ML20153A968
| ML20153A968 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 09/15/1998 |
| From: | Hughey W ENTERGY OPERATIONS, INC. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-96-06, GL-96-6, GNRO-98-00073, GNRO-98-73, TAC-M96815, NUDOCS 9809220251 | |
| Download: ML20153A968 (12) | |
Text
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e-I e, O Enttrgy optrations,Inc. I h P.O. Box 756 Port Gibson, MS 39150 Tel 601437-6470 W.K.Hughey
- . Drector
.N Sh+y & ReguaWy September 15,1998 United States Nuclear Regulatory Commission Mail Stop P1-37 Washington, DC 20555-0001 Attn: Document Control Desk
Subject:
Grand Gulf Nuclear Station ;
Unit 1 Docket No. 50-416 License No. NPF-29 Entergy Operations, Inc.
Response to Request for Additional Information Related to GL 96-06 for Grand Gulf Nuclear Station, Unit 1 (TAC No. M96815)
Ref: Letter GNRO-97/00011, " Required 120 Day Response to NRC Generic Letter 96-06," dated January 28,1997 GNRO-98/00073 Ladies and Gentlemen:
In a letter dated April 27,1998, the NRC requested Entergy Operations, Inc. (Entergy) to provide additional information conceming water hammer and two-phase flow issues related to NRC Generic Letter 96-06, " Assurance of Equipment Operability and Containment integrity During Design-Basis Accident Conditions." Entergy's response to your questions is contained in the attachment to thit etter.
If you have any questions, please contact Wayne Russell (601-437-2717).
Yours truly, WKH/GHD l attachment cc: (see next page) 1 9909220251 980915 ?
l . GNRO-98/00073 Att: chm:nt l Page 2 of 3 cc:
- Ms. J. L. Dixon-Herrity, GGNS Senior Resident (w/a)
Mr. L. J. Smith (Wise Carter) (w/a)
- Mr. N. S. Reynolds (w/a) ;
Mr. H. L. Thomas (w/o) l l Mr. E. W. Merschoff (w/a)
Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 400 {
Arlington, TX 76011 Mr. J. N. Donohew, Project Manager (w/2)
Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop 13H3 Washington, DC 20555 l L
i-b l
GNRO-98/00073
% Att: chm::nt Page 1 of 10.
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION I RELATED TO NRC GENERIC LETTER 96-06 I l
in a letter to the NRC dated January 28,1997 (Letter # GNRO-97/00011), Entergy responded to Generic Letter (GL) 96-06, " Assurance of Equipment Operability and Containment integrity During Design-Basis Accident Conditions," for the Grand Gulf Nuclear Station. In a letter dated i April 27,1998, the NRC requested Grand Gulf to provide additional information concerning water hammer and two-phase flow issues related to GL 96-06. Entergy's response to your questions is provided below. A general plant description and discussion of design features for I Grand Gulf is also included.
General Plant Description and Design Features Grand Gulf's primary containment is a General Electric Mark lli design utilizing a drywell structure inside primary containment. The function of primary containment is to isolate and contain fissior, products released from the reactor primary system following a design basis accident (DBA) and to confine the postulated release of radioactive material to within acceptable limits. The function of the drywellis to maintain a pressure boundary that channels steam resulting from a Loss-of-Coolant Accident (LOCA) to the suppression pool, where it is condensed. See Figure 1 for a simplified layout of the Containment Building.
Grand Gulf's design utilizes a safety-related containment spray mode of the Residual Heat I Removal system (RHR) for cooling the containment area following a DBA LOCA. Also as part of plant design, Grand Gulf has two non-safety-related systems which are available to cool the drywell and primary containment areas during normal operation: (1) the Drywell Cooling system, and (2) the Containment Cooling system. Each of these systems is comprised of fan / coil unit coolers with a cooling water supply. The cooling water sources for the Drywell Coolers and Containment Coolers are the Drywell Chilled Water system (DCW) and the Plant Chilled Water system (PCW), respectively. PCW piping to/from the Containment Coolers penetrates only primary containment while the DCW piping to/from the Drywell Coolers penetrates both primary containment and drywell.
As discussed in the letter GNRO-97/00011, neither the Drywell Coolers nor the Containment Coolers are required nor credited for accident mitigation. The only safety function associated with PCW is primary containment isolation. By the same token, the only safety functions for DCW are to provide primary containment isolation and drywell isolation.
To meet primary containment isolation requirements of General Design Criterion (GDC) 56, each PCW and DCW primary containment penetration utilizes two containment isolation valves.
