ML20086D255
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| Site: | 05200004 |
| Issue date: | 07/05/1995 |
| From: | GENERAL ELECTRIC CO. |
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.a Attachment to MFN 097-95 PRE-TEST ANALYSIS FOR PANTIIERS IC TESTS June,1995 JR Fitch (GENE)
K Kobayashi(JAPC)
AI Yang (GENE) 950710oo30 95o705 PDR ADOCK 0520 4
TABLE of CONTENTS Einge
1.0 INTRODUCTION
1 2.0 TEST FACILITY AND TEST MATRIX
-1 1-l' 3.0 APPLICABILITY OF DATA TO SBWR 5
1 4.0 TRACG MODEL AND NODALIZATION 5
5.0 TEST SIMULATION 10 6.0 RESULTS OF PRE-TEST CALCULATIONS 10 7.0 DISCUSSION 16
8.0 REFERENCES
17 l
l I
l l
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l 1
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i
LIST of TABLES 4-1.
TRACG Components for Simulation of PANTHERS IC Test 4-2.
Comparison of PANTIIERS and SBWR ICS Nodalizations 8
6-1.
Results of Pre-Test Calculation for IC Matrix Test 6 11 6-2.
Results of Pre-Te:t C !;dation for IC Matrix Test 13
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O LIST of FIGURES h
2-1.
PANTHERS IC Test Facility Schematic 3
2-2.
Isolation Condenser Test Article 4
I 4-1.
TRACG Nodalization for Simulation of PANTIIERS IC Test 9
F 6-l.
Accumulator Tank Dome Pressure for Test 6 12 6-2.
Steam Flow and Drain Flow for Test 6 12 6-3.
IC Heat Transfer Rate for Test 6 13 P
6-4.
Accumulator Tank Dome Pressure for Test 13 14 6-5.
- Steam Flow and Drain Flow for Test 13 14 6-6.
IC IIcat Transfer Rate for Test 13 15 e
I P
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ACKNOWLEDGMENTS I
l The authors thank JM IIealzer (currently employed by the Paul Scherrer Institute in Switzerland) for developing and successfully running the first version of the PANTHERS IC TRACG model. Thanks also to L Klebanov, JM Shaug, and BS Shiralkar for helpful suggestions on the TRACG modeling.
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1.0 INTRODUCTION
The purpose of this document is to present and discuss the results of pre-test calculations, performed with the Level-2 version of the TRACG code, for two of the isolation condenser (IC) tests planned for the PAMllERS test facility. TRACG is being used for the calculation of SBWR transient performance and SBWR response to a postulated LOCA. Models of the isolation condenser system (ICS) are incorporated in these simulations. Consequently, it is appropriate to compare a calculation of condenser-performance, using a TRACG model of the PANTHERS IC test facility, with the test data. This will reinforce the qualification of TRACG for the modeling of ICS performance.
The first step in the comparison process, documented in this report, was to perform a
" double-blind" pre-test calculation of two of the thermal-hydraulic performance tests in the PANTIIERS IC test matrix. A double-blind calculation is defined as one in which neither the actual test conditions nor the test data are available. The decision to perform a calculation for two tests was based on the judgment that this is a sufficient number to provide a baseline for code performance. The tests selected for the pre-test calculation are identified in Table A.3-6 of Reference 1 and are described in Section 5.0 of the current report.
It was intended that tne TRACG input model used for the pre-test calculations be based directly on the representation of the ICS in the SBWR TRACG models. This presented a problem because there was some difference in the ICS models incorporated in the SBWR transient, LOCA, and containment TRACG input models. As a result, the SBWR models were modified to achieve a higher degree of consistency with each other and with the PANTIIERS model. This aspect of the pre-test calculation study is discussed in Section 4.0 which includes a detailed comparison of the PANTIIERS and SBWR TRACG representations of the IC system. It is not appropriate (or possible) to enforce strict consistency between the PANTHERS and SBWR representations of the ICS piping outside the boundaries of the IC pool because the PANTIIERS piping layouts differ in detail from the SBWR conceptual design. Ilowever, an attempt has been made to maintain a reasonable degree of modeling consistency between the PANTHERS and SBWR models of the piping outside the pool.
