ermsar 2012, cologne march 21 – 23, 2012 estimation of thermal-hydraulic loading for vver-1000...
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ERMSAR 2012, Cologne March 21 – 23, 2012
ESTIMATION OF THERMAL-HYDRAULIC LOADING FOR VVER-1000 UNDER SEVERE ACCIDENT
SCENARIO
Barun Chatterjee1, Deb Mukhopadhyay1, Hemant G. Lele1, Pavlin Groudev2
1BARC, Mumbai (India)
2INRNE, Sofia (Bulgaria)
ERMSAR 2012, Cologne March 21 – 23, 2012
Study Objective
2
Structural components like SG tubes, RCP seals, hot leg, Pressuriser Surge line and RPV, Different valves of VVER1000 are likely to experience high temperature and pressure under postulated severe accident conditions arising from SBO ( a high pressure event among severe accident scenarios)
These loading may fail the components
These failure estimation will alter the course of the accident
* System depressurisation followed by less inventory/steam available for
hydrogen
generation * converting the possibility of high pressure melt ejection into a low pressure
melt ejection scenario in the Containment. The change in scenario will alter the load on the ultimate barrier
As severe accident analysis are based on realistic models, hence a realistic predictions will help to plan SAMG for Core and containment in a better way
ERMSAR 2012, Cologne March 21 – 23, 2012
VVER-1000 (V320) RCS Layout
3
Hot legSurge
Line
Pump Seal
SG tubes
RPV
ERMSAR 2012, Cologne March 21 – 23, 2012
Station Black Out (SBO) ANALYSIS
4
Following assumptions have been made for SBO simulation
1. Transient is initiated with Station Blackout
2. MCPs and turbine trip at 0.0 s due to SBO
3. Reactor trips at 1.6 s. due to loss of power
4. Feed pumps trip at 5 s due to turbine trip.
5. Pumped Safety Injection systems are assumed to be not available due to SBO
ERMSAR 2012, Cologne March 21 – 23, 2012
COMPUTER CODE ASTECV1.3rev3p1 AND VVER1000 -PLANT MODEL
5
BRU-K
PRZ Relief Valves
To Loop 2, 3, 4 4
SRG_LINE
ULEGP1 (Pump)
Lower Plenum
Reactor Vessel
Baffle
1 2 3 4 5
Lower Plenum
Reactor Vessel
Baffle
1 2 3 4 5
15 Grid Spacers
Lower Plate grid
DOWNCO1
UPPLE1
UPPLE2
HL1
PRZ
SG1
- HCOL
SG1
- CCOL
SG1_SEC
SG1_TUB
Safety valves SG-PSDs -
BRU-A
Upp_cor
INRJ7
Loop1j1
Loop1j2
Loop1j3
Loop1j5
Loop1j7
Loop1j8
Main steam Header
Main Steam Line From 2, 3, 4
From Loop 2, 3, 4
Parameters Design Value
Steady State value
Reactor Power (MW) 3000.0 3000.0
RCS Pressure (Mpa) 15.7 15.5
SG Pressure (MPa) 6.27 6.26
Coolant Temperature at reactor inlet (K)
562.0 562.3
Coolant Temperature at reactor outlet (K)
593.0 592.4
Coolant Flow per loop (kg/s)
4400.0 4387.0
Feed flow per SG (kg/s) 408.0 408.34
Initial Inventory
RCS Inventory (t.) 245.5
UO2 inventory in core (t.) 73.12
Zr inventory in core (t.) 21.6
B4C inventory in core (kg) 369.8
Total Steel Inventory (t.) 263.0
Decay Heat End of life
ERMSAR 2012, Cologne March 21 – 23, 2012
REACTOR BEHAVIOUR UNDER SBO
EVENT Time (s)
SBO 0.0
MCP #1,2,3,4 trip 0.0
Turbine trips 0.0
Reactor trips 1.6
Feed pumps stop 5.0
Beginning of oxidation
14,114.0
Start of FPs release 17,660.0
Total core uncovery 25,116.0
