CNL-14-160, Update to the License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants for the Browns Ferry Nuclear Plant, Units 1, 2 and 3
| ML14260A324 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/16/2014 |
| From: | James Shea Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CNL-14-160 L44 140916 002 | |
| Download: ML14260A324 (25) | |
Text
L44 140916 002 1101 Market Street, Chattanooga, Tennessee 37402 CNL-14-160 September 16, 2014 10 CFR 50.90 10 CFR 2.390 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Units 1, 2, and 3 Renewed Facility Operating License Nos. DPR-33, DPR-52, and DPR-68 NRC Docket Nos. 50-259, 50-260, and 50-296
Subject:
Update to the License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants for the Browns Ferry Nuclear Plant, Units 1, 2, and 3 (TAC Nos. MF1185, MF1186, and MF1187)
References:
- 1. Letter from Tennessee Valley Authority (TVA) to NRC, "License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants (2001 Edition) (Technical Specification Change TS-480)," dated March 27, 2013 (ADAMS Accession No. ML13092A393)
- 2. Letter from TVA to NRC, "Response to NRC Request to Supplement License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants for the Browns Ferry Nuclear Plant, Units 1, 2, and 3 (TAC Nos.
MF1185, MF1186, and MF1187)," dated May 16, 2013 (ADAMS Accession No. ML13141A291)
- 3. Letter from TVA to NRC, "Response to NRC Request for Additional Information Regarding the License Amendment Request to Adopt NFPA 805 Performance-Based Standard for Fire Protection for Light Water Reactor Electric Generating Plants for the Browns Ferry Nuclear Plant, Units 1, 2, and 3 (TAC Nos. MF1185, MF1186, and MF1187) - Set 5,"
dated March 14, 2014 (ADAMS Accession No. ML14079A159)
- 4. NRC Letter, "Summary of June 26, 2014, Meeting with Tennessee Valley Authority Regarding License Amendment Request to Adopt National Fire Protection Association Standard 805 for Browns Ferry Nuclear Plant Units 1, 2, and 3 (TAC Nos. MF1185, MF1186, and MF1187)," dated June 29, 2014 (ADAMS Accession Number ML14183B546)
U.S. Nuclear Regulatory Commission Page 2 September 16, 2014 By letter dated March 27, 2013 (Reference 1), Tennessee Valley Authority (TVA) submitted a license amendment request (LAR) for Browns Ferry Nuclear Plant (BFN), Units 1, 2, and 3, to transition to National Fire Protection Association Standard (NFPA) 805. In addition, by letter dated May 16, 2013 (Reference 2), TVA provided information to supplement the Reference 1 letter.
By letter dated March 14, 2014 (Reference 3), TVA provided discussion of modifications included in LAR AttachmentS, Table S-2, "Committed Modifications," that TVA is either modifying or deleting . During a public meeting on June 26, 2014 (Reference 4), TVA informed the NRC that it planned to submit additional changes to the committed modifications by letter in August 2014. In subsequent telephone communications, TVA agreed to submit the additional changes by September 16, 2014. The enclosure to this letter provides descriptions of the additional changes to the committed modifications described in the LAR, AttachmentS, Table S-2. The changes to the committed modifications described in the enclosure, with the exception of Modification 92 and Modification 94, were discussed with the NRC Staff during a teleconference on August 29, 2014.
Consistent with the standards set forth in Title 10 of the Code of Federal regulations (10 CFR), Part 50.92(c), TVA has determined that the additional information, as provided in this letter, does not affect the no significant hazards consideration associated with the proposed application previously provided in Reference 1.
There are no new regulatory commitments contained in this submittal. Please address any questions regarding this submittal to Mr. Edward D. Schrull at (423) 751-3850.
I declare under penalty of perjury that the foregoing is true and correct. Executed on this 16th day of September 2014.
Enclosure:
Revisions to Committed Modifications cc (Enclosure):
NRC Regional Administrator- Region II NRC Project Manager- Browns Ferry Nuclear Plant NRC Senior Resident Inspector- Browns Ferry Nuclear Plant State Health Officer, Alabama State Department of Health
ENCLOSURE Tennessee Valley Authority Browns Ferry Nuclear Plant, Units 1, 2, and 3 Revisions to Committed Modifications License Amendment Request (LAR) Attachment S, Table S-2, "Committed Modifications,"
provided the list of committed modifications associated with implementing NFPA 805. As a result of continuing reviews of the modifications, TVA has revised the scope or eliminated the modifications discussed in this enclosure. Attachment 1 describes revisions to modifications that are retained in LAR, Attachment S, Table S-2. Attachment 2 describes those modifications that are deleted from LAR, Attachment S, Table S-2. Attachment 3 describes changes to modifications that TVA is evaluating for potential revision in the future.