2.0 TEST FACILITY and TEST MATRIX The IC test facility and test matrix are described in References I through 3. One-half of a prototype IC will be tested at pressures, temperatures and flows representative of SBWR transient and post-LOCA conditions to confirm the thermal hydraulic and structural design. The tests will be performed at the PANTHERS facility of SIET S. p. A. in Piacenza, Italy, 1
A schematic representation of the IC test facility is given in Figure 2-1, and an outline drawing of the heat exchanger assembly is given in Figure 2-2. The IC unit is one module of a full-scale, two-module vertical-tube heat exchanger designed and built by Ansaldo.
In uddition to the condenser unit, the principal test facility components are the simulated RPV (the "acemnulator tank"), the steam supply and condensate drain lines, and the IC pool. An additional component, utilized for transient testing with injection of noncondensable gases, is the vent line emanating from the lower header of the condenser unit. This vent can be activated on a high pressure signal and, thereby, used to simulate automatic venting from the lower header on a high pressure signal in the SBWR. The PANTHERS facility, like the SBWR, also has a vent from the upper header. The upper vent will only be used if the lower vent is unable to satisfactorily purge the unit of noncondensable gases and restore it to full heat transfer capacity. In the SBWR operation of the ICS, only the lower vent will open automatically on a high pressure signal.
The IC test matrix is divided into thermal-hydraulic performance tests and structural tests. The thermal-hydraulic performance tests include steady-state operation at a prescribed inlet pressure, transient tests with noncondensable gas injection followed by venting, transient tests with increasing and decreasing pool water level, and startup demonstration tests. The test matrix covers a wide range of inlet pressures and temperatures characteristic ofIC operation over the full range of operational transient and post-LOCA RPV conditions.
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3.0 APPLICABILITY of DATA to SBWR One of the objectives of the PANTifERS IC test program (Reference 1, paragraph A.3.1.2.2) is to: " Provide a sufficient data base to confirm the adequacy of TRACG to predict the quasi-steady heat rejection performance of a prototype IC heat exchanger, over a range of operating pressures that span and bound the SBWR range." As stated in paragraph A.3.1.2.5 of Reference 1, the primary comparison of analysis with test data will be on the total heat rejection rate and, for transient tests, IC inlet pressure.
The test matrix for the PANTIIERS tests is described in detail in References 2 and 3.
Originally, the focus of the IC tests was on high-pressure conditions, representative of the performance of the IC system to control reactor pressure during operational transients.
Subsequently (Reference 3) the test matrix was modified to collect data at lower pressures, encompassing the range associated with design basis accidents (LOCAs), and to extend the evaluation ofIC transient performance during the ingestion and subsequent venting of noncondensable gas mixtures. The tests with noncondensable gas simulate the mixture of oxygen and hydrogen which could be generated by radiolysis during an isolation transient.
Scaling issues for the PANTHERS IC test are addressed in Section B.3 of Reference 1.
Applicability of the PANTHERS IC test data to the SBWR is based on the fact that the test facility is a full-scale prototype of one-half of an IC unit and the condenser pool.
Considering the dual-module design of the condenser, it is reasonable to conclude that there will be no significant distortion in thermal-hydraulic performance as compared to testing of a full condenser.
i 4.0 TRACG MODEL and NODALIZATION The TRACG model used for pre-test analysis of the PANTHERS IC test facility is shown in Figure 4-1. A listing of the TRACG components and theirjunction numbers is given in Table 4-1. The TRACG simulation explicitly represents the condenser unit, the condenser coolant pool, the accumulator tank, the steam and drain line piping, and the vent line from the lower header of the condenser. All components, with the exception of the accumulator tank and the vent line, were based on Ansaldo or SIET design drawings.
