ML20249B320
| ML20249B320 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 05/31/1998 |
| From: | WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20036E450 | List: |
| References | |
| WCAP-15062, WCAP-15062-R02, WCAP-15062-R2, NUDOCS 9806220314 | |
| Download: ML20249B320 (39) | |
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WESIINGIlOUSE NON-PROPRIETARY (hSS 3 l WCAP-15062 Revision 2 AP600 ACCIDENT ANALYSES-EVALUATION MODELS I J WESTINGHOUSE ELECTRIC COMPANY Energy Systems P.O. Box 355 Pittsburgh, PA 15230 C1998 Westinghouse Electric Company l All Rights Reserved o:\4206w.norulbdM0998
WESTINGHOUSE NoN-PROPRIETARY C1. Ass 3 COPYRIGHT NOTICE The reports transmitted herewith each bear a Westinghouse copyright notice. The NRC is
- permitted to make the number of copies of the information contained in these reports which are necessary for its internal use in connection with generic and plant-specific reviews and approvals as well as the insurance, denial, amendment, transfer, renewal, modification, suspension, revocation, or violation of a license, permit, order, or regulation subject to the requirements of 10CFR 2.790 regarding restrictions on public disclosure to the extent such information has been identified as proprietary by Westinghouse, copyright protection notwithstanding. With respect to the non-proprietary versions of these reports, the NRC is permitted to make the munber of copies beyond those necessary for its internal use which are necessary in order to have one copy available for public viewing int he appropriate docket files in the public document room in Washington, D. C., and in local public document rooms as may be required by NRC regulations if the number of copies submitted is insufficient for this purpose. Copies made by the NRC must include the copy right notice in all instances and the proprietary notice if the original was identified as proprietary.
o:\4206w.non:1bs60998 1
I si TABLE OF CONTENTS Section Title Page
1.0 INTRODUCTION
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 2.0 LOFTRAN CODE MODIFICATION AND VERIFICATION . . . . . . . . . . . . . . 2-1
2.1 REFERENCES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
. 3.0 AP600 WCOBRA/ TRAC VESSEL AND LOOP MODELS FOR LARGE BREAK LOCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
3.1 REFERENCES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9 i 4.0 - AP600 NOTRUMP MODEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
4.1 REFERENCES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 5.0 LONG-TERM COOLING (LTC) ANALYSES METHODOLOGY . . . . . . . . . . 5-1
5.1 DESCRIPTION
OF THE WCOBRA/ TRAC NODING FOR THE AP600 LONG-TERM COOLING ANALYSIS . . . . . . . . . . . . . . . . . . . . . 5-1 5.2 COMPUTATION OF BOUNDARY CONDITIONS FOR THE AP600 EMERGENCY CORE COOLING SYSTEM WCOBRA/ TRAC ANALYSIS WINDOWS . . . . . . . . . . . . . . . . . . . . . . 5-6 ! 5.2.1 IRWST Draindown and Core Boiloff Calculations to l Establish Mass / Energy Releases . . . . . . . . . . . . . . . . . . . . . . . . 5-6 5.2.2 WGOTHIC Containment Pressure Computation . . . . . . . . . . . . . 5-8 5.3 CONSIDERATIONS IN LONG-TERM COOLING EMERGENCY ; CORE COOLING SYSTEM PERFORMANCE CALCULATIONS . . . . . . 5-10 6.0 TRANSIENT MASS DISTRIBUTION (TMD) CODE FOR AP600 ) SUBCOMPARTMENT MODEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6.1 REFERENCES
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 1
1 o:u206w.mmm.060998 May 1998 Revision 2 l
v 1.IST OF TABLES l i Table *Dtle Page 1 6-1 Hoop Flow Path Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3 ( 6-2 Radial Flow Path Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7 6-3 Axial Flow Path Data - . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11 64 TMD Model Node Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15 l o:\4206w.natit>W4996 May 1998 Revision 2
vii LIST OF FIGURES Figure "litle Page
