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Ruthenium behaviour under air ingress conditions : main achievements in the SARNET project

Ruthenium behaviour under air ingress conditions : main achievements in the SARNET project.

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Ruthenium behaviour under air ingress conditions : main achievements in the SARNET project

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  1. Ruthenium behaviour under air ingress conditions : main achievements in the SARNET project P. Giordano (IRSN),A. Auvinen (VTT) , G. Brillant (IRSN), J. Colombani (IRSN), N. Davidovich (ENEA), R. Dickson (AECL), T. Haste (PSI), T. Kärkelä (VTT), J.S. Lamy (EDF), C. Mun (IRSN), D. Ohai (INR), Y. Pontillon (CEA), M. Steinbrück (FzK), and N. Vér (AEKI) ERMSAR 2008 Nesseber, Bulgaria, September 23-25, 2008

  2. CONTENTS 1. Context      2. Main issues to be addressed      3. What was “known”/ “unknown” at SARNET start     4. What has been achieved within SARNET      5. What remains to be addressed      6. Conclusions

  3. Subsequent air ingress into a damaged reactor core may lead to increased FP release, especially that of Ruthenium Ru release Air ingress H2O air CONTEXT

  4. Total activity with RuO4(g) contribution (1% of the initial core inventory not filtered) Increase of total efficient dose (mSv) by 2 to 3 (at 1 month, 2 kms from release) Total activity without considering air ingress effect (i.e. no enhanced release of Ru) • Surface activities (soil) and volumetric activities (atmosphere) calculated by a dispersion model taking into account meteorological data • 4 radio-nuclides considered: 103Ru , 103mRh, 106Ru, 106Rh ; dose coefficients associated are linked with all exposition modes (internal contamination or external irradiation) From D. Corbin, IRSN/DSR/SAGR CONTEXT • Gaseous ruthenium oxides release may lead to significant impact on radiological consequences • Example for a LOCA scenario : vessel failure 6h after the reactor scram; filtered releases from reactor containment after 36h (procedure of containment venting)

  5. Containment building  Fraction of Ru trapped in RCS Remaining UO2 Containment wall Ru behaviour ? Vessel rupture with air ingress Sump H2 , H2O2 , e-aq , H., OH. , O.- …. Precipitates ?  MAIN ISSUES TO BE ADDRESSED Ru release ? Ru transport ? Consequences on fuel degradation (e.g. Zr/air) ? air flows?

  6. Containment building Containment wall Ru behaviour ? no experimental data, no model Sump Precipitates ? WHAT WAS “KNOWN/UNKNOW“ AT SARNET START Ru transport ? no experimental data, no model Ru release ? exp. data (AECL mainly), simple model Zr-UO2/air ? few exp. data NUREG correlation Air flows ? NRC/SNL studies documented in NUREG reports

  7. WHAT HAS BEEN ACHIEVED WITHIN SARNET Air flows ? • Independent calculations have been performed on a series of scenario (breaks size, location,…) : • by EDF with MAAP/SATURNE (CFD) • and by IRSN with ASTEC • Consensus on the range of air mass flows coming in the RPV (~10 mol/s, lasting several hours)

  8. Zr-UO2/air ? • UO2/air interaction : experimental work has started at INR (FIPRED) : isothermal tests from 300°C to 1400°C on UO2 pellets exposed to air (disintegration rates) • Work on going WHAT HAS BEEN ACHIEVED WITHIN SARNET Zr-UO2/air ? • Zr/air interaction(WP9.3) : extensive experimental work performed under prototypical conditions (IRSN/MOZART, Fzk analytical and QUENCH tests, INR tests..), considering mixed atmospheres and pre-oxidation, combined with an extensive modelling work (PSI, IRSN, FzK, EdF,...) : • Strong degradation of cladding material (formation of ZrN and subsequent re-oxidation) • Parabolic correlations may be applied only for high temperatures (>1400°C) and for pre-oxidized cladding (>1100°C). For all other conditions, faster (= more linear) reaction kinetics should be applied • see outcomes from WP9.3 , and papers 2.2, 2.4

  9. WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru release ? • Experimental database : mainly from AECL • AECL / MCE1 series : 8 tests • Fragments of CANDU fuel 10,7 GWd/tU (without clad) ; Tmax between 1973K and 2250K; air / mixed steam-argon-H2 • AECL / HCE 3 series : 6 tests • cladded CANDU fuel 9,2 GWd/tU ; Tmax between 1800K and 2200K ; air / mixed steam-argon-H2 • 4 additionnal data selected by partners : • HCE1-M17 : cladded CANDU fuel 19,1 GWd/tU ; Tmax 1770K; Ar/2%H2 and then air • HCE2-LM4 : cladded PWR fuel 57,3 GWd/tU ; Tmax 1670K; Ar/2%H2 and then air • UCE12-TO2 : fragment of CANDU fuel 18,4 GWd/tU ; Tmax 1670K; steam then air • UCE12-T15 : fragment of CANDU fuel 15,4 GWd/tU ; Tmax 1900K; Ar/2%H2 and then air • CEA data : MERARG-Ru test, defined with partners • PWR UO2 fuel ~72 GWd/t, already used for one of the VERCORS test (“well characterised fuel “) heated at 1350°C under air

