Overview of Containment Issues and Major Experimental Activities

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Paillere The first European Review Meeting on Severe

1 Overview of Containment Issues and Major Experimental Activities L. Meyer, H. Wilkening, H. Jacobs, H. Paillere The first European Review Meeting on Severe Accident Research () Aix-en-Provence, France, November 2005

2 Organization of the CONTAINMENT group (18 partner organisations) WP12: Hydrogen Behaviour in Containment (HBC) WP 12-1: Hydrogen Combustion (HC) WP 12-2: Containment Atmosphere Mixing (CAM) WP13: Fast Interaction with Corium (FIC) WP 13-1: Fuel Coolant Interaction (FCI) WP 13-2: Direct Containment Heating (DCH) 2

3 Organization of the CONTAINMENT group WP12: Hydrogen Behaviour in Containment (HBC) WP 12-1: Hydrogen Combustion (HC) PARTNER (7) FACILITY CODE IRSN (France) ENACCEF TONUS FZJ (Germany) REKO-3 REKO-DIREKT FZK (Germany) COM-3D GRS (Germany) COCOSYS-DECOR JRC (EU) REACFLOW TUS (Bulgaria) ASTEC VEIKI (Hungary) GASFLOW *CFD-codes *Lumped parameter codes 3

4 Hydrogen Combustion Topics of the EURSAFE PIRT addressed in WP 12-1: Hydrogen Combustion (HC) Flame Propagation Pressure loads Hydrogen removal / mitigation Physical effect involved Flame Acceleration in non-uniform hydrogen/air/steam mixtures Scaling effects in hydrogen Combustion The use of recombiners might limit the explosion loads but could also cause ignition. Experimental Facility addressing the issue ENACCEF RUT REKO-3 4

5 Hydrogen Combustion The ENACCEF test facility (Enceinte d ACCElération de Flamme) The upper dome part with a total volume of 0.66 m 3 The lower driver tube with a length of 3.2 m and a diameter of m 5

Hydrogen Combustion ENACCEF test facility experimental details The ENACCEF test facility can be filled with any type of hydrogen-air-steam mixtures.

6 Hydrogen Combustion ENACCEF test facility experimental details The ENACCEF test facility can be filled with any type of hydrogen-air-steam mixtures. Within the acceleration tube obstacles can be installed to increase turbulent flame propagation/acceleration. The facility is equipped with pressure transducers and photomultipliers. The driver tube has also optical access to allow LDV and PIV measurements. 6

7 Hydrogen Combustion / Removal From the recombiner via the experiment to the model outlet inlet catalyst sheets Box-type recombiner REKO-3 REKO-DIREKT 7

8 Hydrogen Combustion / Removal REKO-3 test facility outlet gas analysis recombiner unit catalyst sheets inlet 8

9 Hydrogen Combustion/Removal REKO-3 - Measurements OUTLET gas temperature gas composition INLET PARAMETERS OF EXPERIMENTS - flow rate ( m/s) - inlet temperature (ambient..150 C) - inlet hydrogen concentration (0..5 vol.%, limited by safety concerns) - inlet steam concentration (0..60 vol.%, depending on flow rate) - inlet oxygen concentration CATALYST PLATE catalyst temperature at 10 different locations REACTION ZONE gas composition at 14 different locations INLET flow rate gas temperature gas composition 9

10 Hydrogen Combustion / Removal REKO-3 experiments: transient measurements 143 x 143 mm² (1,5 mm sheets) x/mm min 8 min 7 min 6 min H 2 + air y H2 = 4 vol.% T = 25 C v = 0.5 m/s min 2 min 3 min 4 min 5 min T / C 10

11 Hydrogen Combustion / Removal REKO-3 experiments: stationary behavior T' = 25 C 120 v' = 0.80 m/s 120 T' = 25 C v' = 0.80 m/s y H2,E / Vol.-% x / mm x/mm y H2,E / Vol.-% y H2 / vol.% T / C 11

Adaptation Variables adaptation on the flame front (H2O

12 Hydrogen Combustion Hydrogen explosion modeling with the CFD-code REACFLOW Advances in Grid Adaptation by Multiple Adaptation Variables adaptation on the flame front (H2O concentration) adaptation on the pressure wave ahead of the flame front 12

Hydrogen Combustion Studying different ignition scenarios for hydrogen combustion in a reactor using CFX and REACFLOW TEMPERATURE at 0.5 s 0.68 s 0.

