ML24141A251
| ML24141A251 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 05/20/2024 |
| From: | James Holloway Virginia Electric & Power Co (VEPCO) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 24-072A | |
| Download: ML24141A251 (1) | |
Text
VIRGINIA ELECTRIC AND Po,vER Col\\IPANY
RICHMOND, VIRGINIA 23261
May 20, 2024 10 CFR 50.90
U.S. Nuclear Regulatory Commission Serial No.: 24-072A Attention: Document Control Desk NRA/GDM: RO Washington, DC 20555-0001 Docket Nos.: 50-280 50-281 License Nos.: DPR-32 DPR-37
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 PROPOSED LICENSE AMENDMENT REQUEST-RECLASSIFICATION OF LOW HEAD SAFETY INJECTION FLOW INDICATION REGULATORY GUIDE 1.97 VARIABLE -SUPPLEMENTAL INFORMATION
By letter dated August 10, 2023 {ADAMS Accession No. ML23226A186), Virginia Electric and Power Company {Dominion Energy Virginia) submitted a license amendment request (LAR) for Surry Power Station (SPS) Units 1 and 2 to revise the SPS Technical Specifications (TS) to add Low Head Safety Injection (LHSI) flow indication as required accident monitoring instrumentation. The addition of LHSI flow indication to the TS is due to reclassification of the Regulatory Guide (RG) 1.97, Revision 3, "Criteria for Accident Monitoring Instrumentation for Nuclear Power Plants," Type D Category 2 variable to a Type A Category 1 variable. The reclassification of the LHSI flow instrumentation resulted from a reanalysis of the LHSI pumps' net positive suction head (NPSH) requirements that was performed to obtain additional operating margin. The reanalysis identified the need for manual operator action to throttle LHSI pump flow when only a single pump is in operation for a brief period of time under certain operating conditions. This operating scenario identified the commensurate need to reclassify the existing RG 1.97 flow instrumentation and to incorporate the instrumentation into the Accident Monitoring TS.
In support of their review of the LAR, the NRC technical staff conducted a virtual audit of certain, non-docketed Dominion Energy Virginia analysis information with the intent to gain understanding, to verify information, or to identify information to be docketed to support the basis of the licensing or regulatory decision. Dominion Energy Virginia and the NRC review staff discussed the NRC's audit results during April 18 and May 9, 2024, post-audit calls. As an outcome of the audit, Dominion Energy Virginia agreed to provide supplemental information further describing the LHSI NPSH analysis in support of the NRC review of the LAR. The supplemental information is provided in the attachment.
Serial No. 24-072A Docket Nos. 50-280/281 Page 2 of 3
If you should have any questions regarding this submittal, please contact Mr. Gary D.
Miller at (804) 273-2771.
Respectfully, y-
James E. Holloway Vice President - Nuclear Engineering and Fleet Support
Attachment:
Supplemental Information Associated with LHSI Pump NPSH Margin Analysis
Commitments contained in this correspondence: None
COMMONWEAL TH OF VIRGINIA )
)
COUNTY OF HENRICO )
The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mr. James E. Holloway, who is Vice President - Nuclear Engineering and Fleet Support, of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me this 1o+'n day of /\\1\\o..'{, 2024.
My Commission Expires: :fa.n w av-'/ 3 11 1..0 28.
