Recent progress in the synthesis and characterization

of uranium carbide compounds.SCR/CSM, Université de Rennes1, UMR CNRS 6226

Institut de Physique Nucléaire, IPN-Orsay, Université Paris-Sud 11.

40ieme Journées des Actinides 2nd Workshop an Actinide Targets

Genève, 27mars -01 avril

Recent progress efforts on the synthesis and characterization sintering

of uranium monocarbide compounds.SCR/CSM, Université de Rennes1, UMR CNRS 6226

Institut de Physique Nucléaire, IPN-Orsay, Université Paris-Sud 11.

40ieme Journées des Actinides 2nd Workshop an Actinide Targets

Genève, 27mars -01 avril

Outline :

Part I : Objective of the studyA- Frame of the work (GFR-He, ISOL-target) B – Aim the study

Part II : Synthesis of uranium monocarbide.A – Overview on the binary phases diagram U-C B – Melting of U and C using an arc furnaceC – Carbothermal reduction at high temperature

Part III : Sintering of dense UC pellets.A- Natural sintering B- Hot pressing of powder.

Part IV : Conclusions and future workA- Synthetic routesB- sintering of carbides

Gen-IV : Gas-Fast Neutron Reactors (Allegro)

(U, Pu, MA*)C/ SiC-SiCf

•WORKING CONDITIONS : GFR-He concept-T°: - working conditions : 500-1000°C

- incidental / accidental conditions : 1600 -2000°C for one hour, without melting

-η : - fast neutrons , fluence 1.1027 η/m2, - Cycle - 3 years

•ASSEMBLY : Needle-likeSTRUCTRAL & MATRIX MATERIALS : SiC-based meterials LINER M : W, (W-Re) alloysFUEL : (U, Pu)C solid solution, with insertion of MA*

- atomic ratio of the composition : U : Pu : MA* of 80-85 : 10-15 : 0-5.

- compromise between high densification and porosity * Minor actinides : Np, Am, Cm

Needle-like assembly

Liner : M

Improve the performance of reactors and fuel cycles with current nuclear system (security , resources sustainability , reprocessing ,..)

Targets for Isotope Separation On Line (ISOL) facilities

ISOL target of 3rd generation (SPIRAL2)INCIDENT BEAM : - Energetic light (deutons) or heavy ions or

thermal neutrons - Properly focusedREACTIONS : - spallation, fission or fragmentation mechanisms EJECTION FROM THE TARGET :- ionized, accelerated, purified WORKING CONDITIONS- T° # 2000°C under high vacuum- heavy irradiationTARGET- composition : UCx

Mixed UC / UC2 or UC2 + nC.

- Compromise between density and open porosity

Working temperature, T = 2000°C

Production of rare-isotope beams for nuclear physics

Pellets are pilled up in a graphite container

New generations of nuclear systemsGen IV – GFR-He reactors & ISOL facilities

CHALLENGES : Comprehensive study

Advanced materials working under extreme conditions (T°, η, D+, … long-time.)

Stability / Evolution (Fuel or Target) under working conditions microstructure of the pellets : grain sizes, morphology

porosity,distribution of the porosity

Identify the main parameters which controlled the microstructure of UC pellets.Prospective works on :

- synthetic routes, - microstructural parameters of the powder, - sintering mechanisms.

Binary phase diagram of U-C

UC : - congruent melting compound T°f # 2530°C

- solid solution UC-UC2 at high T°- line compound at low T°- NaCl type of structure, a =

4.9510(3)

R. Benz, C.G. Hoffmann, G.N. Rupert, High Temp. Science, 1 (1969) 342.

Synthesis of uranium monocarbide

Arc-melting :

U + n Cg UCn n = 1T > 2600°C Easy to melt

High purity of the product ReproducibleFast (20 min)Ingots of 0.5 – 3g

Need to be grinded

Rietveld analysis of a samples with nominal composition UC1.02

Detection limit below 1 wt % of a secondary phase, UC2.