.3-1 AP600 ECOBRA/ TRAC Vessel Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12 3-2 WCOBRA/ TRAC Vessel Model (Section 1) . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13 3-3 WCOBRA/ TRAC Vessel Model (Section 2) . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14 34 WCOBRA/ TRAC Vessel Model (Section 3) . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15 3-5 WCOBRA/ TRAC Vessel Model (Section 4) . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16 3-6 WCOBRA/ TRAC Vessel Model (Section 5) . . . . . . . . . . . . . . . . . . . . . . . . . . 3-17 3-7 WCOBRA/ TRAC Vessel Model (Section 6) . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18 3-8 WCOBRA/ TRAC Vessel Model (Section 7) . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19 3-9 WCOBRA/ TRAC Vessel Model (Section 8) . . . . . . . . . . . . . . . . . . . . . . . . . 3-20 3-10 WCOBRA/ TRAC Vessel Model (Section 9) . . . . . . . . . . . . . . . . . . . . . . . . . . 3-21 3 WCOBRA/ TRAC Vessel Model (Section 10) . . . . . . . . . . . . . . . . . . . . . . . . . 3-22 3-12 Vessel Noding Diagram for Guide Tube Hot Assembly Location . . . . . . . . . 3-23 3-13 WCOBRA/ TRAC Loop Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-24 4-1 Base Noding Scheme Used for the AP600 Fluid Nodes and Flow Links . . . . 4-3 5-1 Elevation of the Vessel for LTC Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13 5-2 Coarse Noding Plan View (Sheets 1 to 6) . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-14 5-3 Cold Leg Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20 5-4 Hot Leg Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-21 5-5 WCOBRA/ TRAC Loop Model for DEDVI Break LTC Analysis . . . . . . . . . . . 5-22 5-6 Small Break LOCA IRWST Drain Boiloff Calculation . . . . . . . . . . . . . . . . . . . 5-23 7 Small Break LOCA IRWST Drain Boiloff Calculation . . . . . . . . . . . . . . . . . . . 5-24 5-8 Small-Break LOCA LTC Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25 5-9 Simplified AP600 Internal Containment Flow Network . . . . . . . . . . . . . . . . . 5-26 6-1 TMD Model Noding Diagram (Sheets 1 through 12) . . . . . . . . . . . . . . . . . . . 6-18 i
l o:\4206w.non:1b.060998 May 1998 Revision 2 I l i l L_____________________.___._________ _ _ . - _ . _ _ - . - - - - - - - - - - _ - - - - - - - - - - - - -
1-1
1.0 INTRODUCTION
This document discusses the evaluation models and parameters used in the AP600 Accident l Analyses completed for Design Certification. Information corresponding to that in Sections 2 through 5 was previously documented in Chapter 15, Appendices B through E, of the AP600 Standard Safety Analysis Report (SSAR) (Revision 4). Note that Appendix 15A still exists at the end of SSAR Chapter 15, Revision 23. Information corresponding to that in Section 6 was previously documented in Chapter 6 of the AP600 SSAR (Revision 5). Introduction May 1998 c:\4206w.ron:1b.060998 Revision 2
2-1 2.0 LOFTRAN CODE MODIFICATION AND VERIFICATION LOFTRAN (Reference 1) is a code developed by Westinghouse which is used for studies of the transient response of a pressurized water reactor (PWR) system to specified perturbations in process parameters. LOFTRAN simulates a multiloop system and models the reactor vessel, hot and cold leg piping, steam generators (tube and shell side), and the pressurizer. The pressurizer heaters. spray, and safety valves are also modeled in the program. Point kinetics and the reactivity effects of moderator, fuel, boron, and rods are included. The secondary side of the steam generator utilizes a homogeneous, saturated mixture for the thermal transients and a water level correlation for indication and control. Reactor protection system signals, such as reactor trip, neutron flux, high and low pressure, low flow, and low steam generator water level, are modeled. Control systems are also simulated, including rod control, steam dump, and feedwater control. Standard emergency core cooling systems, such as pumped safety injection and accumulators, are modeled. The original LOFTRAN verification includes fourteen transients and consists of a comparison of LOFTRAN results to actual plant data and to other similar thermal-hydraulic programs. The U.S. Nuclear Regulatory Commission (NRC) determined that the data comparisons and the computer program results comparisons demonstrate the ability of LOFTRAN to analyze the types of events which has been used in licensee safety analyses, and that the verification for LOFTRAN is judged to be adequate. The LOFTRAN code is modified to allow the modeling of the AP600-specific systems. In particular, models for the passive residual heat removal (PRHR) and core makeup tank (CMT) are included in the program. A description of the modifications made to LOFTRAN is contained in Reference 2.
2.1 REFERENCES
- 1. Burnett, T.W.T. et al., "LOFTRAN Code Description," WCAP-7907-P-A (Proprietary) and WCAP-7907-A (Nonproprietary), April 1984.
- 2. Carlin, E.L., Bachrach, U., "LOFTRAN & LOFITR2 AP600 Code Applicability Document," WCAP-14234, Revision 1 (Proprietary), June,1997.