A revision to the LAR incorporating changes associated with the modification revisions and deletions discussed in this enclosure will be provided to the NRC after the Fire PRA is updated and additional quantification is performed in response to remaining NRC Requests for Additional Information (RAIs). When the final risk numbers are calculated, they will be verified to meet the acceptance criteria in RG. 1.174, as required by LAR, Table S-3, Implementation Items, Item 32.
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ATTACHMENT 1 TO ENCLOSURE Tennessee Valley Authority Browns Ferry Nuclear Plant, Units 1, 2, and 3 Revisions to Committed Modifications Revisions to Modifications Retained in LAR, Attachment S, Table S-2 E-2
Modification 29 Description of Modification:
"Replace 250V Turbine Building Distribution Boards (1, 2, and 3) Normal and Alternate Feeder Breakers to provide breaker coordination."
Description of Revision to Modification:
License Amendment Request (LAR), Attachment S, Table S-2, Plant Modifications Committed, item 29 is revised to "Change circuit protective scheme for 250V Turbine Building Distribution Boards (1, 2, and 3) Normal and Alternate Feeder Breakers to provide breaker coordination."
Justification:
TVA will provide an equivalent modification which may not involve replacement of the breakers.
Available replacement breakers may not fit in the existing panel.
Variance from Deterministic Requirements (VFDR), Recovery Action, and LAR, Attachment A, NEI 04-02 Table B-1 Transition of Fundamental Fire Protection Program & Design Elements, Changes:
This issue is not associated with any VFDR.
Estimated Probabilistic Risk Impact:
This change is consistent with the PRA model and therefore will have no adverse effect on risk quantification.
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Modification 31 Description of Modification:
"Change breaker sizes or settings; or cables to protect approximately 139 BOP cables from auto ignition."
Description of Revision to Modification:
LAR, Attachment S, Table S-2, item 31 is revised to "The population of circuits identified in of Calculation EDQ0999870077, Revision 32, "BFN Analysis of the Auxiliary &
Control Power System to Identify Associated Circuits - 10CFR50 Appendix R," as not having adequate protection from auto ignition will be further evaluated and those that could propagate a fire from the initial scenario to another location will be modified to protect cables from auto ignition."
Justification:
The basis for this modification is to support the fire modeling analysis assumption that fire scenarios do not initiate a fire in other locations due to inadequate protection against cable auto ignition. Some of the circuits require modification; however, this basis can be demonstrated in some of the circuits by analysis.
A population of circuits is identified in the BFN Associated Circuits analysis as not having adequate protection against cable auto ignition. For Appendix R compliance, these circuits were dispositioned by analysis alone.
NFPA 805 transition necessitates refinement of the Appendix R analysis to use more restrictive requirements that address fire scenarios rather than fire areas. These circuits may be found acceptable by analysis using one of the following methods.
- 1. The cable is routed totally within a compartment only analyzed by full compartment burn.
- 2. Cable impedance is credited to limit available fault current provided that the minimum required cable length from the source panel is located within a compartment only analyzed by full compartment burn.
- 3. Cable impedance is credited to limit available fault current provided that the portion of required cable length routed externally to the source panel remains within the horizontal footprint of the source panel.
Circuits not found acceptable by analysis will be modified to provide cable protection as required by the revised modification wording.
VFDR, Recovery Action, and LAR, Attachment A Changes:
This issue is not associated with any VFDR.
Estimated Probabilistic Risk Impact:
This change is consistent with the PRA model and therefore will have no adverse effect on risk quantification.
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Modification 50b Description of Modification:
"Re-route cable 0PP277-B (86-U1B cable) in FA 01-01 to prevent spurious closure of alternate feeder breaker (1712) when Normal feeder is closed."
Description of Revision to Modification:
LAR, Attachment S, Table S-2, item 50b is revised to "Install an interposing relay to isolate cable 0PP277-B from the closing circuit of alternate feeder breaker 1712 to prevent closure when the Normal feeder breaker is closed."