KATHRYN HILL BARRET NOTARY PUBLIC COMMONWEALTH OF VIRGINIA MY COMMISSION EXPIRES JANUARY 31, 2021 otary Public Serial No. 24-072A Docket Nos. 50-280/281 Page 3 of 3
cc: U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303-1257
NRC Senior Resident Inspector Surry Power Station
Mr. L. John Klos NRC Project Manager - Surry U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, MD 20852-2738
Mr. G. Edward Miller NRC Senior Project Manager-North Anna U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, MD 20852-2738
State Health Commissioner Virginia Department of Health James Madison Building - 7th floor 109 Governor Street Suite 730 Richmond, VA 23219 Serial No. 24-072A Docket Nos. 50-280/281
Attachment
SUPPLEMENTAL INFORMATION ASSOCIATED WITH LHSI PUMP NPSH MARGIN ANALYSIS
LICENSE AMENDMENT REQUEST - ADDITION OF LOW HEAD SAFETY INJECTION FLOW INSTRUMENTATION TO RG 1.97 INSTRUMENTATION TABLE
Virginia Electric and Power Company (Dominion Energy Virginia)
Surry Power Station Units 1 and 2 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
SUPPLEMENTAL INFORMATION ASSOCIAT E D WITH LHSI PUMP NP SH MARGIN ANALYSIS
LICENSE A ME NDMENT R EQU EST - ADDITION O F LOW HEAD SAFETY INJECTION FLOW INSTRUM E NTATION TO RG 1.97 INSTRUMENTATION TA B LE
SURRY POWER STATION UNITS 1 AND 2
BACKGROUND:
By letter dated August 10, 2023 (ADAMS Accession No. ML23226A186), Virginia Electric and Power Company (Dominion Energy Virginia) submitted a license amendment request (LAR) for Surry Power Station (SPS) Units 1 and 2 to revise the SPS Technical Specifications (TS) to add Low Head Safety Injection (LHSI) flow indication as required accident monitoring instrumentation. The addition of LHSI flow indication to the TS is due to reclassification of the Regulatory Guide (RG) 1.97, Revision 3, "Criteria for Accident Monitoring Instrumentation for Nuclear Power Plants," Type D Category 2 varia b le to a Type A Category 1 variable. The reclassification of the LHSI flow instrumentation resulted from a reanalysis of the LHSI pumps' net positive suction head (NPSH) requirements that was performed to obtain additional operating margin. The reanalysis identified the need for manual operator action to throttle LHSI pump flow when only a single pump is in operation for a brief period of time under certain operating conditions. This operating scenario identified the commensurate need to reclassify the existing RG 1.97 flow instrumentation and to incorporate the instrumentation into the Accident Monitoring TS.
In support of their review of the LAR, the NRG technical staff conducted a virtual audit of certain, non-docketed Dominion Energy Virginia analysis information with the intent to gain understanding, to verify information, or to identify information to be docketed to support the basis of the licensing or regulatory decision. Dominion Energy Virginia and the NRG review staff discussed the NRC's audit results during April 18 and May 9, 2024, post-audit calls. As an outcome of the audit, Dominion Energy Virginia agreed to provide supplemental information further describing the LHSI NPSH analysis in support of the LAR. The supplemental information is provided below.
SUPPLEMENTAL INFORMATION
Nuclear Systems Performance Branc h (SNSBJ Audi t Cla rification # 1:
The NPSH analysis for the LHSI pumps for the design basis LOCA sump recirculation phase from the time of initiation of recirculation mode transfer (RMT) should be based on the methodologies for analyzing LOCA mass and energy (M&E) release in containment,
LOCA containment response, i.e., transient containment pressure, vapor temperature, and sump water temperature.
Page 1 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
a) Provide the NRG-approved methodologies used for the analyses of LOCA M&E release in containment, LOCA containment response, i.e., transient containment pressure, vapor temperature, and sump water temperature.
b) Provide the changes to the key inputs and assumptions used in the item (a) analyses, confirming the inputs are conservatively biased for determining the limiting transient NPSH. Justify if the conservatisms in any of the inputs and assumptions are reduced.
c) Provide the results of the item (b) analyses, specifically the containment pressure, vapor temperature, and sump water temperature responses, including their peak values.
d) Provide the available NPSH and required NPSH values with single LHSI pump operating at high (unthrottled) flow and at the proposed design (throttled) flow.
e) Provide the values of containment accident pressure (CAP), if used, in determining the available NPSH at the flows in item (d) stating if it is below or above the vapor pressure at the sump water temperature.
Dominion Energy Virginia Response to SNSB Audit Clarification #1:
a) Provide the NRG-approved methodologies used for the analyses of LOCA M&E release in containment, LOCA containment response, i.e., transient containment pressure, vapor temperature, and sump water temperature.
