RC-05-0204, Response to NRC Questions Regarding Response to Generic Letter 96-06

Response to NRC Questions Regarding Response to Generic Letter 96-06

ML053490109
Person / Time
Site:	Summer
Issue date:	12/12/2005
From:	Archie J South Carolina Electric & Gas Co
To:	Martin R Document Control Desk, Office of Nuclear Reactor Regulation
References
GL-96-006, RC-05-0204, TAC M96872
Download: ML053490109 (36)

Text

Jeffrey S. Archie Vice President, Nuclear Operations 803.345.4214 December 12,2005 RC-05-0204 A SCANA COMPANY Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTN: Mr. R. E. Martin

Subject:

VIRGIL C. SUMMER NUCLEAR STATION (VCSNS)

DOCKET NO. 50/395 OPERATING LICENSE NO. NPF-12 RESPONSE TO NRC QUESTIONS REGARDING RESPONSE TO GENERIC LETTER 96-06 (TAC NO. M96872)

References:

1) Stephen A. Byrne letter to Document Control Desk, RC-04-0018, January 20, 2004 (ADAMS Accession Number ML040220466)

2) K. R. Cotton (NRC) Electronic Letter to R. Sweet (SCE&G), "GL 96-06 Questions" dated October 14, 2004

3) Stephen A. Byme letter to Document Control Desk, RC-04-01 11, August 4, 2004 (ADAMS Accession Number ML042220080)

4) J. Turkett (SCE&G) Electronic Letter to K. R. Cotton (NRC), 2005 Draft Response to NRC Questions Regarding SCE&G Response to Generic Letter 96-06 (TAC NO. M96872), April 15,2005

5) R. E. Martin (NRC) Electronic Letter (FAX) to R. Sweet (SCE&G), 'The NRC Staff reviewed SCE&G's draft response and additional information is needed...", June 29, 2005 On October 14, 2004, South Carolina Electric & Gas Company (SCE&G) received an electronic communication (Reference 2) presenting an NRC request for additional information (RAI) regarding the VCSNS response to Generic Letter (GL) 96-06 submitted August 4,2004 (Reference 3). SCE&G reviewed these questions in consideration of the activities conducted to address the GL 96-06 issues. On January 13,2005, a telephone conference between SCE&G, the NRC, and the technical reviewers for the NRC was held to discuss the questions of the RAI and explain the SCE&G position regarding the responses developed for VCSNS. SCE&G provided Reference 4 based on an understanding reached with the reviewers during the referenced telephone conference. On June 29, 2005, the NRC responded with a series of questions (Reference 5) addressing additional information needed.

SCE&G is providing the attached response to address questions presented in Reference 2 and Reference 5.

-Ac),7 SCE&G I Virgil C.Summer Nudear Station

• P.O.Box 88. Jenkinsville, South Carolina 29065 .T (803) 345.5209 .www.scana.com

Document Control Desk C-02-3455 RC-05-0204 Page 2 of 2 Summary of Commitments SCE&G makes the following commitments as further discussed in the attachment to this letter:

VCSNS has initiated a plant modification that will accomplish three changes to the current plant configuration for Service Water (SW) discharge from the Reactor Building Cooling Units (RBCUs). First, this modification will delay the opening of gate valves 3107ANB upon start up of SW booster pump (SWBP) ANB. This delay will allow the SWBPs to build up fluid momentum and full fluid flow prior to the opening of these valves preventing gravity drain-down of fluid to the SW pond thereby preventing the creation of a vacuum void. Second, the modification will install vacuum relief valves downstream of valves 3107A/B to replace with air any vacuum developed in the downstream piping during normal operations and eliminate the need for manual action to "vent" the piping. The air in lieu of vacuum will tend to cushion the water column impact as the SWBPs are energized after a station blackout. Third, SCE&G will replace valve 3107A/B with fast closing butterfly valves that close in seven seconds upon de-energizing of SWBP A/B. The fast valve closure will trap water in the high points above the valve and prevent void formation from gravity drain-down of the water to the SW pond. SCE&G is confident that the combined affects of these modifications will reduce the waterhammer loads in the piping to very low levels.

These changes are not required to address any deficiencies in the ability of the plant to meet its current design and licensing basis, but they will reduce operator burden and increase design margins. These changes are currently scheduled for completion in RF-1 6 (October 2006).

If you have any questions or require additional information, please contact Mr. Robert Sweet at (803) 345-4080.

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

Ekecuted on Jeffrey B. Arched JT/JBA/dr Attachment c: N. 0. Lorick S. A. Byrne N. S. Carns G. S. Champion (w/o Attachment)

R. J. White W. D. Travers NRC Resident Inspector K. M. Sutton NSRC RTS (C-02-3455)

File (815.14)

DMS (RC-05-0204)

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 1 of 34 South Carolina Electric & Gas Company (SCE&G)

Virgil C. Summer Nuclear Station (VCSNS)

Response to NRC Request for Additional Information (RAI)

Regarding SCE&G Response to Generic Letter (GL) 96-06 Review of GL 96-06 waterhammer condition as it applies to V. C. Summer Nuclear Station Refer to Figure 1 on page 19 of this attachment.

There are two system alignments for the cooling of the Reactor Building Cooling Units (RBCUs),

via the non-safety Industrial Cooling (IC) System or via the safety related Service Water (SW) system. Cooling via the IC system is the normal plant operation alignment. Cooling is automatically transferred to the SW system after an Engineered Safeguards Features Actuation Signal (ESFAS). With the RBCUs aligned for normal plant operations (aligned to the IC system), a void as noted in Figure 1 is present in the piping downstream of valve 3107A/B (this void will be referred to as the first void). This first void is formed by gravity drain-down of fluid in the RBCU return piping to the SW pond upon realignment of the RBCU from the SW system to the IC system. During this realignment, valve 3107A/B is closed and the gravity drain-down occurs. This void contributes to the waterhammer event as will be explained later. Analysis has shown that if the void contains air in lieu of a vacuum, the affects of the waterhammer are greatly reduced, i.e.,

the air in the void tends to cushion the impact of the two columns of water as the void collapses versus no cushion with a vacuum in the void. Therefore, plant operating procedures have been revised to include venting of the piping to replace the vacuum void with air. This venting is performed per procedure immediately after the realignment of RBCU cooling from the SW system to the IC system. During normal plant operation the venting process is only required after quarterly system testing (SW supplied in lieu of IC).

The waterhammer condition postulated in GL 96-06 is caused by the coincident initiating occurrences of a Main Steam Line Break (MSLB) or Loss of Coolant Accident (LOCA) and a Loss of Offsite Power (LOOP).

Note: For piping loads only, the loads from a seismic event are conservatively combined with those caused by a LOCA event. Refer to the Response for the RAI Question regarding load determination methodology on page 9 of this attachment for further details.

It is assumed that prior to these events the RBCUs are operating in their normal lineup such that they are being cooled by the non-safety IC System. The initiation of a MSLB/LOCA would cause the temperature in the Reactor Building (RB) to begin to rise. After approximately 20 seconds, the temperature in the containment would reach 260 degrees Fahrenheit (OF). A concurrent LOOP would cause the IC flow to the RBCUs to stop due to the loss of the system pumps. From the time of the LOOP, it would take approximately 41.5 seconds for the emergency diesel generators (EDGs) to start and load sequencing by the ESFAS to be completed. After 41.5 seconds, the SW booster pumps (SWBPs) are re-energized and the alignment of RBCU cooling to SW begins.

Therefore, the stagnant cooling water in the RBCUs could be exposed to a 260 0 F temperature for aproximately 41.5 seconds. Heat transfer from containment to the RBCU cooling coils could

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 2 of 34 produce steam voids in the SW pipe. However, It should be understood that until valve 3107AIB begins to stroke open simultaneously with SWBP A/B startup (41.5 seconds following LOCA/LOOP) there is no possibility of steam generation in the RBCUs because fluid pressure in the RBCUs remains above the corresponding saturation pressure for the FSAR peak containment temperatures for LOCA or MSLB. The analysis of the waterhammer condition in VCSNS considered that a steam void did not develop in the RBCUs due to the heat transfer from containment. (It is noted that this is conservative as compared to the consideration of steam void formation. This will be explained in detail in the Questions and Responses that follow.). Upon re-energizing SWBP A/B and initiation of the transfer to SW system for RBCU cooling, valve 3107A/B (a gate valve under current plant configuration) begins to open. The characteristics of a gate valve are such that a signficant amount of flow occurs in the early stages of valve opening. Contrary to this, it takes several seconds for SWBP A/B to build up fluid momentum and commence full fluid flow. Due to these discrepancies, the fliud flows rapidly through valve 3107A/B to the SW pond and creates a vacuum void. This is the second void as described in the Figure 1. Collapse of the first air void and the second void occur when the SWBPs achieve operating speeds at full flow parameters.

Note: A waterhammer will not occur upstream of the RBCUs because there are two check valves near the containment penetration that trap the water above the RBCUs upon loss of flow and thus prevent voiding.

Application of the EPRI Methodology at VCS The occurrence of multiple independent column-closure waterhammer sites separated in time by up to ten seconds, the complicating effects of containment isolation valves stroking open slowly at different rates, and the presence of a large static air volume in the RBCU return piping take the VCSNS transient outside the realm of the approved EPRI GL 96-06 methodology. Significant effort was expended to apply the EPRI methodology to VCSNS. However, the calculations required so many simplifying assumptions to the transient scenario that the EPRI GL 96-06 methodology was not considered an adequate evaluation tool for the VCSNS configuration. This conclusion was validated during verification by an outside consultant with considerable experience in fluid hydraulic analysis.

Questions and Responses Question:

RELAP5 is a computer code with a largely empirical basis for its closure relations.

Therefore, RELAP5 must be assessed against experimental data that is applicable to the present analysis. Please provide the RELAP5 assessment that was performed that qualifies it for the present application. Describe how the range of conditions in the experiments correspond to the waterhammer conditions that might occur at Virgil Summer Nuclear Station during an accident with LOOP. Consider both thermal/hydraulic as well as geometrical considerations.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 3 of 34

Response

SCE&G has very high confidence that the support loads and pipe stresses calculated through the meticulous application of the RELAP5/MOD3 and PIPESTRESS computer codes bound the conditions that would be experienced in the plant should a GL 96-06 waterhammer event occur.

References I and 2 (pp.20 through 23 and pp.24 through 30 respectively of this attachment) are engineering papers showing that RELAP5/MOD3 can be successfully applied to conservatively calculate hydrodynamic forces resulting from both two-phase and single-phase waterhammer events. The RELAP5 modeling techniques used in the fluid transient analyses performed for VCSNS for GL 96-06 are similar to those applied in References 1 and 2. Furthermore, the cold column-closure waterhammer event on the RBCU discharge piping that has been identified as the bounding VCSNS waterhammer transient for GL 96-06 is almost identical to the normal transient which occurs during SWBP quarterly testing and RBCU cooling supply transfer from IC to SW cooling. Despite the relative frequency of this transient, no related damage to SW piping or supports has ever been reported.

Reference 1 is a recent engineering paper presenting analysis results directly applicable to the use of RELAP5/MOD3 for calculation of waterhammer loads for GL 96-06. The calculations were based on piping loads calculated using the EPRI methodology (References 3 and 4) and RELAP5 (Reference 5) to simulate the hydraulic behavior of the system. The RELAP5 generated loads were compared to loads calculated using the EPRI GL 96-06 methodology. This evaluation was based on a pressurized water reactor's Reactor Containment Fan Cooler (RCFC) coils thermal hydraulic behavior during a LOOP and a LOCA. The paper concludes that the EPRI methodology and the RELAP5 calculations can be used to generate hydraulic loads for the RCFC system. The RELAP5 calculated hydraulic loads for this analysis produced larger loads than the loads developed using the EPRI methodology.

Reference 2 is a 1994 engineering paper documenting the acceptability of the default two-velocity momentum equation option in the RELAP5/MOD3 computer program for the estimation of hydrodynamic loads associated with steam safety relief valve discharge. A RELAP5 analysis of the EPRI/Combustion Engineering Safety Valve Test Loop Facility was performed and time-dependent hydrodynamic forcing functions for the four pipe segments of the Combustion Engineering (CE) Test Facility were developed. These forcing functions were subsequently used in an elastic piping analysis model to estimate the resultant structural responses. The calculated loads were then compared to the values from the original 1981 Test data (Dresser safety valve Test 1017 with cold water loop seal). The results verify that RELAP5/MOD3 and the REFORC post-processor can be used with confidence to calculate hydrodynamic forces for use in pipe stress and support analysis. While the Safety Relief Valve (SRV) test cases were conducted at significantly higher pressures than would occur for the GL 96-06 waterhammer scenarios, the CE 1017 test scenario is a cold water slug propelled down an empty 12-inch diameter discharge pipe.

Because of relief valve chatter the water slug is released incrementally and does not remain intact.

The hydrodynamic conditions are similar to the GL 96-06 waterhammer scenario at VCSNS in which a cold water column is released into a voided (air-filled) 16-inch diameter RBCU return pipe when containment isolation valve 31 07A/B opens slowly over a 30 seconds stroke period. An important conclusion from this study is that the RELAP5-computed forces become significantly more conservative (by factors of 1.5 to 2.0) compared to the test data as the water slug is accelerated down successive pipe segments. The Reference 2 analysis methodology is very similar to the RELAP5-based waterhammer analyses performed for VCSNS for GL 96-06.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 4 of 34 Dynamic net axial forces were computed by calculating the total wave (momentum) force in each pipe segment during each RELAP5 time step (maximum 0.0002 second). The net forces were written to the RELAP5 restart-plot file every 0.002 second after being processed through a lag filter control function with a 0.002 second time constant. Because the VCSNS RBCU piping lengths are much longer than the CE SRV test facility pipe segments, and because approximately the same node length/diameter ratio is used for the VCSNS GL 96-06 analyses as was used for the Reference 2 RELAP5 model, it is anticipated that the RELAP5-calculated forces for GL 96-06 have significant conservatism compared to forces that would be experienced in the actual plant piping during GL 96-06 transient scenarios. The VCSNS RELAP5 model for GL 96-06 contains approximately 476 volumes for each RBCU train.

The bounding waterhammer scenario for GL 96-06 at VCSNS occurs as follows. The inside containment RBCU cooling loops between containment isolation valves 3106A/B (RBCU supply) and 3107ANB (RBCU return) is pressurized and filled with cold water from the IC System, the normal cooling water supply for the RBCUs. The IC system contains a large accumulator tank that passively maintains system pressure even when the IC pumps are unpowered following a LOOP'.

The piping immediately downstream of valve 3107A/B is manually filled with air at atmospheric pressure. The air vent is accomplished by procedure whenever the SW supply to the RBCUs is secured. Following a LOCA with coincident LOOP the Emergency Diesel Generators (EDGs) start 11.5 seconds after LOCA/LOOP. The SW pumps (SWPs) start and containment isolation valves 311 IA/B and 3112A/B begin stroking closed over a 60 seconds stroke time to isolate the non-safety IC system from the safety-related SW supply to the RBCUs. At 41.5 seconds after LOOP, SWBP A/B starts and containment isolation valves 3106A/B and 3107A/B begin to stroke open.

Valve 3107A/B opens in approximately 30 seconds and 3106A/B opens in approximately 45 seconds.

Because gate valve 3107A/B in the RBCU return line has flow at a relatively high capacity early in its opening stroke, the drain flow rate from the RBCU header temporarily exceeds the fill rate from SWBP A/B (which is conservatively modeled to ramp to full flow over a period of 5 seconds.) The drain flow causes vapor voids2 to develop in the 10-inch piping downstream of the RBCUs. No attempt to credit steam cushioning is taken because, per References 3 and 4, the cold water column collapse (LOOP only) scenario has been shown to bound the LOCA scenarios with steam generation in the RBCUs3. The RELAP5 analysis predicts that moderate waterhammer forces due to void collapse occur in the two 10-inch piping segments downstream of the RBCUs as the SWBP refills the header inside containment. Meanwhile containment isolation valves 3106A/B and 3107A/B continue to stroke open and a third column-closure waterhammer occurs in the 16-inch RBCU return piping outside containment. The severity of this column-closure event is mitigated by the presence of the large air volume between the incident water column from valve 3107A/B and the standing water column near orifice 99A/B and the 412-ft elevation floor penetration. The incident water column is also broken up by flow element 4468/4498 and orifice 29A/B.

1 No credit for the ICaccumulator tank maintaining pressure is taken in the RELAP5 analysis.

2 Void formation is exacerbated inthe RELAP5 analysis because the fill/pressurization benefits of the IC system are not included.

3 It should be understood that until valve 3107A/B begins to stroke open simultaneously with SWBP A/B startup 41.5 seconds following LOCA/LOOP there is no possibility of steam generation in the RBCUs.

Fluid pressure in the RBCUs remains above the corresponding saturation pressure for the UFSAR peak containment temperatures for LOCA or MSLB.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 5 of 34 Question:

Identify any valves that are credited for preventingdrain-down or backflow in the system in order to minimize the void size and to the extent this is applicable, discuss the specific seat leakage assumptions that are credited in the analysis and describe periodic testing that is performed in accordance with the IST program to assure that the seat leakage assumptions remain valid.

Response

On the discharge side of the RBCUs, following shutdown of SWBP A/B and transfer to IC, a vacuum void downstream of valve 3107A1B is manually filled with air. This was noted in a previous response and will be discussed further in the following responses. Once the vacuum is replaced with air, no additional vacuum void formation or air in-leakage is expected as long as valve 31 07A/B remains closed. The fluid and air will remain stable in equilibrium at a pressure of I atmosphere. When aligned with IC, the fluid pressure and volume upstream of valve 3107A/B is maintained via a surge tank. Due to pressure differentials across the valve and the very small leak path for the development of buoyant forces, any fluid leakage past valve 3107A/B will flow into the void. In order to maintain equilibrium, this leakage will essentially flow through the void to the SW pond and not affect the air void, and is therefore acceptable.

On the supply side of the RBCUs, it has been proposed that during a LOOP or LOCA scenario, voids could form in the piping as a result of water column drain back into the main SW system header through two check valves (31 37A1B and 3135A/B) and a normally closed butterfly valve (3106A/B). The RBCUs are normally aligned to the IC system such that valve 3106A/B is closed.

Another proposed drain back path is to the closed-loop IC via the two check valves (3136A/B and 31 37A/B).

To create a void in the RBCU inlet piping, it is necessary to remove enough cooling water to drain the RBCUs and several segments of the 10"n piping at the RBCU inlet. The RBCU cooling coil volume is approximately 132 gallons. Considering the hypothetical case in which two pipe segments adjacent to the RBCU inlet are voided due to drain back, the volume of the two pipe segments is approximately 13 gallons and their lengths are 1.77 feet and 2.02 feet., respectively.

Conservatively assuming that only 50% of the RBCU volume needs to be drained before the inlet piping begins to uncover, the total back-leakage through the check valves must approach (50%)(132 gal) + 13 gal = 79 gallons over the time period for which back leakage would be a concern.

The time period over which back-leakage may occur is a very important factor. The valve and pump timing following LOOP (or LOOP/LOCA) is as follows.

0.0 sec Event Initiation, SWPs tripped due to assumed loss of offsite power.

1.5 sec ES actuation 11.5 sec EDG started and running, ready to accept loads from ES Sequencer. SWPs and essential motor-operated valves (MOVs) are powered back up at this time.

Safety-related MOVs begin moving as necessary to safety positions, which is "closed" for butterfly valve 31 06A/B.

41.5 sec SWBP A/B starts. Simultaneously, valve 3106A/B begins to open.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 6 of 34 From the above time sequence we can easily conclude that the available time window for drain-back is 41.5 seconds or less. The required leakage rate through the check valves and valve 3106A/B is (79 gal/41.5 seconds) 114.2 gpm, a very large and substantial leak rate. When the SWBP is not running, the pressure at the SWBP outlet is approximately 60 psig when the SWPs are running. The elevation difference between the RBCUs and SWBPs is 107.6 feet, and the associated water column head is 46.5 psi at 66 0F. Thus, SWP pressure is more than sufficient (with a 10+ psi margin) to keep the RBCUs filled and prevent back-leakage into the SW header.

The SWPs restart in the LOOP scenario at 11.5 seconds. Plant data traces from Emergency Safeguards surveillance testing show that the SW header pressure is restored almost instantly upon SWPs startup. Therefore, the time window for back-leakage through the SW system is not 41.5 seconds, but is actually only 11.5 seconds or less (depending on SWP coast down pressure decay following LOOP). The required leakage rate to void the two pipe segments of interest over 11.5 seconds is 412 onm, a rate which is so large as to be considered clearly incredible through two check valves in series and a normally closed butterfly valve. And if a leak path that large did exist, the void would refill at low pressure from the SWPs before the SWBP starts at 41.5 seconds.

Therefore, void formation in the RBCU inlet piping due to back-leakage into the SW system is not a viable concern for GL 96-06 at VCSNS.

If the leakage path is into the closed-loop IC system, we have to postulate a 114.2 gpm leak rate into the system over 41.5 seconds to void the RBCU inlet piping. However, the IC system is a closed-loop system with a pressurized surge tank. For back-leakage to occur from the RBCU piping it is necessary to postulate rapid net leakage out of the IC system. The cover pressure in the surge tank will resist transient inflow from RBCU drainage. Review of monthly plant chemistry data reveals that the average maximum leak rate from the IC system is only 0.06 gpm. Thus, it is impossible to achieve the required 114 gpm back-leakage into the IC system required to void even a small portion of the RBCU inlet piping.

Question:

For the valves that are credited for preventing drain-down or backflow in the system as identified in the draft response, discuss the specific seat leakage assumptions that are credited in the analysis and describe periodic testing that will be performed in accordance with IST requirements to assure that the seat leakage assumptions will remain valid over time (see the Southern Nuclear Operating Company response for the Vogtle plant dated November 5, 2004, for an example).

