RS-13-007, Response to Request for Additional Information Regarding the Use of an Auxiliary Feedwater Cross-tie Between Units

Response to Request for Additional Information Regarding the Use of an Auxiliary Feedwater Cross-tie Between Units

ML13035A017
Person / Time
Site:	Byron, Braidwood
Issue date:	02/01/2013
From:	Gullott D Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-13-007
Download: ML13035A017 (10)

Text

4300 Winfield Roy d Warrenville, I! 60555 Exeton Generation RS-13-007 10 CFR 50.90 February 1, 2013 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-001 Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN-50-457 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455

Subject:

Response to Request for Additional Information Regarding the Use of an Auxiliary Feedwater Cross-tie Between Units.

References:

1)

Letter from D. M. Gullott (Exelon Generation Company, LLC) to U. S.

Nuclear Regulatory Commission, "License Amendment Request for the use of an Auxiliary Feedwater Cross-tie Between Units," dated January 31, 2012 2)

Email from J. S. Wiebe (U. S. Nuclear Regulatory Commission) to R. W.

McIntosh (Exelon Generation Company, LLC), "Preliminary RAls Related to the Auxiliary Feedwater Cross Connect Amendment Request," dated November 9, 2012 In Reference 1, Exelon Generation Company, LLC (EGC) submitted a license amendment request (LAR) to revise the Updated Final Safety Analysis Report (UFSAR) to describe the use of an Auxiliary Feedwater (AF) cross-tie between units. The LAR described the intended use of the cross-tie to support beyond design basis events relating to total loss of secondary heat sink.

In Reference 2, the U.S. Nuclear Regulatory Commission (NRC) requested additional information to complete its review of the proposed license amendment request. Clarification of the information the NRC needs to complete their review was requested in discussions held on November 16, and December 4, 2012. EGC is providing the attached information in response to the request.

EGC has reviewed the information supporting a finding of no significant hazards consideration and the environmental consideration that were previously provided to the NRC in Attachment 1 of Reference 1. The additional information provided in this submittal does not affect the bases for concluding that the proposed license amendments do not involve a significant hazards consideration. In addition, the additional information provided in this submittal does not affect 6306552000 Offc-e 4300 Winfield R03d Warrenville, I~ 60555 Exelon Generation 630 657 2000 Offce RS-13-007 February 1, 2013 10 CFR 50.90 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-001

Subject:

Braidwood Station, Units 1 and 2 Facility Operating License Nos. NPF-72 and NPF-77 NRC Docket Nos. STN 50-456 and STN-50-457 Byron Station, Units 1 and 2 Facility Operating License Nos. NPF-37 and NPF-66 NRC Docket Nos. STN 50-454 and STN 50-455 Response to Request for Additional Information Regarding the Use of an Auxiliary Feedwater Cross-tie Between Units.

References:

1)

Letter from D. M. Gullott (Exelon Generation Company, LLC) to u. S.

Nuclear Regulatory Commission, "License Amendment Request for the use of an Auxiliary Feedwater Cross-tie Between Units," dated January 31, 2012

2)

Email from J. S. Wiebe (U. S. Nuclear Regulatory Commission) to R. W.

Mcintosh (Exelon Generation Company, LLC), "Preliminary RAls Related to the Auxiliary Feedwater Cross Connect Amendment Request, II dated November 9, 2012 In Reference 1, Exelon Generation Company, LLC (EGC) submitted a license amendment request (LAR) to revise the Updated Final Safety Analysis Report (UFSAR) to describe the use of an Auxiliary Feedwater (AF) cross-tie between units. The LAR described the intended use of the cross-tie to support beyond design basis events relating to total loss of secondary heat sink.

In Reference 2, the U.S. Nuclear Regulatory Commission (NRC) requested additional information to complete its review of the proposed license amendment request. Clarification of the information the NRC needs to complete their review was requested in discussions held on November 16, and December 4, 2012. EGC is providing the attached information in response to the request.

EGC has reviewed the information supporting a finding of no significant hazards consideration and the environmental consideration that were previously provided to the NRC in Attachment 1 of Reference 1. The additional information provided in this submittal does not affect the bases for concluding that the proposed license amendments do not involve a significant hazards consideration. In addition, the additional information provided in this submittal does not affect

February 1, 2013 U. S. Nuclear Regulatory Commission Page 2 the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b), a copy of this letter and its attachments are being provided to the designated State of Illinois official.

There are no regulatory commitments contained in this letter.

Should you have any questions concerning this letter, please contact Richard W. McIntosh at (630) 657-2816.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 1st day of February 2013.

Respectfully, David M. Gullott Manager - Licensing Exelon Generation Company, LLC

Attachment:

1.

Response to Request for Additional Information cc:

NRC Regional Administrator, Region III NRC Senior Resident Inspector, Braidwood Station NRC Senior Resident Inspector, Byron Station NRC Project Manager, NRR - Braidwood and Byron Stations Illinois Emergency Management Agency Division of Nuclear Safety February 1, 2013 U. S. Nuclear Regulatory Commission Page 2 the bases for concluding that neither an environmental impact statement nor an environmental assessment needs to be prepared in connection with the proposed amendment.

In accordance with 10 CFR 50.91, "Notice for public comment; State consultation," paragraph (b), a copy of this letter and its attachments are being provided to the designated State of Illinois official.

There are no regulatory commitments contained in this letter.

Should you have any questions concerning this letter, please contact Richard W. Mcintosh at (630) 657-2816.

I declare under penalty of perjury that the foregoing is true and correct. Executed on the 1 st day of February 2013.

