ermsar 2012, cologne march 21 – 23, 2012 source term assessment with astec and associated...
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ERMSAR 2012, Cologne March 21 – 23, 2012
Source term assessment with ASTEC and associated uncertainty analysis using SUNSET tool
K. Chevalier-Jabet1, F. Cousin1, L. Cantrel1, C. Séropian1
(1) IRSN, Cadarache
ERMSAR 2012, Cologne March 21 – 23, 2012
CONTENTS
1. Assessing source term with ASTEC
2. Iodine related models and associated uncertainties
3. Source term assessment
4. Conclusion
1
ERMSAR 2012, Cologne March 21 – 23, 2012
CONTENTS
1. Assessing source term with ASTEC
2. Iodine related models and associated uncertainties
3. Source term assessment
4. Conclusion
2
ERMSAR 2012, Cologne March 21 – 23, 2012
Joint IRSN/GRS development from 1996
1. Provides models for most phenomena of a severe accident enables source term assessment
2. Integrates up-to date models developed on the basis of R&D programs enables uncertainty analysis in association with SUNSET tool
3
ERMSAR 2012, Cologne March 21 – 23, 2012
CONTENTS
1. Assessing source term with ASTEC
2. Iodine related models and associated uncertainties
3. Source term assessment
4. Conclusion
4
ERMSAR 2012, Cologne March 21 – 23, 2012
Iodine behaviour models of ASTEC
In RCS : iodine speciation
modelled with SOPHAEROS module : chemical speciation, retention, aerosol size distribution
Lack of knowledge on thermodynamic/thermokinetics properties
Impacts the iodine gaseous mass fraction at the break : CHIP experiment, (T.Haste Presentation S3.1 ) ; [ 5% -> 95%]
cooler
Gas phasechemical reactions
Inlet flow Supersaturatedvapours
Condensation Deposition
ReleaseAgglomeration
Sorbtion
Nucleation
Aerosol
WALL cooler
Gas phasechemical reactions
Inlet flow Supersaturatedvapours
Condensation Deposition
ReleaseAgglomeration
Sorbtion
Nucleation
Aerosol
WALL
5
ERMSAR 2012, Cologne March 21 – 23, 2012
Iodine behaviour models of ASTECIn containment : modelled with IODE module
1. Species accounted for :
GAS : I, CH3I, I2, HI, IO3
SUMPS : I-, IO3-, I2, CH3I, AgI, HIO
Aerosols computed by CPA
2. Reactions accounted for : mass transfer , thermal reactions, radiolytic reactions
Lack of knowledge :
Organic iodides formation/release rate : uncertainty range ~2 decades
related to iodide oxides behaviour:
1. Ozone production rate influence : uncertainty range ~2 decades
2. iodide oxides deposition rate : uncertainty range [1 4] factor
6
ERMSAR 2012, Cologne March 21 – 23, 2012
The competition between formation/destruction phenomena governs the volatile iodine amount in the containment
Liquid phase
Volatile species are transferred to the gaseous phase (I2, RI)
Ag2 OAg2 O
AgI ( )Ag
( Ag
If Ag is present, iodides ions can form insoluble compounds (AgI…)
Gaseous phase
A trapped fraction of I2 is converted into RI, that are destructed into IOx
I2 reacts with surfaces (adsorption, desorption)
Iodide ions are oxidized by water radicals (OH°) and form I2 that can be hydrolised, adsorbed on immersed paint, or react with organics in solution to form organic iodides
RI
ROH
H2 O
OH -
RRI
ROH
H2 O
OH -
R
-
IO3
IH2 OHOI
3
IH2 OHOI
2
aerosol type
pH
MAg/MI
Th. conditions of the sump
½
% Igaseous/Itot
I-
Iodine aerosols sediment and settle on walls. If soluble (CsI…), they form iodide ions (I-) in the aqueous phase. The insoluble aerosols (AgI…) stay in the bottom of the sump
gazeux
aérosolsI
I
circuit
Iodine oxides sediment and settle on the surfaces (walls, surface developed by aerosols in suspension)
Volatile iodine reacts with air radiolytic products , and oxidizes a fraction of I2 and RI => formation of iodine oxides (considered as fine particles)
RIO
IO 3
3
H2 O (v)
IO 3
3
H2 O (v)
Kads/kdes
I 2
7
ERMSAR 2012, Cologne March 21 – 23, 2012
CONTENTS
1. Assessing source term with ASTEC
2. Iodine related models and associated uncertainties
3. Source term assessment
4. Conclusion
8
ERMSAR 2012, Cologne March 21 – 23, 2012
SOURCE term assessment for a 1300 MWe PWR : various scenarios
SEQUENCES
Containment Spray System
Safety Injection ISMP
Safety Injection Low Pressure
Break location
Loss of feedwater in steam generator – 1 lost at 1 day NO
Direct mode only
Hot Leg
Loss of feedwater in steam generator – 2 NO NO
Direct mode only
Hot Leg
Loss of coolant break size of 12 ’’ NO
Direct mode only
Direct mode only
Cold Leg
Loss of coolant break size of 2’’
NO NO NO Cold Leg
Source term computation : full accidental scenario computation
Uncertainty assessment for this scenario
9
ERMSAR 2012, Cologne March 21 – 23, 2012
Scenario related variability
Depending on the scenario the iodine release ranges from ~0.1g to ~5g.
