Overview of Experimental Programs on Core Overview of Experimental Programs on Core Melt Progression and Fission Product Release Melt Progression and Fission Product Release BehaviourBehaviour

B.J. Lewis, Royal Military College of Canada

R. Dickson, Atomic Energy of Canada Limited

F.C. Iglesias, Candesco Corporation

International VERCORS Seminar

Gréoux les bains, France

October 15-16, 2007

OutlineOutline

Experiment ReviewExperiment Review Integral Severe Accident and Single Effect TestsIntegral Severe Accident and Single Effect Tests

Degraded Core Accident PhenomenaDegraded Core Accident Phenomena Fission Product Release (FPR) BehaviorFission Product Release (FPR) Behavior

In-Pile TestsIn-Pile Tests

Source Term Experiments Project (STEP 1,2,3,4)Source Term Experiments Project (STEP 1,2,3,4) Fission product release (FPR) and aerosol chemistryFission product release (FPR) and aerosol chemistry

Source Term Tests (ST 1,2)Source Term Tests (ST 1,2) FPR & aerosols from highly-irradiated fuel (reducing conditions)FPR & aerosols from highly-irradiated fuel (reducing conditions)

Damaged Fuel (DF 1,2,3,4) Relocation ExperimentDamaged Fuel (DF 1,2,3,4) Relocation Experiment Coolant flow rate, system/fuel-rod pressure, degree of initial clad oxidationCoolant flow rate, system/fuel-rod pressure, degree of initial clad oxidation

Severe Fuel Damage Tests (SFD ST, 1-1, 1-3, 1-4)Severe Fuel Damage Tests (SFD ST, 1-1, 1-3, 1-4) Fuel bundle & FPR (transport/deposition) behavior, HFuel bundle & FPR (transport/deposition) behavior, H22 generation generation

In-Pile Tests Cont’dIn-Pile Tests Cont’d

Full Length High Temperature Tests (FLHT 1,2,4,5)Full Length High Temperature Tests (FLHT 1,2,4,5) Oxidation & HOxidation & H22 generation in full-length rods generation in full-length rods

Loss-of-Fluid Test Facility Fission Product Test (LOFT FP-2)Loss-of-Fluid Test Facility Fission Product Test (LOFT FP-2) Large-scale test on FPR, steam supply/refloodLarge-scale test on FPR, steam supply/reflood

Melt Progression (MP 1,2)Melt Progression (MP 1,2) Ceramic pool behavior in blocked-core accidentsCeramic pool behavior in blocked-core accidents

Blowdown Test Facility (BTF-104, -105A, -105B, -107)Blowdown Test Facility (BTF-104, -105A, -105B, -107) CANDU fuel and FPR behaviour CANDU fuel and FPR behaviour

Phebus SFD Phebus SFD Phebus Fission Product Tests (FPT-0,-1,-2,-3-4) Phebus Fission Product Tests (FPT-0,-1,-2,-3-4) Core, cooling system & containment response including FPR Core, cooling system & containment response including FPR

transport/depositiontransport/deposition Semi-volatile & actinide release from UOSemi-volatile & actinide release from UO22/ZrO/ZrO22 rubble bed rubble bed

Out-of-Pile Tests (Electrically Heated)Out-of-Pile Tests (Electrically Heated)

CORA (19 tests) CORA (19 tests) Quench Quench Temporal behavior of core melt progression & refloodTemporal behavior of core melt progression & reflood

PARAMETER (UOPARAMETER (UO22 pellets and VVER cladding (1% Nb)) pellets and VVER cladding (1% Nb))

Bundle ConfigurationsBundle Configurations

Out-of-Pile Annealing TestsOut-of-Pile Annealing Tests

Single Effects Fission Product Release (FPR) Experiments:Single Effects Fission Product Release (FPR) Experiments: FPR from spent fuel (hydrogen, steam, air)FPR from spent fuel (hydrogen, steam, air)

ORNL: Horizontal Induction (HI 1-6), Vertical Induction (VI 1-7) ORNL: Horizontal Induction (HI 1-6), Vertical Induction (VI 1-7) CEA-CENG: HEVA 1-8, Vercors 1-6, High Temperature (HT 1-3), Release of CEA-CENG: HEVA 1-8, Vercors 1-6, High Temperature (HT 1-3), Release of

