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

1

2

3

4

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

SPENT FUEL DISSOLUTION

Rod14C

Gap14C; 129I;135Cs; 137Cs;79Se; 99Tc;90Sr

UO2-matrix

Actínides & FP

(~ 98 %)

Grain Boundary14C; 129I;135Cs; 137Cs;79Se; 99Tc; 90Sr

Cracks

Bubbles

-8

-7

-6

-5

-4

-3

-2

0 1 2 3 4 5 6 7

log

Frac

tio

nal

Re

leas

e R

ate

(d

-1)

log time (y)

matrix

grain boundaries

gap

L.H. Johnson, D.W. Shoesmith, “Radioactive Waste Forms

for the future“, W. Lutze and R.C. Ewing, Eds., 1988

PREVIOUS UO2-MATRIX DISSOLUTION RATES

• Dynamic experiments

• Air conditions

• Powder

• Fragment

• Segment (Fuel+Cladding)

-12.00

-11.50

-11.00

-10.50

-10.00

-9.50

-9.00

-6 -5 -4 -3 -2 -1

log

r (m

ol/

m2

·s)

log [HCO3-]

Gray_33 MW d/ kgU

Serrano_53 MW d/ kg U

Röllin_43 MW d/ kgU

Gray_28 MW d/ kgU (0.01 M HCl/DIW)

Gray_43 MW d/ kgU (0.01M HCl/DIW)

Serrano_53 MW d/ kgU_segment

Serrano_29 MW d/ kg U_segment

Jegou_60 MW d/kg U_segment

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.

CORE particle

HBS particle

CORE particle

HBS particle

HBSIntermediate zone HBSIntermediate zone

RIM THICKNESS

20

30

40

50

60

70

80

90

100

110

20 30 40 50 60 70 80

Rim

BU

(M

W/

d k

gU)

Average BU (MW/d kgU)

Rt = 5.44BUR – 281

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

RN release from Spent Fuel

Cladding : C

Gap region : C, I, Cs, Se, Tc

Cracks

Pellet gap

20kV x 1.500 10 µ m 030996

Grains: (U,An,Ln)O 2

Grain boundaries: C, I, S, Cs, Se, Tc

RIM or HBS: enriched in Pu

Oxide precipitates: Rb, Cs, Ba, Zr, Nb, Mo, Tc

? - particles/ metallic precipitates Mo, Ru, Pd, Tc, Rh (Ag, Cd, In, Sn, Sb)

Fission Gas bubbles: Xe, Kr, I

Cladding : C

Gap region : C, I, Cs, Se, Tc

Cracks

Pellet gap

20kV x 1.500 10 µ m 030996 20kV x 1.500 10 µ m 030996

Grains: (U,An,Ln)O 2

Grain boundaries: C, I, S, Cs, Se, Tc

RIM or HBS: enriched in Pu

Oxide precipitates: Rb, Cs, Ba, Zr, Nb, Mo, Tc

? - particles/ metallic precipitates Mo, Ru, Pd, Tc, Rh (Ag, Cd, In, Sn, Sb)

Fission Gas bubbles: Xe, Kr, I

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

Burn-up

(MW d/kgU)

48

(MBU) PWR

60

(HBU) PWR

Irradiation cycles 3 5

End of radiation 2000 2001

RIM (µm)

calculated76 µm 155 µm

MBU

HBU

Spent fuel samples

Spent fuel sample preparation

Two different samples were prepared from a different radial position in order to study the

effect of HBS region

RIM width

OUT sample

4. Sieving (50-100 µm)

5. Removing fines

1. Cut pin into segments

2. Drill

3. Separation from cladding

Core sample

OUT sample

HBU: Core (left) and OUT (right) sample after drilling and detachment

Spent fuel sample preparation

SEM characterisation of core sample a) before cleaning b)

after cleaning at 1000 magnification (Scale: 30 µm)

Spent fuel sample preparation

Fuel Parameter Core OUT

60BU

Mean particle size (μm)

68 ± 15 82 ± 8

Specific surface area (m2/g)

0.027 ± 0.007 0.022 ± 0.002

48BU

Mean particle size (μm)

90 ± 40 A: 45 ± 15

B: 140 ± 50

Specific surface area (m2/g)

0.020 ± 0.009A: 0.04 ± 0.01

B: 0.013 ± 0.009

Spent fuel sample characterization

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.

