ML12074A197
| ML12074A197 | |
| Person / Time | |
|---|---|
| Site: | Framatome |
| Issue date: | 03/09/2012 |
| From: | Salas P AREVA, AREVA NP |
| To: | Document Control Desk, Office of New Reactors |
| References | |
| NRC:12:013 | |
| Download: ML12074A197 (65) | |
Text
A AREVA March 9, 2012 NRC:12:013 Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Response to U.S. EPR Design Certification Application RAI No. 403, Supplement 9 In Reference 1, the NRC provided a request for additional information (RAI) regarding the U.S. EPR design certification application. AREVA NP Inc. (AREVA NP) provided a schedule for responses to all of the questions of RAI No. 403 on June 30, 2010 (Reference 2). AREVA NP submitted a letter on November 19, 2010 (Reference 3) providing computer code information related to the response to RAI 403. A final response to RAI 403 Q1 5.06.05-64, 65, 67, 69, 71, 72, 73, 75, 76 and 77 was provided on May 31, 2011 (Reference 4). AREVA NP submitted revised schedules on November 24, 2010 (Reference 5), February 24, 2011 (Reference 6), April 22, 2011 (Reference 7), July 12, 2011 (Reference 8), November 23, 2011 (Reference 9), January 18, 2012 (Reference 10), and February 26, 2012 (Reference 11).
The enclosure provides a technically correct and complete final response to 3 of the remaining questions in RAI 403. AREVA NP considers some of the material contained in the enclosed response to be proprietary. As required by 10 CFR 2.390(b), an affidavit is enclosed to support the withholding of the information from public disclosure. A proprietary and non-proprietary version of this response is enclosed.
The following table indicates the respective pages in the enclosed response that contain AREVA NP's response to the subject questions.
Question #
Start Page End Page RI A403 -
15.06.05-66 2
18 RAI 403 -
15.06.05-68 19 38 RAI 403 -
15.06.05-70 39 49 A schedule for the technically correct and complete responses to the remaining three questions is shown below.
Question #
Schedule RAI 403 - 15.06.05-61 August 30, 2013 RAI 403 -
15.06.05-62 August 30, 2013 RAI 403 -
15.06.05-63 August 30, 2013 AREVA INC.
3315 Old Forest Road, P.O. Box 10935, Lynchburg, VA 24506-0935 Tel.: 434 832 3000 www.areva.com z-Tl
Document Control Desk NRC:12:013 March 9, 2012 Page 2 If you have any questions related to this submittal, please contact Darrell Gardner by telephone at 704-805-2355 or by e-mail to Darrell.Gardner(,areva.com.
Sincerely,
- WiPedro Salas, Manager Corporate Regulatory Affairs AREVA NP Inc.
Enclosures cc:
G.
Tesfaye Docket No.52-020
Document Control Desk NRC:12:013 March 9, 2012 Page 3 References Ref. 1: E-mail, Getachew Tesfaye (NRC) to Martin Bryan, et al (AREVA NP Inc.), "U.S. EPR Design Certification Application RAI No. 403(4439), FSARCh. 15" June 2, 2010.
Ref. 2: E-mail, Martin C. Bryan (AREVA NP Inc.) to Getachew Tesfaye (NRC), "Response to U.S.
EPR Design Certification Application RAI No. 403(4439), FSARCh. 15," June 30, 2010.
Ref. 3: Letter, Sandra M. Sloan (AREVA NP Inc.) to Document Control Desk (NRC), "Computer Code Material Related to Response to U.S. EPR Design Certification Application RAI No.
403," NRC:10:106, November 19, 2010.
Ref. 4: Letter, Sandra M. Sloan (AREVA NP Inc.) to Document Control Desk (NRC), "Response to U.S. EPR Design Certification Application RAI No. 403, Supplement 4," NRC:I 1:052, May 31, 2011.
Ref. 5: E-mail, Martin C. Bryan (AREVA NP Inc.) to Getachew Tesfaye (NRC), "Response to U.S.
EPR Design Certification Application RAI No. 403(4439), FSARCh. 15, Supplement 1,"
November 24, 2010.
Ref. 6: E-mail, Russell Wells (AREVA NP Inc.) to Getachew Tesfaye (NRC), "Response to U.S. EPR Design Certification Application RAI No. 403(4439), FSARCh. 15, Supplement 2," February 24, 2011.
Ref. 7: E-mail, Russell Wells (AREVA NP Inc.) to Getachew Tesfaye (NRC), "Response to U.S. EPR Design Certification Application RAI No. 403(4439), FSARCh. 15, Supplement 3," April 22, 2011.
Ref. 8: E-mail, Dennis Wiiliford (AREVA NP Inc.) to Getachew Tesfaye (NRC), "Response to U.S.
EPR Design Certification Application RAI No. 403(4439), FSARCh. 15, Supplement 5," July 12, 2011.
Ref. 9: E-mail, Dennis Wiiliford (AREVA NP Inc.) to Getachew Tesfaye (NRC), "Response to U.S.
EPR Design Certification Application RAI No. 403(4439), FSARCh. 15, Supplement 6,"
November 23, 2011.
Ref. 10: E-mail, Dennis Wiiliford (AREVA NP Inc.) to Getachew Tesfaye (NRC), "Response to U.S.
EPR Design Certification Application RAI No. 403(4439), FSARCh. 15, Supplement 7,"
January 18, 2012.
Ref. 11: E-mail, Dennis Wiiliford (AREVA NP Inc.) to Getachew Tesfaye (NRC), "Response to U.S.
EPR Design Certification Application RAI No. 403(4439), FSARCh. 15, Supplement 8,"
February 26, 2012.
AFFIDAVIT COMMONWEALTH OF VIRGINIA
)
) ss.
COUNTY OF CAMPBELL
)
- 1.
My name is David White. I am Manager, Product Licensing, for AREVA NP Inc. (AREVA NP) and as such I am authorized to execute this Affidavit.
- 2.
I am familiar with the criteria applied by AREVA NP to determine whether certain AREVA NP information is proprietary. I am familiar with the policies established by AREVA NP to ensure the proper application of these criteria.
- 3.
I am familiar with the AREVA NP information contained in the "Response to U.S. EPR Design Certification Application RAI No. 403, Supplement 9," and referred to herein as "Document." Information contained in this Document has been classified by AREVA NP as proprietary in accordance with the policies established by AREVA NP for the control and protection of proprietary and confidential information.
- 4.
This Document contains information of a proprietary and confidential nature and is of the type customarily held in confidence by AREVA NP and not made available to the public. Based on my experience, I am aware that other companies regard information of the kind contained in this Document as proprietary and confidential.
- 5.
This Document has been made available to the U.S. Nuclear Regulatory Commission in confidence with the request that the information contained in this Document be withheld from public disclosure. The request for withholding of proprietary information is made in accordance with 10 CFR 2.390. The information for which withholding from disclosure is
requested qualifies under 10 CFR 2.390(a)(4) "Trade secrets and commercial or financial information".
- 6.
The following criteria are customarily applied by AREVA NP to determine whether information should be classified as proprietary:
(a)
The information reveals details of AREVA NP's research and development plans and programs or their results.
(b)
Use of the information by a competitor would permit the competitor to significantly reduce its expenditures, in time or resources, to design, produce, or market a similar product or service.
(c)
The information includes test data or analytical techniques concerning a process, methodology, or component, the application of which results in a competitive advantage for AREVA NP.
(d)
The information reveals certain distinguishing aspects of a process, methodology, or component, the exclusive use of which provides a competitive advantage for AREVA NP in product optimization or marketability.
(e)
The information is vital to a competitive advantage held by AREVA NP, would be helpful to competitors to AREVA NP, and would likely cause substantial harm to the competitive position of AREVA NP.
The information in the Document is considered proprietary for the reasons set forth in paragraphs 6(b) and 6(c) above.
- 7.
In accordance with AREVA NP's policies governing the protection and control of information, proprietary information contained in this Document has been made available, on a limited basis, to others outside AREVA NP only as required and under suitable agreement providing for nondisclosure and limited use of the information.
- 8.
AREVA NP policy requires that proprietary information be kept in a secured file or area and distributed on a need-to-know basis.
- 9.
The foregoing statements are true and correct to the best of my knowledge, information, and belief.
SUBSCRIBED before me this day of 2012.
