ML082890534

Nine-Month Response to NRC Generic Letter 2008-01, Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems

ML082890534
Person / Time
Site:	Summer
Issue date:	10/13/2008
From:	Archie J South Carolina Electric & Gas Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GL-08-001, RC-08-0129
Download: ML082890534 (37)

Text

Jeffrey B. Archie Vice President, Nuclear Operations 803.345.4214 2.

A SCANA COMPANY October 13, 2008 RC-08-0129 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

References:

VIRGIL C. SUMMER NUCLEAR STATION (VCSNS)

DOCKET NO. 50/395 NINE-MONTH RESPONSE TO NRC GENERIC LETTER 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems"

1.

NRC Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems" dated January 11, 2008.

2.

Virgil C. Summer Nuclear Station, Supplemental Response to NRC Generic Letter 2004-02, "Potential Impact of Debris Blockage on Emergency Recirculation during Design Basis Accidents at Pressurized-Water Reactors", dated February 29, 2008.

3.

Virgil C. Summer Nuclear Station, Response to NRC Generic Letter No. 88-17, "Loss of Decay Heat Removal", dated January 23, 1989 (Expeditious Actions).

4.

Virgil C. Summer Nuclear Station, Response to NRC Generic Letter No. 88-17, "Loss of Decay Heat Removal", dated February 2, 1989 (Programmed Enhancements).

5.

Virgil C. Summer Nuclear Station, Withdrawal of License Amendment Request-LAR 02-2820, Emergency Core Cooling Systems-Exclusion of Safety Injection Pumps for the Requirement to Vent ECCS Pumps, date June 22, 2005.

6.

Information Notice 88-23, Supplement 4, "Potential for Gas Binding Of High-Pressure Safety Injection Pumps During a Design Basis Accident, dated December 18, 1992 Attachments: 1.

NRC Generic Letter 2008-01 Requested Information for a 9 Month

Response

2.

List of Commitments The Nuclear Regulatory Commission (NRC) issued Generic Letter (GL) 2008-01 (Reference 1) to request 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 Reactor Building (RB) 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.

SCE&G I Virgil C. Summer Nuclear Station

• P. 0. Box 88

• Jenkinsville, South Carolina 29065

• T (803) 345.5209 ° www.sceg.com

Document Control Desk CR-08-00162 RC-08-0129 Page 2 of 2 GL 2008-01 requested each licensee to submit a written response in accordance with 10 CFR 50.54(f) within nine 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 of the GL. This description should provide sufficient information to demonstrate that you are or will be in compliance with the quality assurance criteria in Sections III, V, 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; (b) A description of all corrective actions, including plant, programmatic, procedure, and licensing basis modifications that you determined were necessary to assure compliance with these regulations; and (c) A statement regarding which corrective actions were completed, the schedule for completing the remaining corrective actions, and the basis for that schedule.

In summary, VCSNS has concluded that the subject systems at VCSNS are in compliance with the Technical Specification (TS) definition of Operability, i.e., capable of performing their intended safety functions. VCSNS is currently in compliance with 10 CFR 50 Appendix B, Criterion Ill, V, Xl, XVI and XVII, with respect to the concerns outlined in GL 2008-01 regarding gas accumulation in these systems. to this letter contains the VCSNS nine-month response to the Requested Information in NRC GL 2008-01. Attachment 2 provides a list of the commitments made in response to NRC GL 2008-01.

Should you have any questions, please call Mr. Bruce Thompson at (803) 931-5042 at your convenience.

I certify under penalty of perjury that the information contained herein is true and correct.

Ex'ecuted on Jeffrey B.'Ar6hie GR/JBA/dr Attachment c:

K. B. Marsh K. M. Sutton S. A. Byrne D. L. Abstance N. S. Carns P. Ledbetter J. H. Hamilton INPO Records Center R. J. White J&H Marsh & McLennan L. A. Reyes NSRC K. Browne RTS (CR-08-00162)

R. E. Martin File (815.14)

NRC Resident Inspector DMS (RC-08-0129)

Document Control Desk CR-08-00162 RC-08-0129 Page 1 of 33 Response to Generic Letter (GL) 2008-01 This response to Generic Letter (GL) 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems,"

addresses the nine-month response requested in NRC GL 2008-01, which was dated January 11, 2008. This response provides the following:

a)

A description of the results of evaluations that were performed pursuant to the requested actions in the GL, b)

A description of all corrective actions determined necessary to assure compliance with the quality assurance criteria in Sections III, V, XI, XVI, and XVII of Appendix B to 10 CFR Part 50 and the licensing basis and operating license with respect to the systems identified in the GL, and c)

A statement regarding which corrective actions were completed by October 11, 2008, the schedule for completing the corrective actions not completed by October 11, 2008, and the basis for that schedule.

1.

LICENSING BASIS EVALUATION The VCSNS licensing basis was reviewed with respect to gas accumulation in the Emergency Core Cooling System (ECCS), Residual Heat Removal (RH)

System, and Reactor Building Spray (SP) Systems. At VCSNS the ECCS is comprised of the Safety Injection (SI) System and portions of the Chemical and Volume Control System (CS) which provide high head safety injection and portions of the RH System which provide low head safety injection. This review included the Technical Specifications (TS), TS Bases, Updated Final Safety Analysis Report (UFSAR), responses to NRC generic communications, Regulatory Commitments and License Conditions.

1. Results of the review of the licensing basis documents:

The results of the review of the TS and TS Bases indicate that a revision is required to the TS Surveillance Requirement (SR) 4.5.2.b.2 and its associated bases for the ECCS and SR 4.6.2.1 and its bases for the RB Spray System.

TS Surveillance Requirement (SR) 4.5.2.b.2 requires verification that the ECCS piping is full of water by venting the ECCS pump casings and accessible discharge piping high points every 31 days. The Bases for TS 3.5.2 and 3.5.3 (associated with SR 4.5.2.b.2) do not specifically address the verification requirements for the ECCS piping being full. This SR requires revision to verify that ECCS piping, including suction piping, is sufficiently full by venting/monitoring all necessary locations. The bases also require revision to fully address the reason for the verification requirements and what piping is included in the SR.

Document Control Desk CR-08-00162 RC-08-0129 Page 2 of 33 TS 3.6.2.1 requires that two independent reactor building spray systems shall be operable with each spray system capable of taking suction from the RWST and automatically transferring suction to the spray sumps in Modes 1-4. SR 4.6.2.1 requires periodic verification of proper valve alignment, pump performance testing, automatic actuation of pump and valves and flow testing of spray header and nozzles. There are no specific requirements for verifying RB Spray piping is sufficiently full. This SR requires revision to verify that RB Spray piping, including suction piping, is sufficiently full by venting/monitoring all necessary locations.

The bases also need to be revised to fully address the reason for the verification requirements.

A review of the UFSAR indicates that the requirement for the ECCS, RHR System and RB Spray to be verified sufficiently full of water or vented is not addressed. Filling, venting and maintaining the systems sufficiently full of water is controlled under plant procedures. The design, safety functions and accident mitigation requirements are properly addressed in the UFSAR and no changes were determined to be necessary to the UFSAR as a result of the review for this GL.

A review of the NRC generic correspondence, Regulatory Commitments and License Conditions indicates that all responses, commitments and license conditions have been properly addressed. One change was determined to be necessary as a result of the review for this GL.

A commitment was made in LER-1 998-008 to clarify venting requirements for ECCS pumps and piping. A license amendment request was submitted to the NRC on January 14, 2003. After extensive interaction with the NRC including an onsite visit by the reviewer, the amendment request was withdrawn on June 22, 2005. As discussed in the withdrawal letter, the license amendment request would be resubmitted and include the use of ultrasonic testing as a method of determining the presence of gas voids. VCSNS has been working to that end.

That commitment has been incorporated into this response letter and is included in the Technical Specification revisions as discussed above and below in Section 1.3.

2. Changes to licensing basis documents (Corrective Actions):

VCSNS has not made any changes to the current licensing basis documents as a result of evaluations performed for this GL response.

3. List of items that have not been completed, schedule for completion, and the basis for the schedule:

As discussed above, the TS and associated bases for the ECCS and RB Spray System require revision. TS improvements are being addressed by the Technical Specifications Task Force (TSTF) to provide an approved TSTF Traveler for making changes to individual licensee's TS related to the potential for unacceptable gas accumulation. The development of the TSTF Traveler relies

Document Control Desk CR-08-00162 RC-08-0129 Page 3 of 33 on the results of the evaluations of a large number of licensees to address the various plant designs. VCSNS is continuing to support the industry and NEI Gas Accumulation Management Team activities regarding the resolution of generic TS changes via the TSTF Traveler process. After NRC approval of the Traveler, VCSNS will evaluate its applicability, and evaluate adopting the Traveler to replace the current TS requirements. VCSNS will assign an action under the Corrective Action Program to monitor the status of the TSTF Traveler and to perform the identified evaluation after approval of the TSTF Traveler. A License Amendment Request to revise the TS will be submitted within one year following TSTF approval. These actions are identified as commitments in Attachment 2.