Response

As justified in the previous response, seat leakage is not considered in the analysis for the valves credited for preventing RBCU drain-down or backflow.

Valves 3137A/B, RB Cooling Unit Supply Header Valves perform an active safety function in the OPEN position. These valves are normally open to allow IC flow to the RBCUs. During an accident, the flow is automatically transferred to safety-related SW for cooling flow. These valves open to supply flow from either source. Full flow ASME Code check valve testing is performed

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 7 of 34 quarterly under STP-223.002A at a post accident minimum design basis flow of 2000 gpm. These normally open valves are closed tested in accordance with ASME Code check valve testing requirements each refueling outage under STP-230.006G.

Valves 3135A/B, Service Water Booster Pump Discharge Check Valves, are normally closed valves that perform an active safety function in the OPEN position. These valves must open to allow SW flow to the RBCUs. During an accident, the flow is automatically transferred to safety-related SW for cooling flow, by SWBP auto start, discharge valve opening and isolation of IC flow.

Full flow ASME Code check valve testing is performed quarterly under STP-223.002A at a post accident minimum design basis flow of 2000 gpm. The valves are provided with an adjustable dashpot which controls the opening and closing speed of the disc for prevention of waterhammer.

In the closed position, the valve prevents the diversion of IC into the SW system. This is an operational function, since IC is not a safety-related system. These normally closed valves are closed tested quarterly in accordance with ASME Code check valve testing requirements under STP-223.002A.

Question:

It is stated that in the future the severity of postulated waterhammer events will be reduced by the injection of air into the service water piping and that system operating procedures have been revised to require air injection after system realignment. Please provide the following information concerning the air injection system:

a. Provide drawings of the service water system showing the location of the injected air pocket relative to the location of the postulated waterhammer. Demonstrate the injected air will flow into any steam space caused by LOOP, LOOP/MSLB or LOOPILOCA.

Response

Figure 1 (p.19 of this attachment) shows the locations of the voids and the predicted waterhammer sites for RBCU Train A. Steam voiding in the VCSNS RBCUs does not occur for GL 96-06 scenarios because the fluid pressure in the RBCU coils remains above the saturation pressure corresponding to LOCA peak containment temperature until after SWBP startup.

Following shutdown of SWBP A/B and realignment to IC, a vacuum void forms due to fluid column gravity drainage downstream of valve 3107ANB, the containment isolation valve on the RBCU return piping to the SW pond. Compressed air is injected into the vacuum void by the Operations staff in accordance with plant procedures such that the void is filled with air at a pressure of approximately I atmosphere. The air is supplied via apant air hose (connected only during the fill procedure) and remains trapped between valve 3107A/B and the downstream standing water column until the next time SWBP A/B is started and the associated RBCUs are placed on SW cooling. This relatively large air volume (extending for approximately 119 feet of the 12-inch diameter pipe) cushions the column collapse waterhammer event that analysis predicts could occur following SWBP A/B startup and opening of valve 3107A/B. The waterhammer is projected to occur when the incident water flow from valve 3107A/B reaches the standing water column near flow orifice 99A/B. Figure 1 shows the location of the air volume and column collapse waterhammer locations predicted by analysis.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 8 of 34 Regarding the potential for steam formation in the RBCUs from LOCA/MSLB coincident with a LOOP, the normal RBCU cooling water supply is via the IC system. The IC system is a closed loop design with a pressurized expansion tank and relief valves. Valves 3106A/B and 3107A/B are normally closed, isolating the SW cooling supply to the RBCUs. The VCSNS design basis does not require the consideration of the seismic event occurring coincident with any other transient, such as the LOCA/MSLB. Therefore, the passive function (structural integrity) of the IC system outside containment can be relied upon after the occurrence of the LOCA/MSLB. The LOCA peak containment temperature of approximately 260 0F (

Reference:

VCSNS FSAR) corresponds to a saturation pressure (P.Et) of only 20 psig in the RBCU coils. This pressure is well below the nominal RBCU internal fluid pressure of approximately 50 psig when aligned to the IC system and is far below the RBCU thermal relief valve opening set points. Heat transfer to the RBCU coils will stop when the coils reach 260 OF, and boiling/steam formation cannot occur if the fluid pressure in the coils remains above 20 psig. Following a LOOP/LOCA and EDG startup, the containment isolation valves for the IC cooling water supply to the RBCUs (valves 31 1OA/B, 311 A/B, and 3112A/B) begin to close at a rate of approximately 60 seconds for full stroke. During the 41.5-seconds period between LOOP/LOCA and SWBP startup the expansion tank for the IC system passively maintains fluid inventory and pressure in the RBCU coils well above 20 psig. Therefore, steam formation in the RBCU coils is not expected to occur. If for whatever reason the coil pressure does drop below 20 psig, the volume of steam that can be generated is very small because any steam expansion in a closed loop system will quickly drive the pressure back to equilibrium P.at with the containment temperature.

Question:

b. We understand that following a LOCA or MSLB with LOOP, the service water pumps will be automatically loaded onto emergency power. During this time, a steam void might have formed within the service water system which might cause waterhammer when the service water pumps are restarted. Please discuss the means by which air injection will be assured before the service water pumps are restarted. If the air is injected at an earlier time, please discuss the means which will assure that the air remains present and in the proper location.

Response

The air injection is only required upon restoration of the RBCU cooling to the IC system, the alignment for normal plant operations. Plant operating procedures have been revised to require this injection during this restoration. After this restoration, additional air injection is not required during normal operations. The injected air will remain in place due to the make up of differential pressures between that inside the pipe and the ambient pressures outside the pipe.

As noted in the previous response, following shutdown of SWBP A/B and transfer to IC, a vacuum void forms due to fluid column gravity drainage downstream of valve 3107A/B. Immediately after this transfer, compressed air is then injected into the vacuum void by the Operations staff in accordance with plant procedures such that the void is filled with air. The air is supplied via a plant air hose (connected only during the fill procedure). The air remains trapped between valve

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 9 of 34 3107A/B and the downstream standing water column until the next time SWBP A/B is started and the associated RBCUs are placed on SW cooling. The "injection" of air is merely for the convenience of the Operation staff. Initially, VCSNS Engineering had specified the "venting" of the piping to fill the vacuum with air. However, based on the size of the tubing to be used for this "venting", Operations staff concluded that an unreasonably long time would be required to assure the system was completely filled with air. Therefore, a means to "inject" air into the piping to speed up the process was developed and incorporated into plant procedures. Once the vacuum is replaced with air, no additional vacuum void formation or air in leakage is expected as long as valve 31 07AB remains closed. The fluid and air will remain stable in equilibrium at a pressure of approximately I atmosphere. Any fluid leakage past valve 3107A/B will drain through the void to the SW pond and not affect the air void.

VCSNS is in process of developing a modification that will install vacuum relief valves downstream of 3107A/B to eliminate the need for manual action to "vent" the piping.

Question:

Describe the methodology by which structural piping and support loads were determined, including a description of the load combinations that were applied.

Response

Using the force time histories developed by the RELAP fluid hydraulic analysis as inputs, a classical time history piping analysis was performed using the computer program PIPESTRESS to determine pipe stress and pipe support loads.

VCSNS considers this waterhammer to be an upset event that does not require the inclusion of a seismic event. VCSNS has applied the ASME Code, Section 111, NC-3652 (1971 Edition through Summer 1973 Addenda) stress limits for an upset condition to the piping and pipe support qualifications. The following load combinations were used:

Pipe stress: 9U - Pressure + Deadweight + Waterhammer < 1.2 SH Pipe Support loads: Deadweight + Thermal Expansion + Waterhammer Regulatory Guide 1.48 (Reference 6), with similar discussion in the VCSNS FSAR, states that for piping the code limits for the faulted condition shall not be exceeded when piping is subjected to concurrent loadings associated with the normal plant condition, the vibratory motion of the safe shutdown earthquake (SSE) and the dynamic system loadings associated with the faulted plant condition. Regulatory Guide 1.48 defines "the dynamic system loadings associated with the faulted plant condition" as those dynamic loadings which result from the occurrence of a postulated rupture (e.g., complete severance or equivalent longitudinal break area) of any reactor coolant pressure boundary piping or of any other piping not a part of the reactor coolant pressure boundary. Therefore, in terms of piping, the "LOCA" event to be combined with seismic is an event associated only with the dynamic structural consequences of a pipe break. The waterhammer loads in the SW piping need not be combined with the seismic loads if there is reasonable assurance that the two events would not occur concurrently.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 10 of 34 An initiating event occurs which includes a LOCA or MSLB inside containment and a LOOP happening concurrently which initalizes the ESFAS. For loads on piping systems, the earthquake loads are combined with those from a LOCA. (Note: The VCSNS design basis does not require the consideration of the seismic event occurring coincident with any other transient, such as a LOCA. However, for conservatism, the loads on a structural piping system from a seismic event are combined with the loads from a LOCA event.) After the intiating events, the EDGs are energized and load sequencing is initialized which includes the transfer of RBCU cooling from the IC system to the SW system. VCSNS design basis defines the duration of an SSE to be 20 seconds. Therefore, 20 seconds after the intiating event, the earhquake ceases. 41.5 seconds after the initiating event, the SWBP A/B becomes energized and valve 31 07A/B open restoring cooling flow through the RBCUs. This would cause a collapse of the void in the SW pipe and the consequential waterhammer as described in the above responses. This is depicted on the following timeline:

Power Restored; SW Booster MSLB/LOCA 41.5 Pumps 3107A/B Water and LOOP seconds - energized opening Hammer opening occurs

-II I .

SSE 20 _..._ Earthquake earthquake seconds Ends Therefore, the waterhammer loads do not need to be considered concurrent with the loads from LOCA/MSLB plus earthquake in the piping analysis. VCSNS considers this waterhammer event to be a separate event by itself that will always occur 41.5 seconds after an event causing the plant to enter into the Si mode, or during switch over of RBCU cooling from the IC system to the SW system which is permitted during normal operations and during surveillance testing. (Note:

VCSNS design basis does not require an earthquake to be considered concurrent with these transfers in which the system is in limited operation.)

Conclusion VCSNS believes that the current analysis as described above adequately qualifies the as built piping and pipe supports of the RBCU discharge piping for the loads associated with the waterhammer conditions described in GL 96-06. It is noted that the VCSNS as-built SW piping has experienced the GL 96-06 waterhammer event discussed herein many times over the twenty three years of plant operation. During this time, no damage to the SW piping or pipe supports has ever been reported.

Planned Modifications VCSNS has initiated a plant modification that will significantly improve, if not eliminate, the waterhammer condition associated with the GL 96-06 concerns. These changes are not required to address any deficiencies in the ability of the plant to meet its current design and licensing bases, but they will reduce operator burden and increase design margins. VCSNS is utilizing

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 11 of 34 structural piping analysis that uses bounding fluid hydraulic force time histories developed by RELAP5 in the development of this modification. These changes are currently scheduled for completion in RF-16 (October 2006). This modification will accomplish two changes to the current plant configuration for SW discharge from the RBCUs. First, this modification will delay the opening of valve 3107A/B upon start up of the SWBP A/B. This delay will allow SWBP A/B to build up fluid momentum and full fluid flow prior to the opening of valves 3107A/B. This will prevent the gravity drain-down of fluid to the SW pond thereby preventing the creation of a vacuum void, i.e.,

the second void on Figure 1 will not develop. Preventing creation of this void reduces piping and support loads. Second, the modification will install vacuum relief valves downstream of valves 3107ANB which will automatically fill with air any void formed at this location due to gravity drain-down to the SW pond (first void on Figure 1). These vacuum relief valves will preclude the requirement to manually fill the vacuum void with air whenever the SW supply to the RBCUs is secured. They will provide assurance that air will always be present in the void. The combined affects of these two modifications will reduce the waterhammer loads in the piping to very low levels.

Question:

Confirm that the proposed plant modifications for resolving the GL 96-06 waterhammer issue will satisfy all applicable criteria that have been established for safety-related applications (e.g., seismic, single failure, environmental qualification, power supplies) and that the requirements of 10 CFR 50, Appendix B are fully applicable. Also, describe Technical Specification Requirements that will be established to assure operability.

Response

Station Administrative Procedure SAP-1 33, "Design Control/Implementation and Interface",

controls plant modifications implemented at VCSNS. This procedure is governed by IOCFR50, Appendix B. Design input considerations are evaluated for Appendix B requirements, FSAR Section 17.2 (Quality Assurance) commitments, and Technical Specifications, Section 6.5 (Technical Review and Control). The VCSNS Modification Program also satisfies ANSI N45.2.1 1-1974, "Quality Assurance Requirements for the Design of Nuclear Power Plants". Engineering Services procedure ES-455, "Design Control: Plant Modification' and procedure ES-454, "Design Control: Plant Enhancement" address initiation, design considerations, design reviews, implementation, and documentation of VCSNS plant modifications. SAP-107, "10CFR50.59 Review Process" additionally controls plant changes, where applicable.

There are existing Technical Specification surveillance requirements on the RBCUs and the plant systems, structures, and components that interface with the RBCUs. SCE&G considers these existing requirements sufficient based on our plant design and, therefore, plans no additional Technical Specification requirements.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 12 of 34 Question:

Establish a regulatory commitment to complete any actions that remain, such as plant modifications and TS changes, along with the scheduled completion dates.

The planned modifications will be implemented during VCSNS refueling outage RF-16 and are projected to be complete by December 31, 2006. No other actions are identified for this issue.

Question:

As requested in Section 3.3 of the staffs safety evaluation dated April 3, 2002, that approved the use of the proposed methodology in EPRI Technical Reports 1003098 and 1006456 for resolving the GIL 96-06 waterhammer issue, please provide certification that plant-specific considerations are consistent with the risk perspective that was provided by EPRI in a letter dated February 1, 2002, and included as an enclosure to these technical reports.

Response

Assuming that the planned system modifications have been made, the following is an assessment of the risk to the plant of the application of RELAP5/MOD3 using as a basis the assessment provided by EPRI in a letter dated February 1, 2002 (hereinafter referred to as Reference 7). A review of the "progression" of events that could lead to an unacceptable condition is listed. For the purposes of this evaluation, the unacceptable condition" following a LOOP/LOCA event will be defined as a breach of the service water system pressure boundary. The events are as follows.

1. Occurrence of a LOCA or MSLB - Discussion same as that noted in Reference 7.

2. Occurrence of a LOOP following a LOCA or MSLB - Discussion same as that noted in Reference 7.

3. Occurrence of a Simultaneous LOCANLOOP Event - Discussion same as that noted in Reference 7.

4. Void Formation - A void will form in the SW return piping outside containment due to fluid gravity drain. This void is air-filled (because of the new vacuum breaker), is the normal configuration, and exists whenever the upstream containment isolation valve (3107A or 31 07B) is closed. No significant voiding will occur in the RBCU piping upstream of 31 07A/B.

5. Pump Restart - The pumps will restart with certainty and the velocity of the fluid in the pipe, immediately prior to closing the void, is defined by the dynamic pressure in the void, the piping geometry (losses from wall friction and fittings such as valves, elbows, tees, and orifices) and the pump characteristics. This un-cushioned 4 closure velocity has been 4 Meaning the assumed amount of entrained air in the flow from the SWBP is so small as to be insignificant.

The sonic velocity is approximately 5000 feet per second for the subcooled upstream water column.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 13 of 34 calculated by RELAP5/MOD3. As noted in responses to other NRC questions, the RELAP5-based closure velocities and associated segment forces are considered conservative because they are substantially higher than what was experienced in the plant for one of the analyzed transient scenarios (see response to previous question).

The liquid flow velocity downstream of valve 3107A/B, when the pipe is running full, peaks at about 5.25 feet per second. Because of the 30 seconds opening time of valve 3107A/B, and the flow orifice 29A/B immediately downstream, the incident water column is disorganized (mixed) as it encounters the air mass between valve 3107A/B and the standing water column. Because the standing water column is receding (draining) while the vacuum breaker is open, the effective relative velocity between the incident water column and the receding column is quite small.

6. Column-closure - Discussion same as that noted in Reference 7.

7. Maximum Waterhammer Pressure - Application of the Joukowski correlation to the incident water columns downstream of valve 3107A/B results in very low calculated pressures (typically 25 psi or less increase) because the mixture density is low, the sonic velocity is very low because of the two-phase conditions, and because the slow valve opening time of approximately 30 seconds causes the velocity differentials to be comparatively low. It should be noted, however, that the calculated segment forces were computed not on the analyzed pressure rise, but on the net segment wave force from the total momentum equation. The transient force in each pipe segment is the sum of the liquid total mass-acceleration and vapor mass-acceleration over each 0.0002 second time step. In RELAP5, the mass-acceleration force is computed from the rate of change of the mass rates for each volume. Where the liquid mass rate for a volume is:

The time-derivative (differend) of the quantity: liquid density (rhof) x volume liquid velocity (velo x liquid fraction (voido x volume size (Wol).

The same computation is performed for the vapor phase, for all volumes in each (straight) pipe segment. The computation is performed for each RELAP5 time step, and then smoothed using a lag function with a 0.002 second time constant to ensure that no numerical force peaks are clipped or lost between the 0.002 second minor-edit write intervals required for the piping analysis.

It is this conservative approach that helps ensure the design-basis RELAP5 force-time history data bounds what is experienced in the actual plant during safeguards testing.

8. Cushioned Waterhammer - No credit was taken for cushioning effects5 due to air entrained in solution with the SW source water. In the RELAP5 analysis only a trace amount of non-condensable air was added to the SW supply, to facilitate phase calculation stability when the incident subcooled water encounters the large air volume from the vacuum breaker. The non-condensable quality of the SW supply in the RELAP5 model is 1.OE-8 at 95RF. The resulting code-calculated sonic velocity in the liquid-filled pipe sections was approximately 5000 feet per second.

5 Note that 'Cushioned Waterhammer" as used in the EPRI methodology refers to a reduction in the waterhammer pressure rise when non-condensable gas is dissolved in solution in the SW supply. The pressure reduction is due principally to the decrease in sonic velocity because of the presence of dissolved gas. Cushioning in the EPRI methodology is not the force-reduction effect that occurs when a large air volume is trapped between the incident water columns.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 14 of 34

9. Likelihood of an Unacceptable Event - Discussion same as that noted in Reference 7 except the use of RELAP5/MOD3 replaces the use of the EPRI Users Manual and the Technical Basis Report. The discussion therefore reads: Given the low probability (10 5/year) of the initiating events and the low probability (10-2) of piping failure, the use of the methodology using RELAP5/MOD3 will lead to a likelihood of an unacceptable event that is on the order of 10'7. Again, for the purposes of this evaluation, the unacceptable event" following a LOOP/LOCA event is taken as a breach of the SW system pressure boundary. The probability of 1 0 q7 for this event is below the threshold for significant risk to the plant. Use of the methods employing RELAP5/MOD3, therefore, will not compromise the safety of the plant for the systems within the bound provided by the RELAP5/MOD3 analysis. The methodology should be accepted as recommended.

The change in risk introduced by the use of RELAP5/MOD3 and the method employed is not significant and the methods do not lead to an unacceptable plant risk following a LOOP/LOCA event. Hence, from a risk-informed perspective, the methods proposed are adequate for the plant-specific application for resolution of the GL 96-06 issues.

Additional Discussion Pertaining to VCSNS System Performance Other Waterhammer Condition in SW piping not directly related to the GL 96-06 waterhammer condition:

As noted previously, it is assumed that the GL 96-06 waterhammer condition occurs when the plant is operating in its normal alignment with the RBCUs aligned with the IC system for cooling. During the effort to address the GL 96-06 waterhammer, another waterhammer scenario was identified. This waterhammer is postulated to occur during the time that the RBCUs are aligned with the SW system and a LOOP occurs. This alignment of the RBCUs is not a normal alignment. The RBCUs are aligned to the SW system only during quarterly testing, IC system maintenance and during refueling outages. In addition, this waterhammer condition is simulated in the plant every outage during safeguards testing. No anomalies of the piping or supports have ever been observed due to this waterhammer. However, SCE&G has incorporated the piping loads of this waterhammer into the plant design basis and has performed an analysis of the condition. Even though the actual waterhammer results in no anomalies of the pipe supports, this analysis predicted the presence of very high loads on pipe supports. SCE&G has developed interim measures and has scheduled the implementation of a plant modification to reduce these loads to levels that are analytically acceptable. This waterhammer condition, the interim measures and the plant modification for mitigation are at issue in the following RAls.

Question:

Explain why the scenario with the safety-related service water system aligned to provide cooling for the RBCUs at the onset of the postulated accident does not result in a more severe waterhammer event, or otherwise establish appropriate restrictions in the Technical Specifications on use of the service water system for RBCU cooling during normal plant operation.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 15 of 34

Response

The scenario with the safety-related SW system aligned to provide cooling for the RBCUs at the onset of the postulated accident does result in a more severe waterhammer event than the waterhammer resulting from the GL 96-06 scenario described in the preceding review discussion.

The RBCUs are typically aligned with the SW system during quarterly surveillance tests, IC system maintenance and during plant outages. If a LOOP were to occur during this alignment, as noted in the review discussion (page 1 of 34), from the time of LOOP, it will take approximately 41.5 seconds for the EDGs to start and the ESFAS sequencing to complete. After which the SWBPs will energize.During this 41.5 seconds, the column of fluid in the piping downstream of the RBCUs will gravity drain-down to the SW pond (Refer to Figure 2, p.33 of this attachment). This will form a large void in the piping. Upon SWBP re-start and the commencing of fluid flow, the void will rapidly collapse creating a significant waterhammer. Comparative analysis using RELAP5/MOD3 has shown that the waterhammer event from this scenario to be of greater severity by several magnitudes than that of the GL 96-06 scenario previously described.