- in addition to primary containment isolation, each DCW drywell penetration utilizes two drywell
! isolation valves. The systems use a combination of safety-related motor-operated valves (MOVs) and check valves that are Safety Class 2, Seismic Category 1. The MOVs automatically isolate on a LOCA/ primary containment isolation signal. Also, the containment isolation valves are leak tested per the requirements of 10CFR50, Appendix J, " Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors." Penetration piping is Safety Class 2, Seismic Category I fabricated and installed in accordance with ASME Section Ill. The remaining piping and components are seismic II/l. This piping is fabricated and installed in accordance l
RO-98/00073 r iachm:nt l l Page 2 of 10 '
l l with ANSI B31.1, " Code for Pressure Piping." The Safety Class 2 and ANSI B31.1 piping are
- l. rated for 200 psig at 125 F.
Question 1 I I
l "Although existing procedures do not specify use of the containment coolers for accident )
l mitigation, operators may decide to use these coolers as an option for accident mitigation l purposes. Describe the measures that exist or that will be taken to assure tnat cooling water for i the containment coolers will remain isolated following a plant accident."
l
Response
Containment Coolers and Plant Chilled Water System ,
l In the case of the Containment Coolers and PCW, there is no design feature to allow operators l to defoot or bypass a primary containment isolation signal. Bypassing the PCW primary containment isolation signalis not authorized in the Grand Gulf Emergency Operating l
Procedures (EOPs). [Such operation would be initiated only by invoking 10CFR50.54(x). )
10CFR50.54(x) allows reasonable action that departs from a license condition or technical l specification in an emergency when action is immediately needed to protect the public health l and safety and no action consistent with license conditions and technical specifications can provide adequate or equivalent protection.) Therefore, the Containment Coolers and associated
! PCW piping are not susceptible to the water hammer and two-phase flow events discussed in GL 96-06 since they remain isolated following initiation of a DBA.
Drywell Coolers and Drywell Chilled Water System Unlike the Containment Coolers, the EOPs provide guidance to defeat primary containment and drywell isolation interlocks in order to operate the Drywell Coolers during certain post-accident conditions. This guidance is provided to reflect the generic BWR Owners Group Emergency ;
Procedure Guidelines, which have been previously approved for industry use by the NRC. '
As discussed above, primary containment and drywell penetrations of DCW are Safety Class 2, Seismic Category I utilizing isolation valves per GDC 56. Penetration piping is fabricated and installed in accordance with ASME Section Ill. Other portions of DCW whose failure could affect safety-related equipment were seismically analyzed and supported, as necessary, to prevent collapse on safety-related equipment. Otherwise, DCW piping and components are classified as seismic il/l. DCW piping, except for penetration piping, is fabricated and installed in accordance with ANSI B31.1," Code for Pressure Piping."
Because of their robust design, Entergy would not expect the drywell and primary containment l ' penetrations to be damaged by a water hammer, even though the ANSI B31.1 piping and
, components may fail. For further discussion on the expected effects of water hammer on DCW piping, see Section IV, Effects of Water Hammer on DCW Piping of the ENGINEERING EVALUATION FOR DRYWELL COOLING. (See the response to Questions 2 through 5).
l l Questions 2 through 5:
L
GNRO'-98/00073 L '- Attrchmint
[ Page 3 of 10 p
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Questions 2 through 5 relate to water hammer and two-phase flow analyses performed per . !
l '
NUREG/CR-5220 " Diagnosis of Condensation-Induced Waterhammer," or other methodology.
Response
Entergy has not performed an exhaustive water hammer and two-phase flow analysis as prescribed in NUREG/CR-5220. Rather, Entergy has performed an engineering evaluation ,
t which addresses the current design of the DCW piping (e.g., seismic, safety class, etc.), and the ;
l . effect of water hammer. Instead of responding to Questions 2 through 5 individually, the evaluation is provided below.
ENGINEERING EVALUATION FOR DRYWELL COOLING
- l. DCW System Response to LOCA Conditions i 1
in order for a water hammer to occur, voids must be present in the process fluid, as discussed in Section I, Water Hammer Phenomena. Two factors must exist sequentially to support void formation in the drywell portion of the DCW piping: (1) loss of water mass followed by (2) a decrease in water temperature. I I e Loss of Mass in order to realize a loss of mass, the most likely situation would be a drywell cooler relief valve lifting to expel water from the isolated piping section. This action would be caused by either a spurious lift or by increasing pressure in the piping to the relief valve setpoint.
If exposed to high drywell temperatures for an extended period of time, pressure in the piping could increase to the relief valve setpoint.