II1.

DESIGN EVALUATION The VCSNS design basis was reviewed with respect to gas accumulation in the ECCS, RH System, and SP System. This review included the Design Basis Documents, Drawings, Calculations, and Engineering Evaluations.

1. Results of the review of the design basis documents:

The design basis of VCSNS includes a detailed calculation of the force imbalances during the filling of the Containment Spray discharge header that shows the resultant force imbalances to be within the design margin of the piping and pipe supports.

2. Discussion of new applicable gas volume acceptance criteria for each piping segment in each system where gas can accumulate where no acceptance criteria previously existed and summary of the Corrective Actions, and schedule for completion of the Corrective Actions.

A. The interim allowable gas accumulation in the pump suction piping is based on limiting the gas entrainment to the pump after a pump start. A Pressurized Water Reactor Owners Group (PWROG) program established interim pump gas ingestion limits to be employed by the member utilities. The interim criteria address pump mechanical integrity only and are as follows:

Single-Stage Multi-Stage Multi-Stage Stiff Shaft Flexible Shaft Steady-State 2%

2%

2%

Transient*

5% for 20 sec.

20% for 20 sec.

10% for 5 sec.

QB.E.P. Range 70%- 120%

70%- 140%

70%- 120%

Pump Type WDF CA RLIJ, JHF (transient data)

• The transient criteria are based on pump test data and vendor supplied information.

Document Control Desk CR-08-00162 RC-08-0129 Page 4 of 33 VCSNS procedures provide assurance that the volume of gas in the pump suction piping for the affected systems is limited such that pump gas ingestion is within the above PWROG program established interim criteria.

B. VCSNS contracted Westinghouse to provide a calculation note that determines the acceptable volumes of possible gas accumulation locations in the pump suction piping as a parametric study of gas void fraction at the pump suction. The acceptable gas volumes were determined based on a two-phase gas transport analysis. The methodology used calculated the allowable initial volume at a piping system high point based on allowable pump inlet void fractions. Determining allowable initial volumes in the suction side of these systems included the following steps:

Determine the allowable pump inlet void fraction Determine possible gas accumulation locations Define the suction path from the suction source to the pump for all modes of operation Define the system flow rates Define the suction source maximum elevations Define minimum pump suction pressures Perform a gas transport analysis (by Westinghouse). This analysis correlated the pump inlet void fraction to the volume of trapped gas in the suction side gas accumulation locations. The gas transport analysis was based on the literature data and on the test data in WCAP-16631 -NP.

Two approaches to modeling the distribution and movement of the gas phase from a system high point were developed. Both approaches were based on a detailed analysis of the PWROG program on gas transport, which specifically focused on gas transport on the suction side of the ECCS pumps. The first approach was a gas volume based approach which directly utilized empirical correlations developed in the calculation to calculate the redistribution of the gas phase as it moves through specific geometry and the transport time, or time for the gas void to pass a single location along the pipe. The second approach was based on homogeneous two phase flow arguments. This approach has also been shown to accurately describe the data in WCAP-1 6631-NP. Furthermore, the allowable volume was limited to preclude, with absolute certainty that kinematic shock ingestion into the pump will not occur. The minimum of the volumes calculated from the gas phase distribution models and the volume from the kinematic shock limitation were used as the high point criteria basis.

The results of this analysis were presented in tables that summarize the allowable volumes based on the gas transport analysis for 2%, 3% and 5%

allowable pump inlet void fractions for all the high points identified. All the volumes calculated using the methodology described are conservative and are based on available test data contained in WCAP-16631-NP.

Document Control Desk CR-08-00162 RC-08-0129 Page 5 of 33 C. Westinghouse developed for VCSNS a report to qualitatively evaluate the impact of the injection into the Reactor Coolant System (RCS) of a small amount of non-condensable gas from the high head safety injection (HHSI) discharge headers in a LOCA event. The focus is on high points in the HHSI system discharge headers. Maximum size gas voids have been evaluated and determined for each of the corresponding HHSI discharge headers:

Cold Leg Injection (via valves 8801A/B) Initiated on a "Safety Injection" signal Recirculation (via valve 8885) switchover after -30 minutes (low level signal of Refueling Water Storage Tank (RWST))

Hot Leg Recirculation (via valves 8884 and 8886) switchover after -8 hours With consideration of non-condensable gas intrusion in the ECCS high-head safety injection discharge headers, possible impact of the gas bubbles on the ECCS performance was evaluated. It is assumed that the non-condensable gas voids are present in the headers (via valves 8801A/B, 8885, 8884 or 8886), which are located downstream of the pumps. As such, pump performance would not be affected. In order to evaluate the potential impact of non-condensable gas voids in the ECCS, minimum HHSI flow rates were considered in conjunction with theories of air transport of a two-phase mixture in piping systems. The test program outlined in WCAP-16631-NP documents gas transport test results that were applied to the conditions considered in this evaluation.

The impacts of the identified gas voids on the VCSNS Loss of Coolant Accident (LOCA) analyses were evaluated. There are four general areas of LOCA analyses which are considered: Large Break LOCA (LBLOCA), Small Break LOCA (SBLOCA), Long Term Core Cooling (LTCC), and LOCA Forces. In addition, there are three non-LOCA events potentially impacted by the introduction of gas voids into the Reactor Coolant System (RCS):

Steamline Break, Feedline Rupture and Steam Generator Tube Rupture (SGTR). These events were also considered in the evaluation.

Based on the conclusions made for fluid systems potential impact, the overall ECCS flow rates for cold leg injection, cold leg recirculation and hot leg recirculation remain unchanged when considering gas void sizes discussed in the evaluation. Given that ECCS flows assumed in the LOCA analyses are not impacted, the injection of non-condensable gas, with the volume identified in the evaluation, during a LOCA event would have no impact on the conclusions of the applicable LBLOCA, SBLOCA, LTCC, or LOCA Forces analyses. Similarly, considering no change in the Performance Capability Working Group (PCWG) and ECCS flow, there is no impact on the conclusions of the Steamline Break, Feedline Rupture and SGTR analyses related to ECCS (SI) flow degradation and injection delay. With respect to heat transfer degradation, the presence of non-condensable gas volumes on the order of those determined by the evaluation would not have an appreciable effect.

Document Control Desk CR-08-00162 RC-08-0129 Page 6 of 33 Westinghouse also prepared a similar evaluation for the PWROG covering both the HHSI and LHSI systems. The basis and methodology are basically identical to that prepared directly for VCSNS. The PWROG report includes an allowable void size for the LHSI System.

D. The dynamic affect of gas voids on the discharge and suction piping during system startup was evaluated. Specifically, the potential water hammer caused by gas voids was quantified and the impact on the structural piping and pipe supports evaluated. The margins in the piping and pipe supports design were reviewed to determine if these structures could absorb additional loads generated by the water hammer conditions. The determination of available margins considered the operation of the various systems under a seismic event. If the initiation of flow in a piping system during emergency core cooling and the corresponding water hammer are expected to occur coincidentally as an initiating event, design margins were determined after the water hammer load was added to the system operating loads and the seismic load. If the initiation of flow in a piping system and the corresponding water hammer are expected to occur after the initiating event that includes the seismic event, the design load margin used for the seismic condition was applied to the water hammer load. This evaluation was documented in calculations that reviewed the affects of the water hammer condition due to the gas voids on the pump discharge and suction piping of the SI, RH and SP systems.

This evaluation required an initial determination of the fluid hydraulic effects on the piping. When a gas pocket exists in a pipe segment the momentum forces during steady flow on the upstream and downstream elbows can be temporarily unbalanced because of the density difference between the gas and liquid. At a given system pressure and temperature, the amount of the force difference in a particular pipe size depends on the fluid velocity. Higher velocities create larger net force differences. The gas pocket is assumed to be comprised of air, initially at system operating pressure. Because downstream backpressure exists, acceleration forces are moderate. The maximum velocity occurs when the fluid reaches design flow rate following pump startup or valve opening. The acceleration forces during this velocity increase are no greater than during normal system startup. (In fact, the acceleration forces will be less in gas-filled segments because the accelerated mass is less than when the pipe is liquid filled.). To create the largest differential forces mathematically, the gas void is assumed to fill the entire height of a horizontal pipe segment. No mixing between the liquid and gas is assumed. Unbalanced forces may also be created when liquid displaces gas through a flow orifice. The computations for a flow orifice are similar to the opposing elbows of a pipe segment, except that the control volume boundary is constructed to produce the net unbalanced reaction force due to a liquid jet moving at higher velocity through the flow orifice. It is conservatively assumed that the liquid jet does not expand, and that the pressurized gas pocket is located immediately downstream of the flow orifice.

Document Control Desk CR-08-00162 RC-08-0129 Page 7 of 33 Steady flow is assumed, and the maximum reaction force occurs at maximum velocity at the design system flow rate.

