risk reduction change affected the LERF, LATE, SERF or combination of CDF and LERF, CDF and LATE, or CDF and SERF, and the other contributors to MACR were fixed, the table shows the potential change in MACR available for reduction. Based on comparing the SAMA change to one of these SAMA cases, we can screen for excessive costs based on the maximum potential change in MACR.

In addition to the potential maximum MACR available for reduction

($10,847,823), we can screen based on the potential benefit using the 7 case values in Table 15-2. Costs would have to be equal to or less than the corresponding maximum potential change in MACR to be cost beneficial.

Using the above cost benefit screening guidelines we have reviewed the Phase I SAMAs for Excessive Costs, Very Low Benefit, or low cost benefit (cost greater than potential benefit). All of the Phase I SAMAs that were screened for Excessive Cost or Very Low Benefit were rescreened and the results provided in Table 15-3.

In estimating the potential benefits of each SAMA, often the estimated percentage reduction in MACR was based on observations of RRWs for basic events in the model that would be affected by implementing the associated SAMA. Table 15-3 is sorted first by disposition and then by SAMA number. For others, knowledge of the implementation cost was used to qualitatively bound the anticipated benefit. All of the Phase I SAMAs remain screened out. This conclusion is unchanged if instead of using frequency weighted average consequences for each Release Category to compute MACR, the worst sub-category doses and consequences are conservatively used.

Some of the Phase I SAMAs pertaining to mitigation of Seal LOCA events may be retained for consideration along with the other Seal LOCA SAMAs being considered in Phase I1. See the TVA response to item 16 (Reference 1).

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Table 15-3. Phase I SAMA Candidates SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition 2

Replace lead-acid Extended DC power NEI 05-01 Basis for Screening: For a plant with Excessive batteries with fuel availability during an SBO.

(Rev A) significant construction already completed, Implementation cells.

the cost of implementation caused by Cost. (Table replacing all batteries with fuel cells, 15-2 Case 1) including structural, electrical, and HVAC changes required, including a fuel supply which does not currently exist on site, would exceed $2M and the bounding benefit would be less than 13% reduction in CDF. More complex technology with alternate fuel source requirements.

Combine with SAMA 174.

9 Provide an Increased availability of on-NEI 05-01 Basis for Screening: For a plant with Excessive additional diesel site emergency AC power.

(Rev A) significant construction already completed, Implementation generator.

the cost of implementation ($8,500,000 to Cost. (Table

$22,800,000, representative of similar 15-2 Case 1) nuclear power plants, WBN specific cost estimate $5,000,000) and benefit would be less than 28% reduction in CDF. WBN in process of updating cost estimate for non-SAMA reasons but expected to not be SAMA cost beneficial. Combine with SAMA 233.

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Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition 13 Install an Reduced probability of loss NEI 05-01 Basis for Screening: There are two Excessive additional, buried of off-site power.

(Rev A) existing 161 kV connections to a nearby Implementation off-site power dam switchyard above ground. The Cost. (Table source.

estimated cost of burying them would 15-2 Case 1) exceed $5M and the benefit would be much less than 28% reduction in CDF.

Pricing of above ground 161 kV line from hydro to construction yard was excessive.

Buried would be even more.

14 Install a gas Increased availability of on-NEI 05-01 Basis for Screening: For a plant with Excessive turbine generator.

site AC power.

(Rev A) significant construction already completed, Implementation the estimated cost of implementation Cost. (Table

($3,350,000 to $30,000,000, 15-2 Case 1) representative of similar nuclear power plants) would be much less than 28%

reduction in CDF. Based on cost of completion of 5th Diesel Generator, addition of turbine/gen with extra fuel source and building would be even more expensive.

15 Install tornado Increased availability of on-NEI 05-01 Basis for Screening: A gas turbine Excessive protection on gas site AC power.

(Rev A) generator is not available at the Watts Bar Implementation turbine generator.

site. Based on cost of completion of 5th Cost. (Table Diesel Generator, addition of turbine/gen 15-2 Case 1) with extra fuel source and building would be even more expensive.

24 Bury off-site power Improved off-site power NEI 05-01 Basis for Screening: The distance that Excessive

lines, reliability during severe (Rev A) would be necessary to bury offsite power Implementation weather.

lines would be significant since severe Cost. (Table weather to which transmission lines are 15-2 Case 1) susceptible typically affects a broad area.

For a plant with significant construction already completed, the estimated cost of E1-16

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition implementation would exceed the potential benefit. Similar to #13 except two lines buried. Approx 2 miles underground duct bank and 161 underground cable. Benefit would be much less than 40% of CDF.

25 Install an Improved prevention of NEI 05-01 Basis for Screening: The previous passive Excessive independent active core melt sequences.

(Rev A)

UHI system was removed from the WBN Implementation or passive high design. For a plant with significant Cost. (Table pressure injection construction already completed, the 15-2 Case 1) system.

estimated cost of implementation would exceed the bounding benefit. Design basis safety reanalysis would be around

$3M. Engineering, construction, hardware, and testing costs would be in addition to that. Total costs would greatly exceed $3M and bounding risk reduction benefit would be less than 25% reduction in CDF.

34 Provide an in-Continuous source of NEI 05-01 Basis for Screening: For a plant with Not Feasible to containment water to the safety injection (Rev A) significant construction already completed, implement reactor water pumps during a LOCA the estimated cost of implementation inside storage tank.

event, since water would exceed the bounding benefit. There containment released from a breach of is limited room in containment to install an due to limited the primary system collects in-containment RWST. Complex space available.

in the in-containment engineering problem. Ice condenser Will also screen reactor water storage tank, currently acts as in-containment water on Excessive and thereby eliminates the source approx equal to the RWST after Cost. (Table need to realign the safety melt. Additional tank would reduce 15-2 Case 1) injection pumps for long-containment available volume for pressure term post-LOCA suppression and raise post accident water recirculation.

level with additional post accident water level flooding issues.

