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Effect of Burn-up and High Burn-up Structure on UO2 Spent Fuel Matrix Dissolution
1. 1
4 2
3
Effect of Burn-up and High
Burn-up Structure on UO2
Spent Fuel Matrix Dissolution
D. Serrano-Purroy1, I. Casas2, E. González-Robles3,
J. P. Glatz1, D. Wegen1, F. Clarens3, J. Giménez2,
J. de Pablo2,3, A. Martínez-Esparza4
MRS’11, BUENOS AIRES, OCTOBER 2-6, 2011
2. This work is a part of a Collaboration
Agreement between ITU/JRC-ENRESA-
CTM/UPC to obtain the scientific data
needed to better understanding the
behaviour of High Burn-up Spent Fuels
3. SPENT FUEL DISSOLUTION
-2
log Fractional Release Rate (d-1)
-3
-4
-5
grain boundaries
UO2-matrix
Rod Actínides & FP -6
14C (~ 98 %)
Gap matrix
14C; 129I;
135Cs; 137Cs; -7
79Se; 99Tc;
90Sr
gap
Cracks -8
Grain Boundary
14C; 129I; 0 1 2 3 4 5 6 7
Bubbles
135Cs; 137Cs;
79Se; 99Tc; 90Sr log time (y)
L.H. Johnson, D.W. Shoesmith, “Radioactive Waste Forms
for the future“, W. Lutze and R.C. Ewing, Eds., 1988
5. High Burn-up Structure (HBS)
Increasing burn-ups, neutron capture of U-238 produces Pu-239 generating
an external layer with a higher burn-up (BU), increased porosity and fuel
grain subdivision resulting on the formation of the so-called HBS. The width
of this layer, observed for BU’s higher than 40 MW d/kgU, increases with
the BU and depends on the irradiation history.
Intermediate zone HBS
HBS particle
CORE particle
6. RIM THICKNESS
110
100
90
Rt = 5.44BUR – 281
Rim BU (MW/ d kgU)
80
70
60
50
40
30
20
20 30 40 50 60 70 80
Average BU (MW/d kgU)
Johnson L., Ferry C., Poinssot C., Lovera P. Estimates of the Instant
Release Fraction for UO2 and MOX Fuel at t=0. NAGRA-TR-04-08, 2004
7. RN release from Spent Fuel
Grain boundaries:
C, I, S, Cs, Se, Tc
Grains:
Gap region : (U,An,Ln)O 2
C, I, Cs, Se, Tc Oxide precipitates:
Rb, Cs, Ba, Zr, Nb, Mo, Tc
?-particles/ metallic precipitates
Mo, Ru, Pd, Tc, Rh
20kV x 1.500 µm 030996
10
(Ag, Cd, In, Sn, Sb)
Cracks
Fission Gas bubbles: RIM or HBS:
Xe, Kr, I enriched in Pu
Pellet gap
Cladding : C
8. Objective
Study the leaching behavior of High Burn-up
PWR fuels (48 and 60 Mw d/kgU) with
special emphasis on the HBS region related
to UO2-matrix dissolution
9. Spent fuel samples
Burn-up 48 60
(MW d/kgU) (MBU) PWR (HBU) PWR
MBU
Irradiation cycles 3 5
End of radiation 2000 2001
RIM (µm)
76 µm 155 µm
calculated
HBU
10. Spent fuel sample preparation
Two different samples were prepared from a different radial position in order to study the
effect of HBS region
1. Cut pin into segments
2. Drill
Core sample
3. Separation from cladding
RIM width
OUT sample OUT sample
4. Sieving (50-100 µm)
5. Removing fines
11. Spent fuel sample preparation
HBU: Core (left) and OUT (right) sample after drilling and detachment
12. Spent fuel sample preparation
SEM characterisation of core sample a) before cleaning b)
after cleaning at 1000 magnification (Scale: 30 µm)
13. Spent fuel sample characterization
Fuel Parameter Core OUT
Mean particle
68 ± 15 82 ± 8
size (μm)
60BU
Specific surface
0.027 ± 0.007 0.022 ± 0.002
area (m2/g)
Mean particle A: 45 ± 15
90 ± 40
size (μm) B: 140 ± 50
48BU
Specific surface A: 0.04 ± 0.01
0.020 ± 0.009
area (m2/g) B: 0.013 ± 0.009
14. Spent fuel sample characterization
The percentage of the surface broke through trans-
granular process in the Core sample was 98 % for
48MBU fuel and 97% for 60HBU fuel. Therefore, only
about 3% of the particle surface was estimated to
contain open grain-boundaries in both fuels.
The percentage of HBS particles present in OUT
samples for 48MBU and 60HBU fuels determined by
direct counting from SEM images is 5 and 19
respectively, these values change to 19 and 40 if
geometry is taking into account.