The fluid hydraulic analysis resulted in forces that are applied to each pipe length in the axial direction of the pipe at the end elbows or at an internal orifice. The loads are based upon steady state conditions. For conservatism, and to apply these to a dynamic water hammer condition, a Dynamic Load Factor (DLF) of 2.0 was applied to all the loads calculated by the fluid hydraulic analysis.

It was concluded that these forces will have a negligible effect on the stresses of the piping. It is known that the affects of a water hammer condition on pipe stress is small. The forces are exerted at elbows so quickly (milliseconds) that the piping as a whole with its large dampening factors does not have time to react. This is confirmed by time history analysis of pipe water hammer conditions which result in low pipe stresses. Pipe supports, on the other hand, that restrain the piping in the axial direction will see these forces instantaneously as they are developed and therefore will see virtually the entire force developed by the water hammer. Therefore, the focus of the review was on the affects of these forces on the pipe supports.

To identify the affected pipe supports, each pipe length was reviewed to determine which supports restrain the length along the axial direction of the pipe. These supports could be true axial restraints with welded attachments to the pipe, or a restraint right around an end elbow that is oriented in the axial pipe length direction. A total of 353 axial pipe supports were identified.

After identification, the load generated by the fluid hydraulic analysis was applied to each support in addition to existing design basis loads. To determine if the axial support remained qualified with the additional water hammer load applied, margins within the support design in regards to the loads applied to the support were evaluated. The evaluation identified margins in the load qualification of the support for which the water hammer loads were applied.

The margin evaluations and fluid hydraulic loads were tabulated based on upset conditions. For each of the 353 pipe supports, a comparison was made between the water hammer load calculated by the fluid hydraulic analysis and the acceptable water hammer load based on the pipe support margin evaluations.

The calculations concluded that sufficient margins are available in the design of all 353 pipe supports such that these structures continue to satisfy design basis requirements with the additional loads applied due to the water hammer condition caused by the potential gas voids.

Document Control Desk CR-08-00162 RC-08-0129 Page 8 of 33

3. Summary of changes to the design basis documents.

A. The following calculations have been completed and have been entered into the design basis documentation retention system:

1. Evaluation of the water hammer effects on the RH, SI/CS and SP pump discharge and suction piping and pipe supports

2. Determination of the locations of potential gas accumulation in the RH, SI, CS and SP pump discharge and suction piping.

3. Determination of the disposition (add vent, UT inspect, etc.) of potential gas accumulation locations

4. Evaluation of gas intrusion sources for the RH, SI, CS and SP systems B. The following calculations have been completed by outside contractors:

1. Evaluation of acceptable gas voids sizes in the RH, SI, CS and SP pump suction piping C. Piping design specifications for the RH, CS, SI and SP systems will be revised to include the water hammer loads resulting from possible gas voids during system startup as a new loading condition. The piping design specifications to be revised include: DSP-544EA, DSP-544AA, DSP-544DA, DSP-544EC and DSP-544J. The specification revisions are identified as a commitment in Attachment 2.

D. Engineering Services Procedure ES-427 for the development of plant modification packages will be revised to add a program design change review checklist to address the issues of potential gas intrusion in the RH, CS, SI and SP systems. This checklist will be included in the procedure to determine if the design change introduces or increases the potential for gas accumulation. As an example, replacing a valve with a heavier weight will change the slope of the piping. This will have to be addressed in the plant modification for its affect on potential gas accumulation. The checklist will provide screening questions to determine if the planned design change affects the established design basis for gas accumulation detection and prevention. If the screen indicates the design basis is affected, it will direct the engineer to methods to correctly assess the impact and provide a resolution. This procedure change is identified as a commitment in Attachment 2.

Document Control Desk CR-08-00162 RC-08-0129 Page 9 of 33

4. Results of the system P&ID drawing reviews, isometric drawing reviews and system confirmation walkdowns to identify all system vents and high points.

A review was completed to identify the location of potential gas accumulation in the RH, CS/SI and SP systems. A calculation was developed that identified these locations which are addressed below by component type.

A. Piping GL 2008-01 involves the challenges during the actuation of the noted piping systems. During this actuation, gas accumulated in stagnant branch piping off of the main process headers will not cause the challenges of concern noted within GL 2008-01. Therefore, only the piping in the main process headers were included in the scope of this calculation.

Within piping systems, gas can potentially accumulate at the following locations:

Piping high points Adjacent to orifice plates Adjacent to check valves Adjacent to normally closed valves Adjacent to reducers Adjacent to valves with reduced ports Using piping stress isometric drawings of the piping, locations that fall into any of these categories were identified. The pipe dimensions on these stress isometrics were obtained during walkdowns performed as part of the resolution of NRC IEB 79-14. They contain dimensions for all branch connections, valve locations, support locations, etc. and are highly accurate. Each location of potential gas accumulation was given a numerical identifier.

In addition, this review considered pipe slope of horizontal piping which is oriented in such a manner that a high point exits and could potentially trap an air void. The slope of the horizontal pipe runs were obtained from three dimension laser scans of the piping. Specially developed software allows the user to navigate through the laser scans to obtain as built elevations, dimensions and measurements of the piping. Each pipe run is broken down into five foot long segments with a node at each end. Each node is given a unique identifier. For each node, elevations are obtained.

From this data, a slope report was generated for each horizontal run that provides the following:

0 From/to node Segment length Slope in percentage Slope in angle units

Document Control Desk CR-08-00162 RC-08-0129 Page 10 of 33 An evaluation of each slope was conducted. Slopes that were satisfactory, i.e. do not trap gas, were identified with no further action.

Slopes that could trap gas were given an alphabetic identifier.

Not all piping in the scope of this calculation was included in this slope review. Sections of this piping that need not be considered are addressed in Section 11.10 of this attachment. It was determined that any gas accumulation in certain sections of piping would have either a negligible effect on system operation or it was determined that gas intrusion is not probable at any location within these certain sections. The slope in the horizontal piping within these sections was therefore not evaluated. These sections of piping are:

RH pump discharge piping inside the RB RH pump suction inside the RB SI Charging pump discharge piping inside and outside the RB Spray pump discharge piping 3" spray pump suction piping from the sodium hydroxide storage tank The laser scans and slope derivations were made with the piping at ambient temperature. Pipe thermal expansion due to system operating temperature could affect the slope of the piping if there are insufficient vertical rigid pipe supports located along the pipe length. However, all the piping in these systems is normally not operating and is at ambient temperatures. At the time that the piping is called into service, i.e. pump startup or valve opening, any gas void would then be moved along the piping. At that time, the pipe would still be close to ambient temperature since the piping does not having enough time to fully expand to the system operating temperature. Therefore, obtaining the slope at ambient temperatures is acceptable.

Also, the laser scans were made with insulation on the piping. All insulation has a metal jacket around the insulation which provides a uniform circular shape. Elevations of piping obtained from the scans were obtained every 5 feet along the pipe length. From these elevations, a slope in degrees was obtained for each 5 foot section. The vast majority of the insulated pipe was RH piping with a minimum size of 10 inches.

This pipe will not bend appreciably over a 5 foot length. Therefore, for long runs of pipe where the slope would play a part in potential gas accumulation, there is a high degree of confidence that the vertical direction of the slope (which end of the pipe is up and which end is down) was correctly obtained. This is consistent with observations from the slope report. Along a given pipe length, slopes in one vertical direction will persist for many 5 foot pipe sections until the vertical slope direction changes. For conservatism, the maximum slope in degrees of any 5 foot pipe section was used in the slope evaluation.

Document Control Desk CR-08-00162 RC-08-0129 Page 11 of 33 A table of all the locations where gas could potentially accumulate in piping was produced. There are 114 locations identified and this table assigned an arbitrary alpha/numeric designation to each location.

B. Valves The amount of gas drawn out of the bonnets of gate valves at any given time is significantly less than the calculated ingestible gas volume due to the limited exposed flow area and the flow restriction afforded by the retracted disc within the bonnet. Normally closed gate valves, both manual and motor operated, have relatively slow opening strokes and therefore, permit gradual displacement of gas within the bonnet over the stroke duration. This displacement rate does not challenge functionality of the subject systems, the pumps, or the Reactor Coolant System (RCS).

The entire volume within check valve bonnets is ingestible into the active flow stream. However, the bubble size and the rate at which gas can be drawn out of check valve bonnets is limited by the flow pattern across the gas-water interface at the bonnet entrance and the turbulence generated as the disc is pushed open by the active flow stream. The turbulence generated by the disc movement during flow initiation and the erratic flow pattern past the disc across the bonnet gas-water interface, ensures accumulated gas within the bonnet will be drawn out as tiny bubbles over time instead of an instantaneous withdrawal of the entire bonnet gas volume as one intact bubble. The ratio of the ingestible bonnet gas volume to flow volume at any given time is insignificant. Also, note that the flow pattern across the bonnet gas-water interface is erratic due to the flow stream having to pass through the annulus area formed by the disc and valve body before reaching this interface. Therefore, gas accumulation within check valve bonnets does not challenge functionality of the subject systems, the pumps, or the RCS.