37 Upgrade the For a plant like the NEI 05-01 Basis for Screening: For a plant with Excessive EI-17

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition chemical and Westinghouse AP600, (Rev A) significant construction already completed, Implementation volume control where the chemical and the estimated cost of implementation to Cost. (Table system to mitigate volume control system increase CVCS flow capacity would 15-2 Case 1) small LOCAs.

cannot mitigate a small exceed the bounding benefit. WBN LOCA, an upgrade would currently has 2 trains of high head decrease the frequency of charging pumps. Additional charging core damage.

pump would require additional power source and water supply. Recirculation from the sump would still be required.

Cost would exceed $2M and benefit would be much less than 10% reduction in CDF.

39 Replace two of the Reduced common cause NEI 05-01 Basis for Screening: For a plant with Excessive four electric safety failure of the safety (Rev A) significant construction already completed, Implementation injection pumps injection system. This the estimated cost of implementation to Cost. (Table with diesel-SAMA was originally replace the SI pumps would exceed the 15-2 Case 1) powered pumps.

intended for the bounding benefit. Current SI pumps are Westinghouse-CE System Diesel backed. Diesel driven pumps 80+, which has four trains would require a separate building along of safety injection, with appropriate protection (tornado, However, the intent of this seismic, etc., and ASME piping into SAMA is to provide containment).

diversity within the high-and low-pressure safety injection systems.

41 Create a reactor Allows low pressure NEI 05-01 Basis for Screening: For a plant with Excessive coolant emergency core cooling (Rev A) significant construction already completed, Implementation depressurization system injection in the the estimated cost of implementation to Cost. (Table system.

event of small LOCA and install larger PORVs would exceed the 15-2 Case 1) high-pressure safety bounding benefit. Would require ASME injection failure.

connections to the RCS and appropriately qualified valves and control circuits.

Safety analysis update including seismic RCS loop reanalysis would be required.

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Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition Cost would exceed $2M and benefit would be much less than 10% reduction in CDF.

55 Install an Reduced frequency of core NEI 05-01 Basis for Screening: For a plant with Excessive independent damage from loss of (Rev A) significant construction already completed, Implementation reactor coolant component cooling water, the estimated cost of implementation Cost. (Table pump seal injection service water, or station would exceed the bounding benefit.

15-2 Case 1) system, with blackout.

Hardware, building, facilities support would dedicated diesel.

be high cost. ASME, safety grade interface to CVCS. SAMA 56 (reactor coolant pump seal injection system without dedicated diesel) was screened out in Phase II evaluation. Would be considered with other Seal LOCA SAMAs.

77 Provide a passive, Reduced potential for core NEI 05-01 Basis for Screening: For a plant with Excessive secondary-side damage due to loss-of-(Rev A) significant construction already completed, Implementation heat-rejection loop feedwater events, the estimated cost of implementation Cost. (Table consisting of a would exceed the bounding benefit.

15-2 Case 1) condenser and Potential change is less than 50% of CDF.

heat sink.

A passive heat removal system using air as the ultimate heat sink would be extremely large and expensive to install.

78 Modify the startup Increased reliability of NEI 05-01 Basis for Screening: Implementation of this Excessive feedwater pump so decay heat removal.

(Rev A)

SAMA requires a flow path around the Implementation that it can be used isolation valves. Also for use during a Cost. (Table as a backup to the station blackout the Standby Feedwater 15-2 Case 1) emergency pump would have to be powered from a feedwater system, diesel generator. For a plant with including during a significant construction already completed, station blackout the estimated cost of implementation scenario.

would exceed the bounding benefit.

Would require flowpath from condenser through hotwell pumps, through condensate system and around safety El-19

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition grade isolation valves (or alternate power source to reopen valves and power pumps). Potential change is less than 50%

of CDF.

90 Create a reactor Enhanced debris cool NEI 05-01 Basis for Screening: For a plant with Excessive cavity flooding ability, reduced core (Rev A) significant construction already completed, Implementation system.

concrete interaction, and the estimated cost of implementation Cost. (Table increased fission product

($8,750,000, representative of similar 15-2 Case 2) scrubbing.

nuclear power plants) would yield a benefit of much less than 20% reduction in LERF.

91 Install a passive Improved containment NEI 05-01 Basis for Screening: The source of this Excessive containment spray spray capability.

(Rev A)

SAMA is the AP600 Design Certification Implementation system.

Review submittal. For a plant with Cost. (Table significant construction already completed, 15-2 Cases 2 the cost of implementation ($20,000,000, and 3) representative of similar nuclear power plants) would exceed the bounding benefit.

94 Install a filtered Increased decay heat NEI 05-01 Basis for Screening: For a plant with Excessive containment vent removal capability for non-(Rev A) significant construction already completed, Implementation to remove decay ATWS events, with the estimated cost of implementation Cost. (Table heat. Option 1:

scrubbing of released

($5,700,000, representative of similar 15-2 Case 3)

Gravel Bed Filter fission products.

nuclear power plants) would not reduce all Option 2: Multiple of the LATE consequences and would Venturi Scrubber result in a benefit of less than 50%

reduction in LATE.

95 Enhance fire Improved fission product NEI 05-01 Basis for Screening: Enhancements to the Excessive protection system scrubbing in severe (Rev A)

EGTS and ABGTS filters to provide Implementation and standby gas accidents.

scrubbing for ISLOCA source terms would Cost. (Table treatment system exceed the bounding benefit. This system 15-2 Case 2) hardware and is not currently credited in the PSA and procedures.

has limited capability for beyond design basis events due to filter loading concerns.

Upgrading the system for severe accidents E1-20

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition would require a redesign with more capable equipment. EPSIL already contains instructions for spraying release points with fire water, which would provide fission product scrubbing. Costs would exceed expected benefit.

