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
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

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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
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CONTEXT
Test HCE3-H01 HCE3-H02
Max. temperature (K) 2200 2160
Oxidation temperature (K) 1770 1790
Oxidation duration (s) 8500 8740
Gas phase 90 H2O 10 Ar 0.2 Ar Air
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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)

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MAIN ISSUES TO BE ADDRESSED
Ru release ?
Ru transport ?
Consequences on fuel degradation (e.g. Zr/air) ?
air flows?
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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
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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)

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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 (gt1400C) and for pre-oxidized
  cladding (gt1100C). For all other conditions,
  faster ( more linear) reaction kinetics should
  be applied
• see outcomes from WP9.3 , and papers 2.2, 2.4

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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/2H2 and then air
• HCE2-LM4 cladded PWR fuel 57,3 GWd/tU Tmax
  1670K Ar/2H2 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/2H2 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 1350C under air

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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) gt ruthenium release model based on a
  thermodynamic approach of Ru volatilization from
  Ru metal /oxides precipitates

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WHAT HAS BEEN ACHIEVED WITHIN SARNET
Ru release ?
RuO2
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WHAT HAS BEEN ACHIEVED WITHIN SARNET
Ru release ?

• Model improvements (continued) account for all
  steps of fuel oxidation, i.e.
• Mass transfer in the gaseous phase
• Oxygen exchange at gas/solid interface new
  correlation for fuel oxygen potential in bulk
  UO2x, based on Labroche data (2003)

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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)

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WHAT HAS BEEN ACHIEVED WITHIN SARNET
Ru transport ?
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WHAT HAS BEEN ACHIEVED WITHIN SARNET
Ru transport ?
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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 decrease the surface catalysis effect on
  decomposition of RuOx)

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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)

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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

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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

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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 90C
• 50 of Ru volatilized for a 31 hours heating at
  90C without irradiation strong impact of the
  heating phase
• gt g radiations 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)

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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
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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 nonequilibrium 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)

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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 for UO2 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

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WHAT HAS BEEN ACHIEVED WITHIN SARNET
Appendix Ru transport ?

• Interpretation decomposition process of RuO4 to
  RuO2 was not fast enough to follow the
  equilibrium gt 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