L-PI-08-072, Update to Three-Month Response and Request for Extension to NRC Generic Letter 2008-01, Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems.
| ML082600139 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 09/15/2008 |
| From: | Wadley M Nuclear Management Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-08-001, L-PI-08-072 | |
| Download: ML082600139 (4) | |
Text
Prairie Island Nuclear Generating Plant Operated by Nuclear Management Company, LLC L-PI-08-072 10 CFR 50.54(f)
U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 License Nos. DPR-42 and DPR-60 Update to Three-Month Response and Request for Extension to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decav Heat Removal, and Containment Sprav Svstems"
Reference:
- 1) NRC Generic Letter (GL) 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," dated January 11, 2008.
- 2) NMC Letter, "Three Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," dated April 10, 2008.
- 3) NRC Letter to NEI, dated July 8, 2008.
The Nuclear Management Company, LLC, (NMC) hereby requests an extension to the requirements of Reference 1 (as further explained in Reference 3). Specifically, NMC proposes a nine-month response to Reference 1 that does not include results of the evaluation of piping walkdowns.
In order to support walkdowns in containment and the residual heat removal (RHR) pump pits during the upcoming Prairie Island Nuclear Generating Plant (PINGP) Unit 2 refueling outage (2R25), NMC proposes to deviate from the Nuclear Energy Institute (NEI) guidance for the nine-month response to Reference 1. Specifically, NMC proposes to complete accessible area walkdowns after completing the walkdowns in the Unit 2 containment and RHR pump pits. This would preclude NMC from completing accessible area walkdowns prior to the due date for the nine-month response, however, it would allow completion of walkdowns required by Reference 1 sooner than if the accessible area walkdowns were completed and the Unit 2 containment and RHR pit walkdowns were moved out to the next Unit 2 refueling outage (2R26).
1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1121
Document Control Desk Page 2 The planned actions for PlNGP include developing acceptance criteria and contingency plans for walkdowns and then systematically conducting the walkdowns. This would incorporate direction from the Prairie Island Operations department to conduct walkdowns in the correct work week for the train being walked down. The current project schedule calls for walkdown acceptance criteria to be developed by mid-September. The current schedule for accessible area walkdowns anticipates 24 days to complete both units. Conducting accessible area walkdowns as soon as acceptance criteria and contingency plans are available would preclude conducting walkdowns in the Unit 2 containment and RHR pits in 2R25, which would extend completion of Unit 2 walkdowns to 2R26.
Timeline 111112008 NRC issues GL 2008-01 212008 Prairie Island staff conducts walkdowns in Unit 1 containment 312012008 NEI issues guidance on GL 2008-01 4/4/2008 Prairie Island staff recognize walkdowns did not meet NEI guidance 411012008 NMC issues Reference 2 to extend the final response to GL 2008-01 7/8/2008 NRC expectations documented in letter to NEI In Reference 2, as an alternative to the nine-month response, NMC proposed to complete detailed Unit 1 walkdowns during the next Unit 1 refueling outage (1R26) and complete GL 2008-01 evaluations within 90 days of completing 1R26. Reference 2 did not address completion of Unit 2 or accessible area walkdowns.
Subsequent to Reference 2, NRC issued Reference 3 in which the NRC noted several expectations:
NRC staff expects all addressees to submit a nine-month response by October 11, 2008 that addresses the information and discussion provided in the GL using the guidance provided by NEI.
NRC staff expects all addressees to submit a nine-month response consistent with previous NRC and NEI guidance describing what actions have been completed and what actions are being deferred including a scheduled completion date. A follow-up letter should be provided after completion of the deferred actions within 90 days of startup from the associated refueling outage.
NRC staffs expectation is that, where walkdowns are necessary, the walkdowns of locations where radiation, temperature, scaffolds, or insulation removal are not an operational, ALARA, or hazard issue should be completed and the results described in the October 11, 2008 response.
NRC staff expects that all remaining work where an additional refueling outage is necessary should be accomplished during the first refueling outage that initiates after October 11,2008.