Globe, ball and diaphragm valves are negligibly susceptible to gas accumulation within their bonnets (if they have bonnets). The internal configuration of these valves permits negligible gas accumulation within the valve body above the active flow stream, if any. Therefore, these valves do not challenge functionality of the subject systems, the pumps, or the RCS.

All air operated valves (AOV) in the CS, RH, SI and SP systems have been evaluated in regard to the possibility of their respective instrument air (IA) supply entering the fluid stream in which the AOVs are installed. A total of 62 valves were reviewed (note: no AOVs exist in the SP system).

It was concluded that the designs of the AOVs are such that it is not possible for IA to enter the respective fluid systems, and is, therefore, not a concern in regards to the subject of gas intrusion into these systems.

Document Control Desk CR-08-00162 RC-08-0129 Page 12 of 33 C. Instruments A review of the in-scope instruments reveals that there are no concerns with either inadequate initial venting of the system or excessive accumulation of gas during operation. As the systems are filled and vented prior to mode ascension, the instruments are also vented.

Instrument tubing lines are sloped in a manner to preclude gas accumulation at the instruments. Where there are high points, any gas that could accumulate would be small and not of concern. This small amount of accumulated gas would not preclude the instruments from performing their function.

Tank level instruments were reviewed to determine if any were susceptible to false high readings that would lead to gas being drawn into a pump suction. No instances were found of susceptible instruments.

D. Heat Exchangers The only heat exchangers within the scope of this review are the RH heat exchangers. The RH heat exchangers are Joseph Oat shell and tube type components that are installed in a horizontal position. Gas is not postulated to accumulate within these heat exchangers since the location of the bonnet nozzles are oriented at the top and bottom centerline making the inlet piping the high point.

E. Pumps The RH pumps are Ingersoll Rand Model 8X20WDF vertical single stage centrifugal pumps with a bottom single suction and side discharge. The impeller is a closed single suction type bolted directly to the end of the pump shaft. Each pump is provided with a mechanical seal to minimize leakage of the pumped fluid. The pump seal and casing vent are located at the top. The component and system is vented per station operating procedures and inspected per station surveillance procedures.

The charging pumps which provide HHSI are a self vent design. By manufacturer's design, the Flowserve (Pacific) pump Model 2 1/22 " RL-IJ 11-stage centrifugal pump have vertical suction and discharge nozzles located in the vertical plane that enter at the top of the pump casing. The casing design is for self venting which utilizes the discharge nozzle as the high point within the casing. As stated by the vendor, the pump casing vents through the discharge and suction nozzles. Vents are installed at the intake and discharge piping (instrument high side vent) which are local to the charging pumps. The component and system is vented per station operating procedures with inspections per station surveillance procedures.

Document Control Desk CR-08-00162 RC-08-0129 Page 13 of 33 The RB Spray pumps are Goulds Pump, Inc. Model 3415 horizontal centrifugal, double volute, single stage, 8x10-22. The pumps are rated for 2500 gpm at 450 ft of head. These pumps are vented at the casing.

The casings are vented and inspected per station procedures.

5. New vent valve locations, modifications to existing vent valves, and utilization of existing vent valves based on the drawing review and confirmatory walkdowns, and summary of the Corrective Actions.

A. The first step in this process was to identify the locations in which gas could potentially accumulate in the piping. Refer to the calculation noted in Section 11.4, above. This calculation considered gas accumulation at piping high points, adjacent to orifice plates, adjacent to check valves, adjacent to normally closed valves, adjacent to reducers and at pockets caused by sloped piping. The next step was to determine the effects of a gas void induced fluid transient water hammer on the structural integrity of the piping. The effects were documented in the calculations noted in Section 11.2.D, above. These calculations concluded that sufficient margins are available in the design of all piping and pipe supports such that that these structures continue to satisfy the design basis requirements with the additional loads applied due to the water hammer condition caused by the potential gas void of any size. The final step was to determine a disposition for each location. The disposition will remove the gas void by monthly surveillance to mitigate any affects of possible gas intrusion during system operation, determine that a gas void at that location will have negligible effect on system operation or determine that gas intrusion is not probable at that location. Multiple voids within close proximity and in the same flow path were combined and compared with the acceptable limit. A calculation was developed that determined the appropriate disposition for each of the locations identified in the calculation noted in Section 11.4.

For potential gas voids at reducers, orifices and sloped piping, the maximum volume was calculated. This volume was then compared to the acceptable void size limit as determined by the Westinghouse reports noted in Sections 11.2.B and 11.2.C, above. If the maximum calculated void was less than the acceptable limit, it was concluded that the potential void was acceptable as-is and no surveillance actions were required. If the calculated void size was greater than the limit, surveillance actions were initiated and actions to mitigate the concern were taken.

The PWROG program report noted in Section 11.2.A concludes that for pump type WDF like the VCSNS RH pump, a 5% VF for 20 seconds is acceptable. The calculated allowable voids are relatively small and will pass through the pump within 20 seconds, therefore allowable void size is based on a 5% VF for the RH pumps. Likewise, the PWROG program report noted in Section 2.a, above, concludes that for a pump type RLIJ like the VCSNS charging pump, a 10% VF for 5 seconds is acceptable.

Document Control Desk CR-08-00162 RC-08-0129 Page 14 of 33 The calculated allowable voids are relatively small and will pass through the pump within 5 seconds. To maintain consistency with the RH pump, the allowable void size for the charging pump suction is conservatively based on a 5% VF. In regards to the spray pumps, the PWROG program report noted in Section 11.2.A does not include pump specific data.

Therefore, the allowable void size is based on a 2% VF for the spray pumps.

B. A total of 114 potential gas hold up locations were identified within the scope of this review. These were dispositioned as follows:

1. Dispositions requiring further actions:

a. Additional existing vents have been added to the monthly surveillance test procedures (STPs). If the pipe is not insulated, an ultrasonic test (UT) inspection can be specified first to determine if venting is necessary.

b. New vents will be installed to allow for periodic venting of possible gas intrusion. This venting will be included in a Surveillance Test Procedure (STP) with a monthly frequency. If the pipe is not insulated, a UT inspection may be specified first as a test to determine if venting is necessary.

UT inspections have been implemented as interim surveillances until the new vents are installed.

c.

Holes will be installed in the top of concentric orifice plates to allow the flow of gas through the plate and prevent a trapped gas void pocket.

UT inspections have been implemented as interim surveillances until holes are drilled in orifice plates.

d. The quarterly stroke testing of dual containment recirculation sump isolation valves in the RH system will cause gas voids to enter the system. There are two pairs of sump isolation valves.

Based on the piping layout, the gas will transport to the RH pump suction line from the RCS hot leg (HL). This void location has no impact on the Safety Injection function of the RH pumps. When aligned to the RCS HL suction, the high RCS pressure reduces the bubble size to an acceptable void fraction. While operability is not challenged, VCSNS is investigating means of eliminating the gas intrusion in the future.

e. The quarterly stroke testing of dual containment recirculation sump isolation valves in the SP system will cause gas voids to enter the system. There are two pairs of sump isolation valves.

Document Control Desk CR-08-00162 RC-08-0129 Page 15 of 33 Based on the piping layout, the gas will transport to the main RB spray pump suction line where it is vented. The surveillance procedure for the valve stroke testing has been modified to include venting to immediately remove the gas. While operability is not challenged, VCSNS is investigating means of eliminating the gas intrusion in the future.

2. Dispositions requiring no further actions:

a. An existing vent that is accessible was included in an STP to provide additional vent capability. This venting has a monthly frequency.

b. If the calculated void size was less than the maximum allowable, it was concluded that the potential void was acceptable as-is and no surveillance actions were required.

C. For portions of the RH pump discharge piping inside the RB, the only potential source of gas is RCS in-leakage through RCS boundary check valves or in-leakage from the ECCS check valve test header. In-leakage from RCS is expected to pressurize the RH piping thereby preventing gas from coming out of solution. In-leakage from the ECCS check valve system is directed through two 3/*" globe valves and has not been identified as a historical gas intrusion source. Water hammer calculation noted in Section 11.2.D, above has concluded that a void of any size will not challenge the structural design basis of the piping and supports. This provides justification that any gas voids in this piping will have a negligible effect on system operation.

D. For portions of the charging pump SI discharge piping inside the RB, the pressure is normally maintained at or above the RCS pressure. This precludes gas from coming out of solution and prevents in-leakage.

There is the potential to leak by into the ECCS check valve test system.

However, the system is provided with a nominal 400 psig backpressure regulator which will prevent hydrogen from coming out of solution.

E. For portions of the charging pump SI discharge piping outside the RB, gas intrusion is not possible since the piping is maintained at the high charging pump discharge pressure. All other systems are at lower pressures and cannot enter this piping.