97 Create a large Increased cooling and NEI 05-01 Basis for Screening: For a plant with Excessive concrete crucible containment of molten core (Rev A) significant construction already completed, Implementation with heat removal debris. Molten core debris the estimated cost of implementation Cost. (Table potential to contain escaping from the vessel is

($90,000,000 to $108,000,000, 15-2 Cases 2 molten core debris, contained within the representative of similar nuclear power and 3) crucible and a water plants) would exceed the bounding benefit.

cooling mechanism cools the molten core in the crucible, preventing melt-through of the base mat.

98 Create a core melt Increased cooling and NEI 05-01 Basis for Screening: For a plant with Excessive source reduction containment of molten core (Rev A) significant construction already completed, Implementation system.

debris. Refractory material the estimated cost of implementation Cost. (Table would be placed

($90,000,000, representative of similar 15-2 Cases 2 underneath the reactor nuclear power plants) would exceed the and 3) vessel such that a molten bounding benefit.

core falling on the material would melt and combine with the material.

Subsequent spreading and heat removal from the vitrified compound would be facilitated, and concrete attack would not occur.

99 Strengthen Reduced probability of NEI 05-01 Basis for Screening: For a plant with Excessive primary/secondary containment over-(Rev A) significant construction already completed, Implementation containment (e.g.,

pressurization, the cost of implementation would exceed Cost. (Table El-21

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition add ribbing to the bounding benefit.

15-2 Cases 2 containment shell).

and 3) 100 Increase depth of Reduced probability of NEI 05-01 Basis for Screening: For a plant with Excessive the concrete base base mat melt-through.

(Rev A) significant construction already completed, Implementation mat or use an the cost of implementation caused by Cost. (Table 15-alternate concrete reconstruction of the containment building 2 Cases 2 and material to ensure would exceed the bounding benefit.

3) melt-through does not occur.

102 Construct a Reduced probability of NEI 05-01 Basis for Screening: For a plant with Excessive building to be containment over-(Rev A) significant construction already completed, Implementation connected to pressurization, the cost of implementation ($10,000,000 Cost. (Table primary/secondary and up, representative of similar nuclear 15-2 Cases 2 containment and power plants) would exceed the bounding and 3) maintained at a benefit.

vacuum.

105 Delay containment Extended reactor water NEI 05-01 Basis for Screening: Delay of containment Excessive spray actuation storage tank availability.

(Rev A) spray actuation would require reanalysis of Implementation after a large LOCA.

safety analysis. Current safety analysis Cost. Would does not allow actuation delay. Cost of re-require analysis and implementation would exceed development the maximum benefit (<.0008 CDF) and NRC approval of new gothic containment model and revised mass/energy release model.

Costs are excessive unless done through an E1-22

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition Owners Group cost share with other ice condenser plants. (Table 15-2 Case 1) 106 Install automatic Extended time over which NEI 05-01 Basis for Screening: The estimated cost of Excessive containment spray water remains in the (Rev A) implementing a design change including Implementation pump header reactor water storage tank, reanalysis of the safety analysis is Cost. (Table throttle valves, when full containment considered excessive cost compared to 15-2 Case 1) spray flow is not needed.

the risk benefit. Would require development and NRC approval of new gothic containment model and revised mass/energy release model. Benefit is less than 1% of CDF. Costs are excessive unless done through an Owners Group cost share with other ice condenser plants.

(proposal in progress) 115 Locate residual Reduced frequency of NEI 05-01 Basis for Screening: For a plant with Excessive heat removal ISLOCA outside (Rev A) significant construction already completed, Implementation (RHR) inside containment, the estimated cost of implementation Cost. (Table containment.

($28,000,000, representative of similar 15-2 Case 5) nuclear power plants) would exceed the bounding benefit. Combine with SAMA 178.

119 Institute a Reduced frequency of NEI 05-01 Basis for Screening: The current cost of Excessive maintenance steam generator tube (Rev A) steam generator eddy current inspection is Implementation practice to perform ruptures.

approximately $1 million per steam Cost. (Table a 100% inspection generator. The cost of performing 100%

15-2 Case 5) of steam generator inspection including the cost of the added tubes during each outage time would exceed the bounding refueling outage.

benefit. SGTR IE reduction in CDF is very small.

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Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition 120 Replace steam Reduced frequency of NEI 05-01 Basis for Screening: The cost of replacing Excessive generators with a steam generator tube (Rev A) the steam generators at Watts Bar Unit 1 Implementation new design.

ruptures.

was $221,760,000. This exceeds the Cost. (Table bounding benefit. SGTR IE reduction in 15-2 Case 5)

CDF is very small.

121 Increase the Eliminates release NEI 05-01 Basis for Screening: For a plant with Excessive pressure capacity pathway to the (Rev A) significant construction already completed, Implementation of the secondary environment following a the estimated cost of implementation Cost. (Table side so that a steam generator tube would exceed the bounding benefit.

15-2 Case 5) steam generator rupture.

SGTR IE reduction in CDF is very small.

tube rupture would not cause the relief valves to lift.

122 Install a redundant Enhanced depressurization NEI 05-01 Basis for Screening: Normal and auxiliary Excessive spray system to capabilities during steam (Rev A) pressurizer spray capability is available in Implementation depressurize the generator tube rupture.

the current design. The estimated cost of Cost. ASME primary system implementation of a new pressurizer spray safety grade during a steam system would exceed the potential benefit.

connections to generator tube SGTR IE reduction in CDF is very small.

RCS and rupture.

civil/DBA reanalysis would drive costs high.

(Table 15-2 Case 5) 125 Route the Reduced consequences of NEI 05-01 Basis for Screening: For a plant with Excessive discharge from the a steam generator tube (Rev A) significant construction already completed, Implementation main steam safety rupture.

the estimated cost of implementation of a Cost. (Table valves through a new structure would exceed the bounding 15-2 Case 5) structure where a benefit. Installation of another structure, water spray would additional SRV tailpipe, and new SRVs, condense the larger Steam Gen connections to steam and remove accommodate additional piping pressure El-24

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition most of the fission drops and remain inside the current safety products.

analysis would be costly. SGTR IE reduction in CDF is very small.