Loss FWSG ; CSS
Loss FWSG ; no CSS
12’’ LOCA 2’’ LOCA
RCS Retention : 53%Initial gaseous fraction at
the break : 7.2 %
RCS Retention : 55%Initial gaseous fraction at
the break : 2 %
RCS Retention : 9%Initial gaseous fraction at the break : 10 %
10
ERMSAR 2012, Cologne March 21 – 23, 2012
0 h 20 min Primary motopumps shutdown
2 h 29 min Safety injections starting
2 h 40 min Steam generator isolation
2 h 46 min Pressuriseur POR Valves opening
2 h 56 min Start of SM release
3 h 6 min Accumulators discharge
3 h 7 min Start of FP release
4 h 3 min Safety injections lost
6 h 10 min Total dewatering of core
7 h 11 min Vessel rupture
~ 3 days Filtered containment venting system activation
~ 6 days Basemat rupture
Uncertainty assessment scenario : loss of FWSG without CSS
11
ERMSAR 2012, Cologne March 21 – 23, 2012
Xi
Xn
X1
Yp(
Xi
Yp
YpXn
XnYppn YXcorr
),(
Uncertainties
Sensitivity
LHS sampling Astec runs over sampled variables
Sunset uncertainty assessment and sensitivity assessment
SUNSET
12
ERMSAR 2012, Cologne March 21 – 23, 2012
Iodine in environment (percentiles)
1E-05
1E-04
1E-03
1E-02
1E-01
1E+00
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
Iodi
ne in
env
iron
men
t (k
g)
minimum
5% percentile
median
95% percentile
maximum
The majority of the release is due to FCVUncertainty range ~20 at least (to be compared to scenario variability)Most influent parameters
gaseous iodine mass fraction iodide oxides deposition rate
To a lesser extent, organic formation rate in the containment gas phase ozone formation reaction rate
3.8 g
84 g
13
ERMSAR 2012, Cologne March 21 – 23, 2012
Source term computation : full accidental scenario computation
Source term computation : full accidental scenario computation
Iodine aerosols masses in containment (percentiles)
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
Iodi
ne a
eros
ol m
ass
(kg)
minimum
5% percentile
median
95% percentile
maximum
Total gaseous iodine mass in containment (percentiles)
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E+01
1.00E+02
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
Gase
ous I
odin
e m
ass
(kg)
minimum
5% percentile
median
95% percentile
maximum
The release after containment venting is due to gaseous species
Containment filtered venting Containment filtered venting
14
ERMSAR 2012, Cologne March 21 – 23, 2012
Source term computation : full accidental scenario computation
Source term computation : full accidental scenario computation
IxOy mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
IxOy
mas
s fr
acti
on
minimum
5% percentile
median
95% percentile
maximum
I2 mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
I2 m
ass
frac
tion
minimum
5% percentile
median
95% percentile
maximum
CH3I mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
CH3I
mas
s fr
acti
on
minimum
5% percentile
median
95% percentile
maximum
During core degradation, iodine species in the containment are essentially iodine oxides and
molecular iodine
15
ERMSAR 2012, Cologne March 21 – 23, 2012
Source term computation : full accidental scenario computation
Source term computation : full accidental scenario computation
IxOy mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
IxOy
mas
s fr
acti
on
minimum
5% percentile
median
95% percentile
maximum
I2 mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
I2 m
ass
frac
tion
minimum
5% percentile
median
95% percentile
maximum
CH3I mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
CH3I
mas
s fr
acti
on
minimum
5% percentile
median
95% percentile
maximum
At 1 day iodine oxides prevail for all situations
16
ERMSAR 2012, Cologne March 21 – 23, 2012
Source term computation : full accidental scenario computation
Source term computation : full accidental scenario computation