Transuranics (RT 1-8)Transuranics (RT 1-8) AECL-CRL: >300 tests, e.g., MCE1-1,-6,-7, MCE2-13,-19, HCE2-BM3,-AECL-CRL: >300 tests, e.g., MCE1-1,-6,-7, MCE2-13,-19, HCE2-BM3,-

CM4, UCE12-8CM4, UCE12-8 JAERI: Verification Experiments of radionuclides Gas/Aerosol release (VEGA JAERI: Verification Experiments of radionuclides Gas/Aerosol release (VEGA

1-10) 1-10)

ORNL ExperimentsORNL Experiments

Test conditions:Test conditions: Highly-irradiated Zircaloy-clad UOHighly-irradiated Zircaloy-clad UO22 fuel samples 15-20 cm long (100-200 g) fuel samples 15-20 cm long (100-200 g) Atmospheric pressure up to 1700-2700 K (time at temperature 2-60 min) Atmospheric pressure up to 1700-2700 K (time at temperature 2-60 min) Test atmosphere: steam in VI-3, hydrogen in VI-5, hydrogen followed by steam in Test atmosphere: steam in VI-3, hydrogen in VI-5, hydrogen followed by steam in

VI-6, and air and steam in VI-7 (investigate atmospheric effect on FPR) VI-6, and air and steam in VI-7 (investigate atmospheric effect on FPR) Major differences between VI and HI tests:Major differences between VI and HI tests:

VI tests (vertical) vs HI tests (horizontal) VI tests (vertical) vs HI tests (horizontal) VI test conducted at higher burnup and temperature (2300-2700 K)VI test conducted at higher burnup and temperature (2300-2700 K)

Measurements obtained Measurements obtained Sample temperature vs time measured by optical pyrometrySample temperature vs time measured by optical pyrometry Thermal gradient tube (TGT) downstream to collect condensing vaporsThermal gradient tube (TGT) downstream to collect condensing vapors Graduated filters & impregnated charcoal cartridges to collect particulates and Graduated filters & impregnated charcoal cartridges to collect particulates and

volatile I speciesvolatile I species Charcoal cold trap to measure fission gasesCharcoal cold trap to measure fission gases On-line measurements of fuel location and Cs-137 in TGT and Kr-85 in gas trapsOn-line measurements of fuel location and Cs-137 in TGT and Kr-85 in gas traps Post-test analysis of all components by gamma-ray spectrometry, NAA, spark-Post-test analysis of all components by gamma-ray spectrometry, NAA, spark-

source mass spec, emission spectrometrysource mass spec, emission spectrometry

ORNL Experiments Cont’dORNL Experiments Cont’d

Major test results:Major test results: Similar release rates for noble gases, Cs and ISimilar release rates for noble gases, Cs and I Difference Cs transport behavior in steam relative to hydrogen. Difference Cs transport behavior in steam relative to hydrogen.

Reactive vapor forms of Cs predominate in hydrogen conditions and transportable Reactive vapor forms of Cs predominate in hydrogen conditions and transportable aerosols in steamaerosols in steam

Similar Te and Sb release from UOSimilar Te and Sb release from UO22 as for volatile FPs but retained by metallic as for volatile FPs but retained by metallic

Zircaloy until nearly complete clad oxidationZircaloy until nearly complete clad oxidation Both Eu and Sb showed sensitivity to oxygen potential at high temperature.Both Eu and Sb showed sensitivity to oxygen potential at high temperature.

Limitations:Limitations: Segmented furnace tube did not provide good containment of test environment Segmented furnace tube did not provide good containment of test environment

(oxidation of graphite susceptor)(oxidation of graphite susceptor) Samples at temperature for short period of time (~20 min) which may not be long Samples at temperature for short period of time (~20 min) which may not be long

enough for oxidative release enough for oxidative release

CEA-CENG ExperimentsCEA-CENG Experiments

HEVA program (1983-1989) HEVA program (1983-1989) Heated Zircaloy-clad specimens of irradiated PWR fuel in mixtures of steam/HHeated Zircaloy-clad specimens of irradiated PWR fuel in mixtures of steam/H22 and and

pure Hpure H22 from 1800-2370 K (8 tests) from 1800-2370 K (8 tests)

