Synthesis of uranium oxides by Complex Sol-Gel Processes (CSGP)

Synthesis of uranium oxides by Complex Sol-Gel Processes (CSGP) A.Deptula, M.Brykala, W.Lada, T.Olczak, D.Wawszczak Institute of Nuclear Chemistry and Technology Sol-Gel Laboratory Warsaw, Poland G.Modolo, H.Daniels Forschungszentrum Jülich, Institute of Energy Research, Safety Research and Reactor Technology, 52425 Jülich, Germany

Introduction: In years 1956-1970: Synthesis of nuclear purity uranyl nitrate; Conversion of uranyl nitrate to ADU; Conversion of ADU to sinterable uranium dioxide; Fabrication of sintered UO 2 pellets. Since the year 1970: Synthesis of spherical particles of uranium dioxide by water extraction variant of sol-gel process (ORNL). Process was developed by introducing original elements.

IChTJ PROCESS for production of UO 2 and ThO 2 microspheres Th, U nitrates H 2 O DISSOLVING FOR U 6+ HCOOH CATALYTIC REDUCTION WITH HYDROGEN Pt/ Al 2 O 3 FORMATION OF SOL S DROPS IN DEWATERED 2-ETHYLHEXANOL WITH SPAN-80 (2EH) SOLS Th 4+ STARTING SOLUTION U 4+ PREPARATION OF SOLS BY TWO STAGES EXTRACTION OF ANIONS. AGING OF AQUEOUS PHASE BETWEEN THEM FOR Ø<100 µm VIBRATED FEEDING CAPILLARIES AND MIXING FOR Ø 0,2 1,5 mm IN TWO FLUID NOZZLE 2-ETHYLHEXANOL+SPAN-80(2EH) 2EH REGENERATION GELATION BY EXTRACTION OF WATER WITH 2EH MICROSPHERES Ø< 100 µm OF ThO 2 AND UO 2 Ø 0,2 mm 1,5 mm PRIMENE JMT (principally C 18 H 37 NH 2 ) PETROLEUM-SOLUTION PRIMENE JMT REGENERATION FILTRATION AND WASHING THERMAL TREATMENT (drying and sintering)

Equipment for fabrication of small (Ø< 100 μm) alumina, urania and thoria microspheres.. 7 1,2 reactors for gelation Vs 1 2 3 4 6 3,4 gel ageing tanks 5 sol feed tank 6 retentive reservoir 7 - vacuum dewatering system, 70 o C (polish patent No 83484-1978) V s vibrator and vibrating capillaries 5 Yield - 100 g/h

Equipment for preparation of large (0,2-1,5 mm) thoria and urania gels 1 fluidized column ORNL type, 2 two fluid nozzle, 3 2EH reservoir, 4 sol reservoir, 2EH 2EH 2EH 5 dewatering system (polish patent, No 83484-1978), 6 microspheres collection Yield (10 100 g/h)

Introduction: During the meeting in Vienna (1973) it was declared by the panel that sol-gel products and sol-gel process possess qualities for the industrial application for nuclear fuel fabrication. Unexpectedly the situation changed when the USA government in 1973 stopped the support for fabrication of particulate fuel for breeder reactors, prepared by the sol-gel process. Consequently in 1975 the very promising HTGR-program, which had been planned on a large scale, came to near halt. This decision had repercussions in the European sol-gel program but their reductions were not as drastic (especially in Germany) as in the USA.

Present days Complex Sol-Gel Process (CSGP)

Complex Sol-Gel Process (CSGP) preparation of starting metal salts solution; addition of ascorbic acid; formation of complex sol solution; partial hydrolysis by addition of ammonia aq.; evaporation to desired viscosity; drying and final thermal treatment.

Bidentate coordination of Me ions by ASC Me Me O H O H C C O C CH CHOH CH 2 OH O

Complex Sol-Gel Process (CSGP) preparation of starting metal salts solution; addition of ascorbic acid; formation of complex sol solution; partial hydrolysis by addition of ammonia aq.; evaporation to desired viscosity; drying and final thermal treatment.

Prepared with CSGP: - YBCO, BSCCO families - high temperature superconductors - Ca 10 (PO 4 ) 6 (OH) 2 - hydroxyapatite - bioceramics materials - LiMn 2 O 4, LiNi 0.5 Co 0.5 O 2 - positive electrode materials in high-energy-density lithium and lithium-ion batteries - Li 2 TiO 3 - unique Tritium breeding blanket for Fusion Reactors - LiCoO 2, LiMg 0.05 Co 0.95 O 2 thin films on porous Ni/NiO cathodes for MCFC - TiO 2, (Ba,Sr,Ca)TiO 3 powders, thin films, microspheres - KY(WO 4 ) 2, KY(WO 4 ) 2 + 1% mol Yb laser crystals - TiO 2 -WO 3, ZrO 2 -WO 3, ZrO 2 -SiO 2 -WO 3 materials for W-188/Re-188 generator columns

Characterization - Advantages: + a high degree of amorphicity of the starting gels joined with homogeneous distribution of the components; without ASC with ASC Complex sols of compounds Li-Mn (without and with addition of ASC) with ammonia.

