ML082950483
| ML082950483 | |
| Person / Time | |
|---|---|
| Site: | River Bend  (NPF-047) |
| Issue date: | 10/14/2008 |
| From: | Roberts J Entergy Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-08-001, RBG-46848 | |
| Download: ML082950483 (21) | |
Text
Entergy Operations, Inc.
River Bend Station 5485 U.S. Highway 61 N St. Francisville, LA 70775 nto Tel 225-381-4149 Jerry C. Roberts Director, Nuclear Safety Assurance RBG-46848 October 14, 2008 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk 11555 Rockville Pike, Rockville, MD 20852
Subject:
Nine Month Response to NRC Generic Letter 2008-001,"Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems" River Bend Station, Unit 1 Docket No. 50-458 License No. NPF-47
REFERENCES:
- 1. NRC Generic Letter 2008-001,"Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems" dated January 11, 2008.
- 2. Three Month Response to Generic Letter 2008-001, dated May 15, 2008
Dear Sir or Madam:
The Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 2008-001 (Reference 1), to request that each licensee evaluate the licensing basis, design, testing, and corrective action programs for the Emergency Core Cooling Systems (ECCS),
Residual Heat Removal (RHR) 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 actions are taken when conditions adverse to quality are identified.
GL 2008-001 requested each licensee to submit a written response in accordance with 10 CFR 50.54(f) within 9 months of the date of the GL to provide the following information:
"(a) A description of the results of evaluations that were performed pursuant to the requested actions;
RBG-46848 Page 2 of 3 (b) A description of all corrective actions, including plant, programmatic, procedure, and licensing basis modifications that were determined to be necessary to assure compliance with the quality assurance criteria in Sections III, XI, XVI, and XVII of Appendix B to 10 CFR Part 50 and the licensing basis and operating license as those requirements apply to the subject systems; and, (c) A statement regarding which corrective actions were completed, the schedule for completing the remaining corrective actions, and the basis for that schedule."
Additionally, the NRC requested that if a licensee cannot meet the requested response date, the licensee "shall provide a response within 3 months of the date of the GL." In the 3 month response, the licensee was requested to describe the alternate course of action that the licensee proposes to take, including the basis for the acceptability of the proposed alternative course of action.
On May 15, 2008, Entergy Nuclear Operations, Inc. (Entergy) notified your staff that River Bend Station did not expect to complete all the requested actions required by the GL within 9 months and submitted the required 3 month letter by Reference 2.
In summary, Entergy has concluded that the subject systems/functions at River Bend Station are in compliance with the Technical Specification definition of Operability, i.e.,
capable of performing their intended safety function; and that River Bend Station is currently in compliance with 10 CFR 50, Appendix B, Criterion Ill, V, XI, XVI and XVII, with respect to the concerns outlined in GL 2008-001 regarding gas accumulation in the accessible portions of these systems/functions. This letter contains a complete response to GL 2008-001. An additional follow up letter as committed in Reference 2 is not required. provides a description of the requested confirmation of applicability, and plant-specific verifications. Attachment 2 provides the commitments made in response to the GL.
If you have any questions or require additional information, please contact David Lorfing at (225) 381-4157.
I declare under penalty of perjury that the foregoing is true and correct. Executed on October 14, 2008.
Sincerely, Director, Nuclear Safety Assurance River Bend Station - Unit 1
RBG-46848 Page 3 of 3 JCR/DNL/bmb Attachments:
- 1. River Bend Station Nine Month Response to NRC Generic Letter 2008-001,"Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems"
- 2. List of Regulatory Commitments cc: Regional Administrator U. S. Nuclear Regulatory Commission Region IV 612 E. Lamar Blvd., Suite 400 Arlington, TX 76011-4125 NRC Senior Resident Inspector P. 0. Box 1050 St. Francisville, LA 70775 U.S. Nuclear Regulatory Commission Attn: Mr. C. F. Lyon OWFN MS 8 G14 Washington, DC 20555-0001 Mr. Jeffrey P. Meyers Louisiana Department of Environmental Quality Office of Environmental Compliance Attn:OEC - ERSD P. 0. Box 4312 Baton Rouge, LA 70821-4312 RBG-46848 Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems" to RBG-46848 Page 1 of 15 Nine-Month Response to NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems" This attachment contains the nine-month response to Generic Letter (GL) 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," dated January 11, 2008. This information was developed and being documented in engineering report; RBS-ME-08-00001, "Summary of Activities Associated with the Resolution of GL 2008-01."