IxOy mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
IxOy
mas
s fr
acti
on
minimum
5% percentile
median
95% percentile
maximum
I2 mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
I2 m
ass
frac
tion
minimum
5% percentile
median
95% percentile
maximum
CH3I mass fraction in containment gas phase (percentiles)
1E-02
1E-01
2E-01
3E-01
4E-01
5E-01
6E-01
7E-01
8E-01
9E-01
0.0E+00
1.0E+05
2.0E+05
3.0E+05
4.0E+05
5.0E+05
6.0E+05
7.0E+05
Time (s)
CH3I
mas
s fr
acti
on
minimum
5% percentile
median
95% percentile
maximum
3 bodies system
17
ERMSAR 2012, Cologne March 21 – 23, 2012
CONTENTS
1. Assessing source term with ASTEC
2. Iodine related models and associated uncertainties
3. Source term assessment
4. Conclusion
18
ERMSAR 2012, Cologne March 21 – 23, 2012
Conclusion
Uncertainties on iodine phenomenology knowledge have an important impact, in the same order of magnitude as the variability due to the scenario .
Gaseous iodine mass fraction and iodine oxide mass deposition rate are the major contributors to these uncertainties
To a lower extent organic iodides formation rate and ozone formation rate have contributions of some importance.
These results confirm that the R&D efforts made by IRSN together with many partners in the ISTP and SARNET frames are focused on key issues.
19
ERMSAR 2012, Cologne March 21 – 23, 2012
Conclusion
Sensitivity analysis module of SUNSET helps to establish ranking of the studied effects, disregarding the complexity of the problem.
Regarding uncertainty propagation, interesting complements of this study
– The addition of other epistemic uncertainties would be of some interest, as the ones related to MCCI
– introduction of stochastic uncertainties, and the combined analysis of both epistemic-stochastic influences
20
ERMSAR 2012, Cologne March 21 – 23, 2012
Thank you for your attention
ERMSAR 2012, Cologne March 21 – 23, 2012
ADDITIONAL SLIDES
ERMSAR 2012, Cologne March 21 – 23, 2012
Source term computation : full accidental scenario computation
Source term computation : full accidental scenario computation
1 day 2 days 3 days 6 days
Iodine gaseous mass fraction at primary circuit break
0.72 0.37 0.29 0.35
Iodine oxides deposition rate in containment -0.75 -0.74 -0.39 -0.21
Organic iodine formation rate in containment atmosphere
0.26 0.30 0.31 0.14
Organic iodine formation rate in containment sumps
-0.04 -0.02 -0.04 -0.03
Organic compound release rate in containment atmosphere
-0.05 -0.02 0.09 0.13
Organic compound release rate from sumps 0.05 0.04 -0.07 -0.09
Ozone formation rate (forward reaction) 0.52 0.29 -0.27 -0.40
Ozone formation rate (backward reaction) -0.30 -0.05 0.08 0.14
Table of partial correlation coefficients for iodine release in environment vs. the different uncertain parameters
ERMSAR 2012, Cologne March 21 – 23, 2012
Source term computation : full accidental scenario computation
Source term computation : full accidental scenario computation
table of partial correlation coefficient for different iodine amounts in the containment versus the iodine partition at the primary break
Effect of gaseous mass fraction on iodine amount at…
1 day 2 days 6 days
in/on…
Immerged surfaces -0.98 -0.81 -0.65
Emerged surfaces 0.71 0.66 0.61
Gas phase (organic iodine) 0.43 0.41 0.36
Gas phase (molecular iodine) 0.35 0.54 0.42
Gas phase (Iodine oxides) 0.42 0.59 -0.36
Sumps (I-) 0.71 0.77 0.66
Sumps (iodine oxides) 0.77 0.87 0.63
Sumps (molecular iodine) -0.70 0.85 0.46
Sumps (organic iodine) -0.95 0.88 0.33
Sumps (AgI) 0.56 0.85 0.81
ERMSAR 2012, Cologne March 21 – 23, 2012
ASTEC models the transport in the reactor coolant system (RCS) of vapours and aerosols formed by condensation of material released from the degraded core.
