ACR Technology Base:Containment

by Andrew White, Director, Reactor Safety

Presented to US Nuclear Regulatory CommissionOffice of Nuclear Reactor Regulation

September 26, 2002

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Introduction

� The containment of a CANDU reactor is designed tomitigate the consequences of an accident

� During an accident the containment building could besubjected to a harsh environment of hot vapor, fissionproducts from failed fuel, and hydrogen released fromoxidation reactions

� Research is performed to ensure that we understand:� The time dependent nature of the environment� The behavior of fission products� Any threats posed by released hydrogen (primarily a concern

for severe accidents)

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Containment Performance

� R&D focused on determining behavior of effluent fromthe reactor coolant system in containment

� Experimental:� Large-scale gas mixing facility� Used to study mixing, buoyancy-induced flows, stratification,

condensation, effects of containment partitions� Data used to validate GOTHIC

� Modeling:� GOTHIC, with addition of CANDU-specific models for

hydrogen behavior, used to model containmentthermalhydraulics and hydrogen transport

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Large Scale Gas Mixing Facility

• Volume: 1000 m3

(35000 ft3)

• Atmosphere: air,steam and helium

• Internal partitionssimulate sub-compartments

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Example of a Gas-Mixing Experiment

GMBT137

0

5

10

15

20

25

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Time (s)

Hel

ium

Con

cent

ratio

n (v

ol%

)

A1

A2

A3

A4

A5

C6

C7

C8

C9

C10

C11

Blow er on

Side view

I I

BT injection

C8

C7

C6

C9

C10C11

Helium injection 8.32 g/sbottom inlet

A1 & C6

A3 & C8

A2 & C7

A3

A2

A1

A4

A5

Ceiling I-beams

Plan view

C

A

A4

C9A5

• Steam injectedand formed astratified layer

• Helium injected,breaks throughstratified layer after~200 seconds, andrises

• After 1200seconds, blowerscreate uniform mix

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Fission Product Behavior

� In the event of a LOCA, fission products from failed fuelare discharged from the break

� Fission products that remain in the vapor phase aremore subject to release from containment than thosethat partition to water

� Iodine has been a focus because of its relativeabundance, high biological activity and gaseous forms

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Iodine Behavior in Containment

� Primary concern is the time dependent concentrationof gaseous iodine

� Released from fuel into containment mainly as CsI,which dissolves as non-volatile iodide in water

� Under the oxidizing and high radiation environmentfollowing an accident, non-volatile iodide would reactand become volatile and partition into the gas phase

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Iodine Reactions and Transport

I�, I3�, HOI, IOx�

I(con)

Iaq(ad)

Ig(ad)

I2(aq) RI(aq)

I2(g) RI(g)

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Factors affecting Iodine Behavior

� Iodine exists in various chemical states� Post-accident containment is under irradiation and not

in chemical equilibrium� Iodine chemistry is driven by water radiolysis� Many reactions and processes are inter-dependent� Iodine behavior can not be easily scaled from

correlations based on integrated tests� Requires a correct representation of aqueous

chemistry (which can be scaled)

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AECL Iodine Program Components

� Intermediate-scale integrated-effects tests in theRadioiodine Test Facility (RTF)

� Supporting bench-scale tests to separate and quantifyindividual effects

� Development and validation of containment iodinebehavior models, LIRIC & IMOD, for safety analysis

� International collaboration� EPRI ACEX� PHEBUS� International Standard Problem code comparison exercise

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Radioiodine Test Facility

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50 RTF Tests� Type of Vessel Surface

� Stainless Steel (electropolished, untreated)� Organic Coatings on carbon steel or concrete (Vinyl, Epoxy,

Polyurethane)� Inorganic Coatings (zinc primer)

� Radiation on, Radiation off� pH controlled, pH uncontrolled: range 4.5 – 10.5� Temperature

� constant throughout experiment: 25, 60, 90oC (80, 140, 190oF)� steps from 25 to 80oC (80 to 170oF)

� Condensing, Non-condensing� Organic and Inorganic Additives

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Bench-Scale R&D Areas

� Aqueous Phase Chemistry� Inorganic Iodine Reactions� Water Radiolysis� Effects of Organic Impurities

� Sources of organic compounds dissolved in water� Radiolytic decomposition of organic impurities� Organic iodide formation & decomposition

� Aqueous-Gas Phase Partitioning of Volatile Species� Iodine – Surface Interaction

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Model Development & ValidationLIRIC� A comprehensive mechanistic model, based on our extensive

knowledge of relevant chemical reactions and mass transport� Performs well when tested against bench-scale and RTF tests

carried out over a wide range of conditions� Due to its complexity and size, integration of LIRIC into a safety

analysis code is considered to be impracticalIMOD� Reduced reaction set based on extensive LIRIC analysis and

simulations of various RTF tests� A smaller and simpler model, but maintains many of the

capabilities of LIRIC

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LIRIC

Gas PhaseAqueous Phase

Water radiolysis reactions (~40 rxns)

Inorganic iodine reactions (~80 rxns)

Organic reactions

SurfacesDry, wet, submerged(SS, Al, paints,Polymers)

Dissolution

Radiolytic decomposition

Organic iodide behavior

Mass transfer

All volatile species(I2, RI, H2, O2, CO2) Ads Des

Condensate flow

Des

Ads

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IMOD

Aqueous Phase Gas Phase

SurfacesDry, wet, submerged(SS, Al, paints,Polymers)