LOFTRAN Code Modification and Verification May 1998 oM206w.non:1b-060998 Revision 2
3-1 l 3.0 AP600 WCOBRA/ TRAC VESSEL AND LOOP MODELS FOR LARGE BREAK LOCA i A major portion of a }yCOBRA/ TRAC (References 1 and 2) analysis involves generating the plant-specific vessel, loop model, and the appropriate geometric inputs to that model to properly describe the plant. The vessel model, in particular, requires detailed information regarding the vessel internals. ( Design drawings for the plant are used to define the inputs to the model. For the AP600, the process of developing the model, and inputs to the model, begins with the elevation layout of the vessel and its internals and the creation of vessel component input. Figure 3-1 shows the elevation layout of the vessel for the AP600. The elevations shown are relative to the inside bottom of the vessel. This elevation layout contains most of the information needed to divide the vessel into ten vertical sections. This number of vessel sections is consistent with the detail in WCOBRA/ TRAC input nodalization being implemented in the best-estimate large break loss-of-coolant-accident (LOCA) model analyses at Westinghouse. [ l e AP600 y(COBRA / TRAC Vessel and Iwp Models for Large Break LOCA May 1998 o u206w.non% aces Revision 2
3-2 [ l 1" The input to WCOBRA/ TRAC includes variation tables for several geometric / thermal hydraulic inputs. Through the use of these variation tables, parameters such as contmuity area, momentum area, wetted perimeter, hydraulic diameter, and gap size (for horizontal flow paths), can be varied from cell to cell. This is useful for channels that vary in geometry from bottom to top or for gap flow paths which are blocked over some portion of a channel (for example, gaps 7 through 12 in Section 2, Figure 3-1). Vessel Section 1: Lower Head Region [ ju Vessel Sections 2 and 3: Lower Plenum Region and Bottont Nozzle Region [ ju AP600 ECOBRA/ TRAC Vessel and Loop Models for Large Break LOCA May 1998 o:\4206w.nonutb 060998 Revision 2
3-3
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Vessel Section 4: Core Active Fuel Region [' jae AP600 WCOBRA/ TRAC Vessel and Loop Models for Large Break LOCA May 1998 a:\4m.non:1bwe998 Revision 2
3-4 I
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Vessel Section 5: Counter-Current Flow Limitation (CCFL) Region [ ju AP600 WCOBRA/ TRAC Vessel and Loop Models for Large Break LOCA May 1998 oM206w.non:1besop9s Revision 2
3-5 [ ju Assemblies entering a guide tube at the upper core plate have a flow area through the top of the section. The area is somewhat larger than the other channels. The guide tube assemblies account for 61 of the 145 assemblies in the core. Vessel Section 6: Bottom of Upper Plenum (3 levels) {
}"
l Vessel Section 7: Upper Plenum Nozzle Region (Two Levels) 1 ( 1" AP600 WCOBRA/ TRAC Vessel and Loop Models for Large Break LOCA May 1998 l oM206w.noren>&D998 Revision 2 ! b- - - --------------_________o
3 [. ju Figures 3-1 and 3-8 show the' vertical and radial representations of this section of the vessel
. model.
[ 3" Vessel Section 8: ' Upper Downcomer/ Bottom of Upper Head
't
[L ju AP600 WCOBRA/ TRAC Vessel end Loop Models for Large Break LOCA May 1998 - o:\4206w.non:1baopes Revision 2 i
l 3-7 I-ya l l Vessel Ser. ions 9 and 10: Upper Head ! [ y, AP600 ECOBRA/ TRAC Core Power i To model stored energy heat sources in ECOBRA/ TRAC, code input allows for the
. modeling of both heated conductor geometries and the unheated conductor input. Unheated conductors are simply the typical heat slab inputs for components, such as the vessel wall and the lower core support plate, typical in most thermal / hydraulic computer codes. For the special case of heated conductors, the code allows for detailed radial and axial noding and other fuel rod related inputs, such as rod internal pressure, fuel rod gas molar fractions, clad thickness, and fuel theoretical density.
[. l 1
] Reference 4 presents the ,
axial power shapes modeled in the ECOBRA/ TRAC SSAR analysis to bound the axial power distribution. The axial profile selected for an analysis is applied to fuel rods at differing total power levels. l 1 at AP600 WCOBRA/ TRAC Vessel and Loop Models for Large Break LOCA May 1998 a:\no6w.non:1bam98 Revision 2
3-8
.I j.e
; For cases in which the hot assembly is assumed to reside beneath a guide tube, slight modifications to the Vessel model of Figure 3-1 are necessary. Figure 3-12 depicts the revised nodalization, which includes the addition of Channels 81 and 82.