David M. Gullott Manager - Licensing Exelon Generation Company, LLC

Attachment:

1. Response to Request for Additional Information cc:

NRC Regional Administrator, Region III NRC Senior Resident Inspector, Braidwood Station NRC Senior Resident Inspector, Byron Station NRC Project Manager, NRR - Braidwood and Byron Stations Illinois Emergency Management Agency Division of Nuclear Safety

ATTACHMENT 1 Response to Request for Additional Information NRC Question RAI-1:

In a staff memorandum, dated September 18, 1992, the U.S. Nuclear Regulatory Commission (NRC) approved the staff's position that the General Design Criteria (GDC) will not be applied to plants receiving their construction permits prior to 1971. Since Bryon and Braidwood received their construction permits prior to 1971, Exelon was not required to adhere strictly to the GDCs.

However, Exelon is required to state in their design bases their interpretation of how the plants conform to the intent of GDCs.

Currently, sharing of the auxiliary feedwater (AFW) systems between the two units is not within the licensing basis. The plant recently physically modified the units to create this capability to share AFW through the train A discharge flow path. When a site shares systems, components, or structures, the staff uses guidance provided in 10 CFR 50, Appendix A, General Design Criterion (GDC) 5, "Sharing of structures, systems, and components," to evaluate acceptability.

As stated above, since the plants were not licensed to GDCs, then the licensee must explain how the plants would conform to the intent of the provisions in 10 CFR 50, APP A, GDC 5.

In the Exelon's January 31, 2012, letter, Exelon proposes revisions to the Updated Final Safety Analysis Report (UFSAR) Sections 3.1.2.1.5 and 3.1.2.4.5 to address changes to the plant design basis to implement AFW cross tie operation. The licensee states:

The AF [AFW] system is designed with suitable redundancy to offset the consequences of any single failure, with one exception during AF [AFW] Train A unit cross-tie use. Use of the Train A unit cross-tie results in a temporary relaxation of the single failure criterion for the non-accident unit, which, consistent with overall system reliability considerations, provides a limited time to support the accident unit emergency response, and return the AF [AFW] Train A to an operable status.

In Exelon's evaluation of other systems that share structure, system and components (SSCs) in UFSAR Section 3.1, Exelon finds that the shared systems can sustain a single failure and still accomplish the safety function in both units.

The staff finds by implementing the AFW cross tie between the units, the licensee adversely affects the non-accident unit's AFW system ability to mitigate an accident, because it can no longer sustain a single failure and perform its safety function. The staff finds the licensee proposed change to the UFSAR unacceptable.

Provide justification why the staff should not deny the application.

EGC Response:

This request does not change how the Auxiliary Feedwater (AF) system design complies with the 10 CFR 50, Appendix A, General Design Criteria (GDC), nor does it change the operation of the AF system as allowed by the plant Technical Specifications (TS).

The intent of the license amendment request is to document the design details of the cross-tie in the UFSAR, and how the AF system design continues to comply with the GDCs while the system continues to be operated in accordance with the approved TS.

1 of 8 ATTACHMENT 1 Response to Request for Additional Information NRC Question RAI-1:

In a staff memorandum, dated September 18, 1992, the U.S. Nuclear Regulatory Commission (NRC) approved the staff's position that the General Design Criteria (GOC) will not be applied to plants receiving their construction permits prior to 1971. Since Bryon and Braidwood received their construction permits prior to 1971, Exelon was not required to adhere strictly to the GOCs.

However, Exelon is required to state in their design bases their interpretation of how the plants conform to the intent of GOCs.

Currently, sharing of the auxiliary feedwater (AFW) systems between the two units is not within the licensing basis. The plant recently physically modified the units to create this capability to share AFW through the train A discharge flow path. When a site shares systems, components, or structures, the staff uses guidance provided in 10 CFR 50, Appendix A, General Design Criterion (GOC) 5, "Sharing of structures, systems, and components," to evaluate acceptability.

As stated above, since the plants were not licensed to GOCs, then the licensee must explain how the plants would conform to the intent of the provisions in 10 CFR 50, APP A, GOC 5.

In the Exelon's January 31, 2012, letter, Exelon proposes revisions to the Updated Final Safety Analysis Report (UFSAR) Sections 3.1.2.1.5 and 3.1.2.4.5 to address changes to the plant design basis to implement AFW cross tie operation. The licensee states:

The AF [AFW] system is designed with suitable redundancy to offset the consequences of any single failure, with one exception during AF [AFW] Train A unit cross-tie use. Use of the Train A unit cross-tie results in a temporary relaxation of the single failure criterion for the non-accident unit, which, consistent with overall system reliability considerations, provides a limited time to support the accident unit emergency response, and return the AF [AFW] Train A to an operable status.

In Exelon's evaluation of other systems that share structure, system and components (SSCs) in UFSAR Section 3.1, Exelon finds that the shared systems can sustain a single failure and still accomplish the safety function in both units.

The staff finds by implementing the AFW cross tie between the units, the licensee adversely affects the non-accident unit's AFW system ability to mitigate an accident, because it can no longer sustain a single failure and perform its safety function. The staff finds the licensee proposed change to the UFSAR unacceptable.

Provide justification why the staff should not deny the application.

EGC Response:

This request does not change how the Auxiliary Feedwater (AF) system design complies with the 10 CFR 50, Appendix A, General DeSign Criteria (GOC), nor does it change the operation of the AF system as allowed by the plant Technical Specifications (TS).