First corium slump in vessel lower
head
25,595.0
Lower head vessel failure
48,678.06
0 10000 20000 30000 40000 500004
6
8
10
12
14
16
18
20
Pre
ss
ure
(M
Pa
)
Time (s)
RCS Pressure SG Pressure
SG Boil Off
RCS Pressurisation
Chattering of PRZ Relief Valve
• SG Boil off
• SG Inventory depletion
• Loss of SG as a Heat Sink
• RCS Pressurisation
• Opening of PRZ relief valve
• RCS Boil off
• RCS Inventory Loss
• Core Heat up and Degradaton
• Vessel Failure
ERMSAR 2012, Cologne March 21 – 23, 2012
ASSESSMENT OF RCS AND SURGE LINE PIPE INTEGRITY
7
Material of construction of Reactor Coolant System and Surge line for VVER-1000 (V320) is 10 GN2 MFA steel (Dn-350)
High Temperature creep model for this material is not available in Open Literature,
Hence high temperature creep model for SS316 [R. M. Goldhoff ] for temperature range of 700-1089 K has been used for assessment
Ref. 1. F. R . Larsen and J. Miller, “a time temperature relationship for rupture and creep stress, Transaction of the ASME, July 1952, pp 765-775.
2. R. M. Goldhoff, “A Comparison of Parameter Methods for Extrapolating High Temperature Data”, ASME Journal of Basic Engineering, 1959, pp. 629-643.
ERMSAR 2012, Cologne March 21 – 23, 2012 8
The creep rupture time correlation for SS316 material is given as follows
ASSESSMENT OF RCS AND SURGE LINE PIPE INTEGRITY
ERMSAR 2012, Cologne March 21 – 23, 2012 9
0 10000 20000 30000 40000 50000
500
600
700
800
900
1000
1100
1200
1300
T
emp
erat
ure
(K
)
Time (s)
Upper Plenum Hot Leg Surge Line SG Tube Pump seal Vessel
Vessel Failure
Cre
ep c
orr
elat
ion
ran
ge
Component Temperatures under SBO
ERMSAR 2012, Cologne March 21 – 23, 2012
ASSESSMENT OF RCS AND SURGE LINE INTEGRITY
10
700 800 900 1000 1100 1200 1300 1400 1500 1600 17001E-9
1E-6
1E-3
1
1000
1000000
1E9
1E12
316 SS
Time t
o Rup
ture (
hr)
Temperature (K) Fig. 4: Variation of Rupture Time as function of Temperature
Surge Line
Time Required to Rupture Once the Component remains at a sustained high temperature :
Hot Leg : 22000 hrs[850 mm, 22 ksi (153 MPa)]
Surge Line : 0.11 hrs. (360 s)[400 mm, 14.8 ksi (108 MPa)]
Surge line fails after 360 s once it attains and remained at a Temperature higher than 1089 K :
Hot Leg
ERMSAR 2012, Cologne March 21 – 23, 2012
Conclusion
11
Analysis shows failure of Surge line (35,360 s) prior to Reactor
Vessel rupture from lower plenum creep (48,678 s)
SG tubes, hot leg, pump seal are unlikely to fail by thermal creep as
they remain at a lower temperature
Surge line rupture prior to vessel rupture at a high pressure event will
turn the event into a low pressure event
This situation will cause less severity to the containment as high
pressure melt ejection from lower head will not take place
ERMSAR 2012, Cologne March 21 – 23, 2012
Comparison between ASTECV1 and ASTECV2
EVENT Time (s) ASTECV1.3rev3p1
Time (s)ASTECV2.0r2p1
SBO 0.0 0.0
MCP #1,2,3,4 trip 0.0 0.0
Turbine, Reactor , Feed pumps trip 0.0, 1.6 s, 5.0 0.0, 1.6 s, 5.0
Beginning of oxidation 14,114.0 13,058.5
Start of FPs release 17,660.0 14,679.6
Total core uncovery 25,116.0 16,617.9