The Dominion Energy containment analyses methodology is DOM-NAF-3-0.0-P-A, GOTHIC Methodology for Analyzing the Response to Postulated Pipe Ruptures Inside Containment, which was approved by the NRC in their safety evaluation report dated August 30, 2006 (ADAMS Accession No. ML062420511). DOM-NAF-3-0.0-P-A uses M&E releases specifically developed for Surry Power Station (SPS) Units 1 and 2 by Westinghouse in WCAP-14083, Surry Power Station Units 1 and 2 Containment LOCA Mass and Energy Release Analyses for Core Uprating Engineering Report. WCAP-14083 calculated the long-term Loss of Coolant Accident (LOCA) M&E releases for the pump suction double ended rupture (PSDER) and the hot leg double ended rupture (HLDER) break cases and is based on the NRG-approved LOCA M&Es methodology described in WCAP-10325-P-A, Westinghouse LOCA Mass and Energy Release Model for Containment Design. Subsequently identified issues and Nuclear Safety Advisory Letters {NSALs) 06-06, 11-5 and 14-2 associated with the WCAP-10325 methodology were evaluated and dispositioned for SPS in conjunction with the implementation of the NRG-approved Pressurized Water Reactor Owners Group report PWROG-17034-P-A, "Evaluation of the WCAP-10325-P-A Westinghouse LOCA Mass & Energy Release Methodology, which was approved by the NRG in their safety evaluation report dated January 31, 2020.
Page 2 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
b) Provide the changes to key inputs and assumptions used in the item (a) analyses, confirming the inputs are conservatively biased for determining the limiting transient NPSH. Justify if the conservatisms in any of the inputs and assumptions are reduced.
Depending on the analysis, design inputs are either minimized or maximized to produce conservative results as outlined in DOM-NAF-3-0.0-P-A. Two different analyses performed in accordance with DOM-NAF-3-0.0-P-A are affected by the LHSI throttling action discussed in the LAR: 1) the containment depressurization analyses, which includes both depressurization time and secondary peak pressure analyses, and 2) the NPSH analyses of the pumps taking suction from the containment sump (only the LHSI pumps are affected since the Recirculation Spray (RS) pumps start well in advance of the LHSI throttling action). Containment peak pressure cases are not affected by the LHSI throttling action because the peak pressure in those cases occurs before Containment Spray (CS) is initiated (< 100 seconds), whereas the LHSI pump throttling action is not performed until near the time of transfer to cold leg recirculation ( ~ 2800 - 4100 seconds depending on the analysis).
A planned revision to the Emergency Operating Procedure (EOP) for cold leg recirculation will state to throttle the LHSI flowrate to between 2000 - 2500 gpm during the injection phase when the suction is from the Refueling Water Storage Tank (RWST) and 2000 -
2800 gpm during the recirculation phase when the suction is from the containment sump.
The SPS safety analyses bound these main control room (MGR) indicated flowrates as discussed below.
For the containment depressurization analyses, a bounding low LHSI throttled flowrate of 1800 gpm is used, since a lower LHSI flowrate will put more energy from the core through the break, and thus into containment, thereby increasing containment pressure and temperature. The actual flowrate for a MCR indication of 2000 gpm could be as low as 1804 gpm when including flow indication instrumentation uncertainties. Therefore, the safety analysis utilizes the minimum throttled flowrate allowed. The 1800 gpm was maintained throughout the analyzed throttling sequence for conservatism. Actual flowrate increases once the recirculation phase is initiated due to the procedurally required isolation of the LHSI pump recirculation line back to the RWST, in conjunction with reduced form losses in the sump suction line compared to the RWST suction line. No credit was taken for this flow increase in the containment depressurization analyses.
For the NPSH analyses, a bounding high throttled LHSI flowrate of 2675 gpm was used during the injection phase and 3000 gpm was used during the recirculation phase, since a higher LHSI flowrate will increase the velocity and decrease the NPSH. The actual flowrate for a MGR indication of 2500 gpm could be as high as 2639 gpm and for 2800 gpm as high as 2927 gpm when including flow indication instrumentation uncertainties.
Therefore, the safety analysis utilizes the maximum throttled flowrate allowed.
The throttling values listed above are the only changes to the key inputs and assumptions used in the analyses.
Page 3 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
c) Provide the results of the item (b) analyses, specifically the containment pressure, vapor temperature, and sump water temperature responses, including their peak values.
