Hydrogen Program at AECL

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Hydrogen Program at AECL

• Presented by Matt Krause
• ERMSAR 2007
• Karlsruhe, Germany
• 2007 June 12-14

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Atomic Energy of Canada Limited

• Established 1952
• Commercial Crown Corporation
• Owned by Government of Canada
• Our Business
• Reactor Vendor (CANDU design)
• Reactor Maintenance Services
• Nuclear Safety/Performance Products Services
• Research Development Services
• Waste Management Decommissioning

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CANDU Reactors Worldwide
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Overview

• Hydrogen Risk in CANDU and PWR
• Risk Mitigation Strategies and Hydrogen
  Mitigation RD at AECL
• Dilution
• Deliberate Ignition
• Pre/Post Inertization
• Recombination
• Venting
• Remaining Knowledge Gaps International
  Collaborations

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Hydrogen Risk in CANDU and PWR

• Large Dry Containment Design basically little
  differences
• CANDU multi-unit stations use a separate Vacuum
  Building
• Main H2 or D2 Sources come from Zr-steam
  reactions, water radiolysis, and metal corrosion
  (DBA)
• Difference lies in the DBA envelope for CANDU and
  PWR LOCA/LOECC

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Risk Mitigation Strategies

• Containment Integrity - Mechanical Loads
• Must limit peak pressure and time at pressure
• Equipment Survivability Thermal Loads
• Must limit maximum temperature and time at
  temperature

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Dilution

• Ingredients for Hydrogen Burn
• Fuel and Oxygen
• Transport Mechanism
• Ignition Source
• Only ingredient 1 can be controlled, because 2
  is always present and 3 cannot be ruled out
• Inerting controls Oxygen, while Dilution controls
  Hydrogen concentration
• Must show that H2 lt 4, e.g. present CANDU-6

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Large-Scale Containment Facility (LSCF)

• Objectives
• Investigate hydrogen mixing behavior in a
  large-scale facility, under simulated
  post-accident conditions of high-temperature and
  high-humidity, using Helium as a H2 simulant
• Generate experimental data for validation of
  GOTHIC

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High-Temperature Room ofLarge-Scale Containment
Facility (LSCF)

• Various Tests have been completed in the
  high-temperature room
• Well-mixed conditions
• Stratified initial conditions
• With active condensation on Containment
  Condensers
• Multi-compartment tests

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Dilution - Results

• Adequate mixing ensured during operation of LAC
  or dousing spray
• At question in quiescent containment
• Large number of tests showed adequate air
  entrainment into plumes and jets
• GOTHIC captures this effect
• Validated accuracy better than 2 for relevant
  cases
• Input to DDTIndex for assessment of flame
  acceleration and DDT

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Deliberate Ignition

• Ingredient 3 may occur at any time, i.e. at the
  most inconvenient time
• Solution is to ignite at a convenient time, i.e.
  near the ignition limit
• AECL has tested a variety of igniters over the
  full spectrum of conditions
• Must show igniter qualification and that, when
  ignited, H2 lt 8 to avoid high overpressure,
  e.g. present multi-unit CANDU stations

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Ignitor Performance

• Hot Surface Ignition of H2
• 30 Steam raises ignition temp. by 75-100C
• But vented combustion overpressure is reduced by
  steam

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Vented Combustion

• LSVCTF120-m3 volumeconfigurablecombustion
  andPAR testing
• Vented Combustion experiments from 6 to 14 H2,
  steam, temp., /location of igniters
• PAR performance, qualification, mixing tests

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Vented Combustion - Results

• Steam effect on H2 overpressure and impulse at
  10 H2
• GOTHIC capturesthis effect
• Validated accuracy better than 50

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Vented Combustion - Results

• Peak Pressure de-pends on igniterlocation
• GOTHIC calculates highest pressure for central
  ignition
• Igniter location even more critical for tall
  rooms, due to different up- and downward
  propagation behavior