Design drawings for the accumulator tank and vent line were not available at the time of the preparation of the pre-test model. Modeling of the accumulator tank was based on key parameter values (free volume, height, and inside diameter) provided by SIET. Modeling of the vent line from the lower header was based on the SBWR conceptual design.
The model was completed by the addition of several TRACG " FILL" and "BREK" components (abbreviated by "F" and "B", respectively, on Figure 4-1). FILLO3 (F03) supplies steam to the accumulator tank at a prescribed rate. FILLO4 (F04) acts as a level control on the accumulator tank, withdrawing water at the same rate steam is supplied.
5
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FILLO7 (F07) is used to supply noncondensable gases for transient testing of IC venting performance. BREK02 (B02) and BREK41 (B41) enforce atmospheric pressure boundary conditions at the end of the IC vent line and above the IC coolant pool, respectively.
The IC headers and tubes were modeled by components PIPE 91 (P91), representing the upper header, TEE 25 (T25), representing the lower header, and PIPE 95 (P95),
representing the 120 condenser tubes in a single IC module. Each of the headers is axially nodalized into three equal-length cells. PIPE 95 has eight equal-length cells, each surrounded by a heat-conducting wall which absorbs energy from the fluid within the cell and discharges it to the condenser pool. VLVE51 (V51), the vent line, consists of six equal-length cells and connects to the uppermost cell of the lower header. TEE 40 (T40) represents the PCC pool, which acts as a refill pool for the IC via Junction (J) 70. The airspace above the refill pool is connected to atmospheric pressure via J94 and to the airspace above the IC pool via J71. The IC steam line, TEE 21 (T21), and drain line, VLVE47 (V47), are modeled, respectively, with 24 and 18 one-dimensional cells. The modeling of the drain line is somewhat simplified from the actual piping layout but the total length and elevation change of the line were preserved. Hydraulic loss factor inputs are based on standard handbook calculations.
The accumulator tank and the IC coolant pool are modeled with the TRACG "VSSL" component in r-z geometry with two radial rings. The accumulator tank includes five axial levels and the coolant pool has seven axial levels. In the case of the coolant pool, the two radial rings provide for a buoyancy-driven downcomer/ riser circulation path. The use of the VSSL component for the accumulator tank is primarily for convenience in making the multiple piping connections to the tank. The steam line joins to the inner ring at the top of the tank (J3) and the drain line returns to the outer ring in the second level (J10). Steam supply is from F03 at J6 and liquid removal for level control is to F04 via PIPE 06 (P06) and J12.
A comparison of the nodalization in the PANTHERS and SBWR models of the ICS is shown in Table 4-2. The models are consistent with respect to the nodalization of the upper and lower headers and the condenser tubes. At the start of the PANTHERS TRACG model development activity, there were differences in the tube and header nodalizatioi between the SBWR transient /LOCA models (the transient and LOCA models have the same ICS model) and the SBWR containment model. Modifications were made to make the SBWR tube and header models consistent with each other and with the PANTilERS model. Differences between the PANTHERS and SBWR models of the steam, drain, and vent piping are to be expected because the layouts for these lines in the PANTHERS facility differ from the SBWR conceptual design layouts on which the SBWR models are based. Differences between the representations of these lines in the SBWR transient /LOCA and containment models is an artifact of the historical development of these models. The differences are not large and would not be expected to influence predicted ICS behavior. (Note that TRACG has not been used for calculation of long-term SBWR transient response and, consequently, the transient input model does not include the vent line.)
6
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The remaining difference between the models is in the simulation of the pool The pool model from the SBWR containment model has been used for the PANTHERS simulation. The pool in the transient /LOCA model consists of a one-dimensional TEE component connected to FILL and BREK components. The coolant flow rate and inlet temperature are imposed via the FILL input. The BREK component allows boiloff to atmospheric conditions. With some experience, a circulation rate can be prescribed with comparable accuracy to that which is predicted by the two-dimensional VSSL simulation of the pool used for the SBWR containment and PANTHERS models. The main advantage of the VSSL model is for long term containment performance simulations where it provides the capability to track the decrease in the pool level with time.
