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LEADER Project
Analysis of Representative DBC Events of the ETDR with RELAP5 and CATHARE
Giacomino Bandini - ENEA/BolognaGenevieve Geffraye – CEA/Grenoble
LEADER 4th WP5 MeetingKarlsruhe, 22 November 2012
2
Outline
Analyzed DBC Transients at EOC ALFRED Modeling Transient Results Conclusions
3
Analyzed Transients
TRANSIENT Initiating Event (t = 0 s) Reactor scram and threshold
Primary pump trip
MHX FW trip
MSIV closure
DHR startup
TD-1: Spurious reactor trip Reactor scram 0 s, Spurious trip No No No No
TD-3: Loss of AC power Station blackout
0 s, CR magnet de-energization
0 s 0 s 0 s DHR-1 at 1 s (4 IC loops)
TD-7: Loss of all primary pumps All primary pump coastdown
3 s, ΔT hot FA = 120% nominal
0 s 3 s 3 s DHR-1 at 4 s (3 IC loops)
TO-1: Reduction of FW temperature
FW temperature from 335 °C down to 300 °C in 1 s
2 s, Low FW temperature
No 2 s 2 s DHR-1 at 3 s (4 IC loops)
TO-4: Increase of FW flowrate
20% increase in FW flowrate in 25 s
No, No scram threshold reached
No No No No
Main events and reactor scram threshold
4
RELAP5 Modeling
Feedwater
Steam
521- 8
531- 8
551- 8 561-8
151-
8
Feedwater
Steam
521- 8
531- 8
551- 8 561-8
151-
8
841 - 4
851 - 8441 -8
801 - 4
811-4831 - 4
815
401 - 8
841 - 4
-
801 - 4
811-4831 - 4
815
841 - 4
-
801 - 4
811-4831 - 4
815
611 - 8
841 - 4
-
801 - 4
811-4831 - 4
815
611 -
711 -
731-
741- 4
751 - 8
761- 4
621- 4
641 - 4
771
781 - 8
601- 4
661 - 4
611 -
711 - 8
731- 8
741- 4
751 -
761- 4
621- 4
641 - 4
771 -8
781 -
601- 4
661 - 4
611 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781
601- 4
661 - 4
841 - 8
-
801 - 4
811-4831 - 4
815
841 -
-
801 - 8
811-8831 - 8
815
611 -
841 -
-
801 -
811-831 -
411 -8
611 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771
781
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781 -
601- 8
661 - 8
611 -
711 -
731-
741- 8
751 -
761- 8
621- 8
641 - 8
841 - 4
851 - 8441 -8
801 - 4
811-4831 - 4
815
401 - 8
841 - 4
-
801 - 4
811-4831 - 4
815
841 - 4
-
801 - 4
811-4831 - 4
815
611 - 8
841 - 4
-
801 - 4
811-4831 - 4
815
611 -
711 -
731-
741- 4
751 - 8
761- 4
621- 4
641 - 4
771
781 - 8
601- 4
661 - 4
611 -
711 - 8
731- 8
741- 4
751 -
761- 4
621- 4
641 - 4
771 -8
781 -
601- 4
661 - 4
611 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781
601- 4
661 - 4
841 - 8
-
801 - 4
811-4831 - 4
815
841 -
-
801 - 8
811-8831 - 8
815
611 -
841 -
-
801 -
811-831 -
411 -8
611 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771
781
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781 -
601- 8
661 - 8
611 -
711 -
731-
741- 8
751 -
761- 8
621- 8
641 - 8
ALFRED Nodalization scheme with RELAP5
8 MHXs
8 Secondary loops Primary circuit
8 IC loops
Steam line
Feedwater line
100
101102109
110
115
060061-8 070
050
020
200 151-8
121-8
131-8
141-8
220
230
210
100
101102109
110
115
060061-8 070
050
020
200 151-8
121-8
131-8
141-8
220
230
210
100
101102109
110
180
060061-8 070
050
020
200 151-8
121-8
131-8
141-8
220
230
210
Feedwater
Steam
521- 8
531- 8
551- 8 561-8
151-
8
Feedwater
Steam
521- 8
531- 8
551- 8 561-8
151-
8
841 - 4
851 - 8441 -8
801 - 4
811-4831 - 4
815
401 - 8
841 - 4
-
801 - 4
811-4831 - 4
815
841 - 4
-
801 - 4
811-4831 - 4
815
611 - 8
841 - 4
-
801 - 4
811-4831 - 4
815
611 -
711 -
731-
741- 4
751 - 8
761- 4
621- 4
641 - 4
771
781 - 8
601- 4
661 - 4
611 -
711 - 8
731- 8
741- 4
751 -
761- 4
621- 4
641 - 4
771 -8
781 -
601- 4
661 - 4
611 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781
601- 4
661 - 4
841 - 8
-
801 - 4
811-4831 - 4
815
841 -
-
801 - 8
811-8831 - 8
815
611 -
841 -
-
801 -
811-831 -
411 -8
611 -
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771
781
711 -
731-
741- 4
751 -
761- 4
621- 4
641 - 4
771 -
781 -
5
CATHARE Modeling
ALFRED Nodalization scheme with CATHARE
Primary circuit
2 Secondary loops (weight 4)
2 IC loops (weight 4)
6
TD-1: Spurious reactor trip (1/3)(RELAP5 – CATHARE Comparison)
Total reactivity and feedbacks
ASSUMPTIONS: Reactor scram at t = 0 s Reactivity insertion of at least 8000 pcm in 1 s Secondary circuits are available constant feedwater flowrate
RELAP5 CATHARE
7
TD-1: Spurious reactor trip (2/3)(RELAP5 – CATHARE Comparison)
Core and MHX powers
RELAP5 CATHARE
Core decay power level in CATHARE is much higher than the one in RELAP5 in the initial phase of the transient
Power removal by secondary circuits reduces with reducing primary temperatures
8
TD-1: Spurious reactor trip (2/2)(RELAP5 – CATHARE Comparison)
Core temperatures (inlet, max outlet and max clad)
RELAP5 CATHARE
Initial temperature gradient on the fuel rod clad is about -10 °C/s No risk for lead freezing since the feedwater temperature (335 °C) is above the