F. For the RH suction piping from the RCL hot legs inside the RB, the only potential source of gas intrusion is from gas coming out of solution due to RCS in-leakage. Each suction line is provided with two isolation valves in series. The maximum allowable valve leakage, per surveillance procedure, is 4.65 cc/min. Assuming one of the two valves meets the leakage limit, the maximum void size potentially formed during a 540 day fuel cycle is within the allowable for RH pump operation.

Document Control Desk CR-08-00162 RC-08-0129 Page 16 of 33 G. By design, the spray pump discharge piping is filled only to an elevation between 463.5' to 467.62'. The remaining piping up through the RB riser piping and through the dome piping remains void. Design basis piping analysis has correctly considered the flow transient loads associated with flow moving up through this piping upon pump start. This provides the basis for the acceptability of the unfilled piping.

H. For the 3" spray pump suction piping from the sodium hydroxide storage tank, there are no potential gas intrusion sources. The sodium hydroxide storage tank flow only comprises a small percentage of the total RB spray pump flow. Therefore the void fraction at the pump inlet due to air in-leakage from the sodium hydroxide storage tank flow is negligible.

1. The results of the drawing review and confirmatory walkdowns identified that the following actions were necessary:

12 existing vents were added to surveillance testing for monthly venting or monthly UT inspections to determine if there is a need for venting.

4 new vent valves will be installed under an engineering change.

In the interim, monthly UT inspections with acceptable void size acceptance criteria will be performed.

2 new vents will be installed under an engineering change.

In the interim, monthly UT inspections will be performed to determine the need to stroke an adjacent valve and open an appropriate vent valve.

2 orifices will be drilled with holes under an engineering change Until holes are drilled, monthly UT inspections with acceptable void size will be performed.

J.

In addition to the actions above from the drawing review and walkdowns, the following actions were identified based upon operating experience:

11 existing vents were added to surveillance testing for monthly venting or monthly UT inspections to determine if there is a need for venting.

6. Results of the system confirmation walkdowns that have been completed for the portions of the systems that require venting to ensure that they are sufficiently full of water.

The results of the system walkdowns to confirm piping elevations and slopes are discussed under Section 11.4.

Document Control Desk CR-08-00162 RC-08-0129 Page 17 of 33

7. New vent valve locations, modifications to existing vent valves, or utilization of existing vent valves that resulted from the confirmatory walkdowns, and summary of the Corrective Actions.

The addition of new vent valves and utilization of existing vent valves and UT monitoring is discussed under Section 11.5.

8. Results of the fill and vent activities and procedure reviews for each system.

A. VCSNS had one refueling outage (RF1 7) prior to the nine-month response date. Due to the time constraints in developing the necessary actions, it was assumed gas accumulation might occur anywhere in the HHSI piping (charging pump suction and discharge), LHSI piping (RH pump suction and discharge) and the RB spray piping (spray pump suction and discharge). In order to show compliance with the GL, the premise was used that all the piping within these systems is to be full upon return to power from the refueling outage.

GL 2008-01 also requires the quantification of gas removed as well as identification of gas. However, it is assumed that these actions apply to venting during plant operation at power.

B. A combination of static system venting and dynamic venting was used to ensure the systems were full at the completion of RF1 7 based on the following:

1. A review was conducted to assure that all the available vents were included in the fill and vent steps in each system procedure. In two cases, the ECCS check valve test connection was utilized as a vent.

2. Dynamic venting was completed for the four HHSI discharge headers and the RH system RCS cold leg injection headers inside the Reactor Building. This piping has a calculated Froude numbers greater than 2.5, higher than the lower limit to which dynamic venting is considered effective. Based on conservative calculations evaluating dynamic venting, time was increased from 1 minute per header to 10 minutes for the first header to clear common piping and then 5 minutes for the remaining 3 injection headers. For the RH headers, normal system operation time duration and flow rates during operational Modes 4 and 5 are adequate to dynamically vent the RH headers. Any gas introduced into theRCS was then removed during RCS chemistry control.

C. In regards to maintenance activities during station operation that could introduce gas into the system, a review of the fill and vent process in the

Document Control Desk CR-08-00162 RC-08-0129 Page 18 of 33 station maintenance and operating procedures was performed. Based on this review, it was determined that fill and vent procedures are not included in the maintenance procedures. After a maintenance activity is complete, the fill and vent activity is performed by operations personnel using system operating procedures. The existing fill and vent process in the system operating procedures was reviewed for adequacy following maintenance on system components. It was concluded that for the RB spray and charging systems, the existing normal system fill and vent process could be used for the components with available vents for "on-line" maintenance.

For the RH system, an additional section was added to the system operating procedure that lists those components with available vents for "on-line" maintenance and describes the fill and vent process for each component.

9. Procedure revisions and new procedures resulting from the fill and vent activities.

A. The following procedures were revised and.implemented during the last refueling outage, RF17:

1. SOP1 16, "Reactor Building Spray System", was revised to require outboard sump valve MVG03004A/B to be closed and inboard sump valve MVG03005A/B to be opened when the fill and vent procedure is implemented.

2. SOP1 12, "Safety Injection System", was revised to increase the time of header flush from one minute to five minutes.

3. SOP-1 15, "Residual Heat Removal", was revised to add a new section that listed those components with available vents for "on-line" maintenance and the fill and vent process for each component.

B. In addition, surveillance test procedure, STP-1 12.005, "ECCS Void Removal Verification" was issued to incorporate the actions required to assure that these systems are sufficiently full prior to system startup from an outage. This procedure includes the following provisions and was implemented during the last refueling outage, RF17:

1. The fill and vent steps in all the applicable system procedures are required to be performed prior to Mode 2 entry.

2. The dynamic venting of all four HHSI headers is required as part of the system fill and vent.

3. Both trains of RH must be placed in operation (simultaneously or one at a time) and aligned to the RCS after the system fill and vent has been performed.

Document Control Desk CR-08-00162 RC-08-0129 Page 19 of 33

4. Perform verification to assure the LHSI lines to the RCS hot legs are free of voids by ensuring STP-215.008, SI and RH System Valve Leakage Test, has been completed on the applicable SI and RH check valves C. It is noted that the system fill and vent procedures used during the last outage did not include the consideration of pipe slope. Laser scans of the horizontal piping within these systems were conducted during RF1 7.

These scans were then used to determine the slope of all the horizontal piping within the scope of review. However, the surveillance testing discussed in the 'Testing Evaluation" section has been updated to include the results of the slope evaluation based on the laser scans. This updated surveillance testing has been completed.

10. Discussion of the potential gas intrusion mechanisms into each system for each piping segment that is vulnerable to gas intrusion.

A. VCSNS completed detailed reviews of system piping configuration, layout and interconnections of the following system piping:

1. RH system including normal cooldown function and safety injection function with suction from either the Refueling Water Storage Tank (RWST) or the RB recirculation sump

2. SP system with suction from either the RWST or the RB recirculation sump

3. CS system related to the charging pump suction piping and discharge piping to the HHSI headers. Specifically excluded were the normal and excess letdown lines which empty to the Volume Control Tank (VCT) and the normal charging lines and the Reactor Coolant Pump (RCP) seal injection lines B. Upon review of the subject system piping, the following credible gas sources and potential gas intrusion flow paths were identified:

1. RH System RB recirculation sump containment isolation valves The RH Pumps are aligned to the RB recirculation sumps after the RWST water supply is depleted. Each of the two suction lines is provided with two motor operated gate valves in series. Technical Specifications require these valves to be stroked tested quarterly. An air bubble is introduced to the RH pump suction pipe during the stroke test. Based on the system layout, the air bubble rises to the RH pump suction line from the RCS hot legs. At this location the bubble does not involve the SI function of the RH System. The accumulated air

Document Control Desk CR-08-00162 RC-08-0129 Page 20 of 33 after multiple valve strokes during an 18 month fuel cycle is within the acceptance criteria for the RH pump. This is due to the high pressure of the RCS shrinking the bubble. While operability of the RH pumps is not challenged, VCSNS is evaluating means of reduce or eliminate the air intrusion.

2. SP system RB recirculation sump containment isolation valves The RB spray pumps are aligned to the RB recirculation sumps after the RWST water supply is depleted. Each of the two suction lines is provided with two motor operated gate valves in series. Technical Specifications require these valves to be stroke tested quarterly. An air bubble is introduced to the RB spray pump suction pipe during the stroke test. Based on the system layout, the air bubble remains in the RB spray pump suction piping. The suction piping is provided with a vent valve. The surveillance procedure was revised to immediately vent the air bubble to maintain the RB spray system operable. Note that this gas intrusion source was identified shortly after RF17. The procedure was revised prior to the first stroke testing of the valves.

