3rd International Symposium on Two-Phase Flow Modelling and Experimentation Pisa, 22-24 September 2004
DESIGN, EXPERIMENTS AND RELAP5 CODE CALCULATIONS FOR THE PERSEO FACILITY Roberta Ferri*, Andrea Achilli*, Gustavo Cattadori*, Fosco Bianchi°, Paride Meloni° *SIET S.p.A. Via Nino Bixio, 27 – 29100 Piacenza, Italy
[email protected];
[email protected],
[email protected] °ENEA Via Martiri di Monte Sole, 4 – 40129 Bologna, Italy
[email protected],
[email protected] ABSTRACT Research on innovative safety systems for Light Water Reactors addressed to heat removal by in-pool immersed heat exchangers, led to design, build-up and test the PERSEO facility at SIET laboratories. The research started with the CEA-ENEA proposal of improving the GE-SBWR Isolation Condenser system, by moving the triggering valve from the high pressure primary side of the reactor to the low pressure pool side. A new configuration of the system was defined with the heat exchanger contained in a small pool, connected at bottom and top to a large water reservoir pool, the triggering valve being located on the pool bottom connecting pipe. ENEA funded the whole activity that included the definition and build-up of a new heat exchanger pool, on the basis of the already existing PANTHERS IC-PCC facility, at SIET laboratories, and the new plant requirements. The heat exchanger connections to the Pressure Vessel were maintained. An experimental campaign was executed at full scale and full thermal-hydraulic conditions for investigating the behaviour and performance of the plant in steady and unsteady conditions. The Relap5 code was utilised during all phases of the research: for the heat exchanger pool dimension definition and from pre-test and post-test analyses. The Cathare code was applied too for pre-test and post-test analysis. This paper deals with the experimental and calculated results limited to the Relap5 code.
Introduction
PERSEO test facility: design and build-up
The safety systems for Advanced Light Water Reactors often rely on natural phenomena like gravity injection or natural circulation in order to increase simplicity and improve their safety. The decay heat removal is a fundamental safety function that often employs in-pool immersed heat exchangers (GESBWR IC, AP-600 PRHR, SIR SCS, etc.). The heat transfer actuation in many cases is started by active valves whose reliability is fundamental. In this context, the design of the PERSEO facility (in-Pool Energy Removal System for Emergency Operation) was conceived as an evolution of a previous CEA-ENEA proposal (Thermal Valve device) which moved the SBWR-IC primary side drain line valve to the low pressure pool side [1] [2]. The Thermal Valve device located the triggering valve, steam side, at the top of a bell containing the heat exchanger (with all the negative consequences of the needed large dimensions for steam valve). The PERSEO system locates the valve, liquid side, on a line connecting two pools: one containing the heat exchanger and the other one acting as water reservoir [3] [4]. Full scale heat exchanger and pools have been tested at SIET laboratories, by modifying the existing PANTHERS ICPCC plant, in order to verify the behaviour and the performance of the device during all phases of a long accidental transient in thermal-hydraulic conditions typical of BWR [5] [6]. The Relap5 code has been employed since the early phases of the research activity up to the post-test analyses [3] [6] [7] [8]. The Cathare code has been applied for pre-test and posttest analyses [4] [8] [9].
The PANTHERS IC-PCC plant (Performance Analysis and Testing of Heat Removal System Isolation Condenser – Passive Containment Condenser), utilised in the past for testing a full scale prototype of the GE-SBWR in-pool heat exchanger, was modified and converted in the PERSEO facility. The most representative dimensions for the HX Pool to reproduce the phenomena expected in a real plant were chosen on the basis of physical and economical considerations. Two possibilities were studied: a) to use the original PANTHERS IC pool (16.9 m2 area) and scale the time of phenomena occurrence with respect to the ratio between the pool area and the area of an HX Pool in a real plant; b) to build a new HX Pool with realistic reduced dimensions. After physical and economical considerations on these possible solutions, a 5 m2 area HX Pool was chosen as a good compromise between the others. It well represented the physical phenomena in a real time scale, it could evidence a good steam-water separation at the pool top and allow a quite easy build-up around the existing heat exchanger. The choice of the final solution was supported by Relap5 code parametric calculations [3]. PERSEO test facility: description and operation The primary side of the facility mainly consists of a pressure vessel (43 m3 volume, 13 m height) and a full scale module of the SBWR IC heat exchanger (two cylindrical headers and 120 vertical pipes). Vessel and exchanger are connected by the Feed Line (0.243 m ID), steam side, and the Drain Line (0.146 m ID), liquid side.