Justification:
The interposing relay provides equivalent separation by circuit isolation rather than cable separation to prevent spurious closure of breaker 1712. A similar approach is used for LAR, Table S-2, items 8, 13 and 18 to prevent spurious breaker closure.
VFDR, Recovery Action, and LAR, Attachment A Changes:
Associated VFDR-01-01-0016 and VFDR-01-02-0007 are not affected by the revision of this modification.
Estimated Probabilistic Risk Impact:
This change will have no adverse effect on risk quantification in Fire Area (FA) 01-01, but will reduce risk by eliminating spurious operation of the alternate feeder breaker when the Normal feeder breaker is closed in FA 01-02.
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Modification 55 Description of Modification:
"Install or modify mode switches at the [Reactor Motor-Operated Valve Board] RMOV BD for Shutdown Cooling Suction Valves (FCV-074-0002, 12, 25 and 36 for all 3 Units) and Suppression Pool Suction Valves (3-FCV-074-0001, 12, 35) to prevent spurious actuation during power operation for fires external to the RMOV BD."
Description of Revision to Modification:
LAR, Attachment S, Table S-2, item 55 is revised to "Install or modify mode switches at the Reactor Motor-Operated Valve Board (RMOV BD) for Suppression Pool Suction Valves (3 FCV 074-0001, 12, 35) to prevent spurious actuation during power operation for fires external to the RMOV BD."
Justification:
The purpose of the modification to the Shutdown Cooling Suction Valves was to prevent spurious opening and allow credit for recovery of Residual Heat Removal (RHR) Suppression Pool Cooling (SPC) in the Fire PRA model. Alternate Shutdown Cooling (ASDC), which performs an equivalent decay heat removal function, is being added to the Fire PRA model as an additional success path to SPC.
The original basis for modification 55 was to recover one loop of SPC to accomplish decay heat removal from the primary containment. The same function is accomplished in the Nuclear Safety Capability Analysis (NSCA) and in the current Appendix R safe shutdown analysis using the ASDC mode of RHR. In this mode, water from the Suppression Pool is supplied by an RHR pump to the reactor vessel via the RHR Heat Exchanger and Low Pressure Coolant Injection (LPCI) flow path and returned to the Suppression Pool via the Safety Relief Valves (SRVs).
This forms a closed loop circulation path similar to SPC, but addresses both inventory makeup and decay heat removal with one RHR mode requiring less equipment and having less vulnerability to fire damage. ASDC was not modeled in the internal events PRA or in the Fire PRA developed for NFPA 805 transition, increasing the apparent risk worth of SPC.
ASDC is sufficiently modeled to allow a sensitivity analysis to be performed for elimination of the subject SPC modifications. When the Fire PRA model is in a more refined state with modeling of ASDC and model changes, the risk worth of (or risk improvement gained from) this modification is expected to be minimal and the portion of modification 55 not related to ASDC can be removed from the Fire PRA model.
A qualitative sensitivity study of the risk impact of modifications 55, 56, 59, 66, and 89 was performed by examining the availability of SPC in the Fire PRA model used to develop the LAR (which did not include ASDC) and the availability of both features in the Fire PRA model using the revised modification 55; deleting modifications 56, 59, 66, and 89; and adding ASDC. The results of this qualitative sensitivity study confirm that the proposed revision of modification 55 and deletion of modifications 56, 59, 66, and 89 do not have an unacceptable effect on fire CDF and LERF when ASDC is credited as an alternative decay heat removal method to SPC. The change in risk due to the modification removal is considered small.
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VFDR, Recovery Action, and LAR, Attachment A Changes:
Associated VFDR-16-0126 is not affected by the revision of this modification.
Estimated Probabilistic Risk Impact:
This change may have a small adverse effect on risk quantification, as discussed above.
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Modification 60 Description of Modification:
"Modify the control circuit for Bus Tie breakers 1632, 1732, 1642 and 1742 to prevent spurious closure."
Description of Revision to Modification:
LAR, Attachment S, Table S-2, item 60 is revised to "Modify the control circuit for Bus Tie breakers 1642 and 1742 to prevent spurious closure."
Justification:
Breakers 1632 and 1732 do not have cables outside of the switchgear that can cause spurious closure. Therefore, without a spurious closure concern, they do not require modification.