In order to mitigate the affects of this waterhammer on the piping system, VCSNS has adopted a two-phase approach. The first is an interim phase that provides adminitrative and procedural controls over the use of the SW system for cooling to the RBCUs. The second is a modification to change valve closing and opening times and their coresponding initiating logic to permanently eliminate the waterhammer concerns. This modification is scheduled for implementation during RF1 6 in the fall of 2006. These two phases are discussed in detail in the following paragraphs.

In the first phase until the plant modification is implemented, the procedure for SW system operation, SOP-1 17, "Service Water System", has been revised to include a special set of initial conditions prior to aligning the system to the RBCUs. These conditions are intended to minimize the risk for a LOOP during the SW alignment, minimize the time duration the RBCUs are aligned to the SW system and to remind operations of the potential for a waterhammer in the event of a LOOP. These intial conditions are summarized as follows:

• In Modes 1 through 4, SW shall only be supplied to the RBCUs, when one or more of the following conditions are met:

a. Post Accident or High Containment Pressure Conditions.

b. Loss of Non-ESF power.

c. Loss of IC.

d. During testing.

• In Modes I through 4, when SW is being supplied to the RBCUs, all the following conditions shall be met:

a. No planned work is allowed in the switchyard.

b. The dispatcher confirms that no transmission system work is planned that would decrease the reliability of the off site power supplies.

c. There is no severe weather predicted in South Carolina for the expected duration of the testing.

d. If for surveillance testing or post maintenance testing, the testing has been approved as if it were a (Yellow) MODERATE Risk Activity.

e. If for any other reason, the testing has been approved as if it were an (Orange)

ELEVATED Risk Activity.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 16 of 34 The second phase requires the implementation of a plant modification in the fall of 2006. This modification will include (Refer to Figure 3, p.34 of this attachment):

• The replacement of gate valve 3107AIB with a fast closing butterfly valve that closes in seven seconds upon de-energizing of SWBP A/B. The fast valve closure will trap water in the high points above the valve and prevent void formation from gravity drain-down of the water to the SW pond. This will prevent any waterhammer event that would have occurred upon re-energizing the SWBPs and a consequential rapid collapse of the void.

• The addition of vacuum relief valves downstream of valve 3107A/B. These valves will replace with air any vacuum void downstream of closed valve 3107A/B that may be formed due to gravity drain-down of water to the SW pond. Upon the opening of valve 3107A/B and the re-start of SWBP ANB, the air in the piping will act as a cushion to minimize any waterhammer affects that could occur at that time. In addition, these relief valves will eliminate the need for operations to manually vent the piping downstream of valve 3107A/B immediately after the transfer of RBCU cooling from the SW system alignment to the IC system as noted in the preceding review discussion and discussed in following question responses.

• The opening logic of valve 3107A/B will be modified to have a 5 seconds delayed opening after SWBP A/B start. The delayed start of the valve opening will assure that additional void formation in the RBCU piping inside containment will not occur upon re-energizing the SWBP.

NOTE: The addition of vacuum relief valves and the delayed opening time at the valve 3107A/B location also help to mitigate the GL 96-06 waterhammer condition and are taken credit for as such.

Fluid hydraulic analysis using RELAP5/MOD3 and pipe stress analysis using the computer program PIPESTRESS have concluded that these modifications will largely eliminate the potential for waterhammer in the RBCU piping. The analysis concludes that the post modification waterhammer loads on the piping develop stresses in the piping that are well below the ASME Code allowables.

Question:

Assuming that the planned system modifications have been made, describe the results of a comparative analysis using analytical methods that have been approved by the NRC for this purpose (i.e., EPRI methodology or NUREG/CR-5220) that demonstrates that the RELAP results are conservative for the worst-case waterhammer location that was identified by the RELAP analysis.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 17 of 34

Response

VCSNS Technical Specification surveillance requirement 4.8.1.1.2.g.4 states: "Each EDG shall be demonstrated operable at least once every 18 months by simulating a loss of offsite power by itself..." VCSNS surveillance test procedure STP-125.017, "Diesel Generator'A' Loss of Offsite Power Test", contains the operating instructions that are conducted to demonstrate compliance with this requirement. These instructions, performed each refueling outage, have as an initiating condition the alignment of the SW system to the RBCUs followed by a simulated LOOP.

Therefore, this test simulates exactly the waterhammer condition described in Figure 2. Since initial plant operations, at least ten of these surveillance tests have been conducted. This means that the piping and pipe supports have been subjected to these waterhammer loads at least ten times. Waterhammer within the SW piping during these tests have been reported. However, the severity of the actual waterhammer has not been of the magnitude to cause any concern. This past refueling outage (May 2005) a walk down of the SW piping and pipe supports downstream of the RBCUs was conducted. The intent was to provide assurance that no damage existed in the piping or pipe support components. During this walk down, particular attention was drawn to welded attachments, support rods and support pins for any signs of deformation. In addition, observations were made at pipe welds and fittings for any indications of cracked or flaking paint and at pipe supports for paint rubbed off piping indicating recent pipe motion. No visible anomalies were found. This provided assurance that the actual waterhammer event occurring during each surveillance test was developing acceptable loads within the piping. However, the RELAP5/MOD3 fluid hydraulic analysis (for the Figure 2 scenario) has predicted very high waterhammer loads, loads that would create forces on pipe supports that would easily create deformation in many pipe support components. Therefore, the surveillance tests have provided empirical evidence that the waterhammer loads developed by the RELAP5/MOD3 analysis are very conservative and demonstrate that RELAP5/MOD3 is the appropriate tool to be used in predicting the waterhammer loads for the design of the structural piping system.

Response References

1. Engineering paper ICONE12-49214 Calculation of Forces on Reactor Containment Fan Cooler Piping, by Joseph S. Miller/EDA, Inc. and Kevin Ramsden/Exelon Nuclear, Proceedings of 12t International Conference on Nuclear Engineering, Arlington, Virginia, April 25-29, 2004.

2. Engineering paper Qualification of RELAP5/MOD3 for Safety Relief Valve Hydrodynamic Load Analysis: A Comparison Against EPRI/CE SRV Test 1017, by P. R. Boylan (Touch Base Computing, Inc.), and D.W. Peltola (Vectra Technologies), Presented at the 1994 International RELAP5 Conference, Baltimore, Md.

3. "Generic Letter 96-06 Waterhammer Issues", Technical Report and User's Manual, 1006456, EPRI Project Manager - A. Singh, (April 2002).

4. "Generic Letter 96-06 Waterhammer Issues" - Technical Basis Report, EPRI # 1003098, (April 2002).

5. NUREG/CR-5535/Revl, RELAP5/MOD3.3 VOLUMES 1 through 8, Prepared by Information Systems Laboratories, Inc., Idaho Falls, ID for Division of Systems Research, NRC, Washington, DC 20555. December 2001.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 18 of 34

6. NRC Regulatory Guide 1.48, "Design Limits and Loading Combinations for Seismic Category I Fluid System Components".

7. EPRI Letter to Document Control Desk, U.S. Nuclear Regulatory Commission (Attn: Mr.

Jim Tatum), dated 1/1/202, Subject"Response to ACRS Comments (letter dated 10/23/01) on EPRI Report on Resolution of NRC GL96-06 Waterhammer Issues".

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Document Control Desk Attachment C-02-3455 RC-05-0204 Page 20 of 34 Proceedings of 12th International Conference on Nuclear Engineering

'Nuclear Energy - Powering the Future"

- Hyatt Regency Crystal City Arlington, Virginia (Washington, D.C.), USA April 25-29,'2004

-CONE1249214 Calculation of Forces on Reactor Containment Fan Cooler Piping Joseph S. Miller/EDA, Inc. Kevin Ramsden/Exelon Nuclear 6397 True Lone Mechanical Engineering. LLC Snngfeld VA 22150 - 4300 Winfield Road Warrenville, IL 60555 Phone: 703 597-2459. Fax: 703 313-9138 Phone: 630 657-3892. Fax: 630 657-4328 e-mait JoeMiller@edasolutions.com e-mail: Kevin.ramsden@exeloncorp.com ABSTRACT The purpose of this paper is to present the results of the Reactor NOMENCLATURE '

Containment Fan Cooler (RCFC) system piping load EPRI - Electric Power Research Institute calculations. These calculations are based on piping loads CIWH -Condensation Induced Waterhammer calculated using the EPRI methodology (Refs. I & 2) and LOCA - Loss or Coolant Accident RELAP5 (Ref. 3) to simulate the hydraulic behavior of the -MSLB - main Steam Line Break system. The RELAP5 generated loads were compared to loads RCFCs -Reactor Containment Fan Coolers calculated using the EPRI GL 96-06 methodology. This SX - Emrergency Service Water System evaluation was based on a pressurized water reactor's RCFC coils thermal hydraulic behavior during a Loss or Olfsite Power (LOOP) and a loss of coolant accident (LOCA). The INTRODUCTION RCFC consist of two banks of service water and chill water Following either a Loss of Coolant Accident (LOCA) or a Main coils. There are 5 SX and 5 chill water coils per bank. - Stcam Line Break (MSLB) concurrent with a Loss of Offsite Therefore, there are 4 RCFC units in the containment with 2 - Power (LOOP), pumps that supply cooling water to reactor banks of coils perRCFC. Two Service water pumps provide containment"fan coolers (RCFCs) and fans that supply air to coolant for the 4 RCFC units (S banks total, 2 banks per RCFC RCFCs will temporarily lose power. Cooling water flow will unit and 2 RCFC units per pump). stop due to theloss of pump head. Boiling may occur in RCFC tubes, causing steam bubbles to form in RCFCs and pass into Following a LOOPALOCA condition, the RCFC fans would the attached piping, creating steam voids. As service water coast down and upon being rcenergized. would shift to low- pumps restart. accumulated steam in the fan cooler tubes and speed operation. The fan coast down is anticipated to occur. piping will condense and the pumped water can produce a very rapidly due to the closure of the exhaust damper as a result - watcrharnmer when: the void closes. Ihydrodynamic loads of LOCA pressurization effects.The service water flow would introduced' by.'such a waterhammer event could potentially' also coast down and be restarted in approximately 43 seconds challenge the integrity and function of RCFCs and associated after the initiation of the event. The service water would drain cooling water: system components. The- U.S. Nuclear from the RCFC coils during the pump shutdown and once the Regulatory Commission (NRC) Generic Letter 96-06 identified pumps restart, water' is quickly forced into the RCFC coils ' potential issues for waterhammer 'effects during postulated causing hydraulic loading on the piping. Because of this events that can cause potential :damage 'to 'service water.'

scenario and the potential for over stressing the piping, an systems. 'in response to CL 96-06, the Electric Power Research evaluation was performed by the utility using RELAPS to Institute (EPRI) and the nuclear power plant owners developed assess the piping loads. Subsequent to the hydraulic loads ' methodologies to evaluate these events. ' The EPRI being analyzed using RELAP5, EPRI through GL 96-06 : methodologies are presented in References I and 2.

provided another methodology to assess loads on the RCFC piping system. This paper preseits the results of using the - Another methodology used by the utility was to calculate the EPRI methodology and RELAP5 to perform thermal hydraulic hydraulic loads using RELAP5 (Ref. 3). RELAP5I1O1D3 is a load calculations and compares them. -best estimate" system code suitable for the analysis of all transients 'and postulated accidents in Light Water Reactor (LWR) systems, as well as the full range of operational I' Copyright() byASME I"

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 21 of 34 transients. RELAP5 can also be used to model piping systems A diagram of the RCFC system is shown in Figure 2. The that contain two-phase and sub cooled liquid. The one RCFC consist of two banks of service water and chill water dimensional RELAP5IM0D3 code is based on a non- coils. There are 5 SX and 5 chill water coils per bank.

homogeneous and non-equilibrium model for the two-phase .Th"erefore,there are 4 RCFC units in thecontainment with 2 system that is solved by a fast, partially implicit numerical banks of coils per RCFC. Two Service water pumps provide scheme to permit economical calculation of system transients. coolant for the 4'RCFC units (8 banks total, 2 banks per RCFC unit and 2 RCFC units per pump). In normal operation, both.

The RCFC system was modeled using RELAP5 and hydraulic 'sets of coils have a flow, and the RCFC fan is operating in a' forcing functions were-developed from these analyses. The high'speedmode. FollowingaLOOPALOCA condition,the RELAPS model was initialized using option 4 to include a fans would coast down and upon being rcenergized, would small amount of air in the fluid. The fraction was kept as small shift toliow-speed operation. The fan coast down is'anticipated as possible, typically less than 25% of what could be dissolved to occur very rapidly due to the closure of the exhaust damper in' the fluid. The main reason for the air was not to get as a result ofLOCA pressurization effects. Theexhaust*.

cushioning effects, but rather to prevent negative pressures dampers would also have the effect of trapping air, creating a from terminating the computer run 'during spiking behavior. low now, or an upswept zone around the coils that would not' Draindown of the RCFC system was determined dynamically favor condensation The SX fow would also coast down and by modeling the boundary conditions of pump coast down be restarted in approximately 43 seconds after the initiation of-simultaneous with LOCA temperatures and heat transfer effects the cvent.'The chill water would not be restarted inma typical

-on the fan coolers using RELAP5. The boundary conditions design basis accident scenario.

and modeling assumptions were selected to maximize the void creation and maximize the potential for dynamic effects on SX The schematic of the RCFCISX system is shown in Figure 3..

pump restart. A postprocessor was developed and used to The designation on Figure 3 refers to the same designation calculate the forces from RELAP5 generated pressure, presented in Ref. I for an open loop system (See Figure 7-1 of densities, fluid velocity and user provided areas. The RELAP5 Ref.':1).-Thc designation'of c represents the 'front edge of the nodal diagram for the RCFC is shown in Figure 1. void and d represents the back edge of the void. 'The void is contained -in the volume of the fan cooler unit (fcu)'and the Figure 1 RELAP5 Nodal Diagram attached piping including the 1". riser. The fcu is represented  :

in this case as coils (112 of I RCFC unit). The now path is as or p follows: '-'Water leaves SX pump and branches from a 36"

: '-ctZ Age ~-24 rWOI'*WS  ::header. pipe into a 20", which is designated as the pump t a  ; ;d location.: From the 36 x 20tee, the flow travels 244.35 to a

.f ...  ;;-. 20" x 16", -which is designated as point a.'

Fr m point a, the'

___ ,_____ flow travels through a 16" pipe for 138.85' to the first flow' 3 m

. split into'a' 10" riser going to the 5 fcu coils. -At this point,

which is designated as point b, the low is'split by V. to %, with

.- e . ' .' . ': 1 V-4 of the flow going down the 10" riser and feeding5 the coils flow steam proceeding to the other half of:

_u

i. ' and the remaining %/.

the RCFC 2D and to RCFC 2B.. The'point designated as c is

. located in the 10 "riser at 17.75'. below'the 16" 'x IO" split

-designated as point b. The 10" riser evenly distributes the flow .

.:through the 5 coils through 4" pipes that tee from the 10" riser.

These 4" pipes run in parallel and are reduced 'to 3"'pipes, whichi go" into a coil; The 'point designated 'as c is the front' edge of the void.

DISCUSSION'-.d

.The purpose of this paper is to provide acormparison of thermal.

hydraulic load calculations based'on using EPRI methodology (Ref. I.& 2) and 'using RELAP5 'simulator to 'determine the,:.

hydraulic loads of the RCFC system subsequent to a LOOP and' a LOCA. This paper discusses the results of the evaluation of.-

Reactor 'Containment 'Fan Cooler (RCFC) coils thermal '

hydraulic behavior during a LOOP/LOCA using the EPRI GL 96-06 methodology and RELAP5.

2 Copyright (O by ASME

__- I?

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 22 of 34 Figure 2 RCFC SYSTEM closes. This rising pressure travels upstream and downstream from the closure location. As the pressure pulse encounters area changes, a portion of the original pressure wave is reflected bac toward the closure location. The reflected pressure wave will add to the prcssire it encounters in a positive or, nega tiv manner. If' the reflection comes f'rorn an expansion then it will have a negative magnitude and cause the oncoming-pressure to be reduced. The peak pressure will be clipped" if the reflection reaches the closure location before the pressure peaks. In the case of the RCFC pressure pulse evaluated in this paper,. the distance from the pressure pulse to*

the expansion at point "b". is only 17.75', therefore pressure EZ ~ s L~zJdtrmining Irsur lppn.Since Ref'erences I and 2 are clippingj'is'expected.. Ref. I has provided guidance for proprietay 'documents, only the final res Its will be presented The peak pressure is checked for "clipping" using

'Reference' I Point ha" is checked (See Figure 3). The primary factors used to calculate the peak pressure are: length of void

.'a) release of non-condensables to calculate the cushioned velocity, determine the pressure pulse shape, determine the

-i;_pressurepulsemagnitude, rise time and peak pressureduration, and determine reflective pressure wave. From these elements,

, *.' the clipped peak pressure can be determined. The pressure i reflection from the first major expansion in the system piping will cause the initial pressure wave created from the water harnmer to be'clipped (i.e., reduced) based on the'speed of the" refection wave to and from the major expansion and the degree The steps that are specified by the EPRI methodology are: 1) of expansion. In addition, the pressure pulse is cushioned by Evaluate the System, 2) Model System Hydraulics, 3) the non-condensables in'the water.

Determine Condensation Induced Waterhammer (CIWH) magnitude, 4) Determine Potential Closure Locations and 5) The unclipped pressure is 126 psi and the.clipped pressure Determine Column Closure Waterhammer (CCWII) Magnitude pulse is 64.psi. The system pressure is added to this value.

and Pulse Characteristics. The resultant pressure pulses using the 'EPRI mythology with c:-:cushioning and non-cushion effects considered are presented in Figure 3 Schematic or RCFC According to EPRI . Figure 4.

Methodology RELAP5 was used to simulate the LOOP/LOCA event. The

__  ;. A pressure pulse calculated from the RELAP5 simulation is shown in Figure 5. As you can see from Figure 5, the pressure Sipuls from the RELAP5 calculation is'slightly larger than the pulses calculated using the EPRI methodology.

Ipressure

f*W A-2 .' .To evaluate the loads on the piping system, it was assumed that PA represented the force on the piping system. Figure 6 shows' that hydraulic load of the RELAPS pulse is greatcr'than the hydraulic load of the EPRI pulses.

The most significant aspect of the calculation using the EPRI methodology was determining the peak pressure pulse: The peak pressure pulse is affected by pressure reflections from other obstruction downstream from the initial pressure pulse.

During a column closure event, the pressure rises as the void 3 Copyright C by ASME l.-

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 23 of 34 Igur 6Force Pus CopA sn sn ELP n Figuvre 4 Prsue us sigER Methodology: EPRI 1200 IC'J

.40.

moeing assumptions used in RELAP) hs agssumptions were as follows. Te SX. pump start wa~s assiumed

~FigureS5 RELAPS and EPIU Metoolg Pressure P occur in 1scn.TeHMcoigmdlwsue

-sparingly, only enatbled At the coil exits and at the transit'ions from Inliet eders~to the large bore piping. nyavr ml

_____________quantiyo airwas itouced.

I' ACKNOWLEDGMMENTS Wewoudlk to. thank Jeff Drwe and ExlnNula for

• supportin this work.

REFERENCES I) "Generic Letter 96-06 Waterhaninier Issues",

Technical Report and Usr' anul

___________ 0046 PRI Project Manager - A.Singh (April 2002)

"ceric

'Genms.2 Lte 9-06 Waterhamnmer issues-

-Technical Bai ReprEPRI # 100309,8,: (April.~

2002).

In conclusion,' it Was determined. that the EPRI mnethodology.

.and the RELAPS calculations can be used to generate hydraulic 3) NUREG/CR-55351ev1,: RELAPS/OD3.3 VOUE0Itruh 8,Peardb Inornation loads for the RtCFC system. The RELAPS calculated hyd raichtpl o

lod hsaayi rdcd larger. loads-than the loads*.. Systems Laboratories, lnWidho lFalls, ID for deeoe snih PImtoooy he. reason that Division of Systems Research, NRC, Washingn, :DC REAP eutrdcdalre odwsdue to the 20'555. Deeher 201 4 Copyright C by ASME

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 24 of 34 QUl1CATION OF RELAP51MOD3 FOR SAFETY RELIEF VLEHYDRODYNAMIC

~LOADA A yis:~A COMPARISON AGAINST EPRICE SRV TEST 1017 AppiCatUn offlELAPSNOD3 TSR by ydrodvnamic Load Analysis Philip R. Bo$yn Cmutn, Toc Bs n.,RmeG.Objectives and Cncerns lavid W.Ploa EThe, RELAPS moeiggieie . 2cuneddb Vetra Tcnologies, Inc.,Nrrs.G. WV=ne i qf5jjiomroieswhn nays Miyycantb easonably apled osmcolgrto, Absrac eo ofa1dow patiulrl hoe wih og eal ndi lca pea"Wvlve W estPlcinmte lop ea donsteamalo ceats' j

mis ocwlens th ccpablt ormA thweai w-eoiy nluaiglo-sn eae od rthe Clas 1 pn "j,rr r pqmig rim hav ofe .odor6 hg od npp pefmd iiT qeda yrdnmeitn fntosfrte sgeaibmkimnovWeO~

lc ~ m furip negmdents f te Cstutoi erigl t fCi~r .r ~ ~ ,oe~zIemqie eddt rsre h fmigftntnm ae tdaquny se n Weeeelpe.Ths aerslgreutig nuks-osevzie eig urdontra fi tile orinl 18Tatdata (Dreser 0aftyvaveTes 1017 se bjoc&5 of this stuy wr o()etb~hscesu Wkhj cod wAte lopsa) Temkeiythat RIUAPW/OD)3 becmdsaantteCEtetda thheloac itirds adtheMRERCpost-proeso nbie used with coohdence to its rihflpaeiitza fteSV ndC)ivui e hddyname cacuat npp Aucsfrwtress an Upport moligtciqepcfcayuso hewovocyqton anayss. d Z=chcoldpoenialy edcedonsrem lad wil sil maitaiin adtpstedes cosevatsm Introducton The release ofRE.APSUM Dim the early, 1980s coincide with a nedwithin thle nuclear iindsx to 2elmdetail anlyisof Safety Relief Valve (8.1W)hydrodynamicoe loa&RHAPS i(Reacor#AiO AN Ax-ursion and Leak Anaysi Duvan) VMS trel0 aedSr best- ~vTwai~VA

~" ~ basc" ma1W~

durig a severe accident RJUAPS's abaility to Mode tcnpli steam-.

water ineaton itinemtflipae -Ade-pcn ising carkdidate for apitinkSRV ialsis. The ElectricPou-Research Insitte (EPRI) termournTehooge,"n.?O hid sed(Rf)thtfspcfcodlng rles ol'ern 5Irra O smonay good resuiltculd eaiet The use ofRlAS k

~d W&m user aind developers bersuse the code unrswr l

designedaiaiy ~in simulation ofreactor coolt#n trnusients. Coputatfico of water hammier fet in reltiel,,al piping 'was cmdadoutsid th oves apprved apiain h aaytatEG&GIdaho, Inc. range fion not usingthcoeaalfr these types of problms, to using it withqualifi msr 5 TheC curn~t release oif the code11isREAPS/M(D3. A mnurber of . .

