CPPC: Developm ent of a Sim ple Com puter Code for H 2 and CO Com - - PowerPoint PPT Presentation

Fernando Robledo ( CSN) Juan M. Martín-Valdepeñas ( CSN) Miguel A. Jim énez ( CSN) Francisco Martín-Fuertes ( UPM)

CSNI WORKSHOP ON UNCERTAINTIES IN PSA-2 ANALYSES

CPPC: Developm ent of a Sim ple Com puter Code for H 2 and CO Com bustion in Severe Accidents

What is CPPC?

• Developed by Polytechnic University
• f Madrid for CSN.
• Stand-alone code for fast calculations
• n pressure rises in the containment

from H2 and CO combustion in severe accidents.

• Most recent advances in the field of H2

and CO combustion.

• Useful tool for PSA-2 assessments.

What is CPPC?

I NPUT:

• Masses of H2 and

CO.

• Initial

environmental conditions in the containment, before burning.

• Simple geometric

data: volume of the enclosure. OUTPUT:

• Combustion completeness.
• Adiabatic and isochoric

combustion pressure.

• Chapman-Jouguet

pressure.

• Chapman-Jouguet

reflected pressure.

• Effective pressure.
• Combustion regime.

Main Assumptions

• Ideal gases.
• Gases homogeneously mixed in

containment.

• Steam-saturated atmosphere previous

to the combustion.

• Water properties from Steam Tables.

Flammability Limits

• Correlation for upward propagation:

XH2O = af + bf XH2 + cf exp (df XH2 + bf Tu)

• af, bf, cf, df fitted experimentally.

Combustion Completeness

• Pilch et al (1996).
• Murata et al (1997), taken from

CONTAIN 2.0

• HECTR 1.5, taken from MELCOR 1.8.4

(Gauntt ,1997).

Combustion Completeness

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.05 0.1 0.15 0.2 0.25 0.3 Molar fraction of flammable gases XC Combustion Completeness CC

Pilch (XD=0.0) Pilch (XD=0.3) Pilch (XD=0.6) Pilch Spray (XD=0.0) Pilch Spray (XD=0.3) Pilch Spray (XD=0.6) Murata Murata Spray Gauntt

Combustion Regimes

• Regimes considered:
• Slow deflagrations
• Flame Acceleration
• DDT
• Detonation
• For each gas mixture CPPC calculates:
• Fulfillment of criterion for combustion

regime.

• Effective static pressure.

Combustion Regimes (Kuznetsov, 2003).

4 8 12 t, s 0.0 0.4 0.8 1.2 0.6 0.8 1.0 t, s 2 4 6 8 10

0.2 0.21 10 20 30

Δ P/Po, t, s

B R = . 6 ( a i r )

10 20 30 40 50 60 70

x/D

200 400 600 800 1000 1200 1400

V

,

m /s

520 mm

9%H 2 10% 2 11% 2

80 mm

9%H 2 10% 2 11% 2 13% 2

174 mm

9%H 2 10% 2 11% 2 15% 2 25% 2

slow flames f ast flames quasi-detonations

σ > σ * L>7 λ

Flame Acceleration Criterion

• Selection of

parameter (σ)

• Establishing of

σ critical

b u u b

v v ρ ρ σ = =

σ

σ σ

σ

c u a

T E b a ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ + =

*

Flame Acceleration Criterion

• Definition of index

for FA.

• Quantification of

index for FA

*

σ σ

σ

= i 92 .

*

≥ =σ σ

σ

i

Flame Acceleration Criterion. Dorofeev (2001)

DDT Criterion

• Definition of DDT

index

• D geometric value
• λ: detonation cell

size

• Quantification of

DDT index

λ

λ

7 D i =

3 / 1

V D =

) , , , ( ) ( log

2 , 2 10

p T X X f

O H dry H

= λ

57 . 7 ≥ = λ

λ

D i

DDT Criterion (CSNI SOAR, 2000).

DDT Criterion (Breitung, 2000).

Direct Detonation Criterion

Steam Hydrogen Air

Flammable Detonable Non-flammable H2/air stochiometric mixture

Pressure Rise Calculation: Slow Deflagrations

( ) ( )

CO q CO H q H A u u A v A A AICC b b A v A

q n q n T c n T c n

, 2 , 2 , ,

+ + =∑

∑

( )

R PM R T D T C T B A c

A A A A A vA

− + + + =

3 2

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ =

u b u AICC b u AICC b

n n T T p p

Pressure Rise Calculation: General Case

m t p y f y

i

) ( ) 2 ( ' '

2

= + π

Frequency: input data. 5 to 500 Hz as indicated by Breitung and Redlinger (1995b)

Pressure Rise Calculation: General Case.

• Pi(t) obtained from typical shape of

pressure loads at the different combustion regimes (Breitung and Redlinger (1995b).

• Upper bound values:
• PCJ

= 1.8 (+0.08) PAICC

• PCJ-R

= 4.1 (+ 0.3) PAICC

Pressure Rise Calculation: General case.

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0.00001 0.0001 0.001 0.01 0.1 1 10

time (s) p/pAICC

p SD p FA p DDT p DET

Pressure Rise Calculation: General case.

• Calculation of the effective static

pressure:

max 2

) 2 ( y m f p eff π =

m t p y f y

i

) ( ) 2 ( ' '

2

= + π

Pressure Rise Calculation: General Case.