For the containment depressurization analyses, the results that will be placed into the UFSAR are presented below:
CONTAINMENT DEPRESSURIZATION RESULTS DEPSG Depressurization Depressurization Time Peak Pressure Single Failure ESF Train ESF Train Initial Containment Conditions a Total Pressure 12.52 psia 10.97 psia Temperature 125.0°F 75.0°F Relative Humidity 100% 100%
Service Water Temperature 100.0°F 100.0°F Depressurization Time{< 16.7 psia) 3126 sec 2931 sec Depressurization Peak Pressure 1.02 psig 1.35 psig b Depressurization Peak Pressure Time 6061 sec 5884 sec Remains Subatmospheric Time 13,526 sec 21,152 sec
- a. Instrumentation uncertainties for these parameters have been included in the safety analysis.
- b. Highest analysis value obtained for depressurization peak pressure.
Page 4 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
CONTAINMENT PRESSURE DEPSG DEPRESSURIZATION PEAK PRESSURE ANALYSIS
60. ----- -- --- - - - - - - - ---
55
- 50 -
45 -
-;;-40,
iii *
.e:
41 35 Ill Ill D. 30
- 25
- 20 -
15
- 10 -- - - - - - -- --- - - -
0.1 10 100 1000 10000 100000 Time (seconds)
Peak Value: 54.8 psia@ 19.6 seconds Secondary Peak Value : 16.05 psia@ 5884 seconds
Page 5 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
CONTAINMENT TEMPERATURE DEPSG DEPRESSURIZATION PEAK PRESSURE ANALYSIS
300
250 vapor
sump liquid
150
100 0.1 10 100 1000 10000 100000 Time (seconds)
Peak Value: Vapor = 267.9 °F@ 19.5 seconds Liquid = 240.7 °F @27.8 seconds
Page 6 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
For the LHSI NPSH analysis, the results that will be placed into the UFSAR are presented below:
ANALYSIS PARAMETERS AVAILABLE NPSH ANALYSIS LHSI PUMPSa Initial Containment Air Partial Pressure 10.1 psia Initial Containment Temperature 125°F Service Water Temperature 70°F Refueling Water Storage Tank Temperature 45°F
a. Instrumentation uncertainties for these parameters have been included in the safety analysis.
NPSH REQUIREMENTS SAFETY INJECTION PUMPS Low Head Safety Injection Pumps Injection Recirculationa,b Required 16. 1ft 14.0ft Minimum Available 67.86 ft 17.5 ft Flow per Pump 3371 gpm 3000 gpm
- a. The head loss across the strainer is within available NPSH margin.
- b. Minimum NPSH is attained near RMT with the discharge valve of a single operating LHSI pump throttled.
Page 7 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
LHSI AVAILABLE NPSH, REQU IRED NPSH, AND CONTAINMENT LIQUID LEVEL
30 ~-- --- - - - ----- - --- ---- --------. 5
4.5 25 4
20 3.5
~....
0 -------------
~ 15 I----------*-----------, -- -* -
(/) '
a.
z
10 1.5
5 -LHSI Pump NPSH Ava ilable
--- LHSI Pump NPSH Required 0.5
Containment Liquid (Sump) Level
o ~~ ~~ ~ ~ ~ ~ ~ ~ ~~ ~ ~ ~ ~~ ~ ~ ~~~ ~ ~~ ~~o 2600 2800 3000 3200 3400 3600 3800 4000 Time (s)
Values at RMT (2898.6 seconds): Sump Level= 4.1 ft NPSHA = 17.5 ft NPSHR = 14.0 ft
Page 8 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
CONTAINMENT AND PUMP SUCTION PRESSURES FOR LHSI NPSH AVAILABLE ANALYSIS
-Containment Total Pressure
- - - LHSI Pump Suction Vapor Pressure
40 -+---- ---- - - -- - ---, ~---- - +-- ---,.