Mprovements haebe i= the intilMCD release.

Wmd Significant for bydrodlynaxnic lood analysis was the mplenientaticm of separinte vapor and liquidjunictican calculations. RELAPS/MoDI Used a conibined velocity forf both phiases. 7be sig velocity calcuaton produces la11ger hy&64dnamic loads and remains an input option a RELAPSMMO3. The Work docuniented by this paper shows that Figure I RELAIPS/MOD3, properly applied, can provide' conserVatiVe CE SRV Test Facility Layout hydrtx~sianic; loads for input into "seal-warld piping stippcort design. fCourtesy Electric Power Research Institutes)

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 25 of 34 hetet siilr o eslt. resueinstrument PT-09..a iustalld atl PRELAPS IMOD)S Model of CE Test Facility for Dresser SRV Test 1017 afluna CE Test10)7 r esser model 31709 safetyae -nbe:- 0 selet* Iedr the uinn T resser vtave test was, ;e0ec e

~ ~ ~ w md n~dco eemn iic nu pin becaus (1) fthedata obtaied Ifltn tis paicW a test VaS 11WI documnted, And 4.2) the Sow apcity of this vave VMSsmia hd tidefctotebncarrsut.tiuscfredtt thlat IofCa sVulcan, Pow Oer tdRifav (JPORV). Since .Oh opsa ae lgintefrtt'iesget

.ipprt is critical to reproducing the sd n the e ts T the flu thiszstud wolddbe tised:1bvideinali esuts dioalyc fir a O~w wlnt~apecrfl POR dd1X EI i zntig 6x2ffisauxp segment #2 OfthCEetriha fowr ts waspa the p~taii~ s~xe of odelng dificuly. Thrmalhydrinili codes ntrlyhv troble (related III ptto ='ma rmermig) . the compactness ofthe water slgasitpsestruJ lredifsra Revised Modeling Technliqusi"~ ~ 1 K tonachiei e nPa CEgTest 1017 wasldo3,tmuidbocnre:ctlYlin tagainst detaile dynamic; modeling of the SR: stal position in cccsdanee with the; test.ata (see Fige 2) Full ofpen stlemn: IO slt inches The ]kresser 81 was simulated sn thetee t -hte a spcrte eoctiesvtends 5, tbeiaugdorsav Dispesal ol oe i eue ftesnl eoit hsoeeu)jnto pin trial-rnm-derivednvave, coefficient (Cv = 48) SD tha fth sem flow viatcbe Majutesft and theIRELAP5=66oth ae iilrpeiu tyiezoeei tinwie n icw oea h chngedndel was spcIeLii si xstt teve area mixing i red the slura Iha model i0iidi used the aCbruptfea chane opio wianhd as wihed p}te SI ffisearo _ flo ratSe m e cce Figures 4 trough 7 show t -- fet o Vayingejuncton Opions an th c The RELAP5 nodlatiraon downsteam oteM RV wisnlro Force,peaks for, seget 111,N3, and #4 1rer0ficeablyklwevtie n i tty optinc isusec The egm nt#2p icepean nodalizationused byjF.IUi Reference A added in the eionlhoh 6x2 diffuser in segmt ahi'ge in higher fir thev-VctYotO a ntgtvep anhd SW3L a thneID sertests Weement ed wagfir atr aboequDe Fi co n against other S/lW tes dat that the sRVinglv eloci h S test loop u~ysfiedtiv prssurized tanks t simuiate the IP efflittsteceMSMSrytmoethteia eryls rntefidtt

=, C .1 re-5 %e; Ij5M M;Cv n nte agh nayiprdbisaouin rtd uy e RheLP vohmmnelethwestbiedaasomitna ini ipulacimen ot fies r nn-evbe 'fteit"ue 'dif topp1imtrrtoofapicniy11 bs iendl nula ft& W premur pid oenvati. A ZtELAPth e tine-dep:il of acobestic ndxsent voini Tefn lwveh smulated otio

.e:lt jet zWfl~ inhigher forcesir segent #2alo #Dd Th aoltdfcethstntobcieoecnertves thde;tanklr e 3aidy ofi~ e the SRV cnl:tepispirc Sbcbvz dng.d52 o:S InX0 prdction analysesz schdul budgetand~t000;0 0i ualydoncft$0; per f it the isdattnion Patdicla as evot~ed to iie:ay ..

aOs. hi 700-.

iopC U ~

~ r.inmatnldS Except fir SBG the  : - peak ia  : 600 I

vss ts dt i,

flun Iq*dI IfevL Irh ae it nsis th mat&AOb.'nmw w~ --= 100p lime 3SRV o:f the calculaed ValvetemDnparisont;00 (SecOnds)

Outlet pressure { R T-8 nifficiutto disprs the slg n ule Time(Scods

eflxwa rsue(TO 00:Figure Figure 3 showsin 2MoeigVleSmDyacSRFVr

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 26 of 34 P;udctb gle velocity sinf: jmcOpion as ahwan ta if tfheicmho8n.

used. il s ppg

PREPREF and REFORC Post-Processors (by..

VectraTchnologIes) vsegments juncms. the SRceayhBcgnlcbark =l fov.peitdr ci. 3A wc p-processug well away unthe Bnak3 s fraegmen4s #3 ad4 PEPRE VUc3AanRER

7) dxw atjoicious use of te t-vee t6 devep e nfi (Figue sincant iduoc t ua hs d s tyF p ' REAP5 hc d:fixi=S.

8:4i =_ - .- = 00 = l m anfor xsw was do loped to hel-: g tbis daeaiacts the iSwv &cgexnedxi. mifly.

• 0Thethe9 RV awayfle 511owingllel Sr aplyIgR[P~ftvOD i&iUSr00E CJ-c) reds te REIFagina kdu;sstr;f temainpiug~p loas

.EPPRF V; Rm05 j-iAS' arnd volumes. :PPREFROFmten

• 0D)fe,Us D~theDJmmsogtnwu z0Swtion cen0XyS:t d epXtiall Meads tlhe RELAP S es:aoIle and qi:acts time-depat h

.eoXii-ii00003f00-00000ft00:00020000:0200; X.

&RUCW rcch J:toSo f000t _

lcvd MA-trownz iorqMalvtis of -A .ft emow zin5 Sr= tase t 9i-t -- fSh i SR et U:rocesms tsdt and ti for m suitAl f;Q;t S

ff~ftU~

• eneoff f0d;siftzif:$ft-:ftii~~ cont~ :iufftiax V ibnpr itfi~;:0 ft a ~ 0 e ;f beC S RV fimOp:;d cnt the mainngdwnsbamjwvtcs. RF *1 9¶RAm~E.Q ~S)allows the alstodfergos of the RELAPS model v x~4j lscieauhtob aluae.F heanalysis of the CE SRY testloq model,wuve (UMasie accraio) form w=s calculated Sr each of thebuxr pipe stueg -ments.hese d #te id xia fluid Fo avGied ito net RELAO5

- _Ofy  : :_ 2VELOCITYL .ELA: RP E IT RLAP5VELTIY 8.0  :-Hda 40.0- aran Xdl4-6z0- _Fft;. .;XSf i+_e it0D'in jfrs f iw , th tv Owa 4o 20-.0 2

0.0 UU-L2I 0 C*LL.~

Time Secons) lMe (SetonciS Figure6- Seg:ment#3Calculated Force figure -Segment ti Calculated Force VD2.0 -7i. t 21 21.X t::y02.02 000 22.1:zn) i022.2 0S922.3 0 21.60 . 219 22.f0 .22. 2421.90 .X f22 Z3

.0  :  :

.0~ :15 U-

-40.0 22.0 22.2 :22.3 218 219 220 L 22. L. 222

. .8L 21 .9 L22-1 Tie(Scnds~) Time cns Fiure 7- Segment #4Calculae" oc Figure 5 -Segment #2 Calculated Forte

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 27 of 34 Elastic Piping Analysis Computer Program (X-direcion) supports for Segment 3 'wrei modeled as a single support along the pipe ceritalie, with twice vertical the stifflicss of the support& The 1 singlc intcrrndia suppcrt cn

~:Fcr this evaluation, a linen elastic. piping analysis computer pxogram .

- Frtiswaunaxamca~gaalsscnptt~gar irdividual.

j wasr a d uc toeaP n a an roiiwty C Segmentt 3 vwaslocated per Figure 2-3 of Reforence 3. The two S a auflueh the isSUc p t selc d verticil supports for Segment 4 v.Ae modeled as shown an Figure 3-8

• S is it canprdivc C Q progrm for the lastic . of Refcrnce 2 (in the Y-Zplane. The stilrhess values of Table I sed fr all support.

stmctual analyssand code ctmpliance verification of pipung

systes. It:plaes particular emphasis on nuclear power piping -.-.  :

designed to mect the rqur tof the ASUE Boiler and Pressure The Safey Relief Valve matl was 900 lbs, with a center of gravity Vessel Code, Section IIl. for Class l. 2 or 3 nuear pipinglet, and SW-2 and SW-3 at The prgramnused in this evaluation has the following major fcatures: 3450 lbs each along the centerline of the pipe, per Refernce 3.

i --..- E0.iated masse associated with the grayock fittings re input per

- -p.c.

• ion and plot of system geometry, dynamic the model geomety at their individual node points.

propes and Th-tory anaysis in'individual orsingle coputer runs.

'Determlnation of-Dynamic Propeties, Incuding Analysis Methods'

• 'toatic-enratin ofsuplemetal asspoins r -aic evaluations 'wre performe for this analysis. The pr requed ynwnic c

• Direct Integration Force Trme Ilistory (Dfli) method used as For p n a Bo Modal Superpoasition and Direct Integration the beichma medhod of alyrsis.

Modo .de Force Tine History. also Force Tame-History Analis. s seted in the

. - ld . a - :- . -. - .perfwmcde A discussion of the two methods..........-

swnmarics, - olwfgs - - .

• ePp support toads r~p 'andt displacemtnt rollowing paragraphs.

including time dependent reactions as a frnction of Mode-by-Mode Analysis Technque tune.

More detils of this specific cemputer prgnm are available u. Forithe MMTH optica. the alysisis carried out sing the mo

Reerencshapes a-d fimqu-cies detcrmined in the dynamic properties phase.

Becaus-e- only a limited nmiber of modes are considered (up to 2501 - -high frOequency rwire resporses included byr ing Elastic Piping Model of CE Test Facility  : :d lo &aotcatisothatupto250pipebindgmod The CE Test Facility model s doxuzeed in Rcference 2 is used w~usld be resolved.o ts This zaodalizatioc us WHS used to insure a ann accurate add for the structimal modeL The moderately simple structusal model is - dm-poh' (as ai paten vd c a b ad n may be~jl~ 'ton an based an actual piping sections, distr~bued and cMaente SeSC idvh b~sd iprmg, ad dsmoebs.(as; a patcent d critical) studta'damping c,,,

due to fanes and valves, actua jxe c and realistic d mode b:

support stiffiacs vahus (shown in Table I below fimmReference 3). A 0.001 second integration time step wa used, which matched the No attempt was made to dplicate the complex, non-linear stnrtural tanc step cmftin i the RELAP5/MOD3 time history filc.'This mnodels-used in Referee2 cr3.cnand funion fle ontain fore-time o lit hisory pairs fiom 0.0 to mreforng had identical damping 1.0 seconds. All modes wihin a single n

.v'1alues of 1% or 10% (.01 & 10) of crkiical damping. This resuted Table I1-nAnalyzed Support Stiffness (Ibin) 4.:in a co~nstant, CaM damping curv ovrtentire freueny range of Pipe Scgbment Support SupportStiffness int-r: s.-t:

-Nurber - Direction

-:: - . : .X - .::.6.00ev07..::.-:.-.:.:-::--: - " Damping

.1% - . 10% Damping 2 NLY 1.50e+06 (em.)-. .

3 - X - 7.50I0 -

i4o2S _I _ g _ + _

-:  :-I.::-

_ __ _ 3. .... . 10.00e+N ..

-004- . .s-_ _ _

4 INCLY. 5.0e5(ea) -I - I I . I

.1d .

r Intermnedie Y support only, coleutalld loads were eakud drawings(Fi A-I tough A-17 of . ."_ - T The individual spool p Refrnce 2 and Figure 2-3 of Refcrenoe 3)'wre nodoled and - .--

0.10 coted to match the 101test series gemety, with the gWA X ....i-l A I I axis in the direction of valve dischaWe the global Y axis vertically. -- l---- - --- +---

upward, and theglobal Z axis defined by the right hand rule. For ! I siUplicity thc modcl was anchored at the Safety Relief Valve inlet, . 0.00 -

with a support stifiness representative of the structure in the X 0 50 75 100 125 dirctio and -rigid" (L.OE+]3 lb'in) Y aind Z stiffix= in the other two global diretions. Frequency (Hz)

Both supports on the vertical Segment 2 run were modeled as shown Figure 8 - DITH Damping on Figure 3-7 of Reference 2 (in the Y-Z plane) The pair of axial Y-

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 28 of 34

Dlirct: Integration AnalysTechnilque Taie 40ed UPIU qiirimwihot 1tdyamc ncupin intohid Aayi apn yai

~t~~iskles opt cxi, there fzeoii 006ngmdampw muom ~uc ate :Cd suftema Sthe (Alpha) anMtflis bta4r rtcm ValUes Thijstoa 2 Dii 0ANA.

ftpf W ig= g9shows the: __ ~ff4.1 S The DM1 ehdas uses & .001 scon kktvely damp Mion Atep . 51 er geertedtht dd ot Damingazws fth high6&I low aiqund ge Th apn aua~ na noSRin Ea DamigVau t rqenyIad apn Value~ 2a The agencti smlrf heSget2troug4 ASrul.

0 Frqecy2TevleuedagimeinT bei... Teenen2lasaeti3 /.Teemn~n4lads&

overetimaed &aoot jr

[___ Table 2. DMN7 7am77n7. ~ rl u oteoe~oa~tieASrslsfti emn

_____ 1 ~ ~I Ta~e4-vAnalysls Resutst Summary___

10Ag..6 20 01 00 Case Max ioad Mvai:~a MaxLoadMaod R~t i evluatng k odse lampng alue i~*oiaiic I 8.1 642 2.9 19.

VWeeaeeasl~oic 3 2 97 7. 19.4 The firt t of.vaue rqetS thi loV& bound.damping eaSe,4 8. 7 73 macigterange oausofRefertene 4. Here, th avekw budVale is 1% ad fth 34001k avC~terage (ov~er the rane o sinilcnmos~sIA..6 7.6 88.5 652 1.

Thapn eod etrpeetstehg dapig carrag 1 CE-lol0? 9.3 4126 8.

o nine that "Th stxtxegeclY displayed a ZRfrne DAGS 185 5 0.--07 aa ideaI'Intiidaoersl owr ouiari ofMadMh&30 boudnd validating tthedindalbizw:atio and dynamic pmpcfiefse= uin h AsececeteapnghdltteefCan h magitude of thle Analysis Rjestlts; Test DaavskELA5IOD3 epneo u ppn emn i

and Elastic Piping AmaVsi! Combination lh The iHand threb fleautos= etxe a h iehsoiso h upr reactions~fir eadh stegimnat ar summaized inTal 3. Tabl I vale of ppcxt At swee"rd ii Fgrs9 hog 16 o h blwn ae rw ae1 fh sd n1&t odcss iws9trug 2aefrAnyi fo allkbu ae3 hr n-afte al Tabl 4 povids ~~ausfr a abultionof an deal he Sgmen 1,23 an 4 lad hstoies, repctvly h RenreCe= 3)ath detiedTonrlinearU 1)AGS 1017 TeFSe*eWt=,3Si 4 repetivey.he shapes ofjthein!sar 4

In llbutth fIrt scg anith acuae oasaebewe& faco eoiyoto o ucin ptem o h eodebw of1. t

.0moecosevaie ha heCE117reore tstvlus. dontramo te R. hedealttw-elciy pio wsusd i thaetetEalem 017Tet

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 29 of 34 conc usionlS HERolslons die:0000000 \00 Cbudn902000;kicc Saet 00 0-f02 with thieof.-

CE0170000- -i0 exce-ption oothe~lirs3ctnsgnt;,vwheredifii~e Wer I5 A00-$j0 0of to oTe result lds calculatd= A Athg+30%

A

.- Valvei Ts Loo Valv Fat Tet (Jo T:t.1017) ~U l~~fc122&

L~upFaciity(f~Tcs101) j $firod ~lj: 0;s:

G comparison of these resuts to th detiailed, noi-ineaDAGS results evahafixi ued he dehktwo-velocity mncawnentu, qse pin ~ smlrcreain.Ibuh rdcigteata rorm odeeo time-dpnet i~Cte~ncma ecix hpswr esimilartooh ofte HPSMg) tant The riultse that IELAPSMO canbe wed in concert used in an eastiic piping alYsi miod to estimatethe e structural Tbhese calculat ds vem then cpd to with: suitable potrocessot r (such as. P the Values from flie iginal 1981 CE 1017 Test. and dynamic stctul is code -aab of thyg Didsove:force-time bistoyInt(sc sSPRIEtoensufl rtp eppg modc strfessfifiles dlpuagapo load andO&

strureswith gap oe aiodeingef0exts. The model pitiigii cn_ i coungu 0y generally predictdin cmervativemiaxmutn lcoads (by *a

-IEASSPRPP . ETs 107Dta: - EASU PIPE.CETOAtlIl7Oatal O 4 - - .

0 40 -0 20.G 4~

oco

.00 t0 2 2-t ' * '01! ';* *1t lXi0j $0 CiU) -2. 4 j1. - -;t7t

22. 221 22.2 22tA 22 2t. 22.0 2.1 22 2.

21.6 :21S Figure 9 -9Segent #1 Loadi % Damngih' Fi 11S- e L Damng 1%oo

- RISUPERPIPE.

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Document Control Desk Attachment C-02-3455 RC-05-0204 Page 33 of 34 Inital Configuration - System aligned with SW system Water Hammer Condition - Occurs after LOOP event when SW booster pumps are re-started.

PHASE 1 - LOOP occurs causing SW booster pumps to de-energize.

PHASE 2 - Column of fluid gravity drains down to SW pond causing vacuum void formation PHASE 3 - After 41.5 seconds, SW booster pumps re-energized causing vacuum void to collapse and resulting water hammer Vacuum Void

- Collapses upon pump restart SW Booster Pump De-energized due to LOOP I3106A 3103A 3107A IC Supply IC Return FIGURE 2 To SW Pond

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 34 of 34 Inital Configuration - System aligned with SW system WATER HAMMER MITIGATION - Mod to install:

1. vacuum relief valve downstream of 31 07A

2. replace 31 07A with an air operated butterfly valve that fast closes upon de-energize of SWBP

3. delay opening of valve 3107A for five seconds after start of SWBP PHASE 1 - LOOP occurs causing SW booster pumps to de-energize.

PHASE 2 - Valve 3107A fast closes in 7 seconds and traps column of fluid above it PHASE 3 - Void formed below 31 07A is filled with water by vacuum relief valves PHASE 4 - After 41.5 seconds, SW booster pumps re-energized, 31 07A valve 5 sec delayed opening allows fluid flow momentum to bulld preventing further void formation PHASE 5 - air void downstream 31 07A flushed to SW pond 3106A SW Booster Pump De-energized due to LOOP I ICSupply D C Vacuum relief valve FIGURE 3 replaces vacuum void To SW Pond with air

Text

Jeffrey S. Archie Vice President, Nuclear Operations 803.345.4214 December 12,2005 RC-05-0204 A SCANA COMPANY Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTN: Mr. R. E. Martin

Subject:

VIRGIL C. SUMMER NUCLEAR STATION (VCSNS)

DOCKET NO. 50/395 OPERATING LICENSE NO. NPF-12 RESPONSE TO NRC QUESTIONS REGARDING RESPONSE TO GENERIC LETTER 96-06 (TAC NO. M96872)

References:

1) Stephen A. Byrne letter to Document Control Desk, RC-04-0018, January 20, 2004 (ADAMS Accession Number ML040220466)

2) K. R. Cotton (NRC) Electronic Letter to R. Sweet (SCE&G), "GL 96-06 Questions" dated October 14, 2004

3) Stephen A. Byme letter to Document Control Desk, RC-04-01 11, August 4, 2004 (ADAMS Accession Number ML042220080)

4) J. Turkett (SCE&G) Electronic Letter to K. R. Cotton (NRC), 2005 Draft Response to NRC Questions Regarding SCE&G Response to Generic Letter 96-06 (TAC NO. M96872), April 15,2005

5) R. E. Martin (NRC) Electronic Letter (FAX) to R. Sweet (SCE&G), 'The NRC Staff reviewed SCE&G's draft response and additional information is needed...", June 29, 2005 On October 14, 2004, South Carolina Electric & Gas Company (SCE&G) received an electronic communication (Reference 2) presenting an NRC request for additional information (RAI) regarding the VCSNS response to Generic Letter (GL) 96-06 submitted August 4,2004 (Reference 3). SCE&G reviewed these questions in consideration of the activities conducted to address the GL 96-06 issues. On January 13,2005, a telephone conference between SCE&G, the NRC, and the technical reviewers for the NRC was held to discuss the questions of the RAI and explain the SCE&G position regarding the responses developed for VCSNS. SCE&G provided Reference 4 based on an understanding reached with the reviewers during the referenced telephone conference. On June 29, 2005, the NRC responded with a series of questions (Reference 5) addressing additional information needed.