SEM observations of a UC IngotSEM observations :

- Dense materials, - Low porosity- Well crystallized sample : brittlee & easy to grind

Distribution of the grain size

De 0.375à 2000Nombres 100Moyenne: 1.594Médiane: 1.443D(3,2): 7.068Moyenne/Médiane: 1.105Mode: 1.204Intervalle à 95%: 0.544Intervalle à 95%: 4.671Ecart-type: 1.731Variance: 2.995C.V.: 0Skewness: 1.083Kurtosis: 1.498Surface spécifique m2.g-1 (BET) 2.4

Grinded UC ingots

Carbothermal reduction of uranium oxideReactions (1450 < T < 1900°C):

UO2 + 3 C UC + 2 CO ↑

- Reduction of U3O8 under H2 flux- Control of the stoichiometry of oxygen

!Experimental procedure :

UO2 + nC pellets ( 8, 10) Cgraphite crucible n = 2, 2.5, 3, 3.5, 4, 4.5

1450 - 1900°C (0.5- 6 hours)

300°C/h

High temperature furnace with C graphite resistor

Influence of : Temperatureinitial composition (n)

Carbothermal reduction of uranium oxide

- single phase of UC

n = 3

T = 1700°C for 3h

No significant diffrence on the XRD powder patterns between the arc-melting method and the carboreduction one

Arc-melted sample

T = 1900°C for 1h

SEM observations of a UC compact

x 100 x 1000 x 5000

Large cavities :

gas released

Grain sizes [1-5] µm

UO2 + 3C UCT = 1700°C, t = 3h

Synthesis and sintering in one step impossible (mechanical properties)

Size of the UC particules

!

De 0.375à 2000Nombres 100Moyenne: 10.7800Médiane: 12.3600D(3,2): 6.6040Moyenne/Médiane: 0.8720Mode: 34.5800Intervalle à 95%: 1.6410Intervalle à 95%: 70.7700Ecart-type: 2.6120Variance: 6.8240C.V.: 0Skewness: -0.4480Kurtosis: -0.7680Surface spécifique m2.g-1 (BET) 2.5

No significant diffrence on the grain size and specific area of the powders obtained by arc-melting and by carboreduction.

Natural sintering of UC Pellets

0 10 20 30 40 50 60 70800

1000

1200

1400

1600

1800

Time (min.)Te

mpe

ratu

re (°

C)

0

4

8

12

16

20

0 20 40 601700

1725

1750

1775

1800

Tem

pera

ture

(°C)

Time (min.)

Frittage au four HF d'une pastille de UC (UC1)

Power (%

)

Sintering in a H.F. furnace

7,5

5,85,5

7,5

V = 0.2496 cm² d measured = 10.26 g/cm3d calculated = 13,68 g/ cm3C = 75,0%

Pellet n° 2 : cold pressing 5 tonnes/ cm²

Densification about 75 % is a reproducible value over several experiments

1500 < T < 1900°C

SEM observations of a UC sintered pellet

x 200 x 500

x 5000

Large cavities :

Small single crystals # 50 µm

T Solid state diffusion favor the grain growth

T = 1900°C, 1 h

Hot press sintering of UC Pellets

Sintering in a H.P. furnace Mold of Cgraphite

Sintering conditions : 1500 °C for 2 h under rough vacuum with 80 MPa.

Raw surface

Æ= 10,3 mmh = 3,6 mm

Densification ~ 85%

SEM observations of a H.P UC pellet

x 200 x 2000

Black area : cavitiesGrain size about 5 µm

x 5000

Lamellar morphology - free carbon - UC2

Conclusion

- Preparation of single phase UC powders : NaCl type, a = 4.951(2) Å, [0-5]µm,

- arc-melting, n = 1,- carbothermic reduction, (T = 1700°C, n = 3, t =3h)

- Sintering : competition between grain growth / porosity- Temperature favors the grain growth only - Pressure may help to limit the growth of the grain

methodic procedures not easy task, refractory material

Synthesis by carbothermic reduction Sintering of UC pellets

Sintering of uranium carbides great challenge

Acknowlodgements

GROUPEMENT DE RECHERCHECNRS – CEA/DEN -EDF - ANDRA

R. ELOIRDIF. de BRUYCKERS. MORELD. MANARAE. COLINEAU

B. FOURESTN. DACHEUX

Merci de votre attention et de votre patience !

GROUPEMENT DE RECHERCHECEA CNRS EDF AREVA-NP AREVA-NC