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Fission products and nuclear fuel behaviour under severe accident conditionsSpeciation of fission productsin the Verdon 3 and -4 samples

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HAL Id: cea-02338475

https://hal-cea.archives-ouvertes.fr/cea-02338475

Submitted on 24 Feb 2020

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Fission products and nuclear fuel behaviour under

severe accident conditionsSpeciation of fission

productsin the Verdon 3 and -4 samples

F. Audubert, C. Le Gall, L. Fayette, P. Bienvenu, I. Zacharie-Aubrun, K. Hanifi, Yves Pontillon

To cite this version:

F. Audubert, C. Le Gall, L. Fayette, P. Bienvenu, I. Zacharie-Aubrun, et al.. Fission products and nuclear fuel behaviour under severe accident conditionsSpeciation of fission productsin the Verdon 3 and -4 samples. NUMAT 2018 - The Nuclear Materials Conference 2018, Oct 2018, Seattle, United States. �cea-02338475�

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FISSION PRODUCTS AND NUCLEAR FUEL BEHAVIOUR

UNDER SEVERE ACCIDENT CONDITIONS

:

SPECIATION OF FISSION PRODUCTS

IN THE VERDON 3 AND -4 SAMPLES

NUMAT 2018|October 19th– 23th, 2018

CEA Cadarache|DEN |DEC |SA3E |LAMIR

F. Audubert, C. Le Gall, L. Fayette, P. Bienvenu, I. Zacharie-Aubrun, K. Hanifi, Y. Pontillon

(3)

CONTEXT

Phenomenology of a PWR severe accident

| PAGE 2

Normal operating conditions

Further heat-up

Of the rods Corium formation

Heat-up of Fuel rods Cladding oxidation Production of H2 (Reducing atmosphere) Zr + 2H2O → ZrO2+ 4H2 Production of steam (Oxidizing atmosphere)

Failure of the building

(Oxidizing atmosphere) Oxidation plateau (1100-1500°C) High temp. plateau (≥ 2300°C) Temperature ramp (400-1100°C) Temperature ramp (1500-2000°C) Initial state T0

MOX fuel irradiated t 56 GWd.tML-1 Neutral atmosphere Oxidizing atmosphere Reducing or oxidizing atmosphere O 2300 Thermal treatment up to 2300°C under oxidizing atm. R 2500 Thermal treatment up to 2500°C under reducing atmosphere

(4)

2 PWR MOX fuel pellets + M5 cladding

+

2 unirradiated half pellets (depleted UO2)

reirradiated in OSIRIS

THE VERDON-3 AND 4 SAMPLES

Characteristics

| PAGE 3 VERDON-3, 2300°C, H2O VERDON-4, 2530°C, H2 Father rod, 56 GWd.tHM-1

2 irradiated pellets, scarce visible pieces of cladding

+

2 unirradiated half pellets (depleted UO2)

2 irradiated pellets + molten Zr cladding

+

(5)

EPMA

POST-TEST CHARACTERIZATIONS

Method

| PAGE 4

Qualitative analyses

Quantitative analyses

Phases chemical composition Optical microscopy, SEM,

SIMS, X-ray maps

Microstructure evolution Fuel-cladding interaction

FP distribution and associations

Hotlab : LECA STAR

(6)

* Hanifi NT CEA (2009, 2010)

UO2 matrix (1.6 at% Pu) No more coating phase Pu agglomerates (4.5 at% Pu) Restructured area (0.4R) with

porous agglomerates

Densified agglomerates homogeneously distributed

Restructured area still visible, with densified agglomerates

Pu

U

U

Pu

Pu

U

| PAGE 5

MICROSTRUCTURE EVOLUTION

Father rod, VERDON-3 and VERDON-4 samples

0R 0.5 R 0.75 R VERDON-3, 2300°C, H2O VERDON-4, 2530°C, H2 Father rod *, 56 GWd.tHM-1

UO2matrix (0.5 at% Pu) Coating phase (3 at% Pu) Pu agglomerates (5 at% Pu)

UO2 matrix (1.3 at% Pu) No more coating phase Pu agglomerates (1.8 at% Pu)