VFDR, Recovery Action, and LAR, Attachment A Changes:
Associated VFDR-01-03-0050 and VFDR-01-04-0054 are not affected by the revision of this modification. VFDR-03-03-0057 will be revised to eliminate failure of breakers 1632 and 1732 and will no longer be associated with LAR, Table S-2, item 60.
Estimated Probabilistic Risk Impact:
This change is consistent with the Fire PRA model and therefore will have no adverse effect on risk quantification.
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Modification 76 Description of Modification:
"Install Masterpac breakers in 480V Shutdown Board NORM and ALT feeder breakers which have mechanical trip/close feature."
Description of Revision to Modification:
LAR, Attachment S, Table S-2, item 76 is revised to "Install separate emergency control power fuses in 480V Shutdown Board NORM and ALT feeder breakers."
Justification:
Separate emergency control power fuses provide a function equivalent to the mechanical trip/close features of the Masterpac breakers.
VFDR, Recovery Action, and LAR, Attachment A Changes:
This issue is not associated with any VFDR.
Estimated Probabilistic Risk Impact:
This change is consistent with the Fire PRA model and therefore will have no adverse effect on risk quantification.
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Modification 81 Description of Modification:
"Provide a pull-to-lock function for all RHR pumps using the MCR hand switch."
Description of Revision to Modification:
LAR, Attachment S, Table S-2 is revised to separate item 81 into two separate modifications.
"81a - Modify protective relay logic for all eight DGs to eliminate the lockout feature from the 51V relay and to only trip the DG output breaker.
81b - Provide a pull-to-lock function for RHR pumps 1B, 2C and 3A using the MCR hand switch."
Justification:
TVA has determined that a simple pull-to-lock switch alone will not accomplish the desired equipment protection. This modification is based upon resolution of two separate equipment failure issues for fires in FA 16. TVA plans the following approach:
Un-recoverable overload damage to credited Diesel Generators The original basis for the modification was to prevent unrecoverable damage to a credited Diesel Generator (DG) in case of spurious pump start. Modification 81 originally proposed the use of a pull-to lock circuit to prevent spurious start of RHR pumps for fires in FA 16. TVA initially assumed that loads associated with starting an RHR pump out of sequence (i.e., spurious start of an RHR pump with significant loads already present) would result in permanent damage to the DG. Therefore, a modification was needed to prevent spurious start of loads large enough to cause damage in order to support recovery of 4 kiloVolt (kV) power supplies after securing spurious loads.
TVA subsequently determined that the DGs would not be permanently damaged due to overloading and that existing protective relays for the DGs and the individual motor loads would protect the equipment and allow the DG function to be recovered after the loading issues are resolved by recovery actions.
Proposed modification 81a will modify the protective relay scheme for the DGs to improve the feasibility of the recovery actions assuming actuation of protective relays. Currently, the DG overcurrent relays trip and lock out the associated DG. Modification 81a is intended to only open the DG output breaker thus simplifying recovery actions.
RHR Pump Deadheading Spurious start of RHR pumps with failure of the minimum flow valves requires the capability to stop the pumps immediately from the Main Control Room (MCR). The pull-to-lock feature required by modification 81b will address this failure mode, but is only needed for RHR pumps that are credited in FA 16 scenarios (i.e., RHR pumps 1B, 2C, and 3A). Therefore, modification 81b will require pull-to-lock functions to be installed on RHR pumps 1B, 2C, and 3A in lieu of all RHR pumps.
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VFDR, Recovery Action, and LAR, Attachment A Changes:
This issue is not associated with any VFDR.
Estimated Probabilistic Risk Impact:
This change is consistent with the Fire PRA model and therefore will have no adverse effect on risk quantification.
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Modification 87 Description of Modification:
"Enclose power cables PP626 and ES50-I in ERFBS [Electrical Raceway Fire Barrier System] in Fire Area 05."
Description of Revision to Modification:
LAR, Attachment S, Table S-2, item 87 is revised to "Enclose power cable PP626 in ERFBS in Fire Area 05."
Justification TVA has determined that cable ES50-I is not located in FA 05 and therefore meets separation requirements without the ERFBS modification.
VFDR, Recovery Action, and LAR, Attachment A Changes:
Associated VFDR-05-006 will be revised to delete reference to cable ES50-1. Resolution of the VFDR will not be affected.
Estimated Probabilistic Risk Impact:
This change may result in a decrease in risk.
