ML14177A167

Probabilistic Risk Assessment (PRA) Summary Report - Information Previously Committed to Provide (TAC ME3334). Part 4 of 4

ML14177A167
Person / Time
Site:	Watts Bar
Issue date:	06/25/2014
From:	Tennessee Valley Authority
To:	Office of Nuclear Reactor Regulation
References
MDN-000-999-2008-0151, Rev. 001
Download: ML14177A167 (24)

Text

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Figure 19 - Unit 1 CDF Uncertainty Plot Reference 44, Figure 5.8-1 Li

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Figure 20 - Unat2 CDF Uncertainty PIot Reference 44, Figure 5.8-2

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I Al! Floods r Loss of Offsite Power (Grid Related) r Total Loss of Component Cooling System Unit 1 I Loss of Offsite Power (Plant Centered) r Small LOCA Stuck Open Safety Relief Valve rTotal Loss of ERCW r Scondary Break Outside Containment x Loss of Offsite Power (Weather lnduced)

Fig ure 21 - Unit 1 CDF Initiator Distribution

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r All Floods I Loss of Offsite Power (Grid Related) r Total Loss of Component Cooling System Unit 2 I Loss of Offsite Power (Plant Centered) r Small LOCA Stuck Open Safety Relief Valve rTotal Loss of ERCW I Secondary Break Outside Containment t Loss of Offsite Power (Weather lnduced)

Figure 22 - Unat2 CDF lnitiator Distribution

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6.00E-05 5.00E-06 4.00E-05 3.00E-05 2.00E-05 1.00E-05 0.00E+00

"..c"kW":ffi{d Figure 23 - LERF Comparison with Westinghouse 4-loop PIants Reference 44, Figure 5.4-2

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6.00E-05 5.00E-06 4.00E-05 3.00E-05 2.00E-06 1.00E-05 0.00E+00 Figure 24 - LERF Comparison with Westinghouse lce Condenser Containments

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rr Frcq,acncy / Prob&ilty Figure 25 - Unit 1 LERF Uncertainty PIot

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Figure 26 - Unat2 LERF Uncertainty PIot Lt

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Figure 27 - Unit I LERF Phenomena Distribution rT!-SGTR r PI.SGTR r DCH r ISLOCA and SGTR r SBO CFE (e.9. H2 Burns and EVSE)

I Non-SBO CFE (e.9. H2 Burns and EVSE) r Bypass/lsolation Failure (except TllPl-SGTR) r Hydrogen Detonation

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Figure 28 - Unit 2 LERF Phenomena Distribution ITI-SGTR r PI-SGTR I DCH r ISLOCA and SGTR r SBO CFE (e.9. H2 Burns and EVSE) r Non-SBO CFE (e.9. H2 Burns and EVSE) r Bypass/lsolation Failure (except TUP!-SGTR) r Hydrogen Detonation

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Figure 29 - Unit 1 LERF PDS Distribution IBin4 IBin2,;;Bih1 rBin3

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Figure 30 - Unat 2 LERF PDS Distribution

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r lnternal Flooding (RCW Line Rupture) w Loss of Offsite Power (Grid Related)

I Loss of Offsite Power (Weather lnduced) w Steam Line Break Outside Containment I Internal Flooding (HPFP Line Break)

I Loss of Offsite Power (Plant Centered) r Stuck Open Safety Relief Valve ffi Loss of all CCS Figure 31 - Unit 1 LERF lnitiator Contributions

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I lnternal Flooding (RCW Line Rupture) aa Loss of Offsite Power (Grid Related)

I Loss of Offsite Power (Weather lnduced)

• Steam Line Break Outside Containment r lnternal Flooding (HPFP Line Break)

I Loss of Offsite Power (Plant Centered) r Stuck Open Safety Relief Valve aw Loss of all ccs Figure 32 - Unat 2 LERF Initiator Contributions

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8.0 Conclusion This document represents a summary of the WBN Units 1 and2 Revision 1 CAFTA I PRA model. Appendix B provides the documentation of the Model of record as required by NEDP-26.

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Appendix A - Resolution of F&Os Note: See also notes in revision logs of appropriate system notebooks. For example, changes made to the internal flooding analysis to respond to flooding F&Os are documented in the revision log for the flooding notebook.