  10. WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru release ? • Model improvements : account for the high dependance of the oxygen potential on the Ru release (Mansouri & Olander, 1998, Minato et al, 1997) => ruthenium release model based on a thermodynamic approach of Ru volatilization from Ru metal /oxides precipitates

  11. RuO3 RuO4 WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru release ? RuO2

  12. Oxygen diffusion in bulk UO2+x: • Correlation of Ramirez et al retained • Based on latest experiments (Ruello,2004) • Explicit function of T and x WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru release ? • Model improvements (continued): account for allsteps of fuel oxidation, i.e. • Mass transfer in the gaseous phase • Oxygen exchange at gas/solid interface : new correlationfor fuel oxygen potential in bulk UO2+x, based on Labroche data (2003)

  13. ~2h WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru release ? • New model assessment on AECL data • ruthenium kinetic release from both de-cladded (MCE-1 series) and cladded fuel (HCE1, HCE3 series) well fitted (“old” model : no Ru release predicted)

  14. AEKI experimental set-up : • Sample = Ru/ /Ru+ZrO2/Ru+ZrO2+FP • Air injection starts when furnace is heated up to required T • Released Ru collected in 2 places : • In an inner quartz tube placed into the outlet tube • In an ambiant tube absorber solution • ~40 tests (RUSET1 to 7) Exhaust Pyrex glass tube Flow meter Inner quartz tube Ceramic rod Ice bath 1 M NaOH – 0,05 M NaOCl absorber solution Furnace Reaction chamber with sample Quartz tube Absorber Air WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru transport ?

  15. VTT experimental set-up : • RuO2s sample / RuO4 injection • Air/moist air/ steam-Ar-air • T in furnace : 1100K -1700K • Released Ru collected • In the outlet tube of reaction chamber • On outlet filters and an ambient tube absorber solution • In some experiments, gammatracer was used to determine Ru deposition profile inside the facility • ~20 tests WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru transport ?

  16. Main results RuO2(s) RuO2(s) RuO2(c) • Experimental evidence that volatile forms of Ru can be transported through the RCS up to containment :unexpected amount of gaseous ruthenium RuO4 measured at ambient temperature in both facilities (VTT and AEKI tests) • Ru is transported in RCS either as RuO2 aerosol particles or gaseous RuO4. • wall condensation and particle formation are the dominant processes, when the cooling rate is relatively fast : both phenomena compete with each other RuO4(g) RuO2(s) RuO4(g) RuO3(g) RuO2(g) • Interpretation:decomposition process of RuO4 to RuO2 was not fast enough to follow the equilibrium=>kinetic limitations likely occurred…(transit times are within the range of those of reactor case !) WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru transport ? • Decomposition of of RuO4 to RuO2s significantly influenced by reactions on the surface : oxidized/metallic surfaces, w/wo pre-deposits of RuO2, w/wo presence of other FPs (ex : Molybdenum seems to decreasethe surface catalysis effect on decomposition of RuOx)

  17. Experimental investigations(IRSN, in ISTP frame): • Development of a reliable method for generating pure RuO4 crystals • Study of RuO4(g) decomposition as a function of T and surface type (paint, steel) • Study of ruthenium deposit oxidation : • with an ozone generator • in irradiation facility (EPICUR) after Ru adsorption after O3 contact Initial steel coupon after Ru adsorption after O3 contact Initial steel coupon WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru behaviour in containment building • Literature review • revealed a lack of quantified data on RuO4 gaseous phase stability in our containment temperature range, and on RuO2(c) / RuO4(g) radiolytic conditions. • Study of the oxidation of ruthenium species in the aqueous phase (in EPICUR) : • Dissolved powder of KRuO4 (representative of ruthenium aerosols) • RuO2(s) • RuO4(aq)