Gamma spectrometry measured FPR from fuel and transportGamma spectrometry measured FPR from fuel and transport Aerosols collected in heated (temperature varied) cascade impactor and filters Aerosols collected in heated (temperature varied) cascade impactor and filters Control rod materials used in HEVA-07 (Ag-In-Cd exclusively) and HEVA-08 Control rod materials used in HEVA-07 (Ag-In-Cd exclusively) and HEVA-08

(control rod and fuel material) (control rod and fuel material)

CEA-CENG Experiments Cont’dCEA-CENG Experiments Cont’d

VERCORS program (1989 to 1994)VERCORS program (1989 to 1994) Spent fuel samples heated to maximum temperature of 2620 K (6 tests)Spent fuel samples heated to maximum temperature of 2620 K (6 tests)

3 PWR pellets with 2 half pellets (depleted U at ends) in unsealed Zrly clad3 PWR pellets with 2 half pellets (depleted U at ends) in unsealed Zrly clad Re-irradiated in SILOE reactor to restore short-lived FPs (I, Te, Mo, Ba, La)Re-irradiated in SILOE reactor to restore short-lived FPs (I, Te, Mo, Ba, La)

Post-test gamma scanning (including gamma tomography) (complete FP Post-test gamma scanning (including gamma tomography) (complete FP mass balance)mass balance)

Results of FP behaviour:Results of FP behaviour: Nearly complete release of volatiles (Cs, I, Te and Sb)Nearly complete release of volatiles (Cs, I, Te and Sb) Te and Sb initially trapped in unoxidized cladding Te and Sb initially trapped in unoxidized cladding Semi-volatiles (Mo, Rh and Ba) (~1/2 that of volatile release depending on atmospheric conditions) Semi-volatiles (Mo, Rh and Ba) (~1/2 that of volatile release depending on atmospheric conditions)

Increased Mo release in oxiding conditions Increased Mo release in oxiding conditions 92% release (VERCORS 5) vs 47% (VERCORS 4) 92% release (VERCORS 5) vs 47% (VERCORS 4) Increased Ba and Rh release in reducing conditions Increased Ba and Rh release in reducing conditions 45 and 80% of Rh and Ba, (VERCORS 4) vs 45 and 80% of Rh and Ba, (VERCORS 4) vs

20 and 55% (VERCORS 5) 20 and 55% (VERCORS 5) Low-volatile FPs and actinides between 3 to 10% (Ru, Ce, Np, Sr and Eu)Low-volatile FPs and actinides between 3 to 10% (Ru, Ce, Np, Sr and Eu) Increased Np and Ce release under reducing conditions (VERCORS 4)Increased Np and Ce release under reducing conditions (VERCORS 4) No release of non-volatile FPs (Zr, Nb La and Nd) No release of non-volatile FPs (Zr, Nb La and Nd) No significant enhancement in release in VERCORS 6 (early fuel collapse and partial liquid corium)No significant enhancement in release in VERCORS 6 (early fuel collapse and partial liquid corium)

Similar problems due to flow bypass (as for ORNL tests)Similar problems due to flow bypass (as for ORNL tests)

CEA-CENG Experiments Cont’dCEA-CENG Experiments Cont’d

VERCORS HT and RT program (1996 to 2002)VERCORS HT and RT program (1996 to 2002) Study FP and actinide release during later phase of accident with fuel Study FP and actinide release during later phase of accident with fuel

liquefactionliquefaction Study FPR behaviour as influenced by:Study FPR behaviour as influenced by:

Fuel type (UOFuel type (UO22 versus MOX) versus MOX)

Fuel morphology (intact pellets versus debris fragments) Fuel morphology (intact pellets versus debris fragments) Fuel burnup Fuel burnup Presence of control materials (Ag, In, Cd and boric acid)Presence of control materials (Ag, In, Cd and boric acid) Environmental conditions (oxidizing or reducing conditions) Environmental conditions (oxidizing or reducing conditions)