3. Normal Degassing in the RH System During normal plant startup the RH System circulates reactor coolant which is saturated with hydrogen at the normal VCT pressure of 20 psig. When the RH system is cooled and aligned to the RWST for the Safety Injection function, the RH System pressure is based on the elevation head from the RWST. Based on the RH system layout, portions of the RH pump discharge piping will be at pressures below 20 psig. Degassing of the coolant in the RH pump discharge piping is expected. The gas will rise to local high points in the stagnant RHR system. The quantity of gas calculated to come out of solution is well below the acceptance criteria and is removed by normal monthly surveillance venting. Little or no degassing is expected after the first vent cycle. Since the RH pump suction piping elevation is well below the RWST water level and pressure is maintained above 20 psig, no degassing is expected in the RH pump suction piping. No further action is required to address degassing in the RH System.

C. VCSNS evaluated a wide range of potential gas intrusion sources, some of which are based on industry operating experience (OE). The intrusion sources deemed not credible are covered below on a system basis.

Additional detail is included for selected subjects based on OE and concerns identified by other licensees.

1. RH System

a. Configuration and Layout

Document Control Desk CR-08-00162 RC-08-0129 Page 21 of 33 The RH pump minimum recirculation flow line is provided with a flat plate orifice. Although gas may be stripped out at the orifice vena contracta, this source is within the normal venting surveillance for remediation due to limited operating time and limited hydrogen concentration.

The RH pump suction pipe remains below the RWST outlet pipe at all locations. There is no potential for flashing or gas intrusion.

Containment sump strainer performance, including debris laden suction geometry, vortexing and flashing has been evaluated and was provided to NRC under separate correspondence addressing the supplemental response to Generic Letter 2004-02 (Ref. 2).

b. System Interconnections

1. Sampling System In July, 1998 VCSNS experienced a gas intrusion event in the RH system as documented in CR 98-0667. The Root Cause Analysis determined that the pressurizer steam space post-accident sample system (PASS) containment isolation valves leaked by causing the sample system header to pressurize.

This in turn leaked by a check valve and isolation valve in the RH sampling line into the RH system piping near the RH heat exchanger. Normal surveillance venting identified the bubble, but inadequate vent locations precluded proper venting.

Subsequent RH pump testing resulted in minor water hammer in the RH miniflow line and discharge pipe. Subsequent venting through flow instruments in addition to existing vents adequately vented the RH system.

Corrective actions included monitoring the PASS pressure and the addition of a vent valve. The steps have been effective in addressing the back leakage from the PASS and no further gas intrusion events have occurred.

2. RH Cross-tie to Charging Pump Suction The potential exists for the VCT to leak into the RH system through these lines. There is no history of this occurring and is bounded by RCS back-leakage through the cold leg injection header.

3. Chemical and Volume Control System for letdown The RH system provides low pressure letdown to the CVCS.

The potential exists for the letdown to leak into the RH System

Document Control Desk CR-08-00162 RC-08-0129 Page 22 of 33 through this line. There is no history of this occurring and it is bounded by RCS back-leakage through the cold leg injection header.

4. Refueling Water Storage Tank VCSNS has completed scale model testing of the RWST to characterize the onset of vortex formation. The RWST is provided with a vortex suppression device over the suction outlet which was demonstrated to be effective in the test program. No vortex formation (at maximum system outflow) was noted until the water level dropped to the top of the device which is at approximately 5% RWST level. Evaluation of the switchover from RWST suction to the RB recirculation sump suction has established operator response times to complete the switchover prior to reaching the RWST empty alarm at 6%.

This switchover is semi-automatic. At the RWST low-low level setpoint of 18%, the RB recirculation sump isolation valves are automatically opened for both the RH pumps and RB spray pumps. These valves are interlocked to close the train specific RWST suction isolation valves such that the RH pump and RB Spray pump switchover is fully automatic. Operator action is then required to manually switch the suction of the charging (HHSI) pumps from the RWST to the RH system.

Acceptable operator response times have been demonstrated.

5. Reactor Coolant System - Suction From Hot Legs The allowable leak rate from the two isolation valves is very low. Assuming one of the two valves meet the test requirement, the RCS hot leg suction is not a gas intrusion source.

6. Reactor Coolant System - Discharge to Cold Legs The RH system injects flow to the RCS in each of the three cold legs. The injection lines are isolated by two 6" check valves in series. The check valves are leak tested, but have a higher allowable leak rate than the RCS hot leg suction valves listed above and the three lines are interconnected. Back leakage through these valves has occurred at VCSNS resulting in increased RH system pressure. The increased pressure precluded degassing of the hydrogen and no gas intrusion was reported. This was the expected result. The 10" containment isolation check valves need only apply a small differential pressure to keep the piping above the 20 psig hydrogen saturation limit. Gas intrusion in the RH system piping inside the RB is not expected.

Document Control Desk CR-08-00162 RC-08-0129 Page 23 of 33 Gas accumulation in RH system discharge piping outside the RB similarly is an unlikely scenario. However, this mechanism has been reported as a potential gas intrusion source in Information Notice 88-23, Supplement 4 (Ref.6). Based on the industry OE, the rate of gas accumulation was calculated under conservative assumptions to confirm the adequacy of the Technical Specification required 31 day venting surveillance. The conservative calculation determined a gas void equal to the acceptance criteria could form in approximately 36 days. This supports the 31 day vent surveillance frequency. Note that this assumes a non-deterministic failure mechanism to allow the gas intrusion. An actual gas intrusion of this magnitude is not deemed credible and is not consistent with VCSNS plant experience.

7. ECCS Check Valve Test System The RH system suction from the RCS hot leg and discharge to the RCS cold/hot legs are provided with interconnections to the ECCS check valve testing system. The ECCS check valve testing system also interconnects with the HHSI header and safety injection accumulator lines. The ECCS check valve testing system is provided with a backpressure regulator with a nominal setpoint of 400 psig. With the backpressure regulator set at this value depressurizing the RH System below the hydrogen saturation pressure (20 psig) will not occur.

In-leakage from the ECCS check valve testing system is also a potential source for gas intrusion. The evaluation is bounded by in-leakage from the RCS in terms of hydrogen release.

An additional interconnection with back leakage from the ECCS check valve testing system into the RH System is the safety injection accumulators. If the accumulator leak into the ECCS check valve test header and then the ECCS check valve test header leaks into the RH system a gas intrusion may occur. The accumulator liquid is saturated with nitrogen at a high pressure, approaching the normal accumulator pressure. This means gas can come out of solution at higher pressures than in the case of hydrogen. The leak rate into the LHSI\\RH system would be very low from this path. There are at least two normally closed 3/4" globe valves in the path from the accumulator discharge to the LHSI/RH system discharge.

Leakage from this source has not occurred. While the potential exist, the isolation valves and operating experience identifies this as a low risk and no further evaluation is necessary.

Document Control Desk CR-08-00162 RC-08-0129 Page 24 of 33

8. Safety Injection Accumulators The safety injection accumulators have independent injection nozzles to each RCS cold leg. There is no direct path for accumulator back leakage into the RH System discharge piping.

The safety injection accumulator water supply is from a positive displacement pump with no interconnections to the RH System or the CS System.

The suction supply to the positive displacement pump is from the RWST via a 2" connection to the 20" RWST outlet header.

Theoretically it is possible for the accumulator to back leak into this line through 4 normally closed globe valves and 1 check valve. While this appears somewhat unlikely, based on experience at other plants, back leakage can occur. The slope of the 20" suction line has been demonstrated to be towards the RWST (RWST is the high side). If back leakage occurs, the bubbles would rise into the RWST and not present a gas intrusion concern.

2. RB Spray (SP) System

a. Configuration and Layout The sodium hydroxide storage tank has a nitrogen cover gas.

Two relief valves limit the pressure to 3 psig. The RB Spray pump normal suction pressure is much higher. The sodium hydroxide storage tank is not a source for gas intrusion.

The RB spray pump suction piping is below the RWST outlet pipe at all locations. There is no potential for flashing and no gas intrusion.

The sodium hydroxide storage tank is a gravity feed system. Flow balancing orifices in the suction line from the RWST and sodium hydroxide storage tank balance flows such that the sodium hydroxide storage tank will not drain before the RWST. The sodium hydroxide storage tank is not a gas intrusion source.

Document Control Desk CR-08-00162 RC-08-0129 Page 25 of 33

b. System Interconnections

1. Refueling Water Storage Tank The RB spray pumps take suction on the RWST following a spray actuation signal. As covered under the RH system, vortex formation is not a gas intrusion source for VCSNS.

2. Sample System All sample, drain and vent locations are local and provided with a blind flange or cap. There are no system interconnections with the Sample System.

3. CS System Related to the Charging Pump

a. Configuration and Layout The charging pumps are normally in operation providing reactor coolant pump (RCP) seal injection flow and normal charging to make up for normal letdown. A minimum flow line is continuously provided. The minimum flow line ties into the seal water return line just upstream of the seal water heat exchanger. The seal water return line is from the RCP number 1 seal leak off line.

