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International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 1
Volatile FP release from VERCORS tests
Preamble :
What have we learnt from VERCORS tests ?
Volatile FP behaviour
VERCORS HT Loop
Parameters affectingtheir release
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 2
What have we learnt ?
VERCORS program
VERCORS- 6 tests(from 1989 and 1994)
VERCORS HT/RT-11 tests(from 1996 to 2002)
Fuel collapsetemperature
FP classificationby volatility degree
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 3
What have we learnt : Fuel collapse temperature
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
Te
mp
era
ture
(°K
) .
UO2 RT1, 47 GWd/t HT1, 47 GWd/t HT2, 50GWd/t HT3, 49 GWd/t V_6, 60 GWd/t RT6, 70GWd/t
Fuel Collapse Temperature
70 GWd/T47 - 50 GWd/T 60 GWd/T
Without irradiation
Since the beginning of the RT/HT grid : Systematic fuel collapse for T between 2400/2600 K without
significant difference for high burn up fuel in the range of 45-70 GWd/t:
Relocation at T < UO2 melting point
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 4
What have we learnt : Fuel collapse temperature
HT1
(~47 GWd/t)
HT2
(~47 GWd/t)
HT3
(~47 GWd/t)
T (K) ~2500 ~2300 ~2500
Atm reducing oxidizing reducing
Same fuel rod
Similar temperature evolution histories
Atmosphere effect
Beginning of fuel collapse
Beginning of fuel collapse
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 5
What have we learnt : FP classification
From VERCORS program
Volatile :gases, I, Cs, Te, Sb, Ag, Rb, Cd
Semi-Volatile : Mo, Ba, Rh, Pd,
Tc
Low-Volatile: Ru, Nb, Sr, Y,
La, Ce, Eu
Non-Volatile: Zr, Nd,
Pr
+ actinides : U, Np, Pu, Am, Cm
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 6
What have we learnt : FP classification
FPs Volatility for irradiated nuclear fuel Volatile FP :
Present lecture
Semi-volatile FP :
Release can be as high as for volatile FP, but :
High sensitivity to oxidizing/reducing conditions
Mo very volatile in oxidizing conditions (MoO3)
Ba more volatile in reducing than in oxidizing conditions
Significant retention close to the fuel
Low volatile FP:
Release from few % to 10% BUT potentially higher release (~30-40%) at high burn-up and/or very oxidizing conditions
Deposit very close to the fuel
Non volatile FP:
No significant release (<1%)
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 7
What have we learnt : FP classification
-20%
0%
20%
40%
60%
80%
100%
16:00 17:00 18:00 19:00 20:00 21:00 22:00
0
400
800
1200
1600
2000
2400
Cs 137
Ba 140
Ru103
Zr97
Te mpé ra ture fond du cre us e t (°C)
Time
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 8
Volatile FP Behaviour
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 9
Volatile FP behaviour
For each case :
Kinetics (release from the fuel)
Global release
(Transport : G. Ducros, Tuesday, 16)
{gases} {Cs and I} {Te, Sb and Ag}1 2 3
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 10
Fission gas release: Generalities
Fission gases (Kr and Xe) are composed of isotopes whose half-lives have a very different radiological impact over time under severe PWR accident conditions:
Long half-life for krypton (10.71 years for 85Kr); active over the mid and long term. The other tracer isotopes of the element have sufficiently short half-lives for having no significant impact in the hours following reactor shutdown, with the exception of 85mKr (half-life of 4.48h) whose effects are felt for a little longer.
Short half-lives for the main isotopes of xenon (2.19 days, 5.24 days and 9 h respectively for 133mXe, 133Xe and 135Xe); active in the short term.
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 11
Fission gas release: Kinetics
0,0E+00
2,0E-03
4,0E-03
6,0E-03
8,0E-03
1,0E-02
1,2E-02
1,4E-02
1,6E-02
1,8E-02
10:48 12:00 13:12 14:24 15:36 16:48 18:00 19:12 20:24
Elapsed time
Inst
anta
neo
us
rele
ase
.