Nb and La release in severe VERCORS HT and RT testsNb and La release in severe VERCORS HT and RT tests Fuel collapse temperature (2400 to 2600 K for fuel burnups of 47-70 Fuel collapse temperature (2400 to 2600 K for fuel burnups of 47-70

GWd/tU) ~500 K below UOGWd/tU) ~500 K below UO22 melting temperature melting temperature

AECL-CRL ExperimentsAECL-CRL Experiments

CRL Program (> 300 annealing tests)CRL Program (> 300 annealing tests) FPR from clad & unclad spent fuel samples (800 to 2350 K in Ar/HFPR from clad & unclad spent fuel samples (800 to 2350 K in Ar/H22, ,

steam and air atmospheres)steam and air atmospheres) Bare UOBare UO22 fragments (0.2-1.5 g each) and cladded specimens (Zircaloy foil fragments (0.2-1.5 g each) and cladded specimens (Zircaloy foil

bags and short segments of Zircaloy-clad fuel with end caps)bags and short segments of Zircaloy-clad fuel with end caps)– Presence of Zircaloy can inhibit/delay release of volatile FPsPresence of Zircaloy can inhibit/delay release of volatile FPs

– Associated with time to oxidize Zircaloy cladding. Associated with time to oxidize Zircaloy cladding. – Volatile FP release rates almost independent of temperature from 1670 to 2140 K after complete Volatile FP release rates almost independent of temperature from 1670 to 2140 K after complete

clad oxidationclad oxidation

FPR Behaviour:FPR Behaviour: Deposition and transport of FPs studied. Deposition and transport of FPs studied. Volatiles release (Kr, Xe, I, Cs and Te) low in inert/reducing atmospheres but increase significantly after Volatiles release (Kr, Xe, I, Cs and Te) low in inert/reducing atmospheres but increase significantly after

clad oxidation in oxidizing atmospheresclad oxidation in oxidizing atmospheres Large fuel volatilization in high temperature tests with bare fuel (highly oxidizing environments) Large fuel volatilization in high temperature tests with bare fuel (highly oxidizing environments) low- low-

volatile release (Zr, La, Ba, Ce, Pr, Eu) via “matrix stripping” processvolatile release (Zr, La, Ba, Ce, Pr, Eu) via “matrix stripping” process Eu, Ba released in hydrogen-rich atmospheres vs Mo, Ru, Nb in steamEu, Ba released in hydrogen-rich atmospheres vs Mo, Ru, Nb in steam

Oxygen potential of environment well characterizedOxygen potential of environment well characterized Models developed for steam and air oxidation of UOModels developed for steam and air oxidation of UO22

Significant release of fission products in air (Ru, Nb)Significant release of fission products in air (Ru, Nb)

3120

29602870

2670

2245

2030

1720157314701400

1220

1073

(a)

Temperature (K)

Degraded Core Accident PhenomenaDegraded Core Accident Phenomena

Degraded Core Accident Phenomena: Degraded Core Accident Phenomena: PressurePressure

Comparable behaviorComparable behavior Phebus FP (~0.2 MPa), LOFT FP-2 (~1 MPa), CORA (~0.2 to 1 Phebus FP (~0.2 MPa), LOFT FP-2 (~1 MPa), CORA (~0.2 to 1

MPa), TMI-2 (5 to 15 MPa)MPa), TMI-2 (5 to 15 MPa)

Enhanced clad ballooning & failure (low pressure)Enhanced clad ballooning & failure (low pressure) FPT-0 (trace-irradiated) at 735FPT-0 (trace-irradiated) at 735CC Gap release measured (SFD, LOFT FP-2, Phebus FP)Gap release measured (SFD, LOFT FP-2, Phebus FP)

Aerosol compositionAerosol composition Phebus FPT-0 and FPT-1: control rod (Ag,In,Cd), thermocouple Phebus FPT-0 and FPT-1: control rod (Ag,In,Cd), thermocouple

(Re), fuel rod (Sn,U) materials (~0.2 MPa)(Re), fuel rod (Sn,U) materials (~0.2 MPa) PBF SFD 1-4: FPs more important role (~7 MPa)PBF SFD 1-4: FPs more important role (~7 MPa)

Degraded Core Accident Phenomena: Degraded Core Accident Phenomena: Control Rod EffectsControl Rod Effects