126 Install a highly Increased reliability of NEI 05-01 Basis for Screening: For a plant with Excessive reliable (closed decay heat removal.

(Rev A) significant construction already completed, Implementation loop) steam the estimated cost of implementation of a Cost. (Table generator shell-water cooled isolation condenser would 15-2 Case 5) side heat removal exceed the bounding benefit. Potential system that relies change is less than 50% of CDF. A on natural passive heat removal system using water circulation and as the ultimate heat sink would be stored water extremely large and expensive to install.

sources 129 Vent main steam Reduced consequences of NEI 05-01 Basis for Screening: The estimated cost of Excessive safety valves in a steam generator tube (Rev A) design reanalysis and implementation of Implementation containment, rupture.

hardware changes would exceed bounding Cost. (Table benefit. Implementation would also have 15-2 Case 5) negative consequences since the increase in containment pressure would result in containment isolation phase B which would empty the RWST. This would convert the event into a LOCA with consequential challenges. SGTR IE reduction in CDF is very small.

133 Install an ATWS Increased ability to remove NEI 05-01 Basis for Screening: For a plant with Excessive sized filtered reactor heat from ATWS (Rev A) significant construction already completed, Implementation containment vent events.

the estimated cost of implementation Cost. (Table to remove decay would exceed the potential benefit; i.e.

15-2 Case 1) heat.

<.04 of CDF.

143 Upgrade fire Decreased consequences NEI 05-01 Basis for Screening: Two and three hour Excessive compartment of a fire.

(Rev A) regulatory required fire protection barriers Implementation barriers.

are installed and maintained. Non Cost. (Table regulatory required two hour fire barriers 15-2 Case 1)

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Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition are also credited in IPEEE. For a plant with significant construction already completed, the estimated cost of upgrading to 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> fire barriers would exceed the potential benefit. Potential SAMAs for FIVE contributors were described in the response to RAI 4d.

166 Create a water-This rubble bed would Cook Basis for Screening: For a plant with Excessive cooled rubble bed contain a molten core significant construction already completed, Implementation on the pedestal.

dropping onto the pedestal, the estimated cost of implementation Cost. (Table and would allow the debris

($18,000,000, representative of similar 15-2 Cases 2 to be cooled.

nuclear power plants) would exceed the and 3) bounding benefit.

172 Increase Reduces chance of Cook Basis for Screening: For a plant with Excessive containment containment overpressure significant construction already completed, Implementation design pressure.

failures.

the cost of implementation caused by Cost. (Table reconstruction of the containment building 15-2 Cases 2 would exceed the bounding benefit.

and 3) 211 Replace reactor Reduces core damage Cook Basis for Screening: For a plant with Excessive vessel with contribution due to vessel significant construction already completed, Implementation stronger vessel, failure.

the estimated cost of implementation Cost. (Table would exceed the bounding benefit.

15-2 Case 1) 214 Reinforce the Seismic failure of the steel Cook Basis for Screening: For a plant with Excessive seismic capacity of structure supporting the significant construction already completed, Implementation the steel structure auxiliary building would the estimated cost of implementation to Cost. (Table supporting the lead to collapse of the reinforce the auxiliary building to withstand 15-2 Case 1) auxiliary building.

building. Reinforcing the beyond-design-basis earthquake levels building potentially would exceed the potential benefit.

precludes or lessens this failure mode.

233 Implement The implementation of an Vogtle Basis for Screening: The cost of installing Excessive alternate AC power alternate AC power source an additional EDG has been estimated to Implementation source.

would most likely take the be greater than $20 million in the Calvert Cost. (Table E1-26

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition form of an additional EDG.

Cliffs Application for License Renewal. It 15-2 Case 1)

This SAMA would help was similarly estimated to be about mitigate LOSP events and

$26.09M for both units at Vogtle. As the would reduce the risk per unit cost of approximately $1 OM to during time frames of on-

$13M is greater than the Watts Bar line EDG maintenance, maximum benefit, it has been screened The benefit would be from further analysis.

increased if the additional DG could 1) be substituted for any current diesel that is in maintenance, and 2) if the diesel was of a diverse design such that CCF dependence was minimized.

242 Permanent, This SAMA provides a Wolf Basis for Screening: Local operation of Excessive Dedicated means of limiting the size Creek the TDAFWP is currently proceduralized.

Implementation Generator for the of a seal LOCA and This requires a dedicated DG with auto Cost. (Table NCP with Local providing primary side start capability and auto transfer to meet 15-2 Case 1)

Operation of TD makeup through the the 13 minute criteria to prevent seal AFW after 125V installation of a diesel LOCA. Additionally the DG and Charging Battery Depletion.

generator that can be Pump lube oil cooling and seal cooling rapidly aligned to the NCP would require CCS and ERCW. The from the MCR. Long term estimated cost of implementation of a secondary side cooling can dedicated DG would exceed the potential be provided through the benefit. This SAMA will be considered with operation of the turbine other Seal LOCA SAMAs under driven AFW pump using consideration if SAMA 58 is shown existing Wolf Creek unreliable. See also SAMA 226.

procedures. This arrangement would make it possible to provide adequate core cooling in E1-27

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition extended SBO evolutions.

253 Install SG Isolation Installation of primary side Wolf Basis for Screening: For a plant with Excessive Valves on the isolation valves provides Creek significant construction already completed, Implementation Primary Loop Side.

an additional means of the estimated cost of implementation Cost. (Table isolating and controlling an would exceed the bounding benefit.