13 Hydrogen Combustion Studying different ignition scenarios for hydrogen combustion in a reactor using CFX and REACFLOW TEMPERATURE at 0.5 s 0.68 s 0.98 s Case 1: single point ignition Case 2: symmetric double point ignition With two ignition points the overall burning rate might be larger but flame speeds (overpressure) can be reduced due to shorter flame acceleration distances/time. 13

Hydrogen Combustion Investigating different venting scenarios using CFX and REACFLOW for a simplified nuclear reactor geometry Modified venting could reduce quite drastically the

14 Hydrogen Combustion Investigating different venting scenarios using CFX and REACFLOW for a simplified nuclear reactor geometry Modified venting could reduce quite drastically the pressure between neighboring rooms. Such different pressures could cause the collapse of the wall and trigger a sequence of events within the containment with potentially devastating effects. 14

15 Hydrogen Combustion ASTEC Two combustion options are already available : COVI, COMB in CPA PROCO module is being implemented into CPA: All combustion modes from laminar deflagration to stable detonation are covered Two criteria to decide about Deflagration-to-Detonation Transition: - Mach number of precursor shock > 1.5 (composition dependent) - Characteristic length of compartment > 7 times the detonation cell size λ (geometry and composition dependent) 15

16 Organization of the CONTAINMENT group WP12: Hydrogen Behaviour in Containment (HBC) WP 12-2: Containment Atmosphere Mixing (CAM) PARTNER (12) FACILITY CODE IRSN (France) TOSQAN TONUS, ASTEC CEA (France) MISTRA TONUS DIMNP (Italy) CONAN FLUENT, FUMO, MELCOR FZK (Germany) GASFLOW GRS (Germany) COCOSYS JSI (Slovenia) CFX-4, CONTAIN, MELCOR KTH (Sweden) CFX-4/5 LEI (Lithuania) COCOSYS, ASTEC, CONTAIN NRG (Netherlands) CFX-4/5, STAR-CD, SPECTRA, MAAP RUB-LEE(Germany) COCOSYS UPM (Spain) CFX-4, MELCOR VEIKI (Hungary) GASFLOW, COCOSYS 16

Containment Atmosphere Mixing On-going R&D topics are related to identified gaps related to the formation of combustible gas mixtures in the containment, as identified in the EURSAFE PIRT or in

in-depth analysis of past experiments (TOSQAN and MISTRA tests made available to SARNET) deficiencies, identification of validation needs recommendations on choice of models & best practice

17 Containment Atmosphere Mixing On-going R&D topics are related to identified gaps related to the formation of combustible gas mixtures in the containment, as identified in the EURSAFE PIRT or in recent benchmark exercises such as ISP-47: Condensation modelling in CFD codes (UNIPI task leader) - concerning diffusive models (wall function) or correlations (heat & mass transfer) review or in-depth analysis of past experiments (TOSQAN and MISTRA tests made available to SARNET) deficiencies, identification of validation needs recommendations on choice of models & best practice guidelines recommendations for new experiments (CONAN, MISTRA) Condensing wall Injection pipe CONAN (UNIPI) Non condensing wall TOSQAN (IRSN) MISTRA (CEA) Recirculation zone (Zone 2) recirculated flow induced by the jet Injection region (Zone 1) acceleration/decceleration and gas entrainment by the plume/jet Thermal free convection zone (Zone 4) thermally induced flow 17

performed by IRSN (TOSQAN) and CEA (MISTRA) are being provided as basis for benchmarking of LP and CFD codes possibility to look at scaling effect: TOSQAN (7m 3