. Decrease in Water Temperature Once a loss of mass has been realized, there must be a decrease in water temperature in the isolated piping section to support void formation. The decrease in water temperature would correspond to a decrease in drywell temperature. With a loss of _j mass and decreasing temperature, small amounts of water in the piping would flash to steam in order to reach equilibrium.
Entergy has evaluated the response of DCW to LOCA conditions, as reflected in FSAR accident analyses, for the presence of these two factors. The LOCA conditions evaluated were those resulting from a recirculation line break, a main steam line break, and a small steam line break. Each is discussed below. (Please note - all times given are approximate.)
. Small Steam Line Break f
t
_.~.
- GNRO-98/00073 l -
Attachm:nt Page 4 of 10 l
Upon initiation of a small steam line break, drywell and containment pressures peak in 13 minutes.' The drywell pressure coincides with an enveloping drywell temperature of 330*F, which is maintained for 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.2 Drywell temperature then decreases slightly to 310'F, which is maintained for another 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.
The EOP directs operators to restore DCW if drywell temperatures cannot be maintained below 135 F. If DCW is not returned to service immediately following an accident, a 30 minute restoration time period is assumed.' Under these conditions the piping sees a limited temperature increase and the contained water in the DCW piping heats up and attempts to expand. This expansion would increase piping pressure Since the DCW isolation valves are closed, the increased pressure creates a condition where relief valves on the drywell coolers are expected to lift. In order to form voids in the DCW piping, the temperature of the water in the piping must decrease. There is no mechanism available to cool the drywell; therefore, water temperatures will remain mostly unchanged and no voids are expected to form in the piping. Since no voids form no waterhammer is expected to occur.
. Recirculation Line Break Upon initiation of a recirculation line break, drywell temperature immediately rises, peaking at 240*F in 1.09 seconds.8 Drywell temperature remains at 240*F for no more than 100 seconds at which time it begins decreasing, reaching 200'F 110 seconds following event initiation.8 The total time DCW piping is exposed to high drywell temperatures is less than 120 seconds. This short time period does not support adequate heating of the water in the DCW piping to lift a drywell cooler relief valve. With no loss of mass, water hammer is not expected to occur if DCW is returned to service immediately following a recirculation line break.
If DCW is not returned to service immediately following an accident, a 30 minute restoration time period is assumed. Under these conditions the piping sees a limited temperature increase and the contained water in the DCW piping heats up and attempts to expand. This expansion would increase piping pressure . Since the DCW isolation valves are closed, the increased pressure creates a condition where relief valves on the drywell coolers are expected to lift. In order to form voids in the DCW piping, the temperature of the water in the piping must decrease. There is no mechanism available to cool the drywell; therefore, water temperatures will remain mostly unchanged and no
' FSAR Figure 6.2-24
' FSAR Table 3.11-3 8
lbid.
d i ANSI /ANS 58.8-1984,
- Time Response Design Criteria for Safety-Related Operator Actions"
- FSAR Figure 6.2 3
GNRO 98/00073 Attachmsnt Page 5 of 10 voids are expected to form in the piping. Since no voids form no waterhammer is expected to occur.
. ' Main Steam Line Break Upon initiation of a main steam line break, drywell temperature peaks at 330*F in 1.09 l seconds.7 Drywell temperature then decreases to 240*F within 5-10 seconds and continues decreasing reaching 200*F 120 seconds following event initiation.s The total time DCW piping is exposed to high drywell temperatures is less than 120 seconds. As with the recirculation line break discussed above, this short time period does not support !
adequate heating of the water in the DCW piping to lift a drywell cooler relief valve. With l no loss of mass, water hammer is not expected to occur if DCW is returned to service immediately following a main steam line break, if DCWis not returned to service immediately following an accident, a 30 minute restoration time period is assumed. Under these conditions the piping sees a li nited !
temperature increase and the contained water in the DCW piping heats up and attempts to expand. This expansion would increase piping pressure . Since the DCW isolation valves are closed, the increased pressure creates a condition where relief valves on the drywell coolers are expected to lift. In order to form voids in the DCW piping, the temperature of the water in the piping must decrease. There is no mechanism available to cool the drywell; therefore, water temperatures will remain mostly unchanged and no voids are expected to form in the piping. Since no voids form no waterhammer is expected to occur.