The following information is provided in this response:
a)
A description of the results of evaluations that were performed pursuant to the requested actions, b)
A description of the corrective actions determined necessary to ensure compliance with the quality assurance criteria in Sections III, V, XI, XVI, XVII of Appendix B to 10 CFR Part 50 and the licensing basis and operating license with respect to the subject systems, and c)
A statement regarding which corrective actions have been completed, the schedule for the corrective actions not yet complete, and the basis for that schedule.
The following systems were determined to be in the scope of GL 2008-01 for River Bend Station:
High Pressure Core Spray (HPCS) system; Low Pressure Core Spray(LPCS) system;
£ Residual Heat Removal (RHR) system (for the following modes of operation): Low Pressure Coolant Injection (LPCI) (subsystems A, B, and C), Suppression Pool Cooling (subsystems A and B) and Shutdown Cooling (subsystems A and B).
Note, River Bend Station does not have a containment spray system.
It should be noted that there are related issues that -the nuclear industry is currently considering with respect to the overall performance of these systems (e.g., GSI-1 93).
Consistent with discussions in SECY 2008-108, resolution of these related issues would be addressed independent of the Generic Letter and will not be addressed herein. /
1 LICENSING BASIS EVALUATION The River Bend Station (RBS) licensing basis was reviewed with respect to gas accumulation in the Emergency Core Cooling, Decay Heat Removal, and Containment Spray systems. This review included the Technical Specifications (TS) and TS Bases, Updated Final Safety Analysis Report (UFSAR), the Technical Requirements Manual (TRM) and TRM Bases, responses to NRC generic communications, NRC Commitments, and License Conditions.
to RBG-46848 Page 2 of 15 Summarization of Licensing Basis Review:
Technical Specifications (TS) 3.5.1, "ECCS - Operating" and 3.5.2, "ECCS - Shutdown" Surveillance Requirements (SRs) 3.5.1.1 and 3.5.2.3 require verification that, for each ECCS injection/spray subsystem, the piping is filled with water from the pump discharge valve to the injection valve, at a frequency of 31 days. The two SRs are worded identically; "Verify, for each required ECCS injection/spray subsystem, the piping is filled with water from the pump discharge valve to the injection valve."
TS Bases 3.5.1 contains a detailed background discussion of the ECCS systems. The description of the keep-fill systems is as follows:
"To ensure rapid delivery of water to the RPV and to minimize water hammer effects, the ECCS discharge line keep fill systems are designed to maintain all pump discharge lines filled with water."
The Bases section for SR 3.5.1.1 discusses the underlying need for the surveillance as follows:
"The flow path piping has the potential to develop voids and pockets of entrained air.
Maintaining the pump discharge lines of the HPCS System, LPCS System, and LPCI subsystems full of water ensures that the systems will perform properly, injecting their full capacity into the Reactor Cooling System (RCS) upon demand. This will also prevent a water hammer following an ECCS initiation signal. One acceptable method of ensuring the lines are full is to vent at the high points. The 31 day Frequency is based on operating experience, on the procedural controls governing system operation, and on the gradual nature of void buildup in the ECCS piping." The TS Bases section for SR 3.5.2.3 incorporates that of SR 3.5.1.1 by reference.
The River Bend USAR discusses design aspects of the ECCS systems with respect to maintaining them free of gases. In Section 6.3, "Emergency Core Cooling Systems," the following statements are made regarding piping design:
"Suction piping for the ECCS pumps is conservatively designed to eliminate the potential for local flashing and cavitation. The limiting condition for NPSH available occurs for all of the ECCS pumps when suction is taken from the suppression pool."
"All ECCS pump suction lines are run from their points of origin in the suppression pool to their respective pump suction flanges. Liquid continuity is ensured throughout the entire length of the piping."