NRC staff expects the need for Technical Specification (TS) changes to be addressed in the October 11, 2008 responses, including a description of any short term correction of existing TS weaknesses that have been implemented until a long-term generic program is completed that will provide new and improved TS's to address gas accumulation issues.
Document Control Desk Page 3 At the time of Reference 2, NMC did not expect to be providing a nine-month response to GL 2008-01, but instead expected to provide a final letter after evaluations of all the GL 2008-01 subject systems had been completed (90 days after 1R26). In the meantime, the NRC issued the expectation in Reference 3 that a nine-month response would be required.
As noted above, in order to complete all walkdowns and the PlNGP response to GL 2008-01 as soon as possible and because of the timing of 2R25, NMC proposes to conduct Unit 2 containment and RHR pump pit walkdowns before completing accessible area walkdowns. That is, NMC prefers to take advantage of the opportunity to complete Unit 2 containment and RHR pump pit walkdowns this year instead of waiting for 2R26.
Accessible area walkdowns will be completed after the Unit 2 containment and RHR pump pit walkdowns.
NMC has confidence the RHR, containment spray (CS), and safety injection (SI) systems can fulfill their required functions, based upon past and current operating experience, detailed evaluations, and testing performed since plant licensing.
Significant gas accumulation has not historically been found at the high point vents in these systems during past operations. NMC research identified one case when inadequate venting practices post-maintenance led to voiding in the RHR system. The development of specific post-maintenance venting procedures has been a successful corrective action.
PlNGP has no known issues with regard to void accumulation in suction or discharge piping. PlNGP is not subject to some of the gas accumulation vulnerabilities other plants experience. For example:
Charging pumps are not part of the emergency core cooling system (ECCS) at Prairie Island and are, therefore, not within the scope of the Generic Letter.
SI discharge pipe gas intrusion from the accumulators are not a vulnerability because at PlNGP these lines inject directly into the reactor vessel unlike the more vulnerable configuration in which the SI discharge pipe injects into the accumulator lines.
The SI and CS systems are routinely tested with their pump suctions aligned to the refueling water storage tank (RWST). This alignment dynamically vents portions of their suction piping and portions of their discharge piping. During testing of the SI and CS systems, or when the RHR system is placed in shutdown cooling (SDC), there have not been any effects on flow, or indication of a water hammer. These tests have not indicated any adverse impacts to the ability of RHR or CS to perform their design basis functions. The SI system is periodically tested with its pump suction aligned to the RWST. Since the system flow rate during these periodic tests is near the design flow rate expected under accident conditions, any voids present in the suction piping, while aligned to the RWST, have not adversely affected pump performance. The SI system has not experienced any problems due to gas being transported to the pump suction.
Document Control Desk Page 4 The SI pump can also take suction from the RHR pump. This piping remains full after it has been filled and vented. Historically, non-routine inspections for void formation found no indications for voids. The SI system has experienced several injections to the reactor vessel during the operating life of the units and there have been no reports of water hammer during these events.
Based on the above, completing the walkdowns and their evaluations as discussed above, beyond the requested nine month period, will provide a more timely response, overall, to GL 2008-01. This approach will provide the Unit 2 inside containment walkdown results by the 90 days post-2R25 supplemental response along with the accessible outside containment areas for both units.
Summary of Commitments This letter contains two new commitments:
NMC will submit all the information requested in GL 2008-01 for the nine-month response, with the exception of the results of the evaluation of piping walkdowns.
NMC will submit the results of the evaluation of accessible area walkdowns and Unit 2 containment and RHR pit walkdowns with the follow-up report 90 days following the completion of 2R25.
This letter revises the second commitment made in Reference 2 to:
NMC will submit results of the evaluations of the walkdowns of Unit 1 containment and RHR pits 90 days following the completion of 1R26.