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Modification 92 Description of Modification:
"Enclose normal control power cable 3B193-B2 for 4kV Shutdown Board 3ED in ERFBS in Fire Area 21."
Description of Revision to Modification:
LAR, Attachment S, Table S-2, item 92 is revised to "Re-route cable 3B193-B2 away from Fire Area 21."
Justification Removing the cable from FA 21 provides separation equivalent to enclosure in an ERFBS. The same cable is being re-routed out of the adjacent FA 03-03 for modification 94 and therefore the two modifications will be integrated.
VFDR, Recovery Action, and LAR, Attachment A Changes:
Associated VFDR 21-0007 will not be affected by the revision of this modification.
The ERFBS associated with the original modification 92 was incorrectly treated as a deterministic resolution for VFDR- 21-0007. This modification was to apply a one-hour ERFBS in an area that does not have automatic suppression. The revised modification 92 resolves this deficiency by eliminating the need for an ERFBS in FA 21.
Estimated Probabilistic Risk Impact:
This change will result in a decrease in risk in FA 21 relative to crediting ERFBS.
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Modification 94 Description of Modification:
"Re-route normal control power cable 3B193-B2 for 4kV Shutdown Board 3ED out of Fire Area 03-03."
Description of Revision to Modification:
LAR, Attachment S, Table S-2, item 94 is revised to "Re-route normal control power cable 3B193-B2 for 4kV Shutdown Board 3ED out of Fire Area 03-03 and enclose the new cable route in ERFBS in Fire Area 03-02."
Justification Alternate routes available for cable 3B193-B2 create new separation issues. TVA determined that re-routing the cable into FA 03-02 provides the optimum location for the cable route, but requires the cable to be enclosed in ERFBS to resolve the newly created separation issue.
VFDR, Recovery Action, and LAR, Attachment A Changes:
Associated VFDR-03-03-0064 and VFDR-03-03-0080 will not be affected by the revision of this modification.
Estimated Probabilistic Risk Impact:
This change may have a small adverse effect on risk quantification in FA 03-02. Modeling of ERFBS includes a risk of failure relative to re-routing the cable out of the fire area.
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ATTACHMENT 2 TO ENCLOSURE Tennessee Valley Authority Browns Ferry Nuclear Plant, Units 1, 2, and 3 Revisions to Committed Modifications Modifications Deleted From LAR, Attachment S, Table S-2 E-15
Modification 34 Description of Modification:
"Install a control room switch and fuses to isolate 4 kV Shutdown Board DG breakers (8 total) from the opposite division CAS relay circuit and from the Unit Priority Re-Trip circuit."
Description of Revision to Modification:
LAR, Attachment S, Table S-2 is revised to delete item 34.
Justification:
Modification 34 requires the installation of a hand switch in the MCR for each 4 kV Shutdown Board. This would allow the operators to bypass the accident signals that could trip the DG output breakers due to spurious signals. The same function (i.e., to bypass the accident signal) can be accomplished locally at the 4 kV Shutdown Boards. The modification was proposed in order to make recovery of an affected DG breaker more reliable by providing for an action inside the control room in lieu of an action outside the control room.
When the Fire PRA model is in a more refined state due to the inclusion of other proposed modifications and model changes, the risk worth of (or risk improvement gained from) this modification is expected to be minimal and modification 34 can be removed from the Fire PRA model without an adverse effect on the fire CDF or LERF.
A sensitivity study was performed by removing credit for the human actions associated with the proposed new MCR handswitch, effectively removing the modification from the Fire PRA model.
The results of the sensitivity study performed with the Fire PRA model submitted for the LAR show that modification 34 has little risk worth to the baseline post-transition Fire PRA model used to support the LAR. The change in risk due to the modification removal is considered small (i.e., less than 1% increase in CDF or LERF).
VFDR, Recovery Action, and LAR, Attachment A Changes:
VFDR-02-03-0003 and VFDR-02-03-0012 are being resolved with a recovery action to meet applicable risk criteria rather than a modification.
Estimated Probabilistic Risk Impact:
This change will have a small effect on risk quantification, as discussed above.
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Modifications 56, 59, 66, and 89 Description of Modification:
Modification 56 - "Re-route control cable 2ES676-I (2-FCV-074-0057 control) out of FA 02-02."