Kathleen A. Bennett NOTARY PUBLIC, COMMONWEALTH OF VIRGINIA MY COMMISSION EXPIRES: 8/31/2015 Reg. #110864 F2 "
.1
- 1-OMA N" ftbN A31. 1MG1
Response to Request for Additional Information No. 403, Supplement 9 6102/2010 U.S. EPR Standard Design Certification AREVA NP Inc.
Docket No.52-020 SRP Section: 15.06.05 - Loss of Coolant Accidents Resulting From Spectrum of Postulated Piping Breaks Within the Reactor Coolant Pressure Boundary Application Section: 15.06.05 QUESTIONS for Reactor System, Nuclear Performance and Code Review (SRSB)
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 2 of 49 Question 15.06.05-66:
Since the hot side injection at 60 minutes will be entrained into the hot legs and inlet plenum, there is no assurance that sufficient water will enter the core in a timely manner to prevent boron precipitation. As water enters the steam generators slug flow can increase the loop resistance and upper plenum pressure which can limit the growth of the mixing volume and lower the reflood rate. Stating the water will eventually drain back into the core is inappropriate.
Provide the model and results to demonstrate that hot side injection is not entrained into the loops causing a potential inadequate core cooling conditions. Describe the entrainment model and show the results demonstrating that hot-leg injection is effective in preventing boron precipitation.
Response to Question 15.06.05-66:
S-RELAP5 does not have a specific entrainment model to predict the water entrainment into the loops after the switch of the low-head safety injection (LHSI) from the cold to the hot legs during a large-break loss-of-coolant accident (LBLOCA) in a pressurized water reactor. However, some entrainment is predicted in S-RELAP5 with the basic inter-phase drag package, if the vapor velocity is high.
A base-case computation was performed, with 80 percent of the LHSI flow rate switched from the cold to the hot legs, 60 minutes into the transient. The amount of water entrained into the hot legs after the initiation of hot leg injection was independently calculated with the Wallis entrainment correlation (see Figure 15.06.05-66-1). The results are presented in Figure 15.06.05-66-2 and Figure 15.06.05-66-3. The maximum percentage of LHSI water entrainment into the loops after the LHSI switch from the cold to the hot legs is lower than 15 percent, except for a brief peak at 79 minutes with an entrainment below 45 percent.
Two additional transients were then analyzed, with modified LHSI flow rates into the hot legs after the switch, to take into account the Wallis correlation results for the base case. The calculated amount of water entrained into the hot legs, 20 percent and 50 percent, is added to the entrainment already calculated by S-RELAP5 (interphase drag) to artificially increase the entrainment.
Figure 15.06.05-66-4, Figure 15.06.05-66-5, and Figure 15.06.05-66-6 show integrated mass flow from the upper plenum to loop 1 (which does not receive the hot leg LHSI), loop 2, and loop 3 that receive the hot leg LHSI. The integrated flow is shown to clearly identify the net change in flow for the hot legs receiving LHSI. The transition from a positive to a negative slope, approximately 40 seconds after initiation of hot leg injection, indicates that water is entering the reactor vessel upper plenum from the hot leg.
Figure 15.06.05-66-7 through Figure 15.06.05-66-11 show the core mixing that occurs as the water flows downward in the peripheral, low powered, fuel assemblies, and rises through the central regions of the core. This core mixing between the peripheral region and central regions of the core continues after hot leg injection is initiated.
Figure 15.06.05-66-9 through Figure 15.06.05-66-12 show that there is a flow in each node of the core and that flushing of any highly borated water that has concentrated prior to hot leg injection will occur.
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 3 of 49 Figure 15.06.05-66-13 shows the flow rate from the lower plenum volume to the lower head volume. Figure 15.06.05-66-14 shows trend line equations for plots after the flow reversal (around 3640s), indicating the approximate reverse flow following the initiation of hot-leg injection:
Base case: 477 Ibm/s.
Calculation with 20 percent of LHSI water entrainment into the loops after the switch to the hot legs: 367 Ibm/s.
Calculation with 50 percent of LHSI water entrainment into the loops after the switch to the hot legs: 198 Ibm/s.
Applicability of Wallis Correlation The conditions under which the Wallis entrainment correlation was derived (vertical, annular flow (Reference 2)) differ from those incurred at the hot side injection location. However, based on a review of the literature, the Wallis entrainment correlation remains applicable due to the commonality of the droplet entrainment phenomena for all geometries. This is primarily due to the fact that droplet entrainment is governed by the onset of roll waves (Reference 3).
According to Wallis (Reference 1), the mechanism of droplet entrainment "has been found to be virtually insensitive to pipe orientation and is governed primarily by the drag forces that the gas exerts on irregularities at the interface."
Conservatism in S-RELAP5 Model The Wallis entrainment correlation was used as a source of reasonable entrainment information for developing a more conservative S-RELAP5 model. The conservatism of the S-REALP5 model used for this evaluation does not rely solely on the accuracy of the Wallis correlation.
The cases used to demonstrate adequate upper plenum and in-core penetration, in order to mitigate boron precipitation at the time of hot side injection, assume constant entrainment values of 20 and 50 percent; an integrated effect far greater than the momentary 40 percent entrainment predicted by Wallis (Figure 15.06.05-66-3). The cases also include the inter-phase drag model, which already calculates a percent entrainment at high vapor velocities. In addition, the cases used to model 20 and 50 percent entrainment did so by decreasing LHSI flow rather than injecting the full flow. This conservatively affects the results by decreasing the ECCS condensation potential. Furthermore, de-entrainment is not credited even though according to the work of Richter, et al. (Reference 4), "most of the water droplets do not travel around the bend in the hot leg due to their inertia but impinge on the wall of the bend, and are de-entrained". This de-entrained liquid would contribute to backflow into the upper plenum.
An additional conservatism is based on a comparison of the steam velocity in the steam generator plenum during the time of hot side injection to the critical steam velocity, that is, the minimum steam velocity necessary to suspend a droplet and entrain liquid through the steam generator tubes. Making the assumption that two hot legs are plugged while LHSI injects into the two open legs, and without consideration for condensation caused by hot side injection, the steam velocities were found to be approximately 8.0 ft/s, while the critical velocity was found to be equal to 10 ft/s. Given that the actual steam velocity falls short of the critical velocity, the liquid droplets can be expected to de-entrain in the steam generator plenum and fall back into the hot leg, eventually contributing to the liquid mass flow to the core. Further margin is added to this evaluation by taking into consideration the effects of condensation from subcooled hot-
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 4 of 49 side injection. The minimum expected condensation efficiency in the RV upper plenum during hot-side injection for the U.S. EPR plant is 50 percent. Applying a condensation efficiency of 50 percent, over 40 percent of the total steam produced in the core is condensed. This significantly reduces the steam mass flow rates in the steam generator plenums, providing further margin between the actual and critical steam velocities.
Conclusion An independent calculation of the water entrainment with the Wallis correlation showed that the maximum percentage of LHSI water entrainment into the hot legs after the LHSI switch is below 15 percent, except for a brief peak value slightly below 45 percent. The transient results biased with 20 percent entrainment into the hot legs (and the results with 50 percent entrainment) show that the mass flows into and within the core vessel and produces the desired mixing as water from the hot legs enters the upper plenum, falls along the peripheral assemblies, and rises through the remainder of the core. Also, the hot-leg injection purges the core region and removes concentrated boron that accumulated prior to the initiation of the hot-leg injection.
Therefore, the hot-leg injection with a conservatively applied entrainment is effective at mitigating the boron precipitation event at the time of the hot-leg initiation.
References:
- 1. Graham B. Wallis, One-dimensional Two-phase Flow, McGraw-Hill, 1969.
- 2. Graham B. Wallis, "Phenomena of Liquid Transfer in Two-Phase Dispersed Annular Flow,"
Int. J. Heat Mass Transfer, vol. 11, pp. 783-785, 1968.
- 3. D.A. Steen and G.B. Wallis, "The Transition from Annular to Annular-Mist Co-current Two-phase Downflow," Two-Phase Flow and Boiling Heat Transfer Interim Report. June, 1964.
- 4. Richter et al., "Deentrainment and Countercurrent Air-Water Flow in a Model PWR Hot Leg,"
September 1978.
FSAR Impact:
The U.S. EPR FSAR will not be changed as a result of this question.
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 5 of 49 Figure 15.06.05-66-1-Wallis Correlation for Equilibrium Entrainment 60 60-C.
E
,C
'8 40.
