Diapositive 1

1
Towards a better understanding of iodine
chemistry in RCS of nuclear reactors
N. Girault, C. Fiche, A. Bujan and J. Dienstbier
CONTENTS 1. Objectives 2.
Approach 3. Main Experimental findings 4.
Calculation results 5. Discussion (sensitivity
analyses) 6. Summary - Conclusions
- - 1
ERMSAR 2007, Karlsrühe, 12-14 June 2007
Source Term Issues
2
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Objectives - Context
? HITEMP circle objectives and means ?
provide predictability of iodine species exiting
the RCS in 900/1300 PWR undergoing a severe
accident through different scenarios
containment chemistry analyses can not explain
the early gaseous iodine fraction measured
nearly after the main hydrogen release ?
analyses of PHEBUS FP and VERCORS HT tests with
SOPHAEROS (equilibrium chemistry in gas) to
investigate iodine speciation within different
oxido-reducing conditions and release kinetics of
SIC (or B4C for FPT3 test) ? Earlier and
on-going work ? SOPHAEROS analyses
continuously progressed with regards to thermo
dynamic code MTDATA/SGTE (check of thermodynamic
data of elements) ? besides analysis of
potential chemical kinetics limitations (because
of low residence time, strong thermal gradient in
some parts of RCS (CHIP)
3
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
What needs to be explained in Phebus RCS ?
KEY POINT VAPOUR PHASE CHEMISTRY
4
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Approach
analyses of Phebus tests with SOPHAEROS
Impact of Ag/In/Cd and B
Impact of H2O/H2
? investigation of iodine behaviour in Phebus RCS
? total iodine retention in RCS (in
vertical line and SG hot leg) ? volatile
iodine formation at low T (cold leg) ?
iodine vapour speciation between 700 and 150C in
FPT2 TGT and TL (FPT3)
5
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Thermal Gradient Tubes (3)
Transition Lines (4)
700C filters
150C oven
transition lines
t 180s
t0
150C filters
Ins.
6
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Phebus test Overview
Significant H2 release main Zr oxidation phase
FPT1 FPT2 FPT3
Main characteristics ? AIC rod bursts at
8700-9700s B4C rod bursts at 9550 s
? main H2 peak lasts 2 (FPT1) to 20 min
(FPT2/3), ? release phase initiated
during Zr oxidation phase, lasts 2 hr ? FP ?
SM release rates are very variable and depends on
fuel degradation events (release 50g in FPT2
-150g in FPT1/0)
131I at point G (cold leg of RCS)
FPT1 FPT2 FPT3
7
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Main experimental findings
iodine
1) Iodine vapour speciation (FPT2/3)

• ? iodine species not only depends on oxido
  reducing conditions BUT on FP release kinetics
  (molar ratios I/Cs, Cs/Mo-B-Re)
• ? before H2 release Cs ltltlt I
• ? during H2 release large increase of Cs
• release Mo remaining low
• ? after H2 release large increase of Mo
• ? evidence of volatile iodine not associated to
  Cs in FPT2 whatever H2O/H2 and releases
• (also seen in FPT3 with even more iodine
  condensation peaks )

8
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
. during late steam-rich phase
In transition Line
I ? Cs
700C
I - Cs 450-550C
? despite large Mo release (Cs/Mo ? 1), CsI is
formed
9
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Main experimental findings
2) Volatile iodine formation

• ? no direct evidence of volatile I in primary
  circuit BUT early detection of gaseous iodine in
  containment
• ? higher fraction in tests with higher steam flow
  rate (FPT0/1) or without SIC (FPT3)

10
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Main experimental findings
3) Iodine retention in RCS
? quite similar iodine deposits in FPT1/2 may
be less in FPT3 due to large fraction of
gaseous iodine ? in FPT1/2/3 iodine mainly
deposited in SG (taking into account upstream
part) 25-30 of deposited iodine ? 5-10
of iodine deposited in UPVL in FPT2 and
FPT3 iodine deposited in UP rather than in
VL ? significant deposition of iodine in cold
leg in FPT2 could be due to aerosol
sedimentation in lower steam flow rate
11
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Results
1.1) Integrated I ? Cs speciation predicted in RCS
Caesium
Iodine
1) CdI2
1) CsReO4
2) CsI
2) Cs2MoO4 BCsO2
3) Volatile I

• ? In FPT0/1 large impact of Re and SIC I (CdI2)
  and Cs (CsReO4)
• ? Impact of B in FPT2/3 and small/no AIC I (CsI)
  and Cs (Cs2MoO4 BCsO2)
• ? More volatile iodine species in FPT3 because no
  Cd (Cd HI ? CdI2) and in
• FPT0 because less Cs/CsOH (CsOH HI ? CsI)

12
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Results
1.2) Predicted I speciation in HL samplings
TL(H2) 10050s
TGT (H2O) 15000s
210-450C
CsI Cs2I2
RbI
SOPHAEROS mainly predict CsI and CdI2 (minor
amount of Cs2I2 and RbI) ? in accordance with
similar deposition profiles in 2/3 TGT for I and
Cs ? in contradiction with no/small Cs detection
in TL
when low Mo release (under H2), large amount of
CsOH and HI to form CsI when high Mo release
(late H2O phase) CsOH consumes by H2MoO4 to form
Cs2MoO4, leaving large fraction of HI to react
with Cd
13
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Results
2) Volatile iodine at low T
? According to base-case analysis, HI is the main
candidate in FPT0/1/2 ? HI predicted amount
doesnt significantly depend on H2O/H2 as
measured ? Some other volatile iodine
species are also predicted but only if no Cd
14
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Results
3) I retention in RCS