Mass transfer

Volatile Iodines(I2, HVRI, LVRI) Ads Des

Condensate Flow

Des

Ads

NONVOLI(aq) I2(aq)I2(aq) HVRI(aq), LVRI(aq)HVRI(aq), LVRI(aq) NONVOLI(aq)

Dissolution Radiolytic decompositionAcid-Base Equilibria

Total 16 reactions

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IMOD Simulation of an RTF Test(organic addition in a stainless steel vessel)

6

6.5

7

7.5

8

8.5

9

9.5

10

10.5

0 50 100 150 200 250 300Time (h)

pH

Experimental Data

IMOD-2.0

Slow MIBK Addition Fast (5X) MIBK AdditionpH

ControlpH

ControlpH

Control

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IMOD Simulation of an RTF Test(organic addition in a stainless steel vessel)

0.E+00

1.E-06

2.E-06

3.E-06

4.E-06

5.E-06

6.E-06

7.E-06

8.E-06

9.E-06

0 50 100 150 200 250 300

Time (h)

Con

cent

ratio

n (m

ol/d

m3 )

Experimental DataIMOD-2.0

Total Aqueous Iodine

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IMOD Simulation of an RTF Test(organic addition in a stainless steel vessel)

0

1E-10

2E-10

3E-10

4E-10

5E-10

6E-10

7E-10

8E-10

0 50 100 150 200 250 300

Time (h)

Con

cent

ratio

n (m

ol/d

m3 )

Experimental DataIMOD-2.0

Total Gaseous Iodine

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International Collaboration� EPRI ACE (Advanced Containment Experiments) & ACEX

� RTF tests, critical review of the current understanding of iodinechemistry and model developmental work were performed insupport of ACE & ACEX (extension) projects

� PHEBUS-FP� RTF & Bench Scale experiments investigating LWR severe accident

phenomena� International Standard Problem (ISP) 41 and 41F Phase 1 & 2

� Iodine code comparison exercises endorsed by NEA (NuclearEnergy Agency) CSNI (Committee on the Safety of NuclearInstallations)

� AECL has lead the very successful exercises� AECL’s iodine codes, LIRIC and IMOD are participating

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AECL Iodine Program Status

� We have a good understanding of iodine behavior incontainment

� Models have been developed and shown to predictiodine behavior well

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Hydrogen Behavior In ContainmentSources of Hydrogen� Short-term: reactions between hot fuel and RCS

components and steam� Long-term: water/steam radiolysis and metal

corrosion in containmentAreas of Investigation� Transition from deflagration to detonation (DDT)� Effects of deflagration and standing flames on

containment structures� Development and evaluation of Passive Auto-catalytic

Recombiners

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Results of Hydrogen R&D

� Acquired fundamental understanding of key combustionphenomena:� the mechanisms for flame acceleration and transition to detonation� the dynamics of flame jet ignition� the mechanisms and dynamics of standing flames� the mechanisms and dynamics of vented combustion

� Developed computer models for implementation in GOTHICto predict gas distribution and combustion pressure

� Program based on a variety of facilities

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Containment Test Facility (CTF)

• 6-m3 (200 ft3)sphere and a 10- m3

(350 ft3) cylinder

• pressures up to10MPa (1500 psi)

• temperatures up to150oC (300oF)

• vessels may beinter-connected by 30cm (12 in) and 50 cm(20 in) diameter ducts

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Diffusion Flame Facility (DFF)

• silo: 5 m (16 ft) indiameter and 8 m (26 ft)high

• Tests with H2 / steamjet flames (up to 15 cm(6 in) diameter) in air /steam atmosphere (upto 30% steam byvolume)

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Large Scale Vented Combustion Facility

• rectangular enclosurewith an internal volume of120 m3 (4200 ft3)

• electrically trace-heatedand insulated to maintaintemperatures in excess of100oC (212oF)

•can be subdivided into 2or 3 compartments

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Combustion Codes

GOTHIC� Used to calculate hydrogen distribution inside

containment and the combustion pressure in the eventof an ignition

DDTINDEX� Used to calculate a set of criteria for assessing the

possibility of supersonic flames via flame accelerationand subsequent transition to detonation

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• Hydrogendistribution incontainmentduring a largeLOCA (headerbreak)

GOTHIC Example

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DDTINDEX Outputs

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Passive Autocatalytic Recombiners

• recombine hydrogen withoxygen in a controlledfashion

• based on AECL’s wet-proofed catalyst technologydeveloped for heavy waterproduction

• have been qualified withtests in the large-scalevented combustion facility

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0 10 20 30 40 50 60 70 800.00

0.25

0.50

0.75

1.00

1.25

1.50

mixing fans onat 70 minutes

Test #: RQT006

mixing fans offat 10.5 minutes

Initial Conditions: 1.4% H2, 100% R.H., T=14oC, P=98.4 kPa

G1: Inlet G2: Outlet G3: Floor G4: Top Corner G4: Front

Hyd

roge

n C

once

ntra

tion

(vol

%)

Time (min)

AECL PAR - Self-Start Test

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Summary

� Research programs into areas relevant to containmentare mature and widely-recognized

� Models and computer programs have been developedand validated for CANDU safety, licensing and design

� Only work required to support ACR is minoranticipatory R&D (e.g., qualification of passiverecombiners for ACR conditions)

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