SCE&G is providing the attached response to address questions presented in Reference 2 and Reference 5.

-Ac),7 SCE&G I Virgil C.Summer Nudear Station

• P.O.Box 88. Jenkinsville, South Carolina 29065 .T (803) 345.5209 .www.scana.com

Document Control Desk C-02-3455 RC-05-0204 Page 2 of 2 Summary of Commitments SCE&G makes the following commitments as further discussed in the attachment to this letter:

VCSNS has initiated a plant modification that will accomplish three changes to the current plant configuration for Service Water (SW) discharge from the Reactor Building Cooling Units (RBCUs). First, this modification will delay the opening of gate valves 3107ANB upon start up of SW booster pump (SWBP) ANB. This delay will allow the SWBPs to build up fluid momentum and full fluid flow prior to the opening of these valves preventing gravity drain-down of fluid to the SW pond thereby preventing the creation of a vacuum void. Second, the modification will install vacuum relief valves downstream of valves 3107A/B to replace with air any vacuum developed in the downstream piping during normal operations and eliminate the need for manual action to "vent" the piping. The air in lieu of vacuum will tend to cushion the water column impact as the SWBPs are energized after a station blackout. Third, SCE&G will replace valve 3107A/B with fast closing butterfly valves that close in seven seconds upon de-energizing of SWBP A/B. The fast valve closure will trap water in the high points above the valve and prevent void formation from gravity drain-down of the water to the SW pond. SCE&G is confident that the combined affects of these modifications will reduce the waterhammer loads in the piping to very low levels.

These changes are not required to address any deficiencies in the ability of the plant to meet its current design and licensing basis, but they will reduce operator burden and increase design margins. These changes are currently scheduled for completion in RF-1 6 (October 2006).

If you have any questions or require additional information, please contact Mr. Robert Sweet at (803) 345-4080.

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

Ekecuted on Jeffrey B. Arched JT/JBA/dr Attachment c: N. 0. Lorick S. A. Byrne N. S. Carns G. S. Champion (w/o Attachment)

R. J. White W. D. Travers NRC Resident Inspector K. M. Sutton NSRC RTS (C-02-3455)

File (815.14)

DMS (RC-05-0204)

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 1 of 34 South Carolina Electric & Gas Company (SCE&G)

Virgil C. Summer Nuclear Station (VCSNS)

Response to NRC Request for Additional Information (RAI)

Regarding SCE&G Response to Generic Letter (GL) 96-06 Review of GL 96-06 waterhammer condition as it applies to V. C. Summer Nuclear Station Refer to Figure 1 on page 19 of this attachment.

There are two system alignments for the cooling of the Reactor Building Cooling Units (RBCUs),

via the non-safety Industrial Cooling (IC) System or via the safety related Service Water (SW) system. Cooling via the IC system is the normal plant operation alignment. Cooling is automatically transferred to the SW system after an Engineered Safeguards Features Actuation Signal (ESFAS). With the RBCUs aligned for normal plant operations (aligned to the IC system), a void as noted in Figure 1 is present in the piping downstream of valve 3107A/B (this void will be referred to as the first void). This first void is formed by gravity drain-down of fluid in the RBCU return piping to the SW pond upon realignment of the RBCU from the SW system to the IC system. During this realignment, valve 3107A/B is closed and the gravity drain-down occurs. This void contributes to the waterhammer event as will be explained later. Analysis has shown that if the void contains air in lieu of a vacuum, the affects of the waterhammer are greatly reduced, i.e.,

the air in the void tends to cushion the impact of the two columns of water as the void collapses versus no cushion with a vacuum in the void. Therefore, plant operating procedures have been revised to include venting of the piping to replace the vacuum void with air. This venting is performed per procedure immediately after the realignment of RBCU cooling from the SW system to the IC system. During normal plant operation the venting process is only required after quarterly system testing (SW supplied in lieu of IC).

The waterhammer condition postulated in GL 96-06 is caused by the coincident initiating occurrences of a Main Steam Line Break (MSLB) or Loss of Coolant Accident (LOCA) and a Loss of Offsite Power (LOOP).

Note: For piping loads only, the loads from a seismic event are conservatively combined with those caused by a LOCA event. Refer to the Response for the RAI Question regarding load determination methodology on page 9 of this attachment for further details.

It is assumed that prior to these events the RBCUs are operating in their normal lineup such that they are being cooled by the non-safety IC System. The initiation of a MSLB/LOCA would cause the temperature in the Reactor Building (RB) to begin to rise. After approximately 20 seconds, the temperature in the containment would reach 260 degrees Fahrenheit (OF). A concurrent LOOP would cause the IC flow to the RBCUs to stop due to the loss of the system pumps. From the time of the LOOP, it would take approximately 41.5 seconds for the emergency diesel generators (EDGs) to start and load sequencing by the ESFAS to be completed. After 41.5 seconds, the SW booster pumps (SWBPs) are re-energized and the alignment of RBCU cooling to SW begins.

Therefore, the stagnant cooling water in the RBCUs could be exposed to a 260 0 F temperature for aproximately 41.5 seconds. Heat transfer from containment to the RBCU cooling coils could

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 2 of 34 produce steam voids in the SW pipe. However, It should be understood that until valve 3107AIB begins to stroke open simultaneously with SWBP A/B startup (41.5 seconds following LOCA/LOOP) there is no possibility of steam generation in the RBCUs because fluid pressure in the RBCUs remains above the corresponding saturation pressure for the FSAR peak containment temperatures for LOCA or MSLB. The analysis of the waterhammer condition in VCSNS considered that a steam void did not develop in the RBCUs due to the heat transfer from containment. (It is noted that this is conservative as compared to the consideration of steam void formation. This will be explained in detail in the Questions and Responses that follow.). Upon re-energizing SWBP A/B and initiation of the transfer to SW system for RBCU cooling, valve 3107A/B (a gate valve under current plant configuration) begins to open. The characteristics of a gate valve are such that a signficant amount of flow occurs in the early stages of valve opening. Contrary to this, it takes several seconds for SWBP A/B to build up fluid momentum and commence full fluid flow. Due to these discrepancies, the fliud flows rapidly through valve 3107A/B to the SW pond and creates a vacuum void. This is the second void as described in the Figure 1. Collapse of the first air void and the second void occur when the SWBPs achieve operating speeds at full flow parameters.

Note: A waterhammer will not occur upstream of the RBCUs because there are two check valves near the containment penetration that trap the water above the RBCUs upon loss of flow and thus prevent voiding.

Application of the EPRI Methodology at VCS The occurrence of multiple independent column-closure waterhammer sites separated in time by up to ten seconds, the complicating effects of containment isolation valves stroking open slowly at different rates, and the presence of a large static air volume in the RBCU return piping take the VCSNS transient outside the realm of the approved EPRI GL 96-06 methodology. Significant effort was expended to apply the EPRI methodology to VCSNS. However, the calculations required so many simplifying assumptions to the transient scenario that the EPRI GL 96-06 methodology was not considered an adequate evaluation tool for the VCSNS configuration. This conclusion was validated during verification by an outside consultant with considerable experience in fluid hydraulic analysis.

Questions and Responses Question:

RELAP5 is a computer code with a largely empirical basis for its closure relations.

Therefore, RELAP5 must be assessed against experimental data that is applicable to the present analysis. Please provide the RELAP5 assessment that was performed that qualifies it for the present application. Describe how the range of conditions in the experiments correspond to the waterhammer conditions that might occur at Virgil Summer Nuclear Station during an accident with LOOP. Consider both thermal/hydraulic as well as geometrical considerations.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 3 of 34

Response

SCE&G has very high confidence that the support loads and pipe stresses calculated through the meticulous application of the RELAP5/MOD3 and PIPESTRESS computer codes bound the conditions that would be experienced in the plant should a GL 96-06 waterhammer event occur.

References I and 2 (pp.20 through 23 and pp.24 through 30 respectively of this attachment) are engineering papers showing that RELAP5/MOD3 can be successfully applied to conservatively calculate hydrodynamic forces resulting from both two-phase and single-phase waterhammer events. The RELAP5 modeling techniques used in the fluid transient analyses performed for VCSNS for GL 96-06 are similar to those applied in References 1 and 2. Furthermore, the cold column-closure waterhammer event on the RBCU discharge piping that has been identified as the bounding VCSNS waterhammer transient for GL 96-06 is almost identical to the normal transient which occurs during SWBP quarterly testing and RBCU cooling supply transfer from IC to SW cooling. Despite the relative frequency of this transient, no related damage to SW piping or supports has ever been reported.

Reference 1 is a recent engineering paper presenting analysis results directly applicable to the use of RELAP5/MOD3 for calculation of waterhammer loads for GL 96-06. The calculations were based on piping loads calculated using the EPRI methodology (References 3 and 4) and RELAP5 (Reference 5) to simulate the hydraulic behavior of the system. The RELAP5 generated loads were compared to loads calculated using the EPRI GL 96-06 methodology. This evaluation was based on a pressurized water reactor's Reactor Containment Fan Cooler (RCFC) coils thermal hydraulic behavior during a LOOP and a LOCA. The paper concludes that the EPRI methodology and the RELAP5 calculations can be used to generate hydraulic loads for the RCFC system. The RELAP5 calculated hydraulic loads for this analysis produced larger loads than the loads developed using the EPRI methodology.

Reference 2 is a 1994 engineering paper documenting the acceptability of the default two-velocity momentum equation option in the RELAP5/MOD3 computer program for the estimation of hydrodynamic loads associated with steam safety relief valve discharge. A RELAP5 analysis of the EPRI/Combustion Engineering Safety Valve Test Loop Facility was performed and time-dependent hydrodynamic forcing functions for the four pipe segments of the Combustion Engineering (CE) Test Facility were developed. These forcing functions were subsequently used in an elastic piping analysis model to estimate the resultant structural responses. The calculated loads were then compared to the values from the original 1981 Test data (Dresser safety valve Test 1017 with cold water loop seal). The results verify that RELAP5/MOD3 and the REFORC post-processor can be used with confidence to calculate hydrodynamic forces for use in pipe stress and support analysis. While the Safety Relief Valve (SRV) test cases were conducted at significantly higher pressures than would occur for the GL 96-06 waterhammer scenarios, the CE 1017 test scenario is a cold water slug propelled down an empty 12-inch diameter discharge pipe.

Because of relief valve chatter the water slug is released incrementally and does not remain intact.

The hydrodynamic conditions are similar to the GL 96-06 waterhammer scenario at VCSNS in which a cold water column is released into a voided (air-filled) 16-inch diameter RBCU return pipe when containment isolation valve 31 07A/B opens slowly over a 30 seconds stroke period. An important conclusion from this study is that the RELAP5-computed forces become significantly more conservative (by factors of 1.5 to 2.0) compared to the test data as the water slug is accelerated down successive pipe segments. The Reference 2 analysis methodology is very similar to the RELAP5-based waterhammer analyses performed for VCSNS for GL 96-06.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 4 of 34 Dynamic net axial forces were computed by calculating the total wave (momentum) force in each pipe segment during each RELAP5 time step (maximum 0.0002 second). The net forces were written to the RELAP5 restart-plot file every 0.002 second after being processed through a lag filter control function with a 0.002 second time constant. Because the VCSNS RBCU piping lengths are much longer than the CE SRV test facility pipe segments, and because approximately the same node length/diameter ratio is used for the VCSNS GL 96-06 analyses as was used for the Reference 2 RELAP5 model, it is anticipated that the RELAP5-calculated forces for GL 96-06 have significant conservatism compared to forces that would be experienced in the actual plant piping during GL 96-06 transient scenarios. The VCSNS RELAP5 model for GL 96-06 contains approximately 476 volumes for each RBCU train.

The bounding waterhammer scenario for GL 96-06 at VCSNS occurs as follows. The inside containment RBCU cooling loops between containment isolation valves 3106A/B (RBCU supply) and 3107ANB (RBCU return) is pressurized and filled with cold water from the IC System, the normal cooling water supply for the RBCUs. The IC system contains a large accumulator tank that passively maintains system pressure even when the IC pumps are unpowered following a LOOP'.

The piping immediately downstream of valve 3107A/B is manually filled with air at atmospheric pressure. The air vent is accomplished by procedure whenever the SW supply to the RBCUs is secured. Following a LOCA with coincident LOOP the Emergency Diesel Generators (EDGs) start 11.5 seconds after LOCA/LOOP. The SW pumps (SWPs) start and containment isolation valves 311 IA/B and 3112A/B begin stroking closed over a 60 seconds stroke time to isolate the non-safety IC system from the safety-related SW supply to the RBCUs. At 41.5 seconds after LOOP, SWBP A/B starts and containment isolation valves 3106A/B and 3107A/B begin to stroke open.

Valve 3107A/B opens in approximately 30 seconds and 3106A/B opens in approximately 45 seconds.

Because gate valve 3107A/B in the RBCU return line has flow at a relatively high capacity early in its opening stroke, the drain flow rate from the RBCU header temporarily exceeds the fill rate from SWBP A/B (which is conservatively modeled to ramp to full flow over a period of 5 seconds.) The drain flow causes vapor voids2 to develop in the 10-inch piping downstream of the RBCUs. No attempt to credit steam cushioning is taken because, per References 3 and 4, the cold water column collapse (LOOP only) scenario has been shown to bound the LOCA scenarios with steam generation in the RBCUs3. The RELAP5 analysis predicts that moderate waterhammer forces due to void collapse occur in the two 10-inch piping segments downstream of the RBCUs as the SWBP refills the header inside containment. Meanwhile containment isolation valves 3106A/B and 3107A/B continue to stroke open and a third column-closure waterhammer occurs in the 16-inch RBCU return piping outside containment. The severity of this column-closure event is mitigated by the presence of the large air volume between the incident water column from valve 3107A/B and the standing water column near orifice 99A/B and the 412-ft elevation floor penetration. The incident water column is also broken up by flow element 4468/4498 and orifice 29A/B.

1 No credit for the ICaccumulator tank maintaining pressure is taken in the RELAP5 analysis.

2 Void formation is exacerbated inthe RELAP5 analysis because the fill/pressurization benefits of the IC system are not included.

3 It should be understood that until valve 3107A/B begins to stroke open simultaneously with SWBP A/B startup 41.5 seconds following LOCA/LOOP there is no possibility of steam generation in the RBCUs.

Fluid pressure in the RBCUs remains above the corresponding saturation pressure for the UFSAR peak containment temperatures for LOCA or MSLB.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 5 of 34 Question:

Identify any valves that are credited for preventingdrain-down or backflow in the system in order to minimize the void size and to the extent this is applicable, discuss the specific seat leakage assumptions that are credited in the analysis and describe periodic testing that is performed in accordance with the IST program to assure that the seat leakage assumptions remain valid.

Response

On the discharge side of the RBCUs, following shutdown of SWBP A/B and transfer to IC, a vacuum void downstream of valve 3107A1B is manually filled with air. This was noted in a previous response and will be discussed further in the following responses. Once the vacuum is replaced with air, no additional vacuum void formation or air in-leakage is expected as long as valve 31 07A/B remains closed. The fluid and air will remain stable in equilibrium at a pressure of I atmosphere. When aligned with IC, the fluid pressure and volume upstream of valve 3107A/B is maintained via a surge tank. Due to pressure differentials across the valve and the very small leak path for the development of buoyant forces, any fluid leakage past valve 3107A/B will flow into the void. In order to maintain equilibrium, this leakage will essentially flow through the void to the SW pond and not affect the air void, and is therefore acceptable.

On the supply side of the RBCUs, it has been proposed that during a LOOP or LOCA scenario, voids could form in the piping as a result of water column drain back into the main SW system header through two check valves (31 37A1B and 3135A/B) and a normally closed butterfly valve (3106A/B). The RBCUs are normally aligned to the IC system such that valve 3106A/B is closed.

Another proposed drain back path is to the closed-loop IC via the two check valves (3136A/B and 31 37A/B).

To create a void in the RBCU inlet piping, it is necessary to remove enough cooling water to drain the RBCUs and several segments of the 10"n piping at the RBCU inlet. The RBCU cooling coil volume is approximately 132 gallons. Considering the hypothetical case in which two pipe segments adjacent to the RBCU inlet are voided due to drain back, the volume of the two pipe segments is approximately 13 gallons and their lengths are 1.77 feet and 2.02 feet., respectively.

Conservatively assuming that only 50% of the RBCU volume needs to be drained before the inlet piping begins to uncover, the total back-leakage through the check valves must approach (50%)(132 gal) + 13 gal = 79 gallons over the time period for which back leakage would be a concern.

The time period over which back-leakage may occur is a very important factor. The valve and pump timing following LOOP (or LOOP/LOCA) is as follows.

0.0 sec Event Initiation, SWPs tripped due to assumed loss of offsite power.

1.5 sec ES actuation 11.5 sec EDG started and running, ready to accept loads from ES Sequencer. SWPs and essential motor-operated valves (MOVs) are powered back up at this time.

Safety-related MOVs begin moving as necessary to safety positions, which is "closed" for butterfly valve 31 06A/B.

41.5 sec SWBP A/B starts. Simultaneously, valve 3106A/B begins to open.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 6 of 34 From the above time sequence we can easily conclude that the available time window for drain-back is 41.5 seconds or less. The required leakage rate through the check valves and valve 3106A/B is (79 gal/41.5 seconds) 114.2 gpm, a very large and substantial leak rate. When the SWBP is not running, the pressure at the SWBP outlet is approximately 60 psig when the SWPs are running. The elevation difference between the RBCUs and SWBPs is 107.6 feet, and the associated water column head is 46.5 psi at 66 0F. Thus, SWP pressure is more than sufficient (with a 10+ psi margin) to keep the RBCUs filled and prevent back-leakage into the SW header.

The SWPs restart in the LOOP scenario at 11.5 seconds. Plant data traces from Emergency Safeguards surveillance testing show that the SW header pressure is restored almost instantly upon SWPs startup. Therefore, the time window for back-leakage through the SW system is not 41.5 seconds, but is actually only 11.5 seconds or less (depending on SWP coast down pressure decay following LOOP). The required leakage rate to void the two pipe segments of interest over 11.5 seconds is 412 onm, a rate which is so large as to be considered clearly incredible through two check valves in series and a normally closed butterfly valve. And if a leak path that large did exist, the void would refill at low pressure from the SWPs before the SWBP starts at 41.5 seconds.

Therefore, void formation in the RBCU inlet piping due to back-leakage into the SW system is not a viable concern for GL 96-06 at VCSNS.

If the leakage path is into the closed-loop IC system, we have to postulate a 114.2 gpm leak rate into the system over 41.5 seconds to void the RBCU inlet piping. However, the IC system is a closed-loop system with a pressurized surge tank. For back-leakage to occur from the RBCU piping it is necessary to postulate rapid net leakage out of the IC system. The cover pressure in the surge tank will resist transient inflow from RBCU drainage. Review of monthly plant chemistry data reveals that the average maximum leak rate from the IC system is only 0.06 gpm. Thus, it is impossible to achieve the required 114 gpm back-leakage into the IC system required to void even a small portion of the RBCU inlet piping.

Question:

For the valves that are credited for preventing drain-down or backflow in the system as identified in the draft response, discuss the specific seat leakage assumptions that are credited in the analysis and describe periodic testing that will be performed in accordance with IST requirements to assure that the seat leakage assumptions will remain valid over time (see the Southern Nuclear Operating Company response for the Vogtle plant dated November 5, 2004, for an example).

Response

As justified in the previous response, seat leakage is not considered in the analysis for the valves credited for preventing RBCU drain-down or backflow.

Valves 3137A/B, RB Cooling Unit Supply Header Valves perform an active safety function in the OPEN position. These valves are normally open to allow IC flow to the RBCUs. During an accident, the flow is automatically transferred to safety-related SW for cooling flow. These valves open to supply flow from either source. Full flow ASME Code check valve testing is performed

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 7 of 34 quarterly under STP-223.002A at a post accident minimum design basis flow of 2000 gpm. These normally open valves are closed tested in accordance with ASME Code check valve testing requirements each refueling outage under STP-230.006G.

Valves 3135A/B, Service Water Booster Pump Discharge Check Valves, are normally closed valves that perform an active safety function in the OPEN position. These valves must open to allow SW flow to the RBCUs. During an accident, the flow is automatically transferred to safety-related SW for cooling flow, by SWBP auto start, discharge valve opening and isolation of IC flow.

Full flow ASME Code check valve testing is performed quarterly under STP-223.002A at a post accident minimum design basis flow of 2000 gpm. The valves are provided with an adjustable dashpot which controls the opening and closing speed of the disc for prevention of waterhammer.

In the closed position, the valve prevents the diversion of IC into the SW system. This is an operational function, since IC is not a safety-related system. These normally closed valves are closed tested quarterly in accordance with ASME Code check valve testing requirements under STP-223.002A.

Question:

It is stated that in the future the severity of postulated waterhammer events will be reduced by the injection of air into the service water piping and that system operating procedures have been revised to require air injection after system realignment. Please provide the following information concerning the air injection system:

a. Provide drawings of the service water system showing the location of the injected air pocket relative to the location of the postulated waterhammer. Demonstrate the injected air will flow into any steam space caused by LOOP, LOOP/MSLB or LOOPILOCA.

