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Molybdenum behaviour during U-Al RRSF dissolution
X. Heres, D. Sans, M. Bertrand, E. Brackx, E. Excoffier, C. Eysseric, Jf. Valery
To cite this version:
X. Heres, D. Sans, M. Bertrand, E. Brackx, E. Excoffier, et al.. Molybdenum behaviour during U-Al RRSF dissolution. RRFM 2017 European Research Reactor Conference, May 2017, Rotterdam, Netherlands. �hal-02418112�
[1] Valéry J.F., Domingo X., Landau P., Péchard C., Laloy V. Overview on RRSF reprocessing, from spent fuel transportation to vitrified residues storage. In RRFM 2015 Conference Proceeding, Bucharest, Romania, 19-23 April 2015, ENS conference 2015, p 806-818.
[2] Hérès X., Sans D., Bertrand, M., Eysseric, C., Brackx, E., Domenger, R., Excoffier, E., Valery, J.F., Molybdenum solubility in aluminium nitrate solutions, Procedia Chemistry, 21 2016, 46-53
[3] Visser A.E., Pierce R.A., Laurinat J.E., Purification of Uranium from a Uranium/Molybdenum Alloy, Separation Science and Technology, 43 (2008), 2775–2785
[4] Rempel K.U., Migdisov A.A., Williams-Jones A.E. The solubility and speciation of molybdenum in water vapour at elevated temperatures and pressures: Implications for ore genesis, Geochimica et Cosmochimica Acta 70, 2006, 687–696
[5] Schulz W., Burns R., Duke E.M.. Nitric acid dissolution of uranium molybdenum alloy reactor fuels, Industrial & Engineering Chemistry Process Design and Development, 1(2), 1962, p.156-160
Nuclear Energy Division
Research Department on Mining and Fuel Recycling Processes Separation &Dissolution Process Section
CEA French Nuclear and Alternative Energies Commission
Marcoule Centre,| BP17171 | 30207 Bagnols-sur-Cèze Cedex T. +33 (0)4 66 79 77 00 | F. +33 (0)4 66 79 63 25
Molybdenum behaviour during U-Al RRSF dissolution
X. Hérès – D. Sans – M. Bertrand – E. Brackx – E. Excoffier – C. Eysseric
CEA, Nuclear Energy Division, Research Department on Mining and Fuel Recycling Processes, B.P. 17171,30207 Bagnols-sur-Cèze, France
J.F. Valery
AREVA NC, BUR/DT/RDP, La Défense, France
Reprocessing of Research Reactor Spent Fuel (RRSF) made of plates or cylinders of uranium-aluminium alloy (U-Al) clad with pure aluminium
RRSF are processed in AREVA's La Hague plant by liquid-liquid extraction, after dissolution in concentrated nitric acid and mixing with Light Water Reactor (LWR) spent fuel solutions[1]
Reprocessing capacity can be impacted by solubility values of aluminium and molybdenum in nitric medium, during dissolution step .
To provide more flexible conditions for dissolution operations in the case of treatment of U-Al spent fuels with a high molybdenum content, it is important to accurately determine the solubility of molybdenum under operating conditions of spent fuel dissolution.
Objectives of that work: determination of molybdenum solubility and, in case of precipitation, solid analyses to see if uranium could be included in the solid.
References
Introduction
Experimental
Results
Development of washing procedure for solids
Conclusions
Precipitates obtained during the dissolution experiments of powder U-Al like, with an excess of molybdenum metal, consisted predominantly of MoO3. Small parts could also include Al, according to ICP-AES study.
Uranium was undetectable by ICP-AES in the redissolution solution of washed solids (mass of uranium <0.2% mass).
No additional solid phase or inclusion of uranium was also detected during SEM/EDS measurements. This confirmed that uranium was not included in the solid.
Future studies of Zr impact on Mo solubility are planned to better simulate the operating conditions of U-Al RRSF treatment.
Elemental composition of solids by SEM/EDS and XRD
[1]
xavier.heres@cea.fr Financial support for this work was from AREVA-NC www.cea.fr
Solution analysis
Procedure
Protocols comparison
Structure and morphology of solids by SEM/EDS
Study on powder obtained from high concentration of uranium medium ICP-AES was calibrated daily with fresh standards for each measurement.