!-- - ~, *
- ~ -~--- ~.~... ~--* ~1---------i--1 -
I,.
o~~~~~~~~~~~~-~~~~~-~~~~~~~~~~
0 1 10 100 1,000 10,000 Time (s)
Values at RMT (2898.6 seconds): Containment Pressure= 11.3 psia Suction Vapor Pressure= 7.1 psia
Page 9 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
CONTAINMENT VAPOR AND LIQUID TEMPERATURES FOR LHSI NPSH AVAILABLE ANALYSIS
300 ~-------------.-------------- ---~
,, ------ - ! -- -... --- 1... -...... ____ _
250 +---- - ---- - _ -,,-,,~,,"'*-! - --- - ----=::::::::::;::;=:.t--- -----1
200....----,,,,,
~ I ro 150 4-----:::J.... - =_ =: _ _ _ _.. -.. --- - - - --- - - - ~-.. I
- - - ; --t- - - - -- --- - -.. I
.... Q) I
- a. I E ' I A I *
~.. ;
100 ___.. __ - - +--.. --- _.. __ _ ___ i--- ~ -- - - -
- 50 __ _.. _ _ _ _ __ ____ \\ _ _ __ _ _ _.. _ _ __ _ / _ _ -Containmentliquid(Sump)Temperature
- - -Containment Vapor Temperature
0..L--'---L-L-'-'-..LL.LL-----..L--..L--'-.L..L..1....L.L.1.---'---'---'--JL....L......L....LL..L---'---'-........... -'--'-'--'-'----'-----'----'-'--L'-'u.J 0.1 1.0 10.0 100.0 1000.0 100 00. 0 Time (s)
Peak Value : Vapor = 268. 7 °F @ 19.8 seconds Liquid = 246.2 °F @ 661. 7 seconds
Page 10 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
d) Provide the available NPSH and required NPSH values with single LHSI pump operating at high (unthrottled) flow and at the proposed design (throttled) flow.
The following table summarizes the comparison between the unthrottled configuration to the throttled configuration using the maximum flowrate of one LHSI pump:
Configuration NPSHA (ft) NPSHR (ft) Strainer Loss (ft) Flowrate Margin (ft)
(gpm)
Unthrottled 15.7 13.82 1.0 3330 0.88 (6.4%)
Throttled 17.5 14.0 1.0 3000 2.5 (18%)
Note: Margins include strainer loss.
e) Provide the values of containment accident pressure (CAP), if used, in determining the available NPSH at the flows in item (d) stating if it is below or above the vapor pressure at the sump water temperature.
As documented in the Figure titled "Containment and Pump Suction Pressures for LHSI NPSH Available Analysis" in (c) above, at the time of recirculation mode transfer (RMT),
when the minimum LHSI pump NPSH occurs, the containment pressure is 11.3 psia and the LHSI pump suction vapor pressure is 7.1 psia. The suction vapor pressure is taken as saturation pressure of the liquid temperature at the pump suction (i.e., 177.7 °F).
Therefore, the pressure used in the NPSH calculation credits 4.2 psi above the saturation pressure at the pump suction. This ~redit of CAP (4.2 psi above the suction vapor pressure) is permitted per Dominion Energy's NRG-approved methodology for calculating NPSH available (i.e., DOM-NAF-3-0.0-P-A). The following excerpt is from Dominion Energy's (known at the time as Virginia Power) letter to the NRC dated October 29, 1998 (ADAMS Accession No. ML18152A553) in response to Generic Letter 97-04, "Assurance of Net Positive Suction Head for Emergency Core Cooling and Containment Heat Removal Pumps:"
"Virginia Power summarized the analysis methodology concerning the use of containment overpressure for the determination of NPSH for the emergency core cooling and containment heat removal pumps in the previous response to Generic Letter 97-04 noted above. Furthermore, we have concluded from a review of the relevant correspondence that the methodology to credit containment overpressure is part of the licensing bases for both Surry and North Anna. A specific value for containment overpressure credit in the determination of NPSH for the emergency core cooling and containment heat removal pumps has not been previously provided to the NRC for review and approval. Rather, NRC approval has been directed at verification of the
Page 11 of 13 Serial No. 24-072A Docket Nos. 50-280/281 Attachment
adequacy of the methodology used to determine that the available NPSH is greater than the required NPSH for these pumps."