1 2 3 4 5 6 7 50 100 150 200 250 300 350 400 450 500 frequency (Hz) peff / pAICC peff SD peff FA peff DDT peff DET

Validation & Verification

• Comparison with MELCOR calculations to verify

that CPPC provides an upper bound.

• CPPC code uses combustion completeness = 1.
• T0: scenarios with CHR activation coincident with

vessel failure.

• T1: scenarios with CHR activation coincident with

the maximum of the σ parameter.

• ESF: Spray + Fan-cooling units.
• FCL: Fan-cooling units. Full capacity.
• SPR: Spray system: full capacity. Full capacity.

Validation & Verification

MELCOR CPPC Scenario Duration ( s) H2 ( CO) m ass burnt ( kg) Pm ax ( bar) PAI CC ( bar) Regim e

dryT0 - ESF 7 0 5 1 ( 2 2 9 ) 1 .6 9 4 .1 1 0 SD dryT0 - FCL 5 8 8 0 ( 3 3 1 ) 1 .9 6 4 .1 0 6 SD dryT0 - SPR 3 1 1 2 0 ( 1 1 7 5 ) 2 .2 3 3 .9 9 6 SD w etT0 - ESF 5 7 4 2 4 ( 3 1 4 5 ) 5 .1 1 6 .4 8 3 FA w etT0 - FCL 5 7 4 2 4 ( 3 1 4 9 ) 5 .1 1 6 .4 9 5 FA w etT0 - SPR 1 7 3 7 4 ( 1 9 1 4 ) 4 .4 5 5 .1 7 5 SD

Validation & Verification

MELCOR CPPC Scenario Duration ( s) H2 ( CO) m ass burnt ( kg) Pm ax ( bar) PAI CC ( bar) Regim e

dryT1 - ESF 4 6 3 6 4 ( 2 8 4 8 ) 4 .5 3 5 .3 2 2 FA dryT1 - FCL 5 8 3 6 1 ( 2 6 4 4 ) 4 .4 6 5 .3 3 2 FA dryT1 - SPR 4 4 3 6 0 ( 2 6 3 5 ) 4 .4 6 5 .3 7 8 FA w etT1 - ESF 8 8 4 2 0 ( 3 1 3 8 ) 5 .0 7 6 .3 7 4 FA w etT1 - FCL 8 6 4 2 2 ( 3 1 5 5 ) 5 .0 7 6 .3 7 5 FA w etT1 - SPR 8 9 4 1 9 ( 3 1 2 9 ) 4 .9 2 6 .4 5 3 SD

Validation & Verification

• CPPC results compared with those
• btained with other code for AICC

calculations in case of slow deflagrations.

• Satisfactory results, differences in the

pressure increase range in the 1%.

Validation & Verification. Breitung calculations.

XH2 ( % vol) XH2 O ( % vol) Tu ( * ) ( K) Pu ( * ) ( bar) PAI CC Breitung ( bar) PAI CC CPPC ( bar)

Deviation

( % )

1 5 3 0 3 6 2 2 .2 6 9 .9 5 3 1 0 .0 3

• 0 .8

2 0 4 0 3 8 0 3 .2 6 1 4 .4 8 1 4 .4 0 .6 2 0 3 6 6 2 .5 8 1 3 .2 9 1 3 .5

• 1 .5

1 5 1 5 3 3 5 1 .6 2 7 .4 8 7 7 .9 5

• 1 .3

2 0 2 9 3 1 .2 7 8 .6 1 8 8 .8 2

• 2 .3

2 9 .5 2 9 3 1 .4 4 1 1 .8 7 1 2 .7 7

• 7 .5

3 0 1 5 3 4 2 2 .1 2 1 3 .3 1 1 3 .3 6

• 0 .3

2 5 3 0 3 6 8 2 .8 4 1 4 .2 8 1 4 .2 4 0 .3

Validation & Verification. Breitung calculations.

• Relative errors lie around 1% in wet

mixtures.

• Less than 10% in dry mixtures.
• Results are considered as acceptable.

Plant Applications CSN methodology to calculate the containment failure probability due to hydrogen combustion during the in-vessel phase

Plant Applications

• Obtain containment pressure prior to H2
• combustion. MELCOR calculations.
• Obtain H2 mass in the containment. H2

well mixed.

• Calculate the containment pressurization.

CPPC useful in this step.

• Overlap the containment pressure

distribution with containment fragility curve to obtain containment failure probability.

• Reflooding considered: 20% additional

hydrogen generation (Kuan, 1994).

Plant Applications

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Zr FRACTION OXIDAZED PROBABILITY

pdf cdf

Plant Applications Results obtained

• No reflooding scenarios: negligible

probability.

• Reflooding scenarios: significant

increase in the containment failure probability and potential for flame acceleration.

• Safety significance of these results

under study.

Plant Applications: No reflooding case

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 2 3 4 5 6 7 8 9 10 PRESSURE (BARS) CUMULATIVE PROBABILITY

FRAGILITY 1.39 BARS

Plant Applications

• Future applications are planned:
• Continuation of the verification process.
• Calculation of the containment failure

probability for the ex-vessel phase.

• Analyses of local hydrogen accumulations.