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Recombination

• Ingredients for Hydrogen Burn
• Fuel and Oxygen
• Transport Mechanism
• Ignition Source
• Recombiners manipulate ingredient 2 and do
  away with 3
• Greatly reduce limits for 1, designed to operate
  from 1 to 7 H2
• Convective flow through PAR helps mix containment
  and replenish H2 supply to PAR
• Must show that H2 reaches PAR, that PAR is
  qualified, and H2 lt 8, e.g. ACR

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Recombination AECL PAR

• Uses in-house developed proprietary catalyst
• AECL has done extensive environmental
  qualification testing of PAR
• Self-start requirement (H2 and temperature) is
  specific to the containment and must be
  determined by the client from safety analysis

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Large-Scale Vented Combustion Test Facility
(LSVCTF)
PAR Testing Facilities

• 120-m3 test chamber, electrically heated (for
  operation up to 140C), insulated and
  instrumented
• Design pressure 400 kPa
• Hydrogen, air, and steam addition systems
• A process mass spectrometer to monitor gas
  composition
• Thermocouples to monitor temperature

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6.6-m3 Containment Test Facility (CTF) Sphere
PAR Testing Facilities

• Structural-steel test vessel
• Instrumented, insulated, and temperature-controlle
  d for operation from ambient temperatures up to
  100C
• Rated for internal pressures of 10 MPa
• Equipped with systems for the controlled addition
  of hydrogen, steam, oxygen, and inert gases

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AECL PAR - Results

• Self-start at 1-2 H2, cold, saturated
• Self-stop at 0.5 H2
• Ignition observed at 7-8 in dry atmosphere
• Extensive qualification for
• Thermal/radiation aging
• DBE
• VOC and other contaminants
• Sprays, Fuel Aerosols

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AECL PAR - Results

• Single, two- and three-chamber tests
• Different openings, PAR orientation, initial
  temperature
• In most tests, hydrogen was well-mixed
• Exceptions are some of the dead-end volume tests

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PAR Multi-Chamber Mixing Tests
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Remaining Knowledge Gaps

• Validation for lean-mixture combustion, where
  incomplete combustion is expected. Directional
  propagation and igniter location effects.
• Interaction of PAR operation and containment
  atmosphere
• Quantify EQ effects of H2 burns
• New PAR design and application qualification,
  station-specific and non-nuclear installation
  support

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AECL PAR Model

• GOTHIC was used in CFD-mode with a 25x25 coarse
  2D uniform grid.
• Built-in PAR model burns a user-specified
  fraction of the hydrogen flowing through the PAR.
  Flow through PAR is calculated by the code and
  depends on buoyancy driving force.
• The benchmark specified volumetric
  H2recombination rate was used to first determine
  an overall flowrate, which is forced through the
  GOTHIC recombiner (assumed efficiency of 1.0),
  using a fan component.
• This results in a behavior, that is not expected,
  I.e. a nearly constant (even increasing) total
  flowrate through the recombiner, despite a
  decreasing inlet H2 concentration, and a slow H2
  depletion rate.
• Final results show the expected layering with a
  relatively cool, H2-rich layer remaining near the
  floor.

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AECL PAR Benchmark Results

• Gas velocity field at t1000s
• Symmetric
• Stratified, nearly no flow below PARs

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AECL PAR Benchmark Results

• H2 concentration
• Stratified, nearly no H2 above PAR inlets

lt0.1 H2
1.5 H2
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AECL priorities for JPA4

• WP12-2 CAM
• PAR interest in numerical benchmarks and
  validation data, but not academic (fundamental)
  mechanisms
• Condensation no interest, because the GOTHIC
  condensation models are empirical, while the
  benchmark investigates boundary layer behavior
• Spray interest in transient spray effect (e.g.
  local sprays) on pressure, but not in its effects
  on hydrogen concentration or momentum mixing