Response

Figure 1 (p.19 of this attachment) shows the locations of the voids and the predicted waterhammer sites for RBCU Train A. Steam voiding in the VCSNS RBCUs does not occur for GL 96-06 scenarios because the fluid pressure in the RBCU coils remains above the saturation pressure corresponding to LOCA peak containment temperature until after SWBP startup.

Following shutdown of SWBP A/B and realignment to IC, a vacuum void forms due to fluid column gravity drainage downstream of valve 3107ANB, the containment isolation valve on the RBCU return piping to the SW pond. Compressed air is injected into the vacuum void by the Operations staff in accordance with plant procedures such that the void is filled with air at a pressure of approximately I atmosphere. The air is supplied via apant air hose (connected only during the fill procedure) and remains trapped between valve 3107A/B and the downstream standing water column until the next time SWBP A/B is started and the associated RBCUs are placed on SW cooling. This relatively large air volume (extending for approximately 119 feet of the 12-inch diameter pipe) cushions the column collapse waterhammer event that analysis predicts could occur following SWBP A/B startup and opening of valve 3107A/B. The waterhammer is projected to occur when the incident water flow from valve 3107A/B reaches the standing water column near flow orifice 99A/B. Figure 1 shows the location of the air volume and column collapse waterhammer locations predicted by analysis.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 8 of 34 Regarding the potential for steam formation in the RBCUs from LOCA/MSLB coincident with a LOOP, the normal RBCU cooling water supply is via the IC system. The IC system is a closed loop design with a pressurized expansion tank and relief valves. Valves 3106A/B and 3107A/B are normally closed, isolating the SW cooling supply to the RBCUs. The VCSNS design basis does not require the consideration of the seismic event occurring coincident with any other transient, such as the LOCA/MSLB. Therefore, the passive function (structural integrity) of the IC system outside containment can be relied upon after the occurrence of the LOCA/MSLB. The LOCA peak containment temperature of approximately 260 0F (

Reference:

VCSNS FSAR) corresponds to a saturation pressure (P.Et) of only 20 psig in the RBCU coils. This pressure is well below the nominal RBCU internal fluid pressure of approximately 50 psig when aligned to the IC system and is far below the RBCU thermal relief valve opening set points. Heat transfer to the RBCU coils will stop when the coils reach 260 OF, and boiling/steam formation cannot occur if the fluid pressure in the coils remains above 20 psig. Following a LOOP/LOCA and EDG startup, the containment isolation valves for the IC cooling water supply to the RBCUs (valves 31 1OA/B, 311 A/B, and 3112A/B) begin to close at a rate of approximately 60 seconds for full stroke. During the 41.5-seconds period between LOOP/LOCA and SWBP startup the expansion tank for the IC system passively maintains fluid inventory and pressure in the RBCU coils well above 20 psig. Therefore, steam formation in the RBCU coils is not expected to occur. If for whatever reason the coil pressure does drop below 20 psig, the volume of steam that can be generated is very small because any steam expansion in a closed loop system will quickly drive the pressure back to equilibrium P.at with the containment temperature.

Question:

b. We understand that following a LOCA or MSLB with LOOP, the service water pumps will be automatically loaded onto emergency power. During this time, a steam void might have formed within the service water system which might cause waterhammer when the service water pumps are restarted. Please discuss the means by which air injection will be assured before the service water pumps are restarted. If the air is injected at an earlier time, please discuss the means which will assure that the air remains present and in the proper location.

Response

The air injection is only required upon restoration of the RBCU cooling to the IC system, the alignment for normal plant operations. Plant operating procedures have been revised to require this injection during this restoration. After this restoration, additional air injection is not required during normal operations. The injected air will remain in place due to the make up of differential pressures between that inside the pipe and the ambient pressures outside the pipe.

As noted in the previous response, following shutdown of SWBP A/B and transfer to IC, a vacuum void forms due to fluid column gravity drainage downstream of valve 3107A/B. Immediately after this transfer, compressed air is then injected into the vacuum void by the Operations staff in accordance with plant procedures such that the void is filled with air. The air is supplied via a plant air hose (connected only during the fill procedure). The air remains trapped between valve

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 9 of 34 3107A/B and the downstream standing water column until the next time SWBP A/B is started and the associated RBCUs are placed on SW cooling. The "injection" of air is merely for the convenience of the Operation staff. Initially, VCSNS Engineering had specified the "venting" of the piping to fill the vacuum with air. However, based on the size of the tubing to be used for this "venting", Operations staff concluded that an unreasonably long time would be required to assure the system was completely filled with air. Therefore, a means to "inject" air into the piping to speed up the process was developed and incorporated into plant procedures. Once the vacuum is replaced with air, no additional vacuum void formation or air in leakage is expected as long as valve 31 07AB remains closed. The fluid and air will remain stable in equilibrium at a pressure of approximately I atmosphere. Any fluid leakage past valve 3107A/B will drain through the void to the SW pond and not affect the air void.

VCSNS is in process of developing a modification that will install vacuum relief valves downstream of 3107A/B to eliminate the need for manual action to "vent" the piping.

Question:

Describe the methodology by which structural piping and support loads were determined, including a description of the load combinations that were applied.

Response

Using the force time histories developed by the RELAP fluid hydraulic analysis as inputs, a classical time history piping analysis was performed using the computer program PIPESTRESS to determine pipe stress and pipe support loads.

VCSNS considers this waterhammer to be an upset event that does not require the inclusion of a seismic event. VCSNS has applied the ASME Code, Section 111, NC-3652 (1971 Edition through Summer 1973 Addenda) stress limits for an upset condition to the piping and pipe support qualifications. The following load combinations were used:

Pipe stress: 9U - Pressure + Deadweight + Waterhammer < 1.2 SH Pipe Support loads: Deadweight + Thermal Expansion + Waterhammer Regulatory Guide 1.48 (Reference 6), with similar discussion in the VCSNS FSAR, states that for piping the code limits for the faulted condition shall not be exceeded when piping is subjected to concurrent loadings associated with the normal plant condition, the vibratory motion of the safe shutdown earthquake (SSE) and the dynamic system loadings associated with the faulted plant condition. Regulatory Guide 1.48 defines "the dynamic system loadings associated with the faulted plant condition" as those dynamic loadings which result from the occurrence of a postulated rupture (e.g., complete severance or equivalent longitudinal break area) of any reactor coolant pressure boundary piping or of any other piping not a part of the reactor coolant pressure boundary. Therefore, in terms of piping, the "LOCA" event to be combined with seismic is an event associated only with the dynamic structural consequences of a pipe break. The waterhammer loads in the SW piping need not be combined with the seismic loads if there is reasonable assurance that the two events would not occur concurrently.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 10 of 34 An initiating event occurs which includes a LOCA or MSLB inside containment and a LOOP happening concurrently which initalizes the ESFAS. For loads on piping systems, the earthquake loads are combined with those from a LOCA. (Note: The VCSNS design basis does not require the consideration of the seismic event occurring coincident with any other transient, such as a LOCA. However, for conservatism, the loads on a structural piping system from a seismic event are combined with the loads from a LOCA event.) After the intiating events, the EDGs are energized and load sequencing is initialized which includes the transfer of RBCU cooling from the IC system to the SW system. VCSNS design basis defines the duration of an SSE to be 20 seconds. Therefore, 20 seconds after the intiating event, the earhquake ceases. 41.5 seconds after the initiating event, the SWBP A/B becomes energized and valve 31 07A/B open restoring cooling flow through the RBCUs. This would cause a collapse of the void in the SW pipe and the consequential waterhammer as described in the above responses. This is depicted on the following timeline:

Power Restored; SW Booster MSLB/LOCA 41.5 Pumps 3107A/B Water and LOOP seconds - energized opening Hammer opening occurs

-II I .

SSE 20 _..._ Earthquake earthquake seconds Ends Therefore, the waterhammer loads do not need to be considered concurrent with the loads from LOCA/MSLB plus earthquake in the piping analysis. VCSNS considers this waterhammer event to be a separate event by itself that will always occur 41.5 seconds after an event causing the plant to enter into the Si mode, or during switch over of RBCU cooling from the IC system to the SW system which is permitted during normal operations and during surveillance testing. (Note:

VCSNS design basis does not require an earthquake to be considered concurrent with these transfers in which the system is in limited operation.)

Conclusion VCSNS believes that the current analysis as described above adequately qualifies the as built piping and pipe supports of the RBCU discharge piping for the loads associated with the waterhammer conditions described in GL 96-06. It is noted that the VCSNS as-built SW piping has experienced the GL 96-06 waterhammer event discussed herein many times over the twenty three years of plant operation. During this time, no damage to the SW piping or pipe supports has ever been reported.

Planned Modifications VCSNS has initiated a plant modification that will significantly improve, if not eliminate, the waterhammer condition associated with the GL 96-06 concerns. These changes are not required to address any deficiencies in the ability of the plant to meet its current design and licensing bases, but they will reduce operator burden and increase design margins. VCSNS is utilizing

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 11 of 34 structural piping analysis that uses bounding fluid hydraulic force time histories developed by RELAP5 in the development of this modification. These changes are currently scheduled for completion in RF-16 (October 2006). This modification will accomplish two changes to the current plant configuration for SW discharge from the RBCUs. First, this modification will delay the opening of valve 3107A/B upon start up of the SWBP A/B. This delay will allow SWBP A/B to build up fluid momentum and full fluid flow prior to the opening of valves 3107A/B. This will prevent the gravity drain-down of fluid to the SW pond thereby preventing the creation of a vacuum void, i.e.,

the second void on Figure 1 will not develop. Preventing creation of this void reduces piping and support loads. Second, the modification will install vacuum relief valves downstream of valves 3107ANB which will automatically fill with air any void formed at this location due to gravity drain-down to the SW pond (first void on Figure 1). These vacuum relief valves will preclude the requirement to manually fill the vacuum void with air whenever the SW supply to the RBCUs is secured. They will provide assurance that air will always be present in the void. The combined affects of these two modifications will reduce the waterhammer loads in the piping to very low levels.

Question:

Confirm that the proposed plant modifications for resolving the GL 96-06 waterhammer issue will satisfy all applicable criteria that have been established for safety-related applications (e.g., seismic, single failure, environmental qualification, power supplies) and that the requirements of 10 CFR 50, Appendix B are fully applicable. Also, describe Technical Specification Requirements that will be established to assure operability.

Response

Station Administrative Procedure SAP-1 33, "Design Control/Implementation and Interface",

controls plant modifications implemented at VCSNS. This procedure is governed by IOCFR50, Appendix B. Design input considerations are evaluated for Appendix B requirements, FSAR Section 17.2 (Quality Assurance) commitments, and Technical Specifications, Section 6.5 (Technical Review and Control). The VCSNS Modification Program also satisfies ANSI N45.2.1 1-1974, "Quality Assurance Requirements for the Design of Nuclear Power Plants". Engineering Services procedure ES-455, "Design Control: Plant Modification' and procedure ES-454, "Design Control: Plant Enhancement" address initiation, design considerations, design reviews, implementation, and documentation of VCSNS plant modifications. SAP-107, "10CFR50.59 Review Process" additionally controls plant changes, where applicable.

There are existing Technical Specification surveillance requirements on the RBCUs and the plant systems, structures, and components that interface with the RBCUs. SCE&G considers these existing requirements sufficient based on our plant design and, therefore, plans no additional Technical Specification requirements.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 12 of 34 Question:

Establish a regulatory commitment to complete any actions that remain, such as plant modifications and TS changes, along with the scheduled completion dates.

The planned modifications will be implemented during VCSNS refueling outage RF-16 and are projected to be complete by December 31, 2006. No other actions are identified for this issue.

Question:

As requested in Section 3.3 of the staffs safety evaluation dated April 3, 2002, that approved the use of the proposed methodology in EPRI Technical Reports 1003098 and 1006456 for resolving the GIL 96-06 waterhammer issue, please provide certification that plant-specific considerations are consistent with the risk perspective that was provided by EPRI in a letter dated February 1, 2002, and included as an enclosure to these technical reports.

Response

Assuming that the planned system modifications have been made, the following is an assessment of the risk to the plant of the application of RELAP5/MOD3 using as a basis the assessment provided by EPRI in a letter dated February 1, 2002 (hereinafter referred to as Reference 7). A review of the "progression" of events that could lead to an unacceptable condition is listed. For the purposes of this evaluation, the unacceptable condition" following a LOOP/LOCA event will be defined as a breach of the service water system pressure boundary. The events are as follows.

1. Occurrence of a LOCA or MSLB - Discussion same as that noted in Reference 7.

2. Occurrence of a LOOP following a LOCA or MSLB - Discussion same as that noted in Reference 7.

3. Occurrence of a Simultaneous LOCANLOOP Event - Discussion same as that noted in Reference 7.

4. Void Formation - A void will form in the SW return piping outside containment due to fluid gravity drain. This void is air-filled (because of the new vacuum breaker), is the normal configuration, and exists whenever the upstream containment isolation valve (3107A or 31 07B) is closed. No significant voiding will occur in the RBCU piping upstream of 31 07A/B.

5. Pump Restart - The pumps will restart with certainty and the velocity of the fluid in the pipe, immediately prior to closing the void, is defined by the dynamic pressure in the void, the piping geometry (losses from wall friction and fittings such as valves, elbows, tees, and orifices) and the pump characteristics. This un-cushioned 4 closure velocity has been 4 Meaning the assumed amount of entrained air in the flow from the SWBP is so small as to be insignificant.

The sonic velocity is approximately 5000 feet per second for the subcooled upstream water column.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 13 of 34 calculated by RELAP5/MOD3. As noted in responses to other NRC questions, the RELAP5-based closure velocities and associated segment forces are considered conservative because they are substantially higher than what was experienced in the plant for one of the analyzed transient scenarios (see response to previous question).

The liquid flow velocity downstream of valve 3107A/B, when the pipe is running full, peaks at about 5.25 feet per second. Because of the 30 seconds opening time of valve 3107A/B, and the flow orifice 29A/B immediately downstream, the incident water column is disorganized (mixed) as it encounters the air mass between valve 3107A/B and the standing water column. Because the standing water column is receding (draining) while the vacuum breaker is open, the effective relative velocity between the incident water column and the receding column is quite small.

6. Column-closure - Discussion same as that noted in Reference 7.

7. Maximum Waterhammer Pressure - Application of the Joukowski correlation to the incident water columns downstream of valve 3107A/B results in very low calculated pressures (typically 25 psi or less increase) because the mixture density is low, the sonic velocity is very low because of the two-phase conditions, and because the slow valve opening time of approximately 30 seconds causes the velocity differentials to be comparatively low. It should be noted, however, that the calculated segment forces were computed not on the analyzed pressure rise, but on the net segment wave force from the total momentum equation. The transient force in each pipe segment is the sum of the liquid total mass-acceleration and vapor mass-acceleration over each 0.0002 second time step. In RELAP5, the mass-acceleration force is computed from the rate of change of the mass rates for each volume. Where the liquid mass rate for a volume is:

The time-derivative (differend) of the quantity: liquid density (rhof) x volume liquid velocity (velo x liquid fraction (voido x volume size (Wol).

The same computation is performed for the vapor phase, for all volumes in each (straight) pipe segment. The computation is performed for each RELAP5 time step, and then smoothed using a lag function with a 0.002 second time constant to ensure that no numerical force peaks are clipped or lost between the 0.002 second minor-edit write intervals required for the piping analysis.

It is this conservative approach that helps ensure the design-basis RELAP5 force-time history data bounds what is experienced in the actual plant during safeguards testing.

8. Cushioned Waterhammer - No credit was taken for cushioning effects5 due to air entrained in solution with the SW source water. In the RELAP5 analysis only a trace amount of non-condensable air was added to the SW supply, to facilitate phase calculation stability when the incident subcooled water encounters the large air volume from the vacuum breaker. The non-condensable quality of the SW supply in the RELAP5 model is 1.OE-8 at 95RF. The resulting code-calculated sonic velocity in the liquid-filled pipe sections was approximately 5000 feet per second.

5 Note that 'Cushioned Waterhammer" as used in the EPRI methodology refers to a reduction in the waterhammer pressure rise when non-condensable gas is dissolved in solution in the SW supply. The pressure reduction is due principally to the decrease in sonic velocity because of the presence of dissolved gas. Cushioning in the EPRI methodology is not the force-reduction effect that occurs when a large air volume is trapped between the incident water columns.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 14 of 34

9. Likelihood of an Unacceptable Event - Discussion same as that noted in Reference 7 except the use of RELAP5/MOD3 replaces the use of the EPRI Users Manual and the Technical Basis Report. The discussion therefore reads: Given the low probability (10 5/year) of the initiating events and the low probability (10-2) of piping failure, the use of the methodology using RELAP5/MOD3 will lead to a likelihood of an unacceptable event that is on the order of 10'7. Again, for the purposes of this evaluation, the unacceptable event" following a LOOP/LOCA event is taken as a breach of the SW system pressure boundary. The probability of 1 0 q7 for this event is below the threshold for significant risk to the plant. Use of the methods employing RELAP5/MOD3, therefore, will not compromise the safety of the plant for the systems within the bound provided by the RELAP5/MOD3 analysis. The methodology should be accepted as recommended.

The change in risk introduced by the use of RELAP5/MOD3 and the method employed is not significant and the methods do not lead to an unacceptable plant risk following a LOOP/LOCA event. Hence, from a risk-informed perspective, the methods proposed are adequate for the plant-specific application for resolution of the GL 96-06 issues.

Additional Discussion Pertaining to VCSNS System Performance Other Waterhammer Condition in SW piping not directly related to the GL 96-06 waterhammer condition:

As noted previously, it is assumed that the GL 96-06 waterhammer condition occurs when the plant is operating in its normal alignment with the RBCUs aligned with the IC system for cooling. During the effort to address the GL 96-06 waterhammer, another waterhammer scenario was identified. This waterhammer is postulated to occur during the time that the RBCUs are aligned with the SW system and a LOOP occurs. This alignment of the RBCUs is not a normal alignment. The RBCUs are aligned to the SW system only during quarterly testing, IC system maintenance and during refueling outages. In addition, this waterhammer condition is simulated in the plant every outage during safeguards testing. No anomalies of the piping or supports have ever been observed due to this waterhammer. However, SCE&G has incorporated the piping loads of this waterhammer into the plant design basis and has performed an analysis of the condition. Even though the actual waterhammer results in no anomalies of the pipe supports, this analysis predicted the presence of very high loads on pipe supports. SCE&G has developed interim measures and has scheduled the implementation of a plant modification to reduce these loads to levels that are analytically acceptable. This waterhammer condition, the interim measures and the plant modification for mitigation are at issue in the following RAls.

Question:

Explain why the scenario with the safety-related service water system aligned to provide cooling for the RBCUs at the onset of the postulated accident does not result in a more severe waterhammer event, or otherwise establish appropriate restrictions in the Technical Specifications on use of the service water system for RBCU cooling during normal plant operation.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 15 of 34

Response

The scenario with the safety-related SW system aligned to provide cooling for the RBCUs at the onset of the postulated accident does result in a more severe waterhammer event than the waterhammer resulting from the GL 96-06 scenario described in the preceding review discussion.

The RBCUs are typically aligned with the SW system during quarterly surveillance tests, IC system maintenance and during plant outages. If a LOOP were to occur during this alignment, as noted in the review discussion (page 1 of 34), from the time of LOOP, it will take approximately 41.5 seconds for the EDGs to start and the ESFAS sequencing to complete. After which the SWBPs will energize.During this 41.5 seconds, the column of fluid in the piping downstream of the RBCUs will gravity drain-down to the SW pond (Refer to Figure 2, p.33 of this attachment). This will form a large void in the piping. Upon SWBP re-start and the commencing of fluid flow, the void will rapidly collapse creating a significant waterhammer. Comparative analysis using RELAP5/MOD3 has shown that the waterhammer event from this scenario to be of greater severity by several magnitudes than that of the GL 96-06 scenario previously described.

In order to mitigate the affects of this waterhammer on the piping system, VCSNS has adopted a two-phase approach. The first is an interim phase that provides adminitrative and procedural controls over the use of the SW system for cooling to the RBCUs. The second is a modification to change valve closing and opening times and their coresponding initiating logic to permanently eliminate the waterhammer concerns. This modification is scheduled for implementation during RF1 6 in the fall of 2006. These two phases are discussed in detail in the following paragraphs.

In the first phase until the plant modification is implemented, the procedure for SW system operation, SOP-1 17, "Service Water System", has been revised to include a special set of initial conditions prior to aligning the system to the RBCUs. These conditions are intended to minimize the risk for a LOOP during the SW alignment, minimize the time duration the RBCUs are aligned to the SW system and to remind operations of the potential for a waterhammer in the event of a LOOP. These intial conditions are summarized as follows:

• In Modes 1 through 4, SW shall only be supplied to the RBCUs, when one or more of the following conditions are met:

a. Post Accident or High Containment Pressure Conditions.

b. Loss of Non-ESF power.

c. Loss of IC.

d. During testing.

• In Modes I through 4, when SW is being supplied to the RBCUs, all the following conditions shall be met:

a. No planned work is allowed in the switchyard.

b. The dispatcher confirms that no transmission system work is planned that would decrease the reliability of the off site power supplies.

c. There is no severe weather predicted in South Carolina for the expected duration of the testing.

d. If for surveillance testing or post maintenance testing, the testing has been approved as if it were a (Yellow) MODERATE Risk Activity.

e. If for any other reason, the testing has been approved as if it were an (Orange)

ELEVATED Risk Activity.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 16 of 34 The second phase requires the implementation of a plant modification in the fall of 2006. This modification will include (Refer to Figure 3, p.34 of this attachment):

• The replacement of gate valve 3107AIB with a fast closing butterfly valve that closes in seven seconds upon de-energizing of SWBP A/B. The fast valve closure will trap water in the high points above the valve and prevent void formation from gravity drain-down of the water to the SW pond. This will prevent any waterhammer event that would have occurred upon re-energizing the SWBPs and a consequential rapid collapse of the void.

