G. Borda, D. Ode, J. Duhamet, P. Allegri
CEA Nuclear Energy Division – Fuel Cycle Technology Division – System and Chemical Engineering Device - Marcoule – 30207 Bagnols sur Cèze -France : gilles.borda@cea.fr
Introduction :
The current objective of fabricating nonproliferating nuclear fuel by “direct” coprecipitation of uranium, plutonium and minor
actinides requires a new process to replace the (co)precipitation step. It was necessary to examine its adaptability to a plant
flowsheet implementing devices capable of ensuring this function at suitable continuous flow rates. Coprecipitation of a uranium
fraction together with plutonium results in an appreciable increase in the process flow rates for this step. The technological impact
of the increased capacity could require the development of a different concept for a continuous device capable of ensuring the
proposed throughput, as the flow rate of the Vortex effect reactors currently used for plutonium precipitation at La Hague appears
too limited.
A new type of device designed and patented by the CEA (DTEC/SGCS/LGCI) was tested in 2007.
Device description
The patent is for organic confinement in a pulsed column (PC) (fig 1) tested in 2007 or Couette column (CC) (tests to come) .
Pulsed column device
Pulsed column
Aquous oxalic
phase inlet
Upper settler
2
12
Organic phase
outlet
5
Main aquous nitrate
phase inlet
8b
Hydrophobic
packing
13b
1
9b
First
aquous nitrate
phase inlet
Experimental device
The precipitation reaction between the
oxalate complexing agent and a surrogate
nitrate—cerium(II) alone, or coprecipitated
uranium(IV) and cerium(III)—occurs within
an emulsion created in the device by these
two phases flowing with a counter-current
chemically inert organic phase (for example
TPH) produced by the stirring action of the
pulsator (PC) .
The precipitate (fig 2) is confined and thus
does not form deposits on the vessel walls
(which are also water-repellent); it flows
downward by gravity and exits the column
continuously into a settling tank.
Hydrophobic glass
shaft
10b
Organic phase
inlet
3
Oxalic phase
outlet
4
Recycled oxalic
phase inlet
6
Lower settler
11b
Oxalate
precipitate
7
Figure 2. Precipitate in pulsed column
Figure1. Pulsed column
Figure 3. Experimental column, 15 mm diameter,
2 m high, packed with truncated PTFE disks
Ce 50 mL.h-1
10%
Ce 100 mL.h-1
Ce 200 mL.h-1
8%
Ce 500 mL.h-1
6%
Ce 1000 mL.h-1
The results obtained for precipitation of cerium alone
in a short column of small diameter (fig 3) have
demonstrated that high throughputs (2 L·h-1 with
24 g·L-1 nitrate) are feasible without system
malfunctions. The measured particle sizes of the
precipitates range from 20 to 40 µm on average
(fig 4); sizes increase when the flow rate diminishes
(fig 5). The measured device outflow indicates that the
precipitation reaction is complete.
35
1,2
30
1
d43 for TPH = 2000 mL.h-1
d50 for TPH = 2000 mL.h-1
25
0,8
20
0,6
15
HNO3 and H2C2O4 (mol.L-1)
12%
d43, d50 et d10 size of cerium precipitate versus residence time for liquid
Size (µ)
Simple precipitation tests with cerium nitrate
d10 for TPH = 2000 mL.h-1
d43 for TPH = 500 mL.h-1
d50 for TPH = 500 mL.h-1
d10 for TPH = 500 mL.h-1
0,4
HNO3 concentration
10
H2C2O4 concentration
0,2
5
0
0,00
20,00
40,00
60,00
80,00
100,00
120,00
140,00
0
160,00
Residence time for liquid (s)
Figure 5. Particle size versus residence time
4%
Ce 1500 mL.h-1
2%
Ce 2000 mL.h-1
0%
0,1
1
10
Size (µm)
Figure 4. Particle size distribution of precipitates
formed during tests with cerium
Shocks
Uranium-cerium coprecipitation tests
2 theta (degrees)
Figure 7. X-ray diffraction diagram of the precipitate
formed compared with the theoretical mixed oxalate.
500 mL.h-1 test
100
The morphology of the
precipitates
revealed
increasing agglomeration at
higher flow rates (fig 6). The
agglomerates consisted of
small,
highly
elongated
rodlets .
A UCe coprecipitate was always
obtained regardless of the column flow
rate and the corresponding range of
chemical
conditions
in
which
coprecipitation occurred.
A precipitate of optimum “purity”
(hexagonal close to the theoretical
model) appears to have been obtained
at about 500 mL·h-1 (fig 7).
The precipitation reaction appears to
have been complete over the full height
of the test column.
The particle size of the resulting
precipitate is smaller(~ 10 µm) than
under inactive conditions (Ce alone)
and can be improved (~ 30 µm) when
increasing retention (fig 8).
Test (50 mL·h-1) ~ 1.2 g·h-1
Test (500 mL·h-1) ~ 12 g·h-1 Test (2000 mL·h-1) ~ 48 g·h-1
Figure 6. SEM images (7500×) of Ce precipitates formed in the pulsed column
Test (50 mL·h-1) ~ U 1 g·h-1 Test (500 mL·h-1) ~ U 10 g·h-1 Test (2000 mL·h-1) ~ U 40 g·h-1
Ce 0,5 g·h-1
Ce 5 g·h-1
Ce 20 g·h-1
Figure 7. SEM images (8000×) of UCe coprecipitates formed in the pulsed column
Figure 8. UCe
coprecipitates
formed in the
pulsed column:
Left : low
retention
Right: High
retention
Conclusions The coprecipitation tests again demonstrated stable device operation without clogging. A precipitate flow rate per unit area of about 875 kg·h-1·m-2
was reached during these tests in a short pulsed column; this exceeded the performance obtained with cerium alone, and suggests that the
dimensions of an industrial-scale column will allow suitable capacity.
MARCOULE : DTEC/SGCS
Co-conversion technology based on liquid-liquid extraction columns
NUCLEAIRE
DIRECTION
NUCLEAIRE
L’ENERGIE
DEL’ENERGIE
DIRECTIONDE
P1-16