Selected peaks were: Mo: 202.030 nm, U: 385.958 nm, Al: 396.152 nm.
The determination coefficient of the calibration curve was > 0.9999, with a reproducibility of elemental peak < 3% (3 peaks per element).
Uncertainty of ICP-AES analyses was < 4%
Acidity was measured by potentiometric method with an error < 5%
Scanning Electron Microscopy with X-ray microanalysis
Dilution of the powder in 90% ethanol, 10% distilled water.
Observation after deposit of two to three drops on an aluminium block.
Coating in a transparent resin, ion polishing 5kV for 1h30 or 3h, 15 nm carbon metallization. X-ray crystallography
After manual grinding and dilution in ethanol, a few drops deposit on a plane mirror.. 1600W power cathode copper.
Angular range: 5-140°
Solid analysis
Dissolution apparatus consisted of a stirred tank reactor equipped with a heating jacket and a water cooled condenser in order to retain vapour. Experimental
protocol is described in [2]
To reach solubility values, every experiment was carried out with an excess of Mo Several solids were obtained from Mo solubility studies described in [2].
2 washing protocols were tested: mechanical agitation (left) or impregnation (right)
NO
YES
Powder from washing N-1 is put in a tube containing 50mL of washing solution N
Mixing for 5 min at room temperature (25°C)
Filtration on 0,2 µm filter with a vacuum pump Analysis of U-Al-Mo solution composition (ICP-AES)
Recovering of powder on filter Washing solution N=N+1 in a new tube Complete dissolution to do?
Powder from washing N is put in a Becher containing 300 mL of NaOH 5M or HNO33M
Agitation for 60 min at T=70°C (Becher recovered with Mylar type film) Analysis of U-Al-Mo solution composition (ICP-AES)
NO
YES
Powder is put in a tube containing 50mL of water
Mixing for 5 min at room temperature (25°C)
Filtration on 0,2 µm filter with a vacuum pump Analysis of U-Al-Mo solution composition (ICP-AES)
Powder impregnation on filter with washing solution N (50 mL)
N=N+1
Complete dissolution
to do?
Powder from washing N is put in a Becher containing 300 mL of NaOH 5M or HNO3 3M
Agitation for 60 min at T=70°C (Becher recovered with Mylar type film) Analysis of U-Al-Mo solution composition (ICP-AES) Analysis of U-Al-Mo solution composition (ICP-AES)
Distribution of Mo, Al, U in aqueous impregnation
washing or dissolution solutions for powders from
experiment E3
(like E1 with more uranium) Distribution of Mo, Al, U in aqueous stirred washing or
dissolution solutions tested for powders from experiments carried out with nominal uranium
concentration (E1)
Water and HNO3 10M removed respectively Al and U impregnated on the solid
Washing with simple impregnation of nitric solution on the filter solubilized the same quantity of uranium as with stirring: uranium was likely impregnated
According to ICP-AES, every washed precipitate composed of 96% Mo and 4% Al
(elemental mass percentage relative to total mass of washed solid, oxygen not measured here)
Images obtained for precipitate not washed by 10 mol/L HNO3. Shots 1 and 2, obtained with the detector HE-SE2 of secondary electrons (SE), show that sample is perfectly plane. Images 3 to 6, with the AsB detector of backscattered electrons (BSE),
indicate only one phase even without U washing
All peaks were indexed with the MoO3 orthorhombic symmetry. All samples corresponded to the same crystallographic structure of molybdenum trioxide MoO3, as expected in literature.[3-4-5]
SEM/EDS revealed essentially Mo and O.
Al and Cu came from the ionic polishing support. It was thus not possible here to see if solid phase contained Al.
U was not detected SEM/EDS, confirming ICP-AES results.
Powder made up of small needles of length ranging from 2 to 12 μm.
As shown in the lower pictures, pre-treatment using ultrasonic bath
tended to break these needles.
Influence of Al concentration on precipitation
[2]Results pointed out the decrease in molybdenum solubility with increasing aluminium concentration
Mo solubility seems to be directly linked to aluminium concentration as experimental points gather in a straight line.
0.30 0.32 0.34 0.36 0.38 0.40 0.42 0.44 35 40 45 [Moly bd en um] (g/L) [Aluminium] (g/L)
[HNO3]final=max, [U]nominal, Tnominal
Mo solubility area