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Component J1 J2 J3 Description BREK02 11 bottom header vent to atmosphere BREK41 94 pool vent to atmosphere FILLO3 6
steam flow to accumulator tank FILLO4 13 level control for accumulator tank FILLO7 15 noncondensable gas flow PIPE 06 12 13 FILL 04 connection to accumulator tank PIPE 91 5
7 upper header PIPE 95 7
8 condenser tubes VLVE05 15 16 FILLO7 connection to TEE 21 VLVE47 9
10 condensate drain line VLVE51 4
11 vent line from lower header VSSL01 accumulator tank and pool TEE 21 3
5 16 inlet line TEE 25 8
9 4
lower header TEE 40 70 94 71 refill pool Table 4-1. Components for Simulation of PANTHERS IC Test Number of Cells Segment PANTIIERS SBWR SBWR Transient /LOCA Containment inlet line 24 8
11 upper header 3
3 3
condenser tubes 8
8 8
lower header 3
3 3
drain line 18 22 15 vent line 6
N/A 10 pool 14 6
14 Table 4-2.
Comparison of PANTIIERS and SBWR ICS Nodalizations 8
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h 5.0 TEST SIMULATION A double-blind pre-test calculation was performed for PANTIIERS IC matrix tests 6 and 13 (as per Table A.3-6 of Reference 1). The TRACG simulation of the tests was based on the Test Specification (References 2 and 3) and Test Procedures (Reference 4) documents issued, respectively, by GENE and SIET.
The specification for Test 6 states that steady state operation is to be established at 4.83 I
MPag. The TRACG simulation was performed by calculating a range of steady-state pressures by varying the inlet steam flow (FILLO3 in Figure 4-1). The steam flow which results in an accumulator pressure of 4.83 MPag is the desired result for the pre-test calculation.
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l The specification for Test 13 states that: (1) steady-state conditions are established at an l.
accumulator pressure of 2.07 MPag; (2) an air / helium mixture is injected, causing the pressure to rise; and (3) the lower header is vented when the pressure reaches 7.65 MPag.
At the time the lower header is vented, the air / helium mixture flow is stopped and the pressure allowed to return to a steady-state.
The TRACG simulation of Test 13 began, in the same manner as for Test 6, by detennining the inlet steam flow (FILLO3) which would result in an accumulator pressure of 2.07 MPag. After the steady-state condition is well-established, noncondensable flow is initiated at a rate of 5 g/sec. The 5 g/sec rate is at the high end of the range allowed by the test procedures (Reference 5, Appendix A.3, p. I1, Step 150). The gas is a mixture of helium and nitrogen with a density ratio (nitrogen to helium) of 3.6. (The nominal value of this parameter has recently been revised to 3.5. The difference between 3.6 and 3.5 is within the tolerance allowed by the test procedures (Reference 4).) TRACG control system input was used to open the vent and shut off the noncondensable flow at an accumulator pressure of 7.65 MPa. The vent was held open for a period of ten minutes.
The vent was then re-closed and steady-state conditions with pure steam flow were reestablished.
6.0 RESULTS of PRE-TEST CALCULATIONS l
Test 6 i
The results of the pre-test calculation for matrix Test 6 are shown in Figures 6-1 to 6-3.
The initial transient behavior is uniquely associated with the assumed initial conditions and the manner in which the start of the test is simulated. The reason for showing the
)
transient behavior is to demonstrate thaLa satisfactory steady-state, which represents the focus of the pre-test calculation for Test 6, has been achieved. Figure 6-1 shows the pressure in the dome of the accumulator tank which reaches a steady-state value of 5.01 MPa as compared to the value of 4.93 MPa specified for this test. This is within the range of +/- 3% allowed by the test procedures (Reference 4) and, on this basis, further 10
i iteration of the calculation was judged to be unwarranted. Figure 6-2 shows the steam flow at the entrance to the inlet line (J3 in Figure 4-1) superimposed on the drain flow exiting from the bottom header (J9). The steady state value of these flows is 10.4 kg/sec.