The intent of the license amendment request is to document the design details of the cross-tie in the U FSAR, and how the AF system design continues to comply with the GOCs while the system continues to be operated in accordance with the approved TS.

1 of 8

ATTACHMENT 1 Response to Request for Additional Information The proposed changes to the UFSAR are intended to describe the function and operation of the AF cross-tie between the Unit 1 and Unit 2 Train A of the AF system. As stated in the January 31, 2012, letter, this AF cross-tie piping does not support or accomplish any AF system safety function, design basis function, or normal operating function. The cross-tie may be used in response to a total loss of secondary heat sink beyond design basis event as a mitigating strategy in accordance with the functional restoration procedures. Similar to other plant system functional restoration strategies described in the UFSAR, the purpose of these proposed changes is to describe the cross-tie capability and operation in the UFSAR; not to change the AF system design related to GDC compliance, operation of the system in accordance with the TS, or any of the AF system safety functions. The purpose of the Exelon Generation Company, LLC (EGC) request is not to license the use of the cross-tie as a credited safety function of the AF system.

The AF system design continues to meet requirements of GDC 5 and GDC 34:

With regard to GDC 5, there are no normal operating, abnormal operating occurrences, or design basis events that require or credit the sharing of AF system components between the units. The design and control of the cross-tie piping ensures that the operation of one unit's A train of AF does not support or impact the operation of the other unit's A train of AF during an event or condition where the AF system safety function is required. As described in the January 31, 2012, letter, the AF cross-tie does not impact AF system compliance with GDC 5 since the AF system design continues to be capable of performing its required safety functions on its unit during an accident and is not required to support an orderly shutdown and cooldown of the other unit. In the event of a beyond design basis accident on one unit, which necessitates the use of the cross-tie, the non-accident unit remains capable of an orderly shutdown since plant design does not utilize its dedicated AF system to support this normal, orderly shutdown. Therefore, the use of the cross-tie between units does not constitute a sharing of components in conflict with GDC 5 (i.e., GDC 5 continues to be complied with).

With regard to GDC 34, each unit's AF system continues to be comprised of two redundant and independent trains, each capable of individually performing the system's required safety functions. For normal and design basis operation, each unit's AF system design remains capable of accomplishing its safety functions assuming a single failure.

The cross-tie from the other unit does not support any redundancy required to comply with this GDC. The use of the cross-tie is an operational condition of the AF system that is governed by the unit's TS as discussed below. The cross-tie operation is not a change in the system design that prevents the AF system from meeting the single failure assumptions of GDC 34.

Since there are no AF system safety functions that require sharing of components between units and safety functions can be performed assuming a single failure, the AF system design remains compliant with the GDCs under the proposed change.

TS 3.7.5 provides the limiting conditions for operation of the AF system, along with the required actions to be taken when the specified conditions are not met. TS 3.7.5 presently allows 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of continued unit operation with one AF system train inoperable (i.e., not capable of performing its specified function). EGC will continue to comply with this TS in the unlikely event that the cross-tie is used to support a beyond design basis event on the other unit (i.e., accident unit). This TS compliance applies to the non-accident unit that is donating its Train A of AF to the accident unit. In this condition, the donated train is not capable of performing its specified 2of8 ATTACHMENT 1 Response to Request for Additional Information The proposed changes to the UFSAR are intended to describe the function and operation of the AF cross-tie between the Unit 1 and Unit 2 Train A of the AF system. As stated in the January 31,2012, letter, this AF cross-tie piping does not support or accomplish any AF system safety function, design basis function, or normal operating function. The cross-tie may be used in response to a total loss of secondary heat sink beyond design basis event as a mitigating strategy in accordance with the functional restoration procedures. Similar to other plant system functional restoration strategies described in the UFSAR, the purpose of these proposed changes is to describe the cross-tie capability and operation in the UFSAR; not to change the AF system design related to GOC compliance, operation of the system in accordance with the TS, or any of the AF system safety functions. The purpose of the Exelon Generation Company, LLC (EGC) request is not to license the use of the cross-tie as a credited safety function of the AF system.

The AF system design continues to meet requirements of GOC 5 and GOC 34:

With regard to GOC 5, there are no normal operating, abnormal operating occurrences, or design basis events that require or credit the sharing of AF system components between the units. The design and control of the cross-tie piping ensures that the operation of one unit's A train of AF does not support or impact the operation of the other unifs A train of AF during an event or condition where the AF system safety function is required. As described in the January 31,2012, letter, the AF cross-tie does not impact AF system compliance with GOC 5 since the AF system design continues to be capable of performing its required safety functions on its unit during an accident and is not required to support an orderly shutdown and cooldown of the other unit. In the event of a beyond design basis accident on one unit, which necessitates the use of the cross-tie, the non-accident unit remains capable of an orderly shutdown since plant design does not utilize its dedicated AF system to support this normal, orderly shutdown. Therefore, the use of the cross-tie between units does not constitute a sharing of components in conflict with GOC 5 (Le., GOC 5 continues to be complied with).

With regard to GOC 34, each unit's AF system continues to be comprised of two redundant and independent trains, each capable of individually performing the system's required safety functions. For normal and design basis operation, each unit1s AF system design remains capable of accomplishing its safety functions assuming a single failure.

The cross-tie from the other unit does not support any redundancy required to comply with this GOC. The use of the cross-tie is an operational condition of the AF system that is governed by the unit's TS as discussed below. The cross-tie operation is not a change in the system design that prevents the AF system from meeting the single failure assumptions of GOC 34.

Since there are no AF system safety functions that require sharing of components between units and safety functions can be performed assuming a single failure, the AF system design remains compliant with the GOCs under the proposed change.