SNSB Audit Clarification #2:
The LHSI system functions to remove the long-term decay heat during a design basis LOCA. Since a single LHSI pump flow is proposed to be lowered to increase its NPSH margin, assuming a single failure (as required in GDC 35) of the second LHSI pump, provide the impact of the lesser flow on the long-term decay heat removal and the containment cooling temperature and pressure profile.
Dominion Energy Virginia Response to SNSB Audit Clarification #2:
In accordance with the SPS UFSAR Section 1.4.23 description, the long-term core cooling phase is considered to be when the plant enters the recirculation phase of accident mitigation until the plant enters the cold shutdown mode and has the capability to access faulty equipment. Throttling LHSI pump flow will occur just prior to transfer to the recirculation phase. In other words, the throttling action will occur at the end of the short-term phase when transitioning to the long-term core cooling phase of the accident.
Dominion Energy Virginia evaluated the effects of LHSI throttling on the transient analyses of record. With respect to long-term core cooling, the LOCA analysis and containment analyses were evaluated as described below.
The current SPS Full Spectrum Large Break LOCA (FSLOCA) analysis sequence of events for the limiting peak cladding temperature (PCT) transient shows the end of the transient occurs at 600 seconds. The collapsed liquid level in the core and downcomer during the first 600 seconds shows that, at the end of the LOCA transient, the core is quenched, and the core and downcomer levels are increasing as the pumped Safety Injection flow exceeds the break flow. The core and downcomer levels are expected to continue to rise until the downcomer mixture level approaches the loop elevation. The overall transient behavior indicates adequate core cooling has been established and maintained. 10 CFR 50.46 acceptance criterion (b)(5) requires long-term core cooling be provided following the successful initial operation of the Emergency Core Cooling System (ECCS). This requirement is satisfied if a coolable core geometry is maintained, and the core remains subcritical following the LOCA. The magnitude of the proposed LHSI throttled flow rates and the throttling duration will not affect LOCA long-term transient behavior such that the coolable core geometry and core subcriticality would be impacted.
The SPS Small Break LOCA (SBLOCA) analysis shows the limiting PCT results are obtained for break sizes less than 4 inches. Additionally, for break sizes less than 4 inches, SBLOCA consequence mitigation relies solely on High Head Safety Injection (HHSI) with no LHSI contribution. A sensitivity study on the impact of RWST drain down and switchover of HHSI suction from RWST to LHSI discharge on break sizes ranging from 2.0 inches to 2.4 inches was evaluated. The switchover causes an increase in HHSI
Page 12 of 13 Serial No. 2 4- 072A Docket Nos. 50-280/281 Attachment
fluid temperature during core quenching. The study concluded that the 2.0 inch break case, relying solely on HHSI injection to turn over the cladding temperature, w a s impacted but exhibited small PCT and Maximum Local Oxidation (MLO) increases. For break sizes greater than 4 inches, which rely on LHSI flow for mitigation, the limiting PCT results are obtained before the earliest LHSI throttled time would occur. Therefore, the LHSI throttling approach does not impact the limiting results for SBLOCA and long-term transient behavior such that the coolable core geometry and core subcriticality would be impacted.
The containment analysis was evaluated out to 6.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> with the results provided above in Audit Clarification # 1 (c). The results show, with the unthrottling of the LHSI pumps occurring 4.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after RMT, the containment achieves sub a tmospheric conditions within six hours. A long-term response was run for over 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to determine if the operators could reduce RS requirements. This response showed that even after 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, the containment remained subatmospheric even after securing one of the two RS pump/heat exchanger trains. The results are shown below:
MINIMUM RS LONG-TERM CONTAINMENT PRESSURE RESPONSE
17.7
16.7
--;;-1s.1 S:
! - Dose Profile :J
- - - 24hC4.11'5 i - PreS5l.lre II. 14.7
13.7 ~ - ----!J-ORS pumpsecured@24 hrs
12.7 - ~ - **. *- - * - *- 1. - - - - - - --- - - --- -
0 18000 36000 54000 72000 90000 108000 126000 144000 Time (seconds)
Therefore, the long-term decay heat removal and the containment cooling temperature and p ressure profile are satisfied with the throttling of the LHSI pump discharge valve.
Page 13 of 13