The pool side of the facility consists of the HX Pool (∼30 m3 volume), containing the heat exchanger, and the Overall Pool (∼200 m3 volume), representing the water reservoir. HX Pool and Overall Pool are connected at the bottom by means of the liquid line (0.202 m ID), including the triggering valve, and at the top by means of the steam duct (1.1 m ID) ending into the Overall Pool with an injector about one meter below the water level. A boil-off pipe is connected at the top of the Overall Pool. A scheme of PERSEO facility is shown in Figure 1 and its design features are reported in Table 1. The pressure vessel is maintained at saturation by supplying properly de-superheated steam coming from the nearby EDIPOWER power station and pressure is kept constant by controlling the steam supply valve and a steam discharge valve located at the top of the vessel. In steady state, before a test is started, the vessel is in saturation conditions with water level and pressure at specified values. The Feed Line, Heat Exchanger and Drain Line are full of saturated steam. The HX Pool is full of air or steam, depending on the test, and the Overall Pool is full of cold water at the specified level. The triggering valve is closed. The test is started by opening the triggering valve. The HX Pool is flooded by cold water that causes the steam condensation inside the tubes of the heat exchanger with power transfer from the primary side to the pool side. Steam produced in the HX Pool is driven into the Overall Pool through the steam duct and accelerated under water by the injector. This contributes to the water mixing in the Overall Pool reducing the thermal stratification and delaying the water saturation and steam release into the containment. Steam produced in the Overall Pool flows outside through the Boil-off pipe. As water consumes, the injector is uncovered and no mixing effect is present anymore in the Overall Pool. The water reserve decreases according to the heat transfer rate in the HX Pool.
Table 1. PERSEO facility design features.
Quantity
Value
Power Vessel pressure Vessel temperature Heat Exchanger pressure Heat Exchanger temperature Superheated steam flowrate De-superheating water flowrate Pool side pressure HX pool temperature Overall pool temperature Pool side water flowrate
20 MW 10 MPa 310 °C 8.62 MPa 302 °C 12 kg/s 3 kg/s 0.15 MPa 300 °C 130 °C 25 kg/s
PERSEO facility experimental campaign Two different kinds of tests were performed during the experimental campaign on the PERSEO facility: integral tests and stability tests. The integral tests were aimed at demonstrating the behaviour and performance of the system following a request of operation and during all phases of a long accidental transient. The stability tests were aimed at studying particular critical problems happening in case of sudden condensation at the steam-water interface in the Injector or in case of triggering valve re-opening with cold water inlet in presence of steam in the HX Pool. The performed test matrix is reported in Table 2. Table 2. PERSEO facility test matrix.
Vacuum breaker HX POOL
Boil off Injector Water discharge
Test conditions
1
7 MPa
Integral test interrupted at the beginning of the pool level decreasing
2
7 MPa
Stability test and integral test: partial and subsequent HX Pool filling with reaching of boiling conditions and level decreasing
3
7 MPa
Stability test: partial HX Pool filling with reaching of boiling conditions
4
4 MPa
Integral test: reaching of boiling conditions and level decreasing
Heat Exchanger
OVERALL POOL
Water supply
Test Number
Feed line Triggering valve
Drain line
VESSEL
Description
NWL
The integral test procedure main steps are reported below: pressurisation of the primary circuit to the required pressure; b) opening of the triggering valve; c) reaching of saturation conditions in HX Pool and Overall Pool; a)
To Condenser Steam supply
Figure 1. PERSEO facility scheme.
d) e) f) g)
level decrease in the pools down to the Injector outlet uncovering; level decrease accelerated down to about 3 m from the pool bottom by water discharge; triggering valve closure and HX Pool boil-off; depressurisation of the primary circuit.
scenarios. Thermal-hydraulic best-estimate codes like RELAP5 and CATHARE are suitable to this purpose. Models of the PERSEO facility have been developed for both the codes and pre-test and post-test analyses have been carried out [8] [9] [11]. The nodalisation of PERSEO facility for Relap5 code is shown in Figure 2. It reproduces the geometrical and material characteristics of the plant. The primary circuit is reproduced from the vessel to the heat exchanger and the steam supply provided by means of a control volume. Both the pools are simulated with two parallel channels connected by transversal junctions in order to reproduce the water circulation. The main post-test results, obtained by the Relap5 code, are compared with the experimental data in order to put in evidence capabilities and limits of the code in reproducing qualitatively and quantitatively the experimental trends.