TS 3.7.5 provides the limiting conditions for operation of the AF system, along with the required actions to be taken when the specified conditions are not met. TS 3.7.5 presently allows 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of continued unit operation with one AF system train inoperable (Le., not capable of performing its specified function). EGC will continue to comply with this TS in the unlikely event that the cross-tie is used to support a beyond design basis event on the other unit (Le., accident unit). This TS compliance applies to the non-accident unit that is donating its Train A of AF to the accident unit. In this condition, the donated train is not capable of performing its specified 2 of 8

ATTACHMENT 1 Response to Request for Additional Information function of supplying required flow to the unit's steam generators and from a TS standpoint is considered inoperable. In this case the donating unit's TS will be complied with such that the inoperable AF train must be returned to an operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or the donating unit will be shutdown. Use of the current licensing basis requiring compliance with the GDC and the existing TS 3.7.5 in this manner is appropriate and consistent with the application of TS in similar situations when a single AF train is inoperable due to equipment failure or for planned maintenance.

The NRC issued a Regulatory Information Summary (RIS) 2005-20, "Revision to Guidance Formerly Contained in NRC Generic Letter 91-18, 'Information to Licensees Regarding Two NRC Inspection Manual Sections on Resolution of Degraded and Nonconforming Conditions and on Operability'," dated September 26, 2005. Consistent with the use of RIS 2005-20, and as described in NRC Inspection Manual Part 9900, Appendix C, operation of a structure, system, or component in accordance with TS does not change the fact that the system design remains compliant with the GDCs (e.g., the design remains capable of withstanding a single failure with one train inoperable). As discussed in Position C.1, the GDC and the TS differ in that the GDC specify requirements for the design of nuclear power reactors, whereas the TSs specify the requirements for operation of the reactor. Position C.1 further elaborates on the relationship as follows:

The GDC require redundancy of function for safety systems. This is normally accomplished by incorporating at least two redundant trains into the design of each safety system. The TSs typically allow a facility to continue to operate for a specified time with only one train of a two-train safety system operable. In that case, the GDC are met because the system design provides the necessary redundancy. The TSs permit the operation of the system with only a single train based on an evaluation of the protection provided by the unique system lineup for the specified period.

Application and compliance with the unit's TS provides a temporary relaxation of the single failure criterion as described in Part 9900. Application of the TS in this manner does not allow or imply that the system design is not single failure proof; it is simply an allowance for continued plant operation with one of the redundant trains inoperable for a limited, specified period of time.

The discussion being added to the TS 3.7.5 Bases to require the Train B to be OPERABLE as a condition for making the Train A inoperable to support a beyond design basis accident on the other unit ensures that the cross-tie is not to be put into service and used for operational convenience. As discussed in the TS LCO 3.0.2 Bases, TS's Required Actions are applicable when a system is intentionally removed from service. However, intentional entry into Actions should not be made for operational convenience, and alternatives that would not result in redundant equipment (e.g., both AF trains) being inoperable should be used instead. Doing so limits the time both trains of a safety function are inoperable. Avoiding entry into a condition for operational convenience is consistent with the existing TS LCO 3.0.2 Bases, and the added detail in the TS 3.7.5 Bases reflecting the existence of the normally isolated cross-tie does not change the existing TS requirements. Furthermore, the nuclear safety benefit that is derived from an action to unisolate and use the cross-tie in such an unlikely event (i.e., an event not expected to occur during the lifetime of the station), is reasonably not considered for operational convenience.

Therefore, EGC does not consider the very rare use of the cross -tie and associated inoperability of the Train A and use of the cross-tie during beyond design basis events as operational convenience since the operability of Train B of AF ensures the safety function can be performed and thus this approach does not compromise safety.

3of8 ATTACHMENT 1 Response to Request for Additional Information function of supplying required flow to the unit's steam generators and from a TS standpoint is considered inoperable. In this case the donating unit's TS will be complied with such that the inoperable AF train must be returned to an operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or the donating unit will be shutdown. Use of the current licensing basis requiring compliance with the GDC and the existing TS 3.7.5 in this manner is appropriate and consistent with the application of TS in similar situations when a single AF train is inoperable due to equipment failure or for planned maintenance.

The NRC issued a Regulatory Information Summary (RIS) 2005-20, "Revision to Guidance Formerly Contained in NRC Generic Letter 91-18, 'Information to Licensees Regarding Two NRC Inspection Manual Sections on Resolution of Degraded and Nonconforming Conditions and on Operability'," dated September 26,2005. Consistent with the use of RIS 2005-20, and as described in NRC Inspection Manual Part 9900, Appendix C, operation of a structure, system, or component in accordance with TS does not change the fact that the system design remains compliant with the GDCs (e.g., the design remains capable of withstanding a single failure with one train inoperable). As discussed in Position C.1, the GDC and the TS differ in that the GDC specify requirements for the design of nuclear power reactors, whereas the TSs specify the requirements for operation of the reactor. Position C.1 further elaborates on the relationship as follows:

The GDC require redundancy of function for safety systems. This is normally accomplished by incorporating at least two redundant trains into the design of each safety system. The TSs typically allow a facility to continue to operate for a specified time with only one train of a two-train safety system operable. In that case, the GDC are met because the system design provides the necessary redundancy. The TSs permit the operation of the system with only a single train based on an evaluation of the protection provided by the unique system lineup for the specified period.