4-2 220 2F10-4 6
8 10 112 14x10-4 Dimensionless ga.s velocity, /7, = *vti (0" P)'/i, Fig.
12.10 Wallis48 corrdlation for :equilibrium entrainment.
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 6 of 49 Figure 15.06.05-66-2-Water Entrainment into the Loops after the LHSI Switch from Cold to Hot Legs - Hot Legs 2 and 3, Nodes 210-2 and 310-2 45
% of Water Entrainment in Hot Leg Nodes 40 35 30 S
E 25 0A 15 10 5
LHSI switch to hot leg Ii Base Case - Node 310-2 I
_ Base Case - Node 210-2 I
0k.J 3500 4500 5500 6500 7500 8500 Time (s)
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 7 of 49 Figure 15.06.05-66-3-Water Entrainment into the Loops after the LHSI Switch from Cold to Hot Legs - Hot Leg 3, Nodes 310-1 and 310-2 45 40 35 30 E 25 SC
,20 15 10 5
% of Water Entrainment in Hot Leg 3 Nodes I
LHSI switch to hot leg IBase Case-Node 310-2
-I Base Case - Node 310-1 00 3500 4500 5500 6500 7500 8500 Time (s)
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 8 of 49 Figure 15.06.05-66-4--Upper Plenum Flow to Hot Leg I -
Loop not Receiving the Hot-Leg Injection Integrated Mass Flow - Eq. Cycle Case 24, UP to HLI -Junction 075-0 3.5E+05 3.OE+05 E 2.5E+05
.2 09: 2.OE+05 IV
" 1.5E+05 0
.4)
_* 1.OE+05 5.OE+04 O.OE+00 0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 9 of 49 Figure 15.06.05-66-5-Upper Plenum Flow to Hot Leg 2-Loop Receiving the Hot-Leg Injection Integrated Mass Flow - Eq. Cycle Case 24, UP to HL2 - Junction 075-1 4.OE+05 2.OE+05 T
0.0E+00 Time (s)
E 1000 2000 3000 4000 7000 8000 9000 1000
- -2.0E+05 0
W -4.OE+05 -
I -6.0E+05 0)
S-S_
Base Case
-8.0E+05 20% of entrainment into the loops
-1OE 0
-50%/
of entrainment into the loops
-10.E+06
-1.2E+06
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 10 of 49 Figure 15.06.05-66-6-Upper Plenum Flow to Hot Leg 3 -
Loop Receiving the Hot-Leg Injection Integrated Mass Flow - Eq. Cycle Case 24, UP to HL3 - Junction 075-2 4.OE+05 2.OE+05 0.OE+00 n -2.OE+05 0
UI.
- 0) -4.0E+05 a -6.0E+05
-8.OE+05
- Time (s) 1000 2000 3000 4000 5
600 7000 8000 9000 10 Base Case 20% of entrainment into the loops
-50%
of entrainment into the loops oc
-1.0E+06
-1.2E+06
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 11 of 49 Figure 15.06.05-66-7-Peripheral Core Region Flow to Upper Plenum Integrated Mass Flow - Eq. Cycle Case 24, Peripheral Core to UP -Junction 063-2 2.OE+06 Time (s) 0.0E+00 1000 2000 4000 5000 6000 7000 8000 9000 10 00
-2.OE+06 E -4.0E+06 o -6.OE+06
-8.OE+06
-1.OE+07 Base Case
-1.E_0 20% of entrainment into the loops
-1.42E+07 50% of entrainment into the loops
-1.6E+07
-1.8E+07
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 12 of 49 Figure 15.06.05-66-8-Average Core Region Flow to the Upper Plenum E
0 II-
.1=
"U L.
1.6E+07 1.4E+07 1.2E+07 1.OE+07 8.OE+06 6.0E+06 4.OE+06 2.OE+06 0.OE+00 Integrated Mass Flow - Eq. Cycle Case 24, Average Core to UP - Junction 063-1
-- Base Case
/
20% of entrainment into the loops
-50%
of entrainment into the loops Time (s) 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 13 of 49 Figure 15.06.05-66-9-Lower Plenum Flow to Average Core Region Integrated Mass Flow - Eq. Cycle Case 24, LP to average core -Junction 025-2 6.0E+06 5.OE+06 -
-Base Case
-20%
of entrainment into the loops 0
3.OE+06 2.OE+06 S
1.OE+06 Time (s) 0.0E+00 I....
1000 2000 3000 4000 5000 6000 7000 8000 9000 10 00
_1 tAI::.i tl:
- I.
I.
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 14 of 49 Figure 15.06.05-66-10-Lower Plenum Flow to the Peripheral Core Region Integrated Mass Flow - Eq. Cycle Case 24, LP to peripheral core -Junction 025-3 1.OE+06 O.OE+00
-1.OE+06
.0 a -2.OE+06 0
v -3.OE+06
-S -4.OE+06
-5.OE+06 Time (s) 1000 2000 00 5000 6000 7000 8000 9000 10
-- 20% of entrainment into the loops 50% of entrainment into the loops"*
I00
-6.OE+06
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 15 of 49 Figure 15.06.05-66-11-Lower Plenum Flow to the Hot Assembly, Central Core and Heavy Reflector for Sensitivity 3 Case Integrated Mass Flow - Eq. Cycle Case 24, Case with 50% LHSI Water Entrainment into the Loops 2.OE+05 0.OE+00
-2.OE+05 0i
-4.OE+05 o -6.OE+05
-8.OE+05
-1.OE+06 1000 00 3000 4000 5000 6000 7000 8000 9000 10(
Time (s)
LP to hot assembly 025-0 LP to central core 025-1 LP to heaW reflector - 031-0
-1.2E+06
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 16 of 49 Figure 15.06.05-66-12-Lower Plenum Flow to the Core By-passes for Sensitivity 3 Case Integrated Mass Flow - Eq. Cycle Case 24, Case with 50% LHSI Water Entrainment into the Loops 2.OE+05 0.OE+00
-2.OE+05
.0
=E 0* -4.OE+05 (A
-a -6.OE+05
_ -8.OE+05
-1.OE+06
-1.2E+06
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 17 of 49 Figure 15.06.05-66-13-Lower Head Flow to the Lower Plenum Integrated Mass Flow - Eq. Cycle Case 24, LH to LP - Junction 025-4 1.OE+06 5.OE+05 E
O.OE+00 0
U.
-5.OE+05
-1.OE+06
-1.5E+06 1~Time (s) 1000 2000 3000 4000 5000 60 7000 8
9000 101
-Base Case 20% of entrainment into the loops
-50%
of entrainment into the loops
)OC
-2.0E+06
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 18 of 49 Figure 15.06.05-66-14-Lower Head Flow to the Lower Plenum - Trendlines Integrated Mass Flow - Eq. Cycle Case 24, LH to LP - Junction 025 linear trendlines after LHSI switch 1.OE+06 5.OE+05
-5 0.OE+00 0
LL S-5.OE+05
-1.OE+06
-1.5E+06 6
50% of entrainment:
y 8+02x +
2
.47E+06 rime (s)
D0 4600 0
6600 760 60 60 X
ý 20% of entrainment:
= -67E+02x + 2.09E+06 Base Case 20% of entrainment into the loops 50% of entrainment into the loops
-- Linear (50% of entrainment into the loops)
-- Linear (20% of entrainment into the loops)
Base case:
-- Linear (Base Case) y = -4.77E+02x + 2.50E+06
-2.OE+06
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 19 of 49 Question 15.06.05-68:
The average concentration of all of the boric acid sources was calculated to be 1,929 ppm based on their volumetric contents and boric acid concentrations. Since liquid from the various sources is injected into the reactor coolant system (RCS) at individual flow rates and concentrations over different periods of time, setting the concentration of the fluid entering the core equal to the volume-averaged value is not justified. If the EBS is injecting at its maximum rate, this concentration at this flow rate can be conservatively postulated to enter the core region along with the remainder needed to supply the core boil-off rate at the in-containment refueling water storage tank (IRWST) concentration. The excess spills to containment. Show the timing to boric acid precipitation under these specific flow conditions using all other limiting conditions suggested/questioned above.
Response to Question 15.06.05-68:
The U.S. EPR emergency core cooling system (ECCS) and extra borating system (EBS) configuration has been reviewed to determine limiting scenarios for the injection concentration.