18 Containment Atmosphere Mixing On-going R&D topics are related to identified gaps related to the formation of combustible gas mixtures in the containment, as identified in the EURSAFE PIRT or in recent benchmark exercises such as ISP-47: Spray modelling (IRSN task leader) Organisation of a benchmark Experiments performed by IRSN (TOSQAN) and CEA (MISTRA) are being provided as basis for benchmarking of LP and CFD codes possibility to look at scaling effect: TOSQAN (7m 3 ) MISTRA (100m 3 ) TOSQAN (IRSN) Effect of spray mitigation system on H 2 distribution (risk): - homogenization? - local H 2 enrichment by steam condensation? MISTRA (CEA) 18

PIRT or in recent benchmark exercises such as ISP-47: Interaction PAR atmosphere Organisation

Recombiners with containment atmosphere - issues of modelling (CFD) of thermal plume (burned

19 Containment Atmosphere Mixing On-going R&D topics are related to identified gaps related to the formation of combustible gas mixtures in the containment, as identified in the EURSAFE PIRT or in recent benchmark exercises such as ISP-47: Interaction PAR atmosphere Organisation of a (numerical) benchmark on (CEA task leader) interaction of Passive Autocatalytic Recombiners with containment atmosphere - issues of modelling (CFD) of thermal plume (burned gases) - natural convection effects - effect of positioning of recombiners in a room on global efficiency 19

20 Organization of the CONTAINMENT group WP13: Fast Interaction with Corium (FIC) WP 13-1: Fuel Coolant Interaction (FCI) PARTNER (7) FACILITY CODE IRSN (France) TREPAM MC3D CEA (France) KROTOS MC3D FZK (Germany) ECO MATTINA IKE (Germany) DROPS IKEMIX, IDEMO JSI (Slovenia) ESE-2 KTH (Sweden) MISTEE COMETA-KTH TUS (Bulgaria) *CFD-codes 20

21 Fuel-Coolant Interaction (FCI) WP 13-1: Fuel-Coolant Interaction (FCI) EURSAFE selected: FCI including steam explosion, in-vessel and ex-vessel. Aim: - Increase knowledge about steam explosion energetics. - Develop tools to determine the risk of vessel or containment failure. OECD Research program SERENA: - Aim: Evaluate capabilities of available codes with respect to reactor applications. - Participants from SARNET: IRSN, CEA, FZK, IKE 21

22 Fuel-Coolant Interaction (FCI) Experiment ECO (FZK): Measurement of Energy Conversion (mechanical energy release) Closed system of piston and cylinder kg of Al 2 O 3 (in 4 tests) External trigger applied With full water mass, no explosion. With restricted water mass (tube), 3 strong explosions. Pressures well beyond 100 MPa. Still quite low (and varying) energy conversion: 2.4, 0.8 and 0.6 %. Possible reasons for low conversion: - high water subcooling (-> factor 2) - overstrong confinement (piston mass = 2700 kg) Facility mothballed 22

23 Fuel-Coolant Interaction (FCI) Experiment KROTOS-Cadarache (CEA): Study the effect of material properties on steam explosions. Up to 5 kg corium of variable composition or 4 kg of SS (or 1.5 kg Al 2 O 3 ). External trigger applied. Improvements with respect to KROTOS-Ispra: - reproducible melt release with slide valve; - high-speed X-ray radioscopy to observe premixture. To go in operation end of

24 Organization of the CONTAINMENT group WP13: Fast Interaction with Corium (FIC) WP 13-2: Direct Containment Heating (DCH) PARTNER (7) FACILITY CODE IRSN (France) MC3D, RUPUICUV (ASTEC) EDF (France) MAAP-4 FZK (Germany) DISCO-H/C AFDM, SIMMER GRS (Germany) CONTAIN, COCOSYS RUB-LEE (Germany) TUS (Bulgaria) ASTEC FRA ANP (Germany) *CFD-codes *Lumped parameter codes 24

Direct Containment Heating (DCH) HEAT TRANSFER CORIUM STEAM / GAS CONTAINMENT PRESSURIZATION + H2 - COMBUSTION dispersed corium metal oxidation and hydrogen production

25 Direct Containment Heating (DCH) HEAT TRANSFER CORIUM STEAM / GAS CONTAINMENT PRESSURIZATION + H2 - COMBUSTION dispersed corium metal oxidation and hydrogen production trapped corium corium film formation and entrainment steam blowdown relocated corium breach in the lower head corium jet impact / fragmentation Phenomena occurring during DCH 25

Direct Containment Heating (DCH) PAST RESEARCH PROGRAMS (-1998) Achievements Large database on US reactor type plants. Several analytical models were developed.

