ML11356A088

Response to Request for Additional Information Regarding License Amendment Request to Revise Technical Specification 3.7.4, Atmospheric Dump Valves

ML11356A088
Person / Time
Site:	Palo Verde
Issue date:	12/09/2011
From:	Mims D Arizona Public Service Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
102-06446-DCM/DFS, TAC ME6566, TAC ME6567, TAC ME6568
Download: ML11356A088 (8)

Text

10 CFR 50.90 L A W A subsidiary of Pinnacle West Capital Corporation Dwight C. Mims Mail Station 7605 Palo Verde Nuclear Senior Vice President Tel. 623-393-5403 P.O. Box 52034 Generating Station Nuclear Regulatory and Oversight Fax 623-393-6077 Phoenix, Arizona 85072-2034 102-06446-DCM/DFS December 9, 2011 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Units 1, 2, and 3 Docket Nos. STN 50-528, 50-529, and 50-530 Response to Request for Additional Information Regarding License Amendment Request To Revise Technical Specification 3.7.4, "Atmospheric Dump Valves" (TAC Nos. ME6566, ME6567, and ME6568)

By letter no. 102-06370, dated June 22, 2011 (Agencywide Documents Access and Management System Accession No. ML11182A908), Arizona Public Service Company, (APS) submitted a request to revise Technical Specification Limiting Condition for Operation 3.7.4, "Atmospheric Dump Valves (ADVs)." The proposed change would require four ADV lines to be operable in MODES 1, 2, and 3, as well as MODE 4 when a steam generator is relied upon for heat removal. By letter dated August 31, 2011 (ADAMS Accession No. ML112430084), the NRC provided a request for additional information (RAI).

As discussed with the Plant Licensing Branch IV Chief on November 30, 2011, the enclosure to this letter contains APS's response to questions 1 a and 1 b of the RAI. APS requires additional time to confirm the demonstrative analyses performed in response to the RAI. APS will provide the response to questions 2 and 3 by January 27, 2012.

No commitments are being made to the NRC by this letter. Should you need further information regarding this response, please contact Russell A. Stroud, Licensing Section Leader, at (623) 393-5111.

Acod A member of the STARS (Strategic Teaming and Resource Sharing) Alliance o

Callaway 0 Comanche Peak 0 Diablo Canyon 0 Palo Verde 0 San Onofre 0 South Texas 0 Wolf Creek

ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Response to Request for Additional Information Regarding License Amendment Request To Revise Technical Specification 3.7.4, "Atmospheric Dump Valves" Page 2 I declare under penalty of perjury that the foregoing is true and correct.

Executed on (Date)

Sincerely, DCM/RAS/DFS/gat

Enclosure:

Response to Request for Additional Information Regarding License Amendment Request To Revise Technical Specification 3.7.4, "Atmospheric Dump Valves" cc:

E. E. Collins Jr.

B.K. Singal L. K. Gibson J. R. Hall M. A. Brown A. V. Godwin T. Morales NRC Region IV Regional Administrator NRC NRR Project Manager for PVNGS NRC NRR Project Manager NRC NRR Senior Project Manager NRC Senior Resident Inspector for PVNGS Arizona Radiation Regulatory Agency (ARRA)

Arizona Radiation Regulatory Agency (ARRA)

Enclosure Response to Request for Additional Information Regarding License Amendment Request To Revise Technical Specification 3.7.4, "Atmospheric Dump Valves"

Enclosure Response to RAI Regarding LAR To Revise TS 3.7.4, "Atmospheric Dump Valves"

==

Introduction:==

By letter no. 102-06370, dated June 22, 2011 (Agencywide Documents Access and Management System Accession No. ML11182A908), Arizona Public Service Company (APS), submitted a request to revise Technical Specification Limiting Condition for Operation 3.7.4, "Atmospheric Dump Valves (ADVs)" (Reference 1). The proposed change would require four ADV lines to be operable in MODES 1, 2, and 3, as well as MODE 4 when a steam generator is relied upon for heat removal. By letter dated August 31, 2011 (ADAMS Accession No. ML112430084) (Reference 2), the NRC provided APS with a request for additional information (RAI). This enclosure contains the APS response to questions la and lb of the RAI.

NRC Request 1:

Please provide the technical basis, including a discussion of defense in depth and safety margins, for:

a. Proposed LCO 3.7.4, Condition A, Completion Time of 7 days

b. Proposed LCO 3.7.4, Condition B, Completion Time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

APS Response to Request la:

The following response is based on the guidance in NRC Regulatory Guide (RG) 1.177 revision 1, "An Approach for Plant-Specific, Risk-Informed Decision Making: Technical Specifications," May 2011, sections 2.2.1 and 2.2.2 (Reference 3).