There are three important design characteristics of these systems that bound the possible number of configurations and determine the maximum injection concentration. First, if an emergency diesel generator (EDG) is in preventative maintenance, then both low head safety injection (LHSI) cross-connects will be opened. The cross-connects are between Trains 1 and 2, and Trains 3 and 4. Second, there are two EBS pumps that feed four lines and have four RCS valves, normally closed, and two containment isolation valves, normally open. The EBS isolation valves receive an automatic closure signal upon initiation of a containment isolation actuation signal, but can be immediately reopened, if powered. Third, if the EDG undergoing maintenance is the normal emergency power source for EBS components then those components will be lined up to be alternately fed: EBS functions are linked between EDG 1 and EDG 2; and between EDG 3 and EDG 4. Given the system setups, the configurations which can result from a single failure-preventative maintenance combination are as follows:
- 1. 2 EDGs with cross-connected LHSI lines.
- 2. 2 EDGs without cross-connected LHSI lines.
- 3. 1 EBS pump failed, 1 cross-connected EDG in preventative maintenance.
- a. Preventative maintenance on an EBS pump is performed during an outage.
- 4. 1 EBS pump failed, 1 non-cross-connected EDG in preventative maintenance.
- 5. 1 EBS valve failed closed, same line EDG in preventative maintenance.
- 6. 1 EBS valve failed closed, alternate feed line EDG in preventative maintenance.
- 7. 1 EBS valve failed closed, 1 of the non-alternate feed EDGs in preventative maintenance.
Figure 15.06.05-68-1 through Figure 15.06.05-68-7 provide a representational schematic showing the resulting injections. The same information is also presented in a tabular format in Table 15.06.05-68-1. The purpose of the figures is to show approximate flow rates into the legs, and as such, these figures do not include the break. Assuming the injection from one loop is lost directly out the break, the total injections are provided in Table 15.06.05-68-2. Calculated flow rate weighted concentrations spanning the possible configurations are shown in Table 15.06.05-68-3. These values were then used as the injection concentration variable, Cl,
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 20 of 49 in the model used for the U.S. EPR FSAR, Tier 2 boron precipitation analysis. The equation in the U.S. EPR FSAR, Tier 2 model is as follows: [
Where LBLOCA Figure 15.06.05-8 shows the concentration as a function of time for the various injection concentrations for the large break loss of coolant accident (LBLOCA) scenario. The times for the concentration to reach the boron precipitation limit, 38,500 ppm, are shown in Table 15.06.05-3 along with the time calculated using the volume weighted injection concentration (1929 ppm) that was used in the boron precipitation analysis prior to this RAI. In the calculation of the volume weighted concentration, a value of 955 ppm was used for the RCS concentration. This value corresponds to the maximum pre-LOCA concentration from the all of the (beginning of cycle) BOC and (most reactive exposure) MRE points of the first three cycles and equilibrium cycles of both the 18-month and 24-month designs. Because the U.S. EPR is being licensed with an 18-month cycle, the response to RAI 241, Question 15.06.05-53 only considered the BOC and MRE points of the four cycles from that cycle length design. The maximum value from the 18-month design is 855 ppm, but the flow rate weighted injection concentrations do not use the initial RCS concentration.
With respect to the initial boron concentration in the concentrating volume, the standard U.S.
EPR FSAR, Tier 2 boron precipitation model discussed above conservatively assumes that the pool boiling period begins at the time of reactor trip. A post-reflood volume is established at the mixed injection concentration. This is reasonable considering that the LBLOCA empties the core via the break and refills it with ECCS water. The initial RCS boron concentration is therefore not used in the boron precipitation analyses for the LBLOCA. This is conservative because it neglects any of that lower concentration RCS fluid, which remained and participated in the refill. As an additional conservatism, the mixed injection concentration, which is assumed
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 21 of 49 to refill the vessel, includes the manually initiated EBS system. The majority of the stored energy is removed from the core via the fluid out the break.
Since the boron precipitation analysis assumes a constant volume, the model inherently assumes that the inflow to the core is exactly equal to the amount of boil-off. In addition to a constant volume assumption, the U.S. EPR FSAR, Tier 2 boron precipitation model assumes a constant injection concentration. An additional calculation, (i.e., the maximum EBS/minimum SI case) is performed, which varies the injection concentration with time. The injection concentration is calculated assuming that EBS injects at its maximum rate into one cold leg, while the remainder needed to supply the core boil-off rate is at the initial IRWST concentration.
As decay heat decreases, the required makeup injection lessens. The EBS flow rate is held constant, the flow rate of the safety injection (SI) decreases; therefore, the total injection concentration increases with time.
The worst case, with respect to a 'one cold leg, EBS only' configuration needed for the maximum EBS/minimum SI scenario, is Configuration #2 or Configuration #6. Without considering the break location, Configuration #2 results in one loop getting injection from a half EBS and a half LHSI while Configuration #6 results in one loop getting injection from a full EBS and a half LHSI. However, if the broken loop was cross-connected to maximized EBS loop, it is possible that the LHSI could favor that broken loop and reduce the dilution potential. Therefore, it is conservatively assumed that one loop has just EBS injection and that it is at its full flow rate.
Assuming the injection of one leg goes directly out the break, the remaining makeup flow rate is supplied with a total of 0.5 EBS and 1 SI system injecting (flow rate weighted = '1 EBS + 2 (MHSI+LHSI)') concentration, 1951 ppm (see Table 15.06.05-68-3. The total injection flow rate is the same as in all other boron precipitation calculations (equal to boil-off) and is shown as the "Flow Rate Needed for Makeup" in Figure 15.06.05-68-10. For one EBS pump injecting into one loop, the flow rate is 0.1234 ft3/sec. The injection concentration for this scenario as a function of time is shown in Figure 15.06.05-68-11. The resulting boron concentration in the concentrating region as a function of time is shown in Figure 15.06.05-68-9. It shows that the limit is reached at =1.44 hours5.092593e-4 days <br />0.0122 hours <br />7.275132e-5 weeks <br />1.6742e-5 months <br />, which is still greater than the time to switch to hot leg injection.
The U.S. EPR FSAR, Tier 2 boron precipitation model and the calculations described in this RAI assume that just enough SI is supplied to provide makeup and hold the volume of the concentrating region constant (i.e., the injection rate equals the boil-off rate). The medium head safety injection (MHSI) and low head safety injection (LHSI) pumps are centrifugal pumps, which deliver a flow rate corresponding with the system pressure. The combined injection from the MHSI and LHSI pumps at various pressures and the minimum SI needed for makeup is shown in Figure 15.06.05-68-10. In a large break loss of coolant accident (LBLOCA), after the reactor vessel refills, most of this safety injection would go to the break, but to reach the break, the flow has to traverse the downcomer mixing with all of the injected water from the other legs on its way. As the core boils, it will be refilled from the water in lower plenum and downcomer, which will be at a mixed concentration less than the concentration of the EBS. The maximum EBS/minimum SI scenario neglects this path, essentially assuming the EBS injects directly into the downcomer. But the EBS injects into the cold leg from the same nozzle as the SI; therefore, this scenario is non-physical. The flow rate weighted combinations are more reasonable and the most limiting flow rate weight concentration will be used in the U.S. EPR FSAR, Tier 2 boron precipitation analysis. Using the most penalizing flow rate weighted injection concentration results in a time to boron precipitation of 1.74 hours8.564815e-4 days <br />0.0206 hours <br />1.223545e-4 weeks <br />2.8157e-5 months <br /> (Table 15.06.05-68-3).
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 22 of 49 SBLOCA In a small break loss of coolant accident (SBLOCA), there is not a sudden emptying, refill, and transition to pool boiling period. The size of the break dictates the inventory loss and the initial depressurization. SBLOCA breaks on the larger side of the spectrum behave similarly to a LBLOCA. With these breaks, the RCS depressurizes rapidly, the core empties, and refills from the pumped injection and accumulators. Smaller SBLOCAs retain more inventory, have less pressure drop, and longer periods of natural circulation. With continued natural circulation, the decay heat and stored energy can be removed by the coolant flow through the core.
Furthermore, during this time period, the concentrating volume is comprised of the entire RCS so any steaming which does occur has a negligible impact on the RCS concentration. Once natural circulation ceases, there is insufficient coolant flow through the core and the heat cannot be removed except by boiling. The core continues to be fed by the water from the downcomer, EBS injection (once manually initiated), and ECCS injection (once it reaches the shutoff head) and the concentration increases. Also, as opposed to the LBLOCA, which blows down rapidly, refills, and then maintains a manometric balance throughout the rest of the transient, the SBLOCA event goes through a range of concentrating volumes for several hundred seconds due to the break and the delayed injection (and the delays between the MHSI, LHSI, and accumulator injection).