Pressure-Dependent Phenomena:Pressure-Dependent Phenomena: (i) Low Pressure:(i) Low Pressure:

SS clad/Zry guide tube contact with ballooning (high Cd vapour pressure) SS clad/Zry guide tube contact with ballooning (high Cd vapour pressure) liquid phase ~1150liquid phase ~1150CC

Ejection of molten control rod material Ejection of molten control rod material chemically dissolves guide tube/ chemically dissolves guide tube/ clad of surrounding rods well below Zry MP (1760clad of surrounding rods well below Zry MP (1760 C) (CORA tests)C) (CORA tests)

(ii) High Pressure:(ii) High Pressure: Failure of SS clad at MP (~1450Failure of SS clad at MP (~1450C)C)

Phebus FP tests consistent with low pressure scenarioPhebus FP tests consistent with low pressure scenario Control rod failure at 1120°C (FPT-0) and 1350°C (FPT-1)Control rod failure at 1120°C (FPT-0) and 1350°C (FPT-1)

Degraded Core Accident Phenomena: Degraded Core Accident Phenomena: Metallic Melt FormationMetallic Melt Formation

Interaction of spacer grids/Zry cladding/control materialsInteraction of spacer grids/Zry cladding/control materials RelocationRelocation

PBF SFD & TMI-2 accident (below coolant level) PBF SFD & TMI-2 accident (below coolant level) LOFT FP2, Phebus FP & CORA (cooler bundle regions)LOFT FP2, Phebus FP & CORA (cooler bundle regions) Freezing temperature of melt:Freezing temperature of melt:

1070 K (Ag-In-Cd alloy) to 1220 K (Zr-Fe eutectic), 1230 K (Zr-Ni eutectic & elemental silver) and 1460 K 1070 K (Ag-In-Cd alloy) to 1220 K (Zr-Fe eutectic), 1230 K (Zr-Ni eutectic & elemental silver) and 1460 K (Zr-Ag eutectic)(Zr-Ag eutectic)

Metallic blockages in integral tests similar to TMI-2 but not as extensive (shorter duration)Metallic blockages in integral tests similar to TMI-2 but not as extensive (shorter duration) FPT-0 metallographic examinationFPT-0 metallographic examination

Demonstrates role control rod plays in early melt formation Demonstrates role control rod plays in early melt formation Attack of Zry clad by molten Ag-In-Cd alloyAttack of Zry clad by molten Ag-In-Cd alloy

Zr (20-40 wt%), Ag (10-50wt%), In (10-40wt%), U (<15wt%), O (<10wt%), SS (<5wt%)Zr (20-40 wt%), Ag (10-50wt%), In (10-40wt%), U (<15wt%), O (<10wt%), SS (<5wt%)

Degraded Core Accident Phenomena: Degraded Core Accident Phenomena: Zircaloy OxidationZircaloy Oxidation

Exothermic reaction (6.5 kJ/g-Zr oxidized)Exothermic reaction (6.5 kJ/g-Zr oxidized) Accelerated heatup rates (Accelerated heatup rates (10 K/s) at T > 1500 to 1700 K10 K/s) at T > 1500 to 1700 K In-pile tests (PBF SFD, LOFT FP-2 and Phebus FP) and out-of-In-pile tests (PBF SFD, LOFT FP-2 and Phebus FP) and out-of-

pile tests (CORA)pile tests (CORA)

Degraded Core Accident Phenomena: Degraded Core Accident Phenomena: Hydrogen GenerationHydrogen Generation

Related to steam availabilityRelated to steam availability

Hydrogen PartitioningTest Oxidationof Zry (%)

Time(s) Before

reflood (%)Afterreflood (%)

LOFT FP-2

PBF-STPhebus FPT-0

49

7585

~300a

~600a

~1200b

20

7782b

80

23-

a. T> 1700 K; b. During oxidation phase.