solidification point of lead (327 °C)
9
TD-3: Loss of AC power (1/4)(RELAP5 – CATHARE Comparison)
Active core flowrate
ASSUMPTIONS: At t = 0 s Reactor scram, primary pump coastdown, feedwater and turbine trip At t = 1 s DHR-1 system activation (4 IC loops)
RELAP5 CATHARE
10
TD-3: Loss of AC power (2/4)(RELAP5 – CATHARE Comparison)
Core temperatures Core temperatures
Active core flowrate Active core flowrate
11
TD-3: Loss of AC power (3/4)(RELAP5 – CATHARE Comparison)
Core decay, MHX and IC powers Core decay, MHX and IC powers
Primary lead temperatures Primary lead temperatures
12
TD-3: Loss of AC power (4/4)(RELAP5 – CATHARE Comparison)
MAIN RESULTS: No initial core flowrate undershoot No significant clad temperature peak in the
initial phase of the transient After the initial transient the natural circulation in the primary circuit stabilizes
around 1-2% of nominal value Initial primary temperature decrease is over predicted by RELAP5 with respect to
CATHARE due to differences in core decay power and steam release through safety relief valves
Primary temperature reduction in the long term is faster in RELAP5 calculation due to lack of mixing in the cold pool cold lead at the MHX outlet flows towards core inlet without mixing in the cold pool above MHX outlet (different behavior in CATHARE with similar modeling)
Risk of freezing at MHX outlet is predicted by RELAP5 after about 2 hours, much earlier than with CATHARE
Similar DHR power removal (about 7 MW with 4 IC loops) is obtained by nearly halving the actual heat transfer surface of IC in CATHARE (much larger htc for steam condensation on the inner tube side)
13
TD-7: Loss of primary pumps (1/3)(RELAP5 – CATHARE Comparison)
Total reactivity and feedbacks
RELAP5 CATHARE
ASSUMPTIONS: At t = 0 s All Primary pump coastdown Reactor scram at t = 3 s on second scram
threshold (Hot FA ΔT > 1.2 nominal value) At t = 4 s DHR-1 system activation (3 IC loops)
14
TD-7: Loss of primary pumps (2/3)(RELAP5 – CATHARE Comparison)
Core temperatures Core temperatures
Active core flowrate Active core flowrate
15
TD-7: Loss of primary pumps (3/3)(RELAP5 – CATHARE Comparison)
Core decay, MHX and IC powers Core decay, MHX and IC powers
Primary lead temperatures Primary lead temperatures
16
TO-1: FW temp. reduction (1/3) (RELAP5 – CATHARE Comparison)
Primary lead temperature
ASSUMPTIONS: Loss of one preheater (FW temperature from 335 °C down to 300 °C in 1 s) +
primary pump coastdown reactor scram at t = 2 s on low FW temperature 4 IC loops in service for decay heat removal
RELAP5 CATHARE
17
TO-1: FW temp. reduction (2/3) (RELAP5 – CATHARE Comparison)
Primary lead temperatures Primary lead temperatures
Core decay, MHX and IC powers Core decay, MHX and IC powers
18
TO-1: FW temp. reduction (3/3) (RELAP5 – CATHARE Comparison)
MAIN RESULTS: No risk of lead freezing in the initial phase of the transient due to prompt reactor
scram Primary temperature reduction in the long term is faster in RELAP5 calculation due
to lack of mixing in the cold pool cold lead at the MHX outlet flows towards core inlet without mixing in the cold pool above MHX outlet (different behavior in CATHARE with similar modeling)
Risk of freezing at MHX outlet is predicted by RELAP5 after about 3 hours, much earlier than with CATHARE
19
TO-1: FW flowrate +20% (1/3) (RELAP5 – CATHARE Comparison)
Core and MHX powers Core and MHX powers
Primary lead temperatures Primary lead temperatures
20
TO-1: FW flowrate +20% (2/3) (RELAP5 – CATHARE Comparison)
Core temperatures Core temperatures
Total reactivity and feedbacks Total reactivity and feedbacks
21
TO-1: FW flowrate +20% (3/3) (RELAP5 – CATHARE Comparison)
ASSUMPTIONS: Feedwater flowrate +20% in 25 s
MAIN RESULTS: No significant perturbations on both primary and secondary sides The system reaches a new steady-state condition in about 10 minutes without
exceeding reactor scram set-points The increase in power removal by secondary side is larger with RELAP5 with
respect to CATHARE higher perturbation on primary side with RELAP5
22
Conclusions
In all analyzed DBC accidental transients, the protection system by reactor scram and by the prompt start-up of the DHR-1 for core decay heat removal is able to bring the plant in safe conditions in the short and long term
The core temperatures always remains well below the safety limits No significant vessel wall temperature increase is predicted The time to reach lead freezing at MHX outlet after start-up of DHR-1
system strongly depends on the assumptions taken on cold pool mixing but in any case there is large grace time for countermeasures by operator actions
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