26 Direct Containment Heating (DCH) PAST RESEARCH PROGRAMS (-1998) Achievements Large database on US reactor type plants. Several analytical models were developed. Simple models were integrated into codes (MAAP, CONTAIN, MELCOR). Main conclusions Up to 70% dispersion out of pit Containment integrity maintained No scaling effect for pressure Strong effect of geometry Issue was closed for US plants 26

Direct Containment Heating (DCH) EURSAFE PIRT selected phenomena as most important: corium entrainment out of reactor vessel with lateral breaches corium oxidation coupled with hydrogen production

27 Direct Containment Heating (DCH) EURSAFE PIRT selected phenomena as most important: corium entrainment out of reactor vessel with lateral breaches corium oxidation coupled with hydrogen production generating and trapping of particles particle heat exchange hydrogen combustion Ø700mm S mm S5 S4 S3 S1 S mm Ø4905mm Ø5092mm Ø5270mm 4750mm 4050mm 1610mm 2040mm 800 mm S mm 2540mm GA 301 German KONVOI (similar to EPR) French 1300 MWe VVER

Direct Containment Heating (DCH) Test Facility DISCO-C (FZK) (EPR scale 1:18, P 4 scale 1:16) Cold tests for fluid dynamic investigations Simulant Melt: Driving gas: Water and liquid metal alloys

28 Direct Containment Heating (DCH) Test Facility DISCO-C (FZK) (EPR scale 1:18, P 4 scale 1:16) Cold tests for fluid dynamic investigations Simulant Melt: Driving gas: Water and liquid metal alloys Nitrogen and Helium Failures Modes: Central and lateral breaches Burst pressure: MPa Central holes: Strong influence of initial gas pressure and hole size: - The maximum dispersion (75%) is reached at pressures below 2 MPa - Pressure < 0.5 MPa limits dispersion to <10% Lateral breaches and total circumferential breakaway of lower head lead to less dispersion than central holes Gas Line RPV+RCS Volume Filter Pump Room Steam Generator Nozzle Room RPV support Annular gap Melt Simulant Rupture Disk Cavity 1620 mm 28

29 Test Facility DISCO-H (FZK) (EPR scale 1:18, P 4 scale 1:16) Hot tests including all processes, close to prototypical conditions: Simulant Melt: Iron-alumina melt (2400 K) Driving gas: Steam or Nitrogen Failures Modes: central breaches (3 sizes) Pressure at failure: MPA Containment atmosphere: Air + steam + H 2 or N 2 With or w/t direct flow path from pit to containment Data available to SARNET partners from: 6 Tests in EPR geometry 1 Test in P 4 geometry (LACOMERA-1) Direct Containment Heating (DCH) 1 Test in VVER-1000 geometry (LACOMERA-2) 29

Test Facility DISCO-H (FZK) (EPR scale 1:18, P 4 scale 1:16) Direct Containment Heating (DCH) Without hydrogen combustion pressure rise in containment is low.

30 Test Facility DISCO-H (FZK) (EPR scale 1:18, P 4 scale 1:16) Direct Containment Heating (DCH) Without hydrogen combustion pressure rise in containment is low. Pre-existing hydrogen content in containment can be important for pressure rise. Without direct flow path from pit to containment less hydrogen is burned and pressure rise is low. With small breaches the mixing and combustion of produced hydrogen with the containment atmosphere is too slow to contribute to peak pressure. Investigations are necessary for each specific reactor design. 30

31 Thank you for your attention 31

5.2. Phenomena liable to result in early containment failure

146 Nuclear Power Reactor Core Melt Accidents 5.2. Phenomena liable to result in early containment failure 5.2.1. Direct containment heating 5.2.1.1. Introduction The phenomenon of direct containment heating