Degraded Core Accident Phenomena: Degraded Core Accident Phenomena: Fuel LiquefactionFuel Liquefaction

UOUO22 & ZrO & ZrO22 dissolved by metallic Zircaloy/ dissolved by metallic Zircaloy/-Zr(O) -Zr(O)

(~1760 to 2000°C)(~1760 to 2000°C) Fuel liquefaction in integral testsFuel liquefaction in integral tests

PBF SFD tests (15-18%), LOFT FP-2 (15%)PBF SFD tests (15-18%), LOFT FP-2 (15%) TMI-2 core (~45%)TMI-2 core (~45%) Phebus FPT-1 (20%), FPT-0 (50%)Phebus FPT-1 (20%), FPT-0 (50%)

Separation between ceramic and metallic blockageSeparation between ceramic and metallic blockage (U,Zr)O(U,Zr)O22 freezes at higher temperature freezes at higher temperature

Degraded Core Accident Phenomena: Degraded Core Accident Phenomena: Molten Pool FormationMolten Pool Formation

Ceramic heatupCeramic heatup Steam diversion around blockage & poor thermal conductivitySteam diversion around blockage & poor thermal conductivity FP decay heat (TMI-2) or increased fission/electrical heating (integral tests)FP decay heat (TMI-2) or increased fission/electrical heating (integral tests)

Molten pool (surrounded by U-rich crust) under a cavityMolten pool (surrounded by U-rich crust) under a cavity TMI-2: (U,Zr)OTMI-2: (U,Zr)O22 ceramic with transition metal oxides (Cr ceramic with transition metal oxides (Cr22OO33, Fe, Fe33OO44) ~2700 ) ~2700

KK Phebus FPT-0: (U,Zr)OPhebus FPT-0: (U,Zr)O22 lattice with U (62wt%), Zr (22 wt%) & O(14wt%), lattice with U (62wt%), Zr (22 wt%) & O(14wt%),

Fe(0.6wt%) ~2720 KFe(0.6wt%) ~2720 K

Fuel movementFuel movement TMI-2: Thermo-mechanical failure of crust TMI-2: Thermo-mechanical failure of crust 20 t lower plenum 20 t lower plenum FPT-0: Downward motion of pool (from lower grid spacer) (18100 s)FPT-0: Downward motion of pool (from lower grid spacer) (18100 s)

Comparable to MP testsComparable to MP tests

Degraded Core Accident Phenomena: Degraded Core Accident Phenomena: Debris Bed FormationDebris Bed Formation

TMI-2TMI-2 Top of molten pool & lower plenum regionTop of molten pool & lower plenum region

Integral testsIntegral tests Upper debris bed formed by coolant injection Upper debris bed formed by coolant injection

(fragmentation) (SFD-ST & LOFT FP-2)(fragmentation) (SFD-ST & LOFT FP-2) Less steam-rich transients - decladded fuel/fragments in Less steam-rich transients - decladded fuel/fragments in

upper part of bundle due to melting/relocation of clad upper part of bundle due to melting/relocation of clad (SFD 1-4, Phebus FP) (SFD 1-4, Phebus FP)

FPR BehaviorFPR Behavior

Comparison:Comparison: PBF SFD-ST (steam-rich)/SFD (steam-starved), Phebus FPT-1 PBF SFD-ST (steam-rich)/SFD (steam-starved), Phebus FPT-1

(steam-rich), TMI-2(steam-rich), TMI-2 Ce & actinides (typically < 0.01%)Ce & actinides (typically < 0.01%) Ru,Sr,Sb (<1%)Ru,Sr,Sb (<1%) Ba (few %)Ba (few %) Mo (up to 50%)Mo (up to 50%) Te (between 1 to 83%)Te (between 1 to 83%) I,Cs, Noble Gas (up to ~90%)I,Cs, Noble Gas (up to ~90%)

Comparable to annealing tests (ORNL, CEA, CRL)Comparable to annealing tests (ORNL, CEA, CRL)

FPR PhenomenaFPR Phenomena

FP trappingFP trapping Te release (clad-oxidation state): Sn segregation Te release (clad-oxidation state): Sn segregation SnTe release SnTe release Sb sequestered in metallic melts (Ni, Ag alloys)Sb sequestered in metallic melts (Ni, Ag alloys)

BurnupBurnup Enhanced volatile FPR in SFD 1-4 (high-burnup) vs SFD 1-1 (trace-Enhanced volatile FPR in SFD 1-4 (high-burnup) vs SFD 1-1 (trace-

irradiated)irradiated) Swelling (irradiated rods) in Phebus FPT-1Swelling (irradiated rods) in Phebus FPT-1