15-2 Case 5)

SGTR event. These Would require ASME safety related piping valves would also eliminate and valves in additional to verification by the need for local action to analysis and testing of the increased flow complete a steam resistance. Also seismic reanalysis of the generator isolation after a RCS system. SGTR IE reduction in CDF tube rupture has occurred.

is very small.

261 Guidance to align In the event of a loss of IPE Basis for Screening: The cost to refurbish, Excessive the C-S diesel offsite power followed by complete and license the spare 5th DG Implementation generator.

the failure of both was estimated at -2 to 3 million in 1996.

Cost. See #9.

shutdown boards on one The potential benefit is much less than (Table 15-2 unit, the procedures would 20% reduction in CDF. Procedures to Case 1) be enhanced by adding the align the portable DG have already been guidance to align the C-S implemented.

diesel generator (i.e., the fifth diesel generator) to one of the shutdown buses not powered in the accident sequence due to the loss of a normally aligned diesel generator.

This alignment could be accommodated by including a reference to the spare diesel generator in AOI 35, "Loss of Offsite Power."

270 Delay containment From a severe accident IPE Basis for Screening: The current Watts Bar Excessive spray operation point of view, one potential design basis calculations require sprays to Implementation E1-28

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAM__A Title SAMA Discussion Source Phase I Comments Disposition relative to phase B conditions.

change, for consideration, would be the delaying of spray operations relative to the Phase B condition.

Currently, containment sprays actuate immediately in response to a Phase B condition, and air return fans (ARF) actuate after a 10 minute delay. This is currently a requirement of the design basis LOCA where switchover to containment spray recirculation occurs prior to ice melt; thereby limiting pressure increases below containment design pressure. Modular Accident Analysis Program analyses of representative core damage sequences indicate that actuation of the containment sprays while ice remains in the ice condenser has little impact on severe accident containment performance and may be detrimental in that operation of the sprays rapidly depletes the inventory of the RWST, makina its contents initiate at containment phase B conditions.

This SAMA would require reanalysis of Safety analysis; and the benefit is less than 1% of CDF. Therefore it is considered cost prohibitive.

Cost. See

1. 105. (Table 15-2 Case 1)

I I

I ___________

I El-29

Table 15-3. Phase ISAMA Candidates (Continuedi SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition unavailable for vessel injection. Since many scenarios have successful injection but failure at recirculation, the rapid depletion of the RWST due to spray operation accelerates the time to core damage. Therefore, an evaluation balancing the severe accident versus design basis requirements could be made.

274 Replace CCS Improves reliability of CCS RRW Basis for Screening: PD pump removed Excessive pumps with system.

Review from CVCS due to problems during initial Implementation positive testing on U1. WBN preference to avoid Cost. (Table displacement PD pumps on other systems. For a plant 15-2 Case 1) pumps.

with significant construction already completed, the estimated cost of implementation would exceed the bounding benefit.

287 Increase 0.232 Probability taken from CAFTA Basis for Screening: For a plant with Excessive probability of hot analysis of Sequoyah in IPE significant construction already completed, Implementation leg failure prior to NUREG/CR-4551 the estimated cost of implementation Cost. (Table Vessel breach would exceed the bounding benefit. A 15-2 Case 5) given no fundamental change in RCS piping design temperature would be needed to materially change this induced SGTR probability, plus new safety analysis including civil analysis would be required.

Since this change would not reduce the core damage frequency, the expected benefit is limited.

288 Reduce 5.14E-2 Probabilities taken from CAFTA Basis for Screening: For a plant with Excessive El-30

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition probability of NUREG-1570 IPE significant construction already completed, Implementation temperature the estimated cost of implementation Cost. (Table induced SGTRs for would exceed the bounding benefit. A 15-2 Case 5)

SBO sequences fundamental change in RCS/SGTTR with no secondary piping design would be needed to heat sink materially change this probability, likely including new steam generators. SGTR IE reduction in CDF is very small.

289 Reduce 3.81 E-2 Probabilities taken from CAFTA Basis for Screening: For a plant with Excessive probability of NUREG-1570 IPE significant construction already completed, Implementation temperature the estimated cost of implementation Cost. (Table induced SGTRs for would exceed the bounding benefit. A 15-2 Case 5) non-SBO fundamental change in RCS/SGTTR sequences with no piping design would be needed to secondary heat materially change this probability, likely sink including new steam generators. SGTR IE reduction in CDF is very small.

290 Reduce probability Probabilities taken from CAFTA Basis for Screening: For a plant with Excessive of rocket mode and NUREG/CR-6427 IPE significant construction already completed, Implementation ex-vessel steam the estimated cost of implementation Cost. (Table explosions causing would exceed the bounding benefit. A 15-2 Case 2) early containment fundamental change in Reactor vessel failure cavity design would be needed to materially change this probability.

5 Provide DC bus Improved availability of DC NEI 05-01 Basis for Screening: Since cross-ties are Very Low cross-ties.

power system.

(Rev A) available at the 480V supplies, and the #5 Benefit. (Table spare battery can be aligned to and supply 15-2 Case 1) any of the 4 buses, this SAMA has very little risk benefit (<2% CDF) Combine with SAMA 258.

16 Improve Increased availability of NEI 05-01 Basis for Screening: Four new inverters Very Low uninterruptible power supplies supporting (Rev A) have been incorporated and a spare is Benefit. (Table power supplies, front-line equipment.

already available. PRA modeling changes 15-2 Case 1)

El-31

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition to realistically reduce the loss of 120V AC initiating event frequencies has greatly reduced the importance of these supplies.

Benefit is less than 0.1% of CDF.

28 Add a diverse low Improved injection NEI 05-01 Basis for Screening: See response to item Very Low pressure injection capability.

(Rev A) 10, RAI 4.e.ii regarding the feasibility of a Benefit. (Table system.

similar diverse low pressure injection 15-2 Case 1) system. For a plant with significant construction already completed, the estimated cost of implementation would exceed the bounding benefit.

