PLA-6680, Request for Additional Information Generic Letter 2008-01 Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems
| ML110060808 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 01/06/2011 |
| From: | Rausch T Susquehanna |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| PLA-6680, GL-08-001 | |
| Download: ML110060808 (6) | |
Text
Timothy S. Raurch PPL Susquehanna, LLC I '
I Sr. Vice President & Ch~ef Nuclear Officer 760 Snlem 13oulevard Herwlck. PA 18603 JAM 0 i 2011 Tel 570 542.3445 Fax 570.542 1504 tsrausch@pplweb.com U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Stop OPl-17 Washington, DC 20555 SUSQUEHANNA STEAM ELECTRIC STATION (SSES)
REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 2008-01 "MANAGING GAS ACCUMULATION IN EMERGENCY CORE COOLING, DECAY HEAT REMOVAL, AND CONTAINMENT SPRAY SYSTEMS" Docket Nos. 50-387 PLA-6680 and 50-388
References:
I) NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Deca,v Heat Removal, and Containment Spray Systems, "
dated January 1 I, 2008.
"Nine-Month Response to NRC Generic Letter 2008-01, " dated October 14, 2008.
Request for Additional Information (RAI;) - Susquehanna Steam Electric Station, Units I and 2 (SSES I and 2) - Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems, "
dated December 2. 201 0.
The Nuclear Regulatory Commission (NRG) issued Generic Letter (GL) 2008-01 (Reference 1) to request that each licensee evaluate the licensing basis, design, testing, and corrective action programs for the Emergency Core Cooling Systems (ECCS), Decay Heat Removal system, and Containment Spray system, to ensure that gas accumulation is maintained less than the amount that challenges operability of these systems, and that appropriate action is taken when conditions adverse to quality are identified.
Reference 2 provided PPL7s response to GL 2008-0 1.
Reference 3 is an NRC request for additional information (RAI) to determine that SSES has acceptably demonstrated that the GL 2008-01 systems are in compliance with the current licensing bases, design bases, and applicable regulatory requirements; and that suitable design, operational, and testing control measures are in place for maintaining this compliance.
Document Control Desk PLA-6680 The PPL response to Reference 3 is provided in the enclosure to this letter.
Please direct any questions regarding this RAI response to Mr. Duane L. Filcllner at (6 10) 774-78 19.
I declare under penalty of perjury that the foregoing is true and correct.
Executed on:
b ( \\
i T. S. Raus
Enclosure:
PPL Responses to NRC Request for Additional Information (RAI)
Copy: NRC Region I Mr. P. W. Finney, NRC Sr. Resident Inspector Mr. R. R. Janati, DEP/BRP Mr. B. K. Vaidya, NRC Project Manager
Enclosure to PLA-6680 PPL Responses to NRC Request for Additional Information (R41)
Enclosure to PLA-6680 Page 1 of 3 NRC RAI (1):
Please address any discrepancies between the systems evaluated in the Boiling Water Reactor Owners Group (BWROG) Report and those at SSES and any discrepancies between the pump suction void criteria in the BWROG Report and NRC Inspection Guidance, Rev. 9.
PPL Response:
There were no discrepancies between systems discussed in the BWROG report and the SSES systems. SSES suction piping void acceptance criteria has been established for the Emergency Core Cooling systems (ECCS), which include RHR, Core Spray and High Pressure Coolant Injection, consistent with the current NRC inspection guidance, Rev. 9 referenced above.
Reference 2 provided the PPL submittal of the SSES response to GL 2008-01. At the time of this submittal, the only gas void acceptance criteria guidance that was available was in the BWROG report "BWR Owners' Group Technical Report ECCS Pumps Suction Void Fraction Study," dated August 2008, as discussed in Reference 2. Formal suction piping void acceptance criteria calculations were not performed at that time.
Subsequent to submitting Reference 2, SSES established gas void acceptance criteria for the ECCS suction piping in accordance with the NEI guidance document titled "Industry Guidance for Evaluation of Unexpected Voids or Gas Identified in Plant ECCS and Other Systems. This guidance document was transmitted from James H. Riley, NEI, to Mr. William H. Ruland, NRC, on June 18,2009.