19. Dissolution Rates:
Q Ci
rate i
A
Radionuclide rates normalized to uranium:
massU Mi
normalized ratei ratei
massi MU
20. 60HBU Dissolution & normalized rates for Actinides
CORE CORE
1,E-07 1,E-08
1,E-08
1,E-09 1,E-09
norm. rates (mol/m 2. s)
1,E-10
rates (mol/m 2. s)
1,E-11 1,E-10
1,E-12
1,E-13 1,E-11
1,E-14
1,E-15 1,E-12
1,E-16
1,E-17 1,E-13
0 50 100 150 200 250 300 350 400 450 500 0 50 100 150 200 250 300 350 400 450 500
time (d) time (d)
U Np Pu Am Cm U Np Pu Am Cm
OUT OUT
1,E-07
1,E-08
1,E-09 1,E-08
rates (mol/m 2.s)
1,E-10
norm. rates (mol/m s)
2.
1,E-11 1,E-09
1,E-12
1,E-10
1,E-13
1,E-14
1,E-11
1,E-15
1,E-16 1,E-12
0 100 200 300 400 500
1,E-13
tim e (d)
0 100 200 300 400 500
time (d)
U Np Pu Am Cm
U Np Pu Am Cm
21. 48 MBU Dissolution & normalized rates for Actinides
CORE
1.E-08
1.E-09
1.E-10
rates (mol m-2 s-1)
1.E-11
1.E-12
1.E-13
1.E-14
1.E-15
0 50 100 150 200 250 300 350
time (d)
U Np Pu Am Cm
OUT OUT
1.E-06 1.E-06
1.E-07
1.E-07
1.E-08 normalised rates (mol m s-1)
-2
1.E-08
rates (mol m s-1)
1.E-09
-2
1.E-10
1.E-09
1.E-11
1.E-12 1.E-10
1.E-13
1.E-11
1.E-14
1.E-15 1.E-12
0 50 100 150 200 250 300 350 0 50 100 150 200 250 300 350
time (d) Time (days)
U Np Pu Am Cm U Np Pu Am Cm
23. Some remarks
Uranium and Actinide dissolution rates are twice
faster in the CORE region than in the Periphery
Except for Np in 60HBU fuel, actinides dissolve
congruently with uranium
Uranium dissolution rate is lower in 60HBU fuel than
in 48MBU fuel
24. 60HBU Normalized Rates for Fission Products
CORE OUT
1,E-07 1,E-07
normalized rates (mol/m 2.s)
1,E-08 1,E-08
normalized rates (mol/m2.s)
1,E-09 1,E-09
1,E-10
1,E-10
1,E-11
1,E-11
1,E-12
1,E-12
1,E-13
1,E-13
1,E-14
1,E-14
0 100 200 300 400 500 0 100 200 300 400 500
time (d) time (d)
Rb Sr Y Zr Mo Tc Ru Rh Cs Nd U Rb Sr Y Zr Mo Tc Ru Rh Cs Nd U
25. 48MBU Normalized Rates for Fission Products
CORE OUT
1.E-07 1.E-06
1.E-07
normalised rates (mol m-2 s-1)
1.E-08
normalised rates (mol m-2 s-1)
1.E-08
1.E-09
1.E-09
1.E-10
1.E-10
1.E-11 1.E-11
1.E-12 1.E-12
1.E-13
1.E-13 0 50 100 150 200 250 300 350
0 50 100 150 200 250 300 350
times (t)
time (d)
Rb Sr Y Zr Mo Tc Ru Rh Cs La Nd U Rb Sr Y Zr Mo Tc Ru Rh Cs La Nd U
28. Some remarks
Fission products normalized dissolution rates are
similar in 48MBU for both core and out samples
Fission products normalized dissolution rates are
higher in out than in core samples in 60HBU
Rb, Sr, Mo, Cs are more segregated from UO2-grains
in 60HBU than in 48MBU
30. Conclusions
-phase Dissolution lower
UO2-matrix dissolution rate than UO2-matrix
Grains similar in both HBU
higher in MBU than in HBU Grains
and MBU fuels
Gap Rim Boundaries
IRF
2 options:
Not studied in this IRF or 2 options Congruent dissolution
matrix IRF or with UO2-matrix:
work, no gap was matrix
present Np, Pu, Am, Cm, excep
t for Np in 60HBU.
This work indicates that High BU Rb, Sr, Cs, Mo are
Structure (RIM) can not be more segregated from
considered IRF. OUT Dissolution UO2-grains in 60HBU
rate (including a percentage of RIM) than in 48MBU
lower than CORE rate for both HBU
and MBU Not studied in detail in
this work, only 3% of
grain boundary present
31. THANK YOU FOR YOUR ATTENTION
GRACIAS POR SU ATENCIÓN
And thanks to Argentina for sending
this guy to Barcelona
Que bueno que viniste