29 Provide capability Improved injection NEI 05-01 Basis for Screening: See response to item Very Low for alternate capability.

(Rev A) 10, RAI 4.e.ii regarding the feasibility of a Benefit. (Table injection via diesel-similar diverse low pressure injection 15-2 Case 1) driven fire pump.

system. There is a minimal benefit from this SAMA since it does not provide a recirculation path. Therefore it is not considered further. This SAMA is considered cost prohibitive relative to the potential benefit.

47 Enhance the Reduced potential for loss NEI 05-01 Basis for Screening: The location of the Very Low screen wash of SW due to clogging of (Rev A) intake on the river is protected from debris Benefit. (Table system.

screens.

therefore there is minimal benefit of this 15-2 Case 1)

SAMA (i.e. <1.6% CDF). Combine with SAMA 202 50 Enhance loss of Reduced probability of NEI 05-01 Basis for Screening: Upon receipt of any Very Low component cooling reactor coolant pump seal (Rev A)

RCP seal no. 1 outlet temperature high Benefit. (Table water procedure to failure.

alarm, AO1-15 & 24 require an RCS 15-2 Case 1) underscore the cooldown after isolation of the CCS path to desirability of the RCP thermal barrier and isolation of cooling down the RCP seal injection. This order of actions reactor coolant is deemed appropriate for overall plant system prior to stabilization following a loss of CCS.

El-32

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition seal LOCA.

Enhanced procedure will not affect the risk because of the rapid progression of the seal leak. Therefore, the intent of this SAMA is minimal benefit. This SAMA may be considered with other Seal LOCA SAMAs in Phase I1.

53 On loss of Increased time before loss NEI 05-01 Basis for Screening: AOI-13 for ERCW Very Low essential raw of component cooling (Rev A) system loss or rupture does not provide Benefit. (Table cooling water, water (and reactor coolant directions to quickly implement loss of 15-2 Case 1) proceduralize pump seal failure) during CCS procedure AOl-15 if ERCW cannot shedding loss of essential raw be restored. AOI-13, however, does component cooling cooling water sequences.

provide directions to trip all of the RCPs, water loads to isolate thermal barrier cooling, cooldown extend the the plant and cross-tie ERCW if available.

component cooling There is minimal risk reduction for CCS water heat-up time.

load shedding since this is a timing issue for recovery of ERCW. The PRA model credits manual alignment of fire protection water to ERCW as a backup... Therefore this SAMA has very low risk improvement benefit.

79 Replace existing Increased probability of NEI 05-01 Basis for Screening: The Watts Bar Very Low pilot-operated relief successful feed and bleed.

(Rev A) success criteria for bleed and feed is two Benefit. (Table valves with larger PORVs only if charging is not available.

15-2 Case 1) ones, such that Otherwise one PORV is sufficient. Larger only one is valves would require piping changes, block required for valve changes, and analysis changes.

successful feed There is a larger probability of leakage and bleed.

with larger valves. Based on this, this SAMA provides little benefit for the estimated cost.

80 Provide a Increased availability of NEI 05-01 Basis for Screening: Provisions for Very Low

_9 redundant train or components dependent on (Rev A) compensatory ventilation is in place for the Benefit. (Table E1-33

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition means of room cooling.

480V electric board rooms and margin to 15-2 Case 1) ventilation.

room heatup limits exists in the 480V transformer room. Plant chillers are being upgraded based on Freon considerations.

TVA has committed to purchasing new temporary ventilation equipment. See the response to item 11, RAI 4.e.v. This SAMA is considered not cost beneficial due to low risk benefit.

81 Add a diesel Improved diagnosis of a NEI 05-01 Basis for Screening: The diesel generator Very Low building high loss of diesel building (Rev A) building is manned during DG starts, and Benefit. (Table temperature alarm HVAC.

shiftly operator rounds take temperature 15-2 Case 1) or redundant measurements per SI-2. Therefore this louver and SAMA is considered very low benefit.

thermostat.

92 Use the fire water Improved containment NEI 05-01 Basis for Screening: Although there are Very Low system as a spray capability.

(Rev A) two 2-inch test connections (72-545 & 544)

Benefit. (Table backup source for that could be used to connect fire water to 15-2 Case 1) the containment containment spray, this lineup bypasses spray system.

the containment spray heat exchangers and would not remove containment heat.

It also cannot recirculate water from the containment sump. The low flow rate would be ineffective for fission product removal. Therefore this SAMA is considered very low benefit. Combine with SAMA 170.

116 Ensure ISLOCA Scrubbed ISLOCA NEI 05-01 Basis for Screening: The cost of Very Low releases are releases.

(Rev A) implementation of this SAMA has not been Benefit. (Table scrubbed. One estimated in detail. A minimum value of 15-2 Case 2) method is to plug

$100K for a hardware change is assumed drains in potential for screening purposes. Auxiliary building break areas so that releases are scrubbed by the Aux Building E1-34

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition break point will be Gas Treatment System (ABGTS); however covered with water.

the ABGTS may not be sized for ISLOCA releases. RHR suction and discharge lines are in the overhead and therefore would not be submerged. Contributes

<0.1 % to LERF). Therefore this SAMA is considered very low benefit. Combine with SAMA 237.

124 Provide improved Improved mitigation of NEI 05-01 Basis for Screening: In the latest model, Very Low instrumentation to steam generator tube (Rev A) the contribution of steam generator tube Benefit. (Table detect steam ruptures.

ruptures to the core damage frequency is 15-2 Case 5) generator tube only.0001. For a plant with significant ruptures, such as construction already completed, the Nitrogen-1 6 estimated cost of implementation of rad monitors.

monitors for each steam generator would exceed the bounding benefit.

131 Add a system of Improved equipment NEI 05-01 Basis for Screening: For a plant with Very Low relief valves to availability after an ATWS.