Oxygen potential (HOxygen potential (H22/H/H22O ratio)O ratio) Low Ba, Sr (Eu) release in steam tests (low- volatile oxides/hydroxides) Low Ba, Sr (Eu) release in steam tests (low- volatile oxides/hydroxides)

vs higher release in reducing tests (ST, VI, HEVA, VERCORS, CRL)vs higher release in reducing tests (ST, VI, HEVA, VERCORS, CRL) Enhanced Ba release in FPT-0 during escalation phase (HEnhanced Ba release in FPT-0 during escalation phase (H22 generation) generation)

Low Ru release (POLow Ru release (PO22 too low to form high-volatile oxides) too low to form high-volatile oxides)

Low actinide release (fuel volatilization (UOLow actinide release (fuel volatilization (UO33) ~ )) ~ )2Op

FPR Phenomena Cont’dFPR Phenomena Cont’d

FP behaviour in molten poolFP behaviour in molten pool No enhancement with fuel liquefaction (non-coherent process)No enhancement with fuel liquefaction (non-coherent process) Volatile FPs: bubble nucleation, coalescence/growth & release via Volatile FPs: bubble nucleation, coalescence/growth & release via

buoyancybuoyancy Bubble trapping at pool/surrounding crustBubble trapping at pool/surrounding crust Volatile FPs (I,Cs) in previously molten ceramics in PBF SFD, Volatile FPs (I,Cs) in previously molten ceramics in PBF SFD,

Phebus FP & TMI-2 reactorPhebus FP & TMI-2 reactor

TMI-2: Iron oxides in melt (lower limit of -120 kJ/mol)TMI-2: Iron oxides in melt (lower limit of -120 kJ/mol) La, Ce, Sr as oxide (soluble in (U,Zr)OLa, Ce, Sr as oxide (soluble in (U,Zr)O22))

Ru, Sb metal immiscible in ceramic meltRu, Sb metal immiscible in ceramic melt

Cooldown/refloodCooldown/reflood Small release (fuel relocation) in Phebus FPT-0 vs large release in Small release (fuel relocation) in Phebus FPT-0 vs large release in

LOFT FP-2 (~12% volatile release) (local heating)LOFT FP-2 (~12% volatile release) (local heating)

Ba Release in ORNL, CEA and Phebus Ba Release in ORNL, CEA and Phebus TestsTests

TestTest Temp. (K)Temp. (K) Duration (min)Duration (min) AtmosphereAtmosphere Ba Release (%)Ba Release (%)

HI-4HI-4

HI-5HI-5

VI-2VI-2

VI-3VI-3

VI-4VI-4

VI-5VI-5

HEVA-4HEVA-4

HEVA-6HEVA-6

VERCORS-1VERCORS-1

VERCORS-4VERCORS-4

VERCORS-5VERCORS-5

VERCORS HT-1VERCORS HT-1

Phebus FPT-0Phebus FPT-0

PEBUS FPT-1PEBUS FPT-1

22002200

20252025

23002300

27002700

24402440

27202720

22702270

23702370

21302130

25702570

25702570

30703070

~2700~2700

~2500~2500

2020

2323

6060

2020

2020

2020

77

3030

1717

3030

3030

77

--

- -

H2OH2O

H2OH2O

H2OH2O

H2OH2O

H2H2

H2H2

H2O+ H2H2O+ H2

H2H2

H2O+ H2H2O+ H2

H2H2

H2OH2O

H2H2

H2O/H2H2O/H2

H2O/H2 H2O/H2

<1<1

<1<1

1919

3030

2727

7676

66

2727

44

8080

5555

4949

11

1 1

Difference in Ba Release from Out-Difference in Ba Release from Out-Pile and Phebus TestsPile and Phebus Tests

Short duration of temperature escalation in in-pile testsShort duration of temperature escalation in in-pile tests No “high temperature plateau” as in annealing tests but rather No “high temperature plateau” as in annealing tests but rather

temperature escalation (with formation of molten pool) in Phebus temperature escalation (with formation of molten pool) in Phebus test test