II. Effects of Water Hammer on DCW Piping DCW drywell and primary containment penetration piping and valves are safety-related, Seismic Category 1, Safety Class 2 fabricated and installed in accordance with ASME Section Ill. The remaining piping and components are non-safety-related fabricated and installed per ANSI B31.1. The Safety Class 2 piping and valves receive rigorous analyses (e.g., seismic, high-energy line break and pipe whip, proximity interactions, etc.). Based on the results of these analyses, additional design measures are taken to ensure the components are capable of performing their safety function.
The containment isolation valves are simple gate and check valves designed with straight-through flow paths (i.e., the process fluid is not subjected to a tortuous path while traveling through the valve). Therefore, no water hammer is expected to originate in the valves.
In the extremely unlikely event a water hammer did occur the resulting shock wave is expected to travel through the system. No damage to the drywell and primary containment i penetration piping and valves is expected due to the robust nature of their design, 7
FSAR Table 6.2-5 and FSAR Figure 6.2-11
- FSAR Figure 6.2-11
t l l l
. 1 GNRO-98/00073 Attachm:nt l Page 6 of 10 l fabrication, and installation. The piping inside the containment and drywell has been l supported to withstand seismic and hydrodynamic loadings to preclude seismic II/I type failures. The supports are robust; therefore, the piping system has an inherent capability to l withstand unanticipated dynamic loading of the type that may be caused by a water hammer
- shock wave.
Question 6:
l "The January 28,1997 letter response indicated that if the chilled water system should fail i during a water hammer event, the loss of chilled water inventory would cause the chilled water pumps to trip and annunciate in the control room. Discuss the reliability of the annunciation that is being referred to and assurances that exist that this annunciation will occur as expected (power supplies, quality classification, redundancy, periodic calibration and testing, failure modes, etc.). Also, discuss what effects the chilled water inventory will have on the accident analysis and drywell performance as previously analyzed."
Response
Two non-safety related annunciators exist which alert control room operators of a problem with DCW in containment: (1) DRWL CHILL WTR IN-CTMT, and (2) DRWL CHLD WTR PMP :
DISCH FLO LO.
The DRWL CHILL WTR IN-CTMT TROUBLE annunciator alarms on decreasing DCW heMer pressure inside containment monitored by a pressure sensing instrument loop. The pressure transmitter loop is powered by ESF Division 2 power, the transmitter is QF3 functional class, and the transmitter is environmentally sealed and qualified. This instrumentation loop is calibrated on an 18-month frequency.
The DRWL CHLD WTR PMP DISCH FLO LO annunciator alarms on loss of DCW pump flow monitored by a paddle-type flow switch located at the pump discharge. This type of flow switch requires no calibration and has proven to be highly reliable in this application.
Upon receiving either annunciator, the operator evaluates the cause of the alarm and is instructed by the associated alarm response instructions to close the drywell and primary containment isolation valves. The annunciator system is periodically tested once every shift.
DCW is classified as a " trip-sensitive system" meaning upon loss of the system the plant may be placed into a condition requiring imminent shutdown (in this case elevated drywell temperature).
Because of this situation, operations personnel maintain constant vigilance over the system.
- Any changes in system operation are quickly noted and corrected, as necessary.
The annunciators associated with DCW are powered from the non-safety-related 125 VDC j System. The 125 VDC System is also classified as a " trip-sensitive system" and is maintained
! accordingly. Pilot cells of each battery are tested monthly while a complete battery test is performed once every 3 months. Entergy personnel reviewed maintenance and test records of l the system and condition reports, which are used to document problems in the plant. No l condition that would adversely impact system operation was identified. Therefore, this review
GNRO-98/00073 1 Att: chm:nt l
- Page 7 of 10 l i l provided evidence that the 125 VDC System is highly reliable and would be expected to function if called upon.
L The suppression pool contains approximately 1,000,000 gallons of water. In the improbable event of a DCW pipe rupture, the amount of volume added to the pool would be extremely small compared to the total volume of the pool. Since DCW is isolated during a DBA and is not credited to mitigate an accident, there is no impact on DBA analysis or drywell performance as i previously analyzed.
Question 7:
)
Provide a simplified diagram of the system, showing major components, active components, relative elevations, lengths of piping runs, and the location of any orifices and flow restrictions. I
Response
Simplified diagrams of DCW and PCW are provided in Figures 2 and 3, respectively.
. Conclusions Entergy believes the water hammer concern expressed in GL 96-06 is not a concern at Grand Gulf as discussed in the preceding sections and summarized in the following points:
- 1. Water hammer is not expected to occur in the DCW system when placing the Drywell Coolers and DCW into service following a LOCA. The two factors needed to support water hammer are not collectively present sequentially during the postulated LOCA events.