Section 6.3.2.2.5, "ECCS Discharge Line Fill System," contains the following description of the keep-fill subsystems:
"A requirement of the emergency core cooling system is that cooling water flow to the reactor vessel be initiated rapidly when the system is called on to perform its function. This quick-start system characteristic is provided by quick-opening to RBG-46848 Page 3 of 15 valves, quick-start pumps, and standby ac power sources. The lag between the signal to start the pump and the initiation of flow into the RPV can be minimized by keeping the ECCS pump discharge lines full. Additionally. if these lines were empty when the systems were called for, the large momentum~forces associated with accelerating fluid into a dry pipe could cause physical damage to the piping.
Therefore, the ECCS discharge line fill system is designed to maintain the pump discharge lines in a filled condition.
Since the ECCS discharge lines are elevated above the suppression pool, check or stop-check valves are provided near the pumps to prevent back flow from emptying the lines into the suppression pool. Past experience has shown that these valves leak slightly, producing a small back flow that eventually empties the discharge piping. To ensure that this leakage from the discharge lines is replaced and the lines are always kept filled, a water leg pump is provided for each of the three ECCS divisions. The power supply to these pumps is Class 1 E. Indication is provided in the main control room as to whether these pumps are operating, and alarms indicate low discharge line pressure."
Section 6.3.2.2, "Equipment and Component Descriptions," contains a brief discussion. of the design feature for preventing vortexing in the ECCS pump suction lines in the suppression pool. It states, "A minimum ECCS suction strainer submergence of greater than 3 ft is maintained to preclude vortex formation."
A review of USAR Section 6.3 and TSB 3.5.1 has determined these discussions are consistent with current NRC guidance on the understanding of "full" or "filled."
Summarization of Changes to Licensing Basis Documents, Schedule and Basis for Completion:
RBS will evaluate and submit, as appropriate, changes to the plant Technical Specifications based upon the final, approved version of Technical Specification Task Force (TSTF) Traveler for unacceptable gas accumulation in ECCS. This submittal will be, adjusted, as needed, to account for plant-specific design and licensing basis. The submittal will be within 90 days following NRC publication of the Notice of Approval of the TSTF Traveler in the Federal Register. This action will be documented as a license commitment in this response to the Generic Letter.
2 DESIGN EVALUATION The RBS design basis was reviewed with respect to gas accumulation in the Emergency Core Cooling, and Decay Heat Removal systems. This included Design Basis Document reviews, drawing reviews, system walkdowns, and system reviews. Note, RBS does not have a Containment Spray system.
2.1 Discussion of Design Basis Documents Review:
Design Basis Documents were reviewed for the following:
0 System keep-fill designs and requirements to RBG-46848 Page 4 of 15 System realignments including Design Basis actuations Vortex correlations used to establish minimum water level setpoints How the General Design Criteria (GDCs) or plant specific principal design criteria listed in the Generic Letter are met or applied to the station Periodic venting requirements are addressed later in this Attachment.
Piping for the HPCS, LPCS, and RHR-LPCI systems downstream of the system injection isolation valves are partially voided by design. These void volumes are considered in the loriginal system design and do not impede system function.
Vortex evaluations have been performed for suction of the ECCS systems and found the design functions of the systems would not be adversely affected. These evaluations verify that the required submergence to avoid air ingestion due to vortexing ýis maintained.
Therefore, no air ingestion due to vortexing is anticipated to occur.
Various water hammer calculations with inadvertent air voids demonstrate that the ECCS piping systems can withstand the resulting loads from air present in the piping due to partial discharge line draining. Therefore although RBS may be susceptible to inadvertent air voids in the ECCS discharge piping, the piping has adequate design margin to accommodate the resultant transient loads.
An evaluation of the impact of gas accumulation in the ECCS lines sent to the reactor core during injection was conducted. This evaluation includes a qualitative evaluation that investigates the path and mechanism for air to be injected into the core region.
This evaluation justified that gas voids passing into the reactor vessel do not pose an additional safety concern mainly because of the unlikely path for air to get into the core and high void conditions in the core present during LOCA. In addition, a review of loss of feedwater, anticipated transient without scram, station blackout, and Appendix R fire safe shutdown events were found to have insignificant impact on meeting the acceptance criteria.