• ? in VL is underestimated
• ? underestimation of CsI condensation
• ? improved calculations by considering
• non developped flows
• ? in SG is overestimated by ?2-3
• ? overestimation of CsI thermophoresis
• ? uncertainties on Cd release kinetics

Total iodine retention factor overestimated by ?
1.8
15
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Sensitivity analyses
Discussion
Impact of Cd release kinetics
? Large uncertainties on Cd release potential
release in puffs
steam generator
0.6
0.2
FPT0
? Assuming a continuous Cd release leads to
overprediction of I retention in SG AND low
amount of volatile HI mainly in FPT0/1 tests in
which CdI2 prevailed on CsI ? When limited Cd
release kinetics is assumed better agreement with
I retention factor in SG BUT overprediction
by 10 of HI formation (consistent with a higher
volatile I fraction measured in FPT3)

16
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Sensitivity analyses
Discussion
Impact of Mo chemistry
700C
? at 700C, high volatility of H2MoO4 ?
significant formation of Cs2MoO4 ?
formation of CsI prevented ? large
fraction of volatile HI ? if Psat (H2MoO4) is
decreased (? MoO3) CsI (RbI) is formed (Cd do
not compete with CsOH to form CdI2)
CdI2
CsI
CsOH
H2MoO4
? depending on Mo species more or less CsI is
calculated ? Cs2MoO4 is generally too much
favoured to the detriment of CsI
17
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Sensitivity analyses
Discussion
Impact of aerosol thermophoresis modelling
? Talbot formulation function of (fluid
partic. properties) is used to calculate
particle THP deposition velocity
? Fluid prop.
depend on boundary layer T ? All fluid
properties Talbot correlation coded to
separate talbot.f to evaluate influence of
boundary layer temperature
Tfluid properties ALFA Tf (1.0 ALFA)
Tw with 0.1 ALFA 1.0 (near to
wall T)
ALFA (1/0.1)lt 1.2
with ALFA 0.1 in SG inlet (high ?T) slightly
decreased iodine aerosol deposition (NOT
sufficiently impact total retention in SG because
predominant phenomenon is CdI2 condensation)
18
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Overview of Iodine Chemistry in RCS gas phase
COLD Temperature 700 ltTlt 150C
Steam Generator Cold leg
FP/SM RETENTION
? condensation ?
? condensation ?
I HI, I, (CsI) Cs CsOH, Cs, (Cs2MoO4) Mo
MoO3, H2MoO4 Re ReO, CsReO4,(ReO2 Re2O7) B
BO2,H3B3O6 (BO HBO2 H3BO3) Cd Cd
Cd HI ? CdI2 ?
---- gas ---- vapour ---- condensed state
Potential kinetics limitations due locally to low
residence time and high ?T
19
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings
Summary and Conclusions ? Iodine retention in
primary circuit Base-case calculations ?
overall retention factor overestimated by about
2 ? nearly no retention of I predicted in
UPVL whereas measured RF is about 0.09 in
FPT2 (0.07-0.04 in FPT1/3) ? retention in SG
overestimated by 2-3, mainly CdI2 condensation
Improved calculations by considering ? non
fully developed flows in UP/VL ? near to wall
temperature in SG for THP modelling
20
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings

• Summary and Conclusions
• ? Volatile iodine species at low T
• ? SOPHAEROS implies strong sensitivity to Cd,
  main species HI
• (small amounts of SnI2, SnI4 and I2MoO2 in
  FPT3 with no Cd)
• in Phebus tests (FPT3 excepted) when volatile
  iodine amount
• is correctly predicted, iodine condensation in
  SG is under
• estimated and vice-versa
• ? FPT3 calc. results shows a very high
  volatile I fraction (18 /i.b.i)
• when Cd is completely missing in accordance
  with exp. data (27)
• CHIP programme (investigation of
  nonequilibrium effects)
• Analysis of VERCORS HT tests impact
  of SIC materials

21
Approach
Calc. results
Conclusions
Objectives
Discussion
Exp. Findings

• Summary and Conclusions
• ? Iodine vapour speciation
• Base-case calculations
• ? good agreement between exp. data and
  SOPHAEROS only when
• measured I is associated with Cs
• ? Cs2MoO4 too much favoured to detriment of
  CsI with high Mo
• release,CsI with low Mo release
• ? volatile iodine measured with low Cs or high
  Mo release not well
• predicted (only CdI2 ?) impact of others
  SIC/SM (In, Fe, Cr, Si)
• VERCORS HT1,2,3 and FPT3
• Sensitivity calculations
• ? depending on Mo chemistry ode more or less
  CsI is calculated
• CHIP (investigation of simplified
  systems under equilibrium)
• Continuous check/development of MDB
  (polymolybdates ?)