The stability test procedure main steps are reported below: HX pool full of air; pressurisation of the primary circuit to the required pressure; c) opening of the triggering valve; d) closure of the triggering valve when HX Pool water level reaches the heat exchanger pipe bottom; e) wait for steam production and check for condensation and instabilities; f) re-opening of the triggering valve; g) check for condensation and instabilities with cold water inlet into the HX pool in presence of steam. The tests confirmed the effectiveness of the PERSEO innovative system: the heat transfer from the primary to the pool side is soon actuated after the triggering valve opening, it is stable and decreases according to the HX Pool level. The Steam generated in the HX Pool and accelerated into the Overall Pool by the Injector promotes the water circulation and avoids the thermal stratification in the Overall Pool. Instabilities due to sudden steam condensation, evidenced after an early interruption of the heat transfer and during the HX Pool re-flooding to restart the heat removal, are dumped very soon by means of the vacuum breaker valve at HX Pool top or on the Steam Duct [10]. a) b)
PERSEO data analysis and comparison Tests N. 2 and 4 are summarised in this paper, because considered the most meaningful and representative of the system from the performance and stability point of view and for code assessment. Test N. 2 consists of two phases both starting from 7 MPa primary pressure. The HX Pool is initially full of air and of saturated steam in phase 1 and 2, respectively, with 1.12 m water level in the second case. The experimental and calculated Pool levels are compared in Figures 3 and 4 for phase 1 and 2. In the same figures, the calculated Injector level is reported too. Phase 1 partial HX Pool fill-up is devoted to investigate the occurrence of system instabilities with a steam/cold water interface in the Injector and the total fill-up is addressed to investigate the exchanged power trend versus the HX Pool level with the triggering valve closed and the Overall Pool excluded from feeding the HX Pool.
PERSEO facility numerical simulation A complete assessment of the reliability and efficiency of the PERSEO innovative DHR system requires a numerical analysis of the overall plant response to selected accidental Tmdpvol air
195
Vacuum breaker
OVERALL POOL
HX POOL
190 Trpvlv Tmdpvol steam
Steam duct
180 171
199
408
198
05
160
Trpvlv
162 128 127 126 125 124 123 131 132 133 134 08 135 136 137 138 139 121 122
150 12 13 14 15 16 17 18
18 17
415
715
10
710
720
945
940
625
Steam line
410
930
03
918 917
01 18
630
925
920
02
640
935
03
910
02
03
04
610
Tmdpvol
385
380 435 07
192
01 06
Srvvlv
409
03
02
03
402
02
03
815
02 01
08 Srvvlv
01 05
460 01
13 04
02
404 06
07
01
455
12 05
810
197
Vessel 403
04
Discharge valve
405
406
04
11
450
611
Tmdpvol 05
10
Liquid line
01 03
06
Drain line
06
02
01
01
141
620
02
916
02
440
144
01
04 5
140
650
02
946
01
Heat exchanger
130
950
02
690 Tmdpvol
03
947
03
430
07 06 05 04 03 02 01
685 06
680
02
03
16 15 14 13 12 11 10 09
Boil-off
660 03
Injector
01
661
01
407
05
01
142
143
01
670
01
420
01 02 03 04 05 06 07 08 09 10 11
03 02 01 03 02 04
04
170
425
07
06
05
04
04
03
820
Triggering Valve
Figure 2. PERSEO facility nodalisation for Relap5 Code.
02
401
01
02 01
390 Tmdpvol
395
6.0
6.0 5.0
OVERALL POOL
Exp.
Exp.
5.0
Calc. Calc.
3.0 2.0
Calc.
Exp. Calc.
HX POOL
Exp.
1.0
INJECTOR
Calc.