Application and compliance with the unit's TS provides a temporary relaxation of the single failure criterion as described in Part 9900. Application of the TS in this manner does not allow or imply that the system design is not single failure proof; it is simply an allowance for continued plant operation with one of the redundant trains inoperable for a limited, specified period of time.

The discussion being added to the TS 3.7.5 Bases to require the Train B to be OPERABLE as a condition for making the Train A inoperable to support a beyond design basis accident on the other unit ensures that the cross-tie is not to be put into service and used for operational convenience. As discussed in the TS LCO 3.0.2 Bases, TS's Required Actions are applicable when a system is intentionally removed from service. However, intentional entry into Actions should not be made for operational convenience, and alternatives that would not result in redundant equipment (e.g., both AF trains) being inoperable should be used instead. Doing so limits the time both trains of a safety function are inoperable. Avoiding entry into a condition for operational convenience is consistent with the existing TS LCO 3.0.2 Bases, and the added detail in the TS 3.7.5 Bases reflecting the existence of the normally isolated cross-tie does not change the existing TS requirements. Furthermore, the nuclear safety benefit that is derived from an action to unisolate and use the cross-tie in such an unlikely event (Le., an event not expected to occur during the lifetime of the station), is reasonably not considered for operational convenience. Therefore, EGC does not consider the very rare use of the cross-tie and associated inoperability of the Train A and use of the cross-tie during beyond design basis events as operational convenience since the operability of Train B of AF ensures the safety function can be performed and thus this approach does not compromise safety.

3 of 8

ATTACHMENT 1 Response to Request for Additional Information Note that in the first paragraph of RAI-1, the NRC states that Byron and Braidwood received their construction permits prior to 1971. For purposes of clarification, both Byron and Braidwood's construction permits were issued by the NRC on December 31, 1975.

NRC Question RAI-2:

As described In the UFSAR, both AFW trains actuate automatically on the same initiation signals, except that train A (motor-driven AFW pump) receives a start signal on an undervoltage on Division 1 ESF bus. The staff requests the licensee evaluate the impact of the loss of this function when AFW train A is unavailable during cross tie operation.

EGC Response:

The design of the Train A and B AF pumps differ in their motive force to drive the pump. The Train B AF pump is driven by its own independent diesel engine, while the Train A AF pump is driven by a motor that receives electric power from the 4160 volt Division 1 Engineered Safety Features (ESF) bus.

Upon a loss of power to the Division 1 ESF bus, the undervoltage relays will open all the feed breakers to the bus, trip all the loads on the bus except the 4160/480 volt transformers, and automatically start the Division 1 Emergency Diesel Generator (EDG). Upon loss of voltage to the ESF bus, the ESF loads must be sequentially loaded onto the bus to prevent overloading the EDG. The sequential loading of the EDG is automatically performed with loads required for accident mitigation and safe shutdown of the reactor.

To support this sequential loading requirement of the Division 1 ESF bus when fed from the EDG, the Train A of AF has an additional start signal and time delay. Since the Train B of AF does not receive power from one of the ESF buses / EDGs, there is no requirement for this type of additional start signal to sequentially load the Train B of AF on to an ESF bus.

Therefore, the basis for the additional start signal for the Train A AF pump is to support sequential loading of the Division 1 ESF bus to protect the EDG. This automatic function is not lost when the Train A of AF is operating during cross-tie operation as the relays and actuation circuitry remains capable of tripping and sequentially loading the Train A AF pump motor on to the Division 1 ESF bus. If the Division 1 ESF bus undervoltage condition occurs during cross-tie operation, the donated AF pump motor would trip and restart after the sequencing time delay as designed. If the undervoltage condition on the non-accident unit resulted in a loss of the non-safety related Feedwater System, the Train B AF pump on the non-accident unit would automatically start on a low steam generator water level, safety injection signal, or undervoltage on the reactor coolant pump buses. As discussed in the license amendment request, the Train B of AF provides sufficient feedwater to safely cool the unit to temperatures at which the Residual Heat Removal (RH) system can be utilized.

NRC Question RAI-3:

The licensee does not identify a surveillance or maintenance procedure for demonstrating that the cross tie flow path is functional, if needed, and will not adversely impact either unit when not in use. Since the flow path will be credited in plant analyses and mitigating strategies, a 4of8 ATTACHMENT 1 Response to Request for Additional Information Note that in the first paragraph of RAI-1, the NRC states that Byron and Braidwood received their construction permits prior to 1971. For purposes of clarification, both Byron and Braidwood's construction permits were issued by the NRC on December 31, 1975.

NRC Question RAI-2:

As described In the UFSAR, both AFW trains actuate automatically on the same initiation signals, except that train A (motor-driven AFW pump) receives a start signal on an undervoltage on Division 1 ESF bus. The staff requests the licensee evaluate the impact of the loss of this function when AFW train A is unavailable during cross tie operation.

EGC Response:

The design of the Train A and B AF pumps differ in their motive force to drive the pump. The Train B AF pump is driven by its own independent diesel engine, while the Train A AF pump is driven by a motor that receives electric power from the 4160 volt Division 1 Engineered Safety Features (ESF) bus.

Upon a loss of power to the Division 1 ESF bus, the undervoltage relays will open all the feed breakers to the bus, trip all the loads on the bus except the 4160/480 volt transformers, and automatically start the Division 1 Emergency Diesel Generator (EDG). Upon loss of voltage to the ESF bus, the ESF loads must be sequentially loaded onto the bus to prevent overloading the EDG. The sequential loading of the EDG is automatically performed with loads required for accident mitigation and safe shutdown of the reactor.