0
500
1000
1500
2000
2500
Tem
per
atu
re (
°C)
133Xe
85Kr
Fuel relocation
Below 1000°C
1000°C < T <1200°C
T >> 1200°C
RT6, UO2,~70GWd/t
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 12
Consistent with previously reported results (T<1200°C) :
FIRST PEAK (600-800°C) Grain boundary cracking
MAIN PEAK (T > 1000°C)Bubbles interconnection and release
- Diffusion of intra-granular gas atoms < 2%
0,0E+00
2,0E+12
4,0E+12
6,0E+12
8,0E+12
1,0E+13
1,2E+13
1,4E+13
1,6E+13
1,8E+13
0 40 80 120 160 200 240 280 320
Elapsed time (mn)
85K
r re
leas
e ra
te
(at
/s/g
)
0
200
400
600
800
1000
1200
1400
Tem
per
atu
re (
°C)
Measurement
Calculation
Température
85Kr releaseMETEOR
Y. Pontillon et al., Proceedings of the 2004 International Meeting on LWR Fuel Performance, Orlando, USA, September 2004
UO2, ~70 GWd/t
Fission gas release: Kinetics
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 13
Fission gas release: Global release
Since VERCORS 6: Total release (100% of the initial inventory)
From VERCORS 1 to 5: Released fraction is a function of :
Temperature 1860-1880°C
Test VERCORS 2 VERCORS 1
Release 23% 33%
Temperature 2300°C
Test VERCORS 4 VERCORS 5
Release 86% 87%
Final temperature Duration of high T° plateau
Temperature 1860-1880°C
Test VERCORS 2 VERCORS 1
Duration 13 minutes 17 minutes
Release 23% 33%
Temperature 2300°C
Test VERCORS 3 VERCORS 4
Duration 15 minutes 30 minutes
Release 77% 86%
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 14
Cs and I release: Generalities
FP of great importance with regard to the radiological consequences following a severe accident in a PWR core. They are composed of isotopes with very different half-lives:
Short half-life for iodine (from 1 hour for 134I to 8 days for 131I); the short-term radiological effects are very high in the first few days following an accident, but are negligible after 1 month. Iodine carries 15% of the core's decay heat 1 day after the emergency shutdown;
Long half-life for caesium (30 years for 137Cs); the radiological effects, which are more or less negligible in the short term (there are nevertheless 138Cs and 136Cs with respective half-lives of 30 min and 13 days) stretch into long term over several decades.
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 15
Cs and I release: Kinetics
From VERCORS program
Parameters affecting their release rate:
Burn-up,
Oxidizing or reducing conditions,
Fuel nature:
MOX versus UO2
Initial morphology
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 16
Cs and I release: Kinetics - BU effect
Comparison between RT1 (reference test) and RT6 (High BU test):
Significant increase in release rates for RT6 compared to RT1
00:00 01:12 02:24 03:36 04:48 06:00 07:12 08:24
Elapsed Time
Temperature (RT1)
Temperature (RT6)
Cs137 (RT1)
Cs137 (RT6)
VERCORS RT1:UO2, 47 GWd/TMixed H20/H2
VERCORS RT6:UO2, 70 GWd/TMixed H20/H2
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 17
Cs and I release: Kinetics - Atm effect
Comparison between HT2 and HT3 (same fuel used):
Significant increase in release rates for HT2 compared to HT3
VERCORS HT2 et HT3 : iode, césium, lanthane
0%
20%
40%
60%
80%
100%
17:00 17:30 18:00 18:30 19:00 19:30 20:00 20:30 21:00
Durée (h:mn)
0
500
1000
1500
2000
2500
Iode 132 HT2
Température °C
Cs 137 HT2
La 140 HT2
Température HT2Température HT3
Iode 132 HT3
Cs 137 HT3
La 140 HT3
VERCORS HT2:UO2, 50 GWd/T
steam
VERCORS HT3:UO2, 50 GWd/T
hydrogen
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 18
Cs and I release: Kinetics – Fuel nature (MOX versus UO2)
Significant increase in release rates for RT2 compared to RT1
0:00:00 1:00:00 2:00:00 3:00:00 4:00:00 5:00:00
Time (h:min:s)
MOXtemperature
UO2 (RT1)Cs release
MOX (RT2)Cs release
UO2temperature
Oxidizing plateauT=1770K
Comparison between RT1 (reference test) and RT2 (MOX test):
VERCORS RT1:UO2, 47 GWd/TMixed H20/H2
VERCORS RT2:MOX, 46 GWd/T
Mixed H20/H2
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 19
