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Evaluation of Co-precipitation Processes for the Synthesis of Mixed-Oxide Fuel Feedstock
Emory Collins, Stewart Voit, Ray Vedder
Oak Ridge National Laboratory
June 23, 2011
The focus of this report is the evaluation of various co-precipitation processes for use in the
synthesis of mixed oxide feedstock powders for the Ceramic Fuels Technology Area within the
Fuels Cycle R&D (FCR&D) Program's Advanced Fuels Campaign. The evaluation will include
a comparison with standard mechanical mixing of dry powders and as well as other co-
conversion methods. The end result will be the down selection of a preferred sequence of co-
precipitation process for the preparation of nuclear fuel feedstock materials to be used for
comparison with other feedstock preparation methods.
A review of the literature was done to identify potential nitrate-to-oxide co-conversion processes
which have been applied to mixtures of uranium and plutonium to achieve recycle fuel
homogeneity. Recent studies have begun to study the options for co-converting all of the
plutonium and neptunium recovered from used nuclear fuels, together with appropriate portions
of recovered uranium to produce the desired mixed oxide recycle fuel. The addition of recycled
uranium will help reduce the safeguard attractiveness level and improve proliferation resistance
of the recycled fuel. The inclusion of neptunium is primarily driven by its chemical similarity to
plutonium, thus enabling a simple quick path to recycle. For recycle fuel to thermal-spectrum
light water reactors (LWRs), the uranium concentration can be ~90% (wt.), and for fast spectrum
reactors, the uranium concentration can typically exceed 70% (wt.). However, some of the co-
conversion/recycle fuel fabrication processes being developed utilize a two-step process to reach
the desired uranium concentration. In these processes, a 50-50 "master-mix" MOX powder is
produced by the co-conversion process, and the uranium concentration is adjusted to the desired
level for MOX fuel recycle by powder blending (milling) the "master-mix" with depleted
In general, parameters that must be controlled for co-precipitation processes include (1) feed
solution concentration adjustment, (2) precipitant concentration and addition methods, (3) pH,
temperature, mixing method and time, (4) valence adjustment, (5) solid precipitate separation
from the filtrate "mother liquor," generally by means of centrifugation or filtration, and (6)
temperatures and times for drying, calcination, and reduction of the MOX product powder. Also
a recovery step is necessary because of low, but finite solubility of the U/TRU metals in the
mother liquor. The recovery step usually involves destruction of the residual precipitant and
disposal of by-product wastes. Direct denitrations of U/TRU require fewer steps, but must
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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/m1/1/: accessed November 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.