To support this sequential loading requirement of the Division 1 ESF bus when fed from the EDG, the Train A of AF has an additional start signal and time delay. Since the Train B of AF does not receive power from one of the ESF buses / EDGs, there is no requirement for this type of additional start signal to sequentially load the Train B of AF on to an ESF bus.

Therefore, the basis for the additional start signal for the Train A AF pump is to support sequential loading of the Division 1 ESF bus to protect the EDG. This automatic function is not lost when the Train A of AF is operating during cross-tie operation as the relays and actuation circuitry remains capable of tripping and sequentially loading the Train A AF pump motor on to the Division 1 ESF bus. If the Division 1 ESF bus undervoltage condition occurs during cross-tie operation, the donated AF pump motor would trip and restart after the sequencing time delay as designed. If the undervoltage condition on the non-accident unit resulted in a loss of the non-safety related Feedwater System, the Train B AF pump on the non-accident unit would automatically start on a low steam generator water level, safety injection signal, or undervoltage on the reactor coolant pump buses. As discussed in the license amendment request, the Train B of AF provides sufficient feedwater to safely cool the unit to temperatures at which the Residual Heat Removal (RH) system can be utilized.

NRC Question RAI-3:

The licensee does not identify a surveillance or maintenance procedure for demonstrating that the cross tie flow path is functional, if needed, and will not adversely impact either unit when not in use. Since the flow path will be credited in plant analyses and mitigating strategies, a 4 of 8

ATTACHMENT 1 Response to Request for Additional Information surveillance or maintenance procedure should be considered or alternatively, a justification for not needing it should be provided.

EGC Response:

The AF Train A unit cross-tie flow path is not credited in the accident analyses and the design function is entirely passive and not an active safety function. The AF cross-tie flow path remains isolated between the units unless needed for an event that is beyond design basis.

EGC has appropriate surveillance and maintenance procedures in place to ensure the valves and piping's passive safety function. Description and justification is provided in the balance of this response.

Current surveillance requirements are unaffected by this license amendment request, and are already in place and continue to be performed. These include the current full flow Inservice Testing (IST) surveillance requirements, with an 18 month frequency in which AF is discharged directly to all four steam generators, and a quarterly surveillance in which the AF pumps discharge on recirculation to their respective condensate storage tanks on their respective units.

Neither surveillance requires unisolating the AF Train A unit cross-tie flow path between the units. The design of the AF Train A unit cross-tie, and the configuration of this flow path that remains isolated does not challenge the flow capability of either AF pump to provide feedwater to its unit's steam generators. Therefore, the AF Train A unit cross-tie flow path does not require a new surveillance or maintenance procedures to demonstrate continuing flow path functionality.

Several activities ensure that the AF Train A unit cross-tie flow path remains available if required to mitigate the consequences of a beyond design basis event. These activities are summarized as follows:

1.

Periodic ASME Code, VT-2 leakage examinations are required for this design (once during each inspection period required by the Inservics Inspection Program, approximately every 3 years) at normal operating pressures. The VT-2 leakage examinations can be performed in conjunction with the quarterly AF surveillance tests, allowing the piping between the two manual isolation valves, (the 1AF036 at Unit 1 and 2AF036 at Unit 2), to be pressurized to normal AF pressure to verify no pressure boundary leakage exists, and to verify the valves can be satisfactorily opened and closed. Before an AF Train A unit cross-tie manual isolation valve would be unlocked and opened to perform a leakage VT-2 examination on the system piping, the other unit's AF Train A unit cross-tie manual isolation valve would be verified closed, ensuring the AF Train A unit cross-tie flow path remains isolated from the other unit.

2.

The manual isolation valves were added to the Locked Equipment program for each unit. Therefore, they will be maintained in the closed position and locked when not used for surveillance testing. Additionally, the valves are included in the lineup procedures as locked closed valves.

3.

Preventive maintenance requires lubrication and external inspections of the manual isolation valves in the AF Train A unit cross-tie. This periodic preventive valve maintenance is presently performed at least every ten years and ensures the manual isolation valves can be manipulated as necessary. Additionally and as previously described, the periodic VT-2 leakage examinations that are required by the ASME 5of8 ATTACHMENT 1 Response to Request for Additional Information surveillance or maintenance procedure should be considered or alternatively, a justification for not needing it should be provided.

EGC Response:

The AF Train A unit cross-tie flow path is not credited in the accident analyses and the design function is entirely passive and not an active safety function. The AF cross-tie flow path remains isolated between the units unless needed for an event that is beyond design basis.

EGC has appropriate surveillance and maintenance procedures in place to ensure the valves and piping's passive safety function. Description and justification is provided in the balance of this response.

Current surveillance requirements are unaffected by this license amendment request, and are already in place and continue to be performed. These include the current full flow Inservice Testing (1ST) surveillance requirements, with an 18 month frequency in which AF is discharged directly to all four steam generators, and a quarterly surveillance in which the AF pumps discharge on recirculation to their respective condensate storage tanks on their respective units.

Neither surveillance requires unisolating the AF Train A unit cross-tie flow path between the units. The design of the AF Train A unit cross-tie, and the configuration of this flow path that remains isolated does not challenge the flow capability of either AF pump to provide feedwater to its unit's steam generators. Therefore, the AF Train A unit cross-tie flow path does not require a new surveillance or maintenance procedures to demonstrate continuing flow path fu nctionality.