In order to ensure conservative results, acceptable suction piping void volume calculations were based on the minimum flow at which voids could be transported to the pump suction. (See discussion in response to NRC RAI (3) below). The suction piping acceptance criteria was used for subsequent ECCS suction piping inspections performed by PPL to support system operability in the event aidgas was found in the suction piping.
As expected, there was no significant air/gas found in the SSES ECCS suction piping during these inspections.
It is recognized that there are differences between the NET guidance document and the current NRC inspection guidance, "Guidance to NRC/NRR/DSS/SRXB Reviewers for Writing TI Suggestions for the Region Inspections, Revision 9," dated August 18,2010, (ML102300053). The suction piping acceptance criteria established in accordance with the NET guidance, in effect at that time, is considered reasonable and appropriate for the subject systems. The suction piping inspections that have been performed by PPL did not identify any significant air/gas in the piping. Therefore, based on the SSES ECCS suction
Enclosure to PLA-6680 Page 2 of 3 piping configuration and inspection results. no changes to the suction piping acceptance criteria are necessary.
Tt should also be noted that unlike some other BWR/PWR plants, airfgas voids are not expected to significantly increase in size as the voids get transported to pump suction.
For the SSES ECCS systems, pressure drop calculations demonstrate that suction pressures at the pump inlets remain above atmospheric pressure under all modes of operation. Since the pump inlets remain "flooded during system operation; the suction sources are situated well above the pump suction elevations; and all SSES ECCS suction piping is maintained above atmospheric pressure in standby conditions; no airlgas is expected to infiltrate the system through vents or valve packing leaks. In addition, unlike many PWR plants. there are no sources of air or gas connected directly to the ECCS suction piping.
NRC RAI (2):
The licensee states that pumps in the subject systems are located at the low points in the systems and are not subject to air intrusion. Did the licensee evaluate the possibility of a localized high point created within the pump and affect on pump performance?
PPL Response:
The possibility to create a localized high point within a SSES ECCS pump is determined to be not credible since all the ECCS pumps are located below the suction sources (suppression pool and condensate storage tank). The pumps are under positive pressure while in the standby condition and it is highly unlikely that a void could form in the pump body under these conditions.
Additionally, the core spray and RHR pumps are multi-stage vertical pumps with the pump impellers situated below the suction piping. This configuration is not subject to gas voiding within the pumps.
Pump vents are also installed on the ECCS pumps and are used to vent air from suction piping and the pump casings in accordance with system restoration procedures, follokving maintenance activities.
NRG RAI (3):
It is not clear if the licensee considered gas transport to suction piping from high points in the system at conditions other than minimum flow. Explain how the licensee has evaluated conditions other than minimum flow. For example, test flow rates may be less than that would result during a response to an event or the actual system response may involve two trains as opposed to the design basis that one train has failed. Either of these
Enclosure to PLA-6680 Page 3 of 3 conditions may cause gas to move whereas a minimum flow assumption may not affect the pumps because gas is not expected to move.
PPL Response:
The SSES suction piping evaluations considered all system operating conditions, where voids could be transported from high points in the system to the ECCS pumps. The range of operating conditions considered was determined in accordance with NET guidance referenced in the response to NRC RAT (1) above.
The suction piping void acceptance criteria was established as follows:
1.) The minimum flow at which voids could be transported from high points in the system to the pump suction, was determined assuming a Froude number of 0.3 1 in each of the ECCS pump suction lines, consistent with the NEI guidance.
2.) The range of operating conditions (in terms of % of best efficiency point (BEP)) to apply the gas void acceptance criteria was determined. This typical range was from the minimum flow established (per the NEI guidance) to maximum pump runout conditions for each system, as determined in the evaluation.
3.) After the operating range was established, the criteria provided in Table 1 of the NEI guidance document for transient conditions was used to determine the allowable gas void fraction in the suction piping for each system. Since the minimum flow to transport voids was typically determined to be below 70% of BEP for these systems, a maximum void fraction of 5% over 5 seconds was used to determine the allowable void size in the ECCS on piping.
4.) The m i m u m void size was then calculated based on the minimum flow established for void transport with a void fraction of 5% over 5 seconds. These calculated allowable suction piping void volumes were used as the acceptance criteria for subsequent suction piping inspections performed by PPL.