Experimental Setup

Experimental Setup installed inside Hot Cell

Element 60BU-CORE 60BU-OUT 48BU-CORE 48BU-OUT

Rb 500 ± 10 600 ± 100 320 ± 20 490 ± 20

Sr 800 ± 40 800 ± 100 730 ± 100 700 ± 20

Y 650 ± 10 770 ± 30 540 ± 10 660 ± 30

Zr 6300 ± 200 7900 ± 700 3800 ± 300 4500 ± 200

Mo 5900 ± 300 8000 ± 400 3600 ± 200 4500 ± 200

Tc 1300 ± 100 1600 ± 50 840 ± 30 1090 ± 30

Ru 4400 ± 200 5300 ± 600 2400 ± 100 3200 ± 200

Rh 650 ± 20 800 ± 100 510 ± 20 700 ± 100

Cs 3800 ± 200 4800 ± 400 2600 ± 200 4200 ± 100

Ba 3300 ± 400 4300 ± 500 1800 ± 400 2000 ± 300

La 2000 ± 400 2300 ± 300 2700 ± 1000 2800 ± 500

Ce 4100 ± 500 4500 ± 800 3000 ± 700 3000 ± 400

Pr 1800 ± 200 2100 ± 300 1300 ± 200 1100 ± 200

Nd 7000 ± 1000 8000 ± 900 4900 ± 1300 4000 ± 600

Sm 1270 ± 100 1500 ± 100 1000 ± 200 800 ± 100

Eu 190 ± 10 200 ± 20 130 ± 10 130 ± 10

Gd 620 ± 20 800 ± 200 340 ± 40 300 ± 30

U 780000 ± 10000 770000 ± 60000 790000 ± 10000 780000 ± 10000

Np 810 ± 80 760 ± 80 900 ± 100 750 ± 20

Pu 8000 ± 540 11000 ± 1600 10400 ± 600 15200 ± 400

Am 840 ± 100 1200 ± 100 500 ± 30 800 ± 30

Cm 290 ± 40 460 ± 50 70 ± 10 110 ± 10

Inventory for CORE, OUT (μg of element/g of SNF)

Inventory of each fraction

experimentally

determined by dissolution

in acidic media and

further HR-ICP-MS and

γ-spectroscopy analysis

•NaHCO3 10-3 mol·dm-3

•NaCl 1.9·10-2 mol·dm-3

•In air PO2 21%•Temperature 25 ± 5 ºC•pHi 8.0 ± 0.2 •pHo 7.2 ± 0.5•Flow rate 0.025-0.1 L/min•Weight of solid 1 g

Experimental conditions

Radionuclide rates normalized to uranium:

Dissolution Rates:

ACQ

rate ii

U

i

i

Uii M

Mmassmass

raterate normalized

CORE

1,E-17

1,E-16

1,E-15

1,E-14

1,E-13

1,E-12

1,E-11

1,E-10

1,E-09

1,E-08

1,E-07

0 50 100 150 200 250 300 350 400 450 500

time (d)

rate

s (

mo

l/m

2. s

)

U Np Pu Am Cm

CORE

1,E-13

1,E-12

1,E-11

1,E-10

1,E-09

1,E-08

0 50 100 150 200 250 300 350 400 450 500

time (d)

no

rm.

rate

s (

mo

l/m

2. s

)

U Np Pu Am Cm

OUT

1,E-16

1,E-15

1,E-14

1,E-13

1,E-12

1,E-11

1,E-10

1,E-09

1,E-08

0 100 200 300 400 500

time (d)

rate

s (m

ol/m

2. s)

U Np Pu Am Cm

OUT

1,E-13

1,E-12

1,E-11

1,E-10

1,E-09

1,E-08

1,E-07

0 100 200 300 400 500

time (d)

norm

. rat

es (m

ol/m

2.s)

U Np Pu Am Cm

60HBU Dissolution & normalized rates for Actinides

48 MBU Dissolution & normalized rates for Actinides

CORE

1.E-15

1.E-14

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

0 50 100 150 200 250 300 350

time (d)

rate

s (

mo

l m

-2 s

-1)

U Np Pu Am Cm

OUT

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

0 50 100 150 200 250 300 350

Time (days)

norm

alis

ed r

ate

s (

mol m-2

s-1)

