ERMSAR 2012, Cologne March 21 – 23, 2012 Source term assessment with ASTEC and associated...

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


CONTENTS

1. Assessing source term with ASTEC

2. Iodine related models and associated uncertainties

3. Source term assessment

4. Conclusion

1


CONTENTS




4. Conclusion

2


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


CONTENTS




4. Conclusion

4


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





Sorbtion

Nucleation

Aerosol

WALL

5


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


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


CONTENTS




4. Conclusion

8


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


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


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


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


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




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




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





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


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


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





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


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


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


CONTENTS




4. Conclusion

18


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


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


Thank you for your attention


ADDITIONAL SLIDES




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




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


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





Sorbtion

Nucleation

Aerosol

WALL cooler





Sorbtion

Nucleation

Aerosol

WALL


• 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


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




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


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 %

ERMSAR 2012, Cologne March 21 – 23, 2012 Source term assessment with ASTEC and associated...

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