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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.

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Advances on Containment Iodine Chemistry

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  1. Advances on Containment Iodine Chemistry ERMSAR 2008, Nesseber, Bulgaria, 23-25 September 2008 Presented by : Shirley Dickinson

  2. 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)

  3. 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

  4. 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

  5. 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)

  6. 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

  7. Schematic of EPICUR facility

  8. Example of EPICUR results and modelling

  9. 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

  10. 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

  11. 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

  12. THAI experiments

  13. 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

  14. Comparison of models with THAI data

  15. 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

  16. 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

  17. Modelling of RECI tests

  18. 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

  19. 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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