.[
).e AP600 RCOBRA/ TRAC Loop Model-The input to ECOBRA/ TRAC allows the user to invoke several different modules through use of a descriptive identifier. These modules recognize the need for varying inputs to describe the geometry and function of various components in the reactor coolant system
'(RCS). Tha largest of these modules is the VESSEL module. The vesselinputs are
' distinguished in the ECOBRA/ TRAC input since the VESSEL module is the only recognized three-dimensional component. ' The one-dimensional modules used to describe the various components are listed in the SSAR, subsection 15.6.5.4A.2.3.
' As with the vessel inputs, each component in the one-dunensional loop model can have various cells to allow for modeling changes in geometry alcag the component. In the input structure each component is identified by a module title, a unique component number, and connections to numbered junctions between components. In addition, a descriptive text title can be used to uniquely identify each component.
l l. jae AP600 ECOtlRA/ TRAC Vessel and loop Models for Large Break LOCA - May 1998 a:\4206w.non:n 060998 Revision 2 l .
3-9 I l J.,c
3.1 REFERENCES
1. Dederer, S. I., Hochreiter, L E., Schwarz, W. R., Stucker, D. L., Tsai, C. K., and Young, M Y., " Westinghouse Large Break Best Estimate Methodology, Volume 1 Model Description and Validation, Volume 2, Revision 2, Application to Two-Loop PWRs AP600 }yCOBRA/ TRAC Vessel .tnd Loop Models for Large Break LOCA May 1998 c:\4206w.non:1ba60998 Revision 2
3-10' Equipped with Upper Plenum Injection," WCAP-10924-P-A (Proprietary), December 1988. l 2.' = Bajorek, S. M., Nguyen, S. B., Young, M. Y., Dederer, S. I., Nissley, M. E., Takeuchi, K., l and Ohkawa, K., " Code Qualification Document for Best Estimate LOCA Analysis," Volumes 1 through 5, WCAP-12945-P-A (Proprietary), Revision 1, March 1998.-
- 3. Letter, R. C. Jones, Jr. (USNRC) to N. f. Liparulo (W), " Acceptance for Referencing of the Topical Report, WCAP-12945 (P), Westinghouse Code Qualification Document for Best-Estimate Loss-of-Coolant Analysis," June 28,1996.
- 4. NTD-NRC-95-4575, Letter from N. J. Liparulo (W) to R. C. Jones, Jr. (USNRC),
% visions to Westinghouse Best-Estimate Uncertainty Report," October 13,1995.
- 5. IIaberstroh, R. C., Hochreiter, L. E., and Monahan, E. M., "WCOBRA/ TRAC Core Makeup Tank Preliminary Validation Report," MT01-GSR-003, Westinghouse Electric Corporation, February 1995.
AP600 WCOBRA/ TRAC Vessel and loop Models for Large Break LOCA May 1998 oM206w.non:1be60998 Revision 2
3-11 l Figures 3-1 through 3-13 are Westinghouse proprietary (a,c) and therefore, not included in this Class 3 WCAP i AP600 }YCOBRA/ TRAC Vessel and Loop Models for Large Break LOCA May 1998 a:\4206w.non:1t>o60998 Revision 2
4 t
4-1 4.0 AP600 NOTRUMP MODEL The AP600 nodalization is consistent in approach with the noding used in the NOTRUMP models of the AP600 integral and component test facilities (Reference 1). The noding scheme is based on the NRC-approved NOTRUMP evaluation model (Reference 2) and, when possible, follows the evaluation model methodology. The noding scheme used for this analysis is given in Figure 4-1. Details of the noding for the CMTs are presented in Reference 1. Note that paths identified as " critical flow links" are those with a user-specified boundary condition flow rate. Other features specific to the modeling of the AP600 augment the NRC-approved NOTRUMP evaluation model noding, according to the test facility simulations, as follows: Wherever possible, flow links with elevation changes are avoided. Instead, fluid nodes connected precisely at node boundaries or at horizontal flow links are used. The principal exception to this is the flow link representing the guide tubes. Both of the reactor coolant loops are modeled in full. The PRHR heat exchanger is modeled using metal nodes and heat links connecting the metal nodes to the reactor coolant system and to the in-containment refueling water storage tank. The noding applied is consistent with simulations of the PRHR in Reference 1. The reflector metal mass is modeled as [ ]" metal nodes joined by heat links to the core fluid L #ies and the downcomer fluid node. The automatic depressurization system (ADS) is modeled in full, with fluid nodes and flow links representing the pipework between the first through third stage valves and the sparger. The Henry-Fauske and HEM critical flow models are used to calculate the critical flow through ADS valve flow links 58,184, and 185. The NRC-approved evaluation model break flow model is used for the postulated break.