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RIsKM;il-frodel F&Os E*L rtr CAFTA fqoOef F&Os

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Appendix B - Documentation of Model of Record PRA Mode! of Record (MOR) Documentation Plant and Unit(s)

WBN Units 1 and 2 Model Revision Name and Number WBN PRA CAFTA Revision 1 Required Evaluation Documentation Report Section/Fi lename Name & Version of Software Utilized Summary Report, Table 52 F nal CDF Value Summary Report, Table 54 F na! LERF Value Summary Report, Table 54 Description of Model Reference 44, Section 3 Discussion of Maior Changes Summary Report, Section 6.1.14 Master Frequency File/Type Code Report None Data Titles/Gate Data/Basic Event Data WBN_U1_U2 Flood - NEW.caf, WSBN2 - NEW.rr lnitiating Event Frequency Report Summary Report, Table 3 Initiator Contribution to CDF Summary Report, Table 59, Table 61 lnitiator Contribution to LERF Summary Report, Table 91. Table g3 Model Stability - CDF/LERF versus Truncation Reference 44, Section 5.5, Reference 40, Section 5.4 Narrative of top ten sequences/cutsets Reference 44, Section 5.2 Number of saved sequences/cutsets Summary Report, Table 54 Top 1 00 sequences/cutsets Summary Report, Table 57. Table 58 Basic Event lmportance Report Summary Report, Appendix C FILEKEEPER Number for Model Reference 44, Computer File Storage lnformation Sheet Required MAAP Evaluation Documentation Report Section/F i len ame Version of MAAP Used Summary Report, Table 52 Description of Model Reference 43, Reference 40 Discussion of Model Changes None Parameter File Reference 43 lnput Files Summary Report, Table 23 Output Files None Plot Files None Narrative of Runs Reference 43, Reference 40 FILEKEEPER Number for Model References 43, 40, Computer File Storage lnformation Sheet Required Other Software Documentation Report Section/Fi lename Sofhrvare Utilized lncluding Versions Summary Report, Table 52 Description of Model N/A Discussion of Model Changes N/A Parameter File N/A lnput Files N/A Output Files N/A PIot Files N/A Narrative of Runs N/A FILEKEEPER Number for Model Summary Report, Computer File Storage lnformation Sheet Lndependent Review Report Summary Report, Reference 13 Disposition of Review Comments Letter Sumrnary Report, Appendix A TVA 41118 [06-2010]

Page 1 of 1 NEDP-26-1 [06-03-201 0]

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Appendix C - lmportance Reports tul BE lrportance.xlsx ffi"h iHftflJ Conponent Inportance. xlsx

ENCLOSURE 2 Tennessee Valley Authority Watts Bar Nuclear Plant, Unit 2 Docket No.50-391 lnformation Related to how the ilodel and the Peer Review Process Addressed the ltems ln The Regulatory Guide 1.200 Revision 2 Tables The commitment made in TVA letter dated June 8, 2010, "Watts Bar Nuclear Plant WBN)

Unit 2 - Request for Additional lnformation Regarding lndividual Plant Examination (TAC No.

ME3334)" is as follows:

UTVA will provide information how the model and the peer revielyprocess addressed the items in the Regulatory Guide 1.200 Revision 2 tables related to intemal events including internal flooding for which fhe fiIRC position was stated as 'Qualiftcation.'

TVA Response:

NRC endorsed the ASME PRA Standard but added a limited number of "qualifications" to their endorsement, indicating that they wanted additional information in a few cases. By reference to the ASME PRA Standard, Reg. Guide 1.200, R2, and the WBN peer review report, it was determined that there are three applicable items in Reg. Guide 1.200, R2 for which NRC had a "qualification."

Two items ("DA-C15" and "DA-D9") pertain to how the possibility of repair of failed equipment is modeled in the PRA. The WBN model does not consider repair, see, for example, Page 51 of MDN-000-999-2008-01 43, R1.

One item ("lFSN-A6") pertains to the internalflooding analysis. lt asks:

ASSESS qualitatively the impact of flood-induced mechanisms that are not formally addressed (e.9., using the mechanisms listed under Capability Category lll of this requirement), by using conservative assumptions.

The'Tlood-induced mechanisms" that are referenced include "Failure by submergence, spray, jet impingement, pipe whip, humidity, condensation, temperature concerns, and any other identified failure modes."

The WBN lnternal Flooding Analysis, MDN-OOO-999-2008-0146, R2, page 34 says:

The effects of submergence, spray, and steam on electrical equipment were explicitly considered in the analysis. Equipment failure due to condensation, pipe whip, jet impingement, pressure and temperature concerns are not considered in this analysis (with the exception of temperature concerns for HELB scenarios).

The approach that was taken in the WBN flooding analysis, in conjunction with information from the station HELB and MELB analyses qualitatively supports a conclusion that risk due to the flood-induced mechanisms listed is acceptable. The WBN PRA internalflooding analysis addressed effects of submergence, spray and steam. The other effects should be bounded by the station HELB analysis. That analysis does not quantify risk as described in section 3 of the WBN UFSAR:

E2-1

HELB and MELB flooding effects are evaluated on all essential equipment on a case by case basis. lf it is determined that an essential component is not qualified or cannot be demonstrated to operate under the adverse flood conditions, then the essential component is protected. Protection is accomplished by relocating the component or by installing a barrier or curb. Safe shutdown is ensured for design basis HELB/MELB flooding events through these actions.