3.0 2.0
Calc.
HX POOL
OVERALL POOL
4.0
INJECTOR
Level (m)
Level (m)
4.0
1.0
0.0 10000
11000
12000
13000
14000
0.0
15000
0
1000
2000
Time (s)
3000
4000
5000
6000
Time (s)
Figure 3. Test N.2 (phase 1): HX, Over. Pool and Inj. level
Figure 4. Test N.2 (phase 2): HX, Over. Pool and Inj. level
25
25
20
20
15
15
10 Calc.
5 0 10000 -5
Exp.
11000
12000
13000
14000
15000
Pressure (kPa)
Pressure (kPa)
Exp.
10
Calc.
5 0 0
1000
2000
3000
4000
5000
6000
-5
-10
-10
-15
-15
Time (s)
Time (s)
Figure 5. Test N.2 (phase 1): HX Pool relative pressure
Figure 6. Test N.2 (phase 2): HX Pool relative pressure
25000
25000 Exp.
20000
20000
Exp.
Power (kW)
Power (kW)
Calc.
15000
10000
5000
0 10000
Calc.
15000
10000
5000
0 11000
12000
13000
14000
15000
Time (s)
0
1000
2000
3000
4000
5000
6000
Time (s)
Figure 7. Test N.2 (phase 1): Exchanger power
Figure 8. Test N.2 (phase 2): Exchanger power
Strong condensation shocks are evidenced experimentally during the period of low steam production rate and low level in the HX Pool. The HX Pool relative pressure is dumped down to negative values but air inlet through the vacuum breaker valve is sufficient to recover the pressure, Figure 5. Other downward peaks are observed during the total HX Pool fill-up. Phase 2 is devoted to investigate instabilities as for the phase 1 total fill-up and the power trend versus the HX Pool level with the triggering valve open and the Overall Pool feeding the HX Pool.
The experimental and calculated HX Pool relative pressure are reported in Figures 5 and 6 for both phases of the test. During phase 1, the code underestimates the phenomenon, while it overestimates the pressure downward peaks during phase 2 of the test, when the calculated HX Pool relative pressure approximates zero and the fill-up phase is anticipated with respect to the experimental one. Injector level oscillations are foreseen by the code during the instability period and level rises when the relative pressure decreases, Figures 3 and 4.
25
25
20
Power (MW)
Power (MW)
20
15 Exp.
10
Calc.
15 Calc. Exp.
10 5
5
0
0 1
1.5
2
2.5
3
1
3.5
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
2.8
level (m)
level (m)
Figure 9. Test N.2 (phase 1): Power vs. HX Pool level
Figure 10. Test N. 2 (phase 2): Power vs. HX Pool level
Once passed the instabilities and completely filled the HX Pool, the exchanged power soon reaches the regime value of about 20 MW and then it decreases following the water level, Figures 7 and 8. The trend of power versus the HX Pool level are reported in Figures 9 and 10 for phases 1 and 2.
The HX Pool is initially full of saturated steam and the water level is 1.22 m. The experimental and calculated pool levels are compared in Figure 13. The calculated Injector level is reported too, which strong oscillations correspond to relative pressure diminution for steam condensation during the HX Pool fill-up phase.
120
120 100
80
Temperature (°C)
Temperature (°C)
100
Calc. 60 40
Exp.
20 0 10000
Exp.
Calc
80 60 40 20
11000
12000
13000
14000
15000
Time (s)
0 0
1000
2000
3000
4000
5000
6000
Time (s)
Figure 11. Test N. 2 (phase 1): Overall Pool temperatures
Figure 12. Test N. 2 (phase 2): Overall Pool temperatures
During the heat transfer from the primary to the pool side, steam produced in the HX Pool is driven and accelerated into the Overall Pool through the Injector. This promotes water mixing in the pool reducing the thermal stratification that, on the contrary, would lead to early steam production at the top layers and anticipated steam release into the containment. The Overall Pool temperatures are reported in Figures 11 and 12. It is possible to observe how during phase 1, when the power rejection is lower than during phase 2, the thermal stratification is present in the Overall Pool, but temperature is still far from saturation. When the power rejection is high (phase 2) the OP water reaches saturation almost contemporary at the various elevations. The code foresees a higher homogenisation of water than in the experiments, even with low heat transfer rate. Test N. 4 starts from 4 MPa primary pressure. It is devoted to investigate the plant performance at a lower pressure value.