(Rev A) significant construction already completed, Benefit. (Table prevent equipment the estimated cost of installing a relief 15-2 Case 1) damage from valve system (likely well over $1 million) is pressure spikes judged to be excessive relative to the risk during an ATWS.

benefit since ATWS accounts for only 3.8

% of the total internal event CDF.

137 Provide capability Decreased time required to NEI 05-01 Basis for Screening: Implementation of this Very Low to remove power insert control rods if the (Rev A)

SAMA would require reevaluation of the Benefit. (Table from the bus reactor trip breakers fail loss of the loads on the unit boards.

15-2 Case 1) powering the (during a loss of feedwater Training and procedure changes is control rods.

ATWS which has rapid estimated to cost more than the potential pressure excursion).

benefit. The contribution of ATWS to CDF is 3.8%. Of this fraction roughly 95% is attributable to RCS overpressurization events resulting from inadequate pressure relief within the first couple of minutes.

E1-35

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition The ability to remove holding power from the control rods would have to be under a time constraint of 1-2 minutes in order to affect the resulting peak pressures. This response time is not feasible and later response times would have minimal benefit; i.e. about 0.2% of CDF. Therefore this SAMA is considered very low benefit.

147 Install digital large Reduced probability of a NEI 05-01 Basis for Screening: The FVI of large Very Low break LOCA large break LOCA (a leak (Rev A) break LOCAs to the core damage Benefit. (Table protection system.

before break).

frequency is less than.0008. For a plant 15-2 Case 1) with significant construction already completed, the estimated cost of implementation would exceed the bounding benefit.

152 Develop Reduced consequences of NEI 05-01 Basis for Screening: An anti barge boom is Very Low procedures for transportation and nearby (Rev A) installed at the intake structure to reduce Benefit. (Table transportation and facility accidents.

transportation accidents. There are no 15-2 Case 1) nearby facility identified hazardous barge shipments near accidents.

the Watts Bar site. Therefore this SAMA is considered very low benefit.

153 Install secondary Prevents secondary side NEI 05-01 Basis for Screening: The FVI of all Very Low side guard pipes depressurization should a (Rev A) secondary side breaks, both inside and Benefit. (Table up to the main steam line break occur outside containment, in the current model 15-2 Case 1) steam isolation upstream of the main is just.06. For a plant with significant

valves, steam isolation valves, construction already completed, the Also guards against or estimated cost of implementation (i.e.

prevents consequential greater than $700k) would exceed the multiple steam generator bounding benefit.

tube ruptures following a main steam line break event.

167 Enhance air return Provide an independent Cook Basis for Screening: 10 CFR 50.44 Very Low E1-36

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition fans (ice power supply for the air analysis shows these fans are a negligible Benefit. (Table condenser return fans, potentially contribution to the containment's ability to 15-2 Cases 2 containment),

reducing containment handle a hydrogen burn. Therefore this and 3) failure probability during SAMA is considered very low benefit.

SBO sequences.

183 Implement internal Options considered include Cook Basis for Screening: The current modeling Very Low flood prevention

1) use of submersible MOV of flooding concerns in the WBN PRA Benefit. (Table and mitigation operators, and 2) back flow does not indicate a vulnerability to this 15-2 Case 1) enhancements.

prevention in drain lines, item. Therefore this SAMA is considered very low benefit.

184 Implement internal Implement improvements Cook Basis for Screening: The current modeling Very Low flooding to prevent or mitigate 1) a of flooding concerns in the WBN PRA Benefit. (Table improvements rupture in the RCP seal does not indicate a vulnerability to this 15-2 Case 1) identified at Fort cooler of the CCW system, item. Therefore this SAMA is considered Calhoun Station.

2) an ISLOCA in a very low benefit.

shutdown cooling line, and

3) an AFW flood involving the need to possibly remove a watertight door.

For a plant where any of these apply, potentially reduces flooding risk.

199 Provide auxiliary Enhances ventilation in Cook Basis for Screening: Normal auxiliary Very Low building vent/seal auxiliary building.

building ventilation is not risk significant at Benefit. (Table structure.

Watts Bar unit 2. Therefore this SAMA is 15-2 Case 1) considered very low benefit.

222 Establish a Potentially reduces Cook Basis for Screening: There is a limited use Very Low preventive flooding initiating event of expansion joints at Watts Bar and no Benefit. (Table maintenance frequency and the failure indication of a vulnerability. Therefore this 15-2 Case 1) program for probability of plant SAMA is considered very low benefit.

expansion joints, components.

bellows, and boots.

225 Upgrade main Potentially reduces turbine Cook Basis for Screening: Since the turbine trip Very Low E1-37

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition turbine controls.

trip frequency.

initiator contributes less than 2% CDF and Benefit. (Table most turbine trips are not related to control 15-2 Case 1) problems, the estimated cost of implementation would exceed the minimal risk benefit from this SAMA. Therefore this SAMA is considered very low benefit.

234 Implement The implementation of an Vogtle Basis for Screening: The WBN design Very Low automatic initiation automatic HPI initiation initiates HPSI on low RCS pressure which Benefit. (Table of HPI on low RCS system would reduce the would result from an RCP seal LOCA.

15-2 Case 1) level (after AC potential for core damage The PRA model does not explicitly include power recovery),

from occurring following operator actions to restore the pumps after events where ac power is AC power recovery since this sequence is recovered, but where a dominated by non-recovery of AC power seal LOCA has already sources. Manual start of the pumps after occurred. In these cases, AC power recovery is already RCS level must be proceduralized. Including this operator restored to avoid core action would result in limited risk benefit damage from occurring, and therefore is not analyzed further.

