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

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

What is CPPC? • Developed by Polytechnic University of Madrid for CSN. • Stand-alone code for fast calculations on pressure rises in the containment from H 2 and CO combustion in severe accidents. • Most recent advances in the field of H 2 and CO combustion. • Useful tool for PSA-2 assessments.

What is CPPC? I NPUT: OUTPUT: • Masses of H 2 and • Combustion completeness. CO. • Adiabatic and isochoric • Initial combustion pressure. environmental • Chapman-Jouguet conditions in the pressure. containment, • Chapman-Jouguet before burning. reflected pressure. • Simple geometric • Effective pressure. data: volume of the enclosure. • 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: X H2O = a f + b f X H2 + c f exp (d f X H2 + b f T u ) • a f , b f , c f, d f 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 1 0.9 0.8 Combustion Completeness CC 0.7 Pilch (XD=0.0) Pilch (XD=0.3) 0.6 Pilch (XD=0.6) Pilch Spray (XD=0.0) 0.5 Pilch Spray (XD=0.3) Pilch Spray (XD=0.6) Murata 0.4 Murata Spray Gauntt 0.3 0.2 0.1 0 0 0.05 0.1 0.15 0.2 0.25 0.3 Molar fraction of flammable gases X C

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). Δ 1400 P/Po, 30 B R = 0 . 6 ( a i r ) quasi-detonations 20 1200 174 mm 80 mm 10 t, s 9%H 9%H 2 2 10% 2 10% 2 0 0.2 0.21 11% 2 11% 2 1000 λ 13% 2 15% 2 L>7 25% 2 10 520 mm 8 800 m /s 9%H 2 6 10% 2 4 11% 2 , V f t, s ast flames 2 600 0 0.6 0.8 1.0 400 σ σ > * 1.2 0.8 200 0.4 t, s slow flames 0.0 0 4 8 12 0 10 70 20 30 40 50 60 x/D

Flame Acceleration Criterion ρ v σ = = • Selection of b u ρ parameter ( σ ) v u b c ⎛ ⎞ σ • Establishing of E ⎜ ⎟ σ = + * a a b ⎜ ⎟ σ σ σ critical ⎝ ⎠ T u

Flame Acceleration Criterion σ = • Definition of index i σ for FA. σ * σ = σ ≥ • Quantification of 0 . 92 i σ index for FA *

Flame Acceleration Criterion. Dorofeev (2001)

DDT Criterion D = • Definition of DDT i λ λ index 7 = • D geometric value 1 / 3 D V λ = • λ : detonation cell log ( ) f ( X , X , T , p ) 10 H 2 , dry H 2 O size D = ≥ • Quantification of 0 . 57 i λ λ DDT index 7

DDT Criterion (CSNI SOAR, 2000).

DDT Criterion (Breitung, 2000).

Direct Detonation Criterion Steam Air Detonable Flammable Non-flammable H 2 /air stochiometric mixture Hydrogen

Pressure Rise Calculation: Slow Deflagrations ( ) ( ) ∑ = ∑ + + AICC n c T n c T n q n q A v , A b A v , A u H 2 , q H 2 CO , q CO b u A A ( ) R = + + + − 2 3 c A B T C T D T R vA A A A A PM A ⎛ ⎞ ⎛ ⎞ AICC T n ⎜ ⎟ ⎜ ⎟ = AICC b b p p ⎜ ⎟ ⎜ ⎟ b u ⎝ ⎠ T n ⎝ ⎠ u u

Pressure Rise Calculation: General Case p ( t ) + π = 2 i y ' ' ( 2 f ) y m 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: • P CJ = 1.8 (+0.08) P AICC • P CJ-R = 4.1 (+ 0.3) P AICC

Pressure Rise Calculation: General case. 5 4.5 4 3.5 3 p SD p/p AICC p FA 2.5 p DDT p DET 2 1.5 1 0.5 0 0.00001 0.0001 0.001 0.01 0.1 1 10 time (s)

Pressure Rise Calculation: General case. • Calculation of the effective static pressure: p ( t ) + π = 2 i y ' ' ( 2 f ) y m = π 2 ( 2 ) p eff f m y max

Pressure Rise Calculation: General Case. 7 6 5 peff SD peff / pAICC 4 peff FA peff DDT peff DET 3 2 1 0 0 50 100 150 200 250 300 350 400 450 500 frequency (Hz)

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 H2 ( CO) Pm ax PAI CC Regim e m ass burnt ( bar) ( bar) ( s) ( kg) dryT0 - 7 0 5 1 ( 2 2 9 ) 1 .6 9 4 .1 1 0 SD ESF dryT0 - 5 8 8 0 ( 3 3 1 ) 1 .9 6 4 .1 0 6 SD FCL dryT0 - 3 1 1 2 0 2 .2 3 3 .9 9 6 SD SPR ( 1 1 7 5 ) w etT0 - 5 7 4 2 4 5 .1 1 6 .4 8 3 FA ESF ( 3 1 4 5 ) w etT0 - 5 7 4 2 4 5 .1 1 6 .4 9 5 FA FCL ( 3 1 4 9 ) w etT0 - 1 7 3 7 4 4 .4 5 5 .1 7 5 SD SPR ( 1 9 1 4 )

Validation & Verification MELCOR CPPC Scenario Duration H2 ( CO) Pm ax P AI CC Regim e ( s) m ass burnt ( bar) ( bar) ( kg) dryT1 - 4 6 3 6 4 4 .5 3 5 .3 2 2 FA ESF ( 2 8 4 8 ) dryT1 - 5 8 3 6 1 4 .4 6 5 .3 3 2 FA FCL ( 2 6 4 4 ) dryT1 - 4 4 3 6 0 4 .4 6 5 .3 7 8 FA SPR ( 2 6 3 5 ) w etT1 - 8 8 4 2 0 5 .0 7 6 .3 7 4 FA ESF ( 3 1 3 8 ) w etT1 - 8 6 4 2 2 5 .0 7 6 .3 7 5 FA FCL ( 3 1 5 5 ) w etT1 - 8 9 4 1 9 4 .9 2 6 .4 5 3 SD SPR ( 3 1 2 9 )

Validation & Verification • CPPC results compared with those obtained 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 XH2 O Tu ( * ) Pu ( * ) P AI CC P AI CC Deviation ( % ) ( % vol) ( % vol) ( K) ( bar) Breitung CPPC ( bar) ( bar) 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 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 0 2 9 3 1 .2 7 8 .6 1 8 8 .8 2 -2 .3 2 9 .5 0 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 H 2 combustion. MELCOR calculations. • Obtain H 2 mass in the containment. H 2 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 1 0.9 0.8 0.7 0.6 PROBABILITY pdf 0.5 cdf 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Zr FRACTION OXIDAZED

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 1 0.9 0.8 CUMULATIVE PROBABILITY 0.7 0.6 FRAGILITY 0.5 1.39 BARS 0.4 0.3 0.2 0.1 0 0 1 2 3 4 5 6 7 8 9 10 PRESSURE (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.