Discussion of Changes to Design Basis Documents:
The design control program and design change review checklists are included in procedures EN-DC-115 and EN-DC-141. These procedures are applicable across the Entergy fleet. The existing procedures require consideration of water hammer calculations, appropriate pipe slope, impact on system pumps and impact on system piping including pipe supports. As a result, the current procedure requirements address the issues in the generic letter.
While no specific revisions to the applicable procedures are necessary for RBS, Entergy is reviewing enhancements to EN-DC-141 to identify additional guidance to ensure that design changes maintain gas accumulation less than the amount that challenges operability of ECCS and RHR systems. This action is scheduled to be complete July 2009.
to RBG-46848 Page 5 of 15 During this review a condition was identified where three temporary startup strainers are not listed in the equipment database. These strainers are on the keep-fill pump suction with the strainer elements removed. Presence or absence of these items in the equipment database does not affect the design function of the systems. Resolution of this administrative condition will be tracked in the Corrective Action Process (CAP). No changes were identified which affected ECCS or RHR performance.
No additional changes are required to RBS Design Basis Documents.
2.2 Discussion of System P&ID and Isometric Drawing Reviews Results:
System drawings were reviewed to identify all system vents and potential high points.
System high points include all areas where gas could accumulate in the system, including isolated branch lines, valve bodies, heat exchangers, inappropriately sloped piping, and diameter transitions (orifices, reducers, and flow elements).
The following areas were considered:
High points in pipe runs, including elevation variation in nominally horizontal pipes (e.g. improperly sloped piping) and high points created by closed valves in vertical piping runs RHR system heat exchanger U-tubes, or other heat exchangers Horizontal pipe diameter transitions that introduce traps at the top of the larger piping or piping upstream of components (including orifice plates, reducers, and backing rings)
Tees where gas contained in flowing water can pass into a stagnant pipe where it then accumulates Valve bonnets Pump casings P&IDs were reviewed to determine general system flow paths and to identify major components. Associated isometric drawings were then identified and reviewed to determine and characterize high points in the system..
Each line segment in the system was evaluated for potential areas of gas accumulation or air intrusion and the areas warranting further evaluation (high points) were documented and evaluated.
Surveillance Test Procedure (STP) and System Operating Procedure (SOP) vents, were also compared to the high point vents identified during the drawing review.
to RBG-46848 Page 6 of 15 Identification of New Vent Valve Locations, Modifications to Existing Vent Valves, or Utilization of Existing Vent Valves Based on Drawing Review:
No new vent valve locations are identified as a result of the drawing review, While changes to drawings were identified there were no changes identified as part of this drawing review which affected ECCS or RHR performance. Also no discrepancies with the STP's were noted.
2.3 Discussion of System Confirmation Walkdown Results:
System walkdowns were performed to document high points, or areas vulnerable to gas accumulation.
Walkdowns were performed during original construction for ASME piping in HPCS, RHR and LPCS to verify the as-built configuration as documented and maintained on ASME Piping Control Drawings (PCD). Quality Control (QC) verified that documented measurements were accurate. These walkdowns were performed before piping was insulated or became inaccessible. PCDs are and have continuously been required to be modified to show configuration changes to ASME piping since original construction.
Additional barriers exist to identify any PCD change resulting from field work. As a result, the PCDs remain accurate representations of the field configuration.
Engineering walkdowns of the HPCS, LPCS, RHR 'A';RHR 'B', and RHR-LPCI 'C' pump and heat exchanger cubicles in the Auxiliary Building, and adjacent corridors were conducted in 2008 in response to this GL. These walkdowns, included contaminated and locked high radiation areas. The piping was visually inspected for any areas of possible gas accumulation not identified by the ASME Piping Control Drawing review. Valve, vent, and pump orientations were documented along with the orientation of each component's associated piping. Circumferential location was noted for valves not directly in the main system flow path. Operations assisted by conducting walkdowns of vent valves inside of the drywell to verify their circumferential location at the connection to the main system flow path.
Walkdowns of above ground non-ASME piping were also performed. No notable discrepancies were identified between isometric drawings of the non-ASME relevant to gas accumulation issues, and no additional highpoints were identified.