• The addition of vacuum relief valves downstream of valve 3107A/B. These valves will replace with air any vacuum void downstream of closed valve 3107A/B that may be formed due to gravity drain-down of water to the SW pond. Upon the opening of valve 3107A/B and the re-start of SWBP ANB, the air in the piping will act as a cushion to minimize any waterhammer affects that could occur at that time. In addition, these relief valves will eliminate the need for operations to manually vent the piping downstream of valve 3107A/B immediately after the transfer of RBCU cooling from the SW system alignment to the IC system as noted in the preceding review discussion and discussed in following question responses.

• The opening logic of valve 3107A/B will be modified to have a 5 seconds delayed opening after SWBP A/B start. The delayed start of the valve opening will assure that additional void formation in the RBCU piping inside containment will not occur upon re-energizing the SWBP.

NOTE: The addition of vacuum relief valves and the delayed opening time at the valve 3107A/B location also help to mitigate the GL 96-06 waterhammer condition and are taken credit for as such.

Fluid hydraulic analysis using RELAP5/MOD3 and pipe stress analysis using the computer program PIPESTRESS have concluded that these modifications will largely eliminate the potential for waterhammer in the RBCU piping. The analysis concludes that the post modification waterhammer loads on the piping develop stresses in the piping that are well below the ASME Code allowables.

Question:

Assuming that the planned system modifications have been made, describe the results of a comparative analysis using analytical methods that have been approved by the NRC for this purpose (i.e., EPRI methodology or NUREG/CR-5220) that demonstrates that the RELAP results are conservative for the worst-case waterhammer location that was identified by the RELAP analysis.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 17 of 34

Response

VCSNS Technical Specification surveillance requirement 4.8.1.1.2.g.4 states: "Each EDG shall be demonstrated operable at least once every 18 months by simulating a loss of offsite power by itself..." VCSNS surveillance test procedure STP-125.017, "Diesel Generator'A' Loss of Offsite Power Test", contains the operating instructions that are conducted to demonstrate compliance with this requirement. These instructions, performed each refueling outage, have as an initiating condition the alignment of the SW system to the RBCUs followed by a simulated LOOP.

Therefore, this test simulates exactly the waterhammer condition described in Figure 2. Since initial plant operations, at least ten of these surveillance tests have been conducted. This means that the piping and pipe supports have been subjected to these waterhammer loads at least ten times. Waterhammer within the SW piping during these tests have been reported. However, the severity of the actual waterhammer has not been of the magnitude to cause any concern. This past refueling outage (May 2005) a walk down of the SW piping and pipe supports downstream of the RBCUs was conducted. The intent was to provide assurance that no damage existed in the piping or pipe support components. During this walk down, particular attention was drawn to welded attachments, support rods and support pins for any signs of deformation. In addition, observations were made at pipe welds and fittings for any indications of cracked or flaking paint and at pipe supports for paint rubbed off piping indicating recent pipe motion. No visible anomalies were found. This provided assurance that the actual waterhammer event occurring during each surveillance test was developing acceptable loads within the piping. However, the RELAP5/MOD3 fluid hydraulic analysis (for the Figure 2 scenario) has predicted very high waterhammer loads, loads that would create forces on pipe supports that would easily create deformation in many pipe support components. Therefore, the surveillance tests have provided empirical evidence that the waterhammer loads developed by the RELAP5/MOD3 analysis are very conservative and demonstrate that RELAP5/MOD3 is the appropriate tool to be used in predicting the waterhammer loads for the design of the structural piping system.

Response References

1. Engineering paper ICONE12-49214 Calculation of Forces on Reactor Containment Fan Cooler Piping, by Joseph S. Miller/EDA, Inc. and Kevin Ramsden/Exelon Nuclear, Proceedings of 12t International Conference on Nuclear Engineering, Arlington, Virginia, April 25-29, 2004.

2. Engineering paper Qualification of RELAP5/MOD3 for Safety Relief Valve Hydrodynamic Load Analysis: A Comparison Against EPRI/CE SRV Test 1017, by P. R. Boylan (Touch Base Computing, Inc.), and D.W. Peltola (Vectra Technologies), Presented at the 1994 International RELAP5 Conference, Baltimore, Md.

3. "Generic Letter 96-06 Waterhammer Issues", Technical Report and User's Manual, 1006456, EPRI Project Manager - A. Singh, (April 2002).

4. "Generic Letter 96-06 Waterhammer Issues" - Technical Basis Report, EPRI # 1003098, (April 2002).

5. NUREG/CR-5535/Revl, RELAP5/MOD3.3 VOLUMES 1 through 8, Prepared by Information Systems Laboratories, Inc., Idaho Falls, ID for Division of Systems Research, NRC, Washington, DC 20555. December 2001.

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 18 of 34

6. NRC Regulatory Guide 1.48, "Design Limits and Loading Combinations for Seismic Category I Fluid System Components".

7. EPRI Letter to Document Control Desk, U.S. Nuclear Regulatory Commission (Attn: Mr.

Jim Tatum), dated 1/1/202, Subject"Response to ACRS Comments (letter dated 10/23/01) on EPRI Report on Resolution of NRC GL96-06 Waterhammer Issues".

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Document Control Desk Attachment C-02-3455 RC-05-0204 Page 20 of 34 Proceedings of 12th International Conference on Nuclear Engineering

'Nuclear Energy - Powering the Future"

- Hyatt Regency Crystal City Arlington, Virginia (Washington, D.C.), USA April 25-29,'2004

-CONE1249214 Calculation of Forces on Reactor Containment Fan Cooler Piping Joseph S. Miller/EDA, Inc. Kevin Ramsden/Exelon Nuclear 6397 True Lone Mechanical Engineering. LLC Snngfeld VA 22150 - 4300 Winfield Road Warrenville, IL 60555 Phone: 703 597-2459. Fax: 703 313-9138 Phone: 630 657-3892. Fax: 630 657-4328 e-mait JoeMiller@edasolutions.com e-mail: Kevin.ramsden@exeloncorp.com ABSTRACT The purpose of this paper is to present the results of the Reactor NOMENCLATURE '

Containment Fan Cooler (RCFC) system piping load EPRI - Electric Power Research Institute calculations. These calculations are based on piping loads CIWH -Condensation Induced Waterhammer calculated using the EPRI methodology (Refs. I & 2) and LOCA - Loss or Coolant Accident RELAP5 (Ref. 3) to simulate the hydraulic behavior of the -MSLB - main Steam Line Break system. The RELAP5 generated loads were compared to loads RCFCs -Reactor Containment Fan Coolers calculated using the EPRI GL 96-06 methodology. This SX - Emrergency Service Water System evaluation was based on a pressurized water reactor's RCFC coils thermal hydraulic behavior during a Loss or Olfsite Power (LOOP) and a loss of coolant accident (LOCA). The INTRODUCTION RCFC consist of two banks of service water and chill water Following either a Loss of Coolant Accident (LOCA) or a Main coils. There are 5 SX and 5 chill water coils per bank. - Stcam Line Break (MSLB) concurrent with a Loss of Offsite Therefore, there are 4 RCFC units in the containment with 2 - Power (LOOP), pumps that supply cooling water to reactor banks of coils perRCFC. Two Service water pumps provide containment"fan coolers (RCFCs) and fans that supply air to coolant for the 4 RCFC units (S banks total, 2 banks per RCFC RCFCs will temporarily lose power. Cooling water flow will unit and 2 RCFC units per pump). stop due to theloss of pump head. Boiling may occur in RCFC tubes, causing steam bubbles to form in RCFCs and pass into Following a LOOPALOCA condition, the RCFC fans would the attached piping, creating steam voids. As service water coast down and upon being rcenergized. would shift to low- pumps restart. accumulated steam in the fan cooler tubes and speed operation. The fan coast down is anticipated to occur. piping will condense and the pumped water can produce a very rapidly due to the closure of the exhaust damper as a result - watcrharnmer when: the void closes. Ihydrodynamic loads of LOCA pressurization effects.The service water flow would introduced' by.'such a waterhammer event could potentially' also coast down and be restarted in approximately 43 seconds challenge the integrity and function of RCFCs and associated after the initiation of the event. The service water would drain cooling water: system components. The- U.S. Nuclear from the RCFC coils during the pump shutdown and once the Regulatory Commission (NRC) Generic Letter 96-06 identified pumps restart, water' is quickly forced into the RCFC coils ' potential issues for waterhammer 'effects during postulated causing hydraulic loading on the piping. Because of this events that can cause potential :damage 'to 'service water.'

scenario and the potential for over stressing the piping, an systems. 'in response to CL 96-06, the Electric Power Research evaluation was performed by the utility using RELAPS to Institute (EPRI) and the nuclear power plant owners developed assess the piping loads. Subsequent to the hydraulic loads ' methodologies to evaluate these events. ' The EPRI being analyzed using RELAP5, EPRI through GL 96-06 : methodologies are presented in References I and 2.

provided another methodology to assess loads on the RCFC piping system. This paper preseits the results of using the - Another methodology used by the utility was to calculate the EPRI methodology and RELAP5 to perform thermal hydraulic hydraulic loads using RELAP5 (Ref. 3). RELAP5I1O1D3 is a load calculations and compares them. -best estimate" system code suitable for the analysis of all transients 'and postulated accidents in Light Water Reactor (LWR) systems, as well as the full range of operational I' Copyright() byASME I"

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 21 of 34 transients. RELAP5 can also be used to model piping systems A diagram of the RCFC system is shown in Figure 2. The that contain two-phase and sub cooled liquid. The one RCFC consist of two banks of service water and chill water dimensional RELAP5IM0D3 code is based on a non- coils. There are 5 SX and 5 chill water coils per bank.

homogeneous and non-equilibrium model for the two-phase .Th"erefore,there are 4 RCFC units in thecontainment with 2 system that is solved by a fast, partially implicit numerical banks of coils per RCFC. Two Service water pumps provide scheme to permit economical calculation of system transients. coolant for the 4'RCFC units (8 banks total, 2 banks per RCFC unit and 2 RCFC units per pump). In normal operation, both.

The RCFC system was modeled using RELAP5 and hydraulic 'sets of coils have a flow, and the RCFC fan is operating in a' forcing functions were-developed from these analyses. The high'speedmode. FollowingaLOOPALOCA condition,the RELAPS model was initialized using option 4 to include a fans would coast down and upon being rcenergized, would small amount of air in the fluid. The fraction was kept as small shift toliow-speed operation. The fan coast down is'anticipated as possible, typically less than 25% of what could be dissolved to occur very rapidly due to the closure of the exhaust damper in' the fluid. The main reason for the air was not to get as a result ofLOCA pressurization effects. Theexhaust*.

cushioning effects, but rather to prevent negative pressures dampers would also have the effect of trapping air, creating a from terminating the computer run 'during spiking behavior. low now, or an upswept zone around the coils that would not' Draindown of the RCFC system was determined dynamically favor condensation The SX fow would also coast down and by modeling the boundary conditions of pump coast down be restarted in approximately 43 seconds after the initiation of-simultaneous with LOCA temperatures and heat transfer effects the cvent.'The chill water would not be restarted inma typical

-on the fan coolers using RELAP5. The boundary conditions design basis accident scenario.

and modeling assumptions were selected to maximize the void creation and maximize the potential for dynamic effects on SX The schematic of the RCFCISX system is shown in Figure 3..

pump restart. A postprocessor was developed and used to The designation on Figure 3 refers to the same designation calculate the forces from RELAP5 generated pressure, presented in Ref. I for an open loop system (See Figure 7-1 of densities, fluid velocity and user provided areas. The RELAP5 Ref.':1).-Thc designation'of c represents the 'front edge of the nodal diagram for the RCFC is shown in Figure 1. void and d represents the back edge of the void. 'The void is contained -in the volume of the fan cooler unit (fcu)'and the Figure 1 RELAP5 Nodal Diagram attached piping including the 1". riser. The fcu is represented  :

in this case as coils (112 of I RCFC unit). The now path is as or p follows: '-'Water leaves SX pump and branches from a 36"

: '-ctZ Age ~-24 rWOI'*WS  ::header. pipe into a 20", which is designated as the pump t a  ; ;d location.: From the 36 x 20tee, the flow travels 244.35 to a

.f ...  ;;-. 20" x 16", -which is designated as point a.'

Fr m point a, the'

___ ,_____ flow travels through a 16" pipe for 138.85' to the first flow' 3 m

. split into'a' 10" riser going to the 5 fcu coils. -At this point,

which is designated as point b, the low is'split by V. to %, with

.- e . ' .' . ': 1 V-4 of the flow going down the 10" riser and feeding5 the coils flow steam proceeding to the other half of:

_u

i. ' and the remaining %/.

the RCFC 2D and to RCFC 2B.. The'point designated as c is

. located in the 10 "riser at 17.75'. below'the 16" 'x IO" split

-designated as point b. The 10" riser evenly distributes the flow .

.:through the 5 coils through 4" pipes that tee from the 10" riser.

These 4" pipes run in parallel and are reduced 'to 3"'pipes, whichi go" into a coil; The 'point designated 'as c is the front' edge of the void.

DISCUSSION'-.d

.The purpose of this paper is to provide acormparison of thermal.

hydraulic load calculations based'on using EPRI methodology (Ref. I.& 2) and 'using RELAP5 'simulator to 'determine the,:.

hydraulic loads of the RCFC system subsequent to a LOOP and' a LOCA. This paper discusses the results of the evaluation of.-

Reactor 'Containment 'Fan Cooler (RCFC) coils thermal '

hydraulic behavior during a LOOP/LOCA using the EPRI GL 96-06 methodology and RELAP5.

2 Copyright (O by ASME

__- I?

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 22 of 34 Figure 2 RCFC SYSTEM closes. This rising pressure travels upstream and downstream from the closure location. As the pressure pulse encounters area changes, a portion of the original pressure wave is reflected bac toward the closure location. The reflected pressure wave will add to the prcssire it encounters in a positive or, nega tiv manner. If' the reflection comes f'rorn an expansion then it will have a negative magnitude and cause the oncoming-pressure to be reduced. The peak pressure will be clipped" if the reflection reaches the closure location before the pressure peaks. In the case of the RCFC pressure pulse evaluated in this paper,. the distance from the pressure pulse to*

the expansion at point "b". is only 17.75', therefore pressure EZ ~ s L~zJdtrmining Irsur lppn.Since Ref'erences I and 2 are clippingj'is'expected.. Ref. I has provided guidance for proprietay 'documents, only the final res Its will be presented The peak pressure is checked for "clipping" using

'Reference' I Point ha" is checked (See Figure 3). The primary factors used to calculate the peak pressure are: length of void

.'a) release of non-condensables to calculate the cushioned velocity, determine the pressure pulse shape, determine the

-i;_pressurepulsemagnitude, rise time and peak pressureduration, and determine reflective pressure wave. From these elements,

, *.' the clipped peak pressure can be determined. The pressure i reflection from the first major expansion in the system piping will cause the initial pressure wave created from the water harnmer to be'clipped (i.e., reduced) based on the'speed of the" refection wave to and from the major expansion and the degree The steps that are specified by the EPRI methodology are: 1) of expansion. In addition, the pressure pulse is cushioned by Evaluate the System, 2) Model System Hydraulics, 3) the non-condensables in'the water.

Determine Condensation Induced Waterhammer (CIWH) magnitude, 4) Determine Potential Closure Locations and 5) The unclipped pressure is 126 psi and the.clipped pressure Determine Column Closure Waterhammer (CCWII) Magnitude pulse is 64.psi. The system pressure is added to this value.

and Pulse Characteristics. The resultant pressure pulses using the 'EPRI mythology with c:-:cushioning and non-cushion effects considered are presented in Figure 3 Schematic or RCFC According to EPRI . Figure 4.

Methodology RELAP5 was used to simulate the LOOP/LOCA event. The

__  ;. A pressure pulse calculated from the RELAP5 simulation is shown in Figure 5. As you can see from Figure 5, the pressure Sipuls from the RELAP5 calculation is'slightly larger than the pulses calculated using the EPRI methodology.

Ipressure

f*W A-2 .' .To evaluate the loads on the piping system, it was assumed that PA represented the force on the piping system. Figure 6 shows' that hydraulic load of the RELAPS pulse is greatcr'than the hydraulic load of the EPRI pulses.

The most significant aspect of the calculation using the EPRI methodology was determining the peak pressure pulse: The peak pressure pulse is affected by pressure reflections from other obstruction downstream from the initial pressure pulse.

During a column closure event, the pressure rises as the void 3 Copyright C by ASME l.-

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 23 of 34 Igur 6Force Pus CopA sn sn ELP n Figuvre 4 Prsue us sigER Methodology: EPRI 1200 IC'J

.40.

moeing assumptions used in RELAP) hs agssumptions were as follows. Te SX. pump start wa~s assiumed

~FigureS5 RELAPS and EPIU Metoolg Pressure P occur in 1scn.TeHMcoigmdlwsue

-sparingly, only enatbled At the coil exits and at the transit'ions from Inliet eders~to the large bore piping. nyavr ml

_____________quantiyo airwas itouced.

I' ACKNOWLEDGMMENTS Wewoudlk to. thank Jeff Drwe and ExlnNula for

• supportin this work.

REFERENCES I) "Generic Letter 96-06 Waterhaninier Issues",

Technical Report and Usr' anul

___________ 0046 PRI Project Manager - A.Singh (April 2002)

"ceric

'Genms.2 Lte 9-06 Waterhamnmer issues-

-Technical Bai ReprEPRI # 100309,8,: (April.~

2002).

In conclusion,' it Was determined. that the EPRI mnethodology.

.and the RELAPS calculations can be used to generate hydraulic 3) NUREG/CR-55351ev1,: RELAPS/OD3.3 VOUE0Itruh 8,Peardb Inornation loads for the RtCFC system. The RELAPS calculated hyd raichtpl o

lod hsaayi rdcd larger. loads-than the loads*.. Systems Laboratories, lnWidho lFalls, ID for deeoe snih PImtoooy he. reason that Division of Systems Research, NRC, Washingn, :DC REAP eutrdcdalre odwsdue to the 20'555. Deeher 201 4 Copyright C by ASME

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 24 of 34 QUl1CATION OF RELAP51MOD3 FOR SAFETY RELIEF VLEHYDRODYNAMIC

~LOADA A yis:~A COMPARISON AGAINST EPRICE SRV TEST 1017 AppiCatUn offlELAPSNOD3 TSR by ydrodvnamic Load Analysis Philip R. Bo$yn Cmutn, Toc Bs n.,RmeG.Objectives and Cncerns lavid W.Ploa EThe, RELAPS moeiggieie . 2cuneddb Vetra Tcnologies, Inc.,Nrrs.G. WV=ne i qf5jjiomroieswhn nays Miyycantb easonably apled osmcolgrto, Absrac eo ofa1dow patiulrl hoe wih og eal ndi lca pea"Wvlve W estPlcinmte lop ea donsteamalo ceats' j

mis ocwlens th ccpablt ormA thweai w-eoiy nluaiglo-sn eae od rthe Clas 1 pn "j,rr r pqmig rim hav ofe .odor6 hg od npp pefmd iiT qeda yrdnmeitn fntosfrte sgeaibmkimnovWeO~

lc ~ m furip negmdents f te Cstutoi erigl t fCi~r .r ~ ~ ,oe~zIemqie eddt rsre h fmigftntnm ae tdaquny se n Weeeelpe.Ths aerslgreutig nuks-osevzie eig urdontra fi tile orinl 18Tatdata (Dreser 0aftyvaveTes 1017 se bjoc&5 of this stuy wr o()etb~hscesu Wkhj cod wAte lopsa) Temkeiythat RIUAPW/OD)3 becmdsaantteCEtetda thheloac itirds adtheMRERCpost-proeso nbie used with coohdence to its rihflpaeiitza fteSV ndC)ivui e hddyname cacuat npp Aucsfrwtress an Upport moligtciqepcfcayuso hewovocyqton anayss. d Z=chcoldpoenialy edcedonsrem lad wil sil maitaiin adtpstedes cosevatsm Introducton The release ofRE.APSUM Dim the early, 1980s coincide with a nedwithin thle nuclear iindsx to 2elmdetail anlyisof Safety Relief Valve (8.1W)hydrodynamicoe loa&RHAPS i(Reacor#AiO AN Ax-ursion and Leak Anaysi Duvan) VMS trel0 aedSr best- ~vTwai~VA

~" ~ basc" ma1W~

durig a severe accident RJUAPS's abaility to Mode tcnpli steam-.

water ineaton itinemtflipae -Ade-pcn ising carkdidate for apitinkSRV ialsis. The ElectricPou-Research Insitte (EPRI) termournTehooge,"n.?O hid sed(Rf)thtfspcfcodlng rles ol'ern 5Irra O smonay good resuiltculd eaiet The use ofRlAS k

~d W&m user aind developers bersuse the code unrswr l

designedaiaiy ~in simulation ofreactor coolt#n trnusients. Coputatfico of water hammier fet in reltiel,,al piping 'was cmdadoutsid th oves apprved apiain h aaytatEG&GIdaho, Inc. range fion not usingthcoeaalfr these types of problms, to using it withqualifi msr 5 TheC curn~t release oif the code11isREAPS/M(D3. A mnurber of . .

Mprovements haebe i= the intilMCD release.