Once through the heat exchanger the flow is sent to the VCT through a spray nozzle. A bypass line around the VCT could return flow directly to the charging pump suction. The line is isolated by a locked closed gate valve. The valve is not opened during power operation. The bypass line tee from the seal water return line is higher than the tee to the VCT outlet. The valve is mounted vertically. There is no possibility leak-by will introduce gas into the charging pump suction. Both miniflow and seal return have been noted as gas intrusion sources in various operating experience. Returning miniflow and seal return to the VCT (in lieu of the charging pump suction) eliminates any potential for gas intrusion from these sources.

The charging pumps take suction from the VCT which saturates the reactor coolant with hydrogen at the VCT pressure. If the charging pump suction pressure drops below the VCT pressure, then hydrogen could come out of solution. The VCT is substantially above the charging pump suction and this was demonstrated not to be a gas intrusion source.

The VCT pressure is variable. Normally the VCT pressure is maintained at approximately 20 psig. The operating pressure range is 18 psig to 60 psig. If the VCT is operated at an elevated

Document Control Desk CR-08-00162 RC-08-0129 Page 26 of 33 pressure, portions of the charging pump suction piping could fill with water saturated with hydrogen at a high VCT pressure.

When pressure is adjusted down to 20 psig later during normal power operation, the hydrogen may come out of solution. Based on the water head from the VCT, this would only occur if the VCT is operated above 45 psig. Since there is significant margin to the normal 20 psig further evaluation was not required.

The charging pumps are not used to fill the safety injection accumulators or pressure test the system. There is no direct connection from the safety injection accumulator tanks and the charging pumps. This eliminates the potential for back leakage of water from the accumulator saturated with nitrogen at a high pressure (approximately 600 psig).

The CS system chemical mixing tank provides a means of adding chemicals to the RCS. This is a manual operation. If properly executed, the chemical mixing tank does not present a gas intrusion concern. The tank is nominally 5 gallons, so the amount of air that could be introduced due to error is limited. Given the infrequent operation, simple manual operation, written procedures and normal surveillance remediation, the chemical mixing tank is not a high risk for gas intrusion.

The charging pumps normally take suction on the VCT. On a safety injection signal, suction is automatically swapped over to the RWST. Conservative analysis considering maximum outflows and vortex formation has demonstrated no gas intrusion to the charging pump suction.

The charging pumps discharge header is maintained at a high pressure by the running charging pump. The pressure must be higher than the RCS pressure in order to provide RCP seal injection and normal charging. The HHSI headers are all above the RCS pressure. There are no gas sources that can leak into the charging pump discharge header due to the elevated pressure.

A review of the CS System shows that there are no throttle devices such as orifice plates or globe valves in the Charging Pump discharge header other than the normal charging flow control valve and the miniflow orifice.

The normal charging line goes to the RCS and the outlet of the miniflow orifice is directed to the VCT. These potential gas sources will not enter the HHSI headers.

Document Control Desk CR-08-00162 RC-08-0129 Page 27 of 33 The calculated Froude Numbers for the charging pumps during normal operation for the 8" suction pipe are less than 0.35. This means gas wotild not move down the vertical section of the pipe to the charging pump suction nozzle. Any gas in the pump suction header would not transfer to the pump discharge. This eliminates the charging pump as a source of gas intrusion to the pump discharge pipe.

With the high discharge pressure, no stripping of gas out of solution and no transfer of gas into the system by the charging pump, there are no known mechanisms for gas accumulation from the charging pump discharge to the HHSI header.

b. System Interconnections

1. Reactor Makeup Water/ Boric Acid Transfer Pumps Makeup to the CS system is provided by reactor makeup water system and boric acid transfer pumps. Both of these systems use diaphragms on the storage tanks to limit oxygen in the water. With the VCT pressure at 20 psig, there is substantial over pressure on the fluid to maintain all air in solution. There is no potential for air to come out of solution during reactor makeup operation.

2. RHR Cross-tie for Long Term Post-LOCA Recirculation The RHR cross-tie is through normally closed valves. The charging pump suction piping is normally at a higher pressure due to-the VCT pressure, so out-leakage to the RH system is the likely scenario. If the RH system is pressurized (such as RH pump testing), the RH fluid has the same dissolved hydrogen content as the charging pump suction. There is no potential in-leakage from gas coming out of solution.

3. Boric Acid Storage Tank The Charging Pumps can take suction directly from the Boric Acid Storage Tanks. This line has only the head of the Boric Acid Storage Tank. With the VCT pressure at 20 psig, there is no potential for in-leakage.

Document Control Desk CR-08-00162 RC-08-0129 Page 28 of 33

4. Refueling Water Storage Tank The charging pump suction piping is below the RWST outlet pipe at all locations. There is no potential for flashing and no gas intrusion.

5. Boron Recycle System (BRS)

There are four connections in the charging pump suction piping to the BRS. Two of the connections are relief valve discharge lines to the BRS. These two connections are not gas intrusion sources for the charging pumps. The other two connections are connected to the boron recycle hold-Up tank which is at a lower pressure so in-leakage cannot occur.

Similar to the other interconnections, the VCT pressure prevents in-leakage from the BRS. There are no gas intrusion concerns from the BRS interconnections.

6. Sample System All sample, vent and drain connections are local. There are no interfacing systems to in-leak to the HHSI\\CS.

11. Ongoing Industry Programs A. Ongoing industry programs may impact the conclusions reached during the design evaluation by VCSNS relative to gas accumulation. These programs will be monitored to determine if additional changes to the VCSNS design may be required or desired to provide additional margin.

1. Gas Transport in Pump Suction Piping The PWROG has initiated testing to provide additional knowledge relative to gas transport in large diameter piping. One program performed testing of gas transport in 6-inch and 8-inch piping.

Another program will perform additional testing of gas transport in 4-inch and 12-inch low temperature systems and 4-inch high temperature systems. This program will also integrate the results of the 4-inch, 6-inch, 8-inch and 12-inch testing.

2. Pump Acceptance Criteria Long-term industry tasks were identified that will provide additional tools to address GL 2008-01 with respect to pump gas void ingestion tolerance limits.

Document Control Desk CR-08-00162 RC-08-0129 Page 29 of 33

12. List of items that have not been completed, a schedule for their completion, and the basis for the schedule.

A. The following plant modifications are identified in Attachment 2 as commitments and will be implemented during Refueling Outage 18 in the Fall of 2009:

1. Installation of 6 vents. In the interim, monthly UT inspections are being performed at each of these locations. Several of these vents are required for piping high points created by sloped piping. As an alternative to the installation of vents at these locations, the pipe supports may be readjusted to level out the pipe. This would remove the pocket formed by the slope and allow any gas intrusion to transport to a location that has an existing vent.

2. The modification of 2 concentric orifice plates to have holes drilled in the top portion of the plate to allow gas to flow through the plate. In the interim, monthly UT inspections are being performed at each of these locations. It is noted that as an alternate to placing holes in the top portion of the orifice, an eccentric orifice plate may be installed.

3. Quarterly stroke testing of the RH system sump isolation valves introduces gas (air in this case) to the system. The gas accumulates in the RCS Hot Leg suction piping and does not challenge RH System operability for either Safety Injection or normal cooldown functions.

However, VCSNS is considering means of precluding or further limiting the gas intrusion as a matter of good practice.

4. Quarterly stroke testing of the SP system sump isolation valves introduces gas (air in this case) to the system. The gas accumulates in the RB spray pump main suction header. The surveillance test procedure STP-1 12.003, "Reactor Building Spray System Valve Operability Test', was revised to immediately vent the header and eliminate the gas bubble. However, VCSNS is considering means of precluding or further limiting the gas intrusion as a matter of good practice.

III.

Testing Evaluation

1. Discuss the results of the periodic venting or gas accumulation surveillance procedure review.

As covered under the Licensing Evaluation, SR 4.5.2.b.2 requires verification that the ECCS piping is full of water by venting the ECCS pump casings and accessible discharge piping high points every 31 days. Procedure STP-105.006, "Safety Injection/Residual Heat Removal Monthly Flow Path

Document Control Desk CR-08-00162 RC-08-0129 Page 30 of 33 Verification Test," performed the venting to meet this requirement. The procedure included the RH system and a few select locations such as the main RWST 20" header and a high point in the RH system supply to the charging pump suction used during long-term post-LOCA recirculation.

The vent locations in STP-105.006 were compared to available vent locations and those high points identified by the system reviews and walkdowns (laser scan data). A list of vent locations to address GL 2008-01 concerns was developed and reviewed by engineering and operations staff. The list was issued and used to form the basis of the expanded gas accumulation surveillance activities.

2. Procedure revisions and new procedures resulting from the periodic venting and gas accumulation surveillance procedure review that were developed.