U Np Pu Am Cm

OUT

1.E-15

1.E-14

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

0 50 100 150 200 250 300 350

time (d)

rate

s (

mol m

-2 s-1

)

U Np Pu Am Cm

CORE60HBU

OUT60HBU

CORE48MBU

OUT48MBU

NORMALIZEDRATE

(mol/m2 s)

U 5.1 10-12 2.1 10-12 8.0 10-11 4.0 10-11

Np 1.6 10-10 5.2 10-11 1.0 10-10 8.0 10-11

Pu 1.0 10-11 5.7 10-12 3.0 10-11 1.4 10-11

Am 3.5 10-12 2.5 10-12 5.0 10-11 2.0 10-11

RATIO

Np/U 11.3 15.2 1.4 2.2

Pu/U 1.2 1.7 0.4 0.4

Am/U 0.4 0.6 0.7 0.7

Results

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

60HBU Normalized Rates for Fission Products

CORE

1,E-14

1,E-13

1,E-12

1,E-11

1,E-10

1,E-09

1,E-08

1,E-07

0 100 200 300 400 500

time (d)

no

rma

lize

d r

ate

s (

mo

l/m

2. s

)

Rb Sr Y Zr Mo Tc Ru Rh Cs Nd U

OUT

1,E-14

1,E-13

1,E-12

1,E-11

1,E-10

1,E-09

1,E-08

1,E-07

0 100 200 300 400 500

time (d)n

orm

alize

d r

ate

s (

mo

l/m

2.s

)

Rb Sr Y Zr Mo Tc Ru Rh Cs Nd U

48MBU Normalized Rates for Fission Products

CORE

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

0 50 100 150 200 250 300 350

time (d)

norm

alised r

ate

s (

mol m

-2 s

-1)

Rb Sr Y Zr Mo Tc Ru Rh Cs La Nd U

OUT

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

0 50 100 150 200 250 300 350

times (t)

norm

alised r

ate

s (

mol m

-2 s

-1)

Rb Sr Y Zr Mo Tc Ru Rh Cs La Nd U

Ratio CORE60HBU

OUT60HBU

CORE48MBU

OUT48MBU

Rb/U 25.4 113.7 11.0 4.0

Sr/U 7.7 16.2 3.5 1.4

Y/U 1.8 1.7 2.3 3.0

Zr/U 0.02 0.04 0.2 0.1

Mo/U 4.1 29.7 4.2 2.0

Tc/U 0.5 0.5 1.3 1.1

Ru/U 0.3 0.8 0.3 0.7

Rh/U 0.2 0.5 0.3 0.8

Cs/U 2.0 40.2 10.0 3.1

Results

0,00

20,00

40,00

60,00

80,00

100,00

120,00

Rb/U Sr/U Y/U Zr/U Mo/U Tc/U Ru/U Rh/U Cs/U

dis

solu

tio

n r

ate

rat

io

60core

60out

48core

48out

Results: FP rates/ U rate

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

-12.00

-11.50

-11.00

-10.50

-10.00

-9.50

-9.00

-4.50 -4.00 -3.50 -3.00 -2.50 -2.00 -1.50 -1.00

log

rate

log [HCO3-]

Gray_33 MW d/kgU Röllin_43 MW d/kg U this_work_6OHBU_out this_work_60HBU_core

Serrano_53 MW d/kg U this_work_48MBU_core this_work_48MBU_out

Matrix dissolution rate comparison

Conclusions

Rim

Grains

Gap

Grains Boundaries

IRF 2 options:

IRF or matrix

2 options IRF or matrix

This work indicates that High BU Structure (RIM) can not be considered IRF. OUT Dissolution rate (including a percentage of RIM) lower than CORE rate for both HBU and MBU

Congruent dissolution with UO2-matrix: Np, Pu, Am, Cm, except for Np in 60HBU. Rb, Sr, Cs, Mo are more segregated from UO2-grains in 60HBU than in 48MBU

-phase Dissolution lower than UO2-matrix similar in both HBU and MBU fuels

Not studied in detail in

this work, only 3% of

grain boundary present

Not studied in this

work, no gap was

present

UO2-matrix dissolution ratehigher in MBU than in HBU

THANK YOU FOR YOUR ATTENTION

GRACIAS POR SU ATENCIÓN

And thanks to Argentina for sendingthis guy to Barcelona

Que bueno que viniste