No notable discrepancies were identified between as-built field condition and the isometric ASME Piping Control Drawings relevant to gas accumulation issues. No additional highpoints were identified.
Further walkdowns were also performed using elevation measurements (ZipLevel) which showed that confidence in the PCDs is appropriate.- All measurements were taken on uninsulated pipe.
Walkdowns of the underground non-ASME piping in the vicinity of the Condensate Storage Tank was excluded from the walkdown scope. This non-ASME portion represents to RBG-46848 Page 7 of 15 a very small fraction of the total system piping, and the walkdown and drawing review data did not reveal any notable potential gas accumulation locations.
Identification of New Vent Valve Locations, Modifications to Existing Vent Valves, or Utilization of Existing Vent Valves Based on Confirmatory Walkdowns.
Identification of Remaining Walkdowns:
Because the system walkdowns confirmed the accuracy of the isometric drawings, no drawing changes were identified. No additional areas of potential gas accumulation or intrusion not previously identified during the drawing review phase were found.
No new vent valve locations were identified as a result of the walkdowns. No required changes or enhancements in response to this GL were identified by the walkdowns. No further walkdowns are required to respond to this Generic Letter.
2.4 Discussion of Fill and Vent Activities and Procedure Review Results:
System reviews consisted of a review of the fill and vent procedures in the HPCS, LPCS, and RHR System Operating Procedures (SOP's), Surveillance Test Procedures (STP's) and Alarm Response Procedures (ARP's) that include venting steps.
The normal mode of operation described in the SOP's is standby mode, which requires filling and venting as a prerequisite. Therefore, the fill and vent steps in the SOP's provide inherent protection against potential gas intrusion and as such, gas intrusion mechanisms are not considered further. The potential for gas intrusion from periodic testing under STP's is addressed later in this Attachment.
SOP's associated with the ECCS and RHR systems are:
High Pressure Core Spray (HPCS) fill and vent, restoration for maintenance activities SOP-0030 Residual Heat Removal (RHR) fill and vent, restoration for maintenance activities SOP-0031 Low Pressure Core Spray (LPCS) fill and vent, restoration for maintenance activities SOP-0032 In addition, some ARP's provide steps to vent their associated systems on receipt of associated alarms. Additional barriers to ensure the associated systems are properly vented include guidance in the RBS tagout guidelines and instrument line venting procedures.
Procedure revisions are not required to ensure adequate dynamic venting. Quarterly pump testing achieves a dynamic vent. Monthly system venting is performed with the keep-fill pump in service.
There are no sections of piping in these systems that merit the use of vacuum fill to fill and vent. Vacuum fill is not performed or required at River Bend for these systems.
to RBG-46848 Page 8 of 15 The following Operations procedures will be enhanced to include the acceptance criteria and actions to be taken if voids are detected.
Procedure I Corrective Action High Pressure Core Spray (HPCS) fill and vent, restoration for maintenance activities SOP-0030 Residual HeatRemoval (RHR) fill and vent, restoration for maintenance activities SOP-0031 Low Pressure Core Spray (LPCS) fill and vent, restoration for maintenance activities SOP-0032 ARP-601-16 ARP-601-17
" ARP-601-20
- ARP-601-21 Direction on amount vent valve is
- opened, Write Condition Report if significant air is vented, Document in Condition Report duration of air flow while venting.
Identification of Procedure Revisions. Summarization of Associated Corrective Actions:
Changes to the fill and vent procedures identified above are limited to enhancements. No additional changes were identified.
2.5 Discussion of Test Procedures Review:
RBS HPCS, LPCS and RHR System test procedures were reviewed to ensure appropriate fill and vent practices minimize air intrusion/gas accumulation in the system piping. Procedures reviewed included Operations procedures, and Maintenance procedures.
The periodic venting procedure Contained in the Monthly Functional Test Procedure for each system, the procedure used to show compliance with Technical Specification Surveillance Requirements 3.5.1.1 and 3.5.2.3, was identified and evaluated to determine the procedure's effectiveness in the following:
0 0
0 Determining whether gas is present in the system.
Removing gas from the system and ensuring the system is full.
Follow-up action, if necessary, through the RBS CAP program.