Cs and I release: Kinetics – Fuel nature (Initial morphology)
Comparison between RT1 (reference test), RT3 and RT4 :
0
500
1000
1500
2000
2500
3000
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00
heures relatives
Tem
pér
atu
re (
°C)
0%
20%
40%
60%
80%
100%
120%
Fra
ctio
n r
elâc
hée
tempéaturer_RT1
température_RT4
température_RT3
Cs137_RT1
Cs137_RT4
Cs137_RT3
VERCORS RT1:UO2, 47 GWd/TMixed H20/H2
VERCORS RT3:UO2, debris bed
reducing
VERCORS RT4:UO2, debris bed
oxidising
RT1
RT3
RT4
RT1
RT3
RT4
Release rate
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 20
Cs and I release: Global release
Since VERCORS 6: release almost complete whatever the nature of the test
From VERCORS 1 to 5: Released fraction is a function of :
Temperature 1860-1880°C
Test VERCORS 2 VERCORS 1
Release 30-40%
Temperature 2300°C
Test VERCORS 4 VERCORS 5
Release 87 - 93%
Final temperature Duration of high T° plateau
Temperature 2300°C
Test V_ 3 V_4 and V_5
Duration 15 minutes 30 minutes
Release 70% 87-93%
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 21
Te, Sb and Ag release: Generalities
Te: Main isotopes 132Te (3.26 d) and 131mTe (1.25 d). The short-term radiological effects
are very high in the first few days following an accident. Parent of the corresponding Iodine.
Sb, main isotopes composed of isotope with very different half-lives :
125Sb (2.76 y), acting in the long term 127Sb (3.85 d), acting in the short term
Ag: Main isotope 110mAg (250 d), acting in the middle/long term
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 22
Te, Sb and Ag release: Kinetics
Results obtained are relatively restricted because of:
Problems with detecting antimony and silver in all the VERCORS tests
This made it impossible to monitor their release from the fuel over time
The loss of detectability of 132Te (best tracer isotope for Te) with the use of thoria in the furnace component after VERCORS 6
Data available up to VERCORS 5
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 23
Te, Sb and Ag release: Kinetics
Hour
0 ,0 0 %
2 0 ,0 0 %
4 0 ,0 0 %
6 0 ,0 0 %
8 0 ,0 0 %
1 0 0 ,0 0 %
1 2 0 ,0 0 %
1 3 :5 5 1 4 :2 4 1 4 :5 2 1 5 :2 1 1 5 :5 0 1 6 :1 9 1 6 :4 8 1 7 :1 6 1 7 :4 5 1 8 :1 4
0
5 0 0
1 0 0 0
1 5 0 0
2 0 0 0
2 5 0 0
Mo9 9
Te1 3 2
Cs1 3 7
TUO2
Fuel temperature (° C)Released fraction
Tellurium retention in the cladding until the latter was completely oxidised
VERCORS 4:UO2, 38 GWd/T
hydrogen
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 24
Te, Sb and Ag release: Global release
For tellurium and silver :
Global release was comparable and almost total for all of the most severe VERCORS tests, i.e. from VERCORS 6 onwards
The main difference between these two FP was in terms of the quantities deposited in the hot zones of the experimental loop (transport effect)
For antimony:
Release delay by trapping into the clad For the entire RT grid, the release rates were generally lower than those obtained for
VERCORS 4, 5 and 6 (typically around 80-95% and 97-100% respectively for the RT grid and VERCORS 4 to 6)
Partial retention in the solidified corium
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 25
Sb release: Global release
This retention sometimes (tests VERCORS RT1, RT2 and RT7) involved the dissociation of this element from the solidified corium:
0
1E+13
2E+13
3E+13
4E+13
5E+13
6E+13
7E+13
320 330 340 350 360 370 380 390 400
nu
mb
er o
f at
om
s
0
2E+14
4E+14
6E+14
8E+14
1E+15
1,2E+15
1,4E+15
1,6E+15
1,8E+15
nu
mb
er o
f at
om
s
Sb127 Sb127 AVS Zr95
Sb before the test
Sb after the test
Zr after the test = corium position
International VERCORS Seminar,October 15-16th, 2007 – Gréoux les Bains, France 26
Conclusion
Volatile FP:
Nearly complete release since VERCORS 6, whatever the nature of the test
Up to VERCORS 5: the release is a function of the final Temperature and duration at high temperature plateau
Sensitive to :
Burn up Atmosphere of the test Fuel nature
Global release
Kinetics