Presented by : Shirley Dickinson

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(No Transcript)
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Advances on Containment Iodine Chemistry

• ERMSAR 2008, Nesseber, Bulgaria, 23-25 September
  2008

Presented by Shirley Dickinson
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Iodine Chemistry Participants in SARNET

• Nexia Solutions, Harwell (GB),EDF, Villeurbanne
  (FR)VTT, Espoo (FI)AECL, Chalk River (CA)IRSN,
  Cadarache (FR)AREVA-ANP, Erlangen (DE)Chalmers
  University, Gothenberg (SE) CIEMAT, Madrid
  (ES)Demokritos, Athens (GR)CEA, Cadarache
  (FR)IRSN, Saclay (FR) GRS, Garching (DE)

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Introduction

• Iodine chemistry in containment highlighted in
  5FP EURSAFE further research needed to reduce
  source term uncertainties
• SARNET objectives
• Improve understanding of chemical phenomena in
  containment ? improve predictability of iodine
  behaviour
• Common interpretation of test data
• Production of new / improved models
• Compilation of existing knowledge

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Interpretation Circles

• Radiolytic Oxidation (ROX)
• Sump-Atmosphere Mass Transport (MAT THAI)
• Iodine in Passive Autocatalytic Recombiners
  (IPAR)
• Iodine Data Book (IDB)
• Phebus Interpretation (FPT2)
• See presentation to ERMSAR 2007

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Radiolytic Oxidation of Iodine (ROX)

• Formation of volatile iodine from irradiated
  solutions
• Extensively studied before SARNET, reasonably
  good understanding
• Data sparse in some areas (high T, high D)
• Some improvements to modelling / validation
  required
• Other uncertainties e.g. impurities
• Radiolytic reactions of gaseous iodine to form
  solid oxide aerosols
• Few experimental data
• Limited modelling capabilities (gas phase only)

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Radiolytic oxidation in solution

• New data mainly from EPICUR tests
• On-line measurement of iodine volatility from
  g-irradiated solutions
• 16 tests performed during SARNET High
  temperature (80, 120C), pH 5 or 7, 2 3 kGy/hr,
  painted surfaces, Ar / air atmospheres
• Conditions changed during tests to highlight
  effects
• Data also released from intermediate-scale CAIMAN
  and RTF tests
• Test of radiolytic oxidation models ASTEC-IODE,
  COCOSYS-AIM, INSPECT, LIRIC

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Schematic of EPICUR facility
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Example of EPICUR results and modelling
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ROX conclusions from EPICUR

• Model performance generally satisfactory at pH 5
• Effect of temperature confirmed to 120C
• Improved estimate of borate-catalysed I2 H2O2
  reaction activation energy for INSPECT
• Decrease in volatility at pH 7 less well modelled
• Mechanistic models reasonably OK
• Changes required to COCOSYS-AIM
• Choice of radiolytic oxidation model in
  ASTEC-IODE

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Radiolytic oxidation in gas phase

• Experimental data from PARIS programme
• Extend measurement of radiolytic destruction
  rates to lower concentrations
• Effect of surfaces
• Mechanistic modelling apparently overpredicts
  radiolytic oxidation rate
• Modelling of aerosol formation needs to be
  developed
• More work needed in this area

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Mass transfer (THAI)

• Validation of mass transfer models against
  large-scale test data
• THAI IOD-9 (60 m3 vessel)
• I2 mass transfer from gas sump
• Transport in stratified sump
• Uptake on steel walls
• Condensate wash-out

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THAI experiments
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Mass transfer (THAI) (2)

• Calculations with ASTEC-IODE, COCOSYS-AIM and
  LIRIC
• All codes simulated the test reasonably well
• Identified some improvements needed to models
• More tests to be analysed in SARNET-2

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Comparison of models with THAI data
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Mass transfer (MAT)

• Extension of sump-atmosphere mass transfer models
  to evaporating conditions
• Semi-mechanistic model based on
• Two-film model
• Heat - mass transfer analogy
• Surface renewal theory
• Comparison with data from SISYPHE programme
• Further validation needed on large-scale test data

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Iodine in Passive Autocatalytic Recombiners
(IPAR)

• Thermal decomposition of iodide aerosols by PARs
  ? gaseous iodine production
• RECI experiments showed significant I2 production
  from aerosols heated to PAR operating temperature
• Analysis of RECI results by ASTEC-SOPHAEROS and
  CFD-based aerosol modelling
• I2 production predicted if equilibrium chemistry
  is assumed in the heated zone but chemical
  composition is frozen in the cooling zone
• The chimney of a PAR may be equivalent to the
  RECI cooling zone giving similar effect in
  containment

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Modelling of RECI tests
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Iodine in Passive Autocatalytic Recombiners
(IPAR) (continued)

• Evaluation of the impact of an additional gaseous
  iodine source 24h after severe accident transient
• ASTEC simulation on PWR-900 reactor
• Concludes that recombiner issue merits further
  investigation as there could be a significant
  impact on the iodine source term
• Knowledge gained could be applied to potential
  effect of PARs on ruthenium source term

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Iodine Data Book (IDB)

• A large body of data has been used in the
  development of models and methodologies for
  iodine source term predictions
• Research in the area tends to be diminishing
• UK experimental programme ceased in 2003
• Collation of experimental/theoretical data
  forming the basis of the Sizewell B safety case
• Aqueous inorganic radiation chemistry, organic
  iodine chemistry, surface reactions, mass
  transfer, gaseous radiation chemistry
• Keep up-to-date with results from future
  programmes