Test procedures performed during the system standby mode of operation were reviewed to determine whether the system is filled and vented once surveillance and testing is complete, these procedures include Quarterly Functional Test procedures. This review determined that the system is sufficiently filled and vented prior to being returned to the standby mode of operation.
to RBG-46848 Page 9 of 15 Maintenance or test procedures that are performed during plant refueling or cold shutdown mode were not reviewed since each system will,be filled and vented per the System Operating Instruction fill and vent procedure prior to returning the system to service.
System STP's associated with monthly testing of the ECCS and RHR systems are:
STP-203-0201 HPCS Piping Water Fill and Valve Position Verification STP-204-0201 LPCI A Discharge Piping Fill and Valve Lineup Verification STP-204-0202 LPCI B Discharge Piping Fill and Valve Lineup Verification STP-204-0203 LPCI C Discharge Piping Fill and Valve Lineup Verification STP-205-0201 LPCS Piping Water Fill and Valve Position Verification The following procedures provide steps to vent the ECCS and RHR systems on a quarterly frequency:
STP-203-6501 HPCS Pump and Valve Operability Test STP-203-6305 HPCS Quarterly Pump and Valve Operability Test STP-204-6302 Div II LPCI (RHR) Quarterly Pump and Valve Operability Test STP-205-6301 LPCS Quarterly Pump and Valve Operability Test Summary of Changes to Test Procedures:
Surveillance test procedures for HPCS, LPCS, and RHR systems will be enhanced to include the acceptance criteria and actions to be taken if voids are detected.
The CAP currently requires initiation of a condition report when degraded or.
nonconforming conditions are identified. Trending is also performed as part of the CAP.
The changes to the acceptance criteria and required actions will require initiation of a Condition Report in the CAP allowing the trending of gas present in the line and allow further evaluation. The changes to these procedures are considered enhancements because these changes reinforce the existing requirements of the CAP.
The table below summarizes the enhancements RBS will pursue to ensure that gas accumulation or ingestion does not impact the HPCS, LPCS, or RHR systems. These enhancements are entered into the RBS CAP and will be tracked to conclusion.
to RBG-46848 Page 10 of 15 Procedure I Corrective Action HPCS procedure STP-203-0201 RHR procedure STP-204-0201 RHR procedure STP-204-0202 RHR procedure STP-204-0203 LPCS procedure STP-205-0201 STP-203-6501 HPCS Pump and Valve Operability Test STP-203-6305 HPCS Quarterly Pump and Valve Operability Test STP-204-6302 Div II LPCI (RHR)
Quarterly Pump and Valve Operability Test STP-205-6301 LPCS Quarterly Pump and Valve Operability Test Direction on amount vent valve is
- opened, Write Condition Report if significant air is vented, Document in Condition Report duration of air flow while venting.
As a result of this review; no new vents are required to be added and no new vent valve locations have been identified. The identified procedure enhancements have been entered into the RBS CAP.
The site CAP is the primary program that is used to track and trend gas accumulation.
Gas intrusion/accumulation issues are documented as nonconforming conditions which can be trended to determine if increased or alternate monitoring is required.
- 3. Discussion of Potential Gas Intrusion Mechanisms:
Areas of potential gas intrusion into each system and each system segment vulnerable to subsequent gas accumulation have been reviewed. Potential areas of intrusion/
accumulation are discussed below.
For RHR loop A and B discharge lines, the system response following a loss of the keep-fill system and air in-leakage that could occur through system pathways which allow drainback to the system are bounded by system realignments during Design Basis actuations. This evaluation determined that loads occurring on the piping system from air present in the piping due to partial discharge line draining are small in relation to other transient loads postulated for the piping. These analysis also demonstrate that the RHR loop A and B piping potentially affected by draining during the transition from the suppression pool cooling to the LPCI mode have adequate margin to accommodate the resultant transient loads.
For HPCS, RHR loop C (LPCI-C) and LPCS discharge lines an evaluation concludes that the loads resulting from water hammer due to voiding of the various pump discharge lines due to draining are within the allowable piping loads.