Ba volatility is reduced with significant amount of ZrOBa volatility is reduced with significant amount of ZrO22 in in fuel melt (~47 mol%) and small amounts of iron oxide in fuel melt (~47 mol%) and small amounts of iron oxide in in-reactor testin-reactor test

Thermochemical analysis with GEMINI2Thermochemical analysis with GEMINI2 Reduced Ba vapor pressure in solidus-liquidus transition zone in Reduced Ba vapor pressure in solidus-liquidus transition zone in

the U-Ba-O phase diagram (~2400-3100 K) the U-Ba-O phase diagram (~2400-3100 K)

In- and out-pile experiments on In- and out-pile experiments on severe accident melt progression & severe accident melt progression & FPR behaviour reviewedFPR behaviour reviewed• Melt progression non-coherent process Melt progression non-coherent process • Phebus FPT-0 and -1 tests performed for longer high-temperature period Phebus FPT-0 and -1 tests performed for longer high-temperature period

than earlier in-pile experiments than earlier in-pile experiments information on late-phase behaviour information on late-phase behaviour• Local propagation of core melt due to control rod failure (at lower Local propagation of core melt due to control rod failure (at lower

temperature) temperature) • Metallic blockages result from interactions of spacer grids, fuel rod Metallic blockages result from interactions of spacer grids, fuel rod

cladding material and control rod materials that flow down bundle and cladding material and control rod materials that flow down bundle and solidify at lower (cooler) positionsolidify at lower (cooler) position

– Separation between metallic and ceramic blockages with freezing of (U,Zr)OSeparation between metallic and ceramic blockages with freezing of (U,Zr)O22 melt at higher temperature melt at higher temperature

– Observed melting temperature of ceramic blockage in Phebus FPT-0 test Observed melting temperature of ceramic blockage in Phebus FPT-0 test (~2720 K) slightly lower than pure ceramic (~2800 K) due to eutectic (~2720 K) slightly lower than pure ceramic (~2800 K) due to eutectic interaction (consistent with TMI-2 examination) interaction (consistent with TMI-2 examination)

– Molten pool formed due to increased fission heat generation and reduced heat Molten pool formed due to increased fission heat generation and reduced heat transfertransfer in several in-pile experiments (held in place by ceramic crust)in several in-pile experiments (held in place by ceramic crust)

Concluding RemarksConcluding Remarks

Concluding Remarks Cont’dConcluding Remarks Cont’d

Consistent release behaviour of volatile (Xe, Kr, I, Cs, Te and Sb), Consistent release behaviour of volatile (Xe, Kr, I, Cs, Te and Sb), semi-volatile (Mo, Rh, Ba), low volatile (Ru, Ce, Np, Sr and Eu) and semi-volatile (Mo, Rh, Ba), low volatile (Ru, Ce, Np, Sr and Eu) and non-volatile (Zr, Nb, La and Ne) FPs observed in annealing (ORNL, non-volatile (Zr, Nb, La and Ne) FPs observed in annealing (ORNL, CEA, CRL) and in-pile testsCEA, CRL) and in-pile tests Reduced volatility of Ba for in-reactor experiments (thermochemical Reduced volatility of Ba for in-reactor experiments (thermochemical

effects with presence of iron and zirconium oxides) effects with presence of iron and zirconium oxides) Local atmospheric condition/oxygen potential influences low-volatile Local atmospheric condition/oxygen potential influences low-volatile

fission product release behaviour fission product release behaviour Non-coherent melt progression masks individual release mechanisms Non-coherent melt progression masks individual release mechanisms

identified in out-of-pile experiments identified in out-of-pile experiments Enhanced release due to fuel liquefaction not typically observed in Enhanced release due to fuel liquefaction not typically observed in

separate effects experimentsseparate effects experiments

AcknowledgementsAcknowledgements

Discussions with P. Elder, L. Dickson, M. Discussions with P. Elder, L. Dickson, M. Schwarz, R. Zeyen, B. Clement, M. Kissane and Schwarz, R. Zeyen, B. Clement, M. Kissane and G. DucrosG. Ducros

Funded by NSERC/COG Collaborative Research Funded by NSERC/COG Collaborative Research and Development (CRD) Grantand Development (CRD) Grant