254 Alternate Fuel Oil EDG failures related to Wolf Basis for Screening: Failure of the fuel oil Very Low Tank with Gravity failure of the fuel oil Creek transfer pumps contributes less than 1%

Benefit. (Table Feed Capability.

transfer pumps are the internal event CDF based on RRW 15-2 Case 1) currently considered to be review. Improvements in the fuel oil unrecoverable in the PSA transfer system are judged to be a minimal model. The installation of risk benefit. The cost of this enhancement a large volume tank at an has been previously estimated to be elevation greater than the

$150,000 by Wolf Creek.

EDG fuel oil day tanks would allow for emergency refill of the day tanks in the event of fuel oil transfer pump failure.

262 Provide A potential improvement IPE Basis for Screening: The potential Very Low connections for that could be evaluated is improvement was evaluated and there is Benefit. (Table El-38

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition centrifugal a plant change to provide low benefit to aligning a second charging 15-2 Case 1) charging pumps to connections for both pump to ERCW.

the ERCW system.

centrifugal charging pumps, on both units, to the ERCW system for lube oil cooling in the event of a loss of CCS cooling to the associated pump.

Currently, this capability is only available for centrifugal charging pump A on Unit 1.

273 Provide a Eliminates single failure RRW Check valve 62-504 is a single failure point Very Low redundant path for potential of RWST check Review for ECCS injection but it contributes Benefit. (Table ECCS suction from valve failure to open.

<.00001 to CDF in the SAMA model. The 15-2 Case 1) the RWST around cost of a design change, new hardware check valve 62-and analysis greatly exceeds the potential 504.

risk reduction benefit.

277 Replace shutdown Improved reliability of RRW Basis for Screening: The potential Very Low board chillers.

shutdown board HVAC.

Review improvement was evaluated by reviewing Benefit. (Table the risk reduction worth (RRW) of the 6.9 15-2 Case 1) kV board room ventilation and ventilation recovery. There is low benefit to these ventilation systems. However, these chillers are being upgraded and replaced for other reasons.

284 Improve training for Additional training may CAFTA MD and TD AFW pump isolation test Very Low MD AFW pump reduce assigned error rate IPE restoration errors (WHEMDA_1, Benefit. (Table train A or B WHEDA_2, and WHEAFW) can impact 15-2 Case 1) isolation tests AFW system reliability, especially under conditions of loss of a vital instrument bus or vital battery board. Human failure rate was re-evaluated substantially lower after E1-39

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition initial identification of this SAMA to recognize that the error must occur on at least two steam generators rather than just the flow path to just 1 steam generator.

Revised contribution is much less than 0.1% of CDF. Estimated cost is $26,773 for enhanced training.

286 Improve training to Additional training may CAFTA Human failure rate was re-evaluated Very Low avoid a TD AFW reduce assigned error rate IPE substantially lower after initial identification Benefit. (Table isolation test error of this SAMA to recognize that the error 15-2 Case 1) must occur on at least two steam generators rather than just the flow path to just 1 steam generator. Revised contribution is much less than 0.1% of CDF. Estimated cost is $26,773 for enhanced training.

296 Improve training Needed to address failure CAFTA Leading cutset involves common cause Very Low and procedures to combinations of DC buses, IPE failure of safeguards actuation signal in a Benefit. (Table respond to loss of vital instrument buses, and sequences where there is a plant trip 15-2 Case 1) both trains of AFW failures of SSPS.

without an SI condition (action HAOS3).

actuation signal Event importance markedly reduced to less than 1% now that initiating event frequencies for loss of inverters and battery boards have been lowered.

297 Improve remote Valve indication in MCR CAFTA Difficulty to inspect valves are more likely Very Low valve position allows operators to check IPE to be checked if indicated in MCR. Human Benefit. (Table indication in the realignment failure rate was re-evaluated substantially 15-2 Case 1)

MCR for MD AFW lower after initial identification of this pump isolation SAMA to recognize that the error must valves occur on at least two steam generators rather than just the flow path to just 1 steam generator. Revised contribution is much less than 0.1% of CDF El-40

Table 15-3. Phase I SAMA Candidates (Continued)

SAMA Number SAMA Title SAMA Discussion Source Phase I Comments Disposition 298 Require added Check is to be performed CAFTA Human failure rate was re-evaluated Very Low supervisory check separately from (not IPE substantially lower after initial identification Benefit. (Table to MD AFW pump concurrent to) the initial of this SAMA to recognize that the error 15-2 Case 1) train isolation valve checks must occur on at least two steam test procedure generators rather than just the flow path to just 1 steam generator. Revised contribution is much less than 0.1% of CDF 301 Require added Check is to be performed CAFTA Human failure rate was re-evaluated Very Low supervisory check separately from (not IPE substantially lower after initial identification Benefit. (Table to TD AFW pump concurrent to) the initial of this SAMA to recognize that the error 15-2 Case 1) train isolation valve checks must occur on at least two steam test procedure generators rather than just the flow path to just 1 steam generator. Revised contribution is much less than 0.1% of CDF 302 Improve remote Valve indication in MCR CAFTA Difficult to inspect valves are more likely to Very Low valve position allows operators to check IPE be checked if indicated in MCR. Human Benefit. (Table indication in the realignment failure rate was re-evaluated substantially 15-2 Case 1)

MCR for TD AFW lower after initial identification of this pump isolation SAMA to recognize that the error must valves occur on at least two steam generators rather than just the flow path to just 1 steam generator. Revised contribution is much less than 0.1% of CDF E1-41

ENCLOSURE 2 LIST OF COMMITMENTS

1. RAI 16 of the March 30, 2011, NRC to TVA letter requested the process TVA would use to evaluate SAMAs 215 and 226 if the seal package design is not proven reliable. In our response of May 13, 2011, TVA committed to re-evaluate the benefits of SAMAs 215, 226, 50, 55, and 56 for mitigation of RCP seal LOCA scenarios if SAMA 58 is not implemented. In response to RAI 5b of the March 30, 2011, letter, TVA further commits to add SAMAs 93 and 242 to this list for re-evaluation should SAMA 58 not prove reliable.

E2-1