Vortex induced air entrainment is addressed by the vortex correlations discussion below. Maintaining Suppression Pool and Condensate Storage Tank level greater to RBG-46848 Page 11 of 15 than the minimum submergence prevents vortex induced air entrainment and ensures that the suction source is isolated before it is completely drained.
Therefore, gas is not introduced from vortexing in the Suppression Pool or Condensate Storage Tank suction sources.
Air entrainment from a plunging jet in the Condensate Storage Tank to the HPCS suction nozzle was reviewed. The initial review concluded that gas intrusion into the HPCS suction nozzle is not anticipated to exceed the acceptance criterion.
Formalization of the analysis will document the margin.
The acceptance criteria for pump suction piping gas volume limits are sufficient to ensure the gas volume fraction at the pump suction is acceptable under flowing conditions. Gas volume acceptance criteria was determined to be a bounding 2% void fraction for continuous voiding and 10% void fraction for up to 5 seconds. This acceptance criteria is based on industry guidance for acceptable pump performance. This acceptance criteria also considers the prevention of pump air binding, limits pump wear to within the acceptable mission time of the pump, and limits the hydraulic performance reduction in the pump to limits defined by the safety analyses.
Vortex calculations have been performed for suction from both the Suppression Pool and the Condensate Storage Tank. For the Suppression Pool, the submergence was calculated for the ECCS pump suction strainers. This was compared to the required minimum submergence to prevent vortexing from the suction flange to the surface. The Froude numbers for the ECCS pump suction strainers, based on submergence and suction flange water velocity, are less than 0.8, which demonstrates that air entrainment is prevented into the ECCS pump suction. For HPCS suction from the CST concurrent with Reactor Core Isolation Cooling (RCIC) suction (maximum flow velocity condition), the minimum CST level was shown to be greater than the minimum required submergence.
Acceptance criteria for pump discharge side voiding addresses water hammer.
Acceptance criteria considers force loads on pipes and hangers, peak pressure pulses, secondary water hammer due to check valve slamming, and delays or reduction in flow delivery. Gas volume acceptance criteria was been determined to be 5 cubic feet void volume unless addressed by specific analysis.
Flow through the ECCS piping downstream ofthe injection valves only occurs during accident conditions. An analysis of ECCS piping downstream of the injection valves has been completed and a determination made that the existence of air voids in this piping will have no adverse consequences related to accident conditions.
Summary of Changes Resulting from Gas Intrusion Mechanisms:
The gas intrusion reviews are complete, with the exception of producing additional documentation discussed below.
Initial review determined that there is no impact on the HPCS system function due to the return flow plunging jet in the Condensate Storage Tank. RBS will produce documentation to quantify margin for air entrainment due to a return flow plunging jet of water in the Condensate Storage Tank.
to RBG-46848 Page 12 of 15 This action will be complete by November 15, 2008.
4 Summary List of Items that have Not Been Completed, a Schedule for their Completion, and the Basis for that Schedule:
Current procedures do not have acceptance criteria for the allowable amount of gas which is periodically vented including allowance for measuring inaccuracies. Typically, entrained gas is not present during quarterly venting. As such, River Bend does not utilize a device to capture and quantify the amount of entrained gas in the system piping.
The existing fill and vent procedures indicate that the RHR, LPCS and HPCS are vented from the high point of the system and water flow observed. Clear Tygon hose is attached to the vents. The operators could see entrained gas venting from the system if gas was present.
While there is presently no mechanism to accurately quantify the amount of gas vented, any abnormal gas found during the surveillances would be captured and trended by the CAP.
A Condition Report has been initiated to add specific requirements of writing a condition report when abnormal gas is vented from these systems during surveillances.
Entergy's Corrective Action Program is used to document gas intrusion/accumulation issues as potential nonconforming conditions. Future revisions of procedures for the RHR, LPCS and HPCS systems require entering the Corrective Action Process by initiating a Condition Report if the vented gas volume exceeds the acceptance criteria specified in the procedures. As part of Entergy's Corrective Action Program, Condition Reports related to plant equipment are evaluated for potential impact on operability and reportability. Therefore, Entergy's review concluded that issues involving gas intrusion/accumulation are properly prioritized and evaluated under the Corrective Action Program.