Originally, the standard boron precipitation model was applied to the 6.5 inch SBLOCA. While this model could not capture the transient features of the SBLOCA event, it was judged to be a reasonable simplification. The standard model, though, is not detailed enough to capture all the slow evolving dynamics particularly important in the smaller SBLOCAs. In particular, the features of the event which make the standard model not appropriate are continued natural circulation, higher pressures, additional stored energy, and delays in ECCS injection. A separate, more detailed, model was developed to capture all of the transient behavior in order to demonstrate that the SBLOCA event is bounded by the LBLOCA event. In this model, the concentration is evaluated from the break initiation and the initial concentration is the maximum 18-month RCS boron concentration, but then increases due to flashing, stored energy deposition, and ECCS injection. Two representative SBLOCA break sizes were evaluated with this model: a 2.8 inch break, and a 6.5 inch break. The 2.8 inch break is representative of a case for which the ECCS can refill the RCS and restart natural circulation. The 6.5 inch break, like a large break, would rely on the switch to hot leg injection. Neither is credited in the evaluation of the concentration. The evaluation of these two representative cases illustrates the impact of various contribution factors to the concentrating volume boron concentration.
A key conservatism in the these SBLOCA boron precipitation analyses is that while the transient runs do not show the pressure decreasing to atmospheric pressure, the pressure trend in the analysis is continued to atmospheric pressure to attain the lowest solubility limit. Because the solubility limit is a function of the pressure, the results are best presented as a margin to the limit. The margin to the limit is displayed in Figure 15.06.05-68-12. As can be seen, the smaller the break, the greater the margin throughout the transient. Without hot leg injection or a restart of natural circulation, and assuming the RCS depressurizes to atmospheric pressure, the limit is reached at approximately 3.75 hours8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br /> for the 2.8 inch break and 3.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> for the 6.5 inch break.
For the 2.8 inch break, the results with only two ECCS available for refill show a time to restart of natural circulation around 3.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. In both cases, the hot leg injection flow is sufficient to provide excess ECCS to penetrate and dilute the core well before the limits are reached.
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 23 of 49 Since the LBLOCA boron precipitation time is 1.74 hours8.564815e-4 days <br />0.0206 hours <br />1.223545e-4 weeks <br />2.8157e-5 months <br />, the SBLOCA event is bounded by the LBLOCA analysis.
Conclusion The "maximum EBS/minimum SI" scenario is non-physical and overly conservative because it neglects the physical path the EBS and SI flows from the cold legs. Assuming the most limiting flow rate weighted injection concentration, and a constant volume, the time to reach the boron precipitation limit for the U.S. EPR is 1.74 hours8.564815e-4 days <br />0.0206 hours <br />1.223545e-4 weeks <br />2.8157e-5 months <br />. The SBLOCA event is bounded by the LBLOCA event.
The U.S. EPR FSAR will be updated to reflect the new time to precipitation with the more limiting injection concentration. Additionally, the U.S. EPR FSAR will be updated to include a description of the LBLOCA event with the actual hot leg flow split, as opposed to an assumed 50/50 split.
FSAR Impact:
U.S. EPR FSAR, Tier 2, Section 15.6.5.4.1 will be revised as described in the response and indicated on the enclosed markup.
U.S. EPR FSAR, Tier 2, Figure 15.6-88, Figure 15.6-89, Figure 15.6-90, Figure 15.6-91 and Figure 15.6-92 will be revised as described in the response and indicated on the enclosed markup.
Note that some of the U.S. EPR FSAR changes associated with this RAI response were already processed and included in Revision 3 and are not denoted by "redline-strikeout" on the enclosed markup of U.S. EPR FSAR Interim Revision 4. Other portions of the FSAR changes will be incorporated into Interim Rev. 4 as identified in the FSAR markups.
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 24 of 49 Table 15.06.05-68-1 -Configuration Injection Flows Configuration Loop #
MHSI EBS LHSI 1
0 0
0 2
0 0
0 3
1 0.5 1
4 1
0.5 1
1 0
0.5 0
2 1
0.5 1
2 3
1 0.5 0.5 4
0 0.5 0.5 1
0 0
0.5 2
1 0
0.5 3
3 1
0.5 1
4 1
0.5 1
1 1
0 1
2 1
0 1
4 3
1 0.5 0.5 4
0 0.5 0.5 1
0 0
0.5 2
1 1
0.5 5
3 1
0.5 1
4 1
0.5 1
1 0
1 0.5 2
1 0
0.5 6
3 1
0.5 1
4 1
0.5 1
1 0
0.5 0.5 2
1 0.5 0.5 7
3 1
1 1
4 1
0 1
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 25 of 49 Table 15.06.05-68-2-Total Injection Flows with One Loop Lost Out the Break Configuration Broken Loop #
MHSI EBS LHSI 1
2 1
2 1
2 2
1 2
3 1
0.5 1
4 1
0.5 1
1 2
1.5 2
2 2
1 1.5 1
3 1
1.5 1.5 4
2 1.5 1.5 1
3 1
2.5 3
2 2
1 2.5 3
2 0.5 2
4 2
0.5 2
1 2
1 2
4 2
2 1
2 3
2 0.5 2.5 4
3 0.5 2.5 1
3 2
2.5 2
2 1
2.5 3
2 1.5 2
4 2
1.5 2
1 3
1 2.5 6
2 2
2 2.5 3
2 1.5 2
4 2
1.5 2
1 3
1.5 2.5 7
2 2
1.5 2.5 3
2 1
2 4
2 2
2
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 26 of 49 Table 15.06.05-68-3-Flow Rate Weighted Injection Concentrations and Time to Precipitation Injection Time to Concentration Precipitation DDm second hour No EBS, any number of SI trains 1900 6999 1.94 1 EBS + 2 (MHSI+LHSI)
(same as all systems available: 2 EBS + 4 1951 6733 1.87 (MHSI+LHSI))
2 EBS + 3 (MHSI+LHSI) 1968 6648 1.84 2 (EBS + MHSI + LHSI) 2002 6483 1.80 1.5 EBS + 1 (MHSI+LHSI) 2051 6257 1.74 Volume Weighted Injection Concentration 1929 6846 1.90 Maximum EBS/Minimum SI Varies with time 5189 1.44
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 27 of 49 Figure 15.06.05-68-1 -Configuration #1
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 28 of 49 Figure 1 5.06.05-68-2-CConfiguration #2
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 29 of 49 Figure 1 5.06.05-68-3-Configuration #3
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Desiqn Certification Application Page 30 of 49 Figure 1 5.06.05-68-4-Configuration #4
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 31 of 49 Figure 15.06.05-68-5-Configuration #5
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 32 of 49 Figure 15.06.05-68-6-Configuration #6
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 33 of 49 Figure 15.06.05-68-7-CConfiguration #7
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 34 of 49 Figure 15.06.05-68-8--Precipitation Results - Flow Rate Weighted Injection Concentration Results versus Volume Weighted Injection Concentration 70000 60000 50000 0.
40000 0
r 30000 0U 20000 10000 0
2121F Mixing Limit
-Volume Weighted Cinj = 1929 ppm Flow Rate Weighted Cinj = 1900 ppm Flow Rate Weighted Cinj = 1951 ppm Flow Rate Weighted Cinj = 1968 ppm
-Flow Rate Weighted Cmi = 2002 ppm Flow Rate Weighted Cinj = 2051 ppm
- Fo at eghe in 05 p
0.0 0.5 1.0 1.5 Time (hours) 2.0 2.5 3.0
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 35 of 49 Figure 15.06.05-68-9-Precipitation Results - Maximum EBSlMinimum SI Concentration versus Volume Weighted Injection Concentration 70000 60000 50000 40000 0
C 0
u 30000 20000 10000 0
-212°F Mixing Limit Volume Weighted Cinj = 1929 ppm
-Max EBS, Min SI 0.0 0.5 1.0 1.5 Time (hours) 2.0 2.5 3.0
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 36 of 49 Figure 15.06.05-68-10-MHSI, LHSI, and Core Makeup Flow Rates 8.0 5.0 Z 4.0 Ix o:0~
q, n 0.0 0.5 1.0 1.5 Time (hr) 2.0 2.5 3.0
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Paqe 37 of 49 Figure 15.06.05-68-11 -Maximum EBS/Minimum SI Scenario Injection Concentration Injection Concentration v. Time:
Maximum EBS/Minimum SI Scenario 3000 2900 2800 2700 2600
.2 0S2500 0
230 2200 2100 2000 0
0.5 1
1.5 2
Time (hr) 2.5 3
3.5 4
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 38 of 49 Figure 15.06.05-68-12-Margin to Solubility Limit, 2.8 inch and 6.5 inch Comparison lluuuu
-6.5 inch 120000 2.8 inch EA E 80000
- 3 0
60000 40000 20000 0-0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 13000 14000 Time(seconds)
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 39 of 49 Question 15.06.05-70:
Follow-up to 241, Question 15.06.05-51 The calculations in the response to Question 15.06.05-51 take credit for bypass identified as Path 1 in Figure 15.06-51-1. Since it is difficult to predict the gap sizes and the dimensional changes as the vessel and core barrel cool down, explain why credit for bypass is appropriate and conservative. Justify the minimum gap resistance value used in the analysis.