Characterization - Advantages: + strong bonds in the network of the gels retarding premature crystallization of individual components; + high wettability of sols to metallic supports; + high adherence of the coatings after the thermal treatment, to metal substrates;

Characterization - Advantages: + high sinterability of materials. without ASC with ASC YAG (Y 3 Al 5 O 12 ) sintered in 1750 o C/ 6h

Characterization - Advantages: + various shapes of CSGP products spherical microspheres irregular shaped powders fibers monoliths coatings

Characterization - Disadvantages: - foaming; - sometimes formation of the carbonates. +/- possibility of metallic cation reduction by organic additives;

Synthesis of uranium oxides by Complex Sol-Gel Processes (CSGP) I. Preparation of uranyl sols solution (with ASC and ammonia aq.); II. Gelation of complex sols to gels in various shapes; III. Thermal treatment of gels with reduction to uranium dioxide.

I. Preparation of uranyl sols solutions uranyl substrates (uranium trioxide, ammonium poliuranates, uranyl nitrate) ascorbic acid (ASC) MR ASC/U = 1 ammonium hydroxide up to ph 4-6 blending pre-neutralization 1M uranyl sol solutions

Potentiometric titrations of uranyl sols Potentiometric titration of 0.001 M UO 2 (NO 3 ) 2 with ASC (different MR ASC/U) with ammonia (0.1 M). 0,001 mol/l ASC UO 2 (NO 3 ) 2 UO 2 (NO 3 ) 2 + ASC (MR ASC/U=0.5) UO 2 (NO 3 ) 2 + ASC (MR ASC/U=1.0) UO 2 (NO 3 ) 2 + ASC (MR ASC/U=1.5) UO 2 (NO 3 ) 2 + ASC (MR ASC/U=2.0)

Potentiometric titrations of uranyl sols Potentiometric titration of concentrated sols 1 M UO 2 (NO 3 ) 2 with ASC (different MR ASC/U) by ammonia (25%). ph ph 9 8 7 6 5 4 3 2 1 UO 2 (NO 3 ) 2 MR ASC/U = 0.5 MR ASC/U = 1 0 0 2 4 6 8 10 12 14 MR NH 4 OH/U

uranyl sols solutions II. Preparation of gels in various shapes; irregular agglomerates evaporation of water drying 100 o C

II. Preparation of gels in various shapes; spherical particles (diameter 5-120μm) uranyl sols solutions formation of sol s drops in dewatered 2-ethylhexanol with SPAN-80 gelation by extraction of water with 2EH filtration and washing with acetone

II. Preparation of gels in various shapes; kernels (diameter 200 2000 µm) uranyl sols solutions HMTA Mixing molar ratio HMTA/U = 2,2 formation of sol s drops in hot silicon oil filtration and washing with petroleum ether, dryling on air uranyl gels

Thermal analysis (TG, DTA) from uranium trioxide (microspheres) from uranium trioxide (agglomerates) from ADU (microspheres) from uranyl nitrate (microspheres) o C, temperature

III. Thermal treatment Decomposition of ammonium nitrate 1-2 o C - min/170 o C/1h 1-2 o C - min/250 o C/1h Elimination of organic compounds 2 o C - min/550 o C/2h spherical particles kernels

III. Thermal treatment XRD analysis of uranyl gel after calcination (550 o C/2h)

III. Thermal treatment, reduction to UO 2 Decomposition of ammonium nitrate 1-2 o C - min/170 o C/1h 1-2 o C - min/250 o C/1h Elimination of organic compounds 2 o C - min/550 o C/2h 700 o C 500 o C 900 o C Reduction to UO 2 air N 2 95% N 2 + 5% H 2 N 2 air 0 h 1,5 h 2 h 4,5 h 5 h

III. Thermal treatment, reduction to UO 2 XRD analysis of uranyl gel after reduction (900 o C/2h 5% H 2 +95% N 2 )

Conclusions 1. Complex Sol-Gel Process can be successfully applied to a preparation of homogeneous sols using complexation with ascorbic acid of various uranyl (uranium trioxide, ammonium poliuranates, uranyl nitrate); 2. Gels have been obtained in shapes: - irregular agglomerates; - medium sized microspheres (diameter <150); - kernels (diameter 200-2000 μm).

Conclusions 3. Non destructive thermal treatment of gels to oxides in air atmosphere was elaborated on the basis of their thermal analysis. Special procedures were necessary for nitrate gels due to violent exothermic reactions. 4. Uranium dioxide has to be obtained from gels by reduction with hydrogen (in older works it was 1100 o C, 2h, but in clear hydrogen).

Special thanks: dr Modolo and Juelich s Team Contract No FP7-CP-2007-211267

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