The table below summarizes the corrective actions previously identified and their schedule completion dates.
to RBG-46848 Page 13 of 15 Issue/Procedure Action Due Date EN-DC-141, design Identify additional guidance July 2009 checklists to determine if design changes ensure that gas accumulation is maintained less than the amount that challenges operability of ECCS and RHR systems.
HPCS procedure STP-203-0201 RHR procedure STP-204-0201 RHR procedure STP-204-0202 RHR procedure STP-204-0203 LPCS procedure STP-205-0201
" ARP-601-16 ARP-601-17 ARP-601-20 ARP-601-21 High Pressure Core Spray (HPCS) fill and vent, restoration for maintenance activities SOP-0030 Residual Heat Removal (RHR) fill and vent, restoration for maintenance activities SOP-0031 Low Pressure Core Spray (LPCS) fill and vent, restoration for maintenance activities SOP-0032 STP-203-6501 HPCS Pump and Valve Operability Test STP-203-6305 HPCS Quarterly Pump and Valve Operability Test STP-204-6302 Div II LPCI (RHR) Quarterly Pump and Valve Ooerabilitv Test Direction on amount vent valve is opened, Write Condition Report if significant air is
- vented, Document in Condition Report duration of air flow while venting..
March 2009 to RBG-46848 Page 14 of 15 STP-205-6301 LPCS Quarterly Pump and Valve Operability Test Gas intrusion Produce new November 15, 2008 documentation to quantify margin for suction nozzle air entrainment at the Condensate Storage Tank due to bubbles created by a plunging jet of water (test return flow to the CST).
Changes proposed by the RBS will review for 90 days following NRC Technical Specification applicability the TSTF approval.
Task Force (TSTF)
I Basis For Schedule.
Based on past performance of the procedures involved the ECCS and RHR systems are currently capable of performing their design function.
An initial evaluation of the margin for air entrainment caused by a plunging jet in the Condensate -Storage Tank has been conducted. Formalization of the design documentation will be completed by November 15, 2008.
Enhancement to the EN-DC-141 procedure is not required by RBS. This action will add clarification to ensure that design changes adequately address gas accumulation.
The changes proposed by the TSTF are underdevelopment and therefore, not appropriate for implementation at this time.
- 6. CONCLUSION Entergy has completed its evaluation of the RBS RHR, LPCS and HPCS systems that perform the functions described in this GL. This evaluation has concluded that these systems are operable, as defined in the RBS TS and are in conformance to our commitments to the applicable General Design Criteria (GDC), as stated in the USAR. As described in this response, reviews of the design basis, installation and operation, support the design functions required by the ECCS and RHR systems.
Based upon the above, Entergy has concluded that River Bend Station is in conformance with its commitments to 10 CFR 50, Appendix B, Criterion Ill, V, XI, XVI, and XVII, as described in the Quality Assurance Program.
No deviations have been identified that will impact the ability of the RHR, LPCS and HPCS systems to perform the design functions required.
to RBG-46848 Page 15 of 15 The open actions cited above are considered to be enhancements to the existing programs/processes/procedures for assuring continued Operability of these subject systems. Actions that have not yet been completed are being tracked through final resolution, as described in this Enclosure.
RBG-46848 List of Regulatory Commitments RBG-46848 Page 1 of 1 List of Regulatory Commitments The following table identifies those actions committed to by Entergy in this document.
Any other statements in this submittal are provided for information purposes and are not considered to be regulatory commitments.
TYPE (Check one)
SCHEDULED ONE-TIME CONTINUING COMPLETION COMMITMENT ACTION.
COMPLIANC DATE (If E
Required)
RBS will evaluate and submit, as appropriate, changes to the plant X
90 days Technical Specifications based upon the following NRC final, approved version of Technical approval.
Specification Task Force (TSTF) Traveler for unacceptable gas accumulation in ECCS. This submittal will be, adjusted, as needed, to account for plant-specific design and licensing basis. The submittal will be within 90 days following NRC publication of the Notice of Approval of the TSTF Traveler in the Federal Register.
Produce new documentation to quantify X
November 15, margin for suction nozzle air entrainment 2008 at the Condensate Storage Tank due to bubbles created by a plunging jet of water (test return flow to the CST).
/