Advances on containment iodine chemistry
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Advances on Containment Iodine Chemistry. ERMSAR 2008, Nesseber, Bulgaria, 23-25 September 2008. Presented by : Shirley Dickinson. Iodine Chemistry Participants in SARNET.

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Advances on containment iodine chemistry

Advances on Containment Iodine Chemistry

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

Presented by : Shirley Dickinson


Iodine chemistry participants in sarnet

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)


Introduction

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


Interpretation circles

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


Radiolytic oxidation of iodine rox

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)


Radiolytic oxidation in solution

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, 120°C), 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


Schematic of epicur facility

Schematic of EPICUR facility


Example of epicur results and modelling

Example of EPICUR results and modelling


Rox conclusions from epicur

ROX conclusions from EPICUR

  • Model performance generally satisfactory at pH 5

    • Effect of temperature confirmed to 120°C

    • 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


Radiolytic oxidation in gas phase

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


Mass transfer thai

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


Thai experiments

THAI experiments


Mass transfer thai 2

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


Comparison of models with thai data

Comparison of models with THAI data


Mass transfer mat

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


Iodine in passive autocatalytic recombiners ipar

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


Modelling of reci tests

Modelling of RECI tests


Iodine in passive autocatalytic recombiners ipar continued

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


Iodine data book idb

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…


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