Modification 59 - "Install a backup control emergency switch for 2-FCV-074-0071."
Modification 66 - "Re-route control cables 2ES3910-II, 2ES3911-II and 2ES3912-II for 2-FCV-074-0073 away from Fire Area 02-03 and Fire Area 02-04."
Modification 89 - "Install a backup control emergency switch for 3-FCV-074-0071."
Description of Revision to Modification:
LAR, Attachment S, Table S-2 is revised to delete items 56, 59, 66, and 89.
Justification:
The basis for modifications 56, 59, 66 and 89 was to recover one loop of SPC to accomplish decay heat removal from the primary containment. These modifications would have separated cables or installed local controls to defeat valve interlocks associated with the SPC return valves. The same function is accomplished in the NSCA and in the current Appendix R safe shutdown analysis using the ASDC mode of RHR. In this mode, water from the Suppression Pool is supplied by an RHR pump to the reactor vessel via the RHR Heat Exchanger and LPCI flow path and returned to the Suppression Pool via the SRVs. This forms a closed loop circulation path similar to SPC, but addresses both inventory makeup and decay heat removal with one RHR mode requiring less equipment and having less vulnerability to fire damage.
ASDC was not modeled in the internal events PRA or in the Fire PRA developed for NFPA 805 transition, thereby increasing the apparent risk worth of SPC.
ASDC is being added to the Fire PRA model as an additional success path to SPC. ASDC is sufficiently modeled to allow a sensitivity analysis to be performed for elimination of the subject SPC modifications. When the Fire PRA model is in a more refined state with modeling of ASDC and model changes, the risk worth of (or risk improvement gained from) modifications 55, 56, 59, 66, and 89 is expected to be minimal such that modifications 56, 59, 66, and 89 can be removed from the Fire PRA model and modification 55 can be revised as described in of this enclosure.
A qualitative sensitivity study of the risk impact of these modifications was performed by examining the availability of both SPC in the Fire PRA model used to develop the LAR (which did not include ASDC) and the availability of both features in the Fire PRA model that has been modified to remove modifications 56, 59, 66, and 89 and add ASDC. The results of this qualitative sensitivity study confirm that the elimination of modifications 56, 59, 66, and 89 does not have an unacceptable adverse effect on fire CDF and LERF when ASDC is credited as an alternative decay heat removal method to SPC. The change in risk due to the modification removal is considered small.
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VFDR, Recovery Action, and LAR, Attachment A Changes:
This issue is not associated with any VFDR. RISK-RA-02-03-20, RISK-RA-02-04-16, and RISK-RA-03-03-28 will be eliminated because they were associated with recovery of SPC.
Estimated Probabilistic Risk Impact:
The deletion of these modifications may have a small adverse effect on risk quantification.
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Modifications 61, 62, 65, 68, and 74 Description of Modification:
Modification 61- "Re-route control cable ES143-I for RHR Pump 2A away from Fire Area 02-03."
Modification 62 - "Re-route control cable ES191-I for RHR Pump 2C away from Fire Area 02-03."
Modification 65 - "Enclose in ERFBS and re-route control cable 0ES2675-II for RHR Pump 1D away from Fire Area 02-03 and Fire Area 02-04."
Modification 68 - "Re-route control cable 3ES1561-I for RHR Pump 3A away from Fire Area 03-02."
Modification 74 - "Enclose in ERFBS and re- route control cables 1ES5417-II and 1ES5419-II for Core Spray Pump 1D away from Fire Area 02-03."
Description of Revision to Modification:
LAR, Attachment S, Table S-2 is revised to delete items 61, 62, 65, 68, and 74.
Justification:
Modifications 61, 62, 65, 68 and 74 involve cable separation to prevent the spurious start of large pumps that are not credited in the NSCA analysis for the fire area in which they are located. RHR pump 2A is not credited in FA 02-03, RHR pump 2C is not credited in FA 02-03, RHR pump 1D is not credited in FA 02-03 or 02-04, RHR pump 3A is not credited in FA 03-02, and Core Spray pump 1D is not credited in FA 02-03.
The basis for these modifications, in conjunction with modification 81 described in Attachment 1 of this enclosure, is to prevent unrecoverable damage to credited DGs due to an overload condition. TVA initially assumed that loads associated with starting an RHR pump out of sequence (i.e., spurious start of an RHR pump with significant loads already present) would result in permanent damage to the DG. Therefore, modifications were needed to prevent spurious start of loads large enough to cause damage in order to support recovery of 4kV power supplies after securing spurious loads.