I declare under penalty of perjury that the foregoing is true and correct. Executed on SEP 1. 5 2@
A L ~ - - G ~d&Qh Michael D. Wadley Site Vice President, Prairie Island ar Generating Plant Nuclear Management Company, cc: Administrator, Region Ill, USNRC Project Manager, Prairie Island, USNRC Resident Inspector, Prairie Island, USNRC
Text
Prairie Island Nuclear Generating Plant Operated by Nuclear Management Company, LLC L-PI-08-072 10 CFR 50.54(f)
U S Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Prairie Island Nuclear Generating Plant Units 1 and 2 Dockets 50-282 and 50-306 License Nos. DPR-42 and DPR-60 Update to Three-Month Response and Request for Extension to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decav Heat Removal, and Containment Sprav Svstems"
Reference:
- 1) NRC Generic Letter (GL) 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," dated January 11, 2008.
- 2) NMC Letter, "Three Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," dated April 10, 2008.
- 3) NRC Letter to NEI, dated July 8, 2008.
The Nuclear Management Company, LLC, (NMC) hereby requests an extension to the requirements of Reference 1 (as further explained in Reference 3). Specifically, NMC proposes a nine-month response to Reference 1 that does not include results of the evaluation of piping walkdowns.
In order to support walkdowns in containment and the residual heat removal (RHR) pump pits during the upcoming Prairie Island Nuclear Generating Plant (PINGP) Unit 2 refueling outage (2R25), NMC proposes to deviate from the Nuclear Energy Institute (NEI) guidance for the nine-month response to Reference 1. Specifically, NMC proposes to complete accessible area walkdowns after completing the walkdowns in the Unit 2 containment and RHR pump pits. This would preclude NMC from completing accessible area walkdowns prior to the due date for the nine-month response, however, it would allow completion of walkdowns required by Reference 1 sooner than if the accessible area walkdowns were completed and the Unit 2 containment and RHR pit walkdowns were moved out to the next Unit 2 refueling outage (2R26).
1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1121
Document Control Desk Page 2 The planned actions for PlNGP include developing acceptance criteria and contingency plans for walkdowns and then systematically conducting the walkdowns. This would incorporate direction from the Prairie Island Operations department to conduct walkdowns in the correct work week for the train being walked down. The current project schedule calls for walkdown acceptance criteria to be developed by mid-September. The current schedule for accessible area walkdowns anticipates 24 days to complete both units. Conducting accessible area walkdowns as soon as acceptance criteria and contingency plans are available would preclude conducting walkdowns in the Unit 2 containment and RHR pits in 2R25, which would extend completion of Unit 2 walkdowns to 2R26.
Timeline 111112008 NRC issues GL 2008-01 212008 Prairie Island staff conducts walkdowns in Unit 1 containment 312012008 NEI issues guidance on GL 2008-01 4/4/2008 Prairie Island staff recognize walkdowns did not meet NEI guidance 411012008 NMC issues Reference 2 to extend the final response to GL 2008-01 7/8/2008 NRC expectations documented in letter to NEI In Reference 2, as an alternative to the nine-month response, NMC proposed to complete detailed Unit 1 walkdowns during the next Unit 1 refueling outage (1R26) and complete GL 2008-01 evaluations within 90 days of completing 1R26. Reference 2 did not address completion of Unit 2 or accessible area walkdowns.
Subsequent to Reference 2, NRC issued Reference 3 in which the NRC noted several expectations:
NRC staff expects all addressees to submit a nine-month response by October 11, 2008 that addresses the information and discussion provided in the GL using the guidance provided by NEI.
NRC staff expects all addressees to submit a nine-month response consistent with previous NRC and NEI guidance describing what actions have been completed and what actions are being deferred including a scheduled completion date. A follow-up letter should be provided after completion of the deferred actions within 90 days of startup from the associated refueling outage.
NRC staffs expectation is that, where walkdowns are necessary, the walkdowns of locations where radiation, temperature, scaffolds, or insulation removal are not an operational, ALARA, or hazard issue should be completed and the results described in the October 11, 2008 response.
NRC staff expects that all remaining work where an additional refueling outage is necessary should be accomplished during the first refueling outage that initiates after October 11,2008.