This flow rate is slightly below the steam flow imposed via FILL 03 (Figure 4-1) which is 10.8 kg/sec (see Section 7.0). Figure 6-3 shows the corresponding IC heat removal of 17.3 MW. Table 6-1 summarizes the results of the pre-test calculation for Test 6. Two steam flows are shown in the table. The first is the flow imposed via Fil.LO3 and the second is the flow at the entrance to the IC inlet line.
Inlet Pressure (MPa)
Steam Flow (kg/sec)
Imposed / Inlet 5.01 10.8/10.4 17.3 Table 6-1. Results of Pre-Test Calculation for IC Matrix Test 6 Test 13 The results of the pre-test calculation for matrix Test 13 are shown in Figures 6-4 through 6-6 Figure 6-4 shows the pressure transient. Following the start-up transient, an initial steady-state pressure of 2.11 MPa (compared to the test specification value of 2.17 MPa) is reached. Again, this difference is within the allowable +/-3% so no further iteration was performed. The imposed steam flow to achieve this pressure is 5.56 kg/sec. The IC inlet steam flow (Figure 6.5) is 5.48 kg/sec and the associated IC heat transfer rate (Figure 6-6) is 10.2 MW. Noncondensable gas flow is initir.ted at 8000 sec. and causes the accumulator pressure to increase to 7.65 MPa in 2.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> by which time the injected inventory of noncondensable is 47.1 kg. The vent pipe from the lower header is then opened and, simultaneously, the flow of noncondensable is stopped. The vent pipe is kept open for 10 minutes and then closed. The pressure decreases to a new steady-state value of 2.56 MPa (Figure 6.4). Figures 6-5 and 6-6 show, respectively, the variation in IC inlet steam flow (and drain flow) and heat transfer rate. Following the venting transient, the steam flow to the condenser (Figure 6-5) is 5.13 kg/sec and the IC heat transfer rate (Figure 6-6) is 10.0 MW. Table 6-2 summarizes the results of the pre-test calculation for Test 13. Again, the imposed (constant) steam flow rate is shown together with the inlet stem flow to the IC.
Pressure (MPa)
Steam Flow (kg/sec)
Noncondensable Imposed / Inlet Inventory (kg) 2.11 5.56/5.48 10.2 0.0 7.65 (see " Discussion")
(see " Discussion")
47.1 2.56 5.56/5.13 10.0 (see " Discussion")
Table 6-2. Results of Pre-Test Calculation for IC Matrix Test 13 11
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Ogure 6-6. IC llent Transfer Rate for Test 13 1
15
s 7.0 DISCUSSION The pre-test calculation for Test 6 predicts a steady-state heat transfer rate of 17.3 MW at an inlet pressure of 5.01 MPa. This result can be evaluated in terms of the design rated heat transfer rate of 30 MW for a full (two-module) IC unit at a pressure of 7.24 MPa with a saturated IC pool (Reference 5). The increase in pressure from 5.01 to 7.24 MPa would raise the overall AT from the tubeside steam to the poolside water from 162 K to 186 K (taking the poolside water temperature at a nominal value of 375 K). Increasing the IC power from the present analysis by the ratio of these ATs gives 39.8 MW on a full-unit basis. According to Reference 5, however, the IC heat transfer area includes a 5% tube 2
plugging allowance and an outside tube wall fouling resistance of 0.00009 m -K/W.
When these two factors are taken into account, the extrapolation of the predicted heat transfer performance to 7.24 MPa is 29.4 MW, slightly below the design specification.