First corium slump in vessel lower head 25,595.0 16,516.5
Vessel failure 48,678.0 25,099.8
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Large Discrepancy
In code (V1 –V
2) predictions CORE DEGRADATION ASTECV1 ASTECV2
Corium mass in the lower head (te) 32.9 24.9
H2 mass produced during the in-vessel phase (kg) 742 304
Aerosols mass produced during the in-vessel phase (kg) 885.8 382.5
Aerosols mass in containment at vessel failure (kg) 252.5 11.6
ERMSAR 2012, Cologne March 21 – 23, 2012
Comparison between ASTECV1 and ASTECV2
13
0 5000 10000 15000 20000 25000 300004
6
8
10
12
14
16
18
20
Pre
ssu
re (
MP
a)Time (s)
RCS PressureSG Pressure
ASTECV1 ASTECV2
ERMSAR 2012, Cologne March 21 – 23, 2012
Comparison between ASTECV1 and ASTECV2
14
0 10000 20000 30000 40000 50000
0
50000
100000
150000
200000
250000
Inve
nto
ry (
kg)
Time (s)
Liquid Inventory Vapour Inventory
0 5000 10000 15000 20000 25000
0
50000
100000
150000
200000
250000
Inv
en
tory
(k
g)
Time (s)
Vapour Inventory Liquid Inventory
ASTECV1 ASTECV2
ERMSAR 2012, Cologne March 21 – 23, 2012
Comparison between ASTECV1 and ASTECV2
15
ASTECV1 ASTECV2
Voided core
Voided core
No radial spread
radial spread(Magma
model)
ERMSAR 2012, Cologne March 21 – 23, 2012
Comparison between ASTECV1 and ASTECV2
16
0 5000 10000 15000 20000 25000 30000
500
600
700
800
900
1000
1100
1200
1300
Tem
pera
ture
(K)
Time (s)
Upper Plenum Hot Leg Surge Line
SG Tube Pump Seal Vessel
0 10000 20000 30000 40000 50000
500
600
700
800
900
1000
1100
1200
1300
Tem
per
atu
re (
K)
Time (s)
Upper Plenum Hot Leg Surge Line SG Tube Pump seal Vessel
Vessel Failure
Cre
ep c
orr
elat
ion
ran
ge
Component Temperatures under SBO
ASTECV1ASTECV2
Cre
ep C
orre
latio
n R
ange
ERMSAR 2012, Cologne March 21 – 23, 2012
Comparison between ASTECV1 and ASTECV2
17
700 800 900 1000 1100 1200 1300 1400 1500 1600 17001E-9
1E-6
1E-3
1
1000
1000000
1E9
1E12
316 SS
Time t
o Rup
ture (
hr)
Temperature (K) Fig. 4: Variation of Rupture Time as function of Temperature
Surge Line
700 800 900 1000 1100 1200 1300 1400 1500 1600 17001E-9
1E-6
1E-3
1
1000
1000000
1E9
1E12
316 SS
Time t
o Rup
ture (
hr)
Temperature (K) Fig. 4: Variation of Rupture Time as function of Temperature
Surge Line
ASTECV1 ASTECV2
Surge Line Failure Time : 0.11 hrs
Surge Line Failure Time : 80 hrs
ERMSAR 2012, Cologne March 21 – 23, 2012
Conclusion
18
In both versions of ASTEC, loss of RCS and SG inventory are comparable.
Core heat up and material relocation is faster in case of ASTECV2, hence a
large extent of anomalies are observed in core degradations parameters like
hydrogen, corium relocated mass and aerosol generation AGAINST V1
predictions
In case of ASTECV1, The surge line failure was predicted before vessel
failure. But in case of ASTECV2, there was no surge line failure prior to
vessel failure.Suggestion to SARNET:
Benchmark exercise among SARNET partners is strongly suggested for VVER-1000 SBO case to eliminate user effect, as the SA analyses are used for SAMG verification and Level-2 calculations.
ERMSAR 2012, Cologne March 21 – 23, 2012
Thank You
19