=
[
]"
=
Only safety-related systems are modeled, with the single active failure of one ADS Stage 4 valve as stated in the text of the SSAR Chapter 15.6.5.4B. AP600 NOmUMP Model May 1998 o:\4206w.non:1NM0998 Revision 2
4-2
=
[ ju
. To better represent phenomena associated with flow through the ADS stages, fluid nodes are placed upstream from the ADS valve locations.
. As in the NRC-approved evaluation model, steady-state controller fluid nodes and flow links are employed to initially assist in establishing a steady 102 percent power plant condition at the time of the LOCA.
. When pressure upstream of potential ADS critical flow locations is reduced to the
[ ju
4.1 REFERENCES
- 1. Fittante, R. L., et al., "NOTRUMP Final Validation Report for AP600," WCAP-14807,'
Revision 4 (Proprietary), February 1998.
- 2. USNRC, letter from Cecil O. Thomas to E. P. Rahe, Jr., Westinghouse, " Acceptance for Referencing of Licensing Topical Report WCAP-10079(P), 'NOTRUMP, a Nodal Transient Small-Break and General Network Code'," May 1985.
AP600 NOTRUMP Model May 1998 ' o:\4206w.nore1M61098 Revision 2
4-3 8,C i Figure 4-1: Base Noding Scheme Used for the AP600 Fluid Nodes and Flow Links _ AP600 NOTRUMP Model May 1998 o \4206w.non:H>460998 Revision 2
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5-1 i l 5.0 LONG-TERM COOLING (LTC) ANALYSES METHODOLOGY l To confirm the successful emergency core cooling system (ECCS) performance of the AP600 plant during the long-term cooling (LTC) phase of postulated LOCA events, window mode calculations are performed as described in References 1 and 2. The windows selected for the AP600 are at limiting times during LTC as judged by the prevailing core decay power, sump level, water temperature, and other conditions. A spectrum of LOCA break cases is provided, and the stipulation of conservative assumptions provides confidence in the capability of the plant. In particular, the long-term core cooling analyses in AP600 SSAR subsection 15.6.5.4c are performed in compliance with the conservatism outlined in 10 CFR 50 Appendix K.
5.1 DESCRIPTION
OF THE ECOBRA/ TRAC NODING FOR THE AP600 LONG-TERM COOLING ANALYSIS The WCOBRA/ TRAC vessel noding used for the long-term cooling analyses of the AP600 is { simplified from those used for the AP600 and conventional three and four-loop plant large break LOCA analysis. In a large break analysis, the AP600 is modeled from the time of the break for a period of up to 120 seconds. After this time, the core is fully quenched and the ; analysis of the core can be concluded. In LTC analysis, the objective is to show that the l passive safety systems are adequate in the long term to maintain core recovery and that ; boron precipitation is not a problem. It may be necessary to consider times days after the break to show this. In order to carry out a calculation over such long periods of time, it is necessary to make simplifications to vessel noding to reduce computation time to a practical amount. I The number of sections in the vessel has been reduced, and the number of channels within l each section has also been reduced. This results in a corresponding reduction in the number of cross-flow gaps. The number of sections, channels, and gaps in the reactor vessel is reduced from [ ]", respectively, in Section 3 to [ ]" in the LTC noding scheme. The number of axial levels in each section is reduced; the total number of levels in the vessel is reduced from [ ]". Figure 5-1 shows the elevation of the vessel for LTC analysis. The section boundary heights are relative to the inside of the bottom of the vessel. Figure 5-2 shows plan views of the vessel sections. Values within squares are channel numbers and values within circles are gap numbers. ECOBRA/ TRAC assumes that a flow path exists between vertically connected channels, unless otherwise specified in the input. Transverse flow between channels in the same section only exists if they are specified l as connected by gaps. The volume, axial flow area, and wetted perimeter of each channel is specified in the code input. There is also the capability to vary these quantities within a channel; for example, in long-Term Cooling (LTC) Analyses Methodology May 1998 oM206w.non:H>O60998 Revision 2
5-2 Channel 10, representing the core, the aial flow area at the top of the core is lower than within the core, because of the flow obstructic,n caused by the upper core plate. For the LTC analysis, the cold legs and horizontal portions of the hot legs are also represented by vessel channels; whereas in the large break analysis, all of th.1 loops up to the vessel wall are represented by one-dimensional components. In long-term cooling there is potential for significant counter-current flow in the horizontal portion of the hot and cold legs. The drift flux model in }yCOBRA/ TRAC used for one-dimensional components is not adequate for this type of flow; thus, it is necessary to use vessel channels, which treat the liquid and vapor as separate phases permitting interphase slip. The loop one-dimensional components begin at the point where the loop elevation begins to rise for the hot legs and at the reactor coolant pump (RCP) outlet for the cold legs. The hot and cold legs are modeled in vessel Section 4, which is described later. Vessel Section 1: Lower Head, Lower Plenum, and Bottom Nozzle Regions [ ya Vessel Section 2: Core Active Fuel Region .[ ys Long-Term Cooling (LTC) Analyses Methodology May 1998 o:\4206w.non:H>460998 Revision 2