The HX Pool relative pressure is shown in Figure 14. Condensation shocks are evidenced during the fill-up phase with reached experimental negative values and consequent air inlet through the vacuum breaker valve. The code reproduces the pressure trend, but it does not reach such low pressure values. The experimental and calculated exchanged power curves are reported in Figure 15. As for test N. 2, phase 1, the code shows an oscillatory trend until the regime value of power is reached, then it decreases as the HX Pool level decreases. The trend of power versus the HX Pool level is reported in Figure 16. The Overall Pool temperatures are reported in Figure 17. As for Test N. 2, phase 2, water layers reach saturation almost at the same time. Water mixing obtained by the code is higher than the experimental one. For completeness, Table 3 summarises the absolute maximum error related to the main measured quantities.
120
6.0 5.0
Level (m)
Temperature (°C)
OVERALL POOL
4.0 INJECTOR
Exp.
3.0
Calc.
100
Exp.
Calc.
Calc.
2.0
HX POOL
80 60 Exp. 40 20
1.0
0
0.0 0
1000
2000
3000
4000
5000
6000
7000
8000
0
1000
2000
3000
4000
5000
6000
7000
8000
Time (s)
Time (s)
Figure 13. Test N. 4: HX, Over. Pool and Inj. level
Figure 17. Test N. 4: Overall Pool temperatures
Table 3. PERSEO facility measurement errors. 20
Quantity HX Pool level OP level HX Pool relative pressure OP temperatures Exchanged power
Exp.
Pressure (kPa)
15
10
Calc.
5
0 0
1000
2000
3000
4000
5000
6000
7000
8000
-5
PERSEO Relap5 simulation validity and limits
Time (s)
Figure 14. Test N. 4: HX Pool relative pressure
25000
20000
Power (kW)
Exp. 15000
10000 Calc.
5000
0 0
1000
2000
3000
4000
5000
6000
7000
8000
Time (s)
Figure 15. Test N. 4: Exchanged power
16 Exp.
14
Power (MW)
12
Calc.
10 8 6 4 2 0 1
1.5
2
Maximum absolute error ± 0.04 m ± 0.04 m ± 0.35 kPa ± 1.3 °C ± 500 kW
2.5
3
Level (m)
Figure 16. Test N. 4: Power vs. HX Pool level
3.5
At the end of a deep post-test analysis of the PERSEO facility tests, with the Relap5 code, considerations can be done to underline the model validity and limits. A complete assessment of the reliability and efficiency of the PERSEO device, would require a numerical analysis of the overall plant response to a selection of accident scenarios. For this purpose, a nodalisation of the device is needed, able to reproduce the experimental data, once implementing the initial and boundary conditions of a test. As shown by the above described results, a general good agreement between experimental and calculated data is evidenced, but an important limit of the model must be underlined, in particular the difficulty of the code of reproducing the experimental exchanged power (different for any test) without modifying the heat transfer hydraulic diameter (i.e. heated equivalent diameter) for the heat exchanger pipe heat structure inner face. The analysis of specific phenomena and variables led to the following considerations: a) in the majority of cases, the calculated power shows a strong oscillatory trend in the initial phase of the transients, when the HX Pool is flooded after the triggering valve opening. Such oscillations seem related to sudden changes of the calculated heat transfer modes. Power is quite well reproduced by the code during the HX Pool water level decreasing for water consumption; b) the code overestimates the steam condensation in the HX Pool at the cold water income, after the triggering valve opening. Such overestimation, often, leads the code to foresee an anticipated HX Pool fill-up for water suction through the liquid line between the pools;
c)
d)
the code underestimates the instabilities for condensation strikes at the steam-liquid interface in the Injector, when no or very little steam flow is present from the HX Pool to the Overall Pool, in particular when the exchanged power is limited by the low water level in the HX Pool; the HX Pool and Overall Pool modelling by means of parallel channels, connected with transversal junctions, seems a good solution for the simulation of water re-circulation and mixing in the pools.
SIET
Società Informazioni Termoidrauliche
Calc. Exp. Inj. Over.