Response to Question 15.06.05-70:
Figure 15.06.05-70-1 shows the concept of the static balance model where the bypass is shown as Path 1. See the nomenclature for definition of variables.
Bypass flow is appropriate to include in this analysis, although a conservative choice is not readily identifiable because the results depend on the specific case considered. The bypass flow resistance affects the power/timing of the transition steaming rate where the steam flow in the loops goes to zero. There are two bypass flow paths in parallel that are combined into a single bypass path:
One path is through the hot-leg gap, and that resistance is highly variable with temperature. It is ranged from a closed gap to a nominal gap, and then to a maximum gap.
The other path is through 32 downcomer spray nozzles that provide direct flow paths between the downcomer and the upper plenum during normal operation. Those paths are in parallel to the path through the "hot leg gap". The flow is in the reverse direction (upper plenum to downcomer) for this LTCC analysis.
Each downcomer spray nozzle has machined components as shown in Figure 15.06.05-70-2 and Figure 15.06.05-70-3. There are holes through the top of the downcomer structure and the nozzle bodies (Item 1) are inserted into the top of those holes and welded in place. The spray nozzles extend 10.24 inches into the upper plenum. Each spray head (Item 2) is screwed onto the top of the body. The minimum flow area is through the hole in the spray head shown in Figure 15.06.05-70-2. This flow path is not sensitive to thermal expansion. There are flow paths through the downcomer spray nozzles even if the "hot leg gap" is closed.
There is a unique transition steaming rate related to decay power where all steam is vented through an open bypass and no steam is vented through the loop seal. The transition steaming rate is defined from the static balance model as:
E This equation shows that the transition depends on the bypass flow resistance factor, (K/A 2)Byp.
A low resistance produces a transition at a high steaming rate, and a high resistance produces a transition at a low steaming rate. A closed bypass is unlikely for the U.S. EPR design because of the open spray nozzles, steam is always vented through the bypass.
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 40 of 49 Figure 15.06.05-70-4 shows calculated mixture and collapsed levels for the minimum flow resistance (maximum bypass flow rate). The results are typical of others to follow.
The system collapsed level, Z1, passes through variations caused by the reforming of loop seals. The number of vented loops starts with four and then changes to three, two, and then one, for hot full power. Those variations occur because the loop pressure drop changes with the number of vented loops. Loop venting is based on the depression of Z1 relative to the elevation at the bottom of the loop seal as explained in the response to Question 15.06.05-73.
The reactor vessel collapsed level, ZLRV, is lower than the system collapsed level, Z1, because the two-phase mixture level, Z2, exceeds the elevation at the top of the hot legs, ZHL. The two-phase mixture level in the reactor vessel, ZM_RV, is reported as minimum (Z2, ZHL). Only water up to ZM_RV is included for reactor vessel water inventory and the corresponding reactor vessel collapsed level, ZLRV. The reactor vessel collapsed level (ZLRv) is smooth because it directly relates to the core steaming rate. The mixture level, Z2, is below ZHL at about 100 days and the system and reactor vessel collapsed levels (Z1 and ZL_Rv) become identical, and the two-phase mixture level and reactor vessel mixture level (Z2 and ZMRV) also become identical.
The minimum collapsed and mixture level at 216.6 days occurs at the time of the transition steaming rate, which is a result of the selected minimum bypass flow resistance; the minimum collapsed level is 13.43 ft. The top of active fuel is at 13.78 ft and the two-phase mixture level is at 15.80 ft. The core is covered by 2.02 ft of two-phase mixture.
The collapsed level rises toward the elevation of the cold legs after the transition, and the two-phase mixture level follows at a higher elevation. At hot full power, the nominal and maximum bypass flow resistance factors produce transitions beyond the 1000 days reported in the plot.
They are so far out in time that they are not of interest for this case.
Cases at 1 percent initial power are of special interest. The steaming rate is much lower at low decay power, which produces a lower two-phase level swell. High bypass resistance flow resistance is also of more importance at the lower steaming rates. Two cases are considered:
the maximum bypass flow resistance and a totally closed bypass.
Figure 15.06.05-70-5 reports the reactor vessel collapsed level, ZLRV, and two-phase mixture level, ZM_RV, for the maximum bypass resistance (closed hot-leg-gap, open downcomer spray nozzles) for a LOCA at 1 percent initial power. The steaming rate transition occurs within 0.023 days (1992 seconds) with collapsed level at 13.43 ft. The two-phase mixture level is at 14.17 ft, which translates to the two-phase mixture being above the active core by 0.39 ft. The collapsed and mixture levels rise toward the elevation of the cold legs after the transition.
Figure 15.06.05-70-6 shows the collapsed and two-phase level without bypass flow for a LOCA at 1 percent of full power. The very high resistance (1012 ft4 ) does not produce a minimum collapsed level within 1157 days. The collapsed and two-phase mixture levels continue to decrease with decay power. At 1157 days following a shutdown from 1 percent initial power, the collapsed level is at 13.90 ft and the two-phase mixture level is at 13.96 ft. The two-phase mixture is 0.18 ft above the top of active fuel. This scenario is not considered credible. The complete closure of the bypass is highly unlikely because the downcomer spray nozzles are machined components that are not sensitive to thermal dimensional changes.
The collapsed levels (Z1, ZLRV) shown in Figure 15.06.05-70-4 are for a decay heat multiplier of 1.0 and a top-peaked axial power shape. Figure 15.06.05-70-7 illustrates the impact of
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 41 of 49 increasing the decay-heat multiplier to 1.2. The collapsed levels are lower but with the same general characteristic. The two-phase mixture level is not shown, but, it is high and similar to that shown in Figure 15.06.05-70-4. The variations of the collapsed levels are from the number of loop seals venting and they are shifted in time. The steaming rate transition moves later in time because that transition is directly related to the decay power for a given bypass resistance.
Figure 15.06.05-70-8 shows the impact of switching from a top-peaked to a bottom-peaked axial power shape for the two decay-heat multipliers. The collapsed levels increase with a bottom peaked axial power shape. The collapsed levels presented in the Response to Question 15.06.05.64, Figure 15.06.05.64-1 come from the same computation as presented in Figure 15.06.05-70-8 for a decay-heat multiplier of 1.2. The plots appear different because of the different scales on the time axis.
Table 15.06.05-70-1 shows a summary of each case involving changes of bypass flow resistance. The core is covered by a two-phase mixture for a wide range of bypass flow resistances at 100 percent and 1 percent initial power. Additional evaluations have demonstrated that variations in decay heat multipliers between 1 and 1.2 and variations in axial power shape do not change the conclusion that the core is covered by a two-phase mixture level.
FSAR Impact:
The U.S. EPR FSAR will not be changed as a result of this question.
Nomenclature g
Acceleration of gravity, ft/sec2.
(K/A2)Byp Pressure loss coefficient through the bypass, ftA.
PCL Pressure at elevation cold leg, psia.
PuP Pressure in upper plenum at elevation of hot leg, psia.
WLooP Steam mass flow rate in the loops, Ibm/s.
WBYp Steam mass flow rate in the bypass, Ibm/s.
Zo Elevation at the start of bulk boiling in core, ft.
Z, Elevation of system collapsed water level, ft.
Z2 Elevation of system two-phase mixture level, ft.