5-3 [ y, Vessel Section 3: Counter Current Flow Region and Lower Portion of Upper Plenum I ya Vessel Section 4: Loop Region [ ya Long-Tenn Cooling (LTC) Analyses Methodology May 1998 o:\4206w.non;m.060998 Revision 2
1 I 5-4 ( 1" Vessel Section 5: Lower Portion of Upper Head and Top of Downcomer [
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Vessel Section 6: Top Portion of Upper Head [ l ju AP600 Core Power [ l l l }" l L Long-Term Cooling (LTC) Analyses Methodology May 1998 c:\4206wsoruim8 Revision 2 L - - - _ _ _ - _ - - - - _
5-5
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. Modeling of Loop Components
[ l-ys i - Long-Term Cooling (LTC) Analyses Methodology. May 1998 l- cano6w.non:1be60998 Revision 2 1
5-6 5.2 COMPUTATION OF BOUNDARY CONDITIONS FOR THE AP600 EMERGENCY CORE COOLING SYSTEM .WCOBRA/ TRAC ANALYSIS WINDOWS i Large and small break LOCA events are analyzed in the short term using computer codes specifically designed for each break category. Large break LOCA events (SSAR subsection 15.6.5.4A) are analyzed by applying the WCOBRA/ TRAC best-estimate methodology to the AP600 to analyze the core response until total fuel rod quench is predicted. The small break LOCA events of <1.0 ft.2 in area (SSAR subsection 15.6,5.4B) are analyzed, using a NOTRUMP version specifically created and validated for AP600, to perform an Appendix K analysis until the steady, continuous injection of water from the IRWST is established. The time of completion of the short-term ECCS analyses provides information needed to establish the boundary conditions for the LTC window mode analyses. 5.2.1 IRWST Draindown and Core Boiloff Calculations to Establish Mass / Energy Releases-The containment mass and energy releases for the short-term analysis of an SSAR LOCA transient are supplied to WGOTHIC (Reference 3). In addition, the mass and energy releases during the IRWST injection period must also be determined. To accomplish this, first the drain rate of the IRWST is computed based on the minimum initial inventory and the tank condition at the initiation of IRWST injection. [ ya A NOTRUMP model of the IRWST, and the passive safety system piping connecting it to the reactor vessel, is used to compute the draining of the IRWST during a double-er.ded DVI line break. The method is a simplified application of the NOTRUMP modeling which has been qualified for the AP600 in the code validation effort; [ y.c Long-Tenn Cooling (LTC) Analyses Methodology May 1998 o:\C06w.non:1b&O998 Revision 2
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Long-Term Cooling (LTC) Analyses M<. thodology May 1998 c:\4206w.non:1bam9s Revision 2 j u a
L c5-8 I y 5.2.2 EGOTHIC Containment Pressure Computation Removal of decay heat from the AP600 in the long term occurs via the condensation of steam
- on the inside of the ' containment shell. The AP600 is equipped with gutters to return condensate formed on the containment shell as a result of heat transfer to the environment
'and back into the IRWST.
The AP600 SSAR, subsection 15.6.5.4C, analysis of post-LOCA LTC does not credit condensate return into the EmNcT. axcept for one sensitivity large break LOCA case. When the gutter return is presumed, condensate':-turnmg to the IRWST maintains the water level
. therein to some extent and extends the IRWST drain period. - The increase in the hydrostatic head from the returned condensate increases the rate of IRWST injection into the reactor
. vessel through the DVI lines at any given time durmg the IRWST drain period. Furthermore, when the gutters are assumed to be effective in retuming condensate to the IRWST, injection from the containment sump with its lower liquid head is delayed by several hours during a -
. LOCA LTC transient. The " gutters unavailable" scenario is the more limiting case, and it was the scenario simulated in the Oregon State University LTC tests (Reference 4).
For the SSAR LTC analysis, the ECOBRA/ TRAC calculation of ECCS performance is interfaced with the WGOTHIC prediction of AP600 containment response during postulated 1LOCA events. WGOTHIC is a well benchmarked, state-of-the-art containment analysis computer code that is suited to the AP600 passive systems application. In the SSAR LTC
; analysis methodology, a WGOTHIC analysis is performed using the mass / energy releases
' defined as indicated above. This provides boundary condition information to the WCOBRA/ TRAC long-term ECCS performance analysis window mode calculations such as
; containment pressure, sump levels in the various containment compartments, and the liquid temperatures within those compartments. WGOTHIC is executed from time zero of the LOCA event using mass / energy releases, as indicated in Figure 5-8 for the small break LOCA cases, to generate the subject information for use in WCOBRA/ TRAC. The two computer codes are interfaced as shown in Figure 5-8 to accomplish the analysis of breais postulated to occur in AP600 piping.