NRC staff expects the need for Technical Specification (TS) changes to be addressed in the October 11, 2008 responses, including a description of any short term correction of existing TS weaknesses that have been implemented until a long-term generic program is completed that will provide new and improved TS's to address gas accumulation issues.
Document Control Desk Page 3 At the time of Reference 2, NMC did not expect to be providing a nine-month response to GL 2008-01, but instead expected to provide a final letter after evaluations of all the GL 2008-01 subject systems had been completed (90 days after 1R26). In the meantime, the NRC issued the expectation in Reference 3 that a nine-month response would be required.
As noted above, in order to complete all walkdowns and the PlNGP response to GL 2008-01 as soon as possible and because of the timing of 2R25, NMC proposes to conduct Unit 2 containment and RHR pump pit walkdowns before completing accessible area walkdowns. That is, NMC prefers to take advantage of the opportunity to complete Unit 2 containment and RHR pump pit walkdowns this year instead of waiting for 2R26.
Accessible area walkdowns will be completed after the Unit 2 containment and RHR pump pit walkdowns.
NMC has confidence the RHR, containment spray (CS), and safety injection (SI) systems can fulfill their required functions, based upon past and current operating experience, detailed evaluations, and testing performed since plant licensing.
Significant gas accumulation has not historically been found at the high point vents in these systems during past operations. NMC research identified one case when inadequate venting practices post-maintenance led to voiding in the RHR system. The development of specific post-maintenance venting procedures has been a successful corrective action.
PlNGP has no known issues with regard to void accumulation in suction or discharge piping. PlNGP is not subject to some of the gas accumulation vulnerabilities other plants experience. For example:
Charging pumps are not part of the emergency core cooling system (ECCS) at Prairie Island and are, therefore, not within the scope of the Generic Letter.
SI discharge pipe gas intrusion from the accumulators are not a vulnerability because at PlNGP these lines inject directly into the reactor vessel unlike the more vulnerable configuration in which the SI discharge pipe injects into the accumulator lines.
The SI and CS systems are routinely tested with their pump suctions aligned to the refueling water storage tank (RWST). This alignment dynamically vents portions of their suction piping and portions of their discharge piping. During testing of the SI and CS systems, or when the RHR system is placed in shutdown cooling (SDC), there have not been any effects on flow, or indication of a water hammer. These tests have not indicated any adverse impacts to the ability of RHR or CS to perform their design basis functions. The SI system is periodically tested with its pump suction aligned to the RWST. Since the system flow rate during these periodic tests is near the design flow rate expected under accident conditions, any voids present in the suction piping, while aligned to the RWST, have not adversely affected pump performance. The SI system has not experienced any problems due to gas being transported to the pump suction.
Document Control Desk Page 4 The SI pump can also take suction from the RHR pump. This piping remains full after it has been filled and vented. Historically, non-routine inspections for void formation found no indications for voids. The SI system has experienced several injections to the reactor vessel during the operating life of the units and there have been no reports of water hammer during these events.
Based on the above, completing the walkdowns and their evaluations as discussed above, beyond the requested nine month period, will provide a more timely response, overall, to GL 2008-01. This approach will provide the Unit 2 inside containment walkdown results by the 90 days post-2R25 supplemental response along with the accessible outside containment areas for both units.
Summary of Commitments This letter contains two new commitments:
NMC will submit all the information requested in GL 2008-01 for the nine-month response, with the exception of the results of the evaluation of piping walkdowns.
NMC will submit the results of the evaluation of accessible area walkdowns and Unit 2 containment and RHR pit walkdowns with the follow-up report 90 days following the completion of 2R25.
This letter revises the second commitment made in Reference 2 to:
NMC will submit results of the evaluations of the walkdowns of Unit 1 containment and RHR pits 90 days following the completion of 1R26.
I declare under penalty of perjury that the foregoing is true and correct. Executed on SEP 1. 5 2@
A L ~ - - G ~d&Qh Michael D. Wadley Site Vice President, Prairie Island ar Generating Plant Nuclear Management Company, cc: Administrator, Region Ill, USNRC Project Manager, Prairie Island, USNRC Resident Inspector, Prairie Island, USNRC