Calculated Experimental Injector Overall
REFERENCES 1.
Conclusions This paper summarises the main phases of the research activity on an innovative Decay Heat Removal system developed in cooperation between ENEA and SIET. The PERSEO device, conceived as an improvement of existing systems based on in-pool immersed heat exchangers, was designed, built and operated up to the completion of an experimental campaign that showed the rightness of the project and the viability of the concept for future applications on advanced LWR. The Relap5 best estimate code was utilised as design instrument during all phases of the project, from the definition of the optimum dimensions of the HX Pool, to pre-test analysis and operating procedure set-up up to posttest calculations and global device modelling. A general good agreement between experimental and calculated data was found, even if limits of the code were identified in simulating particular phenomena and quantities. A deeper model investigation and also a wider comparison with other best estimate codes are considered necessary in order to set-up a definitive model suitable for an overall NPP simulation with such innovative DHR system and selected accidental transient scenarios. NOMENCLATURE DHR CEA ENEA
Decay Heat Removal System Commissariat à l’Énergie Atomique Ente per le Nuove tecnologie, l’Energia e l’Ambiente GE-SBWR General Electric - Small Simplified Boiling Water Reactor IC Isolation Condenser ID Inner Diameter HX Heat Exchanger LWR Light Water Reactor NPP Nuclear Power Plant OP Overall Pool PANTHERS Performance Analysis and Testing of Heat Removal System PCC Passive Containment Condenser PERSEO in-Pool Energy Removal System for Emergency Operation LWR Light Water Reactor
Esperienze
F. Bianchi, P.Meloni, J.F. Pignatel, G.M. Gautier Thermal Valve system for LWR applications, Proc. Post-SMIRT14 Seminar, Pisa (Italy),1997, pp. C2-17. 2. P.Meloni, J.F. Pignatel, Theoretical design and assessment of Isolation Condenser System Controlled with Thermal Valve Device, Proc. International Conference ICONE6 ASME/JSME/SFEN, San Diego (CA), 1998. Paper 6283. 3. A. Achilli, G. Cattadori, R. Ferri, M. Rigamonti, F. Bianchi, P. Meloni, PERSEO project: experimental facility set-up and Relap5 code calculations, Proc. 2nd EMSI and 40th ETPFGM, Stockholm, Sweden, 2002. Paper F3. 4. P.Meloni, F. Bianchi, A. Achilli, R. Ferri, G. Cattadori, Analytical assessment of an enhanced configuration of the Thermal Valve System, Proc. of ESDA2002 6th biennial Conference of Engineering Systems Design and Analysis Istanbul, Turkey, 2002. 5. P. Masoni et al., Confirmatory tests on full-scale condensers for SBWR, Proc. International Conference ICONE9 ASME/JSME, San Francisco (CA), 1993. 6. F. Bianchi, F. Mattioda, P. Meloni, A. Achilli, G. Cattadori, R. Ferri, S. Gandolfi., In-Pool Energy Removal System for Emergency operation: Experimental tests and Relap5 code calculations, Proc. International Conference ICONE11, Tokyo (Japan), 2003. Paper 3635. 7. F. Bianchi, P. Meloni, R. Ferri, A. Achilli, In-Pool Energy Removal System for Emergency operation: Experiment and analytical assessment, Proc. International Conference Nuclear Energy for New Europe, Portoroz, (Slovenia), 2003. 8. F. Bianchi, P. Meloni, R. Ferri, A. Achilli, Assessment of RELAP5 mod3.3 and CATHARE2 v15a against a full scale test for PERSEO device, Proc. International Conference ICONE12, Arlington, (VA), 2004. Paper 49474. 9. P. Meloni, F. Bianchi, R. Ferri, Assessment of a CATHARE model of the PERSEO Device on Fullscale tests, Proc. ANS/ENS International Winter Meeting, New Orleans, (LA), 2003. 10. R. Ferri, A. Achilli, S. Gandolfi, PERSEO PROJECT Experimental Data Report, SIET 01 014 RP 02 Piacenza (Italy), 2002. 11. R. Ferri, PERSEO PROJECT Post-test calculations with the Relap5 Mod3.3 beta code, SIET 01 061 RA 03 Piacenza (Italy), 2003.