Several activities ensure that the AF Train A unit cross-tie flow path remains available if required to mitigate the consequences of a beyond deSign basis event. These activities are summarized as follows:

1. Periodic ASME Code, VT-2 leakage examinations are required for this deSign (once during each inspection period required by the Inservice Inspection Program, approximately every 3 years) at normal operating pressures. The VT-2 leakage examinations can be performed in conjunction with the quarterly AF surveillance tests, allowing the piping between the two manual isolation valves, (the 1 AF036 at Unit 1 and 2AF036 at Unit 2), to be pressurized to normal AF pressure to verify no pressure boundary leakage exists, and to verify the valves can be satisfactorily opened and closed. Before an AF Train A unit cross-tie manual isolation valve would be unlocked and opened to perform a leakage VT-2 examination on the system piping, the other unit's AF Train A unit cross-tie manual isolation valve would be verified closed, ensuring the AF Train A unit cross-tie flow path remains isolated from the other unit.

2. The manual isolation valves were added to the Locked Equipment program for each unit. Therefore, they will be maintained in the closed position and locked when not used for surveillance testing. Additionally, the valves are included in the lineup procedures as locked closed valves.

3. Preventive maintenance requires lubrication and external inspections of the manual isolation valves in the AF Train A unit cross-tie. This periodic preventive valve maintenance is presently performed at least every ten years and ensures the manual isolation valves can be manipulated as necessary. Additionally and as previously described, the periodic VT-2leakage examinations that are required by the ASME 5 of 8

ATTACHMENT 1 Response to Request for Additional Information Code for the AF system will also cycle both these manual isolation valves more frequently when system surveillance testing permits.

The Train A unit AF cross-tie feature will remain available to the opposite unit if needed to support a beyond design basis event, while maintaining each AF pump available to its own unit during all other plant operation. The Train A unit AF cross-tie design does not require additional unavailability time or additional entry into an LCO to perform these surveillances, maintenance or inspections since the cross-tie flow path between the units will not be opened to perform the activities.

NRC Question RAI-4:

The licensee provides the risk benefit from applying credit for the ability to cross tie the AFW train A. The licensee shows that the Large Early Release Frequency (LERF) reduction for Bryon is 1 %, whereas, the LERF reduction for Braidwood is 2%.

a) Identify the difference in plants that accounts for this difference, and any impact on the use of the AFW cross tie.

b) Provide the increase in risk to the operating unit (Core Damage Frequency and LERF) when the AFW train A is in use via the cross tie and compare to the risk reduction noted.

EGC Response to RAI-4(a):

The license amendment request does not use a risk informed basis, however, the risk benefit was quantified for the original proposal by evaluating the internal events probabilistic risk assessment (PRA) model for the Byron and Braidwood Stations. The PRA results that were used in the license amendment request were derived from Revision 6F of the PRA model. The current PRA model is Revision BB011 b. The base core damage frequency (CDF) and large early release frequency (LERF) results for the current model still support the basis of gaining risk reduction for all four units from the AF Train A unit cross-tie on an accident unit. With the current PRA model, the table previously provided in the license amendment request is revised as follows:

CDF and LERF Benefits from AF Train A Unit Cross-Tie - PRA Model BB011 b Unit 1 Unit 2 Station CDF Reduction

(%)

LERF Reduction (%)

CDF Reduction

(%)

LERF Reduction (%)

Byron 2.2 0.5 1.7 0.4 Braidwood 2.4 0.5 2.0 0.4 As noted in the question, there is a difference between the stations in the amount of LERF reduction. There are differences in plant specific data used in the PRA model and in certain site specific physical and operational differences that are reflected in the modeling. In the license amendment request, the values were rounded to 1 percent for the Byron Station and 2 percent for the Braidwood Station. The underlying calculations showed approximately 1.3 to 1.4 percent 6of8 ATTACHMENT 1 Response to Request for Additional Information Code for the AF system will also cycle both these manual isolation valves more frequently when system surveillance testing permits.

The Train A unit AF cross-tie feature will remain available to the opposite unit if needed to support a beyond design basis event, while maintaining each AF pump available to its own unit during all other plant operation. The Train A unit AF cross-tie design does not require additional unavailability time or additional entry into an LCO to perform these surveillances, maintenance or inspections since the cross-tie flow path between the units will not be opened to perform the activities.

NRC Question RAI.. 4:

The licensee provides the risk benefit from applying credit for the ability to cross tie the AFW train A. The licensee shows that the Large Early Release Frequency (LERF) reduction for Bryon is 1 %; whereas, the LERF reduction for Braidwood is 2%.

a) Identify the difference in plants that accounts for this difference, and any impact on the use of the AFW cross tie.

b) Provide the increase in risk to the operating unit (Core Damage Frequency and LERF) when the AFW train A is in use via the cross tie and compare to the risk reduction noted.

EGC Response to RAI-4(a):

The license amendment request does not use a risk informed basis, however, the risk benefit was quantified for the original proposal by evaluating the internal events probabilistic risk assessment (PRA) model for the Byron and Braidwood Stations. The PRA results that were used in the license amendment request were derived from Revision 6F of the PRA model. The current PRA model is Revision BB011 b. The base core damage frequency (CDF) and large early release frequency (LERF) results for the current model still support the basis of gaining risk reduction for all four units from the AF Train A unit cross-tie on an accident unit. With the current PRA model, the table previously provided in the license amendment request is revised as follows:

CDF and LERF Benefits from AF Train A Unit Cross-Tie - PRA Model BB011 b Unit 1 Unit2 Station CDF Reduction LERF CDF Reduction LERF

(%)

Reduction (%)

(%)

Reduction (%)

Byron 2.2 0.5 1.7 0.4 Braidwood 2.4 0.5 2.0 0.4 As noted in the question, there is a difference between the stations in the amount of LERF reduction. There are differences in plant specific data used in the PRA model and in certain site specific physical and operational differences that are reflected in the modeling. In the license amendment request, the values were rounded to 1 percent for the Byron Station and 2 percent for the Braidwood Station. The underlying calculations showed approximately 1.3 to 1.4 percent 6 of 8

ATTACHMENT 1 Response to Request for Additional Information for Byron Station and 1.5 to 1.6 percent for the Braidwood Station using Revision 6F of the PRA model. In the table above, using the current PRA model revision, these values are revised. The differences are, however, not as large as the rounded values would indicate.