- 2. In the unlikely event a water hammer did occur, two annunciators exist that would alert the operator to a problem in the DCW ( see response to Question 6 ). Operations personnel could reestablish primary containment by closing the DCW drywell and primary containment isolation valves.
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l GNRO-98/00073 l
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CONTAINMENT BUl! MING LAYOUT CONTAINMENT STRUCTURE l
l 1,4" STEEL LINER POLAR CRANE f
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s u I s AN UPPER CONTAINMENT POOL 2.5 FT CONCRETE
- A_. _ _
f A T
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_ 1TMPORARY DRYWELL
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i ! I s REACTOR VESSEL .s DRYWELL WALL SHIELD WALL E I E I I VENT ANNULUS
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' 2 REACTOR VESSEL SUPPRESSION :- l - SUPPORT PEDESTAL POOL 'I E ilORIZ 2 VENTS
! p CONTAINMENT
! B ASE MAT FIGURE 1
4 GNRO-98/00073 Att: chm:nt Page 9 of 10 DRYWELL CHILLED WATER SYSTEM DRYWELL BLDG. CONTAINMENT BLDG. AUXILIARY BLDO.
E qp e c(p + :"*lr F125 F126 F12 F122 3 lb Hr HF DRYWELL CHILLED WATER pumps 7 __
STEAM j oRYWELL TVNNEL
{ coolers coottR 3r 1 1 '
h L l F147 F124
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F185 F121
,a 33 37 Valve Designation F121 F122 F123 i F124 F125 F126 F147 F165 I Applicable Design Criteria Note 1 Note 1 Note 1 Note 2 Note 2 Note 2 Note 2 Note 1 Valve Type Gate Gate Gate Gate Gate Gate Check Check Actuation Pnmary Mode Remote Remote Remote Remote Remote Remote Back Back Manual Manual Manual Manual Manual Manual Flow Flow Secondary Mode Manual Manual Manual Manual Manual Manual - -
l Valve Position Normal Open Open Open Open Open Open Open Open l Shutdown Open Open Open Open Open Open Closed Closed Post LOCA Closed Closed Closed Closed Closed Closed Closed Closed Power Failure As is Asis As is Asis Asis Asis - -
Line Size (Inches) Note 3 4 4 4 4 4 4 4 4 Penetration Size (inches) $ 5 5 5 5 5 5 5 Closure Time (seconds) 60 60 60 32 32 32 3-5 3-5 Note 1 - GDC 1,2,4,16,54 and 56, SRP 6.2.4, other defined basis, see FSAR Section 18.1.26 l Note 2 GDC 4,16,50, and 53, SRP 6.2.1.1 C Note 3 "Line Size"is pipe diameter at the isolation valves.
l FIGURE 2
t GNRO-98/00073 Attichm:nt 1
Page 10 of 10 1
PLANT CHILLED WATER SYSTEM
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._ .nes Valve Designation F148 F149 F150 F151 F300 F301 F302 F303 F304 i F305 F306 F307 Applicable Design Note 1 Note 1 Note 1 Note 1 Note 2 Note 2 Note 2 Note 2 Note 2 Note 2 Note 2 Note 2 Criteria Valve Type Gate Gate Gate Check Gate Gate Gate Gate Gate Gate Gate Cate Actuation Pnmary Remote Remote Rernote Back Remote Rernote Rernote Remote Rernote Remote Remote Rernote Mode Manual Manual Manual Flow Manual Manual Manual Manual Manual Manual Manual Manual Secondary Manuel Manual Manual - Manual Manual Manual Manual Manual Manual Manual Manual Mode Valve Normal Open Open Open Open Open Open Open Open Open Open Open Open Position Shutdown Open Open Open Closed Open Open Open Open Open Open Open Open Post Closed Closed Closed Opan or Closed Closed Closed Closed Closed Closed Closed Closed LOCA Closed Power Closed Closed Closed - Closed Closed Closed Closed Closed Closed Closed Closed Failure Line Stre (Inches) 4 4 4 4 2.5 2.5 2.5 2.5 8 8 8 8 Note 2 Penetration Size 5 5 5 5 2.5 2.5 2.5 2.5 8 8 8 8
[ (Inches) l Closure Time (seconds] , 60 60 60 3-5 120 120 120 120 120 120 120 120 Note 1 - GDC 1,2,4,16. 54. ar.d 56. SRP 6.2.4. Other defined basis, see FSAR Secten 18.1.26 Note 2, GDC 4.16. and 43, and SRP 6.2.3 Note 3 "Line Size
- is pipe diameter at the isolation valves.
FIGURE 3