Z3 Elevation of water in loop seal (pre-transition), and, on steam generator side of loop seal (post-transition), ft.
ZCORE Elevation at top of active fuel, ft.
ZLp Elevation at extension of downcomer to lower plenum (set to zero), ft.
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 42 of 49 ZLS Elevation at top of loop seal, ft.
ZLRV Reactor vessel collapsed liquid level, ft.
ZM_RV Reactor vessel two-phase mixture level, min (Z2, ZHL), ft.
pg Saturated vapor density, Ibm/ft3.
PICL Liquid density in cold leg and loop seal, Ibm/ft3.
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 43 of 49 Table 15.06.05-70-1-impact of Bypass Flow Resistance on Core Coverage At Time of Transition Two-Collapsed Phase Bypass Liquid Mixture Core Resist.
Initial Power Time of
- Level, Level, Coverage(3 ),
Case (KIA 2)Byp, ft"4
(% of 4590 MW)
Transition ZL RV ZM RV ZM RV-ZcORE 216.6 1
50.33 (Min) 100%
days 13.43 ft 15.80 ft 2.02 ft 2
303.2 (Nom) 100%
>1157 17.08 ft(')
19.33 W) 5.55fW) days 1992 17 1258 (Max) 1%
seconds 13.43 ft 14.17 ft 0.39 ft 18 1012 (Closed) 1%
None(2) 13.90 ft(1) 13.96 ft(1) 0.18 ft(l)
Note:
- 5. Value at 1157 days.
- 6. No formal transition - far out in time.
- 7. Core coverage is the height of the two-phase mixture above the top of active fuel at 13.78 ft.
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Paqe 44 of 49 Figure 15.06.05-70-1-Conceptual Sketch of Static-Balance model with Non-Vented Loop LHSI Brek A
epup
- ZLP
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 45 of 49 Figure 15.06.05-70 Top of Spray Nozzle Assembly
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 46 of 49 Figure 15.06.05-70 Downcomer Spray Nozzle Components
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Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 47 of 49 Figure 15.06.05-70-4-Mixture and Collapsed Levels, Minimum Bypass Flow Resistance WATER LEVELS 25 20 15
-- Z1
-- ZCOREI ZLRV "10 ZMRV 0
0.01 0.1 1
10 100 1000 Time from Full Power Shutdown, days Figure 15.06.05-70-5-Mixture and Collapsed Levels, Maximum Bypass Flow Resistance, 1% Initial Power REACTOR VESSEL WATER LEVELS, 1% POWER, BYPASS KIA2=1258 1lft4 25 20
- 15
-- ZORE
-s--ZLRV 0
L zM-RV 0.001 0.01 0.1 1
10 100 1000 Time from 1% Power Shutdown, days
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 48 of 49 Figure 15.06.05-70-6-Mixture and Collapsed Water Levels, Closed Bypass, 1% Initial Power REACTOR VESSEL WATER LEVELS, 1% POWER, INFINITE BYPASS RESISTANCE 25 ZL_RV 10 ZMRV 5
0 0.001 0.01 0.1 1
10 100 1000 Time from 1% Power Shutdown, days Figure 15.06.05-70-7-Collapsed Water Levels, Impact of Decay Power, Top-Peaked WATER LEVELS, TOP PEAKED 25 20 ZCORE 15 10
---e----Z1, 1.2 ZLRV, 1.2 ZLRV, 1.0 0.01 0.1 1
10 100 1000 Time from Full Power Shutdown, days
AREVA NP Inc.
Response to Request for Additional Information No. 403, Supplement 9 U.S. EPR Design Certification Application Page 49 of 49 Figure 15.06.05-70 Collapsed Levels, Impact of Decay Power, Bottom-Peaked WATER LEVELS, BOTTOM PEAKED 25 20 15 10 S
-J ZCORE
-- @- Z1,1.2 ZLRV, 1.2 S---. *Z1, 1.0 ZLRV, 1.0 5
0.01 0.1 1
10 100 Time from Full Power Shutdown, sec 1000
U.S. EPR Final Safety Analysis Report Markups
AU.S.
EPR FINAL SAFETY ANALYSIS REPORT EPR strain is about 40 percent up to about 1800'F. Because the predicted SBLOCA PCTs are less than 1800'F, the maximum swelling and blockage for the SBLOCA is comparable to the limiting LBLOCA case. This is 75 percent coolant channel blockage or less, depending on the actual cladding temperature and stress time history.
Reference 8 demonstrates that the core remains coolable at decay heat levels for up to 90 percent coolant channel blockage.
15.6.5.3.3 Conclusion - Coolable Core Geometry Based on a conservative swelling and rupture analysis, the evaluation of mechanical degradation of coolable core geometry due to combined seismic and LBLOCA loads demonstrates that the maximum local fuel assembly blockage is 75 percent.
Therefore, it is conservatively assumed that the core-wide average blockage is 75 percent. Because this value is less than the 90 percent coolant channel blockage threshold for adequate cooling, the U.S. EPR maintains a coolable core geometry following a LOCA.
15.6.5.4 Long-Term Core Cooling After the initial mitigation of a LOCA, the calculated core temperature is maintained at an acceptably low value and decay heat is removed for an extended time as required by the long-lived radioactive isotopes remaining in the core. The core remains subcritical.
Several issues are addressed to demonstrate adequate long term cooling following a LOCA:
" Boron precipitation. Boron in the coolant can concentrate and precipitate in the upper region of the core when there is protracted boiling following a LOCA.
Boron dilution during SBLOCA. GSI-185 raises a concern regarding the potential for recriticality during an SBLOCA if unborated water accumulates in the SGs and cold leg piping due to condensation and moves to the core as a slug.
Containment debris. GSI-191 raises concerns regarding the potential damage to ECCS equipment and blockage of core channels due to debris in the water re-circulated from the IRWST.
15.6.5.4.1 Prevention of Boric Acid Precipitation The U.S. EPR provides the operator the capability to redirect an LHSI train so that at least 75 percent of it is injected through the hot leg letdown line of the residual heat removal system (RHRS). Analyses show that switching the LHSI to hot leg injection is effective at limiting the boron concentration in the core region regardless of the break location. When started withi 6200 conds, precipitation is prevented in the core and other regions of the reactor vess nd RCS. The small break analyses show 1.06.0-688 Tier 2 Revision 4-Interim Page 15.6-39
EPR U.S. EPR FINAL SAFETY ANALYSIS REPORT that more water is retained in the core region than for the large break LOCA. Since the core boron concentration, and correspondingly the margin to the precipitation limit, is dependent on the volume of liquid in the core, the large break LOCA bounds small break LOCAs relative to boron precipitation.
The mitigating effect of hot leg injection is confirmed by extending the S-RELAP5 calculations for a representative range of breaks analyzed in Sections 15.6.5.1 and Section 15.6.5.2.
15.6.5.4.1.1 Small-Break LOCA Flow Behavior Five SELOCA effie are analyzed between 1.5 inehes and 6.5 inehes int diameter. For breaks up to approximately 4 inches in diameter, the RCS refills in less than four hours with two trains of MHSI and LHSI and returns to natural circulation.
I 11 /:
In the 6.5 inch break, following completion of the automatic partial cooldown, operator action is assumed at 1800 seconds to continue depressurization of the SGs at a rate corresponding to 907F/h. At the same time, the operator is assumed to realign the two operating trains of LHSI to inject approximately 75 percent of their flow into the respective hot legs. The exact value of the hot leg/cold leg flow split depends on the RCS pressure. Operating procedures control the timing of hot leg injection initiation to within an hour. The S-RELAP5 SBLOCA analysis initiated the hot leg injection at 30 minutes as an example, which is conservative because earlier in time there is a Shigher system pressure, resulting in less LHSI flow, and a higher decay heat, leading t(
J15.06.05-68 slightly more steam production and a greater resistance to reverse flow from the hot legs into the core. As seen in Figure 15.6-84-SBLOCA - 6.5 Inch Break - Integral of Upper Plenum Flow to the Hot Legs, the redirected flow reverses the flow in loops 1 and 4 into the upper plenum, making additional coolant available to the core region.
These are the loops with the operating SI trains and are the same loops receiving EFW.