Computes retention of radionuclides in the RCS
Computes aerosol size distribution and chemical speciation of aerosol and vapour phases along the RCS
Deals with the speciation of approximately 800 species cooler
Gas phasechemical reactions
Inlet flow Supersaturatedvapours
Condensation Deposition
ReleaseAgglomeration
Sorbtion
Nucleation
Aerosol
WALL cooler
Gas phasechemical reactions
Inlet flow Supersaturatedvapours
Condensation Deposition
ReleaseAgglomeration
Sorbtion
Nucleation
Aerosol
WALL
ERMSAR 2012, Cologne March 21 – 23, 2012
• Liquid phase hydrolysis of I2 and RI disappearance of HOI oxidation of I- by O2
reactions with Ag formation of RI
Thermal reactions :
• Gas phase oxidation of I2 by O3 in IxOy
formation of RI
Radiolytic reactions :
• Liquid phase oxidation of I- in I2
radiolytic reduction of IO3-
formation/destruction of RI
• Gas phase formation/destruction of RI in IyOx
formation of O3
Mass transfer processes :
• Liquid – gas (I2, IO3-, RI)• Liquid – surfaces (I2 : steel, paint, concrete)
• Gas – surfaces (I2 : steel, paint, concrete)
ASTEC a SA integral code : presentation of FP related modules – chemistry in containment
ERMSAR 2012, Cologne March 21 – 23, 2012
Uncertainty distributions
Uncertain variable Distribution
Gaseous iodine mass fraction at primary circuit break
Uniform law [min = 0.05; max = 0.95]
Iodine oxides deposition rate in containment Multiplying factor of the default value (16h-1): uniform law [min = 0.5 ; max = 2] ;
Ozone formation rates (forward and backward reactions)
Multiplying factor of the default kinetics constants: Log normal law [µ = 0 ; 1 ] ;
Organic iodine formation rate in containment atmosphere and sumps
Multiplying factor of the default kinetics constant: Log normal law [µ = 0 ; 1 ] ;
Release rate from paints of organic compounds that may react with molecular iodine in containment atmosphere and sumps to form organic iodides
Multiplying factor of the default kinetics constant: Log normal law [µ = 0 ; 1 ] ;
Method : Latin Hypercube, size = 100
ERMSAR 2012, Cologne March 21 – 23, 2012
Source term computation : full accidental scenario computation
Source term computation : full accidental scenario computation
Source Term
Sand bedfilter
Chimney
Containment Auxiliarybuilding
Direct Containment
leak
Direct leak(no filtering)
U5 french procedure
Leak to EEE(90 %)
Double containmentEEE
(PWR 1300 and 1450)
IodineFilter
Filteredleak
No filtered leak
Filtered leak
IodineFilter
Filtered and direct leaks to environment
ERMSAR 2012, Cologne March 21 – 23, 2012
Scenario related variability
Aerosols masses in environment are significant as long as the CSS does not work
For a LFWSG, the gaseous release is higher when CSS does not work
The location of the break has a strong influence on RCS retention
Depending on the scenario the iodine release ranges from ~0.1g to ~5g.
The gaseous mass fraction at primary break is a function of break size, location and other scenario effects.
The calculated gaseous iodine mass fraction seems to be low, though, especially when compared to the orders of magnitudes obtained in PHEBUS experiments, which confirms the importance of the on-going CHIP experiments in the frame of the ISTP program [5].
Loss FWSG ; CSS
Loss FWSG ; no CSS
12’’ LOCA 2’’ LOCA
RCS Retention : 53%
Gaseous fraction : 7.2 % RCS Retention : 55%
Gaseous fraction : 2 % RCS Retention : 9%
Gaseous fraction : 10 %