Condition A of the proposed TS 3.7.4 is applicable when one ADV is inoperable on either one or both steam generators. Since the design at PVNGS consists of two ADVs per steam generator, there is one ADV remaining operable on each steam generator while in Condition A. With one ADV remaining operable on each steam generator, operators continue to have the means to cooldown the plant to mitigate the applicable design basis accidents. One operable ADV on one intact steam generator is capable of mitigation and cool down post design basis accidents. In addition to the available steaming path through the operable ADV(s), operators may use one or both of the two Steam Bypass valves (SBCVs) capable of directing steam to the atmosphere, or maintain the secondary system pressure for a minimum period of four (4) hours (consistent with original plant design) at the opening setpoint for the Main Steam Safety Valves (MSSVs).

Consistency with the defense in depth philosophy is maintained as follows:

A reasonable balance between prevention of core damage, prevention of containment failure, and consequence mitigation is preserved. Since plant cooldown options are not significantly affected by this proposed 7-day limiting condition for operation (LCO) completion time, the mitigation of the consequences of design basis accidents and transients is preserved with a negligible impact on core damage, containment failure, or containment bypass.

In addition, the proposed change does not impact accident prevention.

1

Enclosure Response to RAI Regarding LAR To Revise TS 3.7.4, "Atmospheric Dump Valves" Therefore, the existing balance between accident prevention and accident mitigation would not be changed.

The proposed LCO 3.7.4, Condition A, completion time of 7-days does not require implementation of any programmatic activities as compensatory measures nor does it rely on optimistic program assumptions.

" The existing redundant means for plant cooldown would be preserved. The ADV performance history at PVNGS demonstrates component reliability greater than 99% and continued high ADV availability. In addition, plant procedures and maintenance rule requirements implement restrictions against simultaneous removal of redundant components or voluntary removal of power supply sources during adverse weather conditions.

" Defenses against potential common-cause failures (CCFs) are maintained as there would be no changes to the existing diversity of power supply sources to the ADVs. No new CCF mechanism would be introduced by this request for change in the completion time for LCO 3.7.4, Condition A. Should there be a single random failure of the operable ADV(s), then the plant would enter a more restrictive completion time requirement.

" The proposed completion time for LCO 3.7.4, Condition A, does not degrade any barrier to radiation release to the atmosphere. Integrity of containment penetrations and the containment isolation pressure setpoint would not be affected. Also, no containment bypass route would be created.

Defense against human errors would be maintained. Remote, control room operator action and local, manual operator action to operate an ADV would not be adversely affected. There continues to be a sufficient time window available for event recognition and equipment manipulation. The proposed LCO completion time will permit more time to plan and implement local, manual operation of an ADV or remote operation of the SBCVs, thus reducing the likelihood of errors in these operations. The local environment and ADV accessibility are not affected by this change.

The intent of the plant's heat removal design criteria would be maintained.

Sufficient safety margins for secondary system heat removal are maintained as follows:

The proposed LCO 3.7.4, Condition A, completion time of 7-days would not create any conflict with American Society of Mechanical Engineers (ASME)

Boiler and Pressure Vessel Code, Sections III and XI, or any applicable Institute of Electrical and Electronics Engineers (IEEE) Standards. The proposed change does not alter existing surveillance frequencies and would not affect the ADV design, assembly, wiring scheme, control, diverse power supply sources, or testing method and testing periods. The comparison of risk of available alternatives (section 2.5 of RG 1.177), justifies the change in that the added risk from transitioning the plant from power operation to shutdown conditions is much higher than the risk increment proposed from continued plant operation up to the 7-day limit of LCO 3.7.4, Condition A.

2

Enclosure Response to RAI Regarding LAR To Revise TS 3.7.4, "Atmospheric Dump Valves" Safety analysis acceptance criteria in the Updated Final Safety Evaluation Report (UFSAR) continues to be met and the proposed completion time does not adversely affect any assumption or input to the safety analysis.

APS Response to Request 1 b:

This response is based on the guidance in RG 1.177, sections 2.2.1 and 2.2.2.

Condition B of the proposed TS 3.7.4 is applicable when there are two ADVs inoperable on one or both Steam Generators. This includes the situation where no ADVs are operable. With only one or no ADVs remaining operable on both steam generators, operators continue to have the means to cooldown the plant to mitigate design basis accidents. Operators may take actions to locally operate one ADV on an intact steam generator or use one or both of the two SBCVs capable of directing steam to the atmosphere. During the time required for local, manual ADV operation, the operators may control the secondary system pressure for a minimum period of four (4) hours (consistent with original plant design) at the opening setpoint for the MSSVs. The provision for local, manual operation of an ADV is included in the Standard Post Trip Actions procedure, the loss of offsite power (LOP) procedure, the loss of coolant accident (LOCA) procedure, and the steam generator tube rupture (SGTR) procedure (References 4, 5, 6, and 7, respectively). Also, the steps for local, manual operation of an ADV are listed in Appendix 18 of the emergency operating procedure (EOP),

standard appendices (Reference 8). The Auxiliary Plant Operators are trained on these procedural steps.