Figure 15.6-85-SBLOCA - 6.5 Inch Break - Integral of Core Region Exit Flows shows that the hot leg injected flows further reverse the fuel assembly flow in the peripheral region of the core. Some of the downflow continues out through the lower plenum to the lower head region (Figure 15.6-86-SBLOCA - 6.5 Inch Break - Integral of Lower PPnlenm Flow to Lonwer 4ead). FThis removes the concentrated boron that accumulated p/1rior to the initiation of the hot leg injection. The hot leg injection then maintains the boron concentration below 3000 ppm, which is well below the boron precipitation 115.0605-68limit of 38,500 ppm (see Figure 15.6-92). 1[At 7000 seconds into the event, the continued cooldown ot e steam generators has not caused the secondary side pressure to reach the point where the steam generators will remove decay heat, as illustrated by the RCS pressure and the steam generator 1 pressure (Figure 15.6 SBLOCA - 6.5 Inch Break - Pressurizer and Steam Generator 1 Pressure).
Tier 2 Revision 4-Interim Page 15.6-40 Tier 2 Revision 4--Interim Page 15.6-40
EPR U.S. EPR FINAL SAFETY ANALYSIS REPORT 15.6.5.4.1.2 Large-Break LOCA Flow Behavior A representative LBLOCA case is analyzed to demonstrate the effectiveness of hot leg injection for break sizes too large for the MHSI and LHSI to refill the loops.
In the analysis depicted in the following figures, the operator is assumed to switch to hot leg injection at I hour. As seen in Figure 15.6-88-LBLOCA with Hot Leg Injection at 60 Minutes - Integrated Flow from Upper Plenum to Hot Legs, the switch to hot leg injection causes flow to reverse from the hot legs receiving hot leg injection back into the upper plenum. Flow reversal is indicated when the slope becomes negative. The flow proceeds down the peripheral region, the guide tubes, and the heavy reflector into the lower plenum as seen in Figure 15.6-89-LBLOCA with Hot Leg Injection at 60 Minutes - Integrated Flow from Core Regions to Upper Plenum and Figure 15.6-139-LBLOCA with Hot Leg Injection at 60 Minutes - Integrated Flow through Core Bypass Regions. Forward flow continues into and out of the hot assembly, the central core region, and the average core and into the two loops without hot leg injection. Figure 15.6-90-LBLOCA with Hot Leg Injection at 60 Minutes -
Integrated Flow from Lower Plenum to Core Regions shows the reverse flows into the lower plenum from the peripheral region and the forward flow to the central regions.
Approximately 75 percent of the peripheral region flow mixes with the other core regions, with the remainder penetrating into the lower plenum. The downflow into the lower plenum penetrates further into the lower head, as seen in Figure 15.6 LBLOCA with Hot Leg Injection at 60 Minutes - Integrated Flow from Lower Head to Lower Plenum. The flow reverses to the downcomer, increasing the flow out of the vessel side of the break. This removes the concentrated boron that accumulated prior to the initiation of the hot leg injection. The hot leg injection then maintains the concentration below 3000 ppm, which is well below the boron precipitation limit of 38,500 ppm (see Figure 15.6-92-Time Dependent Boron Concentration During the Pool Boiling Period with and without Hot Leg Injection at 60 Minutes).
115.06.05-68:-
15.6.5.4.1.3 If the LOCA is a large hot leg break, the ECCS injection into the cold leg exceeds the core boil off rate and the excess ECCS has sufficient flow through the core to prevent the formation of a boron concentration that approaches the precipitation limit even with redirection of Vpproximately 75 percenj of the LHSI flow to the hot legs.
Boron Precipitation Assessment 15.06.0568 115.06.05-68 I
The maximum injection concentration, determined by weighting the flow rates of SI and EBS in the most penalizing injection configuration, is 2051 ppm. This value is used in the calculation of concentration over time using the methodology described in U.S. EPR Boron Precipitation and Boron Dilution (Reference 9).
The calculation conservatively neglects the following mitigating processes:
9 Increased boron solubility due to other solutes.
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AU.S.
EPR FINAL SAFETY ANALYSIS REPORT EPR Increased boiling temperature due to boric acid concentration.
Carryout of dissolved boric acid by steam generated in the core.
Carryout of boric acid due to droplet entrainment.
Addition of nonborated water from sources such as the CVCS.
- ~
15.6-92--Time Dependent Boron Concentration During the Pool Boiling P~erio-*with and without Hot Leg Injection at 60 Minutes s+ows the predicted boron concentration over time for the limiting LBLOCA PCT case. and b...nding 6.5 in. h diameter SBLOCA. The eturves for these representative eases demengtrate that far the-
.. mpl.te sp.. trum of br.a.., The LBLOCA has a shorter time to precipitation than the SBLOCA, and therefore is the boundary boron precipitation event. The curve demonstrates that boric acid does not concentrate to the degree that boron precipitates 15.06.05-68 out of solution. Moreover, there is adequate time for the operator to initiate hot leg injection to limit the buildup of boron in the core region and prevent precipitation in other regions of the RCS.
15.6.5.4.2 SBLOCA Boron Dilution GSI-185, "Control of Recriticality Following Small-Break LOCAS in PWRs," raises the concern for SBLOCA events that de-borated water could accumulate in cold leg pump suction piping due to the condensation of steam. When natural circulation is restored, this de-borated water gets flushed as a slug to the RV and core, potentially causing recriticality and fuel damage.
The conditions necessary for this condition to occur develop for a narrow range of break sizes. Breaks smaller than this range do not interrupt natural circulation and therefore do not accumulate de-borated water. Those larger than this range depressurize quickly to low pressure, during which time the secondary sides of the SGs are a heat source to the primary system. Even if heat transfer is re-established to the SGs after they are depressurized, the break is too large for the LHSI to refill the loops.
Because natural circulation does not restart, de-borated water is not flushed to the core as a slug.
AREVA performed tests at the PKL integral-loop test facility to investigate boron dilution during SBLOCA, as described in Final Report of the PKL Experimental Program Within the OECD/SETH Project (Reference 10). Some of the tests simulate the controlled cooldown of the SGs representative of the U.S. EPR plant design. The tests demonstrate that natural circulation does not restart abruptly. It is preceded by a period of intermittent circulation. Moreover, the circulation starts first in one active loop and is followed independently by circulation in other active loops. This thermal-hydraulic behavior provides a basis for evaluating boron concentrations in the cold legs and core.
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EPR U.S. EPR FINAL SAFETY ANALYSIS REPORT Figure 15.6-88-LBLOCA with Hot Leg Injection at 60 Minutes - Integrated Flow from Upper Plenum to Hot Legs 400 200 0
.,0 LL
'a CD
-200
-400
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-800
-1000 0
1000 2000 3000 4000 5000 6000 Time (sec)
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EPR U.S. EPR FINAL SAFETY ANALYSIS REPORT Figure 15.6-89-LBLOCA with Hot Leg Injection at 60 Minutes - Integrated Flow from Core Regions to Upper Plenum 10000 5000
.0 E
0
,k 0
-oD "0
(U 4-e 0
) eo I C e
/ff f, Integrated Cvenrale Core to UP Flow
- -A Integrated Peripheral Core to UP Flow
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1000 2000 3000 4000 5000 6000 Time (sec)
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EPR U.S. EPR FINAL SAFETY ANALYSIS REPORT Figure 15.6-90-LBLOCA with Hot Leg Injection at 60 Minutes - Integrated Flow from Lower Plenum to Core Regions 4000 3000 2000
-oE 0
0
,k a) 0)
o)
C 1000 0
-1000 N.
Ns E e t I La N
N 4N sN dN
-)Integrated LP to Hot Assy Rlow
-E Integrated LP to Central Core Flow
- '. Integrated LP to Average Core Flow
--.. Intearated LP to Perioheral Core Row
-2000
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0 1000 2000 3000 4000 5000 6000 Time (sec)
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EPR U.S. EPR FINAL SAFETY ANALYSIS REPORT Figure 15.6-91-LBLOCA with Hot Leg Injection at 60 Minutes - Integrated Flow from Lower Head to Lower Plenum 1000 800 600
.00 00 0
LL 0
a,
-..CO 400 200 0
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EPR U.S. EPR FINAL SAFETY ANALYSIS REPORT Figure 15.6-92-Time Dependent Boron Concentration During the Pool Boiling Period with and without Hot Leg Injection at 60 Minutes 70000 60000 50000
,S40000
- 30000 0
20000 10000 0
0.0 1.0 2.0 3.0 4.0 5.0 Time (hours)
REV 004
[lDD'74 Tr 6.0 S
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