The new and revised surveillance testing procedures are:

STP-105.006, "Safety Injection/Residual Heat Removal Monthly Flow Path Verification Test" STP-1 12.003, "Reactor Building Spray System Valve Operability Test" STP-1 12.005, "ECCS Void Removal Verification" STP-1 12.010, "Charging Pump Suction Piping Void Removal Verification" STP-112.011, "Spray Pump Suction Piping Void Removal Verification" STP-105.006 was revised to incorporate additional venting requirements as a result of the surveillance procedure review. STP-1 12.003 was revised as discussed in Section 11.12.A.4. STP-1 12.005 was revised as discussed in Section 11.9.B. STP-1 12.010 and STP-1 12.011 were developed as a result of the procedure review to specifically address gas accumulation monitoring and management in the CS/SI and RB spray systems. All procedures have been initially established with a 31 day surveillance frequency consistent with the current SR requirements.

3. Discussion of how procedures adequately address the manual operation of the RH system in its decay heat removal mode of operation.

To ensure RH injection capability from the RWST, SOP-1 15, "Residual Heat Removal", warns that only one train of RH should be in service for heatup or cooldown when RCS temperature is greater than 2500F. SOP-1 15 further states: "Initiating cooldown on A/B RH while RCS hot leg temperatures are greater than 250°F renders that loop incapable of being aligned to the RWST (reference Technical Specification 3.5.3.d) until the RCS hot leg temperatures are reduced to less than 2500F." These statements ensure that at least one train of RHR is available for the ECCS Injection Phase, while the other train is used for cooldown or heatup.

Document Control Desk CR-08-00162 RC-08-0129 Page 31 of 33 The RCS is initially cooled down to 220-230°F by dumping steam to the condenser and pressure is reduced to 350-400 psig using pressurizer spray.

RH boron concentration (Cb) is verified higher than RCS Cb or 100 ppm greater than the shutdown margin requirements for the mode being entered, to avoid an inadvertent dilution when the RH system is placed in service. If it is necessary to increase the RH system boron concentration, low-pressure letdown is established through HCV-142 and PCV-145 and a feed-and-bleed from the RWST through MVG-8809A/B is established. Decay heat removal is shifted to the RH system by closing the RWST suction valve 8809A/B and opening the loop suction valves 8701 A/B, 8702A/B. The RH pumps are not operating when the loop suction valves are being opened.

To limit starting currents on the RH pump, the heat exchanger outlet valve 603 is closed and the heat exchanger bypass valve 605 is reduced to 40% in manual. RH pump is started and amps checked <200 within one minute.

The system is warmed up on minif low until the heat exchanger outlet temperature is within 20'F of THOT. Valve 603 is then opened slowly to limit the thermal shock to the RCS and the RH heat exchanger. Early in the cooldown, the cooldown rate must be limited to keep the CCW out of the heat exchanger less than 1200F. The general operating procedures (GOPs) have a precaution to place only one train of RH in service when RCS temperature is greater than 250°F and to place the protected train of RH in pull-to-lock (PTL). The 250°F limit ensures the RH pump maintains a net positive suction head (NPSH) should the pump be realigned to the RWST as a result of a LOCA.

VCSNS continues to comply with the commitments made to Generic Letter 88-17 (Ref. 3 and 4) to preclude loss of decay heat removal while at reduced RCS inventory (mid-loop) operation. The programs and procedures developed for mid-loop operation remain in effect to assure that air introduction due to vortexing and loss of suction to the RH pumps does not occur. During mid-loop operation the control room operator observes the RH pump current while changing vessel level. Fluctuating motor amps are a symptom of vortexing. If this symptom occurs while changing vessel level, the operator will not start the second RH pump until reactor vessel level is verified on the reactor vessel level monitoring instrumentation.

4. Summary of the results of the procedure reviews performed to determine that gas intrusion does not occur as a result of inadvertent draining due to valve manipulations specified in the procedures, system realignments, or incorrect maintenance procedures.

As discussed in the Design Evaluation section of this response, stroke testing of the RH and SP systems containment sump isolation valves introduces air into the respective systems.

For the B RH train, the void is expected to collect at the pump suction piping high point at reactor building penetration 316 with a total void less than the

Document Control Desk CR-08-00162 RC-08-0129 Page 32 of 33 acceptance criteria established in the design sections of this document.

Ultrasonic testing is being performed at-reactor building penetration 316 per STP-105.006 on a 31 day frequency. A void in this location can only be vented from inside the reactor building via valve XVT00008-RH and would require an "At Power Entry." For the A RH train, the void is being vented via valve XVTOO014 per STP-105.006 at the hot leg suction high point.

For the SP system, the high point in the pump suction line is vented as a part of the valve stroke test procedure. The void is removed and operability is maintained.

No other proceduralized valve manipulations were found to cause gas intrusion.

5. Description of how gas voids are documented, and trended, if found in any of the subject systems.

As an interim process, any locations identified with a void will be documented in a Condition Report generated per the corrective action program. Actions will be generated to direct the inspection of the voided location.

Evidence will be captured and used in determining the source of the void. A test rig will be used to obtain a gas sample, measure pressure, temperature and estimate the volume per STP-105.006.

The gas void size will be compared to acceptance criteria as discussed in the Design Evaluation section. Data collected will be documented within the same condition report and utilized in trending. The data and trending will be used to ensure inspection intervals continue to maintain the system sufficiently full and reliable until the source is located and resolved. The data will also be used to define appropriate surveillance frequency when formal TS revision is submitted as discussed under Section I, Licensing Evaluation.

In the unlikely event of locating a void that exceeds the acceptance criteria and is not accessible by an existing vent, consideration will be made to determine the ability to sweep the void to a desired location (i.e. dynamically vent), adjust pipe slope by moving rigid supports or to initiate an engineering change request to install a vent within the TS allowable action time.

6. List of items that have not been completed and a schedule for their completion.

A station administrative procedure (SAP) will be developed to provide the administrative controls for a gas accumulation management program.

This procedure will provide the program details and establish the roles and responsibilities for the various plant organizations. The development of this procedure will be tracked under the Corrective Action Program and it is addressed as a commitment in Attachment 2.

Document Control Desk CR-08-00162 RC-08-0129 Page 33 of 33 IV.

CORRECTIVE ACTIONS EVALUATION

1. Summary of the results of the reviews regarding how gas accumulation has been addressed at your site.

The Corrective Action Program is used to document gas intrusion/accumulation issues as potential nonconforming conditions.

Existing procedures for the ECCS, RH system and RB spray system require a Condition Report to be initiated, and the control room notified, if the accumulated gas volume acceptance criteria specified in the procedures are exceeded. As part of the VCSNS Corrective Action Program, Condition Reports related to plant equipment are evaluated for potential impact on operability and reportability. The results of this review have concluded that issues involving gas intrusion/accumulation are properly prioritized and evaluated in the Corrective Action Program.

2. List of items that have not been completed, a schedule for their completion, and the basis for that schedule.

Items which are to be completed as a result of the review for Generic Letter 2008-01 are listed as commitments in Attachment 2. A scheduled completion date is included. These commitments will be entered and tracked in the Corrective Action Program.

Document Control Desk CR-08-00162 RC-08-0129 Page 1 of 2 LIST OF COMMITMENTS The following table identifies those actions committed to by VCSNS for Generic Letter 2008-01; "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal and Containment Spray Systems" dated January 11, 2008. Any other statements in this submittal are provided for information purposes and are not considered regulatory commitments. Please direct any questions regarding these commitments to Mr. Bruce L. Thompson, Manager Nuclear Licensing at VCSNS, (803) 931-5042.

REGULATORY COMMITMENT DUE DATE

1. VCSNS will monitor the development of the Technical 6 Months after TSTF issued Specification Task Force (TSTF) Traveler associated with gas accumulation in ECCS, RH System and RB Spray System. An action will be assigned in the Corrective Action Program to monitor this TSTF and evaluate this for submittal of a License Amendment Request.

2. VCSNS will submit a License Amendment Request to 1 Year after TSTF issued revise the Technical Specifications within one year following TSTF approval.

3. Piping Design Specifications (DSP544EA, DSP-October 31, 2008 544AA, DSP-544DA, DSP-544EC and DSP-544J) for the RH, CS, SI and SP Systems will be revised to include as a new loading condition the water hammer loads resulting from possible gas voids during system startup.

4. Engineering Services Procedure ES-427 will be October 31, 2008 revised to add a program design change review checklist to address the issues of potential gas intrusion in the RH, CS, SI and SP Systems.

5. Perform a plant modification to install new vents, or Prior to the completion of adjust piping supports to level piping.

Refuel 18

6. Perform a plant modification to install holes in the top Prior to the completion of of two concentric orifice plates, or install new orifice Refuel 18 plates to allow gas to flow through the piping.

7. Develop a Station Administrative Procedure to August 21, 2009 provide the administrative controls for a Gas Accumulation Management Program.

Document Control Desk CR-08-00162 RC-08-0129 Page 2 of 2

8. Perform an evaluation to determine if there is a better July 31, 2009 method of limiting gas intrusion due to quarterly stroke testing of the RH System sump isolation valves.

9. Perform an evaluation to determine if there is a better July 31,2009 method of limiting gas intrusion due to quarterly stroke testing of the RB Spray System sump isolation valves.