TVA subsequently determined that the DGs would not be permanently damaged due to overloading and that existing protective relays for the DGs and the individual motor loads would protect the equipment and allow the DG function to be recovered after the loading issues are resolved by recovery actions. The required protective relays are included in the separation analysis. Modifications 24 and 30 install fuses to prevent loss of these functions.
Proposed modification 81a, described in Attachment 1 of this enclosure, will modify the protective relay scheme for the DGs to improve the feasibility of the recovery actions assuming actuation of protective relays. Currently, the DG overcurrent relays trip and lock out the associated DG. Modification 81a is intended to only open the DG output breaker thus simplifying recovery actions.
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TVA anticipates that this change in the treatment of DG overloading will not adversely affect risk.
VFDR, Recovery Action, and LAR, Attachment A Changes:
This issue is not associated with any VFDR.
Estimated Probabilistic Risk Impact:
The deletion of these modifications is not expected to adversely affect risk quantification, as discussed above.
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Modification 101 Description of Modification:
"Correct sprinkler head spacing for water curtain protecting Unit 1, El 639 SW corner stair opening between FA 01-05 and 01-06 to meet NFPA 13-2002, 8.14.4.1 and 8.14.3.1."
Description of Revision to Modification:
LAR, Attachment S, Table S-2 is revised to delete item 101.
Justification:
A drawing review and field walkdown verified that the water curtain protecting the floor opening between FA 01-05 and 01-06 on the Unit 1 El 639' SW corner is properly designed to meet NFPA 13-2002, 8.14.4.1 and 8.14.3.1. The deficiency identified in the NFPA code review (LAR Attachment A item 3.9.1) is in error.
VFDR, Recovery Action, and LAR, Attachment A Changes:
This issue is not associated with any VFDR.
LAR, Table B1, Item 3.9.1(1) will be revised to delete modification 101 as an implementation item.
Estimated Probabilistic Risk Impact:
This change involves NFPA code compliance upgrades and does not adversely affect the Fire PRA model.
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ATTACHMENT 3 TO ENCLOSURE Tennessee Valley Authority Browns Ferry Nuclear Plant, Units 1, 2, and 3 Revisions to Committed Modifications Potential Revisions to LAR, Attachment S, Table S-2 Modification E-22
Modifications 78 and 79 Description of Modification:
Modification 78 - "Install area wide Incipient Detection in the Cable Spreading Rooms."
Modification 79 - "Install a new automatic gaseous fire suppression system in the Cable Spreading Rooms."
Discussion of Potential Change:
Modifications 78 and 79 install a new automatic gaseous fire suppression system in the Cable Spreading Rooms (CSRs) actuated by a new incipient detection system. The CSRs currently have detection and automatic suppression and modifications 78 and 79 would install additional systems. Due to the complexity of the installation and operation and issues with automatic initiation, TVA is considering the deletion of one or both of these modifications. Elimination of either or both of these modifications would result in a risk increase for postulated fires in the CSRs, but fire modeling refinements made since the LAR was submitted are expected to offset the risk increases and will result in acceptable baseline risk values. The following fire modeling refinements are being implemented into the CSR fire mode:
Incorporate Fire PRA FAQ 13-0005, "Cable Fires Special Cases: Self Ignited and Caused by Welding and Cutting," into the Fire PRA Refine the previous model assumption that upon ignition of a second cable tray, all targets in the fire compartment are damaged. The fire modeling analysis will include scenarios to capture the damage of two cable trays and assume whole room damage upon ignition of a third cable tray.
Remove whole room damage scenario for floor areas where a transient fire cannot affect secondary combustibles and where the transient itself cannot result in whole room damage by hot gas layer Credit flamemastic coating to delay time to ignition and time to damage for cable trays, in accordance with NUREG/CR-6850, Appendix Q, Section Q.2.1 TVA anticipates that the risk increase due to the removal of the gaseous suppression system and/or the incipient detection system will be offset plant-wide and in Fire Compartment 16-A through the above fire modeling updates. Therefore, TVA does not anticipate these changes to adversely affect the overall plant risk or the risk in Fire Compartment 16-A. The final disposition of these modifications will be reflected in the submittal of updated fire risk results planned for December 17, 2014.
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