Post on 17-Dec-2015
transcript
CRP on Natural Circulation Phenomena, Modelling and Reliability
of Passive Safety Systems that Utilize Natural Circulation
10-13 September, 2007, IAEA, Vienna
Modelling of natural circulation phenomena
in VVER-440 reactors
P. Matejovič, M. Bachratý
VVER-440/V213 design
• 2nd generation of soviet design PWRs of medium power
• incorporated most of design requirements of PWRs built at the same time (e.g. 3 x 100% ECCS)
• constructed in Russia (2), Ukraine (2), CEC (12+2), Finland (2)
• 2 units still under construction (Mochovce 3&4 NPP)
• rather inefficient, but robust and conservative design with large T-H safety margin
• Loviisa NPP upgraded for severe accidents (IVR, PARs)
VVER-440 geometry of primary system:
Natural circulation is influenced by:
• horizontal SG => driving head for the natural circulation is rather small
• six loops configuration
• loop seals in both, hot and cold legs
• large primary and secondary side coolant inventories
PACTEL facility, new configuration
• Volumetric scale 1:305;
• Basic elevations preserved in full scale;
• Reduced number of loops (3 instead of 6);
• Widely used for LOCAs, SG boil-off , etc.;
“Large” diameter PACTEL steam generator
VVER-440 horizontal SG
VVER-440 SG – horizontal cross-section
SG tubing
Natural circulation during boil-off transients
Main Goals of LOF-10:
to study study the SG behavior in VVER-440 reactor geometry during a loss-of-feedwater transient.
to test the ability of thermal-hydraulic computer codes to analyse this kind of phenomena
0.
500.
1000.
1500.
2000.
2500.
3000.
0 10 20 30 40 50 60 70 80
Rows [-]
Heat transfer area [m2]
Heat transfer area versus number of rows for VVER-440 steam generators
LOF-10 boil-off experiment:
the experiment started from steady-state conditions with forced circulation in single loop (1000 s)
RCP was switched off and the FW injection was interrupted
Core heating power was 75 kW, what corresponds to 1.7% power of the reference reactor
65
55
50
5
35
30
15
25
20
3192
165
200
292
300
392
4245
1
260
7070
200
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100
65
192
5
71
RELAP5-3D nodalization of the PACTEL used for LOF-10
129109
600
620 FW
607
180
102
100
192
160 18
2
185
108
622
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601
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610 630
111 - 124
183
103
190
624
621
144
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162 16
3
167
166
Fig. 1.1. Pressure in pressurizer.
69.
70.
71.
72.
73.
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79.
0 2000 4000 6000 8000 10000 12000 14000 16000
Time [s]
Pre
ssu
re [
Ba
r]
RELAP
PACTEL
PACTEL: LOF 10 RELAP5-3D
Fig. 1.3. Mass flow rate through CL No. 3.
0.
0.5
1.
1.5
2.
2.5
3.
3.5
4.
4.5
5.
5.5
0 2000 4000 6000 8000 10000 12000 14000 16000
Time [s]
Flo
w [
kg/s
]
RELAP
PACTEL
PACTEL: LOF 10 RELAP5-3D
Fig. 1.5. Temperature in cold leg No.3.
235.
240.
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255.
260.
265.
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280.
0 2000 4000 6000 8000 10000 12000 14000 16000
Time [s]
Tem
pe
ratu
re [
C]
RELAP
PACTEL
PACTEL: LOF 10 RELAP5-3D
Fig. 1.8. Temperature in RV head.
240.
245.
250.
255.
260.
265.
270.
275.
280.
285.
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0 2000 4000 6000 8000 10000 12000 14000 16000
Time [s]
Tem
pe
ratu
re [
C]
RELAP
PACTEL
PACTEL: LOF 10 RELAP5-3D
Fig. 1.9. Pressure in SG3.
37.
38.
39.
40.
41.
42.
43.
0 2000 4000 6000 8000 10000 12000 14000 16000
Time [s]
Pre
ssu
re [
Ba
r]
RELAP
PACTEL
PACTEL: LOF 10 RELAP5-3D
Fig. 1.10. Level in SG 3.
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0 2000 4000 6000 8000 10000 12000 14000 16000
Time [s]
Le
vel [
m]
RELAP
PACTEL
PACTEL: LOF 10 RELAP5-3D
hot
collector
cold
collector
Calculated natural circulation flow pattern in SG tubing at t = 2000 s
Conclusions:
reasonable results were obtained with RELAP5-3D
necessary condition: sufficiently fine nodalisation should be used with large number of SG tube layers
practical limitations: 6-loop arrangement with 78 layers of heat exchange tubes in 1 SG = > compromises are necessary
An example of improperly designed facility