The Braidwood and Byron Stations use the same CAFTA software developed fault tree for their PRA model. To account for physical differences between the stations (e.g., the essential service water cooling towers at the Byron Station), logic flags are used to turn on or off the appropriate logic subtrees. To account for plant operating experience differences (e.g., failure data, maintenance unavailability, etc.), separate databases are maintained for each station to provide plant specific results. These databases define the basic events used in the PRA model including their associated plant-specific probability values.

The base CDF and LERF values for the Byron and Braidwood Stations are different because the base data used in the quantification of the risk metrics is taken from the plants respective database. These differences in plant specific data will also be reflected in the relative benefit associated with the implementation of the Train A unit AF cross-tie.

EGG Response to RAI-4(b):

The NRC requests the following information:

b)

Provide the increase in risk to the operating unit (Core Damage Frequency and LERF) when the AFW train A is in use via the cross tie and compare to the risk reduction noted.

There is a negligible increase in unavailability that results on the non-accident unit from considering the AF Train A unit cross-tie configuration. That increase in unavailability is derived from considering the following impacts:

Likelihood of needing the AF Train A unit cross-tie on the accident unit Expected Duration for the donated train to be unavailable to the non-accident unit EGG considered the impact of the above items on quantifying the additional unavailability to the AF Train A current configuration, and determined that the additional unavailability resulting from the AF Train A unit cross-tie configuration was negligible. Specifically, the additional unavailability from the AF Train A unit cross-tie is negligible because it was approximated to be at least five orders of magnitude below the baseline unavailability that is averaged for the current AF Train A configuration. The resulting negligible impact on unavailability results in no discernible increase in risk for the proposed AF Train A unit cross-tie configuration. This conclusion is valid for the current model as well as the model in use at the time of the original submittal.

7of8 ATTACHMENT 1 Response to Request for Additional Information for Byron Station and 1.5 to 1.6 percent for the Braidwood Station using Revision 6F of the PRA model. In the table above, using the current PRA model revision, these values are revised. The differences are, however, not as large as the rounded values would indicate.

The Braidwood and Byron Stations use the same CAFTA software developed fault tree for their PRA model. To account for physical differences between the stations (e.g., the essential service water cooling towers at the Byron Station), logic flags are used to turn on or off the appropriate logic subtrees. To account for plant operating experience differences (e.g., failure data, maintenance unavailability, etc.), separate databases are maintained for each station to provide plant specific results. These databases define the basic events used in the PRA model including their associated plant-specific probability values.

The base CDF and LERF values for the Byron and Braidwood Stations are different because the base data used in the quantification of the risk metrics is taken from the plants respective database. These differences in plant specific data will also be reflected in the relative benefit associated with the implementation of the Train A unit AF cross-tie.

EGC Response to RAI-4(b):

The NRC requests the following information:

b) Provide the increase in risk to the operating unit (Core Damage Frequency and LERF) when the AFW train A is in use via the cross tie and compare to the risk reduction noted.

There is a negligible increase in unavailability that results on the non-accident unit from considering the AF Train A unit cross-tie configuration. That increase in unavailability is derived from considering the following impacts:

Likelihood of needing the AF Train A unit cross-tie on the accident unit Expected Duration for the donated train to be unavailable to the non-accident unit EGC considered the impact of the above items on quantifying the additional unavailability to the AF Train A current configuration, and determined that the additional unavailability resulting from the AF Train A unit cross-tie configuration was negligible. Specifically, the additional unavailability from the AF Train A unit cross-tie is negligible because it was approximated to be at least five orders of magnitude below the baseline unavailability that is averaged for the current AF Train A configuration. The resulting negligible impact on unavailability results in no discernible increase in risk for the proposed AF Train A unit cross-tie configuration. This conclusion is valid for the current model as well as the model in use at the time of the original submittal.

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ATTACHMENT 1 Response to Request for Additional Information

References:

1)

Letter from D. M. Gullott (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, "License Amendment Request for the use of an Auxiliary Feedwater Cross-tie Between Units," dated January 31, 2012.

2)

Email from J. S. Wiebe (U. S. Nuclear Regulatory Commission) to R. W. McIntosh (Exelon Generation Company, LLC), "Preliminary RAIs Related to the Auxiliary Feedwater Cross Connect Amendment Request," dated November 9, 2012.

8of8 ATTACHMENT 1 Response to Request for Additional Information

References:

1)

Letter from D. M. Gullott (Exelon Generation Company, LLC) to u. S. Nuclear Regulatory Commission, uLicense Amendment Request for the use of an Auxiliary Feedwater Cross-tie Between Units," dated January 31,2012.

2)

Email fromJ.S.Wiebe(U.S.NuclearRegulatoryCommission)toR... V.Mclntosh (Exelon Generation Company, LLC), npreliminary RAls Related to the Auxiliary Feedwater Cross Connect Amendment Request, II dated November 9, 2012.

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