Given the small likelihood of the HELB and MELB initiating events and given that sufficient equipment will remain available to assure safe shutdown given a HELB / MELB event (i.e.

CCDPs would be substantially< 1), it is expected that the risk associated with the additional failure modes would be acceptable.

The WBN Peer Review did not specifically consider how the HELB failure modes were addressed but classified element IFSN-A6 as "Category ll."

E2-2

ENCLOSURE 2 Tennessee Valley Authority Watts Bar Nuclear Plant, Unit 2 Docket No. 50-391 Information Related to how the Mode! and the Peer Review Process Addressed the ltems In The Regulatory Guide 1.200 Revision 2 Tables The commitment made in TVA letter dated June 8, 2010, "Watts Bar Nuclear Plant WBN)

Unit 2 - Request for Additional !nformation Regarding lndividual Plant Examination (TAC No. ME3334)" is as follows:

• TVA will provide information how the model and the peer revielvprocess addr*sed the items in the Regulatory Guide 1.200 Revision 2 tables related to internal events including internal flooding for which fhe IIIRC position was stated as "Qualification."

TVA Response:

NRC endorsed the ASME PRA Standard but added a limited number of "qualifications" to their endorsement, indicating that they wanted additional information in a few cases. By reference to the ASME PRA Standard, Reg. Guide 1.200, R2, and the WBN peer review report, it was determined that there are three applicable items in Reg. Guide 1.200, R2, for which NRC had a "qualification."

Two items ("DA-C15" and "DA-D9") pertain to how the possibility of repair of failed equipment is modeled in the PRA. The WBN model does not consider repair; see, for example, Page 51 of MDN-000-999-2008-0143, R1 (Attachment to this enclosure).

One item ("lFSN-A6") pertains to the internalflooding analysis. lt asks:

ASSESS qualitatively the impact of flood-induced mechanisms that are not formally addressed (e.9., using the mechanisms listed under Capability Category lll of this requirement), by using conservative assumptions.

The'Tlood-induced mechanisms" that are referenced include "Failure by submergence, spray, jet impingement, pipe whip, humidity, condensation, temperature concerns, and any other identified failure modes."

The WBN lnternal Flooding Analysis, MDN-000-999-2008-0146, R2, page 34 says:

The effects of submergence, spray, and steam on electrical equipment were explicitly considered in the analysis. Equipment failure due to condensation, pipe whip, jet impingement, pressure and temperature concerns are not considered in this analysis (with the exception of temperature concerns for HELB scenarios).

The approach that was taken in the WBN flooding analysis, in conjunction with information from the station HELB and MELB analyses qualitatively supports a conclusion that risk due to the flood-induced mechanisms listed is acceptable. The WBN PRA internalflooding analysis addressed effects of submergence, spray and steam. The other effects should be bounded by the station HELB analysis. That analysis does not quantify risk as described in Section 3 of the WBN UFSAR:

E2-1

HELB and MELB flooding effects are evaluated on all essential equipment on a case by case basis. lf it is determined that an essential component is not qualified or cannot be demonstrated to operate under the adverse flood conditions, then the essential component is protected. Protection is accomplished by relocating the component or by installing a barrier or curb. Safe shutdown is ensured for design basis HELB/MELB flooding events through these actions.

Given the small likelihood of the HELB and MELB initiating events and given that sufficient equipment will remain available to ensure safe shutdown given a HELB/MELB event (i.e.,

CCDPs would be substantially< 1), it is expected that the risk associated with the additional failure modes would be acceptable.

The WBN Peer Review did not specifically consider how the HELB failure modes were addressed but classified element IFSN-AO as "Category ll."

E2-2

Attachment Page 51 of MDN-000-999-2008-01 43, R1 A-1

Calculation No. M DN-000.999 '2008$143 Rev: 001 Plant: WBN Unit 0 Page: 5t Subiect:

WBN PROBASUSNC RlsK ASSESSi'ENT - SYSTEMS ANALYSIS SU]IiMARY SR lndex Capability Category ll Requirement AddrEssed in System Notebook Section Comments SY,\\23 DEVELOP syslem model nomenclature in a consistent manner to allow model manipulation and to represent the sarn designator when a component failure mode is used in multiple systems or trains.

5.4, Aprelndix c-1 Nomenclature is defined in this notebook Section 4.1 SY.\\24 DO NOT MODEL the repair of hardware faults, unless the probability of repair is iusti*ed through an adequate analysis or examination of data. (See DA-C15.)

N/A Repair ol har*rrtare faultE was not modeled. See Section 3,5 of this notebook.

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