WGOTHIC is applied in such a manner that it provides a conservative boundary condition for the WCOBRA/ TRAC computation. The noding of the lumped-parameter AP600-WGOTHIC containment evaluation model is applied to compute not only the containment pressure transient but also the filling of the sump with liquid. The SSAR subsection 15.6.5C
- LTC ECCS performance analysis use of WGOTHIC involves only containment phenomena for which EGOTHIC is already validated; the code version employed is the one used for the Img-Term Cooling (LTC) Analyses Methodology May 1998 c:M206w.non:1b40998 Revision 2 e __ _-- _ _ _ - _ _
5-9 AP600 SSAR Section 6.2 analyses. However, in contrast with the AP600 containment integrity analysis, no penalties in heat transfer or in mixing / stratification modeling are included for this application. The initial and boundary conditions for lyGOTHIC are conservatively establisl.ed as follows to minimize the computed pressure in a manner comparable with that of other 10 CFR 50, Appendix K, analyses: ( l l { ju Img-Term Cooling (LTC) Analyses Methodology May 1998 c:\4206w.non:Im Revision 2
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5.3 CONSIDERATIONS IN LONG-TERM COOLING EMERGENCY CORE COOLING SYSTEM PERFORMANCE CALCULA110NS The WCOBRA/ TRAC nodalization of the AP600 is consistent with the modeling of the OSU Test Facility presented in the LTC validation report (Reference 1). In particular, the RCS hot legs and cold legs are modeled using the COBRA VESSEL component channels to make use of its two-fluid, three-field capability. A simplified reactor vessel noding that is consistent with that of Reference 1 is employed. The PXS and RCS loops are also modeled consistent with the Reference 1 test simulations. Initial conditions are specified consistent with the input boundary conditions that were established in the WGOTHIC analysis. Among the conservatism imposed for compliance with 10 CFR 50 Appendix K are the following: ANS-1971 standard decay heat with +20 percent uncertainty Use of the locked-rotor reactor coolant pump K-factor
. Computation and use of a low containment pressure Also, maximum design resistances for the DVI lines and ADS Stage 4 flowpaths are input to y{ COBRA / TRAC for LTC window mode calculations.
The cases presented in the SSAR address the spectrum of possible LOCA break sizes and the issues of adverse nonsafety-related system operation interactions, potential passive failure (s) in the long-term that degrade the available sump liquid head, and identified Draft Safety Evaluation Report (DSER) open items. Reference 2 provides further information about the cases chosen for the SSAR LTC analysis. LARGE BREAK LOCA EVENTS In subsection 15.6.5.4C of the AP600 SSAR, Revision 13, resulb of three WCOBRA/ TRAC analyses are reported. As discussed in the SSAR, the extended large break LOCA calculation of CMT injection that is presented is bounding for the initiation of IRWST injection. The two window mode analysis results presented for the large break LOCA (SSAR subsections 15.6.5.4C.3.2 and 3) are for the IRWST injection time period; [ ju Long-Term Cooling (LTC) Analyses Methodology May 1998 o:\4206w. north >060998 Revision 2
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SUMMARY
To establish that a margin comparable to that exhibited by current generation PWRs exists in the. post-LOCA LTC performance of the AP600, SSAR subsection 15.6.5.4C presents a spectrum of window mode methodology analyses. These windows are performed with the long-Term Cooling (LTC) Analyses Methodology May 1998 o:\4206w.nore1be60998 Revision 2
5-12 l ' WCOBRA/ TRAC computer code using a nodalization which has been validated by the simulation of pertinent OSU facility tests. Among the many conservatism applied are the use of 10 CFR 50, Appendix K, decay heat, use of design maximum flow path resistances, definition of boundary conditions by a conservative WGOTHIC containment simulation, and identification of early timing of occurrence for the mintmum hydraulic head conditions. The LTC calculations presented in subsection 15.6.5.4C of the AP600 SSAR show that the 10 CFR 50.46 requirement for long-term core decay heat removal is met because the core remains covered, and an adequate flushing flow exists to prevent boron precipitation on the fuel rods. REFERENCES
- 1. Garner, D. C., et al., "WCOBRA/ TRAC Long-Term Cooling Final Validation Report,"
WCAP-14776,~ Rev. 4, March 1998 (Proprietary).
