Evaluation of Co-precipitation Processes for the Synthesis of Mixed-Oxide Fuel Feedstock Materials Page: 3 of 13
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This process is similar to the ammonium diuranate precipitation process which is widely used for
making fuel-grade U02 in current fuel fabrication plants. The co-precipitation process, with
carefully controlled precipitation conditions (illustrated in Fig. 2) and with avoidance of higher
temperature calcination is capable of producing a "very homogeneous" MOX powder, with
respect to plutonium distribution. However, the by-product ammonium nitrate produced in the
mother liquor requires a complex treatment for waste disposal, as illustrated in Fig. 3.
As with the other co-precipitation methods, the ammonia hydroxide co-precipitation process is
only in the R&D stage, thus powder properties may differ widely depending on various control
parameters during the critical steps of precipitation and calcination. In some cases, processing is
difficult because the preparations are gelatinous with the final reduction producing irregularly
shaped particles with a small fraction of fines. Comparison of powder properties with other co-
conversion methods is difficult because very little data is available on the surface area (SA),
particle size (PS), and morphology of mixed actinide oxides prepared by ammonia co-
E. N2, 02
Condensate 95%N20, 5% N2, <0.2%02 - Fu2ce
Acidification / Re-concentration Evaporation / Denitration
Mother Liquor -2.5 MNH4 NO3 6 hours @ 1000C
-2.5 MNH4 NO3 4M HNO3 to7 M HNO3
0.2MHCI 2XVol Reduction
Fig. 3. Mother Liquor from Ammonium Hydroxide Co-Precipitation Ammonium Nitrate
Decomposition Russian Process.
The process steps for the oxalate co-precipitation process are shown in Figures 4 and 5. This
process is being developed in France by the CEA and Areva, and will be operated in a
continuous manner, using equipment similar to that used in the La Hague plant for plutonium
conversion. However, to adapt the process to co-precipitation of uranium, the uranium valence
must be reduced from the normal hexavalent state in nitric acid solution to the tetravalent state to
minimize the uranium solubility in the mother liquor. The pre-reduction step can be done
electroytically by established methods, but in order to maintain uranium in the tetravalent state, a
"holding reductant" (hydrazine) must be present to preferentially react with nitrous acid as it is
generated in the nitric acid solution.
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Collins, Emory D; Voit, Stewart L & Vedder, Raymond James. Evaluation of Co-precipitation Processes for the Synthesis of Mixed-Oxide Fuel Feedstock Materials, report, June 1, 2011; United States. (digital.library.unt.edu/ark:/67531/metadc829973/m1/3/: accessed November 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.