Due to the diversity of power supplies, staggered ADV maintenance, and physical separation of the ADVs, a plant configuration with three or more failed ADVs is considered to be very rare. When ADV failures are combined with a coincidental initiating event, such as a LOP, small break LOCA, or SGTR, plant procedures provide mitigation paths that can maintain the critical safety functions and avert core uncovery.

Consistency with the defense in depth philosophy is maintained as follows:

" Plant cooldown options would either require manual operation of an ADV or use of one or both of the two SBCVs capable of directing steam to the atmosphere.

The mitigation of the consequences of design basis accidents and transients is preserved with a negligible impact on core damage, containment failure, or containment bypass. In addition, the proposed change does not impact accident prevention. Therefore, the existing balance between accident prevention and accident mitigation would not be changed.

" The 24-hour completion time for LCO 3.7.4, Condition B, does not require implementation of any programmatic activities as compensatory measures nor does it rely on optimistic program assumptions.

" The existing alternate means for plant cooldown would be preserved. A plant configuration with three or more failed ADVs is considered very rare. That scenario requires the simultaneous random failure of two or more ADVs. The ADV performance history at PVNGS demonstrates component reliability greater 3

Enclosure Response to RAI Regarding LAR To Revise TS 3.7.4, "Atmospheric Dump Valves" than 99% and continued high ADV availability. In addition, plant procedures and maintenance rule requirements implement restrictions against simultaneous removal of redundant components, or voluntary removal of power supply sources during adverse weather conditions.

• Defenses against potential CCFs are maintained as there would be no changes to the existing diverse power supply sources to the ADVs. No new CCF mechanism is introduced by this request to retain the completion time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for LCO 3.7.4, Condition B.

• The 24-hour completion time for LCO 3.7.4, Condition B, does not degrade barriers to radiation release to the atmosphere. Integrity of containment penetrations and containment isolation pressure setpoint would not be affected.

Also, no containment bypass route would be created.

• Defense against human errors would be maintained. Remote control room Operator action and local, manual operator action to operate an ADV would not be adversely affected. There continues to be a sufficient time window available for recognition of the ADV failures and equipment manipulation. The local environment and ADV accessibility are not affected by this change.

The intent of the plant's heat removal design criteria would be maintained.

Sufficient safety margins for secondary system heat removal are maintained as follows:

" LCO 3.7.4, Condition B, completion time of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> would not create any conflict with ASME Boiler and Pressure Vessel Code, Sections III and XI, or any applicable IEEE Standard. The proposed change does not alter existing surveillance frequencies and there is no impact on ADV design, assembly, wiring scheme, control, diverse power supply sources, or testing method and testing periods. The comparison of risk of available alternatives (section 2.5 of RG 1.177), justifies the change in that the added risk from transitioning the plant from power operation to shutdown conditions is much higher than the risk increment proposed from continued plant operation up to the 24-hour limit of LCO 3.7.4, Condition B.

" Safety analysis acceptance criteria in the UFSAR continues to be met and the proposed completion time does not adversely affect any assumption or input to the safety analysis.

References:

1.

APS letter number 102-06370, "Request for Amendment to Technical Specification 3.7.4, "Atmospheric Dump Valves (ADVs)" dated June 22, 2011 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML11182A908)

2.

NRC letter dated August 31, 2011, "Palo Verde Nuclear Generating Station, Units 1, 2, And 3, Request For Additional Information Regarding License Amendment Request To Revise Technical Specification 3.7.4, Atmospheric Dump Valves" 4

Enclosure Response to RAI Regarding LAR To Revise TS 3.7.4, "Atmospheric Dump Valves" (TAC NOS. ME6566, ME6567, and ME6568)" (ADAMS Accession No. MLl12430084)

3.

Regulatory Guide (RG) 1.177, revision 1, "An Approach for Plant-Specific, Risk-Informed Decision Making: Technical Specifications," May 2011

4.

Procedure 40EP-9EO0, Standard Post Trip Actions procedure, revision 17

5.

Procedure 40EP-9EO07, Loss of Offsite Power/Loss of Forced Circulation, revision 24

6.

Procedure 40EP-9EO03, Loss of Coolant Accident, revision 32

7.

Procedure 40EP-9EO04, Steam Generator Tube Rupture, revision 26

8.

Procedure 40EP-9EO10, Standard Appendices, revision 69 5