(7)

| PAGE 6

FUEL-CLADDING INTERACTION

Father rod, VERDON-3 and VERDON-4 samples

1/2

90

Zr

238

U

16

O

U

Zr

1R 1R 0.5 R

Zr

U

VERDON-3, 2300°C, H2O VERDON-4, 2530°C, H2 Father rod *, 56 GWd.tHM-1 FCI on 5 µm at the periphery of the fuel

FCI: melting of UyPuzZr1-y-zO2±x 0,5R: U0.48Pu0.03Zr0.49O1.58

1R: U0.42Pu0.03Zr0.55O1.50 FCI on 70 µm at the

periphery of the fuel (UyZr1-yO2±x 0 ≤ y ≤ 1)

1R

(8)

| PAGE 7

2/2

U

Zr

FUEL-CLADDING INTERACTION

VERDON-1 and VERDON-4 samples

* Geiger et al. JNM (2017) VERDON-1 *, UO2, 72 GWd.tHM-1 2600°C, H2O/H2= 0.9 VERDON-4, MOX, 56 GWd.tHM-1 2530°C, H2

FCI: melting of UyPuzZr1-y-zO2±x 0,5R: U0.48Pu0.03Zr0.49O1.58

1R: U0.42Pu0.03Zr0.55O1.50

FCI: melting of UyZr1-yO2±x Similar compositions in

both cases

Same phenomena in the case of UO2and MOX fuels

Zr

U

0.5 R 1R 0.75 R U0.77Zr0.23O1.85 U0.48Zr0.52O1.70

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* Hanifi NT CEA (2009, 2010)

| PAGE 8

FISSION PRODUCTS EVOLUTION

Metallic precipitates

1/2

Pu

U

Ru

Mo

Pu

U

Mo

Ru

| PAGE 8

Pu

U

Ru

Mo

0R 0.5 R 0.75 R VERDON-3, 2300°C, H2O VERDON-4, 2530°C, H2 Father rod *, 56 GWd.tHM-1 1R

Mo

Ru

Zr

U

Metallic precipitates Ru-Mo-Rh-Pd-Tc Mainly located in the Pu

agglomerates

Metallic precipitates Ru-Rh-Tc

Migration of the precipitates from the agglomerates to the matrix

Metallic precipitates Ru-Mo-Rh-Tc Mainly located in the Pu

agglomerates

Melting/coalescence in molten UyPuzZr1-y-zO2±x

(10)

* Hanifi NT CEA (2009, 2010)

Zr

Ce

Ba

Cs

| PAGE 9

FISSION PRODUCTS EVOLUTION

Dissolved FP

2/2

90

Zr

140

Ce

16

O

137

Cs

138

Ba

16

O

138

Ba

90

Zr

240

Pu

16

O

238

U

16

O

0R 0.5 R 0.75 R VERDON-3, 2300°C, H2O VERDON-4, 2530°C, H2 Father rod, 56 GWd.tHM-1

Dissolved FP mainly in the Pu agglomerates

Cs mainly in the UO2matrix

Dissolved FP mainly in the Pu agglomerates

Scarce precipitates or bubbles with Ba, Cs, Ce and Zr

Dissolved FP mainly in the Pu agglomerates

(11)

Oxidizing atmosphere:

FCI but no fuel melting (T effect)

Enhanced diffusion (Pu, FP...)

Mo and Cs total release *

| PAGE 10

CONCLUSIONS

Behavior of MOX fuel and

FP in SA conditions?

Post-test qualitative and

quantitative analyses

VERDON-3, 2300°C, H2O VERDON-4, 2530°C, H2 Father rod, MOX, 56 GWd.tHM-1

Reducing atmosphere:

Melting of U

y

Pu

z

Zr

1-y-z

O

2±x

(dissolution of (U, Pu)O

2

by ZrO

2

)

Melting and coalescence of

metallic precipitates

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CEA / DEN / DEC / SA3E / LCPC:

S. Reboul, I. Roure, T. Blay, I. Félines, J. Noirot, V. Basini

DEN / DEC SA3E / LAMIR Commissariat à l’énergie atomique et aux énergies alternatives

Centre de Cadarache| 13108 Saint Paul lez Durance T. +33 (0)4 42 25 70 00

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