  18. WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru behaviour in containment building • Main results : stability of RuO4(g) • RuO4(g) is not as unstable as indicated by the literature : half-life time was experimentally evaluated to ~ 5 hours in representative conditions of a SA • Substrate interaction : no special affinity (steel, epoxy,..) : no influence on the decomposition kinetics • decomposition reaction is accelerated by the presence of steam and deposits of ruthenium oxides, which act as catalysts. • RuO4(g) is not as unstable as indicated by the literature • Half-life time was experimentally evaluated to around 5 hours in representative conditions of a SA (temperature, % steam) • RuO4(g) decomposition process into RuO2 deposits is catalysed by steam and ruthenium dioxide deposits • RuO4(g) is not as unstable as indicated by the literature • Half-life time was experimentally evaluated to around 5 hours in representative conditions of a SA (temperature, % steam) • RuO4(g) decomposition process into RuO2 deposits is catalysed by steam and ruthenium dioxide deposits • RuO4(g) is not as unstable as indicated by the literature • Half-life time was experimentally evaluated to around 5 hours in representative conditions of a SA (temperature, % steam) • RuO4(g) decomposition process into RuO2 deposits is catalysed by steam and ruthenium dioxide deposits • RuO4(g) is not as unstable as indicated by the literature • Half-life time was experimentally evaluated to around 5 hours in representative conditions of a SA (temperature, % steam) • RuO4(g) decomposition process into RuO2 deposits is catalysed by steam and ruthenium dioxide deposits

  19. WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru behaviour in containment building • Main results (continued) : revolatilization from deposits • Revolatilization from ruthenium oxides deposits have been experimentally evidenced, induced by oxidizing effect of ozone producing RuO4(g) • 2 key factors : T, humidity : their increase clearly favours the oxidation reaction

  20. WHAT HAS BEEN ACHIEVED WITHIN SARNET Ru behaviour in containment building • Main results (continued) : revolatilization from aqueous phase • Ruthenium aerosols behaviour : • No Ru volatilization occurred from aqueous solution of RuO4- (KRuO4 : representative of « Ru aerosol »), and from aqueous solution of RuO2,2.6H2O, whatever the sump pH • RuO4(aq) behaviour (made by dissolution of RuO4 vapours ) in the case of a basic sump : • 75% of Ru volatilized for a 16 hours irradiation at 90°C • ≈ 50% of Ru volatilized for a 31 hours heating at 90°C without irradiation: strong impact of the heating phase => gradiations act only as a booster agent for the revolatilisation phenomenon • no formation of new aqueous species from RuO4 (aq) during heating, evidencing that Ru volatilization occurred directly from RuO4 (aq) • Conclusion : the sump is an efficient trap for Ru aerosols species, while it is not for RuO4(g) (at least for basic conditions of pH)

  21. Containment building Ru transport ? new exp. data (VTT, AEKI)…but no model RuO4(g) RuO2(s) RuO4(g) RuO2(s) RuO2(g) RuO4(g)f(T, g, %H2O) RuO2(s) RuO2(c) RuO2(c) Ru release ? new exp. data improved and assessed model Containment wall Ru behaviour ? new exp. data (ISTP), and assessed model RuO2(g)f(T,pO2) RuO4(g) RuO4(g) « Ru aerosol » RuO4(g) RuO2(s) RuO4(g) pH = 5 or 9 Sump H2 , H2O2 , e-aq , H., OH. , O.- ….  Precipitates  RuO2,2H2O WHAT HAS BEEN ACHIEVED WITHIN SARNET Zr-UO2/air ? See papers 2.2, 2.4 Air flows ? Independant studies (EDF, IRSN) : convergence on range flows

  22. Work programme for SARNET 2 ! What remains to be addressed • The issue cannot be considered as completely solved ; remaining key questions : • FP release from high Burn up and MOX fuels (adaptation of model) • FP release under mixed steam-air conditions (adaptation of model) • Thermodynamic and non–equilibrium behaviour of ruthenium oxides during their transport in RCS, reactivity with surfaces and other chemical compounds (model development) • Potential release of pre-deposited FPs (like Iodine), when submitted to oxygen, inducing a delayed release to containment (experimental work)

  23. SARNET added value SARNET added value SARNET added value Consensus on a work programme for SARNET 2 Significant achievements have been reached (9 conference presentations, 6 publications) CONCLUSIONS • Air ingress can occur after a lower head vessel failure : • Air ingress flows have been assessed by independent calculations (IRSN, EDF). • Air ingress situations have significant implication for the source term as ruthenium can form volatile oxide species when exposed to air : • Predictive model for ruthenium release have been improved :satisfactory assessment on analytical tests both forUO2 fragments and clad fuel(AECL, CEA, ENEA, IRSN) • Ruthenium is transported in RCS either as RuO2 particles or gaseous RuO4 :this has been experimentally evidenced (VTT, AEKI) • Predictive model for radio-chemical reactions inside the reactor containment building have been developed based on experimental observations (IRSN et al) SARNET added value • The issue cannot be considered as completely solved; remaining questions identified

  24. WHAT HAS BEEN ACHIEVED WITHIN SARNET Appendix : Ru transport ? • Interpretation:decomposition process of RuO4 to RuO2 was not fast enough to follow the equilibrium=>kinetic limitations likely occurred. Transit times of transported Ru oxides from the hotter zones (furnace areas) to colder zones (liquid traps) : • Transit times from 1 to 4 seconds : within the range of those from the core outlet zone to the reactor containment zone calculated for typical LOCA with a break located at the hot leg or at the PORV of a Pressurizer

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