Wmd Significant for bydrodlynaxnic lood analysis was the mplenientaticm of separinte vapor and liquidjunictican calculations. RELAPS/MoDI Used a conibined velocity forf both phiases. 7be sig velocity calcuaton produces la11ger hy&64dnamic loads and remains an input option a RELAPSMMO3. The Work docuniented by this paper shows that Figure I RELAIPS/MOD3, properly applied, can provide' conserVatiVe CE SRV Test Facility Layout hydrtx~sianic; loads for input into "seal-warld piping stippcort design. fCourtesy Electric Power Research Institutes)

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 25 of 34 hetet siilr o eslt. resueinstrument PT-09..a iustalld atl PRELAPS IMOD)S Model of CE Test Facility for Dresser SRV Test 1017 afluna CE Test10)7 r esser model 31709 safetyae -nbe:- 0 selet* Iedr the uinn T resser vtave test was, ;e0ec e

~ ~ ~ w md n~dco eemn iic nu pin becaus (1) fthedata obtaied Ifltn tis paicW a test VaS 11WI documnted, And 4.2) the Sow apcity of this vave VMSsmia hd tidefctotebncarrsut.tiuscfredtt thlat IofCa sVulcan, Pow Oer tdRifav (JPORV). Since .Oh opsa ae lgintefrtt'iesget

.ipprt is critical to reproducing the sd n the e ts T the flu thiszstud wolddbe tised:1bvideinali esuts dioalyc fir a O~w wlnt~apecrfl POR dd1X EI i zntig 6x2ffisauxp segment #2 OfthCEetriha fowr ts waspa the p~taii~ s~xe of odelng dificuly. Thrmalhydrinili codes ntrlyhv troble (related III ptto ='ma rmermig) . the compactness ofthe water slgasitpsestruJ lredifsra Revised Modeling Technliqusi"~ ~ 1 K tonachiei e nPa CEgTest 1017 wasldo3,tmuidbocnre:ctlYlin tagainst detaile dynamic; modeling of the SR: stal position in cccsdanee with the; test.ata (see Fige 2) Full ofpen stlemn: IO slt inches The ]kresser 81 was simulated sn thetee t -hte a spcrte eoctiesvtends 5, tbeiaugdorsav Dispesal ol oe i eue ftesnl eoit hsoeeu)jnto pin trial-rnm-derivednvave, coefficient (Cv = 48) SD tha fth sem flow viatcbe Majutesft and theIRELAP5=66oth ae iilrpeiu tyiezoeei tinwie n icw oea h chngedndel was spcIeLii si xstt teve area mixing i red the slura Iha model i0iidi used the aCbruptfea chane opio wianhd as wihed p}te SI ffisearo _ flo ratSe m e cce Figures 4 trough 7 show t -- fet o Vayingejuncton Opions an th c The RELAP5 nodlatiraon downsteam oteM RV wisnlro Force,peaks for, seget 111,N3, and #4 1rer0ficeablyklwevtie n i tty optinc isusec The egm nt#2p icepean nodalizationused byjF.IUi Reference A added in the eionlhoh 6x2 diffuser in segmt ahi'ge in higher fir thev-VctYotO a ntgtvep anhd SW3L a thneID sertests Weement ed wagfir atr aboequDe Fi co n against other S/lW tes dat that the sRVinglv eloci h S test loop u~ysfiedtiv prssurized tanks t simuiate the IP efflittsteceMSMSrytmoethteia eryls rntefidtt

=, C .1 re-5 %e; Ij5M M;Cv n nte agh nayiprdbisaouin rtd uy e RheLP vohmmnelethwestbiedaasomitna ini ipulacimen ot fies r nn-evbe 'fteit"ue 'dif topp1imtrrtoofapicniy11 bs iendl nula ft& W premur pid oenvati. A ZtELAPth e tine-dep:il of acobestic ndxsent voini Tefn lwveh smulated otio

.e:lt jet zWfl~ inhigher forcesir segent #2alo #Dd Th aoltdfcethstntobcieoecnertves thde;tanklr e 3aidy ofi~ e the SRV cnl:tepispirc Sbcbvz dng.d52 o:S InX0 prdction analysesz schdul budgetand~t000;0 0i ualydoncft$0; per f it the isdattnion Patdicla as evot~ed to iie:ay ..

aOs. hi 700-.

iopC U ~

~ r.inmatnldS Except fir SBG the  : - peak ia  : 600 I

vss ts dt i,

flun Iq*dI IfevL Irh ae it nsis th mat&AOb.'nmw w~ --= 100p lime 3SRV o:f the calculaed ValvetemDnparisont;00 (SecOnds)

Outlet pressure { R T-8 nifficiutto disprs the slg n ule Time(Scods

eflxwa rsue(TO 00:Figure Figure 3 showsin 2MoeigVleSmDyacSRFVr

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 26 of 34 P;udctb gle velocity sinf: jmcOpion as ahwan ta if tfheicmho8n.

used. il s ppg

PREPREF and REFORC Post-Processors (by..

VectraTchnologIes) vsegments juncms. the SRceayhBcgnlcbark =l fov.peitdr ci. 3A wc p-processug well away unthe Bnak3 s fraegmen4s #3 ad4 PEPRE VUc3AanRER

7) dxw atjoicious use of te t-vee t6 devep e nfi (Figue sincant iduoc t ua hs d s tyF p ' REAP5 hc d:fixi=S.

8:4i =_ - .- = 00 = l m anfor xsw was do loped to hel-: g tbis daeaiacts the iSwv &cgexnedxi. mifly.

• 0Thethe9 RV awayfle 511owingllel Sr aplyIgR[P~ftvOD i&iUSr00E CJ-c) reds te REIFagina kdu;sstr;f temainpiug~p loas

.EPPRF V; Rm05 j-iAS' arnd volumes. :PPREFROFmten

• 0D)fe,Us D~theDJmmsogtnwu z0Swtion cen0XyS:t d epXtiall Meads tlhe RELAP S es:aoIle and qi:acts time-depat h

.eoXii-ii00003f00-00000ft00:00020000:0200; X.

&RUCW rcch J:toSo f000t _

lcvd MA-trownz iorqMalvtis of -A .ft emow zin5 Sr= tase t 9i-t -- fSh i SR et U:rocesms tsdt and ti for m suitAl f;Q;t S

ff~ftU~

• eneoff f0d;siftzif:$ft-:ftii~~ cont~ :iufftiax V ibnpr itfi~;:0 ft a ~ 0 e ;f beC S RV fimOp:;d cnt the mainngdwnsbamjwvtcs. RF *1 9¶RAm~E.Q ~S)allows the alstodfergos of the RELAPS model v x~4j lscieauhtob aluae.F heanalysis of the CE SRY testloq model,wuve (UMasie accraio) form w=s calculated Sr each of thebuxr pipe stueg -ments.hese d #te id xia fluid Fo avGied ito net RELAO5

- _Ofy  : :_ 2VELOCITYL .ELA: RP E IT RLAP5VELTIY 8.0  :-Hda 40.0- aran Xdl4-6z0- _Fft;. .;XSf i+_e it0D'in jfrs f iw , th tv Owa 4o 20-.0 2

0.0 UU-L2I 0 C*LL.~

Time Secons) lMe (SetonciS Figure6- Seg:ment#3Calculated Force figure -Segment ti Calculated Force VD2.0 -7i. t 21 21.X t::y02.02 000 22.1:zn) i022.2 0S922.3 0 21.60 . 219 22.f0 .22. 2421.90 .X f22 Z3

.0  :  :

.0~ :15 U-

-40.0 22.0 22.2 :22.3 218 219 220 L 22. L. 222

. .8L 21 .9 L22-1 Tie(Scnds~) Time cns Fiure 7- Segment #4Calculae" oc Figure 5 -Segment #2 Calculated Forte

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 27 of 34 Elastic Piping Analysis Computer Program (X-direcion) supports for Segment 3 'wrei modeled as a single support along the pipe ceritalie, with twice vertical the stifflicss of the support& The 1 singlc intcrrndia suppcrt cn

~:Fcr this evaluation, a linen elastic. piping analysis computer pxogram .

- Frtiswaunaxamca~gaalsscnptt~gar irdividual.

j wasr a d uc toeaP n a an roiiwty C Segmentt 3 vwaslocated per Figure 2-3 of Reforence 3. The two S a auflueh the isSUc p t selc d verticil supports for Segment 4 v.Ae modeled as shown an Figure 3-8

• S is it canprdivc C Q progrm for the lastic . of Refcrnce 2 (in the Y-Zplane. The stilrhess values of Table I sed fr all support.

stmctual analyssand code ctmpliance verification of pipung

systes. It:plaes particular emphasis on nuclear power piping -.-.  :

designed to mect the rqur tof the ASUE Boiler and Pressure The Safey Relief Valve matl was 900 lbs, with a center of gravity Vessel Code, Section IIl. for Class l. 2 or 3 nuear pipinglet, and SW-2 and SW-3 at The prgramnused in this evaluation has the following major fcatures: 3450 lbs each along the centerline of the pipe, per Refernce 3.

i --..- E0.iated masse associated with the grayock fittings re input per

- -p.c.

• ion and plot of system geometry, dynamic the model geomety at their individual node points.

propes and Th-tory anaysis in'individual orsingle coputer runs.

'Determlnation of-Dynamic Propeties, Incuding Analysis Methods'

• 'toatic-enratin ofsuplemetal asspoins r -aic evaluations 'wre performe for this analysis. The pr requed ynwnic c

• Direct Integration Force Trme Ilistory (Dfli) method used as For p n a Bo Modal Superpoasition and Direct Integration the beichma medhod of alyrsis.

Modo .de Force Tine History. also Force Tame-History Analis. s seted in the

. - ld . a - :- . -. - .perfwmcde A discussion of the two methods..........-

swnmarics, - olwfgs - - .

• ePp support toads r~p 'andt displacemtnt rollowing paragraphs.

including time dependent reactions as a frnction of Mode-by-Mode Analysis Technque tune.

More detils of this specific cemputer prgnm are available u. Forithe MMTH optica. the alysisis carried out sing the mo

Reerencshapes a-d fimqu-cies detcrmined in the dynamic properties phase.

Becaus-e- only a limited nmiber of modes are considered (up to 2501 - -high frOequency rwire resporses included byr ing Elastic Piping Model of CE Test Facility  : :d lo &aotcatisothatupto250pipebindgmod The CE Test Facility model s doxuzeed in Rcference 2 is used w~usld be resolved.o ts This zaodalizatioc us WHS used to insure a ann accurate add for the structimal modeL The moderately simple structusal model is - dm-poh' (as ai paten vd c a b ad n may be~jl~ 'ton an based an actual piping sections, distr~bued and cMaente SeSC idvh b~sd iprmg, ad dsmoebs.(as; a patcent d critical) studta'damping c,,,

due to fanes and valves, actua jxe c and realistic d mode b:

support stiffiacs vahus (shown in Table I below fimmReference 3). A 0.001 second integration time step wa used, which matched the No attempt was made to dplicate the complex, non-linear stnrtural tanc step cmftin i the RELAP5/MOD3 time history filc.'This mnodels-used in Referee2 cr3.cnand funion fle ontain fore-time o lit hisory pairs fiom 0.0 to mreforng had identical damping 1.0 seconds. All modes wihin a single n

.v'1alues of 1% or 10% (.01 & 10) of crkiical damping. This resuted Table I1-nAnalyzed Support Stiffness (Ibin) 4.:in a co~nstant, CaM damping curv ovrtentire freueny range of Pipe Scgbment Support SupportStiffness int-r: s.-t:

-Nurber - Direction

-:: - . : .X - .::.6.00ev07..::.-:.-.:.:-::--: - " Damping

.1% - . 10% Damping 2 NLY 1.50e+06 (em.)-. .

3 - X - 7.50I0 -

i4o2S _I _ g _ + _

-:  :-I.::-

_ __ _ 3. .... . 10.00e+N ..

-004- . .s-_ _ _

4 INCLY. 5.0e5(ea) -I - I I . I

.1d .

r Intermnedie Y support only, coleutalld loads were eakud drawings(Fi A-I tough A-17 of . ."_ - T The individual spool p Refrnce 2 and Figure 2-3 of Refcrenoe 3)'wre nodoled and - .--

0.10 coted to match the 101test series gemety, with the gWA X ....i-l A I I axis in the direction of valve dischaWe the global Y axis vertically. -- l---- - --- +---

upward, and theglobal Z axis defined by the right hand rule. For ! I siUplicity thc modcl was anchored at the Safety Relief Valve inlet, . 0.00 -

with a support stifiness representative of the structure in the X 0 50 75 100 125 dirctio and -rigid" (L.OE+]3 lb'in) Y aind Z stiffix= in the other two global diretions. Frequency (Hz)

Both supports on the vertical Segment 2 run were modeled as shown Figure 8 - DITH Damping on Figure 3-7 of Reference 2 (in the Y-Z plane) The pair of axial Y-

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 28 of 34

Dlirct: Integration AnalysTechnilque Taie 40ed UPIU qiirimwihot 1tdyamc ncupin intohid Aayi apn yai

~t~~iskles opt cxi, there fzeoii 006ngmdampw muom ~uc ate :Cd suftema Sthe (Alpha) anMtflis bta4r rtcm ValUes Thijstoa 2 Dii 0ANA.

ftpf W ig= g9shows the: __ ~ff4.1 S The DM1 ehdas uses & .001 scon kktvely damp Mion Atep . 51 er geertedtht dd ot Damingazws fth high6&I low aiqund ge Th apn aua~ na noSRin Ea DamigVau t rqenyIad apn Value~ 2a The agencti smlrf heSget2troug4 ASrul.

0 Frqecy2TevleuedagimeinT bei... Teenen2lasaeti3 /.Teemn~n4lads&

overetimaed &aoot jr

[___ Table 2. DMN7 7am77n7. ~ rl u oteoe~oa~tieASrslsfti emn

_____ 1 ~ ~I Ta~e4-vAnalysls Resutst Summary___

10Ag..6 20 01 00 Case Max ioad Mvai:~a MaxLoadMaod R~t i evluatng k odse lampng alue i~*oiaiic I 8.1 642 2.9 19.

VWeeaeeasl~oic 3 2 97 7. 19.4 The firt t of.vaue rqetS thi loV& bound.damping eaSe,4 8. 7 73 macigterange oausofRefertene 4. Here, th avekw budVale is 1% ad fth 34001k avC~terage (ov~er the rane o sinilcnmos~sIA..6 7.6 88.5 652 1.

Thapn eod etrpeetstehg dapig carrag 1 CE-lol0? 9.3 4126 8.

o nine that "Th stxtxegeclY displayed a ZRfrne DAGS 185 5 0.--07 aa ideaI'Intiidaoersl owr ouiari ofMadMh&30 boudnd validating tthedindalbizw:atio and dynamic pmpcfiefse= uin h AsececeteapnghdltteefCan h magitude of thle Analysis Rjestlts; Test DaavskELA5IOD3 epneo u ppn emn i

and Elastic Piping AmaVsi! Combination lh The iHand threb fleautos= etxe a h iehsoiso h upr reactions~fir eadh stegimnat ar summaized inTal 3. Tabl I vale of ppcxt At swee"rd ii Fgrs9 hog 16 o h blwn ae rw ae1 fh sd n1&t odcss iws9trug 2aefrAnyi fo allkbu ae3 hr n-afte al Tabl 4 povids ~~ausfr a abultionof an deal he Sgmen 1,23 an 4 lad hstoies, repctvly h RenreCe= 3)ath detiedTonrlinearU 1)AGS 1017 TeFSe*eWt=,3Si 4 repetivey.he shapes ofjthein!sar 4

In llbutth fIrt scg anith acuae oasaebewe& faco eoiyoto o ucin ptem o h eodebw of1. t

.0moecosevaie ha heCE117reore tstvlus. dontramo te R. hedealttw-elciy pio wsusd i thaetetEalem 017Tet

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 29 of 34 conc usionlS HERolslons die:0000000 \00 Cbudn902000;kicc Saet 00 0-f02 with thieof.-

CE0170000- -i0 exce-ption oothe~lirs3ctnsgnt;,vwheredifii~e Wer I5 A00-$j0 0of to oTe result lds calculatd= A Athg+30%

A

.- Valvei Ts Loo Valv Fat Tet (Jo T:t.1017) ~U l~~fc122&

L~upFaciity(f~Tcs101) j $firod ~lj: 0;s:

G comparison of these resuts to th detiailed, noi-ineaDAGS results evahafixi ued he dehktwo-velocity mncawnentu, qse pin ~ smlrcreain.Ibuh rdcigteata rorm odeeo time-dpnet i~Cte~ncma ecix hpswr esimilartooh ofte HPSMg) tant The riultse that IELAPSMO canbe wed in concert used in an eastiic piping alYsi miod to estimatethe e structural Tbhese calculat ds vem then cpd to with: suitable potrocessot r (such as. P the Values from flie iginal 1981 CE 1017 Test. and dynamic stctul is code -aab of thyg Didsove:force-time bistoyInt(sc sSPRIEtoensufl rtp eppg modc strfessfifiles dlpuagapo load andO&

strureswith gap oe aiodeingef0exts. The model pitiigii cn_ i coungu 0y generally predictdin cmervativemiaxmutn lcoads (by *a

-IEASSPRPP . ETs 107Dta: - EASU PIPE.CETOAtlIl7Oatal O 4 - - .

0 40 -0 20.G 4~

oco

.00 t0 2 2-t ' * '01! ';* *1t lXi0j $0 CiU) -2. 4 j1. - -;t7t

22. 221 22.2 22tA 22 2t. 22.0 2.1 22 2.

21.6 :21S Figure 9 -9Segent #1 Loadi % Damngih' Fi 11S- e L Damng 1%oo

- RISUPERPIPE.

E EACEETest101:7Doa. CEostlO 7Data

-_RELAtSPERPIPE.

.0 -

20.0 4 4..10.0 -

-2'0.077 -)-- a t _ L__ _: -

80 .0 .

-4 .. ~**

000 21.9 22.1 2.2 22.3 21.8 21.90 0 22.1 222 2 2.3 21 .8 220 Time (Seends~ me (Seconds)

FIgure 10- Segment #2 Load, 1% Damping Figure 12:- Segment #4 Load, 1% Dampng0

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 30 of 34

-0 0RELApSSUPERPIP . CE Test 1017 Dta- S

_ 4:: 10D --- if li 00.0 _ i-T0 s3 44 a'2-0 0ll!Ole:

Ei0t-10.'00 -----  ; ~t00-

-+--I t:+i0:. .ft E 0 I

2. 21.9 22. 022.1 228. 23 21.6 210. 22.0 27. 22. 22.37 000 Figure 13- Segment9 I Load 10% Dampin g$.000 0 FIgure 15 - Segmnt #3 Loa, 1^0%DampIng 0$t v 4.

.... S40 -) 'f .0-aua In I3 I0 I

-aure 131!Simelg; 1 in F DaI-- I -- F1-0.

-60.0 - i.... .1 0+-- ....... ..

22. 2.10 2.I.-0.~

21. 2.921.8 21* 22.0 22 22.1 2.

Th~e (Secods) ... ~Ime(Scn)

F1gure'I1-ement #2 Load 10% Darpin FuRe418~-S egmen U4 Load 10% Damping This ppqxrdocumcwts I ili1. t ~ tP-77-,,Voemcsutsfy

-weP 3ATs

S Vave WMoe 317, Iiteri Revort Fe aati s to sft rdieicir osadi V 19n3.g 4.Reglatoy Gud .1 Dmpini Values for Seismic Design L:SUPE, SIPERPE .Usof=Nuclar P;Owr Plants", October 1973.

VAX/BMMVersioz dated 5l3:1/90. ;0fffff0.: 5 N R-5535, Vol S. RELAP/MOD3 Code Manual,

2. NP2479 (Reseh Prject V102-28). :Application of' User's Guii", R4, ;h 1992.

RELAP5/MODI for Calculationof Safety and Relief Valve: 6. EPRI NP-2770-, -Volm 10: Structural Results for Discharge Piping Hyodynmic Lds" Final Report, Drer SafetyValve Model 31739A, lnterim Report", March December 1982 193.2

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 31 of 34

-S PRING HANGER 1 m1ir-SIIV TEST VALVE

-'FIRST DISCH. ELBOW'.

8'SCH. 160

., .' a. 6 OR Be SCH. 4

. . . 1 SPR ING HANGER 12' SCH. 80

'- -FIRS ELB

'TSHIR 'EB' H.  :.'

'SECOND DISCH. :ELBOW SPRING -HANGER RUPTURE DISK lR , e , '. ':'it Layout

t. 4 Lay

.- . . . . SRV Test Fclt

-- - CE

cp~0 >0 0 )a; (MD6 00) c 4h. 0 CD Co)

IAFITY:

PM~

U0J 10 Nr "meicift VAL MtJIW GAT

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 33 of 34 Inital Configuration - System aligned with SW system Water Hammer Condition - Occurs after LOOP event when SW booster pumps are re-started.

PHASE 1 - LOOP occurs causing SW booster pumps to de-energize.

PHASE 2 - Column of fluid gravity drains down to SW pond causing vacuum void formation PHASE 3 - After 41.5 seconds, SW booster pumps re-energized causing vacuum void to collapse and resulting water hammer Vacuum Void

- Collapses upon pump restart SW Booster Pump De-energized due to LOOP I3106A 3103A 3107A IC Supply IC Return FIGURE 2 To SW Pond

Document Control Desk Attachment C-02-3455 RC-05-0204 Page 34 of 34 Inital Configuration - System aligned with SW system WATER HAMMER MITIGATION - Mod to install:

1. vacuum relief valve downstream of 31 07A

2. replace 31 07A with an air operated butterfly valve that fast closes upon de-energize of SWBP

3. delay opening of valve 3107A for five seconds after start of SWBP PHASE 1 - LOOP occurs causing SW booster pumps to de-energize.

PHASE 2 - Valve 3107A fast closes in 7 seconds and traps column of fluid above it PHASE 3 - Void formed below 31 07A is filled with water by vacuum relief valves PHASE 4 - After 41.5 seconds, SW booster pumps re-energized, 31 07A valve 5 sec delayed opening allows fluid flow momentum to bulld preventing further void formation PHASE 5 - air void downstream 31 07A flushed to SW pond 3106A SW Booster Pump De-energized due to LOOP I ICSupply D C Vacuum relief valve FIGURE 3 replaces vacuum void To SW Pond with air