' 2. Garner, D. C., et al., "AP600 Long Term Core Cooling Summary Report,"
WCAP-14857, March 1997 (Non-Proprietary).
- 3. Forgie, A., et al., "WGOTHIC Application to AP600," WCAP-14407, Rev. 3, April 1998.
- 4. Andre) .hek, T. S., et al., "AP600 Low-Pressure Integral Systems Test at Oregon State University Test Analysis Report," WCAP-14292, Revision 1, September 1995.
i I 1' l
- Long-Tenn Cooling (LTC) Analyses Methodology May 1998 oM206w non:1b 060998 Revision 2
5-13 Figures 5-1 through 5-9 are Westinghouse proprietary (a,c) and therefore, not included in this Class 3 WCAP l i l l ,. l Long-Term Cooling (LTC) hlys.es Me6Molg May 1998
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6-1 6.0 TRANSIENT MASS DISTRIBUTION (TMD) CODE FOR AP600 SUBCOMPARTMENT MODEL l The Transient Mass Distribution (TMD) code (References 1 and 2) is a mathematical model developed by Westinghouse to simulate the pressure transients subsequent to a LOCA or a main steamline break (MSLB) inside the containment. This code is utilized to calculate the pressure transient for a very short time period during the initial blowdown of the transient. The peak pressure differences on various structures occur within the first few seconds of these transients. The pressure and temperature transients inside the containment are calculated for the postulated breaks using the TMD code. In order to model the various compartments of a containment, a control volume technique is used to spatially represent these regions. The conservation of mass, momentum, energy and the equation of state are solved within each control volume as a function of time and space. The model includes moisture entrainment effects in the momentum and energy equations. The peak pressures in each element, and the peak differential pressures across structures within the containment, are determined from these calculations. The pressure differentials occur because of the propagation of the pressure disturbance around the containment subsequent to the pipe break. The TMD code has been reviewed by the NRC and approved for use in subcompartment differential pressure analyses. SSAR Section 6.2.1.2 provides the maximum differential pressure results for postulated breaks in the AP600 containment subcompartments. The break sizes and locations are defined by the leak before break criteria described in SSAR Section 3.6. The TMD model of the AP600 subcompartments is represented by [ ] separate control volumes with a flow path network that is designated by " hoop", " radial", and " axial" flow paths. The designation of hoop, radial, or axial is of no physical importance for subcompartment analyses (it simply facilitates the ability to model a maximum of three flow paths from one control volume). The specific geometric and friction factor data for the " hoop" flow paths is shown in Table 6-1 (sheets 1 through 4). The data for the " radial" flow paths is shown in Table 6-2 (sheets 1 through 4) and the data for the " axial" paths is shown Table 6-3 (sheets 1 through 4). The free volume of each of the [ ]^* nodes, and the respective initial conditions, is shown in Table 6-1 (sheets 1 through 3). The control volume and flow path network for the [ ] TMD model is shown in Figure 6-1 (sheets 1 through 12) TMD Code for AP600 Subcornpartment Model May 1998 c:\c06w-1.non:1M60998 Revision 2
. l 6-2 The following piping is postulated to break:
. 4-inch SG Blowdown Line
. '4-inch Pressurizer Spray Line
. 3-inch RCS branch lines from the Hot Leg or Cold Leg l . 1.0-ft:MSLB 1-These breaks can be' postulated to occur in tim following AP600 compartments:
- Steam Generator Compartment a Pressunzer Compartment
- Pressurizer Valve Room a' ~ Chemical and Volume Control System (CVS) Room
- CVS Pipe Tunnel
- Pipe Penetration Area
6.1 REFERENCES
'1. Bordelon, F. M., Colenbrander, H. G. C., WCAP-7548, " Analysis of the Transient Flow Distribution Dunng Blowdown in the Ice Condenser Reactor Containment (TMD Code)," July 1970 (Westinghouse Proprietary)
- 2. " Ice Condenser Containment Pressure Transient Analysis Methods," WCAP-8077, March 1973 (Westinghouse Proprietary)
, 'IMD Code for AP600 Subcompartment Model May 1998 c:\4206w.1.non:H>460996 ' Revision 2 L -_ _ _ - _ _
6-3
' Tables 6-1 through 6-4 are Westinghouse proprietary (a,c) and therefore, not included in this Class 3 WCAP.
j Figure 6-1 is Westinghouse proprietary (a,c) and therefore, not included in this Class 3 WCAP. l TMD Code for AP600 Subcompartment Model May 1998 c:u206w-1.non:1balova Revision 2 o ,}}