An additional factor, however, (see below) is that the inside and outside film heat transfer coefficients would be expected to increase with increasing inlet pressure. When this factor is taken into account, it can be concluded that the TRACG result at 5.01 MPa is consistent with an IC design heat transfer capability of 30 MW at 7.24 MPa.
The pre-test calculation for Test 13 is initiated by establishing steady-state conditions at an inlet pressure of 2.11 MPa. The corresponding IC inlet steam flow and heat transfer rate are 5.48 kg/sec and 10.2 MW, respectively. Comparing this result with the Test 6 calculation, it is observed that about two-thirds of the increase in heat transfer rate at the higher pressure can be attributed to the higher AT from the tubeside steam to the poolside water. The poolside water is nominally at 375 K. At 5.01 MPa, the saturated steam temperature is 537 K, resulting in an overall AT of 162 K. At 2.11 MPa, the saturation temperature is 488 K, resulting in an overall AT of 113 K. This difference, by itself, would explain a 43% increase in heat transfer rate as compared with the calculated increase of 70%. The remainder of the increase is due to higher film heat transfer coefficients on both the inner and outer tube surfaces at the higher pressure. The condensate film Reynolds number is in the turbulent regime which means that a higher condensation rate results in less resistance to condensation. Similaily, the poolside film resistance is decreased with increasing heat flux. Both of these factors act to increase the heat transfer rate more than linearly with increasing temperature difference.
Following the initial steady state in the Test 13 simulation, a transient is induced by the injection of a mixture of nitrogen and helium. The key parameter for future comparison with the test data is the gas inventory required to raise the pressure to the 7.65 MPa trip point for venting from the lower header. As shown in Table 6.2, this inventory is 47.1 kg based on a mixture of 3.6 kg of nitrogen per kg of helium. When the vent is opened, both the inlet steam flow and the condenser power undergo a transient increase as steam is flashed from the surface of the accumulator tank. Following the noncondensable purge and re-closure of the vent, the pressure reaches a new steady-shte value of 2.56 MPa at an inlet steam flow of 5.13 kg/sec and IC power of 10.0 MW.
16
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l The higher pressure required to condense the inlet steam following the purge is attributed l
f to retention of a small inventory of noncondensable which slightly degrades the heat l
transfer performance. It should be noted that the test procedure (Reference 4) calls for j
manual venting from the upper header if venting from the lower header has not removed
]
enough of the noncondensable gas inventory to restore the unit to its full heat transfer capability. The upper-header vent is not included in the TRACG model (PANTIIERS or f
SBWR) because it requires operator action in contrast to the lower-header vent which, in SBWR, opens automatically on high pressure.
A notable feature of the TRACG calculation is the difTerence between the steam flow imposed via FILLO3 and the steam flow entering the IC inlet line. This difference is caused by mass transfer from the steam space to the liquid in the accumulator tank.
I Physically, it would be expected that the surface of the tank water would rapidly come to equilibrium with the steam temperature and mass transfer between the phases would effectively stop. It is difficult to model the surface layer heatup with TRACG and, consequently, the calculation tends to overestimate the interfacial mass transfer. Since
)
this aspect of TRACG is not the main focus of the IC pre-test analysis, it was decided that i
further refinement of the model was not justified at this time. This issue will be re-visited as part of the PANTIIERS IC post-test evaluation.
8.0 REFERENCES
I I
1.
NEDC-32391P, "SBWR Test and Analysis Program Description", (Rev. B),
April,1995.
2.
GE Test Specification 23A6999, " Isolation Condenser and Passive Containment Condenser Test", Rev. 4,28-Apr-95.
3.
Attachment to MFN 042-95, "PANTIIERS-IC Testing Reorientation",14-Mar-l 95.
4.
A Achilli, "PANTilERS-IC Test Procedure", SIET 00395PP95, (Rev. 0),12-May-95.
5.
M. Bruzzone and A. Benazzoli," Isolation Condenser lleat Transfer Area Evaluation", Ansaldo